TEdo_APS-DPP2017_Final

Outer Electrode
z-axis
1.0
0.9
0.8
200 150
Inner Electrode
Miniature gun
Gas port
Cross section of gas injection nDistribution of Bias Field with Iron Core and pre-ionization ports
Installation of miniature gun on MCPG
Ø A bias coil is mounted on the outer electrode of the miniature gun to enhance breakdown.
n From the signal of fibers in drift tube, more ”ionized” and/or “high density” CT is generated.
n Breakdown of MCPG reliably occurs within 1 μs.
n By adopting PI system, breakdown can be reproduced easily.
Ø Also, MCPG could be operated at lower gas pressure reduced by ~40% with PI system.
n n
n n
Excess neutral gas cools down a target FRC.
The pre-ionization (PI) system is required to break down MCPG at lower pressure.
The trig. timing and duration can be controlled and the turn-off time of the switching system is 1.45 μs.
The inner electrode is NOT coated with tungsten; however, the impurity influx is small because of its low current.
J×B
Iron-core Bias Coil
546
dFe
dCoil [mWb] 1.2
0.8
0.4 25 20
z-axis
Move hall probe
~ 45 G
Bias current : 1 A
dFe = 2 inch dFe = 12 inch
84
Unit : mm
w/ PI
w/o PI
Fiber 1
w/ PI
w/ PI
w/o PI
#15018
#15019
Performance Improvement of a Magnetized Coaxial Plasma Gun by Adopting Iron-core Bias Coil and New Pre-Ionization System
nIntroduction nIron-core Bias Coil
nPre-Ionization System Gas port
Ø The miniature gun can be installed on the radial or
tangential locations.
Miniature gun
Unit : inch
n A magnetized coaxial plasma gun (MCPG) is a device used to generate a compact toroid (CT), which has a spheromak-like
configuration. Outer pipe
n In order to expand the CT operating range, the distributions of the bias magnetic field and neutral gas have been investigated. n By adopting “iron-core bias coil”, a small current of a few Amps produces a sufficient bias field and the radial distribution of
the bias field can be easily controlled.
n Excess neutral gas for CT injection cools down a target FRC [1,2]. Iron core n By introducing “miniature gun”[3] as pre-ionization (PI) system, MCPG could be operated at lower gas pressure so that the
amount of excess neutral gas can be reduced.
[1] T. Matsumoto et al., Bull. Am. Phys. Soc. 61, CP10.00083 (2016) [2] I. Allfrey et al., Bull. Am. Phys. Soc. 61, CP10.00085 (2016)
[3] T. Asai et al., Rev. Sci. Instrum. 81, 10E119 (2010)
nMagnetized Coaxial Plasma Gun (MCPG) Miniature gun
Inner pipe
Enameled wire
Unit : inch
Enameled wire Inner pipe Outer pipe Iron core
Diameter
Φ0.04 O.D. Φ1.25 O.D. Φ1.75 Φ1
Length Thickness
22 - 24 1/16 48 1/8
27.6 -
Others
500 turns, 2 layers Acrylic Acrylic
Cast Iron
500
400
300
200
100
0 -
#14695
Quantity
MCPG Voltage Gas Pressure Puff Trig. Puff Duration
PI Voltage
PI Trig. PI Duration
Value
9.5 kV
40 psi -1400 μs 1200 μs 2.5 kV
(470 A at peak) -20 μs
20 μs
Unit : mm
Inner
Inner diameter Outer diameter Thickness
Φ48.0 Φ83.1 Φ54.0 Φ89.1 3 3
15
10 5 0 -5 [inch]
T. Edo1, T. Asai1, F. Tanaka1, S. Yamada1, A. Hosozawa1, H. Gota2, T. Roche2, I. Allfrey2, T. Matsumoto2, and the TAE Team
Outer electrode electrode
~ 20 inch 0 Ø The length of plasma formation and Position of iron core and
acceleration regions is 546 mm. solenoid coil
n It consists of a set of coaxial, cylindrical electrodes; iron-core bias coil; gas injection; and pre-ionization ports. n Iron core and solenoid coil move separately. 1
n A plasma is generated between electrodes and accelerated by J×B Lorenz self-force. n According to a simulation result, radial magnetic field, Br, is more 0.8 n The accelerated plasmoid is captured by the interlinkage bias field, and toroidal current is induced by poloidal flux. uniform and spread by adopting iron core.
n The inner electrode is coated with tungsten to reduce impurity influx from the electrode into plasmoid. 0.6
w/o PI 100 50
150
0
-50 cm
4
16 0 8 16 Gas port dCoil [inch]
Schematic view of magnetized coaxial plasma gun
~ 63 G
4
nMCPG Test Stand Diagnostic list
n Br is spread and the result is the same as the simulation.
#14689 n The radial distribution of the bias field can be easily controlled by
Gun current moving iron core position along z-axis.
