Oxford VTI Magnet System

Details

Our group recently acquired an Oxford VTI system with a 10 T superconducting magnet from Terry Orlando's group. It was sitting in the annealer room down the hall getting dusty, so I asked him about it. He said it had been donated to him by Bill Gallagher at IBM's Watson research facilities in 1995, and that he never got around to putting it together. Almost right after he got it, he apparently moved away from doing research that needed large magnetic fields. His words were: "take it and don't give it back".

It didn't come with any documentation, but it did come with a nice rack with a dipolar magnet power supply, magnet power supply with gpib controller, and helium and nitrogen level meters. The are also DIO/relay lines running out the back from the level meters, so it looks like the system was once rigged up for automated helium tranfers.

It has a liquid nitrogen jacket and lambda fridge. The insert is a standard Oxford VTI (Variable Temperature Insert). There are two different ways you run the system depending on what temperature ranges you want:

(i) 1.4 - 4.2 K: In this temperature range, you draw liquid helium into the sample space: the sample sits immersed in liquid helium. To run the system down to 1.2 K, you pump on the sample space and adjust the sample space needle valve to regulate the intake of 4.2K helium from the bath to attain the desired temperature. The sample space effectively becomes a big 1K pot.

(ii) 4.2 - 300 K: Here, the temperature of the sample is controlled by a flow of cold helium gas. The liquid helium is drawn from the bath up the pickup-tube, through the needle vavle, and down to the heat exchanger. At the heat exchanger, it is heated to the desired temperature using a non-inductive heater, and then released into the sample space. A small heater is preferrably also mounted on the sample holder to give close temperature control and to optomize settling times. In this range, you can pump on the insert to pull the helium through the needle valve, or if less cooling power is required it can be run in a gravity-feed mode: you can simply attach the insert pumping line to the recovery system and and helium is pushed through the needle valve by the pressure in the bath.

There is also a heater on the needle valve that is used for clearing blockages.

I've put up some info about the electrical connections.

A rough diagram showing schematically how it is layed out can be found here.

I also found a great page describing in detail the principle of operation, wiring, and other great details of a VTI system used on a neutron beam line here on the RISO facility website.

Pictures

• Pictures of the magnet frame and outside of the system.

• Pictures from inside the IVC.

• Pictures of the magnet coil and some more pictures of the magnet power supply.