Production of quasi-monochromatic MeV photon in a synchrotron radiation facility Presentation at University of Saskatchewan April 22-23, 2010 Yoshitaka Kawashima Brookhaven National Laboratory NSLS-II, Upton, New York U.S.A.
Contents 1. Short review of MeV photon in synchrotron radiation facilities 2. Outline of an ideal synchrotron radiation facility 3. How to produce quasi-monochromatic MeV photon 4. To maintain stored beam current at CLS and any facilities 5. Summary
1. Short review of MeV photon in synchrotron radiation facilities Gamma-Ray Production in a Storage Ring Free-Electron Laser V. N. Litvinenko et. al, Pysisc. Rev. Lett., Vol. 78, Nov.24, 16 June 1997 (4569-4572). Obtained number of Photons: 2.0 10 5 at 12.2 MeV
2. Outline of an ideal synchrotron radiation facility ICFA2006 held at DESY, WG112 Full energy injection system
3. How to produce quasi-monochromatic MeV photon Production of MeV photon * Wavelength of laser light is fixed. * Stored beam energy is variable. Electron Laser photon E(photon) = 4εγ 2 ε : photon energy of laser γ = Ee/ me, me: electron mass Ee: electron energy Monochromatic MeV photons distribute on the axis.
Electron beam Scattering angle photon CO2 laser
CO 2 laser : 10.6 µm (0.11696 ev) Incident angle : 0 degree Obtained MeV photon Merits of CO2 laser (1) Stable (2) Availability of high power (3) Commercialized products (4) Easy polarization Canadian Light Source (CLS): beam energy from 1.5 ~ 2.9 GeV
For example Expected number of monochromatic inverse Compton photon In case of Canadian Light Source (CLS) storage ring (use machine parameters) (1) Laser CO2 : 100 W (CW) cross section : 1 mm 2 interaction length : 10 cm (2) Beam cross section and stored current (CLS) vertical size : 16 m horizontal size : 485 m -> 500 m stored current : 100 ma beam energy : 2 GeV (3) Expected number of scattered photon N γ = 1.48 106 A[cm 2 ] [sec 1 ]
Case 1 Intensities of beam and laser: Gaussian power distributions A=1.76E-2 N γ = 1.48 106 0.0176[cm 2 ] = 8.4 107 [sec 1 ] Case 2 Intensities of beam and laser: Homogeneous distributions A=1.0E-2 N γ = 1.48 106 0.01[cm 2 ] =1.5 108 [sec 1 ] Stored current I=100 ma, Laser power =100 watt Total number of MeV photon ~10 8 [per second]
Experimental scheme as an example KEK developed laser system as shown below: T. Hirose et. al., Nucl. Inst. & Meth. Phys. Rev., A455, 15 (2000)
4. To maintain stored beam current at CLS and any facilities Following two items should be satisfied at least (1) Stability of stored beam Even if higher-order mode instability of cavity is suppressed, there are still instabilities; (a) longitudinal-mode instability (b) transverse-mode instability (2) Top-up (Top-off) operation (This issue has already been completed at CLS)
(1) Stability of stored beam (a)longitudinal-mode instability (This is a kind of human error) Source: low-level RF system & high power equipments 60/50 Hz and its harmonics enter into cavity and shake stored beam * synchrotron oscillation is amplified by them
(b) Transverse mode instability Ion-trapping issue Top-up (Top-off) operation induces this classical ion-trapping issue 1 RF bucket with beam 13 9 5 RF bucket without beam Storage ring Top-up operation gradually fills empty RF buckets with beam. This problem is solved by RF knock-out system installed in a booster ring. (Single-bunch is formed by this method) CLS has already installed RF knock-out system
(2) Top-up (Top-off) operation (my proposal) Strategy of top-up operation (linac + booster + storage ring) (step 1) Make an arbitrary filling pattern and fill an arbitrary current in a storage ring with the injection of train beam or single-bunch beam (step 2) Once beam is stored in the storage ring, set up single-bunch mode and turn on RF knock-out system (step 3) To maintain the stored current, inject single-bunch beam into the storage ring Why do we so? In order to avoid ion-trapping problem, which causes transverse-mode instability (step 4) Look for minimum beam intensity among all RF buckets, which have already been filled with beam (step 5) Inject single-bunch beam into the targeted RF bucket with minimum beam intensity
Timing system for beam injection from Linac (an example of SPring-8) Electron Pulse generator Sampling oscilloscope Gun 13-cell buncher Accelerating structure Fast current transformer 60 MeV µ
(3) Bunch-by-bunch feedback system Insertion devices (ID) with various types are installed in a storage ring IDʼs generate skew component or unknown instabilities Unknown instabilities due to vacuum chamber are induced To suppress longitudinal and transverse mode instabilities, two different bunch-by-bunch feedback systems should be installed in a storage ring
5. Summary (1) An ideal synchrotron radiation facility supplies Ultraviolet light X-ray MeV-photon (quasi-monochromatic) GeV-photon Neutron (coexistence and co-prosperity) (2) MeV-photon production with arbitrary energy Wavelength of laser is fixed Use high power CO2 laser Stored beam energy is variable Maintain stored beam current stable beam without instabilities timing system for top-up operation installation of bunch-by-bunch feedback system