Pumping System of the LHD
The pumping system of the LHD is consist of two parts, pumping system for the vacuum vessel and pumping system of the cryostat. They are normally independent. However the two systems are connected by a bypass duct in a case of emergency. You can see a whole system of the LHD vacuum pumping system by clicking here.
The cryostat chamber contains many materials for thermal isolation, and such materials are sources of outgassing. You can see a further information about outgassing by clicking here
The pumping system of the vacuum vessel has two cryogenic pumps(H2O 70000L/s x 2) and four turbo molecular pumps(N2 5500L/s x2 1800L/s x2). the pumping system of the cryostat has two cryogenic pumps(H2O 25000L/s x2) and two turbo molecular pumps(N2 5500L/s x2). All pumps are installed under pumping ducts. The diameter of the vacuum vessel pumping duct is 120cm and the diameter of the cryostst pumping duct is 80cm. The maximum dimeters are limited by strength of the cryostat chamber.
Pressures of the manifolds are monitored with ion gauges, penning gauges, and pirani gauges. Two mass spectrometers are also available. All these devices are set as far as possible from the LHD, because of high magnetic field.
Considering to the high magnetic field, all valves are controlled by high pressure air.
Almost every valve and all pumps are controled remotely at control building of the LHD. And the pressures, a status of the pumps, and a status of the valves are also monitored at the control building of the LHD.