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

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.

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1. LHe Volume Cap2. G10 Ground Electrode Support3. Macor rod for gradiometers4. HV electrode5. Ground electrode

6. HV feedthrough (25kV)7. SQUID feedthrough (multi-pin)8. LHe needle valve (superfluid- tight)9. SQUID

HV Breakdown vs Pressurization • Janis liquid helium dewar

1. pump on the reservoir to make superfluid

• Pressurization2. 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”

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.

Cryostat Top Flange

Bellows for vertical translation of probe.

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.