Impact of window temperature changes on ITER toroidal interferometer and polarimeter (TIP) measurements
Presenter:
Tsuyoshi Akiyama (General Atomics)
Authors:
Tsuyoshi Akiyama, Michael A. Van Zeeland, Daniel Finkenthal, Michael LeSher, Ryan Finden, Peter Trost, Anthony Gattuso, Sebastian Miranda, Marc-Andre De Looz, Christopher Watts
Abstract:
The Toroidal Interferometer and Polarimeter (TIP) is the primary electron density diagnostic on ITER. For long pulse operation, the interferometer is challenged by phase offsets due to environmental changes such as temperature, humidity, etc. [1,2]. To improve measurement accuracy and provide reliable electron density data to fueling control, it will be essential to minimize and monitor ambient environmental changes. A key element of this will be consideration of temperature changes in window and transmissive optics materials since the index of refraction depends on the temperature.
In TIP, BaF2 and ZnSe are used for vacuum and secondary windows, as well as lens and beam splitter/combiners [1]. Though previously published data on the dependence of the index of refraction on the temperature [3] exists for these materials, the quoted error bars are too large to reliably characterize the expected phase drifts, nor have actual measurement been made yet. Hence, this work experimentally measured the phase shift caused. The TIP prototype, operating at 10.59 and 5.22 microns, was used to measure the phase shifts by temperature changes of BaF2 and ZnSe over typical operating ranges. 3 cm-long BaF2 and ZnSe specimens were placed in an oven in the TIP beam path and the temperature increased up to > 80 °C (ITER vacuum window temperature ~ 70 °C). The temperature dependent vibration compensated phase shifts of BaF2 and ZnSe are +0.012 and -0.27 deg./°C/cm, respectively. The measured phase shift is the sum of two terms: the index of refraction change and the thermal expansion. While signs of these two terms are opposite in BaF2, they are the same in ZnSe. Hence the phase shifts in BaF2 are largely cancelled resulting in smaller temperature dependent vibration compensated phase shift errors.
The primary vacuum window material for TIP is planned to be ZnSe, which has been chosen over BaF2 because it can meet ITER’s strict vacuum window requirements; ZnSe has better resistance to steam ingress and satisfies the mechanical strength required for the helicoflex vacuum sealing. Due to double passage of double 1.4 cm-thickness windows, the total path length of TIP beams in ZnSe is 5.6 cm. Allocating 1 deg. error budget to the vacuum window (10% of TIP’s total error budget), a temperature change of <0.7 °C during a discharge will be required. For temperature changes beyond that value, careful monitoring of the window temperature would be required to remove phase offsets.
This work is supported by US DOE Contract No. DE-AC02-09CH11466. All US activities are managed by the US ITER Project Office, hosted by Oak Ridge National Laboratory with partner labs Princeton Plasma Physics Laboratory and Savannah River National Lab-oratory. The project is being accomplished through a collaboration of DOE Laboratories, universities and industry. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
[1] M.A. Van Zeeland et.al., Plasma Phys. Control. Fusion 59, 125005 (2017).
[2] T. Akiyama et. al., JINST 15, C01004 (2020). , K.J. Brunner et. al., JINST 14, P11016 (2019).
[3] “Optical Materials Characterization Final Technical Report”, NBS technical note 993, 1978
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High-speed imaging for the diagnostics of rotating cluster in radio-frequency (RF) plasma
Presenter:
Maria-Luiza Mitu (National Institute for Laser, Plasma and Radiation Physics, 077125 Bucharest, Romania)
Authors:
Maria-Luiza Mitu, Dorina Ticos, Adrian Scurtu, Nicoleta Udrea, Catalin Mihai Ticoş, Mihai Oane
Abstract:
Dusty plasma diagnostics is mainly performed by means of high-speed imaging techniques [1]. The sequences of images acquired by a high-speed camera are further processed through Particle Tracking Velocimetry (PTV) analysis technique to investigate the cluster dynamics. Here by we show the dusty plasma diagnostics of a cluster rotating under the influence of an electron beam [2]. In the experiment the dust cluster composed of spherical dust particles with radius r_d=5.9 μm and made of melamine-formaldehyde with density ρ=1.5 g 〖cm〗^(-3) is levitated in the sheath of a radio-frequency (RF) plasma. The experiments were performed in a RF discharge in argon at pressure p=90 mTorr and discharge power of 3 W. The microparticles are illuminated by a laser sheet from a diode laser of 20 mW and irradiated by a pulsed electron beam (EB) with energy in the range 8-12 keV and peak current of 4 mA. The electron beam used to irradiate the cluster has pulse frequency of 56 Hz and pulse duration of 40 µs. The images of the dust microparticles trajectories were acquired in time by a Photron CCD camera. For the analysis of the cluster rotation the image data is used to construct Voronoi diagrams, to calculate inter-particle spacing and to obtain pair correlation functions.
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Imaging Neutral Particle Analyzer Measurements of Mode-Induced Fast Ion Distribution Function Fluctuations in the DIII-D Tokamak
Presenter:
Xiaodi Du (General Atomics )
Authors:
Xiaodi Du
Abstract:
Imaging neutral particle analyzers (INPA) provides precise measurements of the radial, energy and pitch angle of confined fast ions in the DIII-D tokamak [1, 2] including the local fast ion distribution function via tomographic inversion [3] and fast ion phase space flow induced by multiple small-amplitude Alfvén eigenmodes (AE) [4,5]. Recently, two significant improvements have been made to the DIII-D INPA system. Photomultiplier tubes (PMT) are now used to monitor the phosphor light emission of the INPA with large bandwidth. To reduce the electromagnetic noise, the emitted photons are transferred out of machine hall via ~100 m optical fibers. Local fluctuations of the fast ion density with frequencies up to ~250 kHz are observed, which are caused by neoclassical tearing modes, ellipticity-induced AE modes and beta-induced AE modes. This new capability to measure the steady and fluctuating fast ion density of fast ions locally in phase space will shed light on the understanding of diffusive and convective transport during resonant interactions between energetic particles and waves. The second improvement is the development and installation of a new INPA. Complementing the initial DIII-D INPA system [1,2] which probes passing fast ions, this new INPA provides energy-resolved radial profiles of local trapped fast ion density. It measures the counter-Ip (co-Ip) leg of trapped particles, when the plasma current is in the counter-clockwise (clockwise) direction. The new system images a broad radial range from the plasma core to the edge and deuterium energies up to >100 keV at a pitch of about 0.45, with energy resolution of ~10 keV, radial spatial resolution of ~10 cm and pitch resolution of ~4 degree. The initial data demonstrates that the system has exceptionally good signal to noise. This new trapped INPA system also provides the opportunity to extend previous studies of AE-induced fast ion flow to the phase space occupied by fast ions on trapped orbits.
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Diagnostics for, and of, the open large volume TCV divertor transiting from attached to detached regimes
Presenter:
Basil Duval (SPC, EPFL, Lausanne, Switzerland)
Authors:
Luke Simons, Marcelo Baquero, Artur Perek, Basil Duval, Bryan Linehan, Curdin Wuethrich, Emanuel Huett, Yanis Andrebe, Christian Theiler, Olivier Février, Holger Reimerdes, Lorenzo Martinelli, Dmytry Mykytchuk, Sophie Gorno, Claudia Colandrea, Nicolas Offendu, Diego Oliveira, Harry Han, golfit@mit.edu Golfinopoulos, Guang-Yu Sun, Cedric Tsui, Yinghan Wang, Martim Zurita, Umar Sheikh, Keneth Lee
Abstract:
TCV has an up/down symmetric open vacuum chamber where diverted configuration’s legs may be placed near anywhere within the capabilities of its 16-element, independently powered, poloidal coil array. Diagnosing such a range of poloidal magnetic configurations originally relied upon a generous array of tile-surface Langmuir probes, floor and high-field-side IR cameras and surveillance imaging. In recent years, diagnostic needs have extended to partially and deeply detached configurations with and without in-vessel neutral gas baffles and this for the widest range of divertor configurations that include a range of two, four (and more) strike points, ranges of divertor leg flux expansion and, in TCV tradition and a wide range of core shapes that include high negative triangularity.
