Generation and suppression of runaway electrons in EAST lower hybrid current drive experiments

Zhou, Ruijie; Hu, Liqin; Lu, Hongwei; Li, E Z; Lin, Shiyao; Xu, Ping; Zhang, L

doi:10.1088/0031-8949/84/01/015501

Cited by 18 publications

(19 citation statements)

References 13 publications

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“…The plasma density and the fast electron density profiles along the normalized minor radius (𝜌 = 𝑟/𝑎) are shown in figure 2(a) and figure 2(b) respectively. Two types of fast electron density profile over normalized minor radius are assumed, one is centered Gaussian and another one is off-centered Gaussian, as these two profiles describe the central and off-axis power deposition profile of lower hybrid waves [35]. A similar kind of observation is experimentally derived and reported in the case of non-inductive current drive [6].…”

Section: Density Temperature and Fast Electron Populationmentioning

confidence: 79%

Conceptual design of multichannel fast electron bremsstrahlung detection system to study fast electron dynamics during lower hybrid current drive in ADITYA-U tokamak

2023

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To drive plasma current non inductively, a Lower Hybrid Current Drive (LHCD) system with a passive-active multijunction (PAM) antenna for injecting lower hybrid wave (LHWs) has been designed, fabricated and to be integrated with ADITYA-U Tokamak. A fast electron population in the energy range of a few keV to several hundreds of keV is generated with the injection of the LHWs. These fast electrons interacting mainly with ions and electrons result in Hard X-Ray (HXR) emission called Fast Electron Bremsstrahlung acronym as FEB emission. A single channel FEB detection system is being used in the earlier experiment of LHCD in ADITYA-U tokamak. However, the single channel detection system can't provide a radial emissivity profile of HXR intensity distribution. In order to determine a radial emissivity profile, for the first time, a multichannel FEB detection system is designed for ADITYA-U tokamak. This paper describes the detailed conceptual design for the selection of suitable detectors, optimization of the collimators, shielding geometry, and low energy filtering cut-off. In the present design analysis, the soller collimator concept is considered over a simple pinhole camera system due to its several advantages. In order to optimize the multichannel FEB system parameters for the best possible performance, a forwarded modelling code has been used. The signal to background ratio at each detector location has been estimated for a few system parameters and reported herein.

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Section: Density Temperature and Fast Electron Populationmentioning

confidence: 79%

Conceptual design of multichannel fast electron bremsstrahlung detection system to study fast electron dynamics during lower hybrid current drive in ADITYA-U tokamak

2023

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“…As mentioned above, the LH produces suprathermal electrons and under the influence of toroidal electric field, these suprathermal electrons further experiences an enhanced driving force, making it less collisional and thereby electrons gain energies greater than some critical energy (E crit ) [21]. These energetic electrons are termed as runaway electrons.…”

Section: Resultsmentioning

confidence: 99%

Current drive experiments in SST1 tokamak with lower hybrid waves

Sharma¹,

Raju²,

Pathak³

et al. 2022

Nucl. Fusion

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The steadystate superconducting tokamak (SST1) is aimed to demonstrate long pulse plasma discharges employing non-inductive current drive by means of lower hybrid current drive (LHCD) system. The major and minor radius of the machine is 1.1m and 0.2m respectively. The LHCD system for SST1 comprises of klystrons, each rated for 0.5MW-CW rf power at a frequency of 3.7 GHz. The grill antenna comprises of two rows, each row accommodating 32 waveguide elements. Electron cyclotron resonance (ECR) breakdown assisted Ohmic plasma is formed in SST1 to overcome the issues associated with low loop voltage start-ups. With recent modifications in the poloidal coils configuration, even with narrow EC pulse (~50ms), good repeatable and consistent Ohmic plasmas could be produced which helped in carrying out LHCD current drive experiments on SST1. These experiments demonstrated both fully as well as partially driven non-inductive plasma current in SST1 tokamak. Discharges with zero loop voltages were obtained. The interaction of lower hybrid waves with plasma and generation of suprathermal electrons could be established using energy spectra measured by CdTe detectors. Various other signatures like drop in loop voltages, negative loop voltages, spikes in hard x-rays and increase in 2nd harmonic ECE signal, further confirmed the current drive by LHW’s. The beneficial effect of LHW’s in suppressing hard x-rays was also demonstrated in these experiments. The non-inductive current drive in SST1 could also be established by modulating LH power. The longest discharge of ~650ms could be obtained in SST1 with the help of LHW’s. In this paper, the experimental results obtained with LHCD experiments on SST1 is reported and discussed in more details.

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“…Because the CdTe detector possesses higher stopping power, [27] as a result, HXR can measure REs in higher energy bands, specifically in the range of 30 keV-300 keV. [27,28] Figure 1 presents the detailed toroidal locations of the essential diagnostics and poloidal view of HXR in EAST. Furthermore, the directions of plasma current and toroidal magnetic field are also noted.…”

Section: Methodsmentioning

confidence: 99%

Runaway electron dynamics in Experimental Advanced Superconducting Tokamak helium plasmas

et al. 2023

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The generation of runaway electrons (REs) is observed during the low-density helium ohmic plasma discharge in the Experimental Advanced Superconducting Tokamak (EAST). The growth rate of hard x-ray (HXR) is inversely proportional to the line-average density. Besides, the RE generation in helium plasma is higher than deuterium plasma at the same density, which is obtained by comparing the growth rate of HXR with the same discharge conditions. The potential reason is the higher electron temperature of helium plasma in the same current and electron density plateau. Furthermore, two Alfvén eigenmodes driven by REs have been observed. The frequency evolution of the mode is not fully satisfied with the Alfvén scaling and when extension of the Alfvén frequency is towards 0, the high frequency branch is ~50 kHz. The different spatial position of the two modes and the evolution of the helium concentration could be used to understand deviation between theoretical and experimental observation.

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Generation and suppression of runaway electrons in EAST lower hybrid current drive experiments

Cited by 18 publications

References 13 publications

Conceptual design of multichannel fast electron bremsstrahlung detection system to study fast electron dynamics during lower hybrid current drive in ADITYA-U tokamak

Conceptual design of multichannel fast electron bremsstrahlung detection system to study fast electron dynamics during lower hybrid current drive in ADITYA-U tokamak

Current drive experiments in SST1 tokamak with lower hybrid waves

Runaway electron dynamics in Experimental Advanced Superconducting Tokamak helium plasmas

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