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SLAC National Accelerator Laboratory
Laser Heater Status
Outline
Laser Heater Motivation
Optical Layout
Controls and MPS
Timing
Baby Pictures
November 12, 2008
Laser Heater Status
Special Thanks:
Sasha Gilevich
Alan Miahnahri
Matt Boyes
Sheng Peng
Richard F Boyce
Bill White
[email protected]
SLAC National Accelerator Laboratory
Motivation
The LCLS injector system will incorporate a laser-electron-beam heater system (an inverse free electron laser) in order to generate an
uncorrelated energy spread in the electron beam [1]. This produces Laudau damping in the bunch compressor chicanes in order to
suppress potential micro-bunching instabilities that may be driven by Coherent Synchrotron Radiation (CSR) in the bunch compressors, and
Longitudinal Space Charge (LSC) forces in the linac. The laser-heater system is shown in Fig. 1. The heater system is located just
downbeam of the L0b accelerator section at 135 MeV in the off-axis LCLS injector housing.
_________________________________________________________
PRD 1.2-004-r2
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Laser Heater Requirements
Laser Heater Beam Parameters
(ESD 1.2-122)
Parameter
Value
Range
Unit
Wavelength
758
750 - 770
nm
Laser Beam Waist Radius (2σ)
(in the center of the undulator)
0.36
0.32 – 0.60
(adjustable)
mm
Laser Beam Rayleigh Range
50
42-1600
cm
Laser Pulse Energy
(nominal/high setting)
44/200
0 - 200
μJ
Laser Pulse Duration (FWHM)
20
10 - 20
ps
Centroid Position Stability
< 35
Spatial Fluence Profile
Gaussian
November 12, 2008
Laser Heater Status
μm
20% (peak-topeak)
Bill White
[email protected]
SLAC National Accelerator Laboratory
Laser Heater Optical Transport
Rack location
LKA-03
Transport
Lines
Mirror
Laser Heater
November 12, 2008
Laser Heater Status
Rack location
LIT-01
Bill White
[email protected]
SLAC National Accelerator Laboratory
Layout of the Laser Heater Optical System in
the Laser Lab
PC &
polarizer
Shutter
Waveplate
& polarizer
PH1
Energy control
PH2
UV beam
Pulse
Stretcher
3 lens
Telescope
Streak
camera
UV
Conversion
Unit
IR
Laser
System
November 12, 2008
Laser Heater Status
To vertical
transport tube
Path Length
Adjuster
Bill White
[email protected]
SLAC National Accelerator Laboratory
Transport to
the Tunnel
Layout of the Laser Heater Optical System in
the Injector Vault
We had to put in
additional lens to get the
required beam size
OTR
MH4
VHC
PD
WP
MH3
MH2
PH3
CH1
November 12, 2008
Laser Heater Status
MH4, MH3, MH2 Motorized mirrors
Waveplate and
polarizer in front of
both cameras
Bill White
[email protected]
SLAC National Accelerator Laboratory
Energy Control
Fast Energy Control – Pockels
Cell and polarizer
Inrad - PKC02-SG20 : KD*P
Dual Crystal Pockels Cell, with
AR coated windows, with sol-gel
coated crystal - Aperture 20mm
Slow Energy Control –
Waveplate and polarizer
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Diagnostics
In the Laser Lab
Two powermeters – beam energy out of the laser / after the
attenuator
Streak camera – temporal diagnostics
Camera – beam shape - optional
In the injector Vault - Upstream of the undulator
Camera VHC – virtual heater (spatial shape and position of the
laser beam)
Powermeter
Downstream of the undulator
Photodiode for timing adjustment
OTR screens
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Alignment
Before the undulator vacuum chamber was
installed a camera was palced on a rail, which was
aligned to the undulator axis
Aligned the laser beam so that it was centered on
the camera at any Z-position
Beam was centered on the cameras VHC and CH1
We adjusted the Z-position of the VHC so that the
beam size on the camera is the same as in the
center of the undulator
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Alignment of the telescope for the required beam
size and waist position in the LH
LH1
LH2
LH3
Telescope
Adjustment of LH2 position for the beam size
Coarse adjustment of LH3 position to collimate the
beam
Precise adjustment of LH3 position for the
minimum beam size in the center of the undulator
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Beam R in the LH center,
mm
Precise alignment of the telescope lens
LH3 for waist position
1.6
1.4
Alignment is
manual
1.2
1
0.8
0.6
0.4
0.2
-5
-4
-3
-2
-1
0
1
2
L3 alignment, mm
November 12, 2008
Laser Heater Status
3
4
5
Beam R in the LH w=0.32mm
Beam R in the LH w=0.6mm
Bill White
[email protected]
SLAC National Accelerator Laboratory
Beam in the Undulator Center and VHC
Undulator Center
November 12, 2008
Laser Heater Status
VHC
Bill White
[email protected]
SLAC National Accelerator Laboratory
Beam on the OTRs
OTR1
November 12, 2008
Laser Heater Status
OTR2
Bill White
[email protected]
SLAC National Accelerator Laboratory
OTR Damage Threshold
Piece of OTR foil was placed on the OTRH1
location and illuminated by the laser beam
for about 3-5 min (beam rms was about 320um).