TCV has an up/down symmetric open vacuum chamber where diverted configuration’s legs may be placed near anywhere within the capabilities of its 16-element, independently powered, poloidal coil array. Diagnosing such a range of poloidal magnetic configurations originally relied upon a generous array of tile-embedded Langmuir probes, floor and high-field-side IR cameras and surveillance imaging. In recent years, diagnostic needs have extended to partially and deeply detached configurations with and without in-vessel neutral gas baffles and this for the widest range of divertor configurations that include a range of two, four (and more) strike points, ranges of divertor leg flux expansion and, in TCV tradition and a wide range of core shapes that include high negative triangularity.
Furthermore, to make physics progress, results from all these configurations are to be compared with edge plasma physics modelling. Two more factors are required: systems that can simultaneously diagnose a large part of the diverted plasma and surrounding, and some direct experimental data validation. This paper describes a wide slew of novel diagnostics that include inversions of images from arrays of spectrally filtered cameras (MANTIS), reciprocating Langmuir Probe arrays (RDPA and fastRP), neutral pressure valves (Baratrons and AUG-in-field types), a highly complete visible spectroscopy array (DSS: survey to high resolution), edge turbulence characterisation (though edge GPI), edge radiation intensities (AXUV and blackened Bolometer Arrays) and Thomson Scattering spectrometers able to measure temperatures to below 1eV. To understand the results of extensive SOLPS simulations, TCV’s magnetic control system was programmed to scan the divertor leg positions across the diagnostics’ positions permitting 2D divertor comparisons/validations both in space and time with model-everything codes (SOLPS-ITER) for detachment relevant conditions. Although each of these diagnostic systems is the subject of both diagnostic and physics publications, their combined, validated, usage provides the basis for a leap forward in diagnostic/modelling comparisons. Finding the physical processes, missing in such models, that are required to generate better experimental agreement will greatly improve extrapolation to upcoming fusion-grade devices.
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Latest developments of SDD detectors for the neutron/gamma sensor for DEMO
Presenter:
Enrico Perelli Cippo (Istituto per la Scienza e Tecnologia dei Plasmi-CNR, Milan, Italy)
Authors:
Enrico Perelli Cippo, Federico Caruggi, Marica Rebai, Davide Rigamonti
Abstract:
In this poster, we present the latest development of neutron/gamma multi-LOS sensor for DEMO. Aim of this sensor is the measurement of fusion power and other relevant plasma parameters (like for instance position or fuel ratio nD/nT) for the control of the future DEMO fusion plant through the monitoring of 14 MeV neutrons and 16.7 photons form the deuterium-tritium reaction in burning plasma. Present plans envisage the use of Single-crystal Diamond Detectors (SDD) as neutron detectors, due to their compactness and well-known characteristics. However, they still need a wide R&D approach to make them completely competitive to other state-of-the-art neutron detection techniques. Moreover, they are affected by gradual degradation due to radiation damage and high temperature. In particular, in this poster we discuss a method to monitor the characteristics of the SDD during its use as a neutron spectrometer. It is known that the good characteristics of SDD as a 14 MeV neutron detector are due to its spectroscopic capabilities, and in particular the presence, in the response function, of a well-defined peak due to the 12C(n,)9Be reaction. However, the radiation damage can cause broadening of such a peak (with loss of energy resolution), reduction of the counting rate and, in definitive, to a failure of the whole detector. During long plasma discharges like the ones envisaged in DEMO, it is impossible to make specific tests on the functionality of neutron detectors; it is thus of paramount importance to develop a monitoring method able to recognize the degradation of the SDD from the same data collected by the detector during its standard use (i.e. neutron spectra from burning plasma). At present, the method is performed off line, but possible developments are discussed that may lead to the implementation of it into an FPGA for real time monitoring of the different SDD in the sensor.
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Real-time Electron Temperature and Density Measurement by Thomson Scattering for Plasma Control on LHD
Presenter:
Hisamichi Funaba (National Institute for Fusion Science)
Authors:
Hisamichi Funaba, Ichihiro Yamada, Ryo Yasuhara, Naoki Kenmochi, Yuya Morishita, Sadayoshi Murakami, Jong-ha Lee, Hideya Nakanishi, Masaki Osakabe
Abstract:
The real-time measurement of the spatial profiles of the electron temperature (Te) and density (ne) is required from the ASTI system, a data assimilation system for integrated transport simulation of fusion plasma [1], on the Large Helical Device (LHD). It is intended to predict and control the temporal development of the plasma parameters, such as Te and ne, through the transport simulation in the ASTI system. Moreover, the real-time information of Te and ne profiles can be used for evaluating or controlling of the heating profiles, the magnetic configurations, the divertor detachment, and so on.
The real-time data processing is realized by applying the fast digitizers, which were installed for the measurement with the high-repetition-rate Nd:YAG laser [2], for the main Thomson scattering system [3, 4] on LHD. These fast digitizers acquire the signals from the 70 polychromators, each of which has 5 or 6 spectral channels. The laser in the main Thomson scattering system is operated in 30 - 50 Hz. The data are transferred from these fast digitizers to the acquisition computer. The analyzing computer, which derives Te and ne, receives the data through the "RTRetrieve" system from the acquisition computer [5]. The frequency of this data transmitting is operated in 10 Hz because it takes almost 70 ms to transfer all the data of 350 channels for the 70 spatial positions. Although the most data are transferred within almost 30 ms, the data in some channels come a few tens of milliseconds later. The time for the signal processing and calculation of Te and ne by the X^2-method is almost 12 ms. Therefore, the delay time in this real-time system is within 100 ms.
The Te and ne profiles are transmitted to a vector engine server SX-Aurora TSUBASA in real-time by the socket communication and used as inputs of the ASTI system. In the recent experiment of LHD, Te was controlled by changing the power of the electron cyclotron heating (ECH) under the prediction of ASTI. The delay time within 100 ms is enough for the ASTI operation at present.
This work is supported by NIFS20ULHH005, NIFS22KIPT008, JSPS KAKENHI Grant Numbers 15KK02451 and JSPS KAKENHI 21K13901.
References
[1] Y. Morishita, et al., Comput. Phys. Commun., 274 (2022) 108287.
[2] H. Funaba, et al., Sci. Rep., 12 (2022) 15112.
[3] K. Narihara, et al., Rev. Sci. Instrum., 72 (2001) 1122.
[4] I. Yamada, et al., Fusion Sci. Tech., 58 (2010) 345.
[5] H. Nakanishi, et al., IEEE Trans. Nucl. Sci., 63 (2016) 222.
