HL-2M托卡马克装置中螺旋波与低杂波的协同电流驱动

Synergistic current drive of helicon wave and lower hybrid wave in HL-2M

螺旋波是一种快磁声波,在托卡马克等离子体中通过电子朗道阻尼和渡越期磁泵效应能够高效地离轴驱动等离子体电流.依托HL-2M装置,根据快波等离子体色散关系,分析获得了螺旋波强阻尼条件下对应的波参数范围;然后,通过联合GENRAY/CQL3D计算程序,针对HL-2M装置稳态运行模式下的螺旋波和低杂波协同电流驱动开展了模拟研究.研究结果表明:高比压等离子体参数下的螺旋波和低杂波都可呈现波射线能量强吸收的现象;双波协同使得波驱动的等离子体电流分布在较大的径向位置范围(ρ=0.2—0.9)内;同时,螺旋波在平行磁场方向加速电子,导致了更多的电子进入低杂波共振区,从而有效地增大了两支波的总驱动电流.此外,在强阻尼条件下,系统地研究了螺旋波平行折射率对双波协同电流驱动的影响,结果表明双波总是呈现正协同效应,协同因子高达1.18.

Non-inductive current drive plays a crucial role in tokamak,especially for its steady state operations.Recently,the helicon wave(HW)has been regarded as a promising tool for driving off-axis plasma current in reactor-grade machine.The lower-hybrid wave(LHW)is the most effective radio-frequency current drive method,however,it has the drawback,which is limited by the conditions of wave accessibility in the high parameter tokamak,making the wave power usually damped at the plasma edge.HW can spiral towards the plasma centre directly under a high electron density.To obtain a long pulse steady state operation of reactor tokamak,the complementarity of HW and LHW in the aspect of driven current distribution in the high parameter tokamak is considered.The synergy current drive of the HW and the LHW is studied numerically in the steady-state scenario of HL-2M.According to the fast wave dispersion relation of plasma,the HW parameters,including its wave frequency and launched parallel refractive index,are obtained firstly.Results of GENRAY code simulation show that a single pass wave power absorption of the HW can be obtained generally through the electron Landau damping and transit time magnetic pumping effects.On the other hand,the LHW parameters are adopted from the equipped system on the machine.Results of single pass wave absorption are also obtained in the case of LHW.And then,the synergy effects of HW and LHW are studied numerically based on the GENRAY/CQL3D models.The cooperation of these two waves results in a broad plasma currentρ=distribution along the radial direction(0.2-0.9)in the machine.Taking the electron distribution functions of these waves into account,it is clear that the electrons are accelerated by the HW in the parallel magnetic field direction,resulting in more electrons entering the region of LHW resonance area.As the consequence,a net plasma current appears.Furthermore,a fine-grained parametric scan is performed by changing the launched parallel refractive index of HW,and the results indicate that positive synergy effects can be generally observed once the related wave current drive profiles are overlapped.Finally,the synergy factor is shown to be proportional to this overlap and reaches its maximum value of 1.18 in HL-2M.