Fully non-inductive plasma start-up with lower-hybrid waves using the outboard-launch and top-launch antennas on the TST-2 spherical tokamak

Tsujii, N.; Takase, Y.; Ejiri, A.; Shinya, Takahiro; Yajima, S.; Yamazaki, H.; Togashi, H.; Moeller, C.P.; Roidl, Benedikt; Takahashi, Wataru; Toida, K.; Yoshida, Yusuke

doi:10.1051/epjconf/201715702009

Cited by 2 publications

(1 citation statement)

References 22 publications

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“…Non-inductive plasma start-up experiments using the LHW are being conducted on TST-2 [3]. Successful ST plasma formation and Ip ramp-up to substantial levels (about 1/4 of the nominal I p for OH operation) have been achieved using CCC antennas [4].…”

Section: Introductionmentioning

confidence: 99%

Development of capacitively-coupled combline antennas for current drive in tokamaks

et al. 2019

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The capacitively-coupled combline (CCC) antenna has been developed for current drive by the lower hybrid wave (LHW) on the TST-2 spherical tokamak. The combline antenna was developed to satisfy the requirements of high directionality, low reflectivity, and simple feeding. Since the combline antenna makes use of mutual coupling between neighboring elements, only the first and the last elements are connected to external feedlines. Each element is an L-C resonant circuit, coupled to neighboring elements by mutual capacitance, and exhibits a passband characteristic. The inductive elements are covered so neighboring elements do not couple inductively to each other and the RF magnetic field does not extend into the plasma. Faraday shield is not necessary. RF powers and power densities of the order of 100 kW and 1 MW/m 2 can be achieved easily in small antennas of the order of 0.1 m 2. The two CCC antennas installed in TST-2 (outboard-launch and top-launch) excite toroidal refractive index (nphi) spectra peaked around 5. Wave excitation calculation using a finite element code shows that the excited power of the nphi = 5 LHW component increases rapidly when the plasma cutoff density layer (where ne = 5 × 10 14 m-3) becomes closer than 27 mm from the antenna surface, in agreement with experiment. Experimentally, the density profile in front of the antenna can be controlled by adjusting the side limiter location or antenna-plasma distance, and should be optimized for antenna-plasma coupling, since too high coupling results in a broadened and less directional nphi spectrum, and too low coupling results in a less efficient power coupling. Using these antennas, successful ST plasma start-up and Ip ramp-up to over 25 kA (about 1/4 of the nominal Ip for OH operation) have been achieved with RF power of less than 100 kW in about 40 ms.

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Section: Introductionmentioning

confidence: 99%

Development of capacitively-coupled combline antennas for current drive in tokamaks

et al. 2019

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Current Drive Experiment Using Top/Outboard Side Lower Hybrid Wave Injection on TST-2 Spherical Tokamak

Yajima

Takase

Ejiri

et al. 2018

Plasma and Fusion Research

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In the TST-2 spherical tokamak device, we carried out a fully non-inductive current startup experiment by Landau damping of the Lower Hybrid Wave (LHW). Capacitively Coupled Combline Antennas (CCCAs) were used for wave injection. The antennas are located on the outboard side and the top side of the vacuum vessel, and by reversing the toroidal magnetic field, it is possible to simulate the case of wave injection from the bottom side. The highest plasma current of 26.7 kA was achieved by top injection with the reversed toroidal magnetic field. According to numerical calculation using ray tracing and Fokker-Planck codes (GENRAY/CQL3D), the downshift of the parallel wavenumber helped the tail of the electron velocity distribution extend to higher energy than the other cases. Additionally, in order to evaluate the directionality of the wavenumber spectrum which is also important for efficient current drive, a finite element solver (COMSOL) was used. In order to avoid deterioration of the wavenumber spectrum, one limiter of the outboard antenna should be moved away toroidally by 70 mm from the current position, and the preferred distance between the antenna and the cutoff density layer is about 2 cm.

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Fully non-inductive plasma start-up with lower-hybrid waves using the outboard-launch and top-launch antennas on the TST-2 spherical tokamak

Cited by 2 publications

References 22 publications

Development of capacitively-coupled combline antennas for current drive in tokamaks

Development of capacitively-coupled combline antennas for current drive in tokamaks

Current Drive Experiment Using Top/Outboard Side Lower Hybrid Wave Injection on TST-2 Spherical Tokamak

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