| Budget Amount *help |
¥4,100,000 (Direct Cost: ¥4,100,000)
Fiscal Year 2003: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2002: ¥2,900,000 (Direct Cost: ¥2,900,000)
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| Research Abstract |
1)We observe an ion current flowing into the central axis of cylindrical magnetized plasma ; the voltage on the axis is negative by applying a negative voltage to the plate at the end of the axis. The advantage of this apparatus is the clear detection of ion current because the ions flowing into the central taxis is produced at the periphery of the cylindrical plasma. As increasing the potential of the axis, we find 4 regions, (A) formation of collisional ion flow, (B) increment of radial ion current and excitation of spiral waves, (C) decrement of radial ion current and off-axis rotating motion, and (D) limitation of ion current and formation of localized low density ring.
2)The increment of ion density at the central axis flowing from the periphery rapidly excites rotating spiral modes of m=1 or 2. As the results, the plasma extends the spiral structure, and diffuses ions in the radial direction. In order to clarify this structure, we use an equation of ion density perturbation including ion Larmor radius effect derived by Rosenbulth & Simon and an equation of electron density perturbation, and derive eigen functions. The theoretical results well explain the data of the experiment in case of small perturbations.
3) Further increasing the negative voltage of the central axis of the cylindrical plasma, there appears a low-density ring indicating the zonal flow, and reduces the perturbations and the diffusive ion flow. Here, the strong velocity shear exists around the central axis. Analyzing collisional drift instability at this condition by using the above equations, we are able to explain that all the mode of this instability and the ion flow into the central axis are suppressed at the same time, in case of strong electric field.
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