nsFFAGs and ADSRs what they are and why you need them 1. The current nsFFAG programme 2. Thorium ADSRs and their advantages 3. Matching the two Roger Barlow Manchester University Seminar 10 th June 2009

Accelerators 101 Cyclic accelerators use dipole magnets p=0.3 B R 10th June 20092Roger Barlow: nsFFAGs and ADSRs

RF acceleration Positive kicks to the particles every time round f RF = N f circulating Problem: putting these together How to keep p = 0.3 B R with increasing p ? How to keep RF frequency in sync with changing particle revolution frequency 10th June 20093Roger Barlow: nsFFAGs and ADSRs

Solution 1: the Cyclotron p=0.3 B R – let R increase, B constant frequency is constant Continuous current 10th June 20094Roger Barlow: nsFFAGs and ADSRs

Solution 2: The Synchrotron p=0.3 B R – let B increase, R constant B t Pulsed current 10th June 20095Roger Barlow: nsFFAGs and ADSRs

Solution 3: the FFAG Field varies in space But not in time – Fixed Field Increase in R is medium/small p=0.3 B R holds 10th June 20096Roger Barlow: nsFFAGs and ADSRs

Focussing Particles in a bunch diverge Need to focus using quadrupole magnet Problem: a quad which focusses in X defocusses in Y Solution: a pair of quads has a net focussing effect Alternating Gradient (aka Strong Focussing) 10th June 20097Roger Barlow: nsFFAGs and ADSRs FFAG field contains quadrupole components

Accelerators 101 (contd.) Off-axis particles oscillate about the reference orbit: Betatron Oscillations Tune: Number of betatron oscillations per turn Integer Tune (Resonance) =death Imperfections: Errors in position, current etc in a magnet means a particle gets the wrong ‘kick’ Over many turns this smears out – if the particle is a different points on its betatron oscillation each time 10th June 20098Roger Barlow: nsFFAGs and ADSRs

Scaling Synchrotron during acceleration cycle: p=0.3 B R Bending dipoles and focussing quadrupoles carry same (increasing) current The optics – prisms and lenses – looks the same Tune stays constant Setting the tune to something sensibly non- resonant means it stays there 10th June 20099Roger Barlow: nsFFAGs and ADSRs

Scaling FFAGs FFAG dipole and quadrupole fields not automatically in step To achieve needs complicated and slowly-varying magnetic field (B ~ R k ) – and hence large beam pipes Built in 1950s for electrons – superseded by synchrotrons Now revived for protons in Japan Why were FFAGs abandoned? Increase in momentum in FFAG ring limited to factor of 2-5(?) by geometry. Synchrotron AC magnets have much larger dynamic range – better for highest energies 10th June Roger Barlow: nsFFAGs and ADSRs

Nonscaling FFAGs FFAGs accelerate fast (hence great for muons): Limited by RF power, not by magnet ramping If we can go through a resonance quickly enough it may not matter. Drop scaling requirement – simpler and more compact. Will it work? Only one way to find out 10th June Roger Barlow: nsFFAGs and ADSRs

EMMA Electron Machine with Many Applications MeV electron accelerator 42 cells. 19 RF cavities. Accelerates in ~16 turns 10th June Roger Barlow: nsFFAGs and ADSRs

nsFFAG Benefits High currents – like a cyclotron High energies – like a synchrotron A ring not a disc – cheaper than cyclotron Simple DC magnets Very large acceptance Fast acceleration time Smaller, more compact systems for proton acceleration – applications in medicine and power 10th June Roger Barlow: nsFFAGs and ADSRs

Part 2. Shrinking our Carbon Footprint We all know fossil fuels are BAD because 1.They cause climate change 2.They are increasingly concentrated in countries with dodgy politics 3.They are going to run out Alternatives (windmills, solar power, improved insulation, retreat to the middle ages) can’t supply the deficit without …. 10th June Roger Barlow: nsFFAGs and ADSRs

Nuclear Power Fossil fuels will need to be replaced by a basket of alternatives It is hard (impossible?) to put such a basket together without nuclear power Big issues (real or in the eyes of the public?) with: Safety: Chernobyl and 3 Mile Island Waste disposal. Storage for millenia - NIMBY Proliferation. Rogue states and terrorist organisations 10th June Roger Barlow: nsFFAGs and ADSRs

Safe Subcritical Reactors Conventional: Run with k=1 exactly k<1 stops k>1 explosion Sub Critical Run with k<1 Use accelerator to supply extra neutrons Hence: Accelerator Driven Subcritical Reactor (ADSR) Each fission absorbs 1 neutron and produces ~2.5 Some neutrons lost, leaving k neutrons to produce k fissions 10th June Roger Barlow: nsFFAGs and ADSRs

ADSRs “Manifestly Safe” Switch off accelerator and reaction stops Energy balance is OK: need 5- 10% of power to run accelerator Can use Thorium as fuel Accelerator Spallation Target Core 10th June Roger Barlow: nsFFAGs and ADSRs

Thorium Fertile, not fissile 232 Th +n  233 Th  233 Pa  233 U Abundant. (Like lead) and spread around Much smaller waste problems (no long-lived actinides) Proliferation resistant 10th June Roger Barlow: nsFFAGs and ADSRs

Energy Amplifier (Rubbia) Idea has been around for years Nobody’s built one yet! Feeling is that the accelerator is the weak point. 10th June Roger Barlow: nsFFAGs and ADSRs

Waste from ADSR Needs storing – but not forever Minor Actinides (Np, Cm, Cf) are not produced 10th June Roger Barlow: nsFFAGs and ADSRs

