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Title	181: Heat pulse propagation in a perturbed magnetic topology
Name:	Todd Evans evans@fusion.gat.com	Affiliation:	General Atomics
Research Area:	ELM Control	Presentation time:	Not requested
Co-Author(s):	K. Ida (NIFS), Y. Suzuki (NIFS), S. Ohdachi (NIFS), S.Inagai (Kyushu University), E. Unterberg (ORNL), M. Shafer (ORNL), J. Harris (ORNL), O. Schmitz (FZ-Juelich), M. Austin (Univ. Texas), and ITPA PEP-19 Group Members	ITPA Joint Experiment :	Yes
Description:	The goal of this experiment is to study changes in the transport and the structure of the equilibrium magnetic field when non-axisymmetric perturbation fields are applied to Ohmic, L-mode and H-mode plasmas. The ECH system will be modulated to increase Te near the center of the discharge in order to generate heat pulses that propagate radially outward to the boundary region. Data will be acquired on the propagation of these heat pulses from the core to the edge using the ECE system. Changes in the characteristics of the heat pulse propagation, as the magnetic topology and plasma conditions are varied, will allow us to understand how the plasma alters the applied vacuum magnetic perturbations. Data from this experiment will be compared with vacuum field calculations and results from similar experiments done in LHD and TEXTOR over the last few years. This techniques has the potential to be able to establish the extent to which the plasma response to externally applied RMP fields screens or amplifies resonant components and gives us a direct measurement of the energy transport in RMP H-modes and can be compared to ELMing H-modes.	ITER IO Urgent Research Task :	Yes
Experimental Approach/Plan:	The first step in this experiment is to use inner wall limited (IWL) Ohmic and NBI heated plasmas with an ECH pulse train modulated at 25 Hz between 0 and 2 MW and a large m/n = 3/1 island positioned close to the last closed flux surface. We need to develop discharge conditions that minimize the size and frequency of sawteeth since heat pulses generated by these instabilities contaminate the ECH pulses and make it difficult to analyze the ECE signals. The second step is to go to a diverted H-mode plasma with RMP ELM suppression and repeat the ECH pulses used in the previous step. This step will also require some discharge development to minimize sawteeth and to optimize the modulation frequency of the ECH since we want the the on-time of the ECH to be long enough to reach a saturated Te at the deposition radius and the off-time to be at least as long as the energy confinement time. It may be necessary to adjust the ECH on-off timing and modulation depth to match the discharge conditions. The toroidal field will be set to give the best possible ECE coverage of the pedestal and the ECH will aimed to heat near the rho = 0.2 surface while minimizing the current drive.
Background:	ECH pulses have been successfully used in LHD and TEXTOR to study changes in the magnetic topology, i.e., nested flux surfaces, small isolated magnetic islands, mixed islands and stochastic layers and regions of strong stochasticity, due to intrinsic resonant magnetic fields and applied RMP fields. These studies have been done primarily in helical (heliotron) and limiter (tokamak) plasmas under Ohmic and L-mode type conditions. During the 2011 DIII-D run period an initial set of data was obtained using IWL and diverted L-mode and H-mode plasmas. Two IWL discharges were obtained with and without RMP fields that had relatively small sawteeth (e.g., 146517). Several ISS ELM suppressed discharges were also obtained (e.g., 146797-146800) but these had significant sawtooth activity and the toroidal field was not well optimized for good ECE coverage of the pedestal. Nevertheless, with a careful analysis of the data several interesting and potentially important effects were observes. Based on what was learned from the 2011 data and the operational experience gained from these discharges we should be able to achieve better plasma conditions (i.e., with reduced sawteeth) and acquire better quality data that will answer several key physics questions about the plasma response to the RMP field in Ohmic, L-mode and RMP H-modes. This experiment is an important part of the ITPA PEP-19 work plan which is focused on understanding how 3D perturbation fields affect transport and confinement.
Resource Requirements:	Detailed resource, diagnostic, analysis and other requirements are listed in D3DMP No.: 2011-01-05.http://fusion.gat.com/pubs-int/MiniP/review/2011-01-05.pdf
Diagnostic Requirements:	ECE correlation-ECC BES reflectometer
Analysis Requirements:	Scheduling of this experiment needs to take into consideration the travel arrangements of international participants.
Other Requirements: