1999 Fiscal Year Final Research Report Summary
RF Heating of Spherical Tokamak Plasmas
| Project/Area Number |
10308018
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Nuclear fusion studies
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| Research Institution | The University of Tokyo |
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Principal Investigator |
TAKASE Yuichi School of Frontier Sciences, The University of Tokyo, Professor, 大学院・新領域創成科学研究科, 教授 (70292828)
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| Co-Investigator(Kenkyū-buntansha) |
SEKI Tetsuo National Institute for Fusion Science, Research Associate, プラズマ過熱研究系, 助手 (60260048)
SHIRAIWA Syun'ichi School of Frontier Sciences, The University of Tokyo, Research Associate, 大学院・新領域創成科学研究科, 助手
EJIRI Akira School of Frontier Sciences, The University of Tokyo, Associate Professor, 大学院・新領域創成科学研究科, 助教授 (30249966)
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| Project Period (FY) |
1998 – 1999
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| Keywords | Spherical Tokamak / ST / RF Heating / RF / Wave / Fast Wave / HHFW / Combline Antenna |
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| Research Abstract |
The Spherical Tokamak (ST) can produce high performance plasmas in a small device. The most important issue for the ST is plasma current rampup and maintenance by noninductive means. The high-harmonic fast wave (HHFW) in the ion-cyclotron frequency range has good propagation and absorption characteristics in ST plasmas with very high dielectric constants. the aim of this study is to study excitation, propagation, and absorption of HHFW. It is indispensable to produce and, maintain a plasma with high enough density for HHFW excitation and high enough electron temperature for its absorption. The TST-2 device was constructed for this purpose and plasmas with the required density and temperature were achieved. A traveling wave antenna called the combline antenna was adopted for wave excitation. Based on optimization using mockup antennas, a six-element antenna was fabricated for the experiment. Magnetic probes installed at various locations on the vacuum vessel wall were used for wave dete
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ction- The plasma loading resistance varied as the plasma evolved, and reached a maximum when the plasma current reached a peak, as expected. On the inboard side (high field side) of the torus, the nonuniformity in the toroidal direction is weak (about 5dB) and the vertical nonuniformity was even weaker. In contrast, the outboard probes detected stronger signals by 10-15dB compared to inboard probes. These results are consistent with the TASK/WM full-wave code. In addition, plasma currents of up to 1.2kAwere achieved with 1kW of electron cyclotron wave. In the presence of a mirror magnetic field configuration in the vertical direction, electrons produced by ionization are trapped by the mirror field and a current can flow by their drill: motion, and subsequently pressure driven currents can flow. If the plasma can be formed and the plasma current can be ramped up by RF waves as shown in these experiments, the central solenoid becomes unnecessary and the attractiveness of the ST as a fusion reactor is greatly enhanced. Less
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