Fast ion transport by interaction of multiple modes

1. Fast ion transport by interaction of multiple modes E D Fredrickson, N N Gorelenkov, G Fu

2. Phase space interactions of multiple modes may enhance fast ion losses • Phase-space island overlap of multiple modes leads to big fast ion losses. • Overlap triggers "avalanche" where multiple modes are destabilized. • Relevant to small * regime Additional data needed: • Higher resolution documentation of modes' structure, amplitudes • NPA/FLIP measurements of affect on fast ion transport. • Power-scaling of onset, MSE-constrained q-profile

3. TAE bursts suggest "Avalanche" physics • No correlation of repetitive small bursts; increased amplitude leads to strong multiple mode burst Berk, et al., PoP 2 3007 • Weak chirping/bursting simulated with M3D-K (Fu) • Strong bursts consistent with model of "island" overlap in fast ion phase space • TAE have multiple resonances, more complex physics 3

4. Goals for this XP: • Higher resolution documentation of modes' structure, amplitudes • Goal is to estimate EP phase-space island sizes, develop capability to predict amplitude at which avalanche is triggered • NPA/FLIP measurements of affect on fast ion transport. • Particularly the fast NPA data to look for transport on TAE burst timescales • Power-scaling of onset • Start from quiescent regime, increase fast ion beta until TAE onset, then until TAE avalanches • MSE-constrained q-profile (best documented avalanche cases pre-date MSE)

5. *AE-quiescent regime developed in '06 • Starting point for documenting affect of fast-ion MHD on current drive • Valuable to understand thresholds for *AE onset . Additional information required: • Document q-profile evolution in quiescent phase. • Benchmark Vertical NPA scan; transition to *AE regime. • Increase fast ion beta by reducing density, increasing beam power to trigger TAE avalanches - clearly identify thresholds for excitation of fast ion modes.

6. Draft run plan - day 1 Step 1, reproduce quiescent regime, try to increase beam power: 10 • Reproduce quiescent plasma as in 121210, with source C at ≈ 60 kV 2 • Increase toroidal field to ≈53 kA (120124), change current waveform 2 • If not quiescent, increase density to lower beam beta 2 • Add source B at ≈60 kV, 2 • If not quiescent, increase density to lower beam beta 2 • If quiescent, increase source B or C voltage in 5 kV steps until TAE appear 2 Use Source A from 70 to 150-200 ms to help startup, document q? Piggy-back HHFW angelfish stabilization during this time? Use n=3 braking from beginning (want it later)? Step 2, Document highest power quiescent plasma 10-20 • Step source A at 90 kV back in time from time tbd in 0.2 s intervals to document q profile evolution: • Acquire reflectometer data on modes present with source A • Start vertical NPA scan • Sparse NPA scan with source A on at 0.3s • Document impact of EPM onset on fast ion redistribution

7. Draft run plan - second run day Requirements: • L-mode ne(0) ≈ 3.5x1013/cm3 on axis for reflectometer coverage. • Best TAE avalanches were with A&B at 65 kV, try with B&C at 65 kV. • Source A at 90 kV tends to excite EPMs • N=3 braking to minimize rotational shear • Argon doping for SXI, HSXI? Step 1: Increase fast ion beta until TAE avalanches start (B&C at 65 kV?) • Start with best quiescent case from Part A, lower ne(0) ≈ 3.5x1013/cm3 3 • Document TAE, if they show up at lower density 4 • Increase beam voltage in 5 kV increments past avalanche onset 4 Step 2: Document avalanches • Document q evolution during avalanches (NPA scan?) 5 Evaluate data acquired to this point, return to conditions where documentation is uncertain. Verify that good reflectometer and MSE data was acquired.