Speaker
Robert John La Haye
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1038.pdf
Twenty-One Years Establishing ECCD Stabilization of NTMs in DIII-D*
R.J. La Haye1 for the DIII-D Team
1
General Atomics, PO Box 85608, San Diego, California 92186-5608, USA
Since the seminal predictions [1] in 1997
of how narrow radially localized electron
cyclotron current drive could stabilize
neoclassical tearing modes (NTMs) by
replacing the “missing” bootstrap current
in an island, DIII-D has been at the
forefront of experimental validation. The
previous commencement of 110 GHz
gyrotron installation on DIII-D enabled
this. The first complete stabilization
(following ASDEX-Upgrade) of an NTM
Fig. 1. Cross-sections of ITER and of a DIII-D ITER
(m/n=3/2) using two gyrotrons injecting 1 Baseline Scenario discharge showing the launch of
MW was achieved in 2000. The most rays (170 GHz 1*fce and 110 GHz 2*fce respectively)
to drive co-ECCD at q=2.
recent DIII-D experiments are in a low-
torque ITER baseline scenario and mimic the ITER geometry for ECCD aligned to the q=2
surface as shown in Figure 1. Initially there was no real-time capability for ECCD alignment
on a rational surface; the development of alignment progressed from fixed mirrors with mirror
angle or toroidal field changed shot-to-shot, to closed-loop control of the entire plasma major
radius and thus island location or control of toroidal field and thus ECCD location, to moving
the mirrors during a discharge [2]. The subsequent increase in the numbers of gyrotrons (and
thus EC power) and the real-time mirror control to keep the ECCD “scalpel” on a given q=m/n
surface allows tests of simultaneous preemption/avoidance of both 3/2 and 2/1 modes in the
IBS in DIII-D. Real-time logics for gyrotron power management progressed from applying
after a saturated mode, to always-on CW for preemption of the mode, to turning on with
detection of a growing mode. Comparison of CW to standby ECCD to “catch” a growing mode
to “subdue” it with return to standby is under yet further development as ITER will need to
keep the average EC power for NTM stabilization at a minimum in order to maximize Q.
*Work supported by the US DOE under DE-FC02-04ER54698.
[1] C.C. Hegna and J.D. Callen, Phys. Plasmas 4, 2940 (1997), H. Zohm, Phys. Plasmas 4, 3433 (1997), F.
Perkins, R. Harvey, M. Makowski, and M. Rosenbluth, 24th EPS Conf. on PPCF, Berchtesgaden, 1997, 1017.
[2] E. Kolemen, A.S. Welander, R.J. La Haye, et al., Nucl. Fusion 54, 073020 (2014).
