Development and characterization of a new soft x-ray diagnostic concept for tokamaks

Abstract

A: Diagnosing soft x-ray (SXR) emission from tokamaks represents a unique source of information, since it allows the study of several plasma parameters, such as the electron and ion temperature, the investigation of the ionization equilibrium, particle and impurities transport and the study of MHD fluctuations and disruptions. A new SXR diagnostic system called EXODUS (Enhanced X-ray Optimized Detector for Use in multiple Scenarios) is under development with the aim to obtain energy resolved SXR emission profiles from the plasma with a high time resolution (< 0.1 ms). The system is based on the Gas Electron Multiplier (GEM) technology coupled with the new data acquisition system especially designed for GEM called GEMINI, which gives the possibility to obtain information about the energy deposited in the detector by the incoming radiation using the so called Time-Over-Threshold technique on each detector channel. The information of the deposited energy allows the study of the SXR emission from the plasma resolved in space, energy and time. There are several advantages in the use of GEM based detector in the harsh environment of a tokamak. First of all, it offers very high rate capabilities (up to 1 MHz/mm 2 ), giving the possibility 1Corresponding author.

Development of a Triple-GEM detector with strip readout and GEMINI chip for X rays and neutron imaging

“…The HV parameter has been optimized to obtain full charge deposition of the incoming events (see [8] for details on the procedure), and the thresholds have been adjusted on the basis of the suppression of noise in the experimental environment. Charge calibration has been performed observing a single photo-emission peak (Ti fluorescence was used, with an energy of 4.5 keV), based on the variation of ToT values depending on the HV value applied, as described in [9].…”

Electronic readout characterisation of a new soft X-ray diagnostic for burning plasma

“…Gaussian-fitting each peak at different gains, the peak positions vs. charge have been plotted in order to obtain the calibration curve for both methods, as shown in figure 5. For a direct comparison, spectra obtained with both methods have to be represented as a function of the deposited charge, that can be exactly calculated by an analytical method ( [11]) for all the X-ray photons and different gains. The ToT vs. charge (at different gains) calibration curve has been fit with…”

“…where q i is the deposited charge, E ion is the ionization energy (28 eV for the ArCO 2 gas mixture), e is the electron charge, G the detector gain and K is the gain corrective factor [11] given by K = Measured energy Expected energy .…”

“…Thanks to these features, in plasma physics, they are one of the prominent diagnostic to detect soft X-ray emissions [11]. The typical X-ray spectrum of a plasma shows several lines in the energy region from 2 keV up to 30 keV.…”

Development of a ceramic double thick GEM detector for transmission measurements at the VESUVIO instrument at ISIS

“…Each ASIC has 16 detecting channels and each channel has a Charge Sensitive Preamplifier (CSP) The discriminator threshold can be set separately for all channels, thus constituting a significant improvement with respect to the previous CARIOCA-based readout [32], where thresholds may be set in groups of 8 channels only. GEMINI ASICs can operate in both Time over Threshold (ToT) [33,34] and Time of Arrival (ToA) mode at the same time. In the present application, where the use of the neutron Time Of Flight (ToF) technique was envisaged, the ToA mode has been used.…”