The JanisULT dry sub-K ARPES cryostat is designed and fabricated for true UHV operation and can be baked to 90C. A two-stage pulse tube refrigerator (PTR) cools two internal platforms and thermal shields to 35 K (first stage) and 3 K (second stage.) The PTR is mounted by metal sealed CF flange to a z-motion linear translation stage. The PTR is raised and detached from the cryostat during vacuum baking, then lowered into position for normal operation. Heat exchangers mounted to the PTR and platforms precool two independent closed loops of recirculating He-4 and He-3 gas. Two separate He-3 condensers can be used to transform the He-3 gas into liquid; the choice of condenser depends upon experimental requirements and is made by valve adjustment. A He-3 pot is used to collect the condensed liquid, and tapped holes in the He-3 pot are used for sample mounting. Precisely aligned slots in the thermal shields allow the synchrotron radiation or laser to reach the sample. Movable shutters are also installed on the thermal shields and are mechanically linked together. Both shutters can be opened simultaneously for sample mounting and removal using a wobble stick, and then closed to improve thermal performance. A multifunction mechanical heat switch is used to precool the system, and to operate the system in variable temperature (He-4) mode. A large capacity gas sealed roots pump is used to circulate the He-3 gas.
The system can be operated in three distinct modes.
- He-4 Mode
- 1 K operation mode
- JT operation mode.