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A beam emission spectroscopy (BES) diagnostic is designed for studying two-dimensional turbulent dynamics by measuring the Doppler-shifted Balmer-Alpha emission (n = 3 → 2) from neutral heating beams on Wendelstein 7-X (W7-X) stellarator. The BES viewing geometry has been determined in the conceptual design previously. However, the small Doppler shifts and small optical throughput compared to a typical BES diagnostic demand dedicated efforts on the optical assemblies and the detector module for the BES system. We present the detailed opto-mechanical design and specifications of BES, including a customized neutral beam viewing optical system, a semi-telecentric optical assembly, and a detector module for electronic amplification. The point spread function is calculated using the pyFIDASIM code with experimental parameters and W7-X magnetic configurations to estimate the BES spatial resolution and beam intensity. The as-manufactured interference filter is applied for the spectral isolated beam radiance calculation. Result shows that the BES system is capable of measuring the ion-scale turbulence for k pi ≤ 0.4 at r/a = 0.75 with reasonable spatial and wavenumber resolutions. An integrated detector module is fabricated where two 8 × 4 avalanche photodiode detectors (APD) are embedded into the custom-designed pre-amplifier circuit to gain signals to the desired level. The detector noise measurement is performed and the signal-to-noise ratio (SNR) is evaluated. A detectable fluctuation level can be achieved as low as ñe/ne ≈ 0.5% at frequency f ≤ 400 kHz with a bandwidth of 1 MHz.

Runaway electron gamma-ray detection system, a novel hard x-ray (HXR) spectrometer optimized for bremsstrahlung radiation measurement from runaway electrons in fusion plasmas, has been developed. The detector is based on a 1‘×1’ LaBr3:Ce scintillator crystal coupled with a photomultiplier tube. The system has an energy dynamic range exceeding 20 MeV with an energy resolution of 3% at 661.7 keV. The detector gain is stable even under severe loads, with a gain shift that stays below 3% at HXR counting rates in excess of 1 MCps. The performance of the system enables unprecedented studies of the time-dependent runaway electron energy distribution function, as shown in recent runaway electron physics experiments at the ASDEX Upgrade and COMPASS tokamaks.

angential compact neutron emission spectrometer (CNES) based on the Cs2LiYCl6:Ce with 7Li-enrichment (CLYC7) scintillator is newly installed in the Large Helical Device (LHD). Measurement of neutron energy spectrum was performed using CNES in tangential neutral beam (NB) heated deuterium plasma discharges. The Doppler shift of neutron energy according to the direction of tangential NB injection has been obtained. When the fast ions moving away from the CNES, lower shifted neutron energy is obtained, whereas the upper shifted neutron energy is obtained when the fast ions moving toward the CNES. The obtained neutron energy is almost consistent with the virgin deuterium-deuterium neutron energy evaluated by the simple two-body kinematic calculation., source:S. Sangaroon et al 2021 JINST 16 C12025, source:https://doi.org/10.1088/1748-0221/16/12/C12025, identifier:0000-0002-0160-0468

The future DEMO tokamak will be equipped with a suite of diagnostics which will operate as sensors to monitor and control the position and operation parameters of DT plasmas. Among the suite of sensors, an integrated neutron and gamma-ray diagnostic system is also studied to verify its capability and performance in detecting possible DEMO plasma position variations and contribute to the feedback system in maintaining DEMO DT plasma in stable conditions. This work describes the progress of the conceptual study of the gamma-ray diagnostic for DEMO reactor performed during the first Work-Package contract 2015-2020. The reaction of interest for this Gamma-Ray Spectrometer Instrument (GRSI) consists of D(T, gamma)He-5 with the emission of 16.63 MeV gamma rays. Due to DEMO tokamak design constraints, the gamma and neutron diagnostics are integrated, both featuring multi-line of sight (camera type), viewing DEMO plasma radially with vertical (12) and horizontal (13) viewing lines to diagnose the. and neutron emission from the DT plasma poloidal section. The GRSI design is based on the investigation of the reaction cross sections, on the calculations performed with GENESIS and MCNP simulation codes and on the physics and geometry constrains of the integrated instrument. GRSI features long collimators which diameters are constrained by the neutron flux at the neutron detectors of the Radial Neutron Camera (RNC) system placed in front, which are key to control DEMO DT plasma position. For these reasons, only few GRSI parameters can be independently selected to optimize its performance. Among these, the choice of the collimator diameters at the back side of the neutron detector box up to the GRSI detector, the use of LiH neutron attenuators in front of the GRSI detectors, the GRSI detector material and shielding. The GRSI detector is based on commercial LaBr3(Ce) inorganic scintillating crystal coupled with a photomultiplier tube or a silicon photomultiplier. They are designed

