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

2. State of the Art Accelerator Facilities
Ringcyclotron MeV protons
superconducting cyclotron
1.2 MW average Beam Power
Radiation Therapy with Spot Scanning and rotating Gantry
high Intensity Muon Beams 5•108 m+/s , m-/s
Spallation Neutron Source 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) 1

3. PSI East SLS PSI West Aare psi forum Auditorium Neutron Source
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 1

5. 43 years later (1974) Ring Cyclotron 590 MeV Protons 15 m Diameter
Hans Willax,
Jean Paul Blaser,
Villigen, Switzerland 1

6. Comet Cyclotron Radiation Therapy with 250 MeV Protons Cyclotron:
superconducting Magnet, 3m Ø
Collaboration: ACCEL & PSI 1

7. Comet Cyclotron, 250 MeV Protons
superconducting Magnet with 4 Sectors
The spiral structure is responsible for the vertical beam focusing
0.5 m 1

8. Proton Therapy with PROSCAN (3D-spot scanning)
Gantry
Does Modulation
sweeper 1
sweeper 2
Dipole
SC-CYCLOTRON
Proton Beam 250 MeV
DEGRADER
=> Rangeshifter (2-30cm)
Patient- table 1

9. Cyclotrons classical Cyclotron Synchro- cyclotron Isochronous
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 1

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 1

11. Injector II Injection Line 870 keV Resonator 50 MHz Extraction Line
72 MeV Protons
(after 100 turns) 1

12. Recipe for high Intensity
the last 5 turns in the Injector II dR
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 !! 1

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 ≈ % 1

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 ? 1

15. Ring Cyclotron
y [mm]
2 T
Contour lines of the magnetic field scaling of average field: B0(R) ~ γ Increase from MeV: 55%
1.5 T
x [mm] 1

16. Orbits in Ring Cyclotron
RF Cavity
Extraction Septum
Magnet Sector
6 Orbits plotted at equidistant energies: 75, 177, 279, 381, 483, 585 MeV (R ~ β) 1

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+2tan2 d) 1

18. Flattop Voltage gives minimum energy spread1

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
many cavities (incl. flattop!) with high voltage
strong vertical focusing
straight sections
small magnet gap
easy construction of injection and extraction elements (no kickers !)
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! 1

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.: p 1 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 1

22. Current Limit in Ring Cyclotron
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) 1

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 1

24. „slow“ Neutrons for Material Research
Production of fast Neutrons
slowing down in Moderator
1. Fission of 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 ! 1

25. Spallation Neutrons 1

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 1

27. Proton Therapy
Irradiation of Tumour from different Directions with Gantry
minimal Dose at Surface 1

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 us
X Sweepermagnet (fast) 5 ms/step
Y Range-shifter (moderate speed) ms
Z Patient Table (slow) 10 mm/s 1

29. Brain Tumour Irradiation with Protons by Spot-Scanning
(E.Pedroni, PSI) 1

30. References
More information on the PSI Accelerator Facilities can be found in:
Some foils from talks by the author are found in:
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. 1