Work on the floating coil continues at Ability Engineering Technology in Chicago. Initial assembly of the coil, shield, and space frame revealed that the lead shield needed additional trimming. This trimming has now been completed. Dummy supports (which center the He vessel within the cryostat) have been completed and now being sized for the final fit up. Darren Garnier has been out to Chicago twice in the last month to oversee preparations for final fit up.
The internal anti-rotation device, designed at MIT, has been received from Capitol Machine in New Hampshire. After some small modification they have been accepted and sent out for silver plating for vacuum service. The warm and cold ends have been taken to Ability for final sizing and inclusion in the final fit-up assembly.
The cryogenic transfer bayonet prototype, designed at MIT (and also manufactured by Capitol Machine) has been received and inspected. Quality Cryogenics Inc then installed the bayonet at the end of a completed He transfer line. Initial LN2 testing indicates excellent performance of the male bayonet and transfer line. The complete bayonet system, including the matching female bayonet, will be fully cold-tested this month with LHe.
The vacuum electrical feedthrough for the floating coil has been manufactured and tested. Initial tests lead to some small modifications.
Good progress continues on the charging coil cryostat at SINTEZ. The strain gauges on the coil clamps have been calibrated to control the coil clamping procedure. The structural elements for the support clamps are being welded and machined. The fiberglass items necessary for the supports of the conductor joints have also being machined. The coil clamping can be made after these support elements have been assembled with the coil and clamps.
The cryostat inner nitrogen can has been assembled from three parts and is being welded. Ribs will be welded to the top and bottom plates of the vacuum vessel and they are being machined to the correct size. Coil supports have been welded to the helium vessel ring and it is being machined. One tube for the main helium vessel structural support has been machined to the correct size and will be polished. A defect that was found in the second tube during machining will require replacing it for a new one.
SINTEZ has sent to MIT the Russian version of the acceptance test procedure for the charging-coil. Alex Zhukovsky is translating it to English for LDX team consideration and approval. Alex will visit SINTEZ-Efremov during the last week of June.
The levitation-coil was tested for a second time in a liquid nitrogen bath at 77K on May 24, 2002. During this second round of testing, we attempted to determine several additional features of the L-coil behavior. The measurements indicate a total coil resistance between 9.5 and 11 micro-Ohm, which is within tolerance of design reference. The coil's critical current was remeasured, and it again showed an acceptable value of roughly 32 A, and an index number "n" of about 12. The coil was tested by impulse testing up to 300V to see if there were any negative electrical breakdown issues, and none were found. The coil's ac characteristics were examined over a frequency range between 0.02 Hz and 4 Hz. This is the target operating range for the ripple currents expected during position control of the floating-coil. The results indicate a relatively constant ac loss per cycle of about 2~3 J/cycle, which is acceptable. The ac results however showed some unusual behavior: the effective inductance decreased with increasing frequency of operation. An explanation for this frequency dependent change in coil inductance is still being modeled.
On June 3, 2002 the coil cryostat was opened to prepare the coil for return shipment to Everson Electric. When the coil was visually examined, extensive debonding was observed between the coil winding and the center support plate. A subsequent cool-down stress
analysis of the coil indicated that this debonding is a consequence of a difference in the radial thermal contraction of the coil windings relative to the center plate. The levitation-coil relies
on the effective thermal contact between the windings and the support plate cooling fins to remove ac losses generated during position control of the floating-coil. The stress analysis indicates that efforts to re glue the outer edge of the windings to the support plate are impractical. An alternate cooling strategy which extracts the ac loss heat generation from these outer debonded sections of the coil is under development. A fortunate consequence to the partial debonding of the coil from the support is that the electrical short between them has disappeared.
OTHER SUPPORTING EFFORTS
The upper-level access gangway and shaping coil support frame has been designed and requests for quotations have been made.