Magnetic Relaxation with Oscillating Field Current Drive on MST

Magnetic Relaxation with Oscillating Field Current Drive on MST

Doug Stone

A.F. Almagri, G. Fiksel, K.J. McCollam, J.S. Sarff

Midwest Magnetic Fields Workshop • Madison, Wisconsin • April 2012

Oscillating Field Current Drive (OFCD)

• Fusion motivation - counter resistive dissipation of helicity to sustain plasma current in steady state using AC fields

• Accomplished by application of sinusoidal poloidal and toroidal voltages:

• Voltages add magnetic helicity to the edge

• Unstable current profile expected to relax through dynamo processes• Physics motivation - unique test of magnetic relaxation

)sin(0 tVV TT)sin(0 tVV PP

Probe Measurement of Dynamo During OFCD

• Dynamo alternates between increasing and decreasing current in the edge

• The dynamo accounts for difference between and moderately well

• There is mode activity associated with both positive edge current drive due to sawteeth and anti-drive due to OFCD

• Relative mode amplitudes vary between sawteeth and anti-drive

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