High Confinement Advanced Tokamak Plasma Alfven Current Drive Theory

Of late years, a reversed magnetic shear configuration has been formed in some tokamak discharges. The safety factor q, one of the important parameters in tokamaks, has directly and accurately been measured in TFTR, Dâ…¢-D, JT-60U, and Tore Supra, etc. The reversed shear configuration, which has negative magnetic shear in the inner region and positive magnetic shear in the outer region, has been proposed as an advanced tokamak operation. Improved confinement and the formation of an internal transport barrier in the negative shear region have been observed. One is tending to research physical subjects in the reversed shear tokamaks. The other factor making confinement improve is plasma rotation which is present in almost all current tokamaks. It has been shown that the plasma rotation plays an important role in creating or maintaining transport barriers. Some researcher have started considering the transport, the instability, and so on in the rotating plasma in the reversed shear configuration. In this work, we think of advanced high confinement tokamak plasma as being a tokamak rotating plasma in a reversed shear configuration.In this Ph.D. dissertation, we study the Alfven wave current drive in the advanced high confinement tokamak plasma. In cylindrical and slab models, respectively, expressions for driving current density are given by means of the single-fluid magnetohydrodynamic (MHD) approach taking both plasma rotation and magnetic shear into account. Furthermore, a set of differential equations for theperturbed fields is derived, and their approximate solutions are given. For the poloidal mode number m = 0 and m 0, we discuss current drive due to the compressional Alfven wave, the shear Alfven wave, and the circularly polarized wave, respectively. The relation between the driven efficiency and the plasma physical factors is given. We obtain not only the results agreeing with previous works but also several new results. For m = 0, if we neglect the rotation and magnetic shear, our result reduces to the corresponding result in Chan et al.'s work [Phys. Fluids B2, 944 (1990)]. The circularly polarized wave can drive current, and the drive efficiency is independent of the plasma density. In the case of m = 0, the compressional Alfven wave and the shear Alfven wave can not drive the plasma current. If we neglect the magnetic shear, in the slab model, the efficiency of the current drive due to the plane polarized compressional Alfven wave is independent of plasma density and dependent on the plasma rotation, which is in agreement with Avinash's result [Phys. Plasmas 4, 2204 (1997)]. We found that in the case of neglecting magnetic shear, the plasma current also can be driven by the shear Alfven wave and the circularly polarized wave, respectively, the efficiency of current drive in the rotation plasma is independent of the plasma density. In addition, it is found that whether m = 0 or m 0, the effect of the magnetic shear on the compressional Alfven wave current drive makes the efficiency be dependent on the plasma density and inversely proportional to it. However, in the presence of magnetic shear, the efficiency of the current drive by shear Alfven wave is independent of the plasma density. It is noticed that theeffect of the negative magnetic shear on the Alfven wave current drive is opposite to the effect of the positive in that the negative shear enhances the driven current density. In particular, the larger the region of the negative magnetic shear and the less the safety factor minimum q() are, the more enhanced the efficiency of the Alfven waves current drive is.In summary, the drive current by Alfven waves can be enhanced by plasma rotation. The negative magnetic shear is favorable for the efficiency of the current drive by Alfven waves. Moreover, in the reversed shear configuration the current drive due to Alfven waves in an rotation plasma can obviously change the plasma current profile. The Alfven wave current drive may be useful in controlling the current profile in order to suppress magnetohydrodynamic...