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Fast ion transport by interaction of multiple modes

Fast ion transport by interaction of multiple modes. E D Fredrickson, N N Gorelenkov, G Fu. Motivation for this XP:. Fast-ion modes move fast ions in phase-space; Even when ions aren't lost Even when no affect on neutron rate is seen. Redistribution can affect stability of other modes.

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Fast ion transport by interaction of multiple modes

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

  2. Motivation for this XP: • Fast-ion modes move fast ions in phase-space; • Even when ions aren't lost • Even when no affect on neutron rate is seen. • Redistribution can affect stability of other modes. • CAE/GAE/TAE/EPM can all interact • CAE may not directly have strong affect fast ion transport, but could trigger EPMs. • Re-distribution in phase-space will: • Affect beam driven current magnitude or profile. • Also affects fast ion heating profile • Concentrated losses could damage PFCs • It would be desirable to have predictive capability of fast ion transport.

  3. Phase space interactions of multiple modes may enhance fast ion losses • Phase-space islands grow as mode amplitude increases. • 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

  4. 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 4

  5. 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)

  6. *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.

  7. Draft run plan - day 1 Phase 1, reproduce quiescent regime, try to increase beam power: 10 • Reproduce quiescent plasma as in 121210, with source C at ≈ 60 kV 1 • Increase toroidal field current to ≈ 53 kA, change current waveform (120124) 1 • If not quiescent, increase density to lower beam beta 2 • Substitute source A from 0.1s to 0.16s and add/substitute after 0.32s 1 • Add source B at ≈ 60 kV, 1 • If not quiescent, increase density to lower beam beta 2 • If quiescent, increase source B or C voltage in 5 kV steps until TAE/CAE appear 2 Step 2, Document highest power quiescent plasma 10-20 • NPA scan with source A on at 0.32s 6 • Document impact of EPM onset on fast ion redistribution • Step source A at 90 kV back in time from 0.32s in 0.02 s intervals to 0.22s 5 • Step source A forward from 0.16s to 0.2s in 0.02s intervals 2 • Acquire reflectometer/sxi data on modes present with source A

  8. 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 • 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, ne(0) ≈ 3.5x1013/cm3 3 • Increase beam voltage in 5 kV increments to avalanche onset 4 • Document TAE (reflectometer/sxi), when they show up 4 Step 2: Document avalanches • Document q evolution during avalanches 5 • n=3 braking to minimize rotational shear, if time • NPA scan if there is time Evaluate data acquired to this point, return to conditions where documentation is uncertain. Verify that good reflectometer and MSE data was acquired.

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