There was small damage at the energy 7uJ.
At the beam energy 2.3uJ we did not see any
damage.
We will put flipper filter to attenuate the laser beam
below 2uJ (at min setting of the energy control
units)
When the filter goes out, a blank plate will go in
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Laser Beam Timing
Photodiode ET-2030 in the output beam
Oscilloscope to watch a PD signal – in the Laser lab
Additional attenuation of the laser beam might be required
Photodiode ET-2030 spec
Detector Type
PIN
Risetime
<300ps
Falltime
<300ps
Responsivity @830nm
0.4A/W
Bias Voltage
Cut Off Frequency (into 50?)
Active Area
Dark Current
November 12, 2008
Laser Heater Status
9V
>1.2GHz
0.4mm dia.
<0.1nA
Bill White
[email protected]
SLAC National Accelerator Laboratory
Laser Heater Required Control Items
Laser Room
Energy Control:
Waveplate
Pockel Cell with Pulse to Pulse DAC control (Required by March)
Energy Measurement: Coherent EPM 2000 Power meter
2 Sensors with Rotation Stages
MPS Shutter
Injector Vault
Laser Steering Feedback
4 Actuators
2 Cameras (CH1 and VHC)
2 Waveplates for Camera Intensity Control
Energy and Time Measurements:
Photodiode
Coherent LabMax-TOP Power meters (verified as BSA compatible)
Virtual Heater Camera (VHC) adjustment
2 Actuators
2 OTRs
MPS
Laser Attenuator
Photodiode Shutter
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Software
Extension of existing Drive Laser System
Use existing IOCs
Few new types of devices
LabMax-Top Power Meter
Verified to be BSA compatibility
Analog Output for beam rate measurement
Will use slow RS-232 communication for configuration and advance features
Laser Heater MPS Shutter
Pockel Cell Driver with DAC control
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Drive Laser EDM Display
Change Between
Systems
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Heater EDM Display
Change Between
Systems
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Machine Protection
MPS protection for OTR screens and photodiode.
MPS Logic:
MPS Shutter blocks IR Laser beam IF
Beam is not attenuated by Laser Attenuator
AND
OTRH1 and OTRH2 are not out
OR
Photodiode is unprotected by photodiode shutter
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Possible Issues
No steering feedback loop upstairs
Feedback loop downstairs should take care of the small
beam motions
Large beam shift can cause clipping on the flipper filter,
lens or tube windows
Multiple reflections on the cameras
Replace tube windows with coated ones
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Before
Laser heater here
Courtesy of
Paul Emma
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
After
Optical LH system installed
Laser heater here
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Transport tubes in the vault
All transport
tubes are
connected
Turbo pump
upstairs
Ion pump
downstairs
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Optics inside the ceiling box
Motorized
mirror
MH4
(open
loop)
Focusing
Lens
Flipper
with a
filter to
protect
OTR (not
in yet)
November 12, 2008
Laser Heater Status
LH
horizontal
tube
UV
beam
tube
Bill White
[email protected]
SLAC National Accelerator Laboratory
Laser Heater Table
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Laser Heater Table in the Vault
MH3
VHC
on
motorized XY stage
To
powermeter
WP
VHC
CH1
WP
CH1
MH2
November 12, 2008
Laser Heater Status
Bill White
[email protected]
SLAC National Accelerator Laboratory
Laser Heater Table in the Vault
From
MH2
Waveplate
To VHC
MH1
November 12, 2008
Laser Heater Status
50%
beamsplitter
Bill White
[email protected]