Reaching the desired electric field in the measurement cell requires an electric potential of hundreds of kilovolts.
It is not practical to produce this large potential external to the main apparatus because of the large size of the required vacuum and cryogenic feedthroughs, and because the direct electrical connection would be an unacceptable breach of the Faraday cage shielding the SQUIDs from electrical noise.
Instead, we use an 18th century technology, developed by Cavallo that uses induction and a moving electrode to attain the desired electric field with a (much more manageable) 50 kV feedthrough. We disconnect the amplifier from the HV supply during the measurement to maintain the integrity of the Faraday cage.
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