VectorFieldFridgeProbe1ColdFinger2Noise

The noise on the DC wirings of the Probe was measured with Standford SR760 FFT Spectrum Analyzer.

130kHz LPF on the Standford rack is used to get rid of the self oscillation of the Spectrum Analyzer.

Noise on the probe

Lemo pin 18 was measured, which is connected to the empty pin on the LCC20 package through semi-rigid CuNi coax.

For comparison, Pin 8 connects to shielded twisted pairs: The Fischer connector on the breakout box connects 24 DC wires which go to the 50mK plate. All the wires are floating at 50mK and showed similar noise. Pin 8 is used.

The Remote motor to the Fridge was turned on and off to identify the source of the noise.

The noise performance of the loom (on the fischer connector) is much better than the CuNi coax (on the lemo). The noise on the coax may be due to the CuNi coax itself or the connectors at the 50mK stage.

Noise in the Fridge

The pins of the thermometers on the cold plates inside the fridge were measured.

Inside the fridge, there is no coax. The wires connected to the thermometers could be the same wires on the probe. The noise could be due to the connectors.

Effect of LPF

The FFT spectrum will give self resonance if high frequency signals are sent in. So LPF is used with cutoff at 130kHz.

Current noise measurements - March 2017

The current noise was also measured on the DC probe wiring.

Setup was:

• Femto current preamp @ 10^7 V/A gain (50KHz bandwidth)
• SIM910 voltage preamp @ 10V/V gain with floating outer to break the ground loop
• SIM965 LPF @ 100KHz, 48dB bessel filter
• Oscilliscope measuring noise for 1 sec (full bandwidth mode)

The pulse tube was then turned on and off to identify the magnitude of the noise

Lemo Pin 21 - semi-rigid CuNi coax (same as pins 1-24)

Pin 25 - PhBr flex coax (same as pins 26 and 27)

Pin 28 - HF flex coax

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