High energy photon - photon collisions can be achieved by adding high average
power short-pulse lasers to the Linear Collider, enabling an expanded physics
program for the facility. The technology required to realize a photon linear
collider continues to mature. Compton back-scattering technology is being
developed around the world for low energy light source applications and high
average power lasers are being developed for Inertial Confinement Fusion.Comment: 3 pages, no figures, Proceedings of the International Workshop on
  Future Linear Colliders, Granada Spain, 26-30 September 201

Gronberg, Jeff

English

arXiv

High energy photon - photon collisions can be achieved by adding high average power short-pulse lasers to the Linear Collider, enabling an expanded physics program for the facility. The technology required to realize a photon linear collider continues to mature. Compton back-scattering technology is being developed around the world for low energy light source applications and high average power lasers are being developed for Inertial Confinement Fusion

Gronberg, J

UNT (University of North Texas) Digital Library

LLNL-PROC-533135Photon Linear ColliderGamma-Gamma SummaryJ. GronbergFebruary 27, 2012International Workshop of Linear CollidersGranada, SpainSeptember 26, 2011 through September 30, 2011Disclaimer  This document was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor Lawrence Livermore National Security, LLC, nor any of their employees makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or Lawrence Livermore National Security, LLC. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or Lawrence Livermore National Security, LLC, and shall not be used for advertising or product endorsement purposes.  Photon Linear Collider Gamma-Gamma SummaryJeff Gronberg ∗Lawrence Livermore National LaboratoryL-050, 7000 East Ave. Livermore, CA, 94550 - USAHigh energy photon - photon collisions can be achieved by adding high average powershort-pulse lasers to the Linear Collider, enabling an expanded physics program forthe facility. The technology required to realize a photon linear collider continues tomature. Compton back-scattering technology is being developed around the world forlow energy light source applications and high average power lasers are being developedfor Inertial Confinement Fusion.1 Physics CaseThe physics case for a high energy photon linear collider has been previously reviewed in [1].While there is a variety of interesting processes, many of the most interesting processesinvolve the direct production of a Higgs boson. The Higgs boson can be produced in photon-photon collisions through a triangle diagram which is sensitive to the existence of chargedparticles of arbitrarily high mass. This single particle production allows for a greater energyreach for the production of supersymmetric Higgs bosons (MSSM H and A) in regions oflow sensitivity at the LHC. Control of the polarization of the Compton photons allows intialstates of definte CP to be created providing a probe of the CP nature of the observed Higgsboson.The photon linear collider also provides an opportunity to search for new physics bysearching for anomalous couplings in double and single W boson production. As well thereis the potential for production of supersymmetric particles in electron-gamma collisions.This would provide a greater energy reach to search for these particles than in the linearcollider.2 Technology RequirementsThe fundamental physics of Compton scattering and the design of a photon collider hasbeen laid out [2, 3]. Compton scattering can transfer 80% of the incident electron energyto the backscattered photons when a 1 micron wavelength laser pulse is scattered from a250 GeV electron beam. A laser pulse of 5 Joules, compressed to 1 ps width and focusedto a diffraction limited spot can convert most of the incoming electrons in a bunch to highenergy photons. An enormous amount of average laser power would be required to provide15,000 laser pulses per second to match the electron beam structure. Since most of the laserenergy goes unused in the Compton process the required energy can be greatly reduced ifthe laser pulses can be recirculated.A design of a recirculating cavity [4] was created in 2001 which takes advantage of thelong inter-bunch spacing in the superconducting machine to recirculate the laser pulsesaround the outside of the detector. Calculations showed that the required laser power could∗This work performed under the auspices of the U.S. Department of Energy by the Lawrence LivermoreNational Laboratory under Contract DE-AC52-07NA273441 LCWS11be reduced by a factor of 300 in this design. Recent studies have shown that a laser withsufficient phase stability to drive such a cavity is probably ahievable with current technologyand would cost in the vicinity of 20 million dollars.Warm RF technology has a different electron bunch structure which precludes use of thelarge recirculating cavity. The small inter-bunch spacing does not allow sufficient time forlaser pulses to travel around the outside of the detector. A concept for a linear collider basedon warm RF systems could be either a single pass system or a much smaller recirculatingcavity within the detector with multiple circulating bunches. A single pass system would stillrequire a prodigous amount of average laser power. Capital costs for such a system would bedriven by the cost of laser diodes to transfer wall plug power to the laser amplifier crystals.The available power saving for a recirculating system would depend on the achievable sizeof the cavity. That would determine how many times a pulse could be reused in a singleelectron bunch train.Implementation of the photon collider option has several requirements for both the de-tector and the electron accelerator. Apertures must be opened in the forward part of thedetector to allow the laser pulses to reach the Interaction Point and be focused a few mil-limeters before the electron beams collide. The electron beam will be left with an enormousenergy spread after the Compton backscatter and a large crossing angle will be required inorder to allow sufficient aperture for the spent beam to be extracted. Finally, the photoncollider option will require its own beam dump design in order to handle the photon beamwhich will have about 50% of the final beam energy.3 Ongoing Developement of Compton TechnologyCompton backscattering for the creation of MeV gamma-ray light sources is a world-wideactivity. The basic techniques of bringing an electron beam and a laser pulse into collision isindependent of the electron beam energy and these facilities are providing vital experience inthe development of these techniques for the linear collider. These facilities are also developingthