Preliminary HV Results in Superfluid Helium eview of HV system design J. Long, J. Boissevain, J. Gomez, S. Lamoreaux, S. Penttila LANL mplification and large-gap E-fields Leakage currents ssure dependence of breakdown (includes normal stat uperfluid LHe production Neutron irradiation ble near future plans (pressurization) HV results Noise issues
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Preliminary HV Results in Superfluid Helium Review of HV system design J. Long, J. Boissevain, J. Gomez, S. Lamoreaux, S. Penttila LANL Amplification and.
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Preliminary HV Results in Superfluid Helium
Review of HV system design
J. Long, J. Boissevain, J. Gomez, S. Lamoreaux, S. Penttila
LANL
Amplification and large-gap E-fields
Leakage currentsPressure dependence of breakdown (includes normal state)
Superfluid LHe production
Neutron irradiation
Possible near future plans (pressurization)
HV results
Noise issues
vacuumchamber
supplycryostat
77 K shield
G-10 foot
linearactuator
air-vacuumHV feedthrough
~2 m
LN2reservoir
Test System Design
Vacuum pump, T- sensor readout attachments
LHe vessel
LHereservoir
Superfluid Production in HV System
1. Fill HV system with normal state LHe at 4 K from full 500-liter supply dewar (1 hr)
2. Pre-cool LHe in both HV system and supply dewar (3 hrs)
HV system: pump bath with roots blower (250 m3/hr) to 40 torr (2.2 K, above -point)
Supply: pump through vent with scroll pump (15 m3/hr) to ~ 230 torr (~3.2 K)
3. Restart LHe transfer, top off HV system with low pressure LHe above -point (1hr)
Leave roots blower on system
Vapor P in HV system rises to ~ 90 torr (2.6 K)
Transfer rate ~ 1 liter/min
4. Stop LHe transfer, leave roots blower on to pump system below -point (3 hrs)
Observe -transition (rapid, complete cessation of all turbulence) at 35 torr (2.14 K)
Process uses ~ 400 liters of LHe, takes 8 hrs
Thanks to John Jarmer (LANSCE-6) for suggesting step 2
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
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
HV-Charger Capacitance
Close HV-G gap
Monitor C with bridge on100 kV feedthrough as increaseCharger-HV separation
cmz
cmpFpFC
1.0
1.5132
Charger retracted to 5.0 cm whereCHC = 1.1 ± 0.1 pF
Largest Potentials Attained6/7/05 17:35, step G from 2.5 to 78 mm, initial V = 13 kV, P = 33.8 torr (T~2.13 K)
= 258 nC
VHG (7.8 cm) = (259 ± 34) kV
CHC error 10%
SR570 zero drift 3%transients 2-13%
n
nnnnHC iittQ 2/11
Truncate sum at each point starting at t = 0
Convert time axis to gap (.085 cm/s)
Potential vs gap curve:
VHG = (570 ± 70) kV
Previous normal state results:
EHG (7.8 cm) = (33 ± 4) kV/cm
(Design = 50 kV/cm…)
EHG = (78 ± 9) kV/cm
Largest Potentials Attained: V < 06/7/05 17:50, step G from 2.5 to 78 mm, initial V = -14 kV, P = 33.4 torr (T~2.13 K)