Noise in Cell 12-An example of a calorimeter measurement Simple procedures reduce measurement noise drastically Isolate the probe from the cryostat ground. Connect instrument racks to racetrack ground at isolation transformer secondary. Connect shield wires from probe to instrument rack ground. Use twisted pair with shield, not coax for thermometers and heaters. This prevents the coax shield from being a sensor lead and picking up radiated noise. Make sure isolated thermometer and heater current source shields are tied to instrument rack ground. Use plastic isolation o-ring carriers to all pumping lines. Result: two-orders-of-magnitude improvement in temperature stability, more than an order of magnitude reduction in platform thermometer noise. Result: From a measurement plagued with excessive scatter to a true-noise limited working measurement.

At lower frequencies, here is what we are up against On the ground—the cryostat frame In cell 12 relative to racetrack ground displays 60 Hz and harmonics orders-of-magnitude greater than the thermometer excitation voltages. In the air—radiated 60 Hz, 600Hz, and more, present in most cells

Calorimeter platform thermometer noise Before isolating the calorimeter from the magnet cryostat ground and using twisted pairs. After— note scope has 500 times more gain!

Lakeshore control heater/thermometer noise before and after grounding the current-source floating shield Control thermometer waveform before connecting current-source shield on Lakeshore temperature controller and platform thermometer current source shields to racetrack ground, and replacing coax with twisted pair. After-from 500mK fluctuations to sub mK temperature stability