1. Status of the HV Test System Purposes of the HV test system Design and assembly progress Vacuum enclosure Projected assembly and test milestones (short-term) J. Long, P. Barnes, J. Boissevain, D. Clark, M. Cooper, J. Gomez, S. Lamoreaux, L. Marek, D. Mischke, S. Penttila LANL LHe volume

2. Issues for HV test system Validate engineering design Cryogen capacity Strength of HV feedthroughs Heat loads Validate amplification mechanism Measure HV properties of LHe (7.6 cm gap, ~10 l volume) Dielectric strength Breakdown probability Proposal: ~ 1500 l superfluid He (200 l HV volume alone) Vessels with stainless wire-seal flanges 50 kV from vacuum to superfluid He Suitable for LHe at.3 K with dilution refrigerator rated 3 mW at.12 K 50 kV to 380 kV with variable capacitor ~10 to 1000 pF want 50 kV/cm: Not known for gaps > 1 cm, volume > 0.1 l Need P ~ 0 over 10 8 s: Existing data up to 100 s Measure electric field via Kerr effect

3. Issues for HV test system (cont.) Measure HV properties of test cells Study effect of electric field on scintillation process Dielectric strength Breakdown probability Electric field stability over measurement cycle Electric field uniformity Target:  E < 1% for ~ 500 s  E < 1% over cell volume Charge buildup on walls

4. stainless can aluminum plate wire seal flange G-10 standoff HV plunger actuator Indium seal ceramic standoff HV electrodeground electrode ground actuator Vacuum-LHe HV feedthrough bearings bellows 0.53 m quartz window Design: LHe Volume

5. Assembly: LHe volume V = 150 l m (with lid and LHe) = 260 kg Flange: MDC standard 27.5” OD wire seal 0.63 cm thick Al (~15 kg) 16  m finish, 50  m flatness R c (HV) = 5.0 cm C ~ 1500 pf (1 mm gap) A = 1600 cm 2 Stainless vesselElectrodes HV GND G-10 Insulator (temporary)

6. Assembly: LHe volume ISI standard weldable, 40 kV Bellows and spiders (HV side) Bearings Vacuum – LHe feedthrough Thomson SSU-12 load capacity: 5000 N G-10 rod bellows attaches to actuator In seal HV contact G-10 flange HV feedthrough 10 cm stroke (HV and ground)

7. vacuum chamber supply cryostat 77 K shield G-10 foot linear actuator air-vacuum HV feedthrough ~2 m LN2 reservoir Design: vacuum enclosure Vacuum pump, T- sensor readout attachments LHe vessel LHe reservoir

8. Design: LHe vessel suspension LHe vessel 77 K shield vacuum chamber kevlar rope positioning jigs (not to scale) P. Huffman; C. Brome, Ph.D. Thesis, Harvard 2002

9. Assembly: vacuum enclosure V = 520 l0.63 cm thick Cu (~100 kg) Vacuum chamber77 K shield Projected P: ~10 -5 torr in ~ 30 min 300 K  77 K in ~12 hr (4 LN2 refills) cryostat jacket 100 kV feedthru conflat cross thick shell end tubes mating cuff

10. Heat loads on test system LHe bath current budget Kevlar rope suspension limits vs T (if cool by pumping on LHe bath) 10 mW 0.5 W1.5 K 3 W2.0 K 15 mW1.0 K G-10 feet10 mW Ground actuator/spider10 mW HV actuator/spider5 mW HV conductor2 mW Unshielded quartz windows30 mW Temperature sensor leads, Other paths above cryostat 67 mW

11. Short-term milestones Assemble 77 K shield (no insulation or T-sensors) June 7 Test vacuum system 77 K cool-down (insulation and T-sensors on shield) Obtain suspension jigs, kevlar Assemble HV conductor (LHe feedthrough to plunger) Modify LHe vessel lid Obtain linear stages and interface to spiders Assemble complete HV system First LHe fills Assemble axial lead wall (X-ray shield) Basic amplification and breakdown tests (ceramic standoffs available) June 20 July 15 Aug 1 Aug-Sept