DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2013 EXPERIMENTAL CAMPAIGN Review | Direct submission with log-in | Request submission without log-in
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Title	53: QH-mode with low torque start-up
Name:	Keith Burrell Burrell@fusion.gat.com	Affiliation:	General Atomics
Research Area:	Inductive Scenarios	Presentation time:	Not requested
Co-Author(s):	W.M. Solomon, A.M. Garofalo, M. Lanctot	ITPA Joint Experiment :	No
Description:	We seek to develop techniques to allow QH-mode operation with low co-Ip NBI torque (< 1 Nm) throughout the discharge.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	The basic approach is to start with an ECH H-mode, turn on the NTV torque using the nonaxisymmetric coils, and then determine the NBI torque limit 1. Use Ohmic startup followed by ECH H-mode to get torque-free H-mode a. Requires SND with grad-B drift towards divertor or DND b. Use reverse Ip, standard Bt, LSND or DND c. This current and field combination allows operation under standard QH-mode conditions in USND to assess wall conditions 2. Need best possible error field correction; accordingly, use I-coil for n=1 error field correction and some even parity n=3; use C-coil with D1 power supply for n=3 NRMF 3. Determine whether n=3 NRMF inhibits L to H transition a. If so, turn on after transition b. If not, turn on before 4. Add sufficient counter beams to create QH-mode a. Use beta feedback to keep beta_N at 2 5. Scan amount of counter torque and start time of beams to determine counter torque limit for QH-mode As part of this investigation, we should also see whether using n=2 NRMF rather than n=3 NRMF provides any advantage.
Background:	QH-mode is an extremely attractive operating mode for future devices, since it exhibits H-mode confinement combined with steady-state operation without ELMs. Work in the 2009-2012 campaigns on D III-D has demonstrated QH-mode operation with zero-net NBI torque or small co-Ip torque by replacing the NBI torque with torque from neoclassical toroidal viscosity produced using nonresonant n=3 magnetic fields. These shots, however, used large (4 Nm), counter-Ip NBI torque to create the QH-mode; the torque was then changed during the QH-mode to the small, co-Ip values. To convince the fusion community that QH-mode is a feasible operating mode in future devices, we must extend our previous demonstration to discharges where the NBI torque is at small, co-Ip levels throughout the discharge. Initial attempts at creating these plasmas in the 2012 campaign were only partially successful; we did discover, however, that we need to use Ohmic startup rather than turning the beams on early as we have done for the counter-Ip NBI cases. The present plan builds on that observation, coupling it with creation of ECH H-mode with zero NBI torque.
Resource Requirements:	Reverse Ip. 6-7 gyrotrons. C-coil configured for maximum n=3 field, 7.1 kA current. I-coil configured for error field correction and as much n=3 field as possible.
Diagnostic Requirements:	Standard profile and all fluctuation diagnostics, especially edge BES and ECE-I for EHO studies
Analysis Requirements:	--
Other Requirements:	--