Speaker
Dr
Robert Pinsker
(General Atomics)
Description
Experiments have begun in DIII-D to evaluate non-inductive current drive by the Landau absorption of a toroidally-directive spectrum of helicon waves (also known as 'very high harmonic fast waves', 'fast waves in the lower hybrid range of frequencies', or 'whistlers'). Modeling has shown [1] that non-inductive current drive at mid-radius (ρ~0.5) should be achievable in DIII-D with fast waves at 0.5 GHz, with an efficiency twice as high as with non-inductive current drive tools currently available on DIII-D (neutral beams and electron cyclotron current drive) in high-beta conditions. An innovative Traveling Wave Antenna (TWA) of the 'comb-line' type with 12 radiating modules has been constructed, installed in DIII-D, and is currently being tested at very low power (<1 kW) to evaluate the antenna coupling in the linear regime, and to prototype technological aspects of such structures in the tokamak environment. Preliminary results indicate strong antenna/plasma coupling, with detailed 3D modeling underway to quantitatively compare the measurements with theoretical expectations. A key input to this model is the edge and far SOL electron density profile, which is being measured with a microwave reflectometer and with fixed and moveable Langmuir probes. An important issue for wave coupling in this regime is the degree to which (undesired) quasi-electrostatic slow waves are excited by the structure; evaluation of this is a point of emphasis in the ongoing work. A high-power system is presently being prepared for installation later in 2016 in which a single 1.2 MW klystron at 476 MHz will be used to power a TWA with ~36 radiating elements in a structure 2 m wide. The goals of the high-power experiments include evaluation of non-linear effects on excitation of the desired waves (ponderomotive effects, parametric decay) and measurements of the deposition profile and of the current drive efficiency. Ray-tracing predicts [1] an rf-driven current of ~60 kA per coupled MW of helicon power, which should result in an easily measurable driven current in DIII-D in high-beta discharges.
This work was supported in part by the US Department of Energy under DE-FC02-04ER54698, DE-FG02-94ER54084, DE-FG02-07ER54917, DE-AC05-00OR22725, DE-AC02-09CH11466, DE-AC04-94AL85000, DE-FG02-08ER54984.
[1] Prater, R. et al 2014 Nuclear Fusion 54 083024.
| Country or International Organization | United States |
|---|---|
| Paper Number | EX/P3-22 |
Primary author
Dr
Robert Pinsker
(General Atomics)
Co-authors
A. Nagy
(Princeton Plasma Physics Laboratory)
A.M. Garofalo
(General Atomics)
C. Lau
(Oak Ridge National Laboratory)
C.C. Petty
(General Atomics)
C.P. Moeller
(General Atomics)
D.C. Pace
(General Atomics)
H. Torreblanca
(General Atomics)
J. Boedo
(University of California-San Diego)
J.G. Watkins
(Sandia National Laboratories)
J.P. Anderson
(General Atomics)
J.S. deGrassie
(General Atomics)
L. Zeng
(University of California-Los Angeles)
M. Porkolab
(Massachusetts Institute of Technology)
R. Prater
(General Atomics)
X. Chen
(General Atomics)
