General Design Features of the Indiana University 200 MeV Cyclotron

Abstract

A multiple-stage four-sector separated magnet isochronous cyclotron is presently under construction at Indiana University. Ions are to be accelerated by potential drop before injection into the cyclotron stages permitting operation with 1 < vz < 1.5. The large flutter required for this axial strength increases the non-relativistic radial focusing frequency so that vr > 1.1. The vr = 4/3 intrinsic radial quadratic resonance is encountered at 0 = 0.43 (100 MeV protons, 300 MeV 3He) but extensive studies indicate that beam deterioration and loss are negligible with the chosen operating parameters. Fourth and higher harmonics of the orbital frequency are to be used for acceleration. A charge-to-mass ratio range of 1/6 . q/M s 1 is planned; this, together with the external ion source, median plane injection, strong focusing and large dimensions, provides an excellent heavy ion capability. A maximum design energy of 200 NeV is planned for protons; maximum energies for other ions are given by E = 240 q2/M MeV. A dee-in-valley design with the very large axial aperture inherent in this facility has many advantages. Among these are the narrow magnet gap, capacitive tuning of the dees, dee voltage increasing with radi.us, and structural simplifications. It also permits sufficient additional vertical aperture inside the dees for second harmonic rf electrodes permitting asymmetrical square-waving of the energy gain per turn versus rf phase. Use of the fundamental and second harmonics of proper amplitudes and phases can provide a uniformity 2:1000 over a 50°phase interval and 1:10000 over a 250 interval. A small additional third harmonic component can double these intervals.

Accelerators for nuclear physics

“…The lst and 2nd harmonic superimposed gives much better "flat-topping" than the lst harmonic alone. (Rickey et al 1969) . .…”