ADSRs and FFAGs Roger Barlow

7 Jan 2008Workshop on ADSRs and FFAGsSlide 2 The ADSR Accelerator Driven Subcritical Reactor Accelerator Protons ~1 GeV Spallation Target Neutrons Reactor Core Neutron multiplication factor typically k=0.98

7 Jan 2008Workshop on ADSRs and FFAGsSlide 3 ADSR properties Manifestly inherently safe: switch off the accelerator and the reactor stops Uses unenriched 238 U or 232 Th as fuel Large flux of neutrons can transmute waste from conventional reactors (especially Pu)

7 Jan 2008Workshop on ADSRs and FFAGsSlide 4 Accelerator requirements Proton Energy ~ 1 GeV For 1GW thermal power: Need fissions/sec (200 MeV/fission) spallation neutrons/sec (k=0.98 gives 50 fissions/neutron) protons/sec (20 spallation neutrons each) Current 5 mA. Power = 5 MW High current rules out synchrotron Compare: PSI proton cyclotron: 590 MeV, 72 MeV injection 2mA, 1MW

7 Jan 2008Workshop on ADSRs and FFAGsSlide 5 Rubbia’s Energy Amplifier 1 GeV,10 mA, 42 MHz, 3 cyclotron stages –10 MeV (dual) – MeV – MeV Very challenging (order of magnitude harder than PSI)

7 Jan 2008Workshop on ADSRs and FFAGsSlide 6 Myrrha 350 MeV, 5 mA Linear Accelerator for reliability Dual RFQ to 5 MeV SC Linac 111 m long (various alternatives) Proposed demonstrator for ADS incineration Stress need for reliability LINACs can be made with redundancy

7 Jan 2008Workshop on ADSRs and FFAGsSlide 7 KURRI 3 stage FFAGs at 120Hz 0.1 – 2.5 MeV 2.5 – 20 MeV (  ½) 20 – 150 MeV (?) Current ~1 nA ‘ADS demonstrator’ Aim: study neutron production

7 Jan 2008Workshop on ADSRs and FFAGsSlide 8 FFAG Cyclotron: B constant, R varies Nonrelativistic: Low energies FFAG: R varies slightly B varies with R but not t High currents High energies Rapid acceleration Synchrotron: R constant, B varies Magnets cycle Low currents

7 Jan 2008Workshop on ADSRs and FFAGsSlide 9 FFAG energies Increase in p= increase in B x increase in R How big an increase in B can we manage? Magnet design Lattice Realistic – factor 2: Optimistic – factor 4 How big an increase in R can we manage? Realistic – factor 1: Optimistic – factor 2

7 Jan 2008Workshop on ADSRs and FFAGsSlide 10 Problems Injection and extraction are difficult Successive orbits are close together Gaps are small If we can break symmetry – racetrack instead of circle – life gets a lot easier Even so, the fewer rings the better

7 Jan 2008Workshop on ADSRs and FFAGsSlide 11 Scenarios Realistic 1 ring 72 MeV injector (Phillips Cyclotron) 1 ring to 262 MeV Optimistic 1 ring 6 MeV RFQ injector 1 ring to GeV Ruggiero 2 ring 50 MeV injector 2 rings to 1GeV Realistic multiring 5 MeV RFQ injector Ring 1 to 20 MeV Ring 2 to 77 MeV Ring 3 to 281 MeV Ring 4 to 880 MeV

7 Jan 2008Workshop on ADSRs and FFAGsSlide 12 FFAG frequencies As particle energy increases: v increases  T falls  f increases L increases  T increases  f falls For cyclotrons these cancel exactly For FFAGs these may cancel approximately. May get away with constant RF frequency Or can scan using low Q Finemet cavities. Go from CW to pulsed operation – high frequency and high duty cycle ~MHz ~kHz ~50%

7 Jan 2008Workshop on ADSRs and FFAGsSlide 13 nsFFAGs Conventional (scaling) FFAGs: B( R)  R k No Chromaticity: Focussing scales with momentum Constant tune resonances avoidable Nonscaling FFAGs: B( x)  x Focussing changes with momentum resonances unavoidable but harmless(?) More compact aperture More compact ring (all magnets bending) EMMA is prototype

7 Jan 2008Workshop on ADSRs and FFAGsSlide 14 Way forward Conventional wisdom says: ADSRs use cyclotrons (low energy) or Linacs (expensive) FFAGs could provide a better alternative and make the whole show viable