Sumitomo RDK-408D Technical Manual

He-Compressor and Cold-Head Service
The AMI magnet (6T) in Osujilab is cryo-cooled by continuous Helium supply by a Sumitomo Compressor
operating at a pressure of ~2.2 MPa. The superconductor in the magnet is cryo-cooled by a cold-head
(Sumitomo Inc.) attached to the magnet. Continuous Helium supply is necessary to maintain the
superconductivity in the system. There are two flux lines (supply and return), 6m long connecting the
He-compressor and the cold-head. The flux lines, cold-head and the compressor have self-locks to
isolate them to avoid contamination. When flux lines are disassembled from the cold-head or He-
compressor the locks will automatically be locked. When the pressure in the He-compressor goes below
1.6 MPa, the compressor should be re-filled with Helium (UHP-300, 99.999% purity). Please follow the
instructions before start refilling the He-compressor. If the He-compressor or flux lines are
contaminated, the pressure reading in the He-compressor will drop (usually it will be zero), also when
the He-gas leaks out of the system. Once the system is contaminated, it is advised to get in touch with
Sumitomo Inc. to do a cleaning service.
Figure1: (a) Zero pressure reading due to contamination of the system. In this case the He-gas was escaped through
accidently loosened screws (b). During operation the pressure reading is about 2-2.2 MPa. However, when the He-
compressor or is switched off, the pressure reading is non-zero (~1.6MPa). If the compressor pressure reads zero, it
would not re-start.
Chilled-water supply is connected to the He-compressor to dissipate the heat from the return supply.
When the temperature of the chilled-water supply rises, the He-compressor might shuts down
automatically, and subsequently the magnet temperature will rise. Sometimes, the main power-supply
switch at the back panel will turn off by itself. Then it has to be turned back on as shown in Figure 2.
Most often, switching OFF the drive switch and turning back ON will resume the He-compressor.