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Proposal for measurement of p-11B reaction in the EHL-2 spherical torus
Presenter:
Bing Liu (1 Hebei Key Laboratory of Compact Fusion, Langfang 065001, China 2 ENN Science and Technology Development Co., Ltd., Langfang 065001, China)
Authors:
Bing Liu, Zhi Li, Tiantian Sun, Xinchen Jiang, Di Luo, Yingying Li, Yuejiang Shi, Huasheng Xie, Shaodong Song, Yuankai Peng
Abstract:
EHL-2 is the next generation of spherical torus under design in the ENN Energy Research Institute towards proton-boron fusion energy. One of the important missions of EHL-2 is to achieve proton-boron (p-11B) reaction in a magnetized plasma possibly driven by external heating systems. A big challenge is the measurement of the reaction rate of these low reactivity events in the magnetic fusion environment. Here, we propose to a strategy for measuring p-11B reaction rate in EHL-2 through integrated modeling. Preliminary analysis shows that considering the H-B plasma in EHL-2, with electron density of , ion temperature of and , more than alpha particles could be produced. Such a number of alpha particles is able to be detected and measured by varies types of detectors (i.e. FILD, NPA, GRS, class of CR39, etc.). A further simulation on the distribution of p-11B reaction in a magnetic environment which considers both the effect of neutral beams and background plasma is in progress, as well as a detector simulation which provides the detection efficiency. Here we would like to discuss the feasibility of the varies types of detectors, which could tell energetic alpha particles from proton.
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Real-time correction of modulator in dispersion interferometer on HL-2M
Presenter:
Haoxi Wang (Southwestern Institute of Physics)
Authors:
Haoxi Wang
Abstract:
To meet the requirement of electron density measurement on HL-2M, a single channel CO2 dispersion interferometer based on second harmonic generation technology has been developed and commissioned on HL-2M Tokamak. In series of discharge experiments, a slowly varying delay of reference signal provided by the modulator caused a phase drift and introduced an extra error of up to 10 degrees. An extra phase correction method is applied on the data processing system to calculate the delay and to eliminate the extra phase drift. An additional phase-tracking method is introduced to eliminate unexpected phase flip in phase correction. These methods are included in data analyzing code and FPGA. The FPGA can derive the phase of delay every 0.1 ms to provide real-time phase drift correction in density feed-back signals. The phase drift occurs no more in 10 seconds measurement with the phase correction method.
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Runaway electron studies via HXR spectroscopy at Golem, COMPASS and TCV
Presenter:
Jaroslav Čeřovský (Institute of Plasma Physics, Prague, Czech Republic)
Authors:
Jaroslav Čeřovský, Ondrej Ficker, Eva Tomesova, Luke Simons, Vojtěch Svoboda, Jan Mlynar, Umar Sheikh, Mathias Hoppe, Joan Decker, Jakub Čaloud, Vladimír Weinzettl, Martin Hron
Abstract:
The research on runaway electrons in tokamaks continues to be important for safe and reliable operation of large fusion devices due to the potential risk of impact of so called runaway electron beams on plasma facing components which could cause a serious damage and lead to putting the machine out of operation. In order to investigate the properties of runaway electrons and provide useful information about their behavior under different experimental conditions (e.g. efficiency of various mitigation techniques or exploration of runaway electrons free regimes) many dedicated diagnostics has been utilized. One way of inferring features of runaway electrons is a measurement of their bremsstrahlung radiation which is generated by collisions with plasma ions or by their impact on the first wall when runaway electrons are deconfined and lost. Recently, diagnostic capabilities at GOLEM [1] were upgraded by installation of two scintillation detectors with CeBr3 crystals (1” x 1”), which were also successfully tested during the dedicated runaway electron campaigns at the COMPASS tokamak [2]. Moreover, both scintillation detectors were also installed at the TCV tokamak to extend for the first time the hard x-ray radiation diagnostics and provide an estimates of the maximal energy of runaway electrons. The aim of this contribution is to describe the diagnostic used and experimental conditions of the different devices. Additionally, illustrative examples of experiments from these three different devices are presented and acquired data by the diagnostic system for HXR spectroscopy is discussed and put into the context. The comparison with other relevant diagnostics is shown. At the GOLEM tokamak the spectroscopy system was used to observe the influence of the initial pressure of the working gas and maximal energy of HXR photons was estimated about 300 keV. On the other hand at the COMPASS tokamak [3], the data recorded in experiments focused on characterizing runaway electron beams properties and the efficiency of various mitigation techniques (e.g. graphite pellet injection). At TCV [4], the installed set of scintillation detectors proved to be useful as a source of complementary information to standard radiation diagnostics and helped to characterized generated runaway electrons beams. This contribution also briefly shows a progress in modeling the radiation transport using FLUKA [5], carried out in order to better interpret the obtained data.
References
[1] V. Svoboda et al. 2019 Jour. Fus. En. 38.2 253-261
[2] J. Cerovsky et al. 2022 JINST 17 C01033
[3] J. Mlynar et al. 2019 Plasma Phys. Control. Fusion 61 014010
[4] J. Decker et al. 2022 Nucl. Fusion 62 076038
[5] C. Ahdida et al. 2022 Front. Phys. 705
* See the author list in M. Hron et al 2022 Nucl. Fusion 62 042021
** See the author list of H. Reimerdes et. al., 2022 Nucl. Fusion 62 042018
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Conceptual design of the visible / near-infrared camera system for the COMPASS Upgrade tokamak
Presenter:
Jordan Cavalier (Institute of Plasma Physics of the CAS, Za Slovankou 3, 182 00 Prague 8, Czech Republic)
Authors:
Jordan Cavalier, Miroslav Kral, Vladimír Weinzettl, Matej Tomes, Peter Vondracek, Petra Bilkova
Abstract:
This contribution describes the visible and near-infrared (~1 μm) camera systems which are planned to observe the interaction between the plasma and the first wall in the first phase of the COMPASS Upgrade operation. The COMPASS Upgrade tokamak is a compact mid-size (R = 0.9 m) device being designed and assembled at the Institute of Plasma Physics in Prague [1]. Extensive auxiliary plasma heating power is foreseen (several megawatts of NBI and ECRH), therefore, extreme heat fluxes of order of tens MW/m 2 towards the plasma facing components are expected in 1-3 s long discharges [2]. Consequently, some of these cameras will also be used as interlocks, protecting the first wall against overheating by monitoring the material temperature.
The requirements for the camera systems to be met are introduced, e.g. temperature range of the first wall to monitor, large field-of-views and spatial and temporal resolutions to be reached. Issues raised with selection and technical implementation of the chosen visible and near-infrared cameras are described in detail, including optical design for visible and infrared spectral regions. Because the first (plasma facing) mirrors have to withstand high operating temperature of the first wall (up to 500oC), the concept is a compromise between the occupied port space (compact tokamak) and the diagnostic requirements. Pros and cons of three different considered concepts [3,4.5] will be discussed. The systems placement and their expected field-of-view and coverage will then be shown.
