2000 Fiscal Year Final Research Report Summary
Synergetic effects between magnetic shear and velocity shear for stability in tokamak and stellarator
| Project/Area Number |
11680483
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
プラズマ理工学
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
WAKATANI Masahiro Kyoto University, Graduate School of Energy Science, Professor, エネルギー科学研究科, 教授 (00109357)
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| Co-Investigator(Kenkyū-buntansha) |
HAMAGUCHI Satoshi Kyoto University, Graduate School of Energy Science, Associate Professor, エネルギー科学研究科, 助教授 (60301826)
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| Project Period (FY) |
1999 – 2000
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| Keywords | tokamak / stellarator / heliotron / instability / magnetic shear / velocity shear / negative shear / Kelvin-Helmholtz instability |
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| Research Abstract |
For the negative magnetic shear configurations in tokamaks on finite beta currentless equilibria in stellarators, there appears zero magnetic shear surface and magnetic shear increases fromn this surface. When plasma flow with velocity shear is generated in these configurations, confinement improvement is often seen in experiments. For understanding physics of the confinement improvement, it is found that synergetic effects exist between the magnetic shear and the velocity shear. Obtained results are summarized in the following.
(l) It is possible to suppress instabilities with an appropriate magnetic shear even without the velocity shear. For example negative magnetic shear is suitable to suppress the ion temperature gradient driven drift mode in tokamaks.
(2) The negative magnetic shear is not always better than the positive one. For example resistive interchange modes become unstable in the negative shear tokamaks.
(3) For suppressing the resistive interchange modes the poloidal flow shear is effective. It is found that radial mode width (d) without the flow is shorter than characteristic length of the velocity shear (L) and rotational frequency is larger than the growth rate multiplied by L/d.
(4) It is noted that Kelvin-Helmholtz mode becomes unstable when the velocity shear of poloidal flow exceeds a critical value.
(5) It is important that Kelvin-Helmholtz mode is stabilized by magnetic shear, although a large velocity shear is destabilizing. Thus in the negative magnetic shear tokamak, electron temperature gradient driven drift wave turbulence generates zonal flows only in the finite magnetic shear region. The velocity shear in the zonal flow contributes to generate the internal transport barrier.
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