SCU R&D Status Update
Lawrence Berkeley National Laboratory
September 1st, 2015
Soren Prestemon
Present Status:
There has been significant progress on a number of fronts. First, we have worked to address the primary risks idnetified in last months reports:
a) Magnet protection:
a. We have developed a quench detection circuit specially tuned to allow for a low detection voltage threshold. Tests on a short prototype have demonstrated the ability to reduce the detection voltage to 50mV by using a central voltage tap and a differential voltage reading that is independent of any inductive component.
b. A fast switch has been added to the protection circuit, allowing us to decouple the power supply from the circuit and introduce an external dump resistor to extract a significant fraction of the stored energy. The switch has been operated with the short prototype, demonstrating switch opening time of 250 micro-seconds.
b) Providing adequate cooling from the cryostat Helium to the undulator cores:
a. We have measured and analyzed the thermal conductance of the main thermal paths to the liquid helium. The limiting element is the connection between Cu cooling plates and the magnet poles; indium foil will be used at the interface. The indium foil interface has been tested and an estimate of the final operating temperature has been determined.
b. Some of the critical thermal link elements have been prototyped, and can be prepared in advance of the final assembly, resulting in reduced final assembly time. The schedule for delivery to ANL is estimated around October 15th, and has remain unchanged over the last few weeks.
We have also worked with the ANL team to transfer pulsed-wire technology developed at LBNL to ANL for 1st and 2nd integral measurement of the superconducting undulators. A pulsed wire setup was shipped to ANL and installed on a prototype vertically-polarizing undulator to test the system. Diego Arbelaez went to ANL to perform first measurements using the system.
Long coils:
The first long coil is ready for testing. The second long coil has been reacted and prepared for vacuum impregnation, which will occur in the next few days. Both long coils have a central voltage tap to allow for a differential quench detection signal, as described earlier. We have also installed voltage taps across each of the Nb3Sn-NbTi lead joints; these are also monitored as part of the quench detection system. The two long coils will be tested in the next couple of weeks, in advance of final system assembly.
The spare coil has been wound, and is ready for reaction. The reaction and other fabrication steps are on hold for the spare, pending need based on testing of the two main coils.
Field corrector:
We have fabricated all of the primary elements for the final tuning system. This includes the lithography of the tuning loops, soldering of the loops to the drive current element with accurate positioning of the loop segments, soldering of the heaters that serve to direct the drive current through the tuning loops, and laser cutting of the drive segments to optimize the thermal performance of the heaters.
Cold mass components and assembly:
Most components for final assembly have been fabricated, including the cooling plates, cooling tubes, etc. The final assembly space has been identified and is being prepared.
Next steps:
Focus is now on the following fronts:
1) Test the long coils in a vertical test dewar to validate performance prior to final assembly.
2) Complete all miscellaneous components in preparation for final assembly.
3) Start final assembly.