Toroidal Plasma Current Sustainment by Lower Hybrid Waves in the WT-2 Tokamak

Nakamura, Masahiko; Cho, T.; Kubo, S.; Shimozuma, Τ.; Kawai, Hideki; Yamazaki, K.; Maekawa, Takashi; Terumichi, Y.; Hamada, Y.; Tanaka, Shigetoshi

doi:10.1103/physrevlett.47.1902

Cited by 67 publications

(37 citation statements)

References 13 publications

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“…Another interesting observation is that when plasma current is fully supported non-inductively by LH, the observed loop voltage remains negative and similar observation is reported earlier also [20]. Here the Ohmic transformer is not playing any significant role beyond 0.25 s when LH is applied.…”

Section: Resultssupporting

confidence: 86%

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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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Section: Resultssupporting

confidence: 86%

“…From figure 10, it is easily seen that with the onset of LH driven plasma current, the hard x-ray emission drastically reduces. This beneficial effect of suppression of hard x-ray with LH driven current [20] is demonstrated on SST1 also. It is widely accepted that runaway electrons are generated via two mechanisms.…”

Section: Resultsmentioning

confidence: 64%

Current drive experiments in SST1 tokamak with lower hybrid waves

Sharma¹,

Raju²,

Pathak³

et al. 2022

Nucl. Fusion

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“…(5) (6) (j> is the amplitude of the wave potential and vn is the electron velocity. We can estimate the wave potential 0 5) and (10), with the plasma parameters in front of the antenna (n e =5 X10 11 cm' 3 , B= 714G)andS a = 576cm 2 .…”

Section: Discussionmentioning

confidence: 99%

“…Applications of radio-frequency (RF) power near the lower-hybrid resonance frequency are quite attractive for the heating and control of tokamak plasmas. Efforts have been directed mainly towards ion heating [1][2][3], but recent experiments are devoted to electron heating [1, 4 -6 ] and current drive [7][8][9][10][11][12][13]. The latter offers the prospect of the realization of a steady-state tokamak reactor [14].…”

Section: Introductionmentioning

confidence: 99%

Experimental studies on current drive by slow lower-hybrid waves

1984

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Very slow lower-hybrid waves travelling unidirectionally with a phase velocity of a few times the electron thermal velocity have been used to drive surface currents in a tokamak plasma. Most of the wave energy is dissipated at the plasma surface by virtue of a strong interaction with the electrons. This leads to electron acceleration up to velocities an order of magnitude greater than the electron thermal velocity. Electron trapping by the wave is discussed as a possible mechanism for surface current generation.

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“…If the plasma current is mainly generated and sustained by non-inductive methods with high efficiency, the OH transformer can be made compact or can be removed. Current drive experiments by lower hybrid waves (LHW) in the last few years [1][2][3][4][5] have demonstrated the possibility of steady state operation of a tokamak. In these experiments, current drive was observed as a drop of the loop voltage or the sustainment of a constant current.…”

Section: Introductionmentioning

confidence: 99%

Plasma current startup by lower hybrid waves in the JIPP T-IIU tokamak

Toi¹,

Ohkubo²,

Kawahata³

et al. 1988

Nucl. Fusion

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The paper describes the characteristic behaviour of lower hybrid current startup in JIPP T-IIU. The current startup is carried out by the injection of 800 MHz lower hybrid waves into cold and low density plasmas (Te = 10 − 20 eV, n̄e = (1−2) × 1012 cm−3 produced by electron cyclotron resonance or lower hybrid waves (LHW) only. The plasma current rises with a characteristic rise-time of τr (≳ 30-50 ms) and approaches a quasi-steady state value, Ipm (= 5-20 kA), whereupon 10-50 kW LHW power is injected into the torus, controlling the vertical field. The rise-time is inversely proportional to the bulk electron density, ne, and is comparable to the collision time of current carrying high energy electrons with the bulk plasmas. On the other hand, the current drive efficiency in the quasi-steady state is almost independent of n̄e, i.e. Ipm/PLH = 0.4−0.7 A·W−1 for n̄e = (0.8−4) × 1012 cm−3. The conversion efficiency of RF energy injected into the torus is typically 5% during the current rise phase and 10% in the most efficienct case. The effects of the initial injection of ECH power and the observed parametric instabilities on the current startup are investigated from the viewpoint of seed current generation. During the rapid current rise when an appreciably negative loop voltage is observed, the bulk electrons are heated up to 150 eV. Various heating mechanisms responsible for the bulk electron heating are discussed.

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Toroidal Plasma Current Sustainment by Lower Hybrid Waves in the WT-2 Tokamak

Cited by 67 publications

References 13 publications

Current drive experiments in SST1 tokamak with lower hybrid waves

Current drive experiments in SST1 tokamak with lower hybrid waves

Experimental studies on current drive by slow lower-hybrid waves

Plasma current startup by lower hybrid waves in the JIPP T-IIU tokamak

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