26th IAEA Fusion Energy Conference - IAEA CN-234

Evidence for Trapped Electron Mode Turbulence in MST Improved Confinement RFP Plasmas

20 Oct 2016, 08:30

4h

Kyoto International Conference Center

Poster EXD - Magnetic Confinement Experiments: Plasma–material interactions; divertors; limiters; scrape-off layer (SOL) Poster 5

Speaker

Dr David Brower (UCLA)

Description

Drift wave turbulence underlies key transport phenomena in toroidal, magnetically confined plasmas. While long-studied for the tokamak and stellarator configurations, the distinguishing features of the reversed field pinch (RFP) allow further development of gyrokinetic models that build on the RFP’s features of high-beta, large magnetic shear (tending to add stability), and relatively weak toroidal field. Since the RFP is poloidal-field-dominated, the role of ballooning is considerably weaker. Standard RFP behavior tends to be governed by tearing magnetic fluctuations driven by the gradient in the current density. However, tokamak-like improved confinement occurs with inductive profile control (PPCD: pulsed poloidal current drive), and large-scale electromagnetic fluctuations are largely suppressed. [1] In this environment, gyro-scale instabilities are anticipated important and could ultimately limit confinement. [2] The role of drift waves is rapidly emerging for the RFP, and this provides a complementary environment to other configurations for exploring basic understanding of turbulent-driven-transport physics and improving confidence in predictive capability for future burning plasmas. Herein we describe detailed measurements of high-frequency density fluctuation spectral features and temporal-spatial dynamics in the MST-RFP. Comparison with modeling results from the gyrokinetic GENE code provide evidence that these fluctuations are consistent with expectations for TEM turbulence and may indeed be playing a role in governing the overall plasma confinement. Work supported by U.S. DOE, Office of Science, Office of Fusion Energy Sciences under Award Numbers DE-FC02-05ER54814, DE-FG02-85ER53212, and DE-FG02-01ER54615. [1] J.S. Sarff, et al., Nuclear Fusion 43,1684-1692 (2003). [2] D. Carmody, et al., Phys. Plasmas 22, 012594 (2015).