While
superconducting magnets easily achieve higher magnetic fields at lower
cost than conventional electromagnets, it is very difficult to ramp
superconducting magnets very quickly. But exactly that is needed at the
planned new facility of GSI, the Gesellschaft für Schwerionenforschung
(Institute for Heavy Ion Research), in Darmstadt, Germany. In the
magnets of the SIS 200 ring, one of the components of the new facility,
the magnetic field must be ramped from 0.5 Tesla to 4 Tesla at a rate of
1 Tesla per second. This ramp rate is almost 25 times faster than the
ramp rate of the Relativistic Heavy Ion Collider (RHIC) magnets at
Brookhaven National Lab (BNL), which ramp at a rate of 0.042 Tesla per
second. While the SIS 200 magnets also require a slightly higher field
strength than the RHIC magnets (4 Tesla as compared to 3.45 Tesla), it
is the capability to ramp the magnetic field quickly that drives BNL’s
research and development work for these superconducting magnets for GSI
The magnets being
developed at BNL for the new GSI facility are based on the RHIC design.
However, there are several modifications to reduce ac losses, the
unwanted heating of magnet components induced by changing magnetic
fields. The by far most significant R&D effort for these fast ramping
magnets focuses on the development of a cored Rutherford cable to
replace the standard Rutherford cable used in the RHIC magnets.
The modified
Rutherford cable features a core in the center of the cable that, by
increasing the crossover resistance Rc between strands,
significantly decreases cable coupling and thus ac losses. The side view
of the cable (with the cable edge machined away) shows the foil
separating the top and bottom layer of the cable.
Side view
Furthermore, a new cabling
cooling scheme ensures that the strands of the cable are in intimate
contact with the liquid helium coolant. The holes that are visible in
the picture below were cut by the University of Jena, Germany. They
allow the liquid helium to penetrate into the cable, thus cooling it
more efficiently.
Cable
The construction of a first model
magnet is completed (see the picture of the magnet in the shell welding
press), and the magnet is awaiting testing.
Magnet in shell welding press
More
information on the planned GSI facility can be found at
http://www-new.gsi.de/zukunftsprojekt/index_e.html
In
addition, work on the project has been described in these publications:
M. Wilson, G. Moritz,
G. Ganetis, A. Ghosh, A. Jain, J. Muratore, R. Thomas, P. Wanderer, W.
Hassenzahl:
Design Studies of Superconducting cos theta Magnets for a Fast-Pulsed
Synchrotron,
IEEE Trans. Applied Superconductivity Vol 12 No. 1 March 2002, p. 313.
G. Moritz, C. Muehle,
M. Anerella, A. Ghosh, W. Sampson, P. Wanderer, N. Agapov, H.
Khodzhibagiyan, A. Kovalenko, W. Hassenzahl, M. Wilson:
Towards
Fast-Pulsed Superconducting Synchrotron Magnets, Proceedings of the 2001 Particle Accelerator Conference, Chicago, pp.
211-213
M. Wilson, A. Ghosh, B.
Haken, W. Hassenzahl, J. Kaugerts, G. Moritz, C. Muehle, A. Ouden, R.
Soika, P. Wanderer, W. Wessel:
Cored Rutherford Cables for
the GSI Fast Ramping Synchrotron, to be published in IEEE Transactions
on Applied Superconductivity
R. Soika, M. Anerella,
A. Ghosh, P. Wanderer, M. Wilson, W. Hassenzahl, J. Kaugerts, G. Moritz :
Inter-Strand Resistance
Measurements in Cored Nb-Ti Rutherford Cables, to be published in
IEEE Transactions on Applied Superconductivity
G. Moritz:
Superconducting Magnets
for the International Accelerator Facility for Beams of Ions and
antiprotons at GSI, to be published in IEEE
Transactions on Applied Superconductivity
For additional
information, contact Rainer Soika via email or visit his webpage at
http://www.bnl.gov/magnets/Staff/soika/
