Speaker: Carol Johnstone
Abstract: The capability to produce high current, low loss, extracted external beams, either ion-specific or comprised of a cocktail of ion species, is an enabling technology for nuclear security, isotope production, and medical applications. A normal-conducting 0.5 to 15 MeV/u FFA with a strong-focusing field gradient has been designed for CW acceleration of light ions with a charge-to-mass ratio of 1/2 for up to a mA current in a separated-sector format. A technically-conservative baseline concept, which is optimal for radioisotope production such as alpha emitters and theranostic radiopharmaceuticals, has been designed to be scalable in gross physical parameters by a factor of 2 to 3 to realize a much smaller and lighter transportable system to advance new approaches in security applications, shown in Fig 1. The light ions species, including a mixed ion beam, can be dynamically chosen to provide a range of characteristic signals appropriate for specific material identification such as special nuclear materials. The central region of the machine has been replaced with an injection system consisting of an ECR source and an ion RFQ which accelerates ions to 0.5 MeV/u for horizontal injection into the ring through an electrostatic inflector. A conceptual design of the sector magnet and and 45 MHz 200 kV RF cavities will be presented in addition to overall engineering and design considerations.
5 replies on “High-current Light Ion FFA for Therapy”
Probably (usually) a stupid question – but why do you get a transverse deflection from the RF cavities?
Chris: The orbit is not necessarily at right angles to the rf gap. Surprisingly, though, this has no effect on the orbit. This is explained section 4.4 here https://ffa20.triumf.ca/wp-content/uploads/2020/11/Cyclotrons-1.pdf . However, there is a kick arising from the rf magnetic field. This field arises if the gap voltage varies with radius (by Maxwell). This is explained, same text, section 4.3.
Carole: Another couple points before I forget.
1. The arrangement of rf leaves you open to driving the nu_r=2/2 socalled “gap-crossing resonance”.
2. Fairly high harmonic number means tighter tolerance on everything else. In particular, it means having to bunch into a very very short phase acceptance.
Thanks! In a TM010 cavity the magnetic field is out of phase with the electric field. Is that not the case in these cavities?
Yes, but please see the referenced work. It follows directly from curl E = dB/dt