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COBALD - An Inverse Compton Back-Scattering (CBS) Source at Daresbury.

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Presentation on theme: "COBALD - An Inverse Compton Back-Scattering (CBS) Source at Daresbury."— Presentation transcript:

1 COBALD - An Inverse Compton Back-Scattering (CBS) Source at Daresbury

2 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.

3 ALICE Layout

4 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

5 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…

6 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.

7 COBALD COmpton BAckscattering x-ray source driven by the multi-10 TW Laser installed at Daresbury

8 CBS on ALICE

9 Optics for both possible interaction angles: 180  “head-on” and 90  “sideways-on”

10 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

11 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 keV on outside and keV at centre

12 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!

13 Giving: Beam waist × μ m (  x ×  y ); 99% of the electrons making it to the pop-in dump. Lattice re-optimised using ELEGANT

14 Beamsize OK?

15 Quadrupole gradients must be within existing power supply range; No apparent problem for beam as far as pop up dump. Magnet power supplies OK?

16 NameLength _CBS 8.5 to 8.4_CBS 8.4_CBS Gradient CurrentGradient CurrentMax Currentc.f. max (m -2) (T/m)(A)(m -2 )(T/m)(A) Changecurrent INJ-MAG-QUAD %13% INJ-MAG-QUAD %17% INJ-MAG-QUAD %13% INJ-MAG-QUAD %12% INJ-MAG-QUAD %59% INJ-MAG-QUAD %22% INJ-MAG-QUAD %40% INJ-MAG-QUAD %34% INJ-MAG-QUAD % INJ-MAG-QUAD %28% INJ-MAG-QUAD %21% INJ-MAG-QUAD %28% ST1-MAG-QUAD %9% ST1-MAG-QUAD %19% ST1-MAG-QUAD %29% ST1-MAG-QUAD %19% AR1-MAG-QUAD %66% AR1-MAG-QUAD %31% AR1-MAG-QUAD %31%

17 NameLength _CBS 8.5 to 8.4_CBS 8.4_CBS Gradient CurrentGradient CurrentMax Currentc.f. max (m -2) (T/m)(A)(m -2 )(T/m)(A) Changecurrent AR1-MAG-QUAD %66% ST2-MAG-QUAD %30% ST2-MAG-QUAD %29% ST2-MAG-QUAD %16% ST2-MAG-QUAD %16% ST2-MAG-QUAD %19% ST2-MAG-QUAD %11% ST2-MAG-QUAD %0% ST3-MAG-QUAD %4% ST3-MAG-QUAD %45% ST3-MAG-QUAD %55% ST3-MAG-QUAD %59% AR2-MAG-QUAD %26% AR2-MAG-QUAD %69% AR2-MAG-QUAD %31% AR2-MAG-QUAD %26% ST4-MAG-QUAD %39% ST4-MAG-QUAD %65% ST4-MAG-QUAD %0% Pop up dump

18 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.


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