References
[1] P. Vondracek et al. Fusion Engineering and Design 169 (2021) 112490
[2] V. Weinzettl et al. Fusion Engineering and Design 146 (2019) 1703-1707
[3] K. Kamiya et al. Fusion Eng. Des. 89 (2014) 3089–3094
[4] E. Gauthier et al. Fusion Eng. Des. 82 (2007) 1335
[5] A. Huber et al 2018 Nucl. Fusion 58 (2018) 106021
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Designing a Midplane Turbulence Probe for MAST-U
Presenter:
Will Fuller (The University of Warwick)
Authors:
Will Fuller, Scott Allan, Bogdan Hnat, John Omotani, Peter Ryan
Abstract:
Throughout the first MAST-U campaign there was focus on investigating the Super-X divertor and how alternative divertor configurations impact the dynamics of the scrape-off layer. Key phenomena born from turbulence, such as profile broadening and filamentary transport must be investigated to avoid possible damage to the first wall in future fusion reactors, including STEP. One way to study such phenomena is by probing edge and SOL plasma with a new probe head of the midplane reciprocating probe system installed on MAST-U. The system allows direct measurement of plasma properties producing a radial profile of the scrape-off layer. Current diagnostics are not specifically designed for the variety of measurements required to fully characterise SOL turbulence. This new probe head design was first synthetically iterated through a variety of models to reach the current design and includes several arrays of probes targeting different turbulence measurements. We include a logarithmically spaced probe array sampling a range of length scales. A five-pin balanced triple probe array has been included to gather fluctuation statistics of temperature and density simultaneously. We incorporated ball-pen probes designed for direct measurements of the plasma potential. There is a linear array of probes including a radial offset to calculate velocity statistics. Along with probes in other arrays, an additional radially offset probe is included to operate a mach probe setup, allowing plasma flows to be measured. This work will present the synthetic approach we used to design our turbulence probe, and the data presented will be compared to experimental and synthetic results from the existing Mach probe head and other diagnostics to determine the turbulence probe’s suitability for purpose. Unique results and future work will also be discussed to fully exploit the diagnostic subsequently.
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Machine-learning correction of misalignment effects in density profiles from Thomson scattering
Presenter:
Golo Fuchert (Max-Planck-Institut für Plasmaphysik (IPP), Greifswald, Germany)
Authors:
Golo Fuchert, Jule Frank, Shan Chen, Andrea Pavone, Marcus Beurskens, Sergey Bozhenkov, Jakob Brunner, Matthias Hirsch, Ekkehard Pasch, Robert Wolf
Abstract:
A number of effects can negatively impact the quality of experimental density profiles measured with laser Thomson scattering. Examples are laser misalignment, coatings on windows or detector drifts. At Wendelstein 7-X (W7-X), it was observed that vibrations and temperature changes along the beam-path lead to laser misalignment, which was the dominant error source for the electron density profiles during the first experimental campaigns. Countermeasures that are being implemented include mechanical improvements and a new calibration method, in which the laser position is monitored, both for the calibration measurements and for the actual experiments. This, however, requires a scan of laser positions during calibration, which has not been performed in the first experimental campaigns of W7-X. In order to correct existing data, the impact of laser misalignment had to be deduced from the density profiles themselves. The machine-learning based solution for this task is described in this contribution.
The first step to correct the impact of laser misalignment is to determine the laser position for the existing data, even though it has not been measured. It is not required to find the laser position in actual lab coordinates, but rather it is sufficient to distinguish different laser positions and to be able to tell which of those positions are close to each other. This is facilitated by the fact that that the laser misalignment does not impact every spatial point of the density profile (scattering volume) in the same way and, hence, leaves a characteristic fingerprint in the point-to-point variation between neighboring points in the profile. A special type of neural network, called an autoencoder, is used to classify these fingerprints and to represent them as an abstract laser position. It was shown experimentally that this abstract laser position is correlated with the actual laser position in lab coordinates. This also means that positions close to each other in one coordinate system can be assumed to also be close in the other. Consequently, the density profiles themselves contain enough information about the laser position to group profiles of similar laser positions together. In the second step, transformations between different laser positions are determined. With these transformations, profiles that have been measured at one abstract laser position can be mapped to a different one to see how the profile would look like, had it been measured at that other laser position. Finally, the abstract laser position that corresponds to the laser position during the absolute calibration has to be identified. Since in magnetically confined toroidal plasmas, density and temperature profiles are symmetric in magnetic coordinates, profiles measured close to the calibration position are more symmetric than profiles that have been measured far away from it. The reference position can be identified by ranking profiles by their symmetry. The transformation from a profile’s position to this reference position is the best estimate for the appropriate correction. Error bars can be estimated by transforming to neighboring positions. In this contribution, we apply this procedure to both synthetic data (for illustrational purpose) and experimental data.
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X-ray radiography of a titanium wire isochorically heated by laser-accelerated electrons
Presenter:
Olena Turianska ( 1)Focused Energy, 64291 Darmstadt, Germany 2)1) Universitè de Bordeaux, CNRS, CEA, CELIA, UMR 5107, F-33405, Talence, France)
Authors:
Olena Turianska
Abstract:
We performed an experiment using the laser Phelix at GSI to isochorically heat a wire and study its following expansion using time resolved X-ray radiography.
A mm-long titanium wire (50 µm in diameter) was irradiated on its tip by the laser pulse with duration τ=0.5 ps, energy E=50 J and intensity I~ 10^18 W/〖cm〗^2. Hot electrrosn were gereated innteh interaction and propagated along the wire isochorically heating the titanium material. X-ray emisison spectroscopy (FSSR) of the titanium K- line was performed to retrieve the wire temperature along the wire, i.e. T=T(z) where z=0 corresponds to the wire tip [1, 2].
After this initial quasi-instantaneous heating, the expansion of the wire was followed using time-resolved X-ray radiography. Backlighter target was 5um tungsten wire illuminated by a second laser beam with similar characteristics. Measurement of wire expansion was done at different time by changing the delay between the two laser beams. X-ray radiography was successfully used to measure plasma expansion and sound velocity cs = cs (z).
We observed how local plasma expansion velocity along the wire is consistent with the temperature extracted from FSSR data [2]
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A fast Thomson scattering system for the transient plasma physics phenomena in LHD
Presenter:
Ryo Yasuhara (National Institute for Fusion Science)
Authors:
Ryo Yasuhara, Hisamichi Funaba, Hiyori Uehara, Daniel Den Hartog
Abstract:
A fast Thomson scattering system is very powerful and has successfully measured various high-speed phenomena such as hydrogen pellet ablation dynamics and a partial plasma collapse phenomena. Also, we plan to challenge repetition rates of 100 kHz or higher by improving the power supply, increasing the thermal shock resistance of a laser medium, and increasing the efficiency of the pump source.
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Feasibility study of a Coherence Imaging Charge Exchange Recombination
Spectroscopy diagnostic for Wendelstein 7-X
Presenter:
Ramón López-Cansino (Department of Atomic, Molecular and Nuclear Physics, University of Seville, Seville, Spain)
Authors:
Ramón López-Cansino, Valeria Perseo, Eleonora Viezzer, Oliver Patrick Ford, David Matt Kriete
Abstract:
A feasibility study of a Coherence Imaging Charge Exchange Recombination Spectroscopy (CICERS) diagnostic has been carried out for the Wendelstein 7-X stellarator (W7-X). This diagnostic, based on Coherence Imaging Spectroscopy (CIS) [1] and Charge Exchange Recombination Spectroscopy [2], is expected to measure charge exchange radiation of the main impurity species present in the plasma. The spectral information of the radiation is encoded in a 2D fringe pattern, which is generated by birefringent plates, in order to obtain 2D maps of relevant impurity ion parameters such as rotation velocity, temperature and density after a demodulation procedure is applied to the fringe pattern.
A synthetic diagnostic has been developed, which enables the optimization of the design and components of the system, based on the already existing CIS diagnostic in W7-X [3], the latter optimized for impurity flow measurements from passive lines in the edge of the plasma. The CICERS system has been set up and characterized in the laboratory, finding good agreement in its behaviour when compared to the simulation results. This also increases the confidence of using the synthetic simulations in the calibration process of the diagnostic, which will be routinely calibrated with a laser before and after every measurement [4].
