Persistent Switch

10 08 2009

I’ve decided to run the superconducting magnet tests inside the dewar of liquid nitrogen. This will give us maximum cooling with minimal loss of LN2. The dewar is non-magnetic. The experimental apparatus must pass through the 50mm opening of the dewar.

I have 180cm of insulated nicrome wire which will serve as a heater for the persistent switch. This length of wire clocks in at 40 ohms, so 0.222 ohm/cm. I’ve ordered Kapton Tape W/silicone Adhesive:

We’ll use this Kapton Tape to secure the nicrome wire to the YBCO cable, and to provide some insulation for the nicrome heater.

Liquid nitrogen boils at 77 K (−196 °C). The critical temperature for YBCO is ~ 92K (-181 °C ). So we need to raise the temperature of the YBCO by 15 °C.

Unfortunately we really don’t know how much of the heat from the nicrome wire is going to warm up the YBCO, and how much is just boiling off LN2. Should be pretty easy to find how much current we will need  with a little trial and error.

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