A real-time control system is being developed for a magnetically driven Fast-Ion Loss Detector (FILD) at the ASDEX Upgrade tokamak. The insertion of the diagnostic head will be adjusted in real-time to react to changes in the graphite head temperature, plasma position and appearance of MHD instabilities. The graphite probe head of the detector is exposed to an intense heat flux (located ∼3–5 cm from separatrix). The control algorithm performance is constrained by: the graphite head sublimation temperature, the ultimate stress limit, the reaction time of the controller and the retraction time. In this work, the temperature and thermal induced stress distribution on the probe head are assessed to determine what temperature-related magnitude is the limiting factor. The heat flux at the probe head has been estimated using the time-averaged parallel heat flux measured at the divertor target via infrared thermography. A field line tracing algorithm determines which regions of the probe head receives a weighted heat flux due to shadowing (self-induced or from other structures) and the incidence angle of the field lines. A finite element model is used to simulate the temporal evolution of the graphite head temperature and to obtain the induced thermal stress. The temperature spatial distribution at the probe head is validated against measurements of the probe head for different FILD systems showing a good agreement. These measurements have been obtained from visible cameras with an infrared filter. The model concludes that the maximum stress (∼100 MPa) does not overcome the graphite mechanical limit (170 MPa) and that the probe head is not affected by fatigue. Therefore, the graphite sublimation temperature (2000 °C) is set as the limiting factor of the new control system.

Unfolding techniques are employed to reconstruct the 1D energy distribution of runaway electrons from Bremsstrahlung hard X-ray spectrum emitted during plasma disruptions in tokamaks. Here we compare four inversion methods: truncated singular value decomposition, which is a linear algebra technique, maximum likelihood expectation maximization, which is an iterative method, and Tikhonov regularization applied to chi(2) and Poisson statistics, which are two minimization approaches. The reconstruction fidelity and the capability of estimating cumulative statistics, such as the mean and maximum energy, have been assessed on both synthetic and experimental spectra. The effect of measurements limitations, such as the low energy cut and few number of counts, on the final reconstruction has also been studied. We find that the iterative method performs best as it better describes the statistics of the experimental data and is more robust to noise in the recorded spectrum.

A scintillating-fiber (Sci-Fi) detector has been employed to measure 14 MeV neutrons for the triton burnup study in the first deuterium plasma campaign of the Large Helical Device (LHD). The pulse-height spectra of the Sci-Fi detector are used to choose a suitable threshold for the discrimination of 14 MeV neutrons from a mix-radiation field of low-energy neutrons and gamma-rays. The measured pulse-height spectra of the Sci-Fi detector have two components with different decay slopes from the LHD experiment. To study the pulse-height property of the Sci-Fi detector, the pulse-height spectra on different energy neutrons have been measured by using the accelerator-based neutron source with d-D, p-Li, and d-Li reactions. Meanwhile, the simulations of the detector response have been performed by using the Particle and Heavy Ion Transport code System (PHITS). In the LHD experiment, the first decay component of the pulse-height spectra in low-pulse-height region has been found to correspond to the signals induced by 2.45 MeV neutrons and gamma-rays. In addition, the high-pulse-height region has been confirmed by both the accelerator experiment and the PHITS calculation to correspond to the recoil-proton edge induced by triton burnup 14 MeV neutrons. The detection efficiency of 14 MeV neutrons for the Sci-Fi detector calculated by the PHITS code agrees well with the detection efficiency of 14 MeV neutrons for the Sci-Fi detector evaluated in the LHD experiment. The Sci-Fi detector can work as a standard detector for the 14 MeV neutron measurement with a suitable threshold., source:Citation N. Pu et al 2019 JINST 14 P10015, source:https://doi.org/10.1088/1748-0221/14/10/P10015

