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NLC - The Next Linear Collider Project
The Photon Collider at NLC
Jeff Gronberg/LLNL
April 24, 2001
This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.
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NLC - The Next Linear Collider Project
Outline
• Review the basic principles behind photon production through Compton back-scattering.
• Discuss the engineering required to actually realize a photon collider.
– Lasers
– Optics
– Interaction Region design
Basic components exist (laser, optics, IR design)Complete engineering design for Snowmass
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NLC - The Next Linear Collider Project
Compton back-scattering
• Two body process
– Correlation between outgoing photon angle and energy
– Maximum energy when the photon is co-linear with the incoming electron
• Proposed by Ginzburg et al. (1982) for producing a photon collider
– Collide a high power laser pulse with an electron beam to produce a high energy photon beam
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NLC - The Next Linear Collider Project
Gamma-Gamma collisions
• Since high energy photons are co-linear with the incoming electron direction they focus to the same spot.
– Lasers are powerful enough to convert most of the incoming electrons
– High energy luminosity is large
• Low energy photons and electrons also travel to the IP and produce a tail of low energy interactions.
• The beam - beam interaction at the IP
– Produces additional low energy beamstrahlung photons
– Deflects the low energy spent electrons.
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NLC - The Next Linear Collider Project
Lasers requirements
• Laser pulses of– 1 Joule, 1.8 ps FWHM, 1 micron wavelength
• One for each electron bunch– 95 bunches / train x 120 Hz = 11400 pulses / second
• Total laser power 10kW
– 2.8 ns between bunches
• Requires:– High peak power ( 1 TeraWatt )
– High Average power ( 10 kW )
– Correct pulse format ( 95 pulses @ 2.8 ns spacing x 120 Hz)
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NLC - The Next Linear Collider Project
Chirped pulse amplification allows high peak power picosecond pulses
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NLC - The Next Linear Collider Project
Diode pumping enables high average powerMatching diode output wavelength to the laser amplifier pump band gives 25% power efficiency
Each array is madeof 5x7 =35 tiles
per array 161 kW
4 pairs of diode arrayslike these are requiredfor Mercury 644 kW
.
diode
v-sp
ring
Si submount
Mo block
Si lensframe
mic
role
ns
55°
Each tile is madeof 23 diode bars
2.3kW
Diode light distribution (green) obtained in a plane normal to the optical axis
7 tiles5 tiles
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NLC - The Next Linear Collider Project
Pulse Format drives the Laser architecture
1J, 1.8ps 2.8ns spacing
120 Hz macro-pulses
12 larger lasers100 J, 10 HzSimple 10 Hz spatial combinerBreak macro-pulse into sub-pulses
100 small lasers1 J, 100 Hzns switches to spatially and temporallyCombine sub-pulses to macro-pulse
ZDR 1996 New Mercury option
95 pulses
…...
NLC bunch format
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NLC - The Next Linear Collider Project
Goals:• 100 J • 10 Hz• 10% electrical efficiency • 2-10 ns• Bandwidth to Compress to 2 ps
vacuum relay
gas-cooledamplifier head
Injection and reversor
Architecture: - 2 amplifier heads - angular multiplexing - 4 pass- relay imaging - wavefront correction
front end
The Mercury laser will utilize three key technologies: gas cooling, diodes, and Yb:S-FAP crystals
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NLC - The Next Linear Collider Project
Wide band amplifier allows polychromatic components of the pulses to be linearly to amplified. Subsequent re-compression gives short, separated pulses.
