Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J....
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![Page 1: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/1.jpg)
Results from the HV Test System
Review of current design and assembly
J. Long,P. Barnes, J. Boissevain, J. Gomez,
S. Lamoreaux, D. Mischke, S. Penttila
LANL
Amplification and large-gap E-fields
Leakage currents
Pressure dependence of small-gap breakdown
Results with normal state LHe
Neutron irradiation
Cool-down and heat loads
Plans for near future
![Page 2: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/2.jpg)
50 kV/cm
76 mm
extrapolation (?)
Electric Field: LHe Breakdown vs Gap
Figure: J. Gerhold, Cryogenics 38 (1998) 1063
Need 50 kv/cm across 8 cm cell ~ 400 kV
Internal amplifier (avoid heat loads, large feedthroughs)
Variable capacitor with C >> Ccells ~ 50 pf
![Page 3: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/3.jpg)
vacuumchamber
supplycryostat
77 K shield
G-10 foot
linearactuator
air-vacuumHV feedthrough
~2 m
LN2reservoir
Design: vacuum enclosure
Vacuum pump, T- sensor readout attachments
LHe vessel
LHereservoir
![Page 4: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/4.jpg)
Assembly: central volume
View of electrodes through side port Leak check of central volume and bellows
![Page 5: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/5.jpg)
Assembly: vacuum system
LHe vessel in Kevlar sling
20 layers superinsulation
Complete system showing HV charger
drive rod, linear actuator and motor
![Page 6: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/6.jpg)
Cooling and filling of central volume (December 2003)
LN2
transfertube
LHevessel
plug
1
2
3
4
5
Temperature sensor locations
3 days to fill from room temperature start (limited by Cu shield), need ~ 400 liters of LHe
![Page 7: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/7.jpg)
Heat loads
Estimated sources
Kevlar rope suspension 10 mW
Ground actuator/spider 10 mW
HV actuator/spider 5 mW
HV conductor 2 mW
Unshielded quartz windows 30 mW
2585 mW (1555 mW)
Supply cryostat neck 1800 mW
(Neck with 77 K anchor) (770 mW)
Temperature sensors 1 mW
Measurement
Average He gas boil-off:(flowmeter near 300 K)
52 liters/min
4 K liquid boil-off: 3.4 liters/hr
Total load: 2660 mW
Estimate after restorationof 77 K anchor: 1600 mW
Radiation through SI 725 mW (?)
![Page 8: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/8.jpg)
CHG
HVPS
50 kV
Q
CHC
CCCCCF
CHF
HC
HC
CCCFHCHCHG C
Q
CCCQV
11
Amplification Measurement: Meter on Charger
• Use SR570 current amplifier
• Readout with ADC at 130 Hz
)( dtiQ HCHC
First attempted load cell on actuator: P = 0E2/2, Unrepeatable backgrounds at 4 K
![Page 9: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/9.jpg)
Readout
10 M
GAMMA 50 kV 1.25 mA
HVPS
RG8 - BNC SR570-ACURRENTPREAMP
TERMINALSTRIP
NI-PCI6024eADC
64
LabVIEW
RG87m500 pF
LAKESHORE218
16GPIB
OMNI-LINK
PCRS-232
THOMSONMOTOR360 W
THOMSONDRIVE
# CDM010i
~ 4500 N max
![Page 10: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/10.jpg)
HV-Charger Capacitance
Close HV-G gap
Monitor C with bridge on100 kV feedthrough as increaseCharger-HV separation
cm1.0
cmpF4.6pF43
z
C
Charger retracted to 4.24 cm whereCHC = 1.6 ± 0.2 pF
C0
Az0
![Page 11: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/11.jpg)
Pull back G electrode at constant 1inch/min
Largest Potentials Attained
Expect initial current (first 2.5 mm pullback):
mm5.2
kV42pF6.1
s 60
mm4.25~ 12 nA
2/25/04 11:00, step G from 2.5 to 73 mm, initial potential = 42 kV
dz
dVCv
dz
dQv
dt
dz
dz
dQ
dt
dQi HG
HCHC HG
HF
HGHG
zA
C
Q
C
QV
Shape should track dV/dz :
20
1~
HG
HGzzdz
dV
(z0 ~ 5 cm)
![Page 12: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/12.jpg)
Largest Potentials Attained
= 862 nC
VHG (7.3 cm) = (570 ± 70) kV
CHC error 13%
SR570 zero drift 3%transients 2%
n
nnnnHC iittQ 2/11
2/25/04 11:00, step G from 2.5 to 73 mm, initial potential = 42 kV
2/20/04 22:15, step G from 2.5 to 73 mm, initial potential = -31 kV
VHG (7.3 cm) = (-360 ± 60) kV
Charging with negative potential:
• Draws steady current > 50 A below –30 kV
• Current independent of charger position
![Page 13: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/13.jpg)
2/20/04 23:15, step G out to 7.3 cminitial potential = 29 kV
Leakage Current
2/21/04 10:47, return G to 3 mm gap
t
Q
C
C
t
VC
t
Qi HC
HC
HGHGHG
HGLEAK
QHC = 566 nC QHC = 568 nC
CHG = 53 pF (bridge, ± 5%)
CHC = (1.6 ± .2) pF
QHC = (-2 ± 24) nC (3% zero shift)iLEAK = (-2 ± 20) pA
t = 11h 32 min ± 5 min
_
(EHG = [52 ± 8] kV/cm)
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Breakdown vs. Pressure – 3 mm gap
Pump LHe bath with roots blower (250 m3/hr)
~ 8 psi check valve limits pressure
Could reduce to 25 kV/3 mm(300 kV/ 7.3 cm) or worse at low P
2/27 data (open circles):
• System had 2 additional days at 4 K
• 5 hr after LHe top-off
• 30 min. prior HV conditioning
![Page 15: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/15.jpg)
Radiation Effects
n-flux in gap Breakdown V (kV) Comments Time
(Background) 30 ± 1 No source 11:00
~106/s, E ~ 1 MeV,
10% ~ 1 keV
34 ± 2 Source behind
2 cm plexiglas
11:03
106/s, E ~ 1 MeV 36 ± 2 Plexiglas removed
11:07
~ 7 Ci n-source, 50 cm from gap, nearly on-axis
Small gap (3 mm), 30 minutes after LHe fill, ~ 5 minutes conditioning, 1 psig
Slight improvement (or conditioning)
Large gap (maintained for 1 minute, no plexiglas, inward trace shown):
VHG (7.3 cm) = (390 ± 60) kV
![Page 16: Results from the HV Test System Review of current design and assembly J. Long, P. Barnes, J. Boissevain, J. Gomez, S. Lamoreaux, D. Mischke, S. Penttila.](https://reader035.fdocuments.in/reader035/viewer/2022062322/56649eb15503460f94bb6c5a/html5/thumbnails/16.jpg)
Conclusions
Normal State LHe holds 570 kV at 7.3 cm (~ 40% higher than “expected”)
73 mm
(570 ± 70) kV
Design field at 7.3 cm holds for > 11 hr
Max leakage current = 20 pA (~ 3% of tolerable limit)
Problem with low-P operation?
Small gap breakdown not affected by neutron radiation (106/s, ~MeV)
Large wire-seal flanges hold LHe(thermal gradients > 60 K / 60 cm)
Superfluid operation (either way…)
E-field measurement via Kerr effect(Discussions with UC…)
Prototype holding cell (Lucite, coatings…) behind HV electrode
Next steps