We have upgraded the multi-channel microwave reflectometer system which uses a frequency comb as a source and measure the distribution of the density fluctuation caused by magneto-hydro dynamics instability. The previous multi-channel system was composed of the Ka-band, and the U-band system has been developed. Currently, the U-band system has eight frequency channels, which are 43.0, 45.0, 47.0, 49.0, 51.0, 53.0, 55.0, and 57.0 GHz, in U-band. Before the installation to the Large Helical Device (LHD), several tests for understanding the system characteristics, which are the phase responsibility, the linearity of output signal, and others, have been carried out. The in situ calibration in LHD has been done for the cross reference. In the neutral beam injected plasma experiments, we can observe the density fluctuation of the interchange mode and obtain the radial distribution of fluctuation amplitude., source:Citation R. Soga et al 2016 JINST 11 C02009, source:https://doi.org/10.1088/1748-0221/11/02/C02009

In order to study fast ion confinement and transport mechanisms both in quiescent plasmas and in the presence of magneto-hydrodynamic (MHD) activity, an electric field parallel to the magnetic field type neutral particle analyzer (E|B-NPA) was installed using Micro-Channel Plates (MCPs) in the Large Helical Device (LHD). The E|B-NPA is an established diagnostic used to measure the energy distribution of charge exchange neutral particles escaping from plasmas corresponding to hydrogen, deuterium, and tritium, respectively. The LHD deuterium experimental campaign started in 2017. To obtain more details of MHD behavior, we improved on time resolution performance of the E|B-NPA using a high-speed Pre-Amplifier and Discriminator (PAD) and Latching Scaler Module (LSM). For the last LHD experimental campaign, the E|B-NPA was installed on nearly the equatorial plane of the vacuum chamber to measure the passing energetic particles generated by tangentially injected neutral beams. As the results of the E|B-NPA commissioning, it is confirmed that the E|B-NPA successfully detected the energetic particles and obtained the energy distributions corresponding to hydrogen. Also, the effect of the neutron to E|B-NPA is estimated using the other neutron diagnostics during the experiments., source:Y. Fujiwara et al 2020 JINST 15 C02021, source:https://doi.org/10.1088/1748-0221/15/02/C02021

A phase contrast imaging (PCI) diagnostic has been developed for the Wendelstein 7-X (W7-X) stellarator. The PCI diagnostic provides a line-integrated measurement of turbulent electron density fluctuations, which is essential for understanding high performance scenarios that can lead to improved confinement at fusion-relevant temperatures and densities. The PCI system is also sensitive to coherent fluctuations, which arise from Alfvén eigenmodes or other MHD activity. This paper provides an overview of the hardware and the optical system and presents an example PCI measurement from the W7-X OP1.2b experimental campaign.

An important instrumental development work has been done in the last two decades in the field of neutron and gamma ray spectroscopic measurements of magnetic confinement plasmas. Starting from the present state of the art instrumentation installed at JET, this paper reviews the recent development that has been carried out within the EUROFUSION programme for the forthcoming high power JET D and DT campaign. This development was dedicated to the realization of new compact neutron and gamma-ray spectrometers which combine very high energy resolution (typically better than 5%) and MHz counting rate capabilities allowing for time resolution in the 10 ms time scale. One of the advantages offered by the compact dimensions of these spectrometers is to make possible their use in multiple sight-line camera configurations, such as for future burning plasma reactors (ITER and DEMO). New compact neutron spectrometers based on single crystal diamond detectors have been developed and installed at JET for measurements of the 14MeV neutron spectrum. Measurements on a portable DT neutron generator have shown that neutron spectroscopy of the accelerated beam ions at unprecedented energy resolution (similar to 1% at 14 MeV) is possible, which opens up new opportunities for diagnosing DT plasmas. For what concerns gamma ray measurements, the JET gamma ray camera has been recently upgraded with new compact spectrometers based on a LaBr3 scintillator coupled to Silicon Photomultiplier with the dual aim to improve the spectroscopic and rate capabilities of the detectors. The upgrade camera system will reconstruct the spatial gamma ray emissivity from the plasma in the MeV energy range at MHz counting rates and energy resolution in the 2-4% range. This will allow physics studies of gamma rays produced by the interaction of fast ions with impurities in the plasma and bremsstrahlung emission from runaway electrons.

