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.

ALICE Layout

Nominal ALICE Parameters

• Gun Energy 350keV

• Injector Energy 8.35 MeV

• Circulating Beam Energy 35 MeV

• Linac RF Frequency 1.3 GHz

• Bunch Repetition Rate 81.25 MHz

• Nominal Bunch Charge 80 pC

• Average Current 13 µA

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 25th 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

CBS on ALICE

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

ALICE and CBS parameters

Parameter Value Units

Energy at interaction point

35 MeV

Train repetition rate 10 Hz

Bunches per train 1

Bunch charge 80 pC

Electrons per bunch 5×108

Average current 0.8 nA

Peak current 6.5 mA

Parameter Value Units

Brightness >1020 photons/mm2/mrad2/s/0.1%

bandwidth

Peak x-ray energy

30 keV (head-on geometry)

15 keV (sideways-on)

X-ray pulse length (rms)

350 fs (head-on geometry)

100 fs (sideways-on)

X-ray source size

(FWHM)

20 × 35

μm

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 μm (x × y);

• 99% of the electrons making it to the pop-in dump.

Lattice re-optimised using ELEGANT

Beamsize OK?Beam sizes through arc 2 and straight 4 (up to the pop-up dump)

0

5

10

15

20

25

30

ar2d

ip01

ar2s

ext01

ar2q

uad0

1

ar2d

rift0

4

ar2q

uad0

2

ar2d

ip02

ar2q

uad0

3

ar2q

uad0

4

ar2s

ext02

ar2d

ip03

st4q

uad0

1

st4q

uad0

2

st4q

uad0

3

Position

Bea

m S

ize

(mm

)

Beam size (x)

Beam size (y)

3 i i

EBeamSize

E

•Quadrupole gradients must be

within existing power supply

range;

•No apparent problem for beam

as far as pop up dump.

Magnet power supplies OK?

