Global particle balance and wall recycling properties of long duration discharges on TRIAM-1M

Abstract

The longest tokamak discharge, with a duration of 11 406 s (3 h 10 min), has been achieved. The global particle balance has been investigated. In the longest discharge, the global balance between the particle absorption and release of the wall was achieved at t ∼ 30 min. After that, the plasma density was maintained by the recycling flux alone until the end of the discharge. The maximum wall inventory is about 3.6 × 10 20 H at t ∼ 30 min, but it is finally released from the wall at the end of the discharge. The hydrogen release seems to be caused by the temperature increase in the whole toroidal area of the main chamber. Moreover, it has been observed that there is a large difference between the properties of wall recycling in the continuous gas feed case (i.e. static condition) and in the additional gas puff case (i.e. dynamic condition). In the static condition, the effective particle confinement time increases to ∼10 s during the 1 min discharge and it increases to ∼100 s before the global balance in the longest discharge. In the dynamic condition, the decay time of the electron density just after the gas puff, i.e. the effective particle confinement time, is constant at 0.2-0.3 s during the discharge. The large difference in the effective particle confinement time between the static and dynamic conditions seems to be caused by the reduction in the recycling coefficient due to the enhanced wall pumping resulting from the additional gas puff.

Plasma-Wall Interaction Study towards the Steady State Operation

“…Hydrogen recycling in long duration discharges has been studied using global particle balance analysis [6,9,[21][22][23][24]. The global particle balance in the main chamber can be written as:…”

“…On the other hand, the characteristics of the PWI length scale range from the nm order (microstructure) to tens of m order (global particle balance) with μm (dust) and cm (hot spot) orders in between. Therefore, PWI phenomena must be comprehensively investigated from multiscale viewpoints because the scale length phenomena are interrelated.In TRIAM-1M, which has SSO capability, plasmawall interaction experiments have been carried out extensively from microscopic and macroscopic viewpoints [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. In this paper, various phenomena of PWI are investigated focusing on their length scales, which are classified according to the length from the order of a diameter of the torus to that of the microstructure of the deposits on author's e-mail: sakamoto@triam.kyushu-u.ac.jp the wall.…”

Observation of Termination Process of Long Pulse Plasma Discharges Using Stereoscopic Fast Framing Cameras in the Large Helical Device

“…However, SSO has been performed in some superconducting tokamaks [2,3], the termination process of the plasma discharges has not yet fully been investigated because of the necessity of huge data storage memories with high time resolution. In LHD, several fast framing cameras have been applied to the investigation of the termination process of the plasma discharges using an end trigger author's e-mail: shoji@LHD.nifs.ac.jp * ) This article is based on the presentation at the 25th International Toki Conference (ITC25).…”

Impact of target temperature on hydrogen recycling in divertor simulation plasma of GAMMA 10/PDX tandem mirror

“…For example, density control was lost due to global wall saturation, which means a recycling coefficient exceeds unity, in long duration discharges in the superconducting tokamak TRIAM-1M [3,4]. Increase in the wall temperature plays a crucial role on the wall saturation.…”