A synthetic diagnostic has been developed for the JET lost alpha scintillator probe, based on the ASCOT fast ion orbit following code and the AFSI fusion source code. The synthetic diagnostic models the velocity space distribution of lost fusion products in the scintillator probe. Validation with experimental measurements is presented, where the synthetic diagnostic is shown to predict the gyroradius and pitch angle of lost DD protons and tritons. Additionally, the synthetic diagnostic reproduces relative differences in total loss rates in multiple phases of the discharge, which can be used as a basis for total loss rate predictions., For complete list of authors see http://dx.doi.org/10.1088/1748-0221/14/09/C09018

This paper discusses the pre-conceptual design of the European DEMO neutron diagnostics aimed at the measurement of the fusion power, the plasma displacement and the fuel ion ratio for plasma burn control. The design has been based on the European DEMO design concept with a single divertor and on the so-called DEMO1 plasma scenario but limited only to the steady phased of the discharge. The suggested neutron diagnostics consist of neutron activation systems, fission chambers and vertical and horizontal collimated neutron flux monitors with spectroscopy capabilities. The fusion power can be measured with an accuracy of 1% with a time resolution of one tenth of the energy confinement time and the plasma displacement with a time resolution of 1 ms. Central ion temperature and fuel ion ratio instead can be measured with a time resolution of about 1 s. Calibration and interfacing issues are discussed.

The work presented is a realistic simulation of the response function for a detection efficiency optimized Thin-foil proton recoil (TPR) neutron spectrometer. The TPR spectrometer consists of a thin foil acting as neutron-to-proton converter followed by Delta E-E detectors operating in coincidence mode. In this work, two different spectrometer designs were considered using segmented silicon detectors. Design 1 has slightly better resolution while design 2 is more compact and has higher efficiency. The TPR spectrometer response functions were simulated in the energy range 8-18 MeV in steps of 40 keV for the two designs using the dedicated Monte Carlo code GEANT4. The resulting simulated response functions were broadened using experimentally determined energy resolutions of the detectors, in order to produce more realistic response functions. Using these broadened response functions together with an ITER like neutron spectrum and neutron induced background simulations Delta E/E energy deposition plots were created. The energy-cuts, for 14 MeV neutron signal identification, were applied to the Delta E-E plots leading to an estimate of the expected signal-to-background ratio. In addition, pile-up fraction and maximum expected count rates were estimated. Results show that the Delta E-E energy cuts show a great prospect of increasing the signal-to background ratio for the TPR spectrometer. In addition the TPR spectrometer has energy resolution (FWHM/E) of around 5% for 14 MeV neutrons for both investigated designs. The spectrometer can cope with maximum count rate expected and have a sufficient signal-to-background ratio in the neutron energy range of interest to perform fuel ion ratio measurements. However an increase of acquisition channels would be beneficial to limit the pile-up rate.

The Neutron Camera installed at the Mega Ampere Spherical Tokamak (MAST) provided fundamental information regarding the neutron emission and the behavior of fast ions. The signal measured by the Neutron Camera depended on its observation direction relative to the plasma region. Furthermore, only a certain part of the energy-pitch region contributed to the measured signal. This region is determined by the fast ion Weight Functions. In this paper, the Weight Functions of the Neutron Camera are calculated using DRESS. The results show that the instrument is most sensitive to neutrons created in fusion reactions involving a thermal ion and an ion in the beam energy region. Synthetic spectra are also calculated and, after folding with the detector's response function, compared with experimental pulse height spectra for three selected plasma discharges. Also, Weight Functions for the Neutron Camera Upgrade on MAST-U are calculated and discussed. The results can be applied for future fast ion studies at MAST-U, combining Neutron Camera Upgrade data with those of other fast ion diagnostics, such as Fast Ion Deuterium Alpha and the Neutral Particle Analyzer diagnostics.

