Transcript ALICEFirstLasing_Finalx

First Lasing of the
ALICE Free Electron Laser
David Dunning
On behalf of the ALICE FEL team (Jim Clarke, Neil Thompson,
Mark Surman and Andy Smith), and all the ALICE team
Introduction
On October 23rd 2010, the ALICE infra-red free electron laser
(FEL) at Daresbury Laboratory was successfully operated for the
first time. This is the first FEL of its type to operate in the UK, and
the first FEL operating with an energy recovery linac accelerator
in Europe.
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What it is
Motivation
How it was done
Results so far
Future prospects
Motivation for the ALICE FEL
Why this particular free
electron laser?
Why free electron lasers?
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Light sources have served as a
powerful tool for scientific experiments
for decades.
A free electron laser is an acceleratorbased light source with an exceptional
combination of properties :
– Applicable over a very wide
wavelength range (THz to x-ray
demonstrated so far)
– Easily tuneable
– High repetition rate
– Short pulse
– High brightness/peak power
– …
FEL facilities increasingly significant:
– FLASH, LCLS
Enabling new science
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A step towards developing a cuttingedge FEL facility for the UK.
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The UK doesn’t have an FEL facility, but has
aspirations to develop one:
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The ALICE FEL has allowed the team
proposing advanced FELs for these facilities
to develop the skills to design, build and
operate such a machine.
The ALICE FEL is an infra-red oscillator FEL it’s not the first of its kind, but it puts us in a
position to seriously consider advanced
concepts in a future machine.
In addition, a free electron laser is kind of
the ultimate test for our prototype
accelerator facility.
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How an Oscillator FEL works
An optical cavity stores the emitted
radiation. The cavity length is set
such that the cavity roundtrip time
matches the repetition time of the
electron bunches
UPSTREAM
MIRROR
UNDULATOR
A hole in one cavity
mirror outcouples a
small fraction of the
stored radiation
DOWNSTREAM
MIRROR
ELECTRONS
Electron bunches
arrive with a fixed
repetition rate
The undulator is a periodic magnetic field which
causes the electrons to oscillate transversely
and emit synchrotron radiation. The transverse
component of the electron velocity allows the
exchange of energy between the electrons and
the stored radiation field
The interaction causes
the electrons to bunch
at the radiation
wavelength, and so
emit coherently
Key components: electron beam, undulator and
optical cavity
ALICE FEL layout
UPSTREAM
MIRROR
UNDULATOR
ELECTRON PATH
Key components: electron beam, undulator,
optical cavity + diagnostics…
DOWNSTREAM
MIRROR
Electron Beam
DOWNSTREAM MIRROR
ELECTRON BEAM AT FEL
UNDULATOR
Energy
27.5MeV
Bunch Charge
60-80pC
FWHM Bunch
Length
~1ps
Normalised
Emittance
~12 mm-mrad
Energy Spread
~0.5% rms
Repetition Rate
16.25MHz
Macropulse
Duration
≤100µs
Macropulse Rep.
Rate
10Hz
UPSTREAM MIRROR
BUNCH COMPRESSOR
ELECTRON PATH
Undulator
UNDULATOR
On loan from JLAB where previously
used on IR-DEMO FEL
Now converted to variable gap
PARAMETERS
Type
Hybrid planar
Period
27mm
No of Periods
40
Minimum gap
12mm
Maximum K (rms)
1.0
Optical Cavity
OPTICAL CAVITY
Mirror cavities on kind loan from CLIO.
Previously used on Super-ACO FEL
PARAMETERS
Type
Near Concentric
Resonator Length
9.2234m
Mirror ROC
4.85m
Mirror Diameter
38mm
Mirror Type
Cu/Au
Outcoupling
Hole
Rayleigh Length
1.05m
Upstream Mirror Motion
Pitch, Yaw
Downstream Mirror Motion
Pitch, Yaw, Trans.
UPSTREAM MIRROR
DOWNSTREAM MIRROR
Diagnostics for IR radiation
LASER POWER
METER
DOWNSTREAM
ALIGNMENT HeNe
FEL BEAMLINE TO
DIAGNOSTICS ROOM
PYRO-DETECTOR
on Exit Port 2
SPACE FOR DIRECT
MCT DETECTOR
MCT (Mercury Cadmium
Telluride) DETECTOR on
Exit Port 1
SPECTROMETER
Based upon a Czerny
Turner monochromator
FEL Commissioning Strategy
In order for the FEL to operate we needed to co-align:
• Undulator axis
• Optical cavity axis
• Electron beam axis
FEL Commissioning Strategy
ALIGNMENT
WEDGES
UNDULATOR
ARRAYS
SPECTROMETER
ALIGNMENT
MIRROR
OPTICAL
OPTICAL TARGET
TARGET
ALIGNMENT
MIRROR
3.
6.
5.
4. Alignment
Downstream
Cavity
Electron
Upstream
length
Beam
Mirror
Mirror
scanned
steered
aligned
aligned
looking
to
using
Alignment
using
for
Downstream
Upstream
enhancement
Wedges
alignment
of spontaneous
laser
(HeNe)
emission,
then
LASING.
2.
Wedges
and
Downstream
Mirror
aligned
optically
using
Theodolite
1.
Undulator
Arrays
and
two
Optical
Targets
surveyed
onto
Reference
Axis with
Laser
Tracker
MCT
DETECTOR
DOWNSTREAM
FEL MIRROR POWER
METER
REFERENCE AXIS
LASER
HeNe
HeNe
TRACKER
UPSTREAM
MIRROR
OPTICAL
OPTICAL TARGET
TARGET
CCD VIEWER
CAMERAS
UNDULATOR
DOWNSTREAM
MIRROR
ALICE IR-FEL Commissioning
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2009
– November: FEL Undulator installation begins.
