Study of Lower Hybrid Current Drive for the Demonstration Reactor

Molavi-Choobini, Ali Asghar; Naghidokht, A.; Karami, Zahra

doi:10.1016/j.net.2016.02.003

Cited by 2 publications

(1 citation statement)

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“…Solutions developed to date include local helicity injection [5], coaxial helicity injection (CHI) [6], plasma merging [7], and radio frequency (RF) wave injection [8]. Methods in which RF waves are used to produce a non-inductive current drive can be categorized into electron cyclotron CD (ECCD) [9], lower hybrid CD [10], and electron Bernstein wave current drive (EBWCD) [11]. As electrostatic waves, EBW are immune to the effects of overly dense plasmas, which can form RF cutoff layers that prevent the further enhancement of plasma density through RF injection.…”

Section: Introductionmentioning

confidence: 99%

Electron Bernstein wave conversion of high-field side injected X-modes in QUEST

Elserafy

Hanada

Kojima

et al. 2020

Plasma Phys. Control. Fusion

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This paper presents a detailed design of the Q-shu University experimental steady state spherical tokamak's (QUEST's) high-field side (HFS) injection system for electron Bernstein wave (EBW) excitation and the results of an experimental comparison of the HFS eXtraordinary X-mode and low-field side (LFS) ordinary O-mode injection of 8.2 GHz radio frequency (RF) power. Waveguides, as an alternative to mirror polarizers for transmitting RF X-mode power from LFS to HFS for EBW conversion, were used instead of the installation of an RF mirror. Testing of LFS-to-HFS RF power transmission at 8.2 GHz, using an RG-50-type vacuum waveguide in a bench-scale device filled with SF 6 gas at 0.03 Mpa, revealed that an RF power of 10.8 kW could traverse the fundamental electron cyclotron resonance layer for 60 s without breakdown. The short-length, open-ended waveguide antenna used in the HFS injection-induced wave diffraction reduced the efficiency of power delivery to the upper hybrid resonance (UHR) by approximately 7% at an electron temperature of 50 eV. The HFS injection was able to produce brighter camera images than the standard LFS injection. The location of the UHR, as estimated by measuring the density with an interferometer, agreed with its location as measured by plasma radiation low-field, side-edge positions shown by fast camera imaging. This indicates that the plasma was produced by modeconverted EBW. The HFS injection had an absorption efficiency of 96%, compared to 40% for LFS. A greater fluctuation of floating potential adjustable to the lower hybrid wave (LHW) was observed in the HFS case by installing a Langmuir probe, confirming that EBW conversion efficiency was higher in the HFS case. Moreover, after setting the poloidal field to B PF =7.6 mT, plasma current (I P ) in the HFS peaked at 1.3 kA, as opposed to 0.3 kA for LFS, despite LFS injection having a total power of 55 kW, compared to 40 kW for HFS. However, as the impurity level was comparatively high, it is believed that this I P is dominated by pressure-drive, which makes it difficult to analyze EBWCD. Finally, the line-integrated density in the HFS injection peaked at 1.6×10 18 m −2 , compared to 8×10 17 m −2 in the LFS one.

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