Study on a Current Channel Shrinkage and a Heating Enhancement Due to a Maqnetic Compressionof ULQ Plasmas

本文对安全系数q（a）小于1的超低q（ULQ）等离子体进行了磁压缩，其中环形磁场B t从0.1 T增加到0.3 T。在磁压缩阶段，观察到回路电压和磁场涨落的增加，表明电阻异常的增强。这可能是由于环向磁场的快速增加引起的极向电场，其方向与入射电动机电场相反。在<alpha>磁压缩过程中，H_2信号被抑制，等离子体柱收缩了几厘米，磁压缩后等离子体电流开始增加，回路电压和磁场起伏在此阶段保持在较低水平。与ULQ等离子体的电阻异常的标度相比，该阶段的等离子体电阻相当低，并且通过对ULQ等离子体施加磁压缩，实现了更稳定和更安静的ULQ等离子体。当等离子体表面出现有理面时，这种稳定的ULQ组态终止，并伴随着磁场涨落的增加和异常离子加热。结果表明，磁压缩对于引入外生极向电场和理解发电机电场在ULQ等离子体中的作用是非常强大的。

The magnetic compresseion has been applied for a Ultra-low-q (ULQ) plasma with a safety factor q (a) of less than unity, where the toroidal magetic field B_t was increased from 0.1 T to 0.3 T.During the magnetic compression phase, the increases of the loop voltage and magnetic fluctuations have been observed, indicating the enhancement of the resistance anomaly. This might be accounted for a poloidal electric field induced by the rapid increase of the toroidal magnetic field, the direction of which is opposite to the incident dynamo electric field. H_<alpha> signals have drastically suppressed during the magnetic compression, accompanied by the shrinkage of the plasma column with a few centimenter.Just after the magnetic compression the plasma current begins to increase, and the loop voltage and magentic fluctuations are kept at low levels during this phase. Compared with the scaling of resistance anomaly for ULQ plasmas, the plasma resistance of this phase is quite low, and more stable and quiescent ULQ plasmas have been realized by applying the magnetic compression for ULQ plasmas. This stable ULQ configuration terminates when the rational surface appears at the plasma surface, accompanied by the increase of magnetic fluctuations and the anomalous ion heating. It is found that the magnetic compression is very powerful to introduce an externally-induced poloidal electric field and to understand the role of the dynamo electric field in ULQ plasmas.