Levitated Dipole Experiment
March, 2002
FLOATING COIL
Ability Engineering continues to make progress assembling the floating-coil cryostat. Mauel and Garnier have visited Ability and inspected the shield, the shield alignment pins, the glass ball grommets, and the lower shield-He vessel gaps. Visual inspection showed a good alignment between the shield and the He vessel. Appropriate shims for positioning the outer ring of the vacuum vessel has been completed.
The assembly procedure has been revised to include trial tests of the final close-out weld (at the ID) of the vacuum vessel and practice of the assembly steps prior to insulation.
The anti-rotation rods have been manufactured using an explosive hammer to form the head-end. The strength of these rods will be tested at MIT. The bayonets for liquid Helium cooling have been manufactured, and a full cryogenic test will be made at MIT.
CHARGING COIL
The winding was successfully vacuum impregnated with epoxy resin. Alex Zhukovsky visited SINTEZ on March 15 - 22, when the winding had been cleaned and all supports removed. Visual inspection indicated that the epoxy was transparent without bubbles or cracks and the quality of impregnation was very good. A glass-like texture was observed through the outside layer of epoxy. Measurements indicated that the resistance and induction of the coil had not changed, which is an evidence that there were no shorts in the winding after impregnation. The vacuum impregnated coil is shown below.
Presently the coil is being cleaned including removal of some extra epoxy from the outer surface of the coil. Afterwards, the outer clamps will be installed on the free standing coil.
The current leads have been welded and inspected by Alex Zhukovsky. All welded samples were successfully subjected to mechanical testing at room temperature, at nitrogen temperature, and after temperature cycling. The welding wire was ordered consistent with the result of tests.
The outer liquid-nitrogen can of the cryostat has been manufactured. Alex Zhukovsky inspected the assembly, and its quality is very good. The top and bottom for the other cryostat cans as well as flanges and other rings have been machined or are presently being machined. After they are completed the inner nitrogen can will be manufactured.
SINTEZ has made several samples of G10 for the tube-to-stainless-steel fitting joint (bonding by epoxy resin) for tests of the helium vessel supports. This lead to a final manufacturing process that exceeded our test requirements correspond to 2 g forces that could develop during the transporting of the charging-coil to MIT.
The quench detection and quench protection systems have been made and they are waiting for the final test with the coil at the SINTEZ stand.
In summary, the quality of manufacturing (coil, current leads, nitrogen can, other items) appears to be very good. Nevertheless, we estimate that there has been a 1.5-2 month schedule slippage in the charging-coil manufacture with respect to the most recent SINTEZ schedule. The administration of SINTEZ believes that, in spite of some delays in the manufacturing schedule, they have sufficient reserve to accelerate the manufacturing process and begin the charging-coil testing on schedule.
LEVITATION-COIL
The coil fabrication portion of the levitation-coil project was completed at Everson Electric. The levitation-coil is a double pancake winding with 52" outer diameter, with one pancake wound to each side of a 3/8" thick stainless steel support plate. The winding for the first of these approximately 1300 turn pancakes was completed on Mar. 2, 2002 and the winding for the second pancake was completed on Mar. 13, 2002.
A first attempt to vacuum pressure impregnate the coil with epoxy resin was performed on Mar. 16, 2002. At this time, the coil was baked out at a slightly higher temperature than specified and the epoxy resin gelled before completely saturating the coil. Also during this first VPI attempt one of the conductor turns near the inner diameter of the second pancake shorted to the coil support plate.
A second attempt to complete the VPI process was performed on April 4, 2002, using a less viscous epoxy with longer working life than the first attempt. During the subsequent bake-out the oven temperature rose above its planned level and the bake-out was abruptly stopped. Subsequent testing indicated the development of additional shorts between the coil and ground. The coil has been sent to MIT for testing and evaluation.
Design and analysis efforts are underway to accommodate a the short from the coil to support plate with respect to mounting the levitation-coil in the cryostat and operating it AC in a feedback control loop (for floating-coil position). The most likely remedy will be to operate the levitation-coil power supply with a floating ground potential, with the ground potential determined by the short location on the support plate.
LAUNCHER
The final construction of the launcher at Hollis Line Machine is essentially complete. Construction will begin soon on parts for the preliminary lifting fixture.