Glossary

4He Can

Also known as helium bath. Used to store helium. Helium gets in through the transfer tube and exits through the exhaust port, cooling the aluminum shield via the copper plate. Helium is also drawn into the 1K pot through the feed capillary, continuous fill capillary and single-shot valve. The bottom of the can has the connection for the thermal link to the sorption pump, miniflange connector to the feed capillary and mount for the IVC tail.

Superinsulation

Thin aluminized mylar. Used to cover the IVC and the aluminum shield to cut on the radiation heat leak and heat transfer due to hot molecules.

IVC Neck

In order to reduce the heat leak via thermal conductivity along the walls of the IVC, the top part of it ("neck") has a folded structure. Effectively, the length of this segment is increased by a factor of 3.

Windows

Windows in the outer dewar and the IVC are made of Kapton. Beryllium is used for the cell windows. The aluminum shield has thin aluminum foil instead of the windows in order to cut down on infrared radiation from the room to the cell.

Cell

The experimental cell, or the sample chamber, consists of two major parts: the body and the lid. The body is just a piece of copper with beryllium windows put into it. The lid has the sample holder and the voltage bias electrode attached from the inside; and the pressure gauge, the sample valve and an indium seal miniflange connector from the outside. The lid and the body are screwed together with an indium gasket between them.

Exhaust Port

Helium exhaust from the helium bath exits here.

Aluminum Shield

The aluminum radiation shield stays at a temperature between that of the helium bath (4 K) and the outer dewar wall (300 K). Its purpose is to intercept radiation flux coming from the outer wall, and to capture hot molecules of the residual gas desorbing from it. It is being cooled by the exiting helium boil-off gas through the top copper plate to which it is attached with a set of screws. The aluminum shield is wrapped around with ~50 layers of superinsulation.

Outer Vacuum Chamber (OVC)

The outer vacuum chamber is a name for the vacuum volume separating the IVC and the helium bath from the outer dewar wall. It has to be pumped out (through the pump ports) to low pressure (less than 10^(-7) torr) in order to reduce heat exchange via thermal conductivity through the gas. The aluminum shield does not separate two different vacui. The pressure in the OVC is monitored by Pirani and Penning pressure gauges.

Outer Dewar Wall and Lid

The most visible part of the cryostat. It separates the OVC from the outside world. In the lower part it has Kapton X-Ray windows, and the mounting support for attaching the cryostat to the Huber goniometer. The top lid of the outside container has the suspension system attached to it. There is a pump port and two pressure gauge ports on the outer wall; and electronics feed-throughs, helium transfer port and the helium exhaust port on the top lid of the dewar.

Pump and Pressure Gauge Ports

The pump station connects to the pump port through flexible bellows. Pirani and Penning pressure gauges connect to the pressure gauge ports.

Sorption Pump

The sorption pump is just a copper container with activated charcoal inside. The charcoal releases almost all of the gas at temperatures above about 35 K and absorbs gas almost perfectly below 10K.

Condenser

The condenser is a piece of copper tubing silver soldered into the 1K Pot. It is connected to the sorption pump from the top and to the ³He Pot from the bottom. When the sorption pump is heated, the gas condenses on the cold surface of the condenser and drips into the ³He Pot.

1K Pot

The 1K pot is a container in the IVC which under normal conditions runs at about 1.3 K. Liquid ⁴He is drawn from the main helium bath through the capillary and the single shot valve. Gasious He then escapes through the pump plumbing and the exhaust port on top of the IVC.

³He Pot

The coldest point of the cryostat. The sorption pump pumps on the ³ He in it lowering its temperature. The sample cell connects to the copper plate on which the ³He Pot is mounted.

Diode Thermometers

There are three diode thermometers in the cryostat. One of them is connected to the sorption pump, and the other two are on the top and the bottom of the aluminum shield.