A Low Power Magnetic Channel with Dipole Compensation

A magnetic channel capable of guiding deflected 60 MeV protons through the fringing field of an AVF cyclotron without perturbing inner orbits, has been tested in a 0.394 scale model. The full scale channel will be composed of a 1010 steel cylindrical shell 3.00 in. O. D., 1.18 in. I.D., and 10 in. long with an external dipole winding extending to 5.92 in. O.D. A cosinoidal distribution of current density is approximated by dividing the winding into 16 sections, with centers about 22.5° apart, and by making N_θo = N_o cos θ, where N is the number of turns in a section and θ is the altitude angle of the center of a section. Scaling the model measurements to full size, the power is 14 kW with 3/8 in. square O.D. and 1/8 in. round I.D. water-cooled copper conductors at 330 A, and the field at the midpoint inside the channel is reduced from 7000 to 90 G, with a 20 G/in. gradient across the channel opening on the median plane. As close as 5 in. from the outside edge of the coil, the first harmonic introduced is 1.1 G. Without dipole current, the field in the channel is 1560 G with a 16.2 G first harmonic, at the same distance.