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Potential of Cyclotrons

Potential of Cyclotrons. Werner Joho, PSI FFAG 2007, Grenoble 12.april 2007. State of the Art Accelerator Facilities. Ringcyclotron 590 MeV protons. superconducting cyclotron. 1.2 MW average Beam Power. Radiation Therapy with Spot Scanning and rotating Gantry.

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Potential of Cyclotrons

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  1. Potential of Cyclotrons Werner Joho, PSI FFAG 2007, Grenoble 12.april 2007

  2. State of the Art Accelerator Facilities Ringcyclotron 590 MeV protons superconducting cyclotron 1.2 MW average Beam Power Radiation Therapywith Spot Scanning and rotating Gantry high Intensity Muon Beams 5•108m+/s , 108 m-/s Spallation Neutron Source 1014 n/s Swiss Light Source SLS(2.4 GeV Electron Storage Ring) • extremely stable photon beams( < 0.5 mm) • „top-up“ and „fast orbit feedback“ (FOFB)

  3. Aerial View PSI East Aare psi forum Auditorium Neutron Source SLS PSI West

  4. The first Cyclotron 1931 E.O.Lawrence, M.S.Livingston Berkeley, California 4 inch diameter 1 kV on the Dee 80 keV Protons

  5. 43 years later (1974) Ring Cyclotron 590 MeV Protons 15 m Diameter Hans Willax, Jean Paul Blaser, Villigen, Switzerland

  6. Comet Cyclotron Radiation Therapy with 250 MeV Protons Cyclotron: superconducting Magnet, 3m Ø Collaboration: ACCEL & PSI

  7. Comet Cyclotron, 250 MeV Protons superconducting Magnet with 4 Sectors The spiral structure is responsible for the vertical beam focusing 0.5 m

  8. Proton Therapy withPROSCAN(3D-spot scanning) Gantry Does Modulation sweeper 1 sweeper 2 Dipole SC-CYCLOTRON Proton Beam250 MeV DEGRADER => Rangeshifter (2-30cm) Patient-table

  9. Cyclotrons classical Cyclotron non relativistic energy limit CW-beam single pole Synchro- cyclotron pulsed beam FFAG with sectors single pole with sectors Isochronous Cyclotron CW-beam Ring Cyclotron

  10. Accelerator Facilities with 4 Cyclotrons Injector 1:Nuclear Physics + Eye Tumours Injector 2:Injection + Isotopes for Hospitals Ring Cyclotron: Muons, Pions, Neutrons, Proton Therapy superconducting Cyclotron:Proton Therapy

  11. Injector II Injection Line 870 keV Resonator 50 MHz Extraction Line 72 MeV Protons (after 100 turns)

  12. the last 5 turns in the Injector II dR Recipe for high Intensity • continuos beam (cw) • very low extraction losses => separated turns with large turn separation dR at extraction • => high energy gain per turn, • powerful RF-system with • high voltage cavities dR ~ Radius R => large machine radius !!

  13. Ringcyclotron 590 MeV Protons 1.2 MW Beam Power (world record!) 8 Magnet à 250 Tons 4 Cavities à 700 kV (upgrade to 1MV) Extraction ≈ 99.97 %

  14. RF Cavity Ring Cyclotron 590 MeV , 50.7 MHz original version: aluminum , V=730 kV 300 kW power loss 216 turns at 2 mA: 300 kW power/cavity delivered to the beam new cavity: copper , V = 1 MV 500 kW power loss 160 turns , current limit > 3 mA ?

  15. y [mm] Ring Cyclotron 2 T Contour lines of the magnetic fieldscaling of average field:B0(R) ~ γIncrease from 72-590 MeV: 55% 1.5 T x [mm]

  16. Orbits in Ring Cyclotron RF Cavity ExtractionSeptum Magnet Sector 6 Orbits plotted at equidistant energies: 75, 177, 279, 381, 483, 585 MeV(R ~ β)

  17. how to scare young students!! (Al Garren 1962) better approach to get focusing frequencies:1. simple approximations 2. numerical calculations Qr2≈ 1+k Qz2≈ -k +F (1+2tan2d)

  18. Flattop Voltage gives minimum energy spread

  19. Ring Cyclotron (1980)turns 26-315, 100-590 MeV

  20. Advantages of Ring Cyclotron (Hans Willax 1963) magnetic field and RF system are decoupled strong vertical focusing straight sections many cavities (incl. flattop!) with high voltage easy construction of injection and extraction elements(no kickers !) small magnet gap fast crossing of resonances good turn separation, low extraction losses low power consumption total magnet weight as low as for a compact warm magnet lots of space for diagnostic and correction elements high intensity penalty: requires injector!

  21. Properties of Cyclotrons versatile CW-Beams excellent Beam Quality all Ions from p to U Energies: p: up to 600 MeV => limit ≈ 10 GeV ? Ions: up to 500 MeV/n => high Intensity (few mA) => polarized Ions (few mA) Coincidence Experiments with high Event Rates continuos Beam allows easy Tuning of Accelerator in all 6 Dimensions transv.: p1 mm mrad (norm.) DE/E ≈ 10-3 Dt ≈ 0.3 ns Pulse Selection at low Energy gives flexible microscopic Time Structure for Time of Flight Experiments

  22. Longitudinal space charge forces increase the energy spread => higher extraction losses => limit on beam current Remedy: higher voltage V on the RF cavities => lower turn number n (V·n = const.) Current Limit in Ring Cyclotron  2000 current limit ~ V3 ! There are 3 effects, each giving a factor V(~1/n): 1) beam charge density ~ n 2) total path length in the cyclotron ~ n 3) turn separation ~ V W.Joho, 9th Int. Cyclotron conference CAEN (1981)

  23. Cyclotrons are still attractive ! • Commercial Cyclotrons for Radiation Therapy and Isotope Production • Acceleration of Radioactive Beams • Injectors for Ion Storage Rings • Intense Neutron Sources, replacing Reactors • Energy Amplifier Concept (Carlo Rubbia) • Transmutation of Nuclear Waste

  24. „slow“ Neutrons for Material Research • Production of fast Neutrons • slowing down in Moderator 1. Fissionof Uranium (U235) in a Reactor 2. Spallation of heavy Nuclei (e.g. lead) by Bombardment with Protons from an Accelerator => safe and fast turning off !

  25. Spallation Neutrons

  26. Energy Amplifier Concept (C.Rubbia) Example for a test facility: the 600 MeV PSI Cyclotron operating at 3 mA (1.8 MW) could produce 100 MWth from a reactor running with a criticality factor k=0.95 For a real power plant with 1 Gwel one needs an accelerator with 50 mA at 1 GeV => Linac

  27. Proton Therapy • Irradiation of Tumour from different Directions with Gantry • minimal Dose at Surface

  28. Spotscanning (E.Pedroni) • Pencil Beam: 7 mm in Air • Volume Scanning on a 5 mm Grid: 10’000 Application Points per Liter still world wide the only Gantry with Proton Scanning ! Scanning Elements : Tim Spot-Dosis Monitor + Kicker 100 us X Sweepermagnet (fast) 5 ms/step Y Range-shifter (moderate speed) 30 ms Z Patient Table (slow) 10 mm/s

  29. Brain Tumour Irradiation with Protons by Spot-Scanning (E.Pedroni, PSI)

  30. References More information on the PSI Accelerator Facilities can be found in: www.psi.ch Some foils from talks by the author are found in: http://abe.web.psi.ch/accelerators/vortraegeWernerJoho/ vortraegeWernerJoho.php In the paper “Fun with Formulas” there is e.g. a cute approximation for the end fields of a magnet with a binomial formula.

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