Transmutation Neutron flux can burn actinides produced by conventional reactors. MYRRHA project. Also destroy most-problematic fission products (e.g. 99 Tc: soluble, T ½ =211,000 Y) by ‘Adiabatic Resonance Crossing’. Lead moderator to ensure neutrons hit the resonance for absorption 10th June Roger Barlow: nsFFAGs and ADSRs

Accelerator requirements Proton Energy ~ 1 GeV gives ~20 spallation neutrons per proton. For 1GW thermal power: Need fissions/sec (200 MeV/fission) spallation neutrons/sec (k=0.98 gives 50 fissions/neutron) protons/sec Current 5 mA. Power = 5 MW Reliable! Spallation target runs hot. If beam stops, target cools and stresses and cracks: no more than 3 trips per year Compare: PSI cyclotron: 590 MeV, 2mA, 1MW ISIS synchrotron: 800 MeV, 0.2mA, 0.1 MW Several trips per day 10th June Roger Barlow: nsFFAGs and ADSRs

Reliability: the 3 rd Frontier In the real world: Accelerators often trip for seconds/hours/days. They are complicated systems operating in real world environments But there are complex real world pieces of apparatus trip that trip rarely. Planes, computers, radio sets… 10th June Roger Barlow: nsFFAGs and ADSRs

How to achieve Reliability Reliability must be paid for: Parallelism Robustness under failure Under-rating Preventive Maintenance Must throw money accurately at the problem Need thorough understanding of complete system and to learn from experience (with prototypes?) 10th June Roger Barlow: nsFFAGs and ADSRs

Accelerators for ADSRs Cyclotron Energy too high for classical cyclotron. On the edge for other types FFAG Looks like the answer “Cyclotron currents at Synchrotron energies” Simplicity = reliability Linac Can do the job. But VERY expensive Synchrotron Current far too high. Complicated (ramping magnets) 10th June Roger Barlow: nsFFAGs and ADSRs

Proliferation: Issues and Questions “Thorium fuel system does not produce weapons” Explains why nuclear power went the U/Pu route back in the 1950’s Solves today’s dilemma of states like Iran Is it true? 1.‘Dirty bomb’ 2.‘Little boy’ type device 3.‘Fat man’ type device 10th June Roger Barlow: nsFFAGs and ADSRs

“Dirty Bomb” (Spent) fuel rods will contain fission products Dispersal over civilian areas would cause panic, expense, and few fatalities It is thought that during the 1960s the UK Ministry of Defence evaluated RDD*s, deciding that a far better effect was achievable by simply using more high explosive in place of the radioactive material.UK Ministry of Defence Wikipedia * RDD: Radiological Dispersion Device 10th June Roger Barlow: nsFFAGs and ADSRs

Enriched Thorium Can you build a bomb from Thorium, the counterpart of the 235 U device? No 10th June Roger Barlow: nsFFAGs and ADSRs

233 U device In principle possible Critical mass ~15kg No spontaneous fission problems: simple gun- type device 233 U ratio in fuel stabilises after about 5 years. Extract chemically from Thorium 10th June Roger Barlow: nsFFAGs and ADSRs

Together with 232 U 232 Th(n,2n)  231 Th  231 Pa then 231 Pa(n,  )  232 U 14 mb for neutron energies above threshold ~6 MeV 233 U(n,2n)  232 U 4 mb for neutron energies above threshold ~6 MeV Fast neutrons from tail of fission spectrum – or spallation 10th June Roger Barlow: nsFFAGs and ADSRs

232 U : makes 233 U unworkable 232 U decays with a half life of 69 y, producing 228 Th which decays producing a 2.8 MeV  ray. Really nasty stuff 50 ppm 232 in 233 gives (long term) ~2 rem/hr for a worker 0.5m from a 5kg sphere. Health and safety limit 5 rem/y. Lethal doses rem It is also bad for electronics 10th June Roger Barlow: nsFFAGs and ADSRs

Possible loophole Can’t separate U isotopes Can chemically isolate the intermediate 233 Pa. Wait (27 d half life) for it to decay to pure 233 U Some MSR schemes use just this 10th June Roger Barlow: nsFFAGs and ADSRs

Ionium to the rescue Ionium is 230 Th It does not occur in Thorium, which is pure 232 It does occur in Uranium, part of the 238 U decay chain ‘spike’ Thorium with Ionium: get Pa and 232 U 10th June Roger Barlow: nsFFAGs and ADSRs

Proliferation: Conclusions Safety depends on design Advantage to have all fuel exposed to fast neutrons to ensure 232 U concentration Ionium may be needed Building a device will be very difficult. Technology beyond the reach of back street terrorists, detectable by WMD inspectors 10th June Roger Barlow: nsFFAGs and ADSRs

Summary ADSRs provide a possible form of Nuclear Power that avoids the problems of Critical accidents Long-lived waste Proliferation FFAGs may provide the best accelerator technology We (UK, Particle Physicists, Manchester, Cockcroft Institute) are working hard to make it happen 10th June Roger Barlow: nsFFAGs and ADSRs

Formation of the Thorium Energy Amplifier Association: Universities and labs and industry A research consortium aimed at Networking (website, workshops) Sharing knowledge, within and outside UK Arousing interest in Research Councils, Whitehall, etc. Collaborative response to funding opportunities Design of a Thorium ADSR, aimed at power generation with transmutation as bonus. FFAG is baseline accelerator If you’re interested, see Next Meeting: Daresbury – July 10th A way forward 10th June Roger Barlow: nsFFAGs and ADSRs