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	102: TBM mock-up effects on confinement at high β
Name:	Joseph Snipes Joseph.Snipes@iter.org	Affiliation:	ITER Organization
Research Area:	Stability & Disruption Avoidance	Presentation time:	Requested
Co-Author(s):	J. Hanson, Y. In, R. La Haye, N. Oyama, J-K. Park, C. Paz-Soldan, H. Reimerdes, W. Solomon, T. Strait, T. Tala	ITPA Joint Experiment :	No
Description:	This proposal seeks to operate the TBM mock-up in high β H-mode plasmas to clearly determine how much the change in confinement due to the TBM mock-up fields can be affected by optimizing the I-coil error field correction. The 2009 TBM mock-up experiments clearly showed that the effects of the TBM mock-up fields on energy and particle confinement increased with increasing βN [1,2]. The 2011 TBM mock-up experiments [3] were operated at relatively low βN < 2 where effects on rotation were observed, but there were no clear changes in energy and particle confinement (except for a reduction in the confinement of energetic neutral beam ions [4]). Several methods to optimize the n=1 error field correction were attempted and a 25% increase in rotation was observed under conditions believed to optimize the n=1 error field correction in the presence of the TBM mock-up field. However, it is not clear that the optimum error field correction was actually found and the optimum is likely to depend on βN. So, this proposal aims to revisit the error field correction in the presence of the TBM mock-up fields to further optimize the correction with the I-coils at high βN. In particular, we will minimize the n=1 resonant field amplification magnetic response of the plasma to the TBM mock-up perturbation for conditions with βN > 2.5 in an ITER similar shape. In addition, since the attempts to use Dynamic Error Field Correction (DEFC) were not optimized in the 2011 experiments, additional run time should be devoted to DEFC to compare these two techniques at high βN. The new 3D magnetics array will allow up to n=2 DEFC. Another approach that should be attempted to correct the TBM error field is to obtain a more localized correction around the TBM by optimizing the two C-coil currents nearest the TBM in addition to the n=1 error field correction. The main purpose of these experiments is to quantify how much optimum error field correction can reduce the impact of the TBM mock-up fields at high βN. This is best carried out in highly rotating plasmas to avoid locked modes and disruptions. If time permits, the error field correction optimization could also be carried out at high βN with balanced NBI and ECH to operate in low rotation conditions.	ITER IO Urgent Research Task :	Yes
Experimental Approach/Plan:	The experiments should be carried out in an ELMy H-mode with ITER similar shape with βN > 2.5. EFC will be applied with the I-coils in the presence of the TBM mock-up fields. The currents will first be optimized by minimizing the n=1 magnetic response of the plasma to resonant field amplification. Since the TBM mock-up fields can increase the likelihood of locked modes under low rotation conditions, the experiments will be carried out with co-NBI in highly rotating plasmas. After optimizing the error field correction by minimizing the n=1 magnetic response of the plasma, the optimum I-coil currents will be maintained during the TBM mock-up pulse throughout the plasma flattop for several discharges to check reproducibility. ECH may be applied to reduce NTMs, if necessary. DEFC should also be applied to re-optimize up to n=2 error field correction, now enabled with the new 3D magnetics array, in the presence of the TBM mock-up fields at the same βN. Then, additional corrections should be attempted by optimizing the two C-coil currents nearest the TBM mock-up. These three methods to optimize error field correction should be attempted and several discharges may be repeated with the optimum correction to check reproducibility and ECH may again be applied to reduce NTMs, if required. If time permits, low NB torque plasmas could also be investigated at the same value of βN, possibly with additional ECH to reduce NTMs or reach sufficient βN. The error field correction techniques will likely need to be re-optimized under low rotation conditions. The optimum error field correction will be compared for each of these conditions and techniques and the effect on particle and energy confinement of the TBM mock-up fields will be quantified comparing optimum error field correction in the absence of the TBM mock-up fields with that in the presence of the TBM mock-up fields.
Background:	The 2009 TBM mock-up experiments clearly showed that the effects of the TBM mock-up fields increase with increasing βN. The 2011 TBM experiments provide a good starting point to determine the optimum error field correction based on minimizing the n=1 magnetic response, but they will need to be re-optimized at βN = 2.5. The 2011 TBM experiments also attempted DEFC, but were unsuccessful so more experimental time would be required to optimize this technique. The higher n error field correction with the 2 nearest C-coils is a more recent idea that should also be attempted. The new 3D magnetics array will allow up to n=2 DEFC.
Resource Requirements:	TBM mock-up coil, co- and possibly also counter-NBI. ECH may also be required to reduce NTMs and to operate at high βN with low rotation if time permits. The I-coils and 2 nearest C-coils to the TBM mock-up and associated power supplies are also required.
Diagnostic Requirements:	Locked mode (RWM) sensors. Particle and energy confinement and rotation measurements. Interferometer. Thomson scattering and ECE measurements.
Analysis Requirements:	Analysis of error fields and their correction. Standard energy and particle confinement.
Other Requirements:	--