[1] J. Howard 2010 J. Phys. B: At. Mol. Opt. Phys. 43 144010
[2] R. J. Fonck 1985 Rev. Sci. Instrum. 56 855
[3] V. Perseo et al 2020 Rev. Sci. Instrum. 91 013501
[4] D. Gradic et al 2019 Fusion Eng. Des. 146 995–998
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CVD Diamond Tomography for the DTT Fusion Device
Presenter:
Silvia Palomba (“Tor Vergata” University of Rome, Italy)
Authors:
Claudio Verona, Gianluca Verona-Rinati, Marco Marinelli, Maurizio Angelone, Matteo Iafrati, Francesca Bombarda, Silvia Palomba, Silvia Cesaroni
Abstract:
The DTT tokamak [1] presently under construction at Frascati (Rome, Italy) is a relatively large device of major radius R= 2.19 m, minor radius a= 0.70 m, toroidal field on axis BT= 6 T, plasma current Ip= 5.5 MA. Even if designed to operate with Deuterium fuel, the neutron and gamma radiation flux will pose very substantial challenges for any diagnostic system required to operate in the proximity of, or inside the vacuum vessel, as in the case of typical Si diodes used for Soft-X-ray Tomography.
For this reason, a different kind of UV-SX photon detectors diodes is envisaged, namely the single crystal, Chemical Vapor Deposition (CVD) diamond detectors being produced at the laboratory of Industrial Engineering Department of the University of “Tor Vergata” in Rome. These have been successfully tested on JET [2] and FTU [3], but never in full tomographic layout (in fact only two detectors were installed on each machine), and their locations so removed from the torus that both radiation and heat were not a concern.
The CVD diamonds exhibit a number of attractive features: they are sensitive to radiation from 5.5 eV up to tens of keV but are visible blind and much more radiation resistant than silicon, especially the thin samples suitable for photon detection. They can also operate at room temperature with very high S/N ratios, are very small in size and, most importantly, they can be placed in the machine high vacuum, without need for Be windows. Furthermore, considering the geometry of DTT port ducts, the coverage of the plasma poloidal section required for a proper tomographic inversion is allowed only by placing the diodes very close to the plasma itself, but no vacuum breaks are permitted at such location: this essentially rules out the possibility of using standard Si or CdTe diodes, in addition to their poorer resistance to neutrons that would make them very short lived.
The main features of the CVD diamond tomography systems proposed for DTT are presented, with the results of the simulations used to guide the design of the optical layout and the various detector configurations adopted for different applications. The main technical issues associated with the mounting of a large number of diodes in close proximity to the plasma, insulation, cabling, heat and radiation loads, and front-end electronics will be discussed.
[1] R. Ambrosino et al, Fus. Eng. & Des.167 (2021) 112330
[2] M. Angelone et al., Nucl. Instrum. Methods A 623 (2010) 726
[3] F. Bombarda et al., Nucl. Fusion 61 (2021) 116004
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Application of a sparse sensor placement technique to the limited diagnostic set in DEMO
Presenter:
Joost Raukema (DIFFER - Dutch Institute for Fundamental Energy Research)
Authors:
Joost Raukema, Thomas Bosman, Ivo Classen, Tijs Wijkamp, Artur Perek, Gijs Derks, Jesse Koenders, Roger Jaspers
Abstract:
In DEMO, a demonstration fusion power plant, the amount of diagnostics will be reduced compared to current experimental nuclear fusion reactors. A sparse sensor placement technique [1] is used to deal with the limited diagnostic set for the case of spectroscopy, required for wall heat load control. Experimental camera data from the MANTIS system [2] at TCV [3] is used to create and verify a synthetic diagnostic approach. The synthetic diagnostic consists of a set of lines of sight looking at the divertor leg, with the aim of identifying the CIII emission profile. However, the method is expected to be applicable to other diagnostics as well.
The sparse sensor placement algorithm takes as input the radiation measured for a large set of lines of sight, resolved over a range of timesteps. A singular value decomposition (SVD) is performed to obtain a number of eigenmodes, or “eigen-emission profiles”. Then a pivoted QR-factorization is done to obtain the optimal sensor locations for reconstruction of the emission profile. Using the measurements of this limited set of sensors, the whole emission profile along the leg is reconstructed by multiplying the measured radiation of only those few lines of sight with their corresponding eigenmode. We demonstrate that it is feasible to use a calibration based on either data from previous experiments or simulated data from SOLPS. For DEMO, this means that a line of sight selection and set of eigenmodes can already be calculated before experiments are performed. This method can also be applied to reconstruct other profiles from emission measurements by adding them in the SVD, if they have sufficient relationship to the shape of the emission profile. For example, the peak target current density obtained with Langmuir probes can be reconstructed using the synthetic spectroscopy measurements.
[1] Manohar, K., et al. "Data-driven sparse sensor placement for reconstruction: Demonstrating the benefits of exploiting known patterns." IEEE Control Systems Magazine 38.3 (2018): 63-86.
[2] Perek, A., et al. "MANTIS: a real-time quantitative multispectral imaging system for fusion plasmas." Review of Scientific Instruments 90.12 (2019): 123514.
[3] Reimerdes, H., et al. "Overview of the TCV tokamak experimental programme." Nuclear Fusion 62.4 (2022): 042018.
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The first results of the HCN interferometer measuring atmospheric pressure air plasmas
Presenter:
Jibo Zhang (Institute Of Plasma Physics Chinese Academy Of Sciences)
Authors:
Jibo Zhang
Abstract:
A HCN heterodyne interferometer has been designed for measuring electron densities of Experimental Research Apparatus for Electromagnetic Science (ERAES) for hypersonic vehicle plasma in near space, whose density is from 1×1015 to 3×1019/m3 and the pressure is from 50Pa to 1500Pa. The light source is hydrogen cyanide (HCN) laser with wavelength of 337m, which has high spatial resolution compared with microwave interferometer. The interferometer is configured as a Mach-Zehnder interferometer, which intermediate frequency (IF) is generated by the Doppler shift with a rotating grating. The spatial and temporal resolution of the HCN interferometry is reach to about 14mm and 100s respectively. The antenna-coupled ALGaN/GaN-HEMT have been used as detectors which have more high sensitivity— typical RF responsivity is around 900 V/W — than VDI planar-diode Integrated Conical Horn Fundamental Mixers. The first results of the HCN interferometer designed for ERAES have been obtained in the recent experimental campaign, with phase resolution up to 0.04π, corresponding to a minimum detectable change of the line integral density 1.32×1013cm-2, which is sufficient to measure the electron density in the range of 1×1012-3×1013cm-3.
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Clippers ESTER Metrology Results
Presenter:
Patrice Bertelli (CEA-DAM)
Authors:
Patrice Bertelli
Abstract:
The LASER MEGA JOULE (LMJ) is a high power laser facility used and operated by the CEA. Located in the south of France, this facility provide an extrordinary instrument to study High Energy Density physics.
The experimental LMJ require the installation of several hundred measurement channels connected to high bandwidth digitizers whose inputs channel are regularly damaged by high amplitude parasitic pulses circulating in the facilty The ESTER Limiters (Limiteurs Electronique de Surtensions Transitoires Electriques Rapides Electronic Clippers Fast Transient Electric Surge), presented in this article, are the result of studies carried out by CEA teams for several years. In 2022, they made it possible to design and provide, a reliable and robust solution to ensure the protection of digitizer inputs (protection function) while ensuring the integrity of high-frequency experimental signals (integrity function). This article aims at presenting the technology used and afterwards at providing the results obtained that are related to the protection function for two transient pulse shapes (Amplitude: 600V/LMH: 200 ns; Amplitude: 1 kV/LMH: 6 ns). The integrity function is also addressed. The results show that the ESTER Limiters ensure the passage of 3 GHz HF signals without degradation in an amplitude range between -8 and +8V. Several tests on long experimental links (10, 20, 30 and 40 meters), typical of LMJ coaxial links used, are also presented. The results show that after appropriate digital processing, the original signal is perfectly reconstructed, without distortion, even in the presence of limiters. All the metrological results are presented on a sample of 20 limiters in order to check the homogeneity of the characteristics and the absence of manufacturing default processing.
