Tangential hard x-ray diagnostic array on the EXL-50 spherical tokamak

Abstract

A tangential hard x-ray (HXR) diagnostic on the newly constructed ENN XuanLong-50 (EXL-50) spherical tokamak for fast electron emission studies is presented. The HXR detection system consists of a symmetrical CdZnTe semiconductor detector array with a spectral sensitivity range of 20–300 keV. 25 channels have been designed on the 270° horizontal vacuum port with 12 sight lines to observe the forward emission, 12 sight lines to observe the backward emission of fast electrons, and 1 for viewing the central. Currently, ten channels have been in operation in the EXL-50 experiments. The systems are designed to measure the x-ray spectra for the estimation of fast electron temperature and electron velocity distribution in the EXL-50 experiment, which will be useful for understanding the dynamics of fast electrons generated by electron cyclotron resonance heating, for plasma instability and transport studies and for the analysis of plasma heating efficiency.

Generation of energetic electrons by an electron cyclotron wave through stochastic heating in a spherical tokamak

“…In EXL-50, the bulk electron density and temperature are typically in the range of – and –, respectively, while the energetic electron temperature is approximately – (Cheng et al. 2021; Ishida, Peng & Liu 2021; Li et al. 2021; Guo et al.…”

“…Referring to the work of (Ikegami et al 1973), EXL-50 uses a smooth metal wall, and observation windows are shielded with 28 GHz shielding materials, and the distribution of the ECWs in the vacuum chamber is approximately stochastic with cold plasma (Ikegami et al 1973). The plasma density is diagnosed using an interferometer (Li et al 2021). Energetic electron energy is diagnosed by the HX bremsstrahlung radiation from the plasma (figure 1a).…”

“…The HX detectors with improved lead shielding are applied. Beside the original shielding (10 mm lead +5 mm steel) (Cheng et al 2021), the CdZnTe detectors have their own independent 50 mm lead shielding. For this improved shielding HX system, there are two detectors with a collimator and one blinded detector without a collimator (figure 1b).…”

“…In EXL-50, the bulk electron density and temperature are typically in the range of 4-40 × 10 17 m −2 and 10-200 eV, respectively, while the energetic electron temperature is approximately 100-300 keV (Cheng et al 2021;Ishida, Peng & Liu 2021;Li et al 2021;Guo et al 2022;Li et al 2022;Shi et al 2022;Wang et al 2022Wang et al , 2023d. Figure 2(a) illustrates the relationship between single-pass wave power absorption coefficient and electron energy, calculated using GENRAY (Smirnov & Harvey 2001) (with a bulk plasma temperature of 100 eV).…”

Design of a composite collimator for the hard X-ray camera in HL-2M tokamak

“…A 32-channel HXR detector was used in the Alcator C-Mod tokamak for a lower hybrid current drive experiment that used a pinhole with a conical aperture [7]. Cheng et al developed a tangential HXR diagnostic array for the EXL-50 spherical tokamak device, which used a collimated square pinhole [8]. Zhang et al developed a pinhole camera system to diagnose the fast electron bremsstrahlung in the HL-2A tokamak, which used a pinhole with a bipolar cone structure [9].…”