Laser system for ILC diagnostics Laser system for ILC diagnostics

Sudhir Dixit: The John Adams Institute (Oxford)

Two main features of ILC

1. High accelerating gradient – High energy (TeV) & high average power (10s MW) lepton beams

2. Low emittance, very small size lepton beams - High Luminosity (1034 cm-2 s-1)

We, at oxford, plans to develop a suitable laser to map the time resolved e-/e+ beam emittance/luminosity within a single ILC pulse of 950 s

Method

To measure the e-/e+ bunch profiles/sizes within a single ILC pulse with a sub-micron resolution, high-coherence, high average power mode-locked laser all along the 40 km accelerator complex

Damping ring Linac Beam delivery section

ILC e-/e+ pulse ILC e-/e+ pulse structurestructure

ILC beam sizesILC beam sizes

Methodology of Lepton beam size estimation: Laser-wire

Vertical scanning: y

Horizontal scanning: x

We plan to have about 100 measurements within an ILC pulse by time synchronised laser and e-/e+ pulses and fast, EO/Piezo, laser deflectors

The LASER-WIRE

Guidelines on the choice of Laser for the LASER-WIRE

flaser = femicrobunch (3 MHz, timing accuracy < 0.5 ps, Mode locked laser)

2. Laser pulse duration, tmicro and tmacro

Tmicro= e- bunch length (0.5 mm) = 2 ps (But may be relaxed to 10 ps) Tmacro = 950 s (Long pulse ML Laser)

3. Laser spot size, L

m2 = e

2 + L2 + L jitter

2 + e jitter2 + ……

We require, jitter < L < e [L 1 m] Gaussian profiles in space and time, TEMoo mode spatial coherence (M2 1) Focussing lens f# = 1.5-2

4. No. of Comptons (NC) & Laser peak power (P)

NC=P NeC h-1 c-2 -1/2 m-1/2 exp [- 0.5 (/m)2]

For good accuracy, NC > 2000 and good energy stability. This requires P 10MW (100 J/10ps)

1. Laser repetition rate, flaser

5. Laser wavelength, L & Rayleigh Range, RL

We want, RL = 4 L2/ = x and L < Y

Also we know, C reduces as L is reduced

L M2 f#

The net choice L = 250 nm – 500 nm

The The Laser system

The laser system has to be an master oscillator followed by power amplifier/s (MOPA)

Laser oscillator choice:

A conventional mode-locked Nd:YLF (1047 nm/1053nm) or Nd: YAG (1064 nm) laser

A mode-locked fiber laser (1047/1053/1064 nm)

Laser Amplifier choice:

High power diode pumped Nd:YLF or Nd:YAG

Choice on 2nd harmonic crystal : LBO/BBO (250 nm – 500 nm)

Attractiveness of Fiber laser baser oscillator-preamplifier systems

High quality beams: Diffraction limited divergence, excellent beam profiles, very low pointing jitter, pulse-width – from 100 fs to 10 ps, rep. Rate = KHz to 10s of MHz

Available pulse energies: 10 micro-joules (6 MHz, 1 ps pulses)

1000 micro-joules (50 KHz, 200 fs pulses)

Issues to be resolved: Exact rep. Rate control and synchronization to external signal

Current status: Vendors are being contacted for part of laser systems/components

The proof of principle will be tested in ATF-2 at KEK on pulse structure similar to ILC

The laser being developed for ‘The laser-wire’ will have some overlapping with the laser systems used in

Photo-injector

Polarimeter

In long term future, one may think about suitable laser for collider experiments!

Thank You