|LDX Project Status
June 3, 2004
The floating coil cyrostat tests were completed during the first week of May.
The test began with several days of vacuum pumping to out-gas the fiberglass shield and the multi-layer super insulation (MLI) (which tends to absorb water). As liquid helium (LHe) was supplied to the heat exchanger tubings, the inconel vessel provided cryopumping, and the vacuum within the cryostat reached 8.7 x 10(-7) Torr. This verified the vacuum integrity of the cryostat, and the cryostat's vacuum pumping port was sealed on May 3.
On May 4 the helium vessel was successfully cooled to a temperatures of 4.5K. The shield was between 4.7K and 8.6K. The temperature of helium at the outlet of the cryostat (in the inlet of the transfer line) was 9.5K. The instrumentation system worked well, and all measured temperatures were consistent. For this initial cool-down, we used 231 liters of LHe.
During a second helium cooling on May 6, we cooled the helium vessel from the liquid nitrogen temperature in about 5 hours and kept the helium vessel at 4.4-4.8 K for 22 minutes. About 110 liters of helium was used in the second cooling. A third helium vessel cooling, which utilized about 35 liters of liquid helium, was started at a helium vessel temperature of 15.6-18.6 K with the shield at 39-55 K. Within 33 minutes the helium vessel was cooled to 4.7-5.2 K.
After both the second and third helium cooling, the helium flow was shut off, and the helium vessel was allowed to warm. The rate of warming determines the total heat leaks through the cryostat. As designed, the helium within the heat exchanger tubing was pumped out to eliminate any heat leak due convection of helium gas in the heat exchanger. The helium vessel was observed to warm from 4.5K to 10K in slightly longer than 1 hour. A preliminary analysis of this result indicates that the warming rate is dominated by heat conduction through the top and bottom supports of the helium vessel, which may have been compressed during cryostat assembly and final welding. Although the helium vessel warming time is less than the design time, the 1 hour warm-up time is sufficient for the needs of the physics program. This cryostat performance could be improved in a future modification.
The cryostat was warmed up after the cold test. New extensions for guard tube seals were welded to the inlet and outlet ports and these exterior welds were vacuum leak tested.
The charging station was cleaned and all parts at the bottom were assembled. The cryostat was then cleaned and installed in the LDX vacuum vessel charging station on the rotating table.
On May 21, the floating coil was installed into the charging station. Preparations are under way for the integrated coil test that includes (1) full-inductive energization of the floating coil by the charging coil and (2) determination of the (disconnected/floating) operation time of the floating coil.
[Photo: Floating Coil installed within LDX Charging Station.]
The control systems user interface and data recording was upgraded. The floating-coil temperature monitors and charging station force measurement load cells were integrated into the data and control systems to allow continuous monitoring and recording during charging and discharging of the floating coil.