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Laser based Emittance Measurement for LINAC4
Project Overview & Current Status
T. Hofmann, E. Bravin, U. Raich, F. Roncarolo, F. Zocca (CERN)G. Boorman, A. Bosco, S. Gibson, K. Kruchinin (RHUL)
08.5.2014
Thomas HofmannCERN – Beam Instrumentation (BE/BI/PM)[email protected]
LINAC 4 overview
4
160 MeV
100 MeV
50 MeV
Transfer line to PSB
Linac length ~ 80 m
Laser Emittance Meter
• Particles: H- ions• Top Energy: 160 MeV• Current: 40 mA• Pulse length: 400 µs
DiamondDetector
5
H- beam H0 beamlet< 1 ppm
beamletafter drift
Principle:
H-
H0
Bending Magnet
x-scan
y-scan
H- beam
Concept of Laser Emittance Meter for 160 MeV
Pulsed Laser1064 nm
NON invasive!
Laser-Particle Interaction
• Stripping Probability
• In rest frame of H- beam:– Lorentz-Shift of Photon Energy– – At 160 MeV: 1064 nm -> 909 nm
Laser requirements:• Laser wavelength: 1064 nm • M2 < 3 for diameter < 200 µm• PPeak > 1 kW
Ref: J.T. Broad and W.P. Reinhardt, Phys. Rev. A14 (6) (1976) 2159
Stripping & propagation to detector
Laser
Drift
3.0 m
• Emittance measurement possible via vertical detector scan
• H- Beam• Size (1 Sigma): y = 1.6 mm• Div (1 Sigma): y’ = 2.2 mrad
• Laser Beam• Size (1/e2): = 150 µm• Rayleigh length = 10 mm
Lasers
11
Laser MOPA Fiberlaser (used at 3MeV)
Solid-State(as reference)
Energy per pulse 0.1 mJ 50 mJ
Diameter ~ 150 µm ~ 150 µm
Pstrip @ 3 MeV 0.5 % 100 %
tpulse 110 ns 5 ns
Repetition rate 60kHz 10 Hz
Beam transport Fiber Free Space
Integration Laser Setup
Diagnostics rack
Linear stage with 500 mm lens
Class 4 fiber laser
Coupling
tube
PXI-System
Ref: Fiber Laser Transport for the Photodetachment Emittance Measurements at FETS, Alessio Bosco
Optical setup
Focusing & Diagnostics
5m LMA fiber (20/130 µm; NA =0.08)
Photodiode
CCD with filterwheel on stage
Focusing lens Beam ExpanderFiber input with collimator lens
Laser – Fiber Coupling
H- Beam
Detector
Diamond Detector
Type Polycrystalline Diamond on ceramics PCB
Size 20 x 20 mm
Resolution 5 channels
Thickness 500 µm
Readout 46 dB; 300 MHz preamplifier
CIVIDEC Instrumentation, Austria
Scope
50 Ohm
500 V
Preamp1 µF
Ref: G. Mann et al: ›Nanosecond laser damage resistance of differently prepared semi-finished parts of optical multimode fibers‹, Applied Surface Science 254, pp.1096-1100 (2007)
Troubleshooting
• Burned fiber end-facets– ~ 250 J/cm2
• Noise of motor driver on signal of diamond detector
• Pre-amplifiers for Diamond
Outlook
• 12 MeV Testbench– 10 m LMA fiber for laser transport– Particles traverse diamond detector
• 160 MeV setup– Detector (Readout & Calibration)– Fiber delivery setup (20 m needed)