Name Length

8.5 8.4_CBS  8.5 to

8.4_CBS

8.4_CBS

Gradient   Current Gradient   Current Max Current c.f. max

(m-2) (T/m) (A) (m-2) (T/m) (A) (A) Change current

INJ-MAG-QUAD-01 0.15 -8.62 -0.24 -0.65 -9.29 -0.26 -0.70 5.5 8% 13%

INJ-MAG-QUAD-02 0.15 9.50 0.26 0.72 12.00 0.33 0.91 5.5 26% 17%

INJ-MAG-QUAD-03 0.15 2.63 0.07 0.20 -9.09 -0.25 -0.69 5.5 -446% 13%

INJ-MAG-QUAD-04 0.15 -11.77 -0.33 -0.89 -8.59 -0.24 -0.65 5.5 -27% 12%

INJ-MAG-QUAD-05 0.15 25.60 0.71 2.27 25.60 0.71 2.27 3.9 0% 59%

INJ-MAG-QUAD-06 0.15 10.91 0.30 0.97 9.55 0.27 0.85 3.9 -12% 22%

INJ-MAG-QUAD-07 0.15 -17.03 -0.47 -1.51 -17.23 -0.48 -1.53 3.9 1% 40%

INJ-MAG-QUAD-08 0.15 14.63 0.41 1.30 14.72 0.41 1.31 3.9 1% 34%

INJ-MAG-QUAD-09 0.15 0.00 0.00 0.00 0.00 0.00 0.00 3.9 0% 0%

INJ-MAG-QUAD-10 0.15 11.95 0.33 1.06 11.95 0.33 1.06 3.9 0% 28%

INJ-MAG-QUAD-11 0.15 -8.95 -0.25 -0.79 -8.94 -0.25 -0.79 3.9 0% 21%

INJ-MAG-QUAD-12 0.15 11.95 0.33 1.06 11.95 0.33 1.06 3.9 0% 28%

ST1-MAG-QUAD-01 0.1524 1.20 0.14 0.30 2.24 0.26 0.58 6.8 94% 9%

ST1-MAG-QUAD-02 0.1524 -3.35 -0.39 -0.94 -4.61 -0.54 -1.28 6.8 37% 19%

ST1-MAG-QUAD-03 0.1524 7.30 0.85 1.96 7.29 0.85 1.96 6.8 0% 29%

ST1-MAG-QUAD-04 0.1524 -5.91 -0.69 -1.63 -4.66 -0.54 -1.29 6.8 -21% 19%

AR1-MAG-QUAD-01 0.15 11.43 1.33 3.63 11.43 1.33 3.63 5.5 0% 66%

AR1-MAG-QUAD-02 0.15 -5.35 -0.63 -1.70 -5.36 -0.63 -1.70 5.5 0% 31%

AR1-MAG-QUAD-03 0.15 -5.35 -0.63 -1.70 -5.36 -0.63 -1.70 5.5 0% 31%

Name Length

8.5 8.4_CBS  8.5 to

8.4_CBS

8.4_CBS

Gradient   Current Gradient   Current Max Current c.f. max

(m-2) (T/m) (A) (m-2) (T/m) (A) (A) Change current

AR1-MAG-QUAD-04 0.15 11.43 1.33 3.63 11.43 1.33 3.63 5.5 0% 66%

ST2-MAG-QUAD-01 0.1524 -7.99 -0.93 -2.20 -7.53 -0.88 -2.07 6.8 -6% 30%

ST2-MAG-QUAD-02 0.1524 7.48 0.87 2.01 7.39 0.86 1.99 6.8 -1% 29%

ST2-MAG-QUAD-03 0.1524 -2.32 -0.27 -0.66 -3.92 -0.46 -1.09 6.8 66% 16%

ST2-MAG-QUAD-04 0.1524 2.56 0.30 0.67 -3.92 -0.46 -1.09 6.8 -263% 16%

ST2-MAG-QUAD-05 0.1524 4.17 0.49 1.11 4.81 0.56 1.28 6.8 16% 19%

ST2-MAG-QUAD-06 0.1524 -10.55 -1.23 -1.55 -2.75 -0.32 -0.42 3.7 -73% 11%

ST2-MAG-QUAD-07 0.1524 11.40 1.33 1.64 0.00 0.00 -0.02 3.7 -101% 0%

ST3-MAG-QUAD-01 0.1524 0.00 0.00 -0.02 -0.80 -0.09 -0.14 3.7 626% 4%

ST3-MAG-QUAD-02 0.1524 -4.69 -0.55 -0.70 11.67 1.36 1.68 3.7 -340% 45%

ST3-MAG-QUAD-03 0.1524 11.87 1.39 3.20 -13.75 -1.61 -3.77 6.8 -218% 55%

ST3-MAG-QUAD-04 0.1524 -8.77 -1.02 -2.41 14.92 1.74 4.04 6.8 -267% 59%

AR2-MAG-QUAD-01 0.15 10.82 1.26 3.43 4.49 0.52 1.43 5.5 -58% 26%

AR2-MAG-QUAD-02 0.15 -7.71 -0.90 -2.45 -12.00 -1.40 -3.81 5.5 56% 69%

AR2-MAG-QUAD-03 0.15 -7.71 -0.90 -2.45 -5.36 -0.63 -1.70 5.5 -30% 31%

AR2-MAG-QUAD-04 0.15 10.82 1.26 3.43 4.49 0.52 1.43 5.5 -58% 26%

ST4-MAG-QUAD-01 0.1524 -7.56 -0.88 -2.08 -9.72 -1.13 -2.67 6.8 28% 39%

ST4-MAG-QUAD-02 0.1524 8.06 0.94 2.17 16.39 1.91 4.43 6.8 104% 65%

ST4-MAG-QUAD-03 0.1524 -1.66 -0.19 -0.53 0.00 0.00 0.00 5.5 -100% 0%

Pop up dump

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.