2010
– January: FEL Undulator and Cavity Mirrors installed and
aligned: all hardware in place to start commissioning.
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17th November 2009
Throughout 2010: FEL programme proceeded in parallel with
installation & commissioning of EMMA, plus THz programme.
One shift per day for commissioning. Of available beam-time,
FEL programme got 12%.
– February: First observations of undulator spontaneous
emission.
• Stored in cavity immediately, indicating transverse prealignment reasonable.
• Scanned cavity length but no enhancement (limited to 40pC
bunch charge, design was for 80pC).
4th February 2010
5
12
x 10
x = -1.0 mm
x = 0.0
x = +1.0 mm
10
– May/June: Spectrometer installed and tested. First
spectra of undulator spontaneous emission.
• Analysis of spontaneous emission used to optimise
electron beam steering and focussing
• Also indicated pre-alignment was acceptable.
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P( ) (a.u.)
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6
4
2
0
-2
7
7.5
8
Wavelength  (m)
8.5
13th June 2010
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ALICE IR-FEL Commissioning
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2010 (continued)
28th June 2010
– June: Strong coherent emission with dependence on
cavity length
• Indication of correct cavity length.
• BUT NO LASING! Gain not exceeding losses.
– Identified need to:
• Reduce losses
• Increase gain
• Get reliable measure of cavity length
– July: Changed outcoupling mirror from 1.5mm radius
to 0.75mm to reduce losses
• Re-gained cavity enhancement but still no lasing
• Installed encoder to get cavity length measurement
• Mirror radius of curvature tested, and matched spec.
• EO measurements indicated correct bunch compression.
– 17th October: installed a Burst Generator to reduce
laser repetition rate by a factor of 5, from 81.25MHz
to 16.25MHz. This enabled us to increase the bunch
charge to >60pC and hence increase the gain…
27th July 2010
17th October 2010
23rd October 2010: ALICE FEL First Lasing
Simulation (FELO code)
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Outcoupled Average Power (mW)
Outcoupled Average Power (mW)
First Lasing Data: 23/10/10
12
10
8
6
4
2
0
-5
0
5
10
15
20
Cavity Length Detuning (m)
25
50
40
30
20
10
0
-5
0
5
10
15
20
Cavity Length Detuning (m)
25
Results
• Highest recorded average power = 32 mW
– Macropulse length = 100 μs, repetition rate = 0.1 s.
– Micropulse repetition rate = 16 MHz, micropulse spacing =
0.0615 μs, i.e. 1626 pulses per macropulse, 16260 pulses
per second.
– Energy per pulse = 32mW/16260 = 2 μJ per pulse.
– Average power within a macropulse = 32 W
– Transmission efficiency of vacuum window=0.7 – so power
from FEL ~1.4x higher.
• The FEL pulse duration has been inferred from the
spectral width to be ~1 ps The peak power is
therefore ~3 MW.
Further Progress
The first demonstration of wavelength tuning of the ALICE FEL has been carried
out. By increasing the undulator gap the wavelength was continuously tuned from
8.0 μm to 5.7 μm, with lasing maintained throughout the range.
FEL Spectra at Different Gaps
g
g
g
g
g
1
P( )(a.u.)
0.8
0.6
= 16 mm
= 15 mm
= 14 mm
= 13 mm
= 12 mm
0.4
0.2
0
5
5.5
6
6.5
7
7.5
8
8.5
1.8
900
1.6
1.4
1.2
1
800
700
600
6
7
8
Wavelength ( m)
500
6
7
8
Wavelength ( m)
2.5
3.5
2
3
PPk (MW)
1000
Pulse Energy ( J)
2
FWHM  t (fs)
Bandwidth (%)
 (m)
1.5
1
0.5
2.5
2
6
7
8
Wavelength ( m)
1.5
6
7
8
Wavelength ( m)
Further Progress
The FEL radiation has been transported to a diagnostics room, and the first
measurements of the transverse profile have been made.
ALICE FEL Future Plans
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Simulation results
6
5
Ppeak (MW)
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4
3
2
1
0
4
5
6
7
8
9
10
11
 (m)
6
5
(MW)
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Improved electron beam set-ups with
reduced energy spread and jitter.
Improve transport of FEL beam to
diagnostics room, then full output
characterisation.
Reduced Mirror ROC to improve gain, plus
selection of outcoupling hole sizes to
optimise output power.
Plan to run and characterise at two different
energies
– 27.5MeV (5-8µm)
– 22.5MeV (7-12µm)
peak
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4
3
27.5MeV,
22.5MeV,
27.5MeV,
22.5MeV,
27.5MeV,
22.5MeV,
0.75mm Hole radius
0.75mm Hole radius
1.5mm Hole radius
1.5mm Hole radius
2.25mm Hole radius
2.25mm Hole radius
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Summary
Further work on characterising the FEL performance and output is continuing,
with lasing now achieved routinely. The successful operation of the free electron
laser is a significant achievement for the team, and provides invaluable experience
for future FEL facility proposals.
Thanks to everyone who
contributed to the project, and
thanks to you all for listening!
ALICE FEL Layout
ALIGNMENT
MIRROR
ALIGNMENT
WEDGES
SPECTROMETER
MCT DETECTOR
INFRA-RED
(OPTICAL
TARGET)
ALIGNMENT
MIRROR
ALICE FEL Systems
Schematic
POWER
METER
ELECTRONS
HeNe
HeNe
UPSTREAM
MIRROR
(OPTICAL
TARGET)
CCD VIEWER
CAMERAS
UNDULATOR
DOWNSTREAM
MIRROR