Study of the Current Circulation through the End Region of a Tandem Mirror and Its Suppression

点击翻译按钮获取中文摘要

Electrically floating end plates are used for suppression of the non ambipolar diffusion stemming from the open filed configuration in a tandem mirror. However, experiments show that many issues are still open. 1. A residual non ambipolar diffusion remains. 2. Secondary electron emission due to ECRH - induced end loss electrons leads to a thermal loss to the end plates. 3. The mechanism of the three dimensional potential profile is not clear.Therefore, the present research has been carried out on the GAMMA 10 tandem mirror with two main objectives. 1. To Evaluate the non ambipolar current at the end plate from an integrated analysis of the current balance at the end plate. 2. To obtain a physical picture of the current circulation through the end plate and to reveal the current distribution through the plasma and the vacuum vessel.Main results of the present research are1. Necessity of a new current component at the end plate has been shown which compensates the current imbalance. This current amounts to a few tens of percent of the end loss electron current.2. Two ion current components have been discovered as counter parts of the new current. One is the ion current through the backside of the end plate ant the other originates from ionization neutral hydrogen atoms in the end region.3. A radial ion current has been observed during ECRH as a limiter current in the plug/barrier cell.4. A strong correlation has been shown between the radial ion current and the new current component at the end plate, which indicates a current circuit is formed between the plug/ barrier cell and the end plate. Furthermore, a current component has been observed in the radial ion current that likely originates in the central cell region.