Transcript UV Demo Lasing 12-10

UV FEL Status and Plans
George Neil and Gwyn Williams
JSA Science Council
January 7, 2011
* This work was supported by U.S. DOE Contract No. DE-AC05-84-ER40150, the Air
Force Office of Scientific Research, DOE Basic Energy Sciences, the Office of Naval
Research, and the Joint Technology Office.
Existing JLab IR/UV Light Source
E = 135 MeV present limit
Up to135 pC pulses @ 75 MHz
20 μJ/pulse in (250)–700 nm UV-VIS
120 μJ/pulse in 1-10 μm IR
1 μJ/pulse in THz
The first high current ERL
14 kW average power
Ultra-fast (150 fs)
Ultra-bright Slide 2
Initial UV FEL Specifications
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Specification from UV Demo proposal (May, 1995)
Average Power
> 1000 W
Wavelength range
1–0.25 mm
Micropulse energy
~25 mJ
Pulse length
~0.1-1 ps FWHM nominal
PRF
74.85, 37.425, 18.7, 9.36, 4.68 MHz
Bandwidth
~ 0.2–1.5 %
Timing jitter
< 1 ps
Amplitude jitter
< 2 % p-p
Wavelength jitter
0.02% RMS
Polarization
linear, > 100:1
Transverse mode quality
< 2x diffraction limit
Beam diameter at lab
2 - 3 cm
Initial UV FEL Performance
IR FEL
UV FEL
3rd
Projected
UV FEL
Harmonic
5th
UV FEL
Harmonic
Photon energy range of
fundamental
0.1 – 1.4 eV,
(12 -0.8 microns)
1 – 3.4 eV
(1200-360 nm)
3-10.2 eV
(410-120 nm)
5-17 eV
(250-73 nm)
Photon energy per
pulse
100 microJoules
20 microJoules
20 nanoJoules
0.2 nanoJoules
Repetition rate
4.678 – 74.85 MHz
4.678 MHz
4.68 MHz
4.68 MHz
Photon Pulse length
(FWHM)
100 fs – 2 ps
100 fs – 2 ps
100 fs – 2 ps
100 fs – 2 ps
Nominal pulse
bandwidth
1%
.2%
.2%
.2%
Electron Beam Energy
80 – 140 MeV
80 – 140 MeV
80 – 140 MeV
80 – 140 MeV
Charge per electron
bunch
135 picoCoulombs
60 picoCoulombs
60 picoCoulombs
60 picoCoulombs
IR Demo Harmonic Power Measurements
1
0.1
10-h
Relative power
0.01
0.001
0.0001
10
10
10
-5
-6
-7
0
1
2
3
4
5
6
7
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Harmonic Number
Third harmonic power is down by about a factor of 1000. We get about 50 W
at 372 nm so we expect about 50 mW of VUV light.
Projected harmonic performance - water cooled mirrors
Working in the UV is challenging
• Short wavelengths require higher electron beam energies; the higher the better.
IR Upgrade was fine with 110 MeV; we are limited to 135 MeV at present
• The transverse emittance and energy spread needs to be lower by ~ 2X
compared to the IR Upgrade.
• Achieve this by operating at ½ the IR Upgrade FEL charge/bunch.
• The vacuum requirement is high and must be achieved to maintain a stable
output and avoid mirror degradation.
• Manufacturing mirrors with l/10 figure in the UV is a challenge.
• Must also have metrology capable of verifying specs.
• Must mount without inducing aberrations.
• UV coatings are more lossy than those in the visible, although exact numbers
are hard to pin down. They may be only a few 100 ppm
• We use mirrors with hole outcoupling to let the VUV out. FELs with high gain
don’t like this; the mode tries to avoid the hole. A careful match is required for
optimal performance
Estimates of FEL performance
• Both pulse propagation and one-dimensional spreadsheet models are first
used to estimate the gain and power.
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Gain is (photon power out of wiggler)/(power going in) measured at low power before
saturation effects enter the picture
Efficiency is [1- (ebeam power exiting wiggler)/(ebeam power entering wiggler)]
measured at saturation or equivalently (photon power out)/(ebeam power in) if mirror
losses are small
400nm 3D simulation results from Genesis/OPC
• Assumes 0.3% energy spread.
