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Charge Exchange Recombination Spectroscopy (ChERS) diagnostics will provide measurements of ion temperature, velocity and density profiles in C-2W field-reversed configuration (FRC) plasmas. Currently, two diagnostic systems are planned, one for impurity ions and the other dedicated to main ion measurements. Both diagnostic systems will use a common diagnostic neutral beam, currently under development, and high-speed CCD cameras coupled with intensifiers using high-efficiency optics. Impurity ion ChERS can also be used as a passive diagnostic in the absence of a diagnostic neutral beam, and is able to provide a full radial profile every hundred microseconds.
n To measure the ion properties and understanding ion dynamics in a high performance FRC in C-2W device.
n Knowledge of the main-ion temperature and velocity profiles is required to understand plasma dynamics. These parameters describe the basic plasma properties and govern the equilibrium and stability of an FRC plasma. Spatial profiles of main-ions play role in plasma confinement and transport physics.
n Impurity ions information is used for defining Z-effective, resistivity, radiation loss, current drive, plasma confinement, and transport, etc. in an FRC. These play an important part in the sustainment of the FRC. Impurity transport is also important as we look ahead to ash removal in a potential p-B11 burning plasma.
Diagnostic Neutral Beam (DNB)
Charge Exchange Signal Collection
Impurity-ion Charge Exchange Recombination Spectroscopy (i-ChERS)
Linear Fiber Array
1280x800 pixels; 20μm each
Projection of Intensifier on CCD
n Measurements at 16 radial locations using multi-diagnostic collection mounts at two ports and 600 μm core fibers.
n Linear array of 16+1 fibers (total span of 12.32 mm + 0.66 mm) is imaged on the linear slit at the input of 1.0 m Acton spectroscope.
n Acton spectroscope with 2400 Gr/mm grating provide dispersion of 0.417 nm/mm at the output focal plane, where an image intensifier of diameter 18 mm is placed.
n Intensifier can provide a gain up to 3000x, and its gating can be synchronize with camera using either external or camera clock.
n Two fast lenses De Oude Delft 50 mm 0.75 Lens optically couple image intensifier output to the Miro Lab301 camera with 1:1 ratio.
n Resolution of 25 lines/mm (with 20μm camera pixels size) was measured with this lens-camera system.
n A 1:1 imaging of slit on camera provides a dispersion of 8.34e-3 nm/px, with a spectral span of 5.3 nm.
n System provides a velocity resolution of 9.0 km/s-px at lower wavelength, e.g. 278.1 nm (O-V), and 3.8 km/s-px at higher wavelength, e.g. 6565.2 nm (D-I).
Main-ion Charge Exchange Recombination Spectroscopy (m-ChERS)
n Measurements at five radial locations between 0 and 40 cm, separated by 10 cm.
n The spatial resolution is defined mainly by the DNB size, and is estimated to be about 6 cm.
n Peak neutral beam modulation frequency of 10 kHz governs the minimum temporal resolution of approximately 50 μs.
n The light collection optics is coupled to a 2.0 m, 1800 Gr/mm Acton spectrometer, that provides an inverse linear dispersion of 0.27 nm/mm at the output slit.
n The spectral image is magnified and focused onto an image intensifier photo cathode using additional optics. The image intensifier is synchronized with the DNB current output.
n The amplified spectrum produced by the image intensifier is imaged onto a fast camera detector.
n The current setup allows us to measure the main ion temperature with 10 eV accuracy, and the rotational velocity with 15 km/s precision.
Development of Charge Exchange Recombination Spectroscopy Diagnostics
for the C-2W Field-Reversed Configuration Plasma
Deepak K. Gupta, Dima Osin, Mark Connaughton, Daniel Sheftman, Matthew C. Thompson and the TAE Team
TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610, USA
   n Impurity and main ions are observed on C-2 and C-2U to behave significantly different.
n Plasma impurity ions are observed to rotate in the electron diamagnetic direction, which is opposite to the main-ion rotation (ion diamagnetic direction).
n Under certain divertor electrode biasing conditions, the impurity ions get preferentially heated to significantly higher temperature compared to main-ions.
Expected Parameters of Diagnostic Neutral Beam
Control and DAQ diagram for i-ChERS
12.7 mm (635 px)
      Control / Data Network
         Beam type
Full energy of neutrals
40 keV
Full energy fraction
80 %
Total current in neutrals
8.5 Amps
Current density on axis
0.3 A/cm^2
Beam size
6 x 8 cm^2
Ion optics focal distance
Beam divergence
< 10 mRad
Modulation frequency
10 kHz
Modulation depth
> 60%
Pulse duration
30 ms
Operation frequency
10 min
0-5V DC
Serial to Ethernet
LabView Control
DSP10 Spectrometer
  DC Voltage (D/A)
  Stepper Motor
  Control/ Timing
CLK Intensifier
  Intensifier Ctrl & PS
Light Signal from C-2W
 ß DNB
Deepak K Gupta, TAE Technologies, Inc., “Development of Charge Exchange Recombination Spectroscopy Diagnostics for the C-2W Field-Reversed Configuration Plasma ” Poster - 14.39 ; 22nd High Temperature Plasma Diagnostics Conference, April 16-19, 2018 • San Diego, California, USA
12.7 mm (635 px)
De Oude Delft 50mm 0.75 Lens