Role of magnetic island on the formation of internal transport barrier

(1)研究了紧凑螺旋系统（CHS）中具有不同等离子体参数的EC H或NBI+EC H等离子体，产生m=2/n=1磁岛的微扰线圈对内部输运势垒（ITB）形成的影响。其中一个极向磁场线圈电源（内垂直线圈）为磁岛微扰线圈供电。当电子密度低而电子温度高时，摄动线圈通电后电子温度不表现出磁岛现象，而当电子密度高而电子温度低时，电子温度表现出扁平的磁岛现象。(2)这被称为“磁岛愈合”，被认为是由于有限β等离子体中的自引导电流在径向流动以抵消扰动磁场。在托卡马克系统中，自举电流通常会增强磁岛，但在螺旋系统中，自举电流在某些等离子体参数下会抵消磁岛。在CT-IS中，愈合发生在无碰撞状态下。这不利于研究磁岛对ITB形成的影响，因为ITB是在与电子根无碰撞的状态下实现的。(3)采用以下参数产生与ITB无碰撞的等离子体；磁场强度B = 0.88特斯拉，真空磁轴位置= 0.92m， ECH功率= 220kW， NBI功率= 650kW × 2。真空容器壁密集地加入抗氧剂，以抑制容器壁的内流。当微扰线圈通电时，其磁场形态与没有微扰场时略有不同，导致电子密度略低。比较了有扰动场和无扰动场等离子体的电子温度分布。在有微扰场的情况下，中心电子温度比无微扰场时要高，但在有微扰场的情况下，ITB更容易形成，即在更高的电子密度下形成。少

(1)Effect of perturbation coil, with which the m=2/n=1 magnetic island can be produced, on formation of the internal transport barrier (ITB) is investigated for EC H or NBI+EC H plasmas that have various plasma parameters in Compact Helical System (CHS). One of power supplies for poloidal field coils (inner vertical coil) is used to energize the perturbation coil for the magnetic island. When the electron density is low and the electron temperature is high, the electron temperature does not show any indication of the magnetic island under energizing the perturbation coil, while the density is high and the temperature is low the electron temperature shows the flattened profile indicating the presence of magnetic island.(2)This is called "healing of magnetic island" and is thought to be due to the bootstrap current in a finite beta plasma that flows to cancel the perturbation magnetic field in the radial direction. Usually the bootstrap current enhances the magnetic island in tokamaks, h … More owever, in helical system the bootstrap current cancels the magnetic island under some plasma parameters. In CT-IS the healing happens in the collisionless regime. This is unfavorable to study the effect of magnetic island on formation of ITB, because ITB is realized in the collisionless regime with the electron root.(3)The collisionless plasma with ITB is produced with the following parameters ; magnetic field strength B = 0.88Tesla, vacuum magnetic axis position = 0.92m, ECH power = 220kW, NBI power = 650kW x 2. Vacuum vessel wall is conditioned intensively with Ti-Bettering to suppress the influx from the wall. When the perturbation coil is energized the magnetic field configuration is slightly different from the configuration without the perturbation field, causing the electron density a little bit lower. The electron temperature profiles are compared for the plasmas with and without perturbation field. The central electron temperature is higher with perturbation field than that without perturbation field, however it is not shown clearly that the ITB is formed more easily with the perturbation field, that is, is formed at higher electron density. Less