Presentation on theme: "COBALD - An Inverse Compton Back-Scattering (CBS) Source at Daresbury."— Presentation transcript:
COBALD - An Inverse Compton Back-Scattering (CBS) Source at Daresbury
Introduction to ALICE ALICE (Accelerators and Lasers In Combined Experiments) - known formerly as ERLP: High-voltage DC photoemission electron gun; Superconducting linacs operating in energy recovery mode; A mid-IR free-electron laser (FEL); PLUS a source of ultrashort x-ray pulses produced by inverse Compton scattering of multi-terawatt 100 fs laser pulses by the electron beam.
Nominal ALICE Parameters Gun Energy350keV Injector Energy8.35 MeV Circulating Beam Energy35 MeV Linac RF Frequency1.3 GHz Bunch Repetition Rate81.25 MHz Nominal Bunch Charge80 pC Average Current13 µ A
Status Gun currently fitted with “Stanford ceramic” – limits operating voltage to ~250 kV; Gun diagnostic test line gone - ready for beaming into booster module and beyond; Booster module warm window cracked & replaced – investigation underway; Shutdown on 25 th October; 3 weeks operation in Dec - ~ 6 months operation in 2009; Priorities – energy recovery, injector tuning, diagnostics, CBS…
Compton Back-Scattering Compton scattering of photons off a high-brightness electron beam: A collision between a photon and an electron; Or the electromagnetic field of the laser beam acts as a very short period undulator; Produces ultra-short pulse x-ray radiation from low-energy e - beam; Collision geometry determines flux and energy.
COBALD COmpton BAckscattering x-ray source driven by the multi-10 TW Laser installed at Daresbury
Optics for both possible interaction angles: 180 “head-on” and 90 “sideways-on”
ALICE and CBS parameters ParameterValueUnits Energy at interaction point 35MeV Train repetition rate10Hz Bunches per train1 Bunch charge80pC Electrons per bunch5×10 8 Average current0.8nA Peak current6.5mA ParameterValueUnits Brightness>10 20 photons/mm 2 /mrad 2 / s/0.1% bandwidth Peak x-ray energy 30keV (head-on geometry) 15keV (sideways-on) X-ray pulse length (rms) 350fs (head-on geometry) 100fs (sideways-on) X-ray source size (FWHM) 20 × 35 μmμm
X-ray output The angular distribution of the x- rays for head-on collision geometry collision; each colour is a 1 keV energy band with 20-21 keV on outside and 30-31 keV at centre
FEL wiggler to remain in place ( no extra quadrupoles); Smallest possible transverse electron beam size at interaction point; After photon-electron interaction most of e - beam must make it round the second arc Lattice 8.4 used as starting point Figure shows lattice 8.5; only slightly different!
Giving: Beam waist 13.45 × 19.81 μ m ( x × y ); 99% of the electrons making it to the pop-in dump. Lattice re-optimised using ELEGANT
Summary ELEGANT used to re-optimise MAD-derived lattice 8.4 to give minimum beam size at interaction point, while: Wiggler stays in place; All of the beam makes it further round to the pop-up dump; Quadrupole gradients are compatible with existing PSUs; 10Hz, single bunch, so no energy recovery needed; First experiments next year.