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Title	14: Control of toroidal mode number of EHO
Name:	Keith Burrell Burrell@fusion.gat.com	Affiliation:	General Atomics
Research Area:	Inductive Scenarios	Presentation time:	Not requested
Co-Author(s):	A. Garofalo, M. Lanctot	ITPA Joint Experiment :	No
Description:	Investigate how the toroidal mode number n of the edge harmonic oscillation(EHO) changes with plasma shape, q, density and n-number and parity of the externally imposed nonresonant magnetic field (NRMF)	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Run QH-mode plasmas and make systematic single parameter scans to see the effect of each parameter on the n-number of the EHO. For example, in shots with the same shape as 141439, use odd parity, n=3 NRMF from the I-coil and systematically vary I-coil current and find the threshold where the EHO switches from n=1 to n=3. For the investigation of the q dependence, we will need both current and toroidal field scans. Experiments in 2011 have shown that toroidal field scans can be done dynamically during one shot. Another variable to investigate is the n-number of the NRMF to see if n=2 NRMF has the same n-number changing effect on the EHO that the n=3 NRMF does. If there is an effect of the n=2 NRMF, then we need to investigate whether this can be further optimized by changing the phasing between the upper and lower set of I-coils.
Background:	The edge harmonic oscillation (EHO) is a key feature of the QH-mode which provides the extra particle transport to allow the plasma to reach a transport steady state at edge parameters below the explosive ELM limit. Experiments in 2011 and 2012 revealed that control of the toroidal mode number of the EHO is an important part of running QH-modes with low or co-Ip torque. If the EHO has a toroidal mode number n=1, it can lock to the wall at low rotation. EHOs with n=2 or greater or the broadband MHD do not have this problem. Over the years, we have empirically developed techniques to change the n-number. These include increasing the plasma density, changing the plasma shape, altering the edge q and using odd parity n=3 NRMF. One of the most fascinating observations is the switch of the EHO from n=1 to n=3 when odd parity NRMF is applied to the plasma. However, we have never systematically investigated these to establish the range over which they work and, more importantly, how to optimize them. The goal ofthe present experiment is to perform that systematic investigation.
Resource Requirements:	Reverse Ip. 8 NBI sources.
Diagnostic Requirements:	All profile diagnostics. Fluctuation diagnostics for edge measurements of EHO, especially BES and ECE-I
Analysis Requirements:	--
Other Requirements:	--