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Impact of ambient temperature on the filter polychromators performance and accuracy of Thomson scattering diagnostics
Presenter:
Tongchuan Zhang (zhangtongchuan@swip.ac.cn)
Authors:
Tongchuan Zhang
Abstract:
Thomson scattering is one of the most important diagnostic methods for measuring plasma electron temperature and electron density. However, the performance of the avalanche photodiodes (APD) used in polychromators is greatly affected by the ambient temperature, and subsequently the change of ambient temperature will seriously affect the accuracy of Thomson scattering diagnostics. With the increase of ambient temperature from 17.7 to 21 degrees, the signals of all measuring channels of the polychromator are significantly reduced by ~30% (Fig. 1). Using the relative spectral response measured at different ambient temperatures, the electron temperature and electron density can be obtained. When the ambient temperature rises from 17 ℃ to 27 ℃, the electron temperature changes within ± 2%, while the electron density decreases by about a factor of 2. In general, the ambient temperature has little influence on the measurement of electron temperature, but has a greater influence on the electron density. These measurement and modeling results show that tight control and monitoring of the ambient temperature is required for high quality Thomson scattering diagnostic measurements.
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Novel multi-energy soft x-ray camera in the WEST tokamak: first data and synthetic diagnostic
Presenter:
Oulfa Chellai (Princeton Plasma Physics Laboratory)
Authors:
Oulfa Chellai, Luis F. Delgado-Aparicio, Didier Vezinet, Tullio Barbui, Rémi Dumont, Kenneth Hill, Philippe Malard, Novimir Pablant, Brentley Stratton
Abstract:
During the C6 campaign, the tungsten (W) Environment in Steady-state Tokamak (WEST)
tokamak was operated for the 1st time with a water-cooled full tungsten divertor -similar to that
of ITER- and long-pulse scenarios, making it an ideal environment for high-Z impurity transport
studies. In that context, a compact multi-energy ( 2-30 keV) soft x-ray diagnostic (MESXR)
[1] was deployed by PPPL in WEST for high-Z impurity transport studies and electron
temperature profile measurements. The ME-SXR consists of the PILATUS3 photon-counting
detector manufactured by DECTRIS Ltd. mounted on a pinhole camera with a temporal and
spatial resolution of 2 ms and 1-2 cm, respectively. The novelty of this soft x-ray diagnostic lies
in the fact that the lower-energy threshold is set independently on each one of the 100k pixels
with a high energy resolution (< 1 keV). The design, capabilities and engineering challenges of
the ME-SXR diagnostic are briefly presented here.
This contribution mainly presents the first data of the ME-SXR diagnostic acquired during
C6. A tentative comparison of the experimental x-ray emissivity with predictions made using
the synthetic diagnostic based on the FLYCHK suite [2] for the computation of the charge-state
distribution and x-ray emissivity of the plasmas as well as the ToFu [3] open-source python
library will also be presented.
This work is supported by the U.S. DOE-OFES under Contract No. DE-AC02-09CH11466.
References
[1] O Chellai, LF Delgado-Aparicio, P VanMeter, T Barbui, J Wallace, KW Hill, N Pablant, B Stratton, C Disch,
B Luethi, et al. Calibration of a versatile multi-energy soft x-ray diagnostic for west long pulse plasmas.
Review of Scientific Instruments, 92(4):043509, 2021.
[2] H-K Chung, MH Chen, WL Morgan, Yu Ralchenko, and RW Lee. Flychk: Generalized population kinetics
and spectral model for rapid spectroscopic analysis for all elements. High energy density physics, 1(1):3–12,
2005.
[3] D Vezinet. "https://github.com/tofuproject/tofu".
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CCD Direct Detection on a SPRED Spectrometer
Presenter:
Umar Sheikh (SPC, EPFL, Lausanne, Switzerland)
Authors:
Umar Sheikh, Basil Duval
Abstract:
Spectroscopic measurements are critical for tokamaks as they provide information on a range of plasma parameters such as composition, power loss channels, impurity content and plasma-wall interaction. The vacuum ultraviolet (VUV) spectral range is of particular importance due to the photon energies emitted by ions in the core and hot divertors. The standard diagnostic used on tokamaks in this spectral range is a grazing incidence “survey, poor resolution, extended domain” (SPRED) spectrometer [1]. This spectrometer is combined with a microchannel plate (MCP) image intensifier, fiber-optically coupled to a Reticon photodiode array. The high voltage and vacuum requirements of the MCP led to reliability issues on the SPRED system installed on the TCV tokamak. Currents induced during plasma disruptions, and increases in vacuum pressure during divertor experiments, were enough to cause arcing and trips on the power supply. These issues were more prevalent on TCV due to the proximity of the system to the tokamak (~3m). It was therefore decided to simplify the system using a direct detection CCD camera.
A thinned, back-illuminated CCD from GreatEyes® was selected due to its sensitivity in the VUV, camera design flexibility and price. A camera design modification was required to offset CCD chip itself from the camera base in order to place it in the focal plane. Once installed, the system was aligned and calibrated using a hollow cathode lamp and visible light sources. As the CCD could operate at atmospheric pressure, a new alignment procedure using zeroth order reflections was developed and will be outlined in this paper. The spectral resolutions achieved were 2.5A and 0.7A for the 450g/mm and 2105g/mm gratings respectively. This represented a 2-3x increase in spectral resolution over the legacy MCP detector system. The CCD detector system has now worked reliably on TCV for over 20,000 plasma discharges. It has been routinely used to assess plasma core content variations due to impurity seeding or the sputtering of material, and provide long term stability analyses that have led to the identification of events which produced impurity injections into the machine.
