Ion Flow Measurement on the C-2W Open Field Line Plasma

S. Outer Divertor
S. Formation
N. Inner Divertor
N. Formation
N. Outer
Divertor 1019
T e
The C-2W device1 is equipped with eight 1.6 MW neutral beams which inject large-orbit fast ions to sustain a field-reversed configuration embedded within an axisymmetric magnetic mirror. Collisional energy transfer from fast ions is intended to be the pri- mary source of heating of the bulk plasma; therefore, the spatial and velocity distribu- tion of fast ions strongly affects the overall power balance and understanding fast ion loss is critical. At typical injected energies (15 keV) and external fields (0.7-1 kG) fast ions sample the core, scrape-off-layer, and diffuse outer-edge plasmas where they can be lost via charge-exchange with neutrals. Careful vacuum practices and titanium get- tering successfully reduced neutral recycling from the vessel walls. As a result, warm neutrals generated from beam capture via charge-exchange with bulk plasma ions con- stitute a large fraction of the remaining neutrals. Balmer-α emission measured with a fil- tered high-speed camera is used with DEGAS22 neutral particle modeling to reconstruct the strongly non-axisymmetric neutral distribution. This distribution is then used with Monte Carlo modeling to estimate the charge-exchange loss rate of fast ions.
Nonlinear camera response:
Optical nonuniformity: 0.00
2.00 1.75 1.50 1.25 1.00 0.75 0.50 0.25 0.00
1.0 1017
0.5
0.0 1016
Mechanical Design Wide-angle Radial View
3 2 1 0 1 2 3 1014 Z [m]
Retracts during gettering, removable for cleaning
• sapphire viewport alternative configuration has a protective cap around in-vessel mirror
304SS mirror
[1] [2]
M. W. Binderbauer et al. THE PHYSICS OF PLASMA-DRIVEN ACCELERATORS AND ACCELERATOR-DRIVEN FUSION: The Pro- ceedings of Norman Rostoker Memorial Symposium. Ed. by Toshiki Tajima and Michl Binderbauer. Vol. 1721. 1. Newport Beach, CA, USA: AIP Conference Proceedings, Aug. 2016, p. 030003.
Daren Stotler and Charles Karney. en. Contributions to Plasma Physics 34.2-3 (1994), pp. 392–397.
sapphire window
10x 2" dia filter wheel
support electronics
camera black anodizedwith lens
enclosure
mirror adjustment screw
end-cap
0.0
3D neutral distribution in C-2W determined from visible imaging and interpretive modeling
C-2W machine layout
S. Inner
Divertor Confinement
TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610
DEGAS2 interpretive modeling framework
Neutral distribution
Source weights optimized to best match experimental images
• A (npx × nsources ) simulation images • m (nsources ) unknown source magnitudes
1.5 Magnets 1018
750 500 250
0 0.0
• b (npx) measurement • non-negative least-squares solution: Ti A·m=b
1.0 0.5 0
1017 1016
0.75 10 0.50
0.0
0.2
0.000
0.4 R [m]
0.6
0.8
0.2
0.4 R [m]
0.6
0.8
1.00 0.75 0.50 0.25 0.00
Neutral distribution with NBI
cut along an azimuthal plane
0.0 0.2
0.4
Electrodes
-10
Abstract
NB injection
2.00 0.4 1.75
1.50 0.2 1.25
-5
0
Axial distance (m)
Separatrix 5
Instrument Calibration 0.25
0.05 0.04 0.03 0.02 0.01 0.00
Scrape-off layer
FRC
Plasma gun
re-entrant tube
motorized bellows actuator
0.2 1.5 1.0 0.1 0.5 0.0 0.0
E.M. Granstedt, K. Zhai, B. Deng, D.K. Gupta, S. Dettrick, D. Osin, T. Roche, and the TAE Team
Ex-situ and In-situ spatial calibration
0.2 0.1 0.0
0.5 1.0
Various spectral filters highlight different phenomena
beam emission in DEGAS2, but outside
experimental filter bandwidth
simulation assumes Z = 1, ⇒ over- eff
predicts warm neutral source simulation treats thermal plasma as H not D
absolute calibration error?
0.08 0.04 0.00
0.0
neutral beam #1
cold gas bleed #1
neutral beam #4
beam dump recycling
Neutral distribution without NBI
cut along an azimuthal plane
256×256
0.8 0.6 0.4 0.2 0.0
42024 Z [m]
Separate simulations for each source type
0.2
Source image data value [arb]
0.4
0.6
0.8
0.4 0.5
0.3 0.0 1016
60th Annual Meeting of the APS Division of Plasma Physics
Portland, Oregon
Midplane plasma profiles extended to 2D assuming flux functions
0.050
0.020
0.010
-0.001
0.005
0.002
0.001
Synthetic cameras map simulation to experiment
7 6 5 4 3 2 1 0
0.5 0.4 0.3
Warm neutrals dominate in the core, recycled neutrals in the edge
2.5 2.0 1.5 1.0 0.5 0.0
3.5 3.0 2.5 2.0
17
Mean effective neutral density
NBs on, 0.97ms NBs off, 1.17ms
0.2 0.4 0.6 R [m]
• • • • •
DEGAS2 warm-neutral emission ≲ 8 22
10 1016 1015 1014
W/m -sr and measurement ≲ 2 W/m -sr
0.5
1.0 1017
0.5 1.0
1015
3210123 1014 Z [m]
1015
bleed brightness [W/m2-sr]
NBI brightness [W/m2-sr]
recycling brightness [W/m2-sr]
dump brightness [W/m2-sr]
Magnetic Flux [Wb]
nHeff [m 3]
measured [W/m2-sr] R [m]
measured [W/m2-sr] R [m]
Effective H density [m 3]
Effective H density [m 3]
residual [W/m2-sr]
RMS Error
NUC
R [m]
ne [m 3]
hg20180106.tae.1
Radius (m)
fit [W/m2-sr]
Temperature [eV]