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Gamma Beam Systems
a simple introduction
Purpose of the machine
Deliver a high performance photon beam:• Variable energy• Highly polarized• High intensity• Low bandwidth
Where photons come from?Scattering of photons on high energy electrons.
What is the photon energy after scattering?
Where photons come from?Scattering of photons on high energy electrons.
What is the photon energy after scattering?
24photonEMeV
Ee511.0
Example
)520(5.2 greennmeVE f )500(1000 MeVEe
MeVEg 10
24photonE
High correlation: photon energy and photon direction
Scattering in the direction of the electron
Purpose of the machine
Deliver a high performance photon beam:• Variable energy: variable energy of the
electron beam• Highly polarized• High intensity• Low bandwidth
Purpose of the machine
Deliver a high performance photon beam:• Variable energy: variable energy of the
electron beam– Large energy range - > magnetic machine
• Highly polarized• High intensity• Low bandwidth
Purpose of the machine
Deliver a high performance photon beam:• Variable energy: variable energy of the
electron beam• Highly polarized: Compton scattering retains
the polarization of the laser photon• High intensity• Low bandwidth
Purpose of the machine
Deliver a high performance photon beam:• Variable energy• Highly polarized• High intensity: from intense photon and
electron beams• Low bandwidth
electrons laser
High intensity photon beam
•Many photons -> High intensity laser
•Many electrons ->High charge electron bunches
•Large overlap between photons and electrons
Purpose of the machine
Deliver a high performance photon beam:• Variable energy• Highly polarized• High intensity: from intense photon and
electron beams• Low bandwidth: from collimation of photons
– We retain 0.1% of the photons after collimation
Principle of operation of GBS
1. Electron bunches generated at photocathode2. Electron bunches transported to Interaction
Point – acceleration– focusing
3. Laser transported to interaction point4. Electron-Photon interaction5. Collimation of photons6. Experiments
Why is it a complicated machine?
• Interaction laser– High intensity = low repetition rate (100 Hz) ->
recirculator to artificially increase the frequency
Recirculator: gives the time structure of the beam (1ns = 30 cm)
Why is it a complicated machine?
• High charge electron bunches(250 pC):– High space charge effects
leads to high emittance (size of beam) ----
--- --
•Low bandwidth needs very low emittance:• size of beam at interaction point• direction of photon given by direction of
electron
Why is it a complicated machine?
• Beam time structure:– Complex recirculator– Complex cathode laser– Complex synchronisation– Wakefields in RF cavities– Complicated electron beam diagnostics– Complicated photon beam diagnostics
Gamma Beam System – Layout
e– RF LINACLow Energy
300 MeV
Interaction LaserLow Energy
Photo–drive Lasere– source
Interaction PointLow Energy
Photogunmultibunch
e– beam dump
g beam coll&diag
e– beam dump
Low Energy StageGamma rays up to 3.5 MeV
ControlRoom
RacksRoom
RacksRoom
Gamma Beam System – Layout
e– RF LINACHigh Energy
720 MeV
Interaction LaserHigh Energy
Interaction LaserLow Energy
Photo–drive Lasere– source
Interaction PointHigh Energy
Photogunmultibunch
e– beam dump
g beam coll&diag
e– beam dump
High Energy StageGamma rays up to 19.5 MeV
ControlRoom
RacksRoom
RacksRoom
Gamma Beam System – Layout
e– RF LINACLow Energy
300 MeV
Interaction LaserHigh Energy
Interaction LaserLow Energy
Photo–drive Lasere– source
Master clock synchronization @ < 0.5 ps
Interaction PointHigh Energy
Interaction PointLow Energy
Photogunmultibunch
e– beam dump
e– beam dump
g beam coll&diag
g beam coll&diag
e– beam dump
ControlRoom
RacksRoom
RacksRoom
e– RF LINACHigh Energy
720 MeV
