High Current Test of Superferric Magnet

VLHC is a 80km synchrotron aiming at the energy of over 100TeV. The first stage of the VLHC is made with force-free superferric magnets. The excitation test of the VLHC magnet was performed at Fermilab leaching the high current of 104kA. KEK asymmetric force-free magnet was tested together with the Fermilab VLHC magnet.
The transmission line magnet is a new concept of superconducting accelerator magnet. It has a very simple structure with having only one conductor at the center. The magnetic field is produced by high current in the conductor. It also has an advantage in the charcteristics that this structure is electro-magnetic force free.
A cooldown required 4000 litter of liquid helium. The test was made three times resulting some 10000 litter consumption of helium. The difficulty of cooling the current lead was anticipated but the real problem was in the magnet part. The cryostat was not a simple vessel nor a pipe. The flow velocity is much smaller than the convection at some position. A complicated flow pattern left hot spos at many places. The unstable instumentation was also a problem in the cool down.
The excitation of the magnet was done by the gradual increase of the trapezoidal excitation pattern. After a few tens of ramp, the magnet quenched at 104kA.
The magnet was safe through the violent quench. It showed a nice 101kA ramp without a quench.
The most fundamental measurement of the magnet is the excitation curve. The excitation curve of the VLHC magnet was as expected. The force balance of the magnet is probably as esigned.
The KEK magnet was designed to saturate at 1.7T but the field looks saturate at 1.4T. This is because of the end effect of the field. 10cm was too short to see the 2D field structure
The detail of the force balance can be analyzed by the field shape. The measurement of magnet field accuracy was done by a hall prove allay. The primitive plot of the field showd a lot of up-down. The calibration of the hall probe is necessary to use these data for the field analysys.
A longer magnet with a simpler cryostat is being made at KEK for the test at low current. KEK magnet cross section was confirmed using this model.
The magnetic field at 66A was measured by ESR. The field distribution looks good even at very low field.
One ofthe good applications of this magnet is an LHC2 injector. Injection energy of present LHC is too low to have high luminosity. A ring with low field in the same tunnel would work to bring the injection beam energy suitable for LHC. It may be necessary to increase the aperture of the magnet. It is possible to make aperture larger if the field is less.
Field with
the same current