References
[1] Fonck, R. J., A. T. Ramsey, and R. V. Yelle. "Multichannel grazing-incidence spectrometer for plasma impurity diagnosis: SPRED." Applied Optics 21.12 (1982): 2115-2123
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Investigation of the released p-11B fusion energy from proton beam interaction with 11B target
Presenter:
Chrysovalanti Daponta (Technical University of Crete)
Authors:
Chrysovalanti Daponta, Stavros Moustaizis, Paraskeuas Lalousis
Abstract:
Between the so-called “advanced fusion fuels”, p-11B nuclear fusion reaction is of interest, due to the production of three (3) iso-energetic charged alpha particles with 8.7 MeV total energy, which can directly be converted into electricity [1, 2, 3]. In the present work, we examine the possibility of exploiting the energy of these three (3) fusion produced alpha particles, considering the interaction of a beam of accelerated protons with a solid 11B target. During this kind of interaction, protons with a kinetic energy between 650 keV and 1MeV are of particular interest, as in this energy range, the exploitation of the 675keV resonance is possible. As the protons move through the solid 11B target, they lose gradually their initial kinetic energy EK(0), in the context of a Continuous Slowing Down Approximation (CSDA). Stopping power expresses the specific energy loss rate per unit path length of the protons inside the 11B target and can be used for the determination of their range – penetration depth (RCSDA) in the solid 11B material, through the integration of the Bethe-Bloch formula. Protons deposit the biggest part of their energy in the Bragg peak. However, until the end of their range in the 11B target, where they have eventually lost all of their initial kinetic energy and stop, p -11B nuclear fusion reactions are induced. In a specific position z inside the 11B target, the production of alphas depends on the number of protons, the solid 11B target particle density and the cross section corresponding to the residual energy of protons. As it is observed through our numerical evaluations, when the protons initial kinetic energy is higher, the production of alpha particles increases significantly, while the maximum production of alpha particles occurs at a greater depth within the 11B target. The alpha particles produced from p-11B nuclear fusion reactions inside the 11B target, can either exit its two sides (in a straight line or at an angle θ), or remain inside it, if the distance to be travelled is greater than their range in solid 11B. The use of the Bragg-Kleeman rule enables us to determine the alpha range in the 11B target. Determining a suitable 11B target thickness and considering a uniform alpha particle energy loss across their path, we calculate the energy spectrum and the angular distribution of the alphas exiting the 11B target. This evaluation could be useful for the determination and the development of a potential experimental diagnostics configuration, concerning the alpha particles production detection. The study of two schemes, one electrical and one thermal, for the conversion of alpha energy into electrical energy, shows that the configuration of the proton beam interaction with the 11B target is not effective for energy production. The number of protons in the beam remains relatively small, regardless of whether it is produced using a high-intensity laser beam [4, 5, 6] or high current pulsed power technology [7]. As an example, it is noteworthy to mention that a compact pulsed power device, operating at 800 kV-1MV, with a pulse duration between 100ns - 1 μs, produces a proton beam current of 15 kA [7], that is able to deliver ~ 10 17 protons to the Boron target. Considering a repetition rate of a 10Hz, a 100% conversion efficiency of the proton beam to three (3) 2.9 MeV fusion born alphas and no input power losses for the operation of the pulsed power device, the output p-11B fusion power would be of the order of 1.5 MW. However, in a more realistic case, the alpha production efficiency is 10-3–10-4, the input electric power losses are ~20% for the proton beam generation and the remaining alphas in the Boron target reduce the useful electric output power to the range of kWatt, which is much lower than the input power of the proton beam. Thus, in the context of more efficient schemes, recent efforts concern a hybrid configuration, in which a proton beam interacts with a plasma [8] or with a relatively low temperature 11B medium (~< 100 eV) [9]. These two schemes allow the determination of the stopping power and the fusion probability (as a function of the electron density), as well as of the contribution of potential related processes, such as the chain reaction and the avalanche effect [9, 10].
References
[1] H. Hora, S. Eliezer, G. J. Kirchhoff, N. Nissim, J. X. Wang, Y. X. Xu, G. H. Miley, J. M. Martinez-Val, W. McKenzie, and J. Kirchhoff, “Road map to clean energy using laser beam ignition of boron-proton fusion,” Laser and Particle Beams, vol. 35, no. 4, p. 730–740, 2017.
[2] H. Hora, “Clean boron fusion using extreme laser pulses: A laser-driven technique to ignite proton-boron fuel offers the possibility of nuclear fusion for clean, Sustainable energy generation”, SPIE, The international society for optics and photonics, httpt://spie.org/, 14 July 2015.
[3] https://hb11.energy
[4] A. Picciotto, D. Margarone, A. Velyhan, P. Bellini, J. Krasa, A. Szydlowski, G. Bertuccio, Y. Shi, A. Margarone, J. Prokupek, A. Malinowska, E. Krouski, J. Ullschmied, L. Laska, M. Kucharik, and G. Korn, “Boron-Proton Nuclear-Fusion Enhancement Induced in Boron-Doped Silicon Targets by Low-Contrast Pulsed Laser”, Phys. Rev., vol. X 4, p. 031030, 2014.
[5] D. Margarone, A. Picciotto, A. Velyhan, J. Krasa, M. Kucharik, A. Mangione, A. Szydlowsky, A. Malinowska, G. Bertuccio, Y. Shi, M. Crivellari, J. Ullschmied, P. Bellutti, and G. Korn, “Advanced scheme for high-yield laser driven nuclear reactions”, Plasma Physics Controlled Fusion, vol. 57, p. 014030, 2015.
[6] D. Margarone, J. Bonvalet, L. Giuffrida, A. Morace, V. Kantarelou, M. Tosca, D. Raffestin, P. Nicolai, A. Piccioto, Y. Abe, Y. Arikawa, S. Fujioka, Y. Fukuda, Y. Kuramitsu, H. Habara, and D. Batani, “In-Target Proton-Boron Nuclear Fusion Using a PW-Class Laser”, Applied Sciences, vol. 12, p. 1444, 2022.
[7] K. Perrakis, S. D. Moustaizis and P. Lalousis, “Numerical investigations on high flux neutron production from a high-current pulsed ion device”, Proceedings of the 47th Conference on Plasma Physics, 2021.
[8]Thomas. A. Mehlhorn, L. Labun, B. M. Hegelich, et al., "Path to Increasing p-B11 Reactivity via ps and ns Lasers", LPB, 2022, 2355629, 16 p, (2022).
[9] N. Nissim, Z. Henis, C. Daponta, S. Eliezer, S.D Moustaizis, P. Lalousis and, Y. Schweitzer, “Parametric scan of plasma parameters for optimization of the avalanche process in p11B fusion”, Presentation in the 2nd International Workshop on proton-Boron fusion, Catania, Sicily, 5-8 September 2022.
[10] S. Moustaizis, C. Daponta, S. Eliezer, Z. Henis, P. Lalousis, N. Nissim and, Y. Schweitzer, “Alpha heating and avalanche effect simulations for low density proton-boron fusion plasma”, Presentation in the 2nd International Workshop on proton-Boron fusion, Catania, Sicily, 5-8 September 2022.
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First results of a multi-energy hard x-ray camera on the WEST tokamak
Presenter:
Tullio Barbui (Princeton Plasma Physics Laboratory)
Authors:
Tullio Barbui, Luis F. Delgado-Aparicio, Brentley Stratton, Oulfa Chellai, Rémi Dumont, Kenneth Hill, Novimir Pablant
Abstract:
The WEST tokamak recently completed its first experimental campaign with the new water-cooled full tungsten divertor, which enables long pulse operation. Heating is provided by radiofrequency systems, including lower hybrid current drive (LHCD). In this context PPPL has operated for the first time a compact multi-energy hard x-ray camera (ME-HXR) for energy and space-resolved measurements of the electron temperature, the fast electron tail density produced by LHCD and runaway electrons, and the beam-target emission of tungsten at the edge due to fast electron losses interacting with the target.
The diagnostic is a pinhole camera based on a 2D pixel array detector equipped with a CdTe sensor. The novelty of this diagnostic technique is the detector capability of adjusting the threshold energy at pixel level. This innovation provides a great flexibility in the energy configuration allowing simultaneous space, time and energy resolved x-ray measurements.
This contribution presents first measurements of the new diagnostic on the WEST tokamak. Line-integrated measurements of hard x-rays were acquired during LHCD discharges along ~80 lines-of-sight covering most of the plasma cross section including the lower divertor. 4-6 discreet energy threshold settings were used over the range of 10-100keV. Radial position of LH power deposition was identified from the slope of the HXR profiles. Beam-target emission was observed along the lines-of-sight intersecting the lower divertor.
