Sokolov_HTPD_2020_Ver.5_final2

Study of Neutral Gas Pressure Dynamics in C-2W Using Inverted Magnetron Ionization Gauges
Introduction
In TAE Technologies’ current experimental device, C-2W (also called “Norman”), record breaking, advanced beam-driven field reversed configuration (FRC) plasmas are produced and sustained in steady state [1]. Measuring the evolution of gas pressures at different areas of vacuum vessel during a plasma experiment is still an
important issue.
Commercially available MKS 423 I-Mag inverted magnetron gauge (cold cathode sensor) has been equipped with custom-made plasma protection and magnetic shielding to be suited for fast-response measurements in the magnetic field on C-2W. The measurement circuit of controller MKS 943 has also been modified and improved.
[1] H. Gota et al., Nucl. Fusion 59, 112009 (2019).
MKS 423 Inverted Magnetron (IM)
C-2W Overview
Magnetic Shield Design
Heat-treated shields: 1020 Mild Steel with thermal annealing 600C, 2hr
South Outer Divertor (SOD)
7 4
Neutral beams: up to 21MW, 30ms
Double layer shield B < 300 G, NORMAN Divertors CV
B < 10 G
Triple layer shield for B < 2.5 kG, NORMAN CV
V. Sokolov, A.Dunaevsky, A.Van Drie, J.Kinley and the TAE Team TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, CA 92610
South Inner Divertor (SID)
1
3
Cold Cathode Vacuum Gauge Fast Ionization Gauge (FIG 1-7)
2
North Inner Divertor (NID)
5
6
North Outer Divertor (NOD)
C-2W divertors:
Volume ~ 15 m3 CryopanelsA~20m2 Strong Ti gettering => ~2000 m3/s (proved by our measurements)
t ~ 7.5 ms
hg20180106.tae.1
Radius (m)
§ Fast response < 100μks
§ Sufficiently large internal magnetic field > 1400G § No filament cathode
Gas loads [kA] 10
1 kA plasma flow can pump out about 1022 atoms/s from CV
Additional buffer amplifier
Courtesy – A.Korepanov & V.Matvienko
Calibration of IM 423
Pressure in Inner and Outer Divertors (ID, OD) and Confinement Vessel (CV)
Red curve corresponds to N2
Green curve – log approximation
PH2 = PN2*2.5 PD2 = PN2*2.7
FIG_1 FIG_2
FIG_3 FIG_4
FIG_5 FIG_6 FIG_7
Green Magenta
Black Cyan
Red Orange Yellow
North Inner Divertor South Inner Divertor
North Outer Divertor South Outer Divertor
Confinement Vessel North Outer back South Outer back
Gas dynamics in typical shot :
• - 5 ms gas puffing in Formation; response first in Outer
divertor FIGs 3,4,6,7; then in Inner divertors [1,2] and CV[5]. • NBs turn on before “0” => pressure rises in CV earlier than
in Inner divertors.
• “0”- time of plasma ignition; at the same time gas pressure
in CV, IDs and ODs begins to rise due to the plasma recombination and recycling process on CV walls, limiters and electrode plates.
• Gas pressures in CV and IDs are very similar during plasma shot due to good gas conductivity.
• CV pumping decreases when plasma disappears after 30 ms. • Pumping speed of NOD was less than SOD in this shot.
n K = 1, bandwidth > 10kHz, Rout ~120 Ohm n 1.5 kV galvanic isolation
n Over spike protection circuit [ Vmax 10V ]
Operational parameters
• • • • •
Volume[m3] 7 Pumping speed [1000 m3/s]
Pumping time [ms]
Gas throughput [m3/s]
0.35
7
3
200
200
0.35
Standard MKS 943 cold cathode pressure controller is used as power supply for gauge and DC vacuum meter.
Our buffer amplifier is connected to IM 423 sensor via MKS 943 and produces high frequency signal proportional to gas pressure.
Buffer amplifier:
C-2W as vacuum
vessels: 2 2
10
0.5 - 3
>3
3-10
7
3
7
10
• •
•
Modified Measurement Circuit
1.5 1.0 0.5
0
-5
0 FRC Axial distance (m)
Field on sensor < 50G at central field of 0.08T
Field on sensor < 250G at central field of 0.3T
S. Outer Divertor
S. Formation
Electrodes
S. Inner Divertor
Scrape-off layer
Confinement
NB injection
N. Inner Divertor
N. Formation
Magnets
N. Outer Divertor
§
§
§
§
§
0.5 mm stainless steel disc protects the vacuum sensor from plasma, ultraviolet and X-ray radiation.
Ceramic break is used for electrical insulation (noise reduction in signal)
Gas time response < 2 ms
Separatrix 5
15 15 15 15
-10
10
Plasma gun
2 2 •
Courtesy – G.Snitchler & C.Killer
Magnetic field [T] simulation for geometry of CV in our experiment
qTime response modified gauge and controller is < 3 ms. qPressure measurement range is from 10-9 to 5´10-4 Torr. qCold Cathode sensor with magnetic shield is
operational in external magnetic field of up to 3 kG.