Page 1 - Improved density profile measurements in the C-2U advanced beam-driven FRC plasmas

Abstract
The first measurements of fast-ion D-alpha (FIDA) radiation [1] have been acquired on C-2U, Tri Alpha Energy’s (TAE’s) advanced, beam-driven field- reversed configuration (FRC) [2]. This is the first measurement and simulation of its kind on an FRC topology. FIDA spectra are forward modeled by FIDASIM 1.0 [3][4]. Initial measurements of bandpass-filtered signals view only the highest energy ions and show a high spatial correlation with FIDASIM. Conditionally-averaged, un-shifted D-alpha measurements pick out halo radiation and match FIDASIM’s spatial dependence as well. Highly Doppler-shifted radiation isolates beam emission that is measured with a high-speed camera and is compared to FIDASIM.
FIDA System (FIDA Emission)
 1 movable line-averaged line-of-sight, 8 times, 8 unique views, 26-shot average
 652.4x2nm bandpass filter captures only FIDA (fully rejects halo and beam emission)  FIDASIM inputs optimized for this data set
 Future plans include full spectra and several fixed views
What is FIDA?
FIDA measurements are of Doppler-shifted D- alpha light from reneutrals born of the charge exchange (CX) between confined fast-ions and neutral beam or halo neutrals. The radiation occurs so quickly after CX that the location and velocity of the reneutral are effectively that of the confined fast ion. Viewing geometry and fast-ion velocities produce broad FIDA spectra detectable beyond the range of thermal emission. While a full beam deposition and collisional-radiative model (FIDASIM) is used to fully deconvolve the data, a simple control-room level interpretation is also afforded as (all else being equal) signals are proportional to fast-ion densities.
What is FIDASIM?
FIDASIM models neutral beam deposition and produces synthetic D-alpha radiation and neutral particle analyzer signals. Simulated hydrogen- and deuterium-alpha light is calculated by a collisional radiative model and is produced by neutral protium and deuterium atoms in the form of injected beam neutrals, thermal halo neutrals resulting from multiple charge-exchange events between beam neutrals and thermal plasma ions, and finally from fast neutrals, which form when confined fast-ions CX with beam and/or halo neutrals.
See also poster: "FIDASIM: A Fast Neutral Beam and Fast-ion Diagnostic Modeling Suite for Axisymmetric Fusion Devices” by L. Stagner
FIDASIM Inputs
Camera (Beam Emission)
First Fast-Ion D-Alpha (FIDA) Measurements and Simulations on C-2U
N.G. Bolte1, D. Gupta1, L. Stagner2, M. Onofri1, S. Dettrick1, E.M. Granstedt1, P. Petrov
1 TRI ALPHA ENERGY, INC., P.O. Box 7010, Rancho Santa Margarita, CA 92688-7010 2 University of California, Irvine. Irvine, CA 92697
 Fast-camera Sanstreak Edgertronic
 Typically operated using 192x192 frame size at 9527fps
 Fitted for a wide-angle, radial view near the C-2U midplane
 Views largely toward oncoming beam (NB5)
Camera*
NB5 (SE)
[1] W.W. Heidbrink., Rev. Sci. Instr. 81, 10D727 (2010).
[2] M.W. Binderbauer et al, AIP Conf. Proc. 1721, 030003 (2016). [3] W.W. Heidbrink, Commun. Comput. Phys. 10, 716 (2011).
[4] http://d3denergetic.github.io/FIDASIM/
D-Alpha System (Halo & Beam Emission)
Single, movable line of sight
 Utilizes same 652.4x2nm filter to * See also poster: "Fast Imaging
image beam emission
Diagnostics on the C-2U Advanced Beam- Driven Field-Reversed Configuration“ by E. Granstedt
X
NB5 (SE)
v
 14 fixed line-averaged lines-of-sight, 9 times, 7-shot average
 Broad10nmfiltercaptureshaloandbeam emission
 FIDASIM inputs not optimized for this data set
 Future use of narrow 656.1nm filters will isolate halo emission and help verify plasma profiles
fi
NB6 (NE)
X
NB6
D-Alpha View Port
Experimental plasma parameters compared to FIDASIM inputs
FIDA View Port
NB5
Inputs for FIDASIM for this work are produced using a mixture of experimental data and modeling values. Experimentally-obtained plasma radial profiles at the midplane are utilized. TAEs experimentally-validated simulation Q2D [5], which is a two- temperature, 2D MHD model with an added neutral fluid component combined with a 3D Monte Carlo fast-particle code, provides the 2D E and B fields and the 3D fast-ion distribution. Experimental profiles are mapped onto radial and axial dimensions assuming them to beflux functions of the Q2D equilibrium.
[5] M. Onofri et al, “Simulations of the C-2 and C-2U Field Reversed Configurations with the Q2D code”, APS DPP 2015 Conference
Summar y
 FIDA signals are measurable in C-2U FRCs.
 FIDASIM predicts spatial variation well.
 Halo, beam, and FIDA light can be experimentally isolated.
 Measured FIDA signals much larger then predicted.
Camera View Port