In:
Nuclear Fusion, IOP Publishing, Vol. 51, No. 6 ( 2011-06-01), p. 063017-
Abstract:
Spherical tokamaks (STs) have the advantage of high beta capability, but the realization of a compact reactor requires the elimination of the central solenoid (CS). The possibility of using the lower hybrid wave (LHW) to ramp up the plasma current ( I p ) from zero to a high enough level required for fusion burn in ST is examined theoretically and experimentally. Excitation of a travelling fast wave (FW) by the combline antenna installed on TST-2 was confirmed by a finite element analysis, but efficient current drive requires excitation of the LHW, either directly by the antenna or by mode conversion from the FW. The analysis using the TORLH full-wave solver indicates that core current drive by LHW is possible in the low-density, low I p plasma formed by electron cyclotron heating (ECH). It is important to keep the density low during I p ramp-up, and the wavenumber must be reduced as I p increases. Initial results from TST-2 demonstrate that RF power in the LH frequency range (200 MHz) can achieve initial I p formation, and is more effective than ECH for further ramp-up of I p . I p ramp-up to over 12 kA was achieved by combining ramp-up of the externally applied vertical magnetic field and ramp-up of the RF power. The significant asymmetry observed between co-current drive and counter-current drive is attributed to the presence of RF driven current. An optimized LHW antenna with appropriate polarization and wavenumber spectrum controllability is being designed. The success of the TST-2 experiment would provide a scientific basis for quantitatively evaluating the required CS capability for a low-aspect-ratio reactor.
Type of Medium:
Online Resource
ISSN:
0029-5515
,
1741-4326
DOI:
10.1088/0029-5515/51/6/063017
Language:
Unknown
Publisher:
IOP Publishing
Publication Date:
2011
detail.hit.zdb_id:
2037980-8
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