(300 nsec)
70-00-0800-6274
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NLC - The Next Linear Collider Project
Appropriate spectral sculpting of the input pulse can lead to a linearly chirped gaussian output pulse (2 psec stretched output pulse case)
RJB/VG 3-Oct-00 short Pulse Mercury Laser
Extraction Pulse Temporal Profile
0.0E+00
5.0E+09
1.0E+10
1.5E+10
2.0E+10
2.5E+10
3.0E+10
3.5E+10
4.0E+10
-8.E-09 -6.E-09 -4.E-09 -2.E-09 0.E+00 2.E-09 4.E-09 6.E-09 8.E-09
(sec)
(W)
Pass 4 (output)Pass 3Pass 2Pass 1Input Pulse
Normalized Emission Line and Saturated Gain for Yb:S-FAP
00.10.20.30.40.50.60.70.80.9
1
1035 1040 1045 1050 1055 1060
nm
Input Pulse Temporal Profile
0.0E+00
1.0E+06
2.0E+06
3.0E+06
4.0E+06
5.0E+06
6.0E+06
7.0E+06
8.0E+06
9.0E+06
-8.E-09 -6.E-09 -4.E-09 -2.E-09 0.E+00 2.E-09 4.E-09 6.E-09 8.E-09
(sec)
(W)
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NLC - The Next Linear Collider Project
We are developing diode-pump solid state lasers as the next-generation fusion driver - Mercury will deliver 100 J at 10 Hz with 10% efficiency.
Mercury Lab
Pump Delivery
Diodes Gas flow and crystals
Heliumgas
Slabmetalvanes
Channelsection
Diffusersection
Nozzlesection
Edge claddingWindow
Gas flowconcept
Diode array capable of 160 kW
Yb:S-FAPcrystals
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NLC - The Next Linear Collider Project
Diode requirements
NlasersEnergy / pulse
upper12
100Joules
0.510 3 sec2.5MW $24M
w/ 100% contingency@ $5 / Watt
Total peak diode power
Average PowerTotal Power Required
Tot
15 kW
0.1150 kW
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NLC - The Next Linear Collider Project
Tesla bunch structure
• 1 millisecond is the laser amplifier upper state lifetime– Tesla must produce 30 times as many pulses on that timescale
• Since most laser power goes unused they are investigating– Multipass optical cavities
– Ring lasers
• No baseline design in TDR
TESLA-500NLC-500H
B ns337
2.8/1.4
NB
282095/190
f Hz5
120
z m300110
N 1010
2.01.5/0.75
Tesla bunch structure is very differentMajor impact on Laser Architecture
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NLC - The Next Linear Collider Project
Optics and IR
• Optics requirements
– Keep accumulated wave-front aberrations small
– Prevent damage to optics from high power pulses
• All regimes; ps, 300 ns, continuous
– Prevent accumulation of non-linear phase aberration
• Vacuum transport lines
• Reflective optics - transmissive optics only where necessary
• IR/Optics integration
– Optics must be mounted in the IR
– All hardware required to accomplish this must not:
• Interfere with the accelerator
• Degrade the performance of the detector
• Generate backgrounds
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NLC - The Next Linear Collider Project
Focusing mirrors - tight fit
• Essentially identical to e+e- IR
• 30 mRad x-angle
• Extraction line ± 10 mRadian
• New mirror design 6 cm thick, with central hole 7 cm radius.– Remove all material
from the flight path of the backgrounds
LCD - Large with new mirror placement
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NLC - The Next Linear Collider Project
Compton Backscattering
• After backscattering the bunch contains both high energy photons and electrons.
• Angular spread photons ~ 1/– Micro radian at 250 GeV
• 63% Conversion efficiency
• Low energy tail due to electrons scattering more than once.
Photons
Electrons
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NLC - The Next Linear Collider Project
Disrupted Beam
• High Energy photons means low energy electrons.– Large beam-beam deflection
– Large rotation in solenoid field
• Requires extraction line aperture +/- 10 milliradians
• Leads to increase in crossing angle to avoid conflict between final quadrupole and extraction line.
