Demo

CHARACTERIZATION OF THE C-2W PLASMA GUNS
Ami M. DuBois, Vladimir Sokolov, Sergey Korepanov, Dima Osin, Gabriel Player, and the TAE Team
TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610
ABSTRACT
Previous use of coaxial arc discharge plasma guns on the C-2U device exhibited great
success in plasma stabilization and improved confinement. On the C-2W experiment, arc
discharge plasma guns will again be used to facilitate the electrical connection between
the plasma core and the divertor electrodes in order to maintain the electrode edge
biasing and induce E × B shear to control plasma rotation. Each plasma gun contains an
internal solenoid used to shape the plasma stream. Characterization of electron density
(n ), electron temperature (T ), floating potential (V ), and total plasma flux in an arc eef
discharge lasting 6 ms without the internal solenoid are presented. A Langmuir probe
located 27 cm axially outside of the plasma gun anode measures a bell-like radial ne
profile with peak n ~ 1018 m-3 and T ~ 2 - 10 eV. Observed spectral lines of impurity ions ee
provide an estimate of T , and Balmer series line ratios of the main ion component are e
used to evaluate ne at both the probe location and near the plasma gun anode. A calorimeter measures the plasma flux to be ~1 kA.
MOTIVATION
 The Field Reversed Configuration (FRC) plasma core rotates in ion-diamagnetic drift direction, leads to growth of n = 2 rotational instability – confinement significantly decreased [1]
𝑽𝑫𝒊 + 𝑽𝐄×𝑩 𝑽𝑫𝒊
Eapp: α < 1, n = 2 suppression vDi
C-2W PLASMA GUNS
 PG design previously used on Gas Dynamic Trap (GDT) magnetic mirror device [3,4]
ELECTRON DENSITY
SPECTROSCOPY
 Typical spectra at z = 1 cm & z = 26 cm
 Dα intensity shows Gaussian-like emission with jet divergence ~ 24°
 C III intensity ions (Zi > 1) located closer to jet axis, jet divergence ~ 20°
 Jet diameter at z = 27 cm calculated from divergence & FWHM at z = 3 cm:
 Dα diameter (z = 27 cm) = 26 cm
 C III diameter (z = 27 cm) = 23 cm
 Diameter from LP (z = 27 cm) = 24 cm
z = 3 cm
[1] M. Tuszewski et al., PRL 108, 255008 (2012)
[2] M. W. Binderbauer et al., PoP 22, 056110 (2015)
[3] D.I. Davidenko et al., Preprint BINP 86-104 (1986) [Russian] [4] A. A. Ivanov et al., PRL 90, 105002 (2003)
[5] T. Fujimoto et al., J. Appl. Phys. 66, 2315 (1989)
 LP measurements show increasing ne with increasing Varc
 Plasma jet diameter of 24 ± 4 cm at 27 cm away from PG anode obtained from Gaussian fit of measured ne profile (dashed lines)
 Jet diameter independent of Varc & pressure, may slightly decrease with increasing peak ne
55 PSI
1.3 kV
1.0 kV
0.7 kV
0.6 kV
0.5 kV
Gas Valve
Auxiliary Solenoid
 Arc discharge (10kA/500V) generates plasma stream in deuterium with 6 ms
Anode Cathode Cavity
Pulse Solenoid
 PG contains pulsed solenoid (~ 1 T) to generate cusp field, shape plasma
stream
C III emission with solenoid LP seen at bottom of photo
0.7 kV
1.0 kV
1.1 kV
1.2 kV
1.3 kV
1.4 kV
1.7 kV
1.8 kV
 Balmer series × LP
 Peak ne calculated from LP (x) & spectrometer () data for various pressures, Varc
 Balmer series estimates show n has linear
dependence on pressure
e
flattop
 LP measurements consistent with Balmer series ne estimates for PSI < 100
 For PSI ≥ 100, LP measurements appear to saturate due to depleted electrons during high pressure discharges
Shot 32320 No solenoid
𝛂 = 𝐫𝐨𝐭𝐚𝐭𝐢𝐨𝐧𝐚𝐥 𝐩𝐚𝐫𝐚𝐦𝐞𝐭𝐞𝐫 =
 LP measurements at z = 27 cm indicate 𝑻𝒆 ≤ 𝟏𝟎 eV with little radial dependence
 Consistent with estimated Te from impurity ion (O II, O IV, C III) spectral lines
EFRC: α > 1, n = 2 growth vDi
PLASMA FLUX
v BE EBExB
PLASMA DIAGNOSTICS
4 tipped LP (4.5 mm long) placed 27 cm axially outside of PG anode for profile measurements
6 E-type thermocouples located 10, 20, 30 cm radially from PG center, 43.5 cm axially outside of PG anode
Thermocouple connections
 Thermocouple data shows temperature peaks near center of plasma column
50 PSI
80 PSI
120 PSI
zFRC appz EFRC v E


  
 Peak temperature increases with increasing pressure and V
 Plasma flux (𝑰) is calculated from LP & thermocouple measurements
 𝑰𝑳𝑷 = 𝑱 𝑨 = 𝒆𝒏𝒆𝑽𝒅𝒓𝒊𝒇𝒕 𝑨=𝝅𝑭𝑾𝑯𝑴𝟐 𝟒
 FWHM = plasma jet diameter = 24 ± 4 cm  Vdrift = 3.1x106 cm/s
 𝑰𝒕𝒉𝒆𝒓𝒎𝒐𝒄𝒐𝒖𝒑𝒍𝒆 = 𝒎𝑪𝚫𝐓 𝑻𝒆𝚫𝐭  Te = 10 eV
 Δt = 6 ms
 𝟏 ≤ 𝑰 𝐀 𝐜𝐦𝟐 < 𝟔
 𝑰𝑳𝑷 consistent with 𝑰𝒕𝒉𝒆𝒓𝒎𝒐𝒄𝒐𝒖𝒑𝒍𝒆
 𝑰𝑳𝑷 increases with V & pressure
Diagnostic
Measurement
Langmuir probe (LP)
V , n , T , Plasma flux fee
Thermocouple
Heat, Plasma flux
Survey spectrometer
n,T ee
Fast camera
Composition
FRC Core
FRC Core
ExB FRC
arc
 Velocity shear is well known to suppress instabilities & improve confinement [1]
 In C-2, plasma guns (PG) were installed in divertor, biased to produce inward radial
electric field [1]
 Reduction in bulk plasma rotation
 Improved FRC particle transport and global confinement
 Use of PGs also tightly centers plasma via line tying to electrodes to mitigate n = 1
wobble motion [2]
 On C-2W, PGs will be used to facilitate electrical connection between plasma core
& divertor electrodes to maintain electrode edge biasing & induce E x B shear to control plasma rotation
 PGs are optimized & characterized without solenoid before use on C-2W
0.7 kV
1.0 kV
1.4 kV
1.7 kV
1.8 kV
Survey spectrometer provides estimation of ne from line ratios of Dα, Dβ, Dγ (Balmer series) [5] at different axial positions relative to PG anode
Spectral lines of impurities with different ionic charges (O II, O IV, C III) used to estimate Te
Sub-ms-exposure, 1 nm spectral 2D plasma images yield PG jet profile & composition
LP
 Thermocouple
4 tipped LP
arc
 LP measures total particles (1 < neA (1015 cm-1) < 5) to increase linearly with PSI