Research on transport barrier and two-fluid relaxation phenomenon based on radial electric field caused by an orbit loss of high energy electrons

我们利用2.45GHz微波产生超高β等离子体，并利用Mini-RT内线圈装置，基于Mahajan-Yoshida提出的双流体弛豫理论，对超高β等离子体进行了研究。2.45 GHz电磁波的截止密度限制在7.4 × 10 ~（-1）<16>m ~ 2<-3>。在这里，我们考虑引入电子伯恩斯坦波（EBW），以克服这种密度限制，因为EBW没有约束的等离子体密度的波传播。我们正在研究从弱场一侧发射的X模通过模转换激发电子束，到目前为止，在浮置线圈实验中，我们已经获得了1.5 × 10 ~（13）m ~ 2的等离子体密度<17><-3>，这比截止密度高出约2倍。为了有效地实现从X模式到EBW的模式转换，陡峭的密度梯度应该是先决条件;即，理论预测，密度标度长度和磁场强度的乘积应该是5 × 10 - 4 <-4>Tm。这意味着在Mini-RT情况下，密度标度长度应小于1 cm。因此，我们在分界线区域引入了陡峭的密度梯度，这是由浮动和悬浮线圈的组合产生的。在内部线圈装置中出现了许多电子回旋共振的高次谐波，因为偶极磁场的场强迅速衰减;即，B是R^<-3>.此外，模式转换发生在上混合共振区，这是敏感的等离子体密度。这可以通过改变上混合谐振区域的位置来引入加热轮廓控制的可行性。初步的实验结果表明，电子加热的径向位置随等离子体密度的变化而移动。这些结果可能有助于探索超高β等离子体的内部线圈装置。

We are exploring ultra-high beta plasmas based on two-fluid relaxation theory proposed by Mahajan-Yoshida with an internal coild device Mini-RT, where the plasma is produced by 2.45 GHz microwave. The cut-off density of 2.45 GHz electromagnetic microwave is limited up to 7.4x10^<16> m^<-3>. Here we have considered to introduce an Electron Bernstein Wave (EBW) in order to overcome this density limit, because EBW has no constraint on the plasma density for wave propagation. We are studying an excitation of EBW through the mode-converstion from X-mode launched from the weak-field side.Up to now, in floating coil experiments, we have achieved the plasma density of 1.5x10^<17> m^<-3>, which is about 2 times higher than the cut-off density. To realize a mode conversion to EBW from X-mode efficiently, the steep density gradient should be prerequisite ; i.e., theory predicts that the product of the density scale length and the magnetic field strength should be 5x10^<-4> Tm. This means that the density scale length should be less than 1 cm in the Mini-RT case. We have therefore introduced the steep density gradient at the separatrix region, which is produced by the combination of the floating and levitation coils.There appears many higher harmonics of the electron cyclotron resonance in the internal coil device, because the field strength of the dipole magnetic field is rapidly decaying ; i.e., B 〜 R^<-3>. In addition, the mode-conversion takes place at the upper hybrid resonance region, which is sensitive to the plasma density. This might introduce the feasibility of heating profile control, by changing the position of the upper hybrid resonance region. Our preliminary experimental results show that the radial position of electron heating moves according to the change of the plasma density. These results might be useful for exploring ultra-high beta plasmas in the internal coil device.