Morton-APS-DPP-2020-poster_v2

Fast ion !" diagnostic (FIDA) on C-2W
L. A. Morton, E. Granstedt, N. Bolte, R. Magee, D. Gupta, G. Player, S. Dettrick, L. Galeotti, and the TAE Team
TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610
n Key points
n Fast ions diagnostics are important for C-2W
FIDA complements existing NPA & fusion product diagnostics
n Data from mCHERS demonstrates feasibility of FIDA measurement We expect improved performance with dedicated FIDA system
n FIDASIM* & in-house MC fast ion transport code qualitatively reproduce FIDA features
*B. Geiger et al, PPCF 2020
*Stagner, Geiger, & Heidbrink, doi:10.5281/zenodo.1341369
n Fast ion behavior in FRC has unique features
n We are using simulations to aid design of dedicated FIDA system
n ‘Active’ FIDA signal observed with mCHERS viewing DNB n Establishes feasibility of measurement
n We expect >10x larger signal from FIDA system & modulated NBI
Halo
FIDA
DNB BES
n 'Passive’ FIDA signal is more substantial on mCHERS n Mixed signal from edge neutrals & 2 glancing NBI beams
n Pronounced asymmetry in spectrum, consistent with significant co-current fast ion population
Fast ion orbits
n FIDASIM + MC fast ion code qualitatively reproduces FIDA
n Strong asymmetry in FIDA spectrum due to co-current fast ions
n Monte Carlo fast ion transport modeling predicts interesting velocity-space structures in fast ion distribution
n Includes charge-exchange, electron/ion and ion/ion collisions n Full orbit calculations necessary – orbits are global
n Beams inclined 20 degrees into the z-direction
n 3 energy components modeled
n Coupled self-consistently to equilibrium solver
Fast ion density
n Fast ion density locally up to 15-20% of thermal ion density
n Axial & radial bounce motion apparent
n Fast ion orbits extend beyond separatrix
Electron temperature
Global distribution
& ≈ (, * ≈ +( ,-
Electron density
& ≈ (, * ≈ +( ,-
& ≈ (, * ≈ +( ,-
n Viewing optimization has many requirements, some conflicting
n Target single tunable NBI ‘Upstream’ portion
Impact parameter: from 50cm to minimum (~20 cm)
n Avoid background from other beams Avoid the need to turn any other beams off
n View perpendicular to beam (~#$∘ leeway) Avoid BES pollution of FIDA wings
n Probe parallel/perpendicular to Bz
Parallel: conflicts with perpendicularity to beam due to beam tilt Perpendicular: causes LOS to intersect background beams
n Select accessible/available port Perpendicular viewing of beam
n FIDA diagnostic hardware (temporarily in use for mCHERS)
n Andor Holospec f/1.8 VPG spectrometer Reciprocal dispersion ~ 1.4 nm/mm Resolution ~ 0.25 nm
n Phantom Miro Lab310 camera
n Photek (MCP125) intensifier
n NA 0.22 fibers, 600um à 5x 200um @ entrance slit
n Independently-adjustable 1” fiber collimators for each fiber
n Future work
n Final selection of FIDA views & optical design
n Hardware implementation, testing, & calibration n Bayesian integrated data analysis
n Validation of simulated fast ion distribution
n C-2W is good candidate for FIDA diagnosis
n Total fast ion energy matches or exceeds thermal component n 8 heating neutral beams (NBI), each 130 A
4 fixed (15 kV), 4 tunable (15 to 40 kV) Tunable beams can be modulated @ 1kHz Beams tilted 20 degrees along axis
n Diagnostic beam (DNB): 40kV, 8.5 A, ~5cm radius
n FIDA will complement existing C-2W fast ion diagnostics
n Neutral particle analyzer provides highly-selective look at particular velocity vectors
n Fusion product diagnostics sensitive to global fast ion content
n FIDA will provide multiple 1-D velocity distribution measurements
Fast neutrals emit Doppler-shifted !" light
We infer approximate velocity distribution along sightline
Use multiple sightlines to probe features of 3D velocity distribution