1. HV-SQUID Compatibility Test Study the SQUID performance in a HV environment. Study the HV breakdown –in superfluid under pressure. –using different materials for electrodes. Craig Huffer, Chen-Yu Liu, Josh Long Indiana University

2. Squid Performance in HV environments Physical damage Direct HV discharge hitting the SQUID chip would destroy the SQUID. Large induced current flowing in the feedback circuit could destroy components. Large induced current flowing through the SQUID could destroy the Josephson junctions. Most of you are concerned with this. However, these extreme conditions are unlikely to happen. HV ripple and micro-discharge inside the dielectric materials in electrodes, cell, etc... High frequency components could disturb the feedback circuit and cause SQUID readings to jump randomly. increase the noise level. This could be a bigger concern. Remedy: RF shield.

3. 1 2 3 4 5 6 7 9 8 1. LHe Volume Cap 2. G10 Ground Electrode Support 3. Macor rod for gradiometers 4. HV electrode 5. Ground electrode 6. HV feedthrough (25kV) 7. SQUID feedthrough (multi-pin) 8. LHe needle valve (superfluid- tight) 9. SQUID

4. HV Breakdown vs Pressurization Janis liquid helium dewar 1. pump on the reservoir to make superfluid Pressurization 2. Close superfluid-tight needle valve. 3. Test probe has a bellows at bottom. It can be pressed against the bottom of the liquid helium reservoir. 4. Temperature is maintained and controlled by the superfluid outside. 5. ~5% volume change to make 1atm. to pump 17” 7”

5. Some design details The HV electrode is on top, to be screwed onto the end of the HV feedthrough. The ground electrode will be attached to the G- 10 sleeve via 3 screws. The HV conductor (or cable) is placed inside a SS tube, which can be evacuated. This protect the HV from breaking down in helium vapor. A lot of room below the ground electrode to accommodate different SQUIDs & pickup coils.

6. Cryostat Top Flange Bellows for vertical translation of probe.

7. Progress Currently preparing Janis cryostat. –modify components, leak checking, etc.. Design is finalized (please comment...) –Some major components (HV feedthrough, bellows) ordered. –Physics machine shop is scheduled to machine parts (electrodes). Waiting for SQUIDs and electronics to be shipped from Los Alamos. Cool down test in ~ 1 month. Preliminary results may be possible next collaboration meeting.