Small-signal net gain = 139%
Electronic gain = 165%
Efficiency = 0.704%
Cornell Undulator A Prototype
UV Demo Commissioning Timeline
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January 2006 - Install and commission Cornell wiggler with new gap
mechanism.
Spring and Summer 2009 – Install beamline components except for
optical cavity and wiggler chamber.
Fall 2009 – CW beam through UV beamline.
Spring 2010 – Install new zone 3 module and commission.
June 2010 – Lase at 630 nm, 67 pC in IR laser with 135 MeV beam.
July 2010 – Recirculate laser quality 1 mA CW beam through wiggler
sized aperture.
August 17, 2010 – First electron beam through wiggler.
August 19, 2010 – First lasing, 150 W CW at 700 nm.
August 31, 2010 – First lasing in UV, 140 W @400 nm, 68 W @372 nm
December 9, 2010 – First measurement of 124 nm light
FEL performance at 700nm
Gain at low power is ~100%, detuning curve is 12.5 µm in length
Images while lasing at 100W
Light
scattered
from HR
mirror
Light
scattered
from power
probe
Power meter
Time
dependent
diagnostics
FEL performance at 400nm
• We had to run with the OC mirror de-centered, as the metallization
technique created a damage spot at the mirror center.
Characterization of 10eV photons
Bob Legg had built a chamber for the SRC at Univ.
Wisconsin that we adapted for our purposes:
VUV Chamber
Just measure diode photoelectric
current. No filter required; only
responsive to photons > 10 eV.
Calibration is traceable to NIST.
10eV viewer
Ce:YAG viewer
Viewport
VUV photodiode
Code Comparison with Experiment
• Besides the aforementioned spreadsheet and 1-D pulse propagation codes,
we have 3D & 4D codes that better model the FEL interaction.
• These codes are: a code developed at NPS, as well as Genesis and
Medusa.
• In conjunction with a resonator simulation code we can also model the
effects of aberrations (from thermal absorption, off-axis tilts, etc) and the
mode shape within or outside the optical cavity.
• This is the Optical Propagation Code (OPC).
• Performance of the UVFEL has greatly exceeded the predictions of
simulations.
Parameter
Simulations
Experiment
Turn-on time
8.6 µsec.
5 µsec.
Gain
~100%
~180%
Detuning curve
4.5 µm
>7 µm
Efficiency
0.4-0.7%
0.8%
Very High Gain Seen at 400 nm
from the announcement:
“ 5 nanoJoules of fully coherent light was measured in each 10eV micropulse,
which represents approximately 0.1% of the energy in the fundamental, as
expected.
These numbers allow us to anticipate being able to deliver 25 - 100 mW by
operating CW at up to 4.687 MHz with more optimized water-cooled optics, and
several 100's of mW with cryogenically-cooled optics. Optics upgrades, and
installation of an optical transport beamline to a user laboratory for full
characterization, including bandwidth, are in progress.
We note that for many applications the anticipated narrow bandwidth
eliminates the need for a spectrometer. This allows substantially higher flux to
be delivered to user experiments than is possible at storage rings. “
What happens next on the UV FEL?
• Present mirror is lossy and hole size is somewhat mismatched for proper
outcoupling at these high gains. As a result we cannot lase stably at as high
a power as may be possible even with water cooled mirrors. We are
obtaining a better water cooled mirror set and will have ROC control.
• We are presently installing Optical Transport to Lab 1 and will test it in
February
• We are returning UV wiggler to Cornell and adapting an APS Undulator A
at the manufacturer (STI Optronics).
• A high power test in the IR for the ONR will follow in April and early
May followed by a shutdown till mid July during which time the cooled
mirrors and new undulator will be installed. We will recommission and
perform User runs. (Gwyn’s talk)
• We also intend to install a new R100 cryomodule and get higher beam
energy for shorter wavelength lasing. Perhaps in June if assembly
/installation schedule permits. Lasing in fundamental down to 250 nm may
be achievable depending on energy. If not June then October.