Ø By changing the distribution of the bias field, the amount of poloidal
flux and velocity of a generated CT can be controlled.
Fiber 2 nEvaluation of CT Parameters (Velocity, Bz, Energy, and Density)
Intensity of plasma light in drift tube
MCPG
Drift tube
y z
Glass Tube
Rogowski coil
Chain resistor
B-dot probe
Collimated fibers (Time-of-Flight)
Triple Langmuir probe
Fiber 2 Fiber 1
250 Velocity 200
150 100 50
6
Bias position [inch]
n Ejected CT has a speed of over 100 km/s in most cases.
n At dFe = 12 or 18 inch case, iron core is NOT inserted inside a portion of solenoid
coil and the total flux is lower so that ”high velocity” and “less flux” CT is generated. n A CT is generated with holding more / less flux by moving iron core position so that
we can easily generate a high velocity or high flux CT.
B-dot probe Triple probe
15 10 5 0
Energy
nConclusion and Future work
n By inserting the iron core into a solenoid coil, a current of a few Amps produces the required bias field of a few milli-teslas
and Br distribution is more uniform and spread.
n PI system can easily produce breakdown and reduce neutral gas so that MCPG could be operated at lower gas pressure;
reduced by ~40% with PI system.
n CT is generated with more / less flux by moving iron core position so that we can easily vary a high velocity or more flux CT. n We will optimize iron core position and inject “high energy” or “high flux” CT into the similar environment of C-2W.
Triple Langmuir probe
n
n
By expanding iron core region, the radial magnetic field does NOT bunch up so that the accelerated plasmoid holds high velocity without deceleration by the interlinkage bias field.
At longer dCoil case, the interlinkage magnetic field increases by the leakage magnetic field so that the generated CT holds “more flux”.
Drift Tube
100 50
MCPG
0 10 20 30 40 50 60 8 Time [μs] 6
Time sequence of the signals from each diagnostic
Schematic of the test stand, which includes MCPG and Drift tube
Measured parameters
Gun current
Gun voltage
Toroidal and Poloidal flux Velocity
Electron density and temperature
200 150 100
50
0
200
150
100
50
0
800
600
400
200
0 -200
50
25
0 20
10 0
0
Fiber 1
100 Bx 90 Bz 80 70
300 Velocity 250
200 150 100
50 0816 0
dCoil [inch]
Density
Bz
Ø Parameters change depending on the bias field distribution
Quantity
Gun Voltage Gas Pressure Puff Trig. Puff Duration Bias Current dCoil dFe
Value
9.5 kV
40 psi
- 1600 μs 1600 μs
2 A
0 / 8 /16 inch 0 / 2 / 4 inch
12 18
0
6
Bias position [inch]
Te
CT pass through
drift tube 60
I 16 sat 14
12 10
8 16 dCoil [inch]
dFe = 0 inch dFe = 2 inch dFe = 4 inch
0
8 dCoil [inch]
1Nihon University, Chiyoda-ku, Tokyo 101-8308, Japan 2TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610
Saturation Current [A]
Electron Flux Temperature density [G]
Intensity Current [A.U.] [kA]
Electron density [×1020 m-3]
Velocity [km/s]
Kinetic energy density [kJ/m3]
Max Bz [G]
[eV]
Velocity [km/s]
Max Bz [G]
Normalized Br
Normalized intensity
Current [A]
MCPG Current [kA]
Configuration of iron-core bias coil
n In order to inject CTs repetitively for a long-lived target plasma, the iron-core bias coil system is adopted because it can generate a stationary bias field.
n The iron-core bias coil with a current of a few Amps produces the required bias field of a few milli-teslas.
0 10
Simulation result of a magnetic flux profile with iron-core bias coil
n The radial position of hall probe is in the middle of gap between the 0.4 electrodes. 0.2
Fiber 2
16
14 12 10
z-axis [inch]
Distribution of radial magnetic field Br by changing iron-core position
200 150 100
50
0
Bz
dFe = 0 inch dFe = 6 inch dFe = 12 inch dFe = 18 inch
Quantity
MCPG Voltage
Bias Current
dCoil dFe
Gas Pressure Puff Trig. Puff Duration
PI Voltage
PI Trig. PI duration
Value
9.5 kV
1 A
0 / 6 / 12 / 18 inch
0 / 6 / 12 / 18 inch
30 psi
-1400 μs
1400 μs
3.2 kV (700 A at peak)
-26 μs 20 μs
8
6
2
0
nCT Parameters at Lower Bias Current and Gas Pressure Operation
Gas flow
Bias coil
View port
Trig.
Break down
1.45 μs
Duration
- 10
Time [μs]
Typical current waveform of the
miniature gun
30
- 20
12 18
0
0 10 20 30 40 50 Time [μs]
Breakdown timing of MCPG