The use of Thin-foil Proton Recoil (TPR) spectrometers to measure neutrons from Deuterium-Tritium (DT) fusion plasma has been studied previously and is a well established technique for neutron spectrometry. The study presented here focuses on the optimisation of the TPR spectrometer configurations consisting of Delta E and E silicon detectors. In addition an investigation of the spectrometer's ability to determine fuel ion temperature and fuel ion density ratio in ITER like DT plasmas has been performed. A Python code was developed for the purpose of calculating detection efficiency and energy resolution as a function of several spectrometer geometrical parameters. An optimisation of detection efficiency for selected values of resolution was performed regarding the geometrical spectrometer parameters using a multi-objective optimisation, a.k.a. Pareto plot analysis. Moreover, the influence of detector segmentation on spectrometer energy resolution and efficiency was investigated. The code also produced response functions for the two selected spectrometer configurations. The SPEC code was used to simulate the spectrometer's performance in determining the fuel ion temperature and fuel ion density ratio n(t)/n(d). The results presented include the selected spectrometer configuration with calculated energy resolution and efficiency. For a selected spectrometer resolution of 5% a maximum efficiency of around 0.003% was achieved. Moreover, the detector segmentation allows for a 20% increase in spectrometer efficiency for an energy resolution of 4.3%. The ITER requirements for a 20% accuracy on the n(t)/n(d) ratio determination and 10% on the temperature determination within a 100 ms sampling window can be achieved using a combination of several TPR's of same type, in order to boost efficiency., Correction in: JOURNAL OF INSTRUMENTATION, Volume:16, Issue:1Article Number:E0100, DOI:10.1088/1748-0221/16/01/E01001

The upgrade of the high field side (HFS) edge charge exchange recombination spectroscopy (CXRS) system of ASDEX Upgrade is presented. This diagnostic provides temperature, rotation and radiance measurements of impurity species by taking advantage of the gas puff based CXRS technique (GP-CXRS). The system is formed by a fast piezoelectric valve, that injects thermal neutrals into the plasma, and two optical heads. The localized gas injection together with properly aligned lines of sights (LOS) lead to a high spatial resolution of 5–19 mm. Fast gas puff modulation allows a precise subtraction of the passive part of the signal. The existing poloidal optical head has been replaced with a new one to increase the radial resolution. The number of lines of sight (LOS) of the poloidal optical head has been increased from 8 to 16 covering around 7 cm of the plasma edge at the HFS. The same radial range is also viewed by a toroidal optical head. The neutral deposition, needed to calculate the impurity density profile, has been modelled using the FIDASIM code. A realistic gas puff geometry has been implemented in the code. The first measurements of impurity temperature, rotation and radiance utilizing the upgraded diagnostic are presented.

Collective Thomson scattering (CTS) is a microwave diagnostic allowing measurements of a number of plasma parameters such as the bulk ion temperature, the plasma composition, drift velocities and fast ion velocity distribution function. A CTS system has been successfully installed and commissioned on the Wendelstein 7-X (W7-X) stellarator. The measured spectra are analyzed by the means of the CTS forward model eCTS and the Minerva scientific framework enabling the use of Bayesian inference of relevant plasma parameters. Here we discuss the options for further optimization of the CTS diagnostic and focus on two topics of importance for the inference of bulk ion temperature values from CTS spectra: influence of impurities on the CTS spectra and the width of the notch filters that are employed to protect the receiver from high-power radiation. In addition to that we discuss the possibility of effective charge measurements by CTS. We explore the existence of an optimal notch filter width.

A forward model to resolve the fast-ion loss velocity-space on a fast-ion loss detector (FILD) probe head (FILDSIM) has been extended, making it possible to perform real-time analysis of the FILD data ("real-time FILDSIM"). Parametric pre-processing with FILDSIM enables real-time mapping of the raw FILD measurements to the velocity-space of the fast-ion distribution reaching the FILD probe, which depends on the local magnetic field at the probe head. Such parametric pre-processing facilitates the study of fast-ion losses in stages of the discharge other than the flat-top, such as the ramp-up phase when changes in the local magnetic field at the probe head cannot be neglected. Real-time FILDSIM has been applied to the existing and newly installed FILDs in ASDEX Upgrade and will be used for the forthcoming FILD in MAST-Upgrade. Due to the larger size of the MAST-U FILD probe, the approximation used in FILDSIM of a uniform magnetic field in the FILD region has been generalised to the case of a non-uniform field, with gyro-orbits calculated numerically in this field.

