Research advances to understanding mode stabilization physics and reliably maintaining the high beta plasmas Motivation - Maintenance of high N with sufficient physics understanding allows confident extrapolation to ITER and CTF
Outline - Active control of beta amplified n = 1 fields / global instabilities
- Mode dynamics and evolution during active control
- Control performance compared to theory, connection to ITER
- Kinetic effects on resistive wall mode (RWM) stabilization
- Non-axisymmetric field influence on plasma rotation profile
NSTX equipped for passive and active RWM control External midplane control coils closely coupled to vacuum vessel Varied sensor combinations used for feedback - 24 upper/lower Bp: (Bpu, Bpl)
- 24 upper/lower Br: (Bru, Brl)
Active RWM control and error field correction maintain high N plasma
Probability of long pulse and <N>pulse increases significantly with active RWM control and error field correction - Ip flat-top duration > 0.2s (> 60 RWM growth times)
During n=1 feedback control, unstable RWM evolves into rotating global kink RWM grows and begins to rotate - With control off, plasma disrupts at this point
- With control on, mode converts to global kink, RWM amplitude dies away
- Resonant field amplification (RFA) reduced
Conversion from RWM to rotating kink occurs on w timescale Kink either damps away, or saturates
Soft X-ray emission shows transition from RWM to global kink
Experimental RWM control performance consistent with theory VALEN code with realistic sensor geometry, plasmas with reduced V
Significant N increase expected by internal coil proposed for ITER
Stronger non-resonant braking at increased Ti Examine Ti dependence of neoclassical toroidal viscosity (NTV) Li wall conditioning produces higher Ti in region of high rotation damping Expect stronger NTV torque at higher Ti (-d/dt ~ Ti5/2 )
Advances in global mode feedback control, kinetic stabilization physics and magnetic braking research Active n = 1 control, DC n = 3 error field correction maintain high N plasma over ideal Nno-wall limit for long pulse Control performance compares well to theory - Significant N increase expected for ITER with proposed internal coil
Kinetic modifications to ideal stability can reproduce behavior of observed RWM marginal stability vs. V - Simple critical rotation threshold models for RWM stability inadequate
Non-resonant V braking observed due to n = 2 applied field
Backup slides
Non-resonant rotation braking produced using n = 2 field n = 2 has broader braking profile than n = 3 field (from field spectrum)
Dostları ilə paylaş: |