• Zero field extraction line, no optics.
e+e- IRIR
Chargedparticles
e+e- IRIR
Chargedparticles
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NLC - The Next Linear Collider Project
IR Background changes from e+e-
• Increased disruption of beam, Larger extraction line 10 milliradians extraction line
• Crossing angle increased to 30 milliradians to avoid conflict with incoming quad. Should be reduced to minimum when final design of quad is known.
– First two layers of SVX now have line of sight to the beam dump
• Fluence of neutrons 1011 /cm2/year
• Need rad hard SVX
• Higher rate of qq, minijets– Currently evaluating in pythia
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NLC - The Next Linear Collider Project
Accelerator differences
• None needed - Some desired
– Rounder beams
• Relaxes requirements on beam stabilization
• Increases luminosity by factor 2
– More bunch charge, fewer bunches
• Most laser power unused no cost for increased bunch charge
• Fewer bunches, more time between bunches
– Laser architecture easier
• Halving the number of bunches and doubling the bunch charge increases luminosity by factor 2
– e-e- running
• Electrons are easier to polarize
• Reduce e+e- physics backgrounds
• Reduce beamstrahlung photons
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NLC - The Next Linear Collider Project
New Final Focus
• Maximally compatible with e+e- running.
• One new quadrupole after the big bend.
• Spot size 15nm x 60 nm.
• Luminosity increase of a factor ~2.
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NLC - The Next Linear Collider Project
Increase bunch charge
• Lasers prefer bunch spacing of 2.8 ns– Current 190 bunch 1.4 ns machine parameter sets are not optimal
• Tor Raubenheimer provides optimized machine parameters for – 95 bunches, 2.8 ns spacing
– All other parameters as per NLC-A
– Twice the bunch charge
In the high energy peakthe luminosity is now ~4 times higher than for the standard
machine parameters
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e-e- running
• Easy (sort of)– Changeover requires rotating all quads in one arm of the linac
• Order 1 month required
– Polarized electron production needed in the positron injection complex with positron target bypass
• The base e-e- luminosity is down a factor of 3 from the e+e- luminosity. The beam beam attraction become repulsion.– Beam-beam interaction has no effect of high energy peak
– Improved polarization increases luminosity in the high energy peak
– Most ee backgrounds reduced by a factor 3
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NLC - The Next Linear Collider Project
Realistic luminosity spectrum
• For 120 GeV Higgs on-peak running
• Polarization control enhances spin-0 and suppresses spin-2– Higgs is spin-0
– Dominant, bb, background is spin-2
• bbg breaks the suppression
• Expect ~5400 Higgs / Year
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NLC - The Next Linear Collider Project
Benchmark Higgs mode
• For new machine parameters and round beams– ~5000 Higgs / year
• Evaluating Higgs @– 120, 140, 160 GeV/c mass
– bb, WW, ZZ modes
• UC Davis students evaluating– chargino pairs
– e Lightest SUSY partner
Still plenty of physics modes to be evaluated
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NLC - The Next Linear Collider Project
Ongoing Physics efforts
• Groundswell of interest in • NWU and FNAL physicists have organized an international workshop on gamma-gamma interactions @ FNAL, March 14-17.– http://diablo.phys.nwu.edu/ggws/
• parallel session @ JHU LC– http://hep.pha.jhu.edu/~morris/lcw
• session at Snowmass– http://snowmass2001.org
Virtuous circle
Missing Monte Carlo evaluations of physics mode analyses
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NLC - The Next Linear Collider Project
Machine Optimization
• Basic design of photon collider exists.
• Detailed choices about machine configuration must be driven by physics analyses.– How important is electron polarization?
– Must the low energy tail be suppressed?
– Is it important to do Higgs runs on peak or can we take advantage of higher luminosity in the tail while running at max energy for SUSY / new physics searchs.
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NLC - The Next Linear Collider Project
Conclusion
• Livermore is proceeding with a complete engineering design of a photon collider for Snowmass
• No show stoppers have been found for either the laser technology, optics or the IR integration
All enabling technologies existTask is mainly engineering now