The fast-ion phase-space coverage of the ASDEX Upgrade Fast-Ion Loss Detectors (FILD) has been estimated and the results are presented here. To that end, a numerical tool has been developed to determine particle orbits that can be accepted by each detector in the machine, depending on their radial position, without colliding to the first wall. Two different plasma shapes have been analyzed and results show excellent phase-space coverage for mostly all the detectors, especially for those located at the midplane and below it. The methodology developed provides an excellent way to estimate the signal of these detectors depending on the plasma scenario and can be easily extended to other machines. Also, this study can be complemented with thermal analysis to consider the structural integrity of the detectors, allowing determining optimal operation parameters both from the signal and safety standpoints.

Magnetoplasma accelerator (MPA) accelerates and compresses plasma formed within the electrode system during the process of capacitor discharge. The lifetime of the compressed plasma flow is around 150 mu s, plasma velocity is up to 100 km/s, electron density and temperature are close to 10(23) m(-3) and 2 eV, respectively. Energy and energy flux density distribution along the axis of discharge have been measured for different working gases: hydrogen, helium with 5% of hydrogen and argon with the aim of determination of the optimal position and type of the gas for investigation of the plasma-material interaction. Steel (type 16 MnCr5) samples have been treated with plasma pulses, using helium with 5% of hydrogen as a working gas. Modification of the steel surface under high thermal loads was studied and roughness and hardness of steel targets were measured before and after plasma treatment. Improvement of physical and mechanical properties of a treated type of steel has been achieved. Additionally, the mean value of the electron density in the region of the plasma-surface interaction has been determined.

Collective Thomson scattering (CTS) is a microwave diagnostic allowing measurements of a number of plasma parameters such as the bulk ion temperature, the plasma composition, drift velocities and fast ion velocity distribution function. A CTS system has been successfully installed and commissioned on the Wendelstein 7-X (W7-X) stellarator. The measured spectra are analyzed by the means of the CTS forward model eCTS and the Minerva scientific framework enabling the use of Bayesian inference of relevant plasma parameters. Here we discuss the options for further optimization of the CTS diagnostic and focus on two topics of importance for the inference of bulk ion temperature values from CTS spectra: influence of impurities on the CTS spectra and the width of the notch filters that are employed to protect the receiver from high-power radiation. In addition to that we discuss the possibility of effective charge measurements by CTS. We explore the existence of an optimal notch filter width.

Collective Thomson scattering (CTS) is a microwave diagnostic allowing measurements of a number of plasma parameters such as the bulk ion temperature, the plasma composition, drift velocities and fast ion velocity distribution function. A CTS system has been successfully installed and commissioned on the Wendelstein 7-X (W7-X) stellarator. The measured spectra are analyzed by the means of the CTS forward model eCTS and the Minerva scientific framework enabling the use of Bayesian inference of relevant plasma parameters. Here we discuss the options for further optimization of the CTS diagnostic and focus on two topics of importance for the inference of bulk ion temperature values from CTS spectra: influence of impurities on the CTS spectra and the width of the notch filters that are employed to protect the receiver from high-power radiation. In addition to that we discuss the possibility of effective charge measurements by CTS. We explore the existence of an optimal notch filter width.

In this paper we present the results of the R&D work that has been performed on avoiding electron cyclotron (EC) gas breakdown inside the launcher transmission line (TL) of the ITER collective Thomson scattering (CTS) diagnostic, due to encountering the fundamental EC resonance, which is located inside the port plug vacuum for the baseline ITER magnetic field scenario. If an EC breakdown occurs, this can lead to strong local absorption of the CTS gyrotron beam, as well as arcing inside the ITER vacuum vessel, which must be avoided. Due to the hostile, restrictive, and nuclear environment in ITER, it is not possible to implement the standard method for avoiding EC breakdown - a controlled atmosphere at the EC resonance. Instead, the CTS diagnostic will include a longitudinally-split electrically-biased corrugated waveguide (SBWG) in the launcher transmission line. The SBWG works by applying a transverse DC bias voltage across the two electrically-isolated waveguide halves, causing free electrons to diffuse out of the EC resonant region before they can cause an electron-impact ionisation-avalanche, and thus an EC breakdown. Due to insufficient experimental facilities, the functionality of the SBWG is validated through Monte Carlo electron modelling.