||LDX Project Status
February 17, 2004
The leak in the floating coil helium fill tube was repaired.
Photo: Newly repaired weld in floating coil's helium filling tube.
The multi-layer insulation (MLI) that shields the heat exchanger circuit is being replaced. The portion of the shield and the MLI in the vicinity of the high pressure filing line will be replaced and the cryostat will be sealed. The fixtures for installation of the bottom vacuum pump-out port are under construction.
The acceptance test of the LDX charging coil was completed. These tests were successfully conducted at MIT from 21 - 31 January 2004. The tests demonstrated the operation of the cryogenic, electrical, and protection systems of the coil following its installation in the LDX experimental hall.
Photo: Charging coil during the acceptance test.
During the initial cooling of the cryostat liquid nitrogen was slowly transferred to the radiation shield reservoir and to the magnet vessel. Next liquid helium transfer to the magnet vessel was then initiated and during 47 hours the magnet and magnet vessel were cooled and filled by liquid helium up to a level indicator reading of 91.5%. During all charging tests of the C-coil, the power-supply output-voltage command signal was used to set the nominal current ramp rate. Various methods for controlling flat top currents were examined during this series of test sequences. A series of tests were also performed to demonstrate proper operation of the quench protection system. Several magnet dumps were initiated from 50, 88, 120, and 125 A. The final series of tests involved going to high current (high field) operation. These were made in a series of ramps and flattops to ensure good operation of the cryogenic systems during charging. In addition, different current ramping rates, 13.5, 27, and 32.5 V were used. The coil was operated up to 401 A, or 10% below the known quench current limit that was demonstrated in Russia.
Although the vacuum level in the C-coil cryostat was significantly better than that achieved during the acceptance test performed at Sintez, the helium boil-off rate remained significantly higher than specified in the cryostat design. The tuning of the C-coil power supply, the PLC programming and the quench detector circuitry was carried out so as to obtain reliable operation of the C-coil. By the conclusion of the acceptance test, the C-coil was reliably charged to 401 A current at current ramp rates up those that will be used for plasma experiments. The charging coil current was held for extended periods of time near 400 A current.
The 6.4 GHz source is in place in the LDX cell, the electrical power has been connected and it is operational. The 2.45 GHz source is also powered and nearly operational. Waveguide lines have been run
from two sources to the vacuum chamber.
Flux loops have been installed at the chosen locations on the vacuum chamber. A visible camera has also been installed. Electrostatic probes, magnetic pickup coils, and X-ray pulse-height analyzers are being readied for installation during the next scheduled vacuum break.