Speaker
Dr
Jayson Barr
(General Atomics)
Description
Recent experiments on DIII-D and EAST are developing the techniques and scientific understanding that ITER and future devices will need for safe, low-disruptivity shutdown. ITER needs options for reliable termination both in normal operation as well as in response to an off-normal event, where speed to soft landing is paramount. A large survey of ramp-down techniques in a variety of DIII-D plasma conditions shows disruptivity in fast ($I_p$ ramp-rates of 2-3 MA/s), diverted ramp-downs is similar or improved compared to historical, limited ramp-downs with $I_p$ ramp-rates typically ≤ 1 MA/s. The survey used the ramp-down phase of over 370 DIII-D discharges to develop improved soft-landing techniques scalable to ITER. The disruptivity is shown to be minimized by keeping neutral beam injection (NBI) power on for the duration of ramp-down, and at modest power levels roughly comparable to the average radiated power during shutdown. Experiments on ITER Baseline Scenario (IBS) plasmas have tested the limits of the planned ITER ramp-down as well as faster yet "full-bore" ramp-downs, in which the flat-top ITER shape is maintained through ramp-down. Disruptivity statistics for this scenario have been measured to inform ITER operation, and fast (2 MA/s), full-bore ramp-downs reduced the disruptivity to 25% from the historical rate of 58% using DIII-D's standard 1 MA/s, limited ramp-down method. The planned, shape-evolving (dropping elongation) ramp-down of the 15 MA ITER Q=10 scenario has been experimentally simulated at speeds scaling to the fastest ramp-down ITER is expected to be capable of (~60s [1]), and the scenario is found to be capable of maintaining the required $l_i$ < 1 during the H-mode phase of ramp-down while the elongation is reduced. Experiments on the EAST tokamak have likewise identified robust, fast, diverted ramp-down techniques using sustained lower hybrid (LH) power for the duration of ramp-down. Surveys of plasma current ramp-rate and LH power were conducted in the ramp-down phase of EAST discharges to complement the ramp-down survey performed on DIII-D. By continuing application of 2 MW of LH heating power, the fastest ramp-down yet on EAST of 0.5 MA/s has been demonstrated.
This work was supported in part by the US Department of Energy under DE-FC02-04ER54698 and DE-SC0010685.
[1] A.C.C Sips, et al 2015 Physics of Plasmas 22, 021804
| Country or International Organization | United States of America |
|---|---|
| Paper Number | EX/P6-21 |
Primary author
Dr
Jayson Barr
(General Atomics)
Co-authors
Dr
Bingjia Xiao
(Institute of Plasma Physics, Chinese Academy of Sciences)
Dr
Brian Sammuli
(General Atomics)
Dr
David Humphreys
(General Atomics)
Dr
Jinping Qian
(Institute of plasma physics, Chinese academy of sciences)
Dr
Nicholas Eidietis
(General Atomics)
Dr
Timothy C. Luce
(General Atomics)
