1. PAMELA Contact Author: CONFORM is an RCUK-funded Basic Technology Programme PAMELA: Concepts Particle Accelerator for MEdicaL Applications K.Peach(JAI, Oxford University) (k.peach1@physics.ox.ac.uk) Ring #1 (p, C)Ring #2 (C) Energy30~250MeV (p) ; 8~68MeV/u (c)68~400MeV/u # of Cell12 Diameter12.5m18.4m Orbit excursion18cm21cm Rev. freq1.94~4.62MHz(p) ; 0.98~2.69MHz(c)1.92~3.91MHz MagnetTriplet (FDF), SC length57cm113cm aperture25cm33cm Long Drift1.3m1.2m Inj./Ext 1 turn injection & extraction; 2 LD (each) The PAMELA Accelerator Design Over the last 20 years there has been a big expansion in hospital-based charged particle therapy facilities, mainly with cyclotrons or synchrotrons to accelerate the ions. These technologies have limitations – cyclotrons produce ion beams of fixed energy which require degradation to target properly the tumour volume and synchrotrons have limitations on the rate of dose delivery. FFAGs offer the possibility of rapid variable energy extraction with high dose rate delivery. PAMELA will produce a conceptual design for an accelerator system to deliver protons and light ions such as carbon, using a new type of FFAG accelerator which combines the advantages of a scaling FFAG (small tune variation during acceleration) with a relatively small orbit excursion. The proton lattice is shown in Figure 1. The upper plot in the inset shows the tune variation through the acceleration for protons from injection to extraction. The lower plot shows the tune variation from injection to extraction for the C 6+ ring. Figure 1: Layout of a PAMELA proton and carbon ion facility. Table 1: Main parameters of PAMELA ring Challenges 1 : Stability and flexibility In an accelerator for particle therapy, acceleration is slow because the particles are heavy, that is they are non- relativistic. This requires a stable “betatron tune” (the oscillations made by the particles about the ideal orbit), so that there is no beam loss during acceleration through resonance crossing (where the betatron oscillations are a multiple of the rotation frequency). To achieve a stable tune, the scaling FFAG principle is modified to employ (1) truncated multipole magnetic fields, (2) rectangular magnets, and (3) linear magnet configurations. In addition, with superconducting magnets, the orbit excursion is small and there are relatively long straight sections, which is especially important for variable energy beam extraction, and also makes the design of the ring easier. For construction, a novel combined function magnet was developed, which has the ability to vary individual multipole fields, allowing the operating point to be defined flexibly, a unique feature of this design. (2) Truncated multipole field (PAMELA) (1) Scaling FFAG field Figure 2: Field for FFAG, (1): Scaling FFAG field, (2): Truncated multipole field for PAMELA, and “Double helix” magnet and its prototype coil support. Protons Carbon Figure 3: Betatron tune of PAMELA proton ring (left) and carbon ring (right) For both ring, the flat tunes are realized. Challenges 2. rapid acceleration In PAMELA, the target repetition rate was set to 1 kHz for medical reasons. This is more than one order of magnitude higher than existing rapid cycling synchrotrons. To achieve rapid acceleration, a key component is radio-frequency cavity. The combination of a high field gradient with a manageable heat load is a big challenge. PAMELA employs ferrite loaded cavity. With the relatively higher Q-factor of ferrite, the heat load is expected to be less than 100kW per cavity 1.1m 2 ferrite core layers Figure 4: side view of PAMELA rf cavity (plan view). It has two acceleration gap and generates rf field of 8kV for each gap.