Issue 76

Beam Dynamics Newsletter

5.3 Investigation of a Compact Accelerator for Radioisotope Production

CANDIDATE: David Bruton, University of Huddersfield, U.K.
SUPERVISOR: Prof. R. Barlow
GRADUATION: February 2019

This thesis covers the design and performance of a non-linear non-scaling Fixed Field Alternating Gradient (FFA) accelerator. The imagined application of the design is for radioisotope production and in particular the production of \( ^{99m} \)Tc and \( ^{211} \)At. The performance of the design in combination with an internal target and recycled beam is also investigated as a potential way to increase isotope yields.

The basic design consists of four separate radial sector magnets and two RF cavities. The design differs from a conventional cyclotron in that the edge angles have been optimised with the field gradient to produce a lattice that is isochronous to \( \pm \)0.15% and has stabilised tunes.

Simulations conducted using the OPAL code showed that the dynamic apertures are large, peaking at 150 and 41.4 \( \pi \) m.mrad in the horizontal and vertical planes respectively. Acceleration with protons is possible at up to the 5th harmonic with an accelerating gradient of 100 kV/turn and at the 1st harmonic for alpha particles.

Space charge simulations suggest strong performance under high current conditions. A proton beam of 20 mA was simulated with 2.3% losses, dropping to 0% losses at 4 mA. Alpha particle beams were simulated with beam currents of up to 800\( \mu \)A with minimal losses. The best harmonic to operate at for handling high currents was found to be either the 2nd or 3rd.

Simulations of the internal target demonstrated that ionisation cooling has an effect even with high Z materials. Two aspects were identified as key to increasing beam survival; the vertical aperture and cooling the beam longitudinally. It was found that increasing the vertical aperture by \( \pm \)1 cm could double the beam survival time. Additionally by using a combination of a wedge shaped target and RF stabilisation to cool the beam longitudinally, a 140% increase in beam survival time was achieved.

Finally several iterations of the design were created investigating possible improvements including tune adjustment by introducing a magnet shift, a dual proton alpha particle design and a compact 35 MeV design.