非均匀波导阵抑制低杂波天线烧蚀和提高电流驱动效率研究

Lower hybrid wave is an important auxiliary heating and current drive means for plasma discharge in tokamaks. The spurious emission of the radiated power spectrum of generally used multi-junction antenna and Passive Active Multijunction (PAM) is serious, and more than 25% of the energy is in the opposite direction of the main peak of the desired parallel refractive index. The spurious emissions lead to energy dispersion and decrease the current drive efficiency, moreover, the high n// part of the spurious wave can accelerate the edge low energy electrons to fast ones, resulting in waveguide mouth arc breakdown and antenna ablation. In this proposal, the non-uniform waveguide array with Chebyshev power distribution will be used and the weighted control of the amplitude and phase in the waveguides will be applied, so as to reduce the spurious emission of the launched spectrum in plasma, improve the energy near the main peak and achieve unidirectional radiation. The weighted compensation method of the active multijunction antenna and PAM, the coupling with plasma, and the optimization of microwave components for non-uniform waveguide array will all be studied. Combined with the experiments on EAST, the spectrum will be optimized by using 4.6GHz LHCD antenna with non-uniform distribution of the power and phase or antenna sub-waveguide modification. The main objective is to improve the current drive efficiency, reduce the risk of antenna mouth ablation and finally satisfy the EAST high parameter and long pulse operations.

低杂波是托卡马克等离子体放电时一种重要的辅助加热和电流驱动手段。常用低杂波多结波导和PAM天线的功率谱杂散辐射较多，且25%以上的能量位于所需平行折射率的主峰反向。杂散辐射导致能量分散,不但降低电流驱动效率，而且，高平行折射率的杂散波还会引起天线外围低能电子加速而产生快电子，导致波导端口击穿打火而烧蚀天线。鉴于以上原因，本项目拟采用功率为切比雪夫分布的非均匀波导阵列，通过对波导内电场幅度和相位的加权控制，减少低杂波在等离子体中功率谱的杂散辐射，提高主峰附近能量分布，使天线达到单向辐射。研究有源多结波导和PAM天线的幅度和相位加权补偿方法、与等离子体的耦合、以及非均匀波导阵的物理和微波器件优化。结合EAST实验，利用主波导非均匀功率和相位分布的4.6GHz天线，或天线子波导改造，优化功率谱，以提高电流驱动效率和降低天线端口烧蚀风险，满足EAST高参数和长脉冲运行。

托卡马克等离子体电流驱动长脉冲实验中，常用低杂波多结波导和PAM天线的功率谱杂散辐射较多，且25%以上的能量位于平行折射率主峰反向。杂散辐射导致能量分散,降低电流驱动效率，高平行折射率的杂散波还会引起天线外围低能电子加速而产生快电子，导致波导端口击穿烧蚀天线。本项目从阵列天线合成的理论出发，研究了主波导和子波导内功率为切比雪夫分布和泰勒分布的非均匀波导阵列，以及整阵列泰勒分布等几种情况下与等离子体的耦合性能，探索减少低杂波天线功率谱的杂散辐射的方法。计算表明子波导内的非均匀分布，可有效提高低密度时方向性系数，意味着距离等离子体较远时，可保持较高的驱动效率，同时可减少天线烧蚀风险。针对功率谱各种杂散平行折射率，从理论上分析了天线各种杂散副瓣和栅瓣形成的原因，并提出消除的办法。完成了2.45GHz PAM天线的物理设计研究和工程设计，分析比较了新PAM天线和原有FAM天线的耦合特性。结合EAST物理实验，通过远红外热像仪观察波导天线端口，仔细研究了4.6 GHz天线杂质喷射和波导口击穿的原因，监测到了天线端口和石墨限制器的温度分布，并在高功率测试台上开展了充气压力和温度对功率容量影响的实验。通过本项目研究，掌握了非均匀多结波导和PAM天线的设计理论和技术，以提高电流驱动效率和降低天线端口的烧蚀风险，为EAST、CRAFT以及CFETR发展高性能长脉冲低杂波天线提供了技术支持。