2003 Fiscal Year Final Research Report Summary
Control of the Translation Velocity and Position on a Field Reversed Configuration
| Project/Area Number |
14580528
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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 |
Nuclear fusion studies
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| Research Institution | Ninon University |
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Principal Investigator |
TAKAHASHI Tsutomu Ninon University, College of Science and Technology, Associate Professor, 理工学部, 助教授 (50179496)
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| Co-Investigator(Kenkyū-buntansha) |
NOGI Yasuyuki Ninon University, College of Silence and Technology, Professor, 理工学部, 教授 (90059569)
SHIMAMURA Shinn Ninon University, College of Silence and Technology, Associate Professor, 理工学部, 助教授 (00059627)
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| Project Period (FY) |
2002 – 2003
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| Keywords | Field Reversed Configuration / Control of Translation Velocity and Position / Passive control by metal liner / Active control by pulsed magnetic field / n=1 mode Global Motion / Field Gradient of Confinement Field / Conducting ring / Internal Structure estimation by Optical and magnetic measurement |
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| Research Abstract |
The translation velocity and the plasma position in translation experiments of a field reversed configuration are controlled by passive and active methods in order to control a rebound co-efficient of the reflection and to reset the plasma in short period without bouncing
In the passive method, a resistive metal liner is installed in the region. A pulsed inductive current is induced on the metal liner by the excluded magnetic field due to the translation plasma. The pulsed magnetic field is applied on the FRC plasma. The induced force is dependent on the resistance of the metal Tuner, ratio of the plasma radius to the liner radius. Deuterium plasma of 3mg with the translation velocity of 10km/s is settled down by a metal liner of 0.005ms skin time.
In active method, the pulsed magnetic field coil, installed in the translation region. The pulsed current is supplied to the pulse coil from the power supply, synchronizing the plasma motion. By the control of the current value and the current
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form, the plasma is reflected and settled down. By the pulsed current of 40kA and the rising time of 0.01ms, the FRC plasma with 40km/s is reflected and settled down in dependent of the wave form. These experimental results agree with that of a simple computer simulation, which is based on energy conservation of system and with a rigid body.
The control of n=1 mode motion is reconsidered from the point view of the field gradient of the confinement field. A negative field gradient suppresses the motion. The investigation suggests that the plasma having high separatrix elongation is preferable for reducing the amplitude of. the n=1 mode motion because of a small negative gradient of the confinement field around the plasma. In order to produce highly elongated plasmas, auxiliary conductors are installed into a device. The observed amplitudes of the n=1 mode motion are controlled to about a half level of those without any auxiliary conductors, which is explained well from the magnetic structure.
Several plasma diagnostic for the internal structure have been improved. 60 channel visible optical diagnostic system and multi one turn excluded measurement system are developed. By the combining of the magnetic measurement and the optical measurement, magnetic field and plasma structure with the open field line region, for example, plasma beta value and the depth of edge layer and the asymmetrical pressure profile with the n=1 mode motion are clarified. Separatrix shapes and internal structures of field-reversed configuration (FRC) plasmas are determined by comparing the measured magnetic fluxes with the Grad-Shafranov equation. This analysis also suggests a width of an edge-layer plasma w^*r_i (w is the number of ion gyro-radius r_i), a beta value at the separatrix (b_s), and the formation of magnetic islands near the field null. In order to confirm these findings by the magnetic method, a radiation power density of the FRC is measured. It is found that the w and b_s, values agree well with those obtained by the radiation measurement. However, the positions of the magnetic islands do not coincide with those appearing in an intensity contour map of the radiation. Asymmetrical profiles of the radiation are also discussed with respect to the nonconcentricity of the pressure constant surface. The measured profiles can be explained when the center of the FRC is shifted by 0.1-0.2r_s (r_s is a separatrix radius) without any shift of the separatrix surface. Less
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