Potential of Cyclotrons

W.Joho 2007

Potential of Cyclotrons Potential of Cyclotrons

Werner Joho, PSI

FFAG 2007, Grenoble 12.april 2007

W.Joho 2007

State of the Art Accelerator FacilitiesState of the Art Accelerator Facilities

Ringcyclotron 590 MeV protonsRingcyclotron 590 MeV protons

1.2 MW average Beam Power

high Intensity Muon Beams 5•108 /s , 108 /s

Spallation Neutron Source 1014 n/s

Radiation Therapywith Spot Scanning and rotating Gantry

Swiss Light Source SLS(2.4 GeV Electron Storage Ring)

Swiss Light Source SLS(2.4 GeV Electron Storage Ring)

• extremely stable photon beams ( < 0.5 m)

• „top-up“ and „fast orbit feedback“ (FOFB)

superconducting cyclotron

superconducting cyclotron

W.Joho 2007

PSI East

PSI West

Aare

psi forum

Auditorium

SLS

Neutron Source

Aerial View

W.Joho 2007

The first Cyclotron 1931

The first Cyclotron 1931

E.O.Lawrence,

M.S.Livingston

Berkeley, California

4 inch diameter

1 kV on the Dee

80 keV Protons

W.Joho 2007

43 years later (1974)

43 years later (1974)

Ring Cyclotron

590 MeV Protons

15 m Diameter

Hans Willax,

Jean Paul Blaser,

Villigen, Switzerland

W.Joho 2007

Comet CyclotronComet Cyclotron

Radiation Therapy with

250 MeV Protons

Cyclotron:

superconducting Magnet, 3m Ø

Collaboration: ACCEL & PSI

W.Joho 2007

Comet Cyclotron, 250 MeV Protons

Comet Cyclotron, 250 MeV Protons

superconducting Magnet

with 4 Sectors

The spiral structure

is responsible for the

vertical beam focusing

0.5 m

W.Joho 2007

Proton Therapy with PROSCAN(3D-spot scanning)

Proton Therapy with PROSCAN(3D-spot scanning)

SC-CYCLOTRON

DEGRADER=> Rangeshifter

(2-30cm)

sweeper 1Does Modulation

Patient-table

sweeper 2

Proton Beam250 MeV

Dipole

Gantry

W.Joho 2007

Cyclotrons

Cyclotrons

Synchro-

cyclotron

Isochronous Cyclotron

classicalCyclotron

CW-beamsingle polewith sectors

CW-beam

pulsed beam

Ring Cyclotron

non relativisticenergy limit

single pole

FFAG with sectors

W.Joho 2007

Accelerator Facilities with 4 Cyclotrons

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

W.Joho 2007

Injector IIInjector II

Injection Line

870 keV

Extraction Line

72 MeV Protons

(after 100 turns)

Resonator

50 MHz

W.Joho 2007

Recipe for high Intensity

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 !!

the last 5 turns in the Injector II

dR

W.Joho 2007

RingcyclotronRingcyclotron

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 %

W.Joho 2007

RF CavityRF CavityRing 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 ?

W.Joho 2007

Ring Cyclotron

Ring Cyclotron

y [mm]

x [mm]

Contour lines of the

magnetic field

scaling of average field:

B0(R) ~ γ

Increase from 72-590 MeV: 55%

2 T

1.5 T

W.Joho 2007

Orbits in Ring Cyclotron

Orbits in Ring Cyclotron

Extraction

Septum

RF Cavity

Magnet

Sector

6 Orbits plotted at

equidistant energies:

75, 177, 279, 381, 483, 585 MeV

(R ~ β)

W.Joho 2007

how to scare young

students!!

how to scare young

students!!

better approach to get

focusing frequencies:

1. simple

approximations

2. numerical calculations Qr

2 ≈ +k

Qz2 ≈ -k +F (1+2tan2

)

(Al Garren 1962)

W.Joho 2007

Flattop Voltage gives minimum energy

spread

Flattop Voltage gives minimum energy

spread

W.Joho 2007

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

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

W.Joho 2007

Advantages of Ring Cyclotron (Hans Willax 1963)

Advantages of Ring Cyclotron (Hans Willax 1963)

magnetic field and RF system are decoupled

many cavities (incl. flattop!)

with high voltage

strong vertical focusing

small magnet gap

low power consumption

total magnet weight as low as

for a compact warm magnet

straight sections

easy construction of injection and extraction elements(no kickers !)

lots of space for diagnostic and correction elements

fast crossing of resonances

good turn separation, low extraction losses

high intensity

penalty: requires injector!

W.Joho 2007

Properties of Cyclotrons

Properties of Cyclotrons

=> high Intensity (few mA)

=> polarized Ions (few A)

Coincidence Experiments with

high Event Rates

continuos Beam allows

easy Tuning of

Accelerator

in all 6 Dimensions

transv.: 1 mm mrad (norm.)

E/E ≈ 10-3

t ≈ 0.3 ns

Pulse Selection at low Energy gives flexible microscopic Time Structure for Time of Flight Experiments

all Ions from p to U

Energies:

p: up to 600 MeV => limit ≈ 10 GeV ?

Ions: up to 500 MeV/n

versatile

CW-Beams

excellent Beam Quality

W.Joho 2007

Current Limit in

Ring Cyclotron

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.)

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)

current limit ~ V3 !

2000

W.Joho 2007

Cyclotrons are still attractive !

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

W.Joho 2007

„slow“ Neutrons for Material Research

„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 !

W.Joho 2007

Spallation Neutrons

Spallation Neutrons

W.Joho 2007

Energy Amplifier Concept (C.Rubbia)

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

W.Joho 2007

Proton TherapyProton Therapy

Irradiation of Tumour

from different

Directions with Gantry

minimal Dose at

Surface

W.Joho 2007

Spotscanning (E.Pedroni)Spotscanning (E.Pedroni)

still world wide the only Gantry with Proton Scanning !

X Sweepermagnet (fast) 5 ms/step

Y Range-shifter (moderate speed) 30 ms

Z Patient Table (slow) 10 mm/s

Tim Spot-Dosis Monitor + Kicker 100 us

Scanning Elements :

– Pencil Beam: 7 mm in Air

– Volume Scanning on a 5 mm Grid: 10’000 Application Points per Liter

W.Joho 2007

Brain TumourBrain Tumour

Irradiation with

Protons by

Spot-Scanning

(E.Pedroni, PSI)

W.Joho 2007

ReferencesReferences

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.