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Motional Stark effect modelling for CASPER
Presenter:
Péter Balázs (Institute of Nuclear Techniques, Budapest University of Technology and Economics, Budapest, Hungary ; Centre for Energy Research, Budapest, Hungary)
Authors:
Péter Balázs, Aleksei Shabashov, Matej Tomes, Mireille Schneider, Maarten De Bock, Gergő Pokol
Abstract:
The motional Stark effect (MSE) describes the spectral splitting of the light emitted by neutral atomic beams traversing a strong magnetic field. The degree of splitting is dependent on the magnitude of the magnetic field, while the polarization is determined by the direction of the field. Therefore, observing this effect in the heating or diagnostic beams of fusion devices allows for local magnetic field measurements inside the plasma. The splitting itself is rarely resolvable in todays’ machines, leaving the method for only field direction measurements. However, in a machine like ITER, with a stronger magnetic field, the splitting will be stronger and the spectrum is expected to be resolvable. With this capability, the planned MSE system on the machine will primarily be used to measure the q-profile, but it will also be useful for plasma current and toroidal field measurements.
CASPER (CAmera & SPectroscopy Emission Ray-tracer) is the code responsible for the modelling of several optical plasma diagnostics for ITER, such as charge exchange or visible spectroscopy. CASPER uses the Integrated Modelling and Analysis Suite (IMAS) [1], making it generic to simulate the light spectrum for various synthetic diagnostics in the visible range. It is designed to build scenes for Raysect & Cherab [2], a framework tailored for the ray-tracing simulation of fusion environments. With this method, it is possible to simulate the observed spectrums realistically, burdened by background emissions and reflections. CASPER has been designed to be progressively extended with new physics processes and new diagnostics. So far CASPER lacked the ability to also simulate the emission of neutral beams with the MSE accurately taken into account, however, with plans of multiple dedicated MSE diagnostics observing the heating and diagnostic neutral beams in the machine, this is a serious requirement that the code has to fulfill.
This issue has been recently addressed and accurate beam emission calculation has been added to CASPER. The spectrum calculation was adopted from the MSESIM [3] code, and has a quantum mechanical basis. This has been integrated into CASPER together with a branch of Cherab still under development, allowing for flexible beam modelling. The first test results produced by the improved code are presented here.
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
References:
[1] F. Imbeaux et al, 2015 Nucl. Fusion 55 123006
[2] M. Carr, et al, Rev. Sci. Instrum. 89, 083506 (2018)
[3] M. F. M. De Bock, et al, Rev. Sci. Instrum. 79, 10F524 (2008)
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Simultaneous measurement of co- and counter-current ions with a Fast Ion Loss Detector on the TCV tokamak
Presenter:
Jesús Poley (Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland.)
Authors:
Jesús Poley
Abstract:
Supra-thermal ions play an essential role in the plasma’s heating, current drive, and production of the fusion reactions. The supra-thermal ion confinement is critical to prevent degradation of the fusion performance and damage to the plasma-facing components [1]. To study the supra-thermal ion confinement on tokamaks, a wide range of diagnostics can be used, such as Neutral Particle Analyzers (NPA), Fast Ion Deuterium Alpha detectors (FIDA) and Fast Ion Loss Detectors (FILD) [2]. To this end, a new FILD has been designed, installed, and used for the first time on the TCV tokamak. The diagnostic has a high-resolution medium-speed (up to 10 kHz) camera to characterise the velocity space parameters of the supra-thermal ion losses and a fast acquisition system (up to 2MHz) based on a Photo Multiplier Tube (PMT) to characterise the supra-thermal ion losses frequency spectra. However, recently the PMT has been replaced with a 128-avalanche photodiode matrix camera which allows a fast response (up to 4MHz) with a medium spatial resolution (~ 5-10 keV in energy and ~ 0.1-0.15 in pitch, 𝑣∥/𝑣). A double collimator has been installed to simultaneously measure co- and counter-current supra-thermal ions for the first time. A fast removal system was also installed, which retracts the FILD if the temperature in the head (measured by means of a pyrometer) reaches more than 300 degrees Celsius. This allows respectively measuring the FI losses in both plasma current directions and inserting the detector closer to the plasma without the risk of damaging the FILD head. A synthetic characterization of the diagnostic using the e-FILDSIM code [3] has been developed, allowing the data interpretation and possibly the implementation of reconstruction techniques currently under development. Measurements over a wide range of equilibria have already been taken to explore the detector’s capabilities showing the FI first orbit losses of both NBI beams installed on TCV, as well as the FI interaction with MHD activity at frequencies up to 100kHz, which appear correlated with the magnetic perturbations, the neutron measurements, and the soft X-ray emission. Modelling using the orbit following code ASCOT5 agrees qualitatively with the experimental observations of the first orbit losses on the FILD. With the already installed NPA, FIDA, and fast neutron detector, the FILD extends the FI studies on the TCV tokamak.
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Novel approach to proton-boron fusion using protons generated through laser-induced thermonuclear DD reaction
Presenter:
Przemysław Tchórz (Institute of Plasma Physics and Laser Microfusion)
Authors:
Przemysław Tchórz, Tomasz Chodukowski, Marcin Rosiński, Maciej Szymański, Stefan Borodziuk
Abstract:
Majority of current research related to proton-boron approach of laser fusion employ hundreds of TW and PW-class laser systems to increase yield of alpha particles produced during p+(_^11)B reaction [1][2]. Recently, such laser systems became much more accessible, however the importance of enabling as many research groups as possible to contribute in the laser-fusion field requires seeking alternative approaches that could be implemented using moderate laser intensities. In this work we report generation of energetic (E_max>4 MeV), intense and directed proton beam during Cavity Pressure Acceleration (CPA) scenario of laser-matter interaction, where CD_2 foils were used inside the target cavity [3][4]. The origin of these protons is one of deuterium-deuterium fusion reaction channels, in which (_1^3)H and p^+ are produced. The measurements of proton energy spectra carried out during this experiment served as an input for preliminary Monte Carlo simulations (FLUKA) [5]–[7] of proton beam colliding with boron targets of different thickness, which suggest potential for few-TW laser systems to generate alpha particle flux comparable to these achieved using the most powerful laser beamlines.
References
[1] J. Bonvalet et al., “Energetic α-particle sources produced through proton-boron reactions by high-energy high-intensity laser beams,” Phys Rev E, vol. 103, no. 5–1, May 2021, doi: 10.1103/PHYSREVE.103.053202.
[2] D. Margarone et al., “In-Target Proton-Boron Nuclear Fusion Using a PW-Class Laser,” Applied Sciences 2022, Vol. 12, Page 1444, vol. 12, no. 3, p. 1444, Jan. 2022, doi: 10.3390/APP12031444.
[3] T. Chodukowski et al., “Neutron production in cavity pressure acceleration of plasma objects,” AIP Adv, vol. 10, no. 8, Aug. 2020, doi: 10.1063/5.0005977.
[4] S. Borodziuk, A. Kasperczuk, and T. Pisarczyk, “Cavity pressure acceleration: An efficient laser-based method of production of high-velocity macroparticles,” Appl. Phys. Lett, vol. 95, p. 231501, 2009, doi: 10.1063/1.3271693.
[5] V. Vlachoudis, “FLAIR: A POWERFUL BUT USER FRIENDLY GRAPHICAL INTERFACE FOR FLUKA,” 2009.
[6] G. Battistoni et al., “Overview of the FLUKA code,” Ann Nucl Energy, vol. 82, pp. 10–18, Aug. 2015, doi: 10.1016/J.ANUCENE.2014.11.007.
[7] C. Ahdida et al., “New Capabilities of the FLUKA Multi-Purpose Code,” Front Phys, vol. 9, p. 705, Jan. 2022, doi: 10.3389/FPHY.2021.788253/BIBTEX.
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Program