Speaker
Dr
Rajesh Maingi
(Princeton Plasma Physics Laboratory)
Description
The role lithium wall conditioning on the achievement of high performance, long pulse discharges in NSTX and EAST is documented. Common observations include a reduction in hydrogenic recycling, confinement enhancement, and the elimination of ELMs. The plasma confinement and pulse length in both devices improve with increasing lithium conditioning. In NSTX, the impurity accumulation which occurred when natural ELMs were suppressed by lithium conditioning, was ameliorated by triggering controlled ELMs, e.g. with pulsed 3D fields. In EAST, active lithium conditioning during discharges has overcome this problem, producing an ELM-free H-mode with controlled density and impurities.
In NSTX, analysis was done on lithium scans with high δ and κ, more prototypical of the shapes envisioned for NSTX-U. The improvements in pulse length, reduction in recycling, and elimination of ELMs in these highly shaped discharges reflect those with lower shaping. The edge density and pressure gradients were reduced in the outermost 5% of the profile in both the high and intermediate shapes, which is critical for the edge stability improvement. Moreover, while the pressure gradient was reduced, the pedestal broadened, increasing the pressure at the pedestal top and overall performance.
In EAST, the extensive lithium wall conditioning routinely applied via evaporators prior to a run day was integral to the 32 second long H-mode pulse lengths. However, during the course of a run day, the efficacy of the lithium coating can decline, and thus conditioning during discharged by injecting lithium powder into the edge plasma has been investigated. As in NSTX, large ELMs were eliminated, in this case with real time lithium injection. Although the radiated power and edge soft X-ray emission were moderately higher in the discharges with active conditioning, these and the line-averaged electron density remained relatively constant in time, in contrast to the NSTX observations which showed secular rises in these quantities with large lithium doses.
In summary, the results from both devices demonstrate several common benefits of lithium conditioning. The new observation on EAST of a quasi-steady discharge devoid of large ELMs improves the prospects for the applicability of lithium conditioning for future devices, removing one of the obstacles to progress in NSTX experiments.
| Country or International Organisation | US |
|---|---|
| Paper Number | EX/P6-54 |
Primary author
Dr
Rajesh Maingi
(Princeton Plasma Physics Laboratory)
Co-authors
Dr
Baonian Wan
(Institute of Plasma Physics, Chinese Academy of Sciences)
Dr
Dennis Mansfield
(Princeton University Plasma Physics Laboratory)
Dr
Guosheng Xu
(Institute of Plasma Physics, Chinese Academy of Sciences)
Dr
Henry Kugel
(Princeton Plasma Physics Laboratory)
Prof.
Houyang Guo
(Institute of Plasma Physics, Chinese Academy of Sciences)
Prof.
Jiangang Li
(Institute of Plasma Physics, Chinese Academy of Sciences)
Dr
Jiansheng Hu
(Institute of Plasma Physics, Chinese Academy of Sciences)
Dr
Michael Bell
(Princeton Plasma Physics Laboratory)
Dr
Robert Kaita
(Princeton Plasma Physics Laboratory)
Dr
Stanley Kaye
(Princeton Plasma Physics Laboratory, Princeton University, Princeton NJ, 08543 USA)
Dr
Vsevolod Soukhanovskii
(Lawrence Livermore National Laboratory)
Prof.
Xianzu Gong
(Insititute of Plasma Physics, Chinese Academy Sciences)
Dr
Y. Duan
(Institute of Plasma Physics, Chinese Academy of Sciences)
Mr
Z Sun
(Institute of Plasma Physics, Chinese Academy of Sciences)
