Formation of Second-Stable, Ultra-High-Beta Spherical Tokamaks by Use of Field-Reversed Configuration

在TS-3和TS-4合并实验中，利用磁重联的高功率加热，发展了一种新型的无中心螺线管的超高β球形托卡马克(ST)结构。在A型合并中，两个ST合并在一起，以建立高达β_T[大致相等]0.5的血浆β。重新连接的高功率加热在很短的重新连接时间内将低β合并的ST转变为高β合并的ST。在B型合并中，首先由两个环向磁场相反的球面合并形成扁平的FRC，然后在外加环向磁场的情况下将其转变为超高β(β-r[约等于]0.8)ST。通过B型合并得到的超高βSTS具有抗磁环向场和绝对最小B型组态。我们首次对所产生的STS进行了气球代码稳定性分析，得出第一稳定/边缘气球稳定区域的形成与测量的高n不稳定性基本一致的结论。这两个合并地层的不稳定STS遭受了高n磁起伏，并在10-30阿尔文时间内被破坏。我们的实验观察发现，气球稳定窗口与测量的高n不稳定性一致。随着电流剖面的空心度和压力剖面宽度的增大，稳定区域明显变大。本文还讨论了(2)与Troyon标度相比较所产生的6-17标度的归一化ββ_N，以及(3)有希望的重联加热的B^2标度。这些事实表明，对于没有强大CS的高βSTS，轴向合并是最有效的启动方法之一。

Novel CS(center solenoid)-less formations of ultra-high-beta Spherical Tokamaks (ST) have been developed in the TS-3 and TS-4 merging experiment using high power heating of magnetic reconnection. In Type-A merging, two STs were merged together to build up the plasma beta up to β_T【approximately equal】0.5. High power heating of reconnection transformed the low-beta merging STs into a high-beta ST within a short reconnection time. In Type-B merging, an oblate FRC was first formed by two merging spheromaks with .opposing toroidal field, and was transformed into an ultra-high-beta (β-_r【approximately equal】0.8) ST by applying external toroidal magnetic field. The ultra-high-beta STs by Type-B merging were found to have diamagnetic toroidal field and absolute minimum-B type configurations. We made (1) the BALLOO code stability analyzes of the produced STs for the first time and concluded formations of the first-stable / marginally ined ballooning-stable regime was almost consistent with measured high-n instabilities. The unstable STs by both merging formations suffered from high-n magnetic fluctuation and disrupted within a 10-30 Alfven time. Our experimental observation identified the ballooning stability window consistent with measured high-n instabilities. The stable regime became larger significantly by increasing the hollowness of current profile and broadness of pressure profile. This paper also addresses (2) normalized betas β_N of thus produced STs as large as 6-17 for comparison with the Troyon scaling and (3) a promising B^2 scaling of the reconnection heating. Those facts indicate that the axial merging is one of the most efficient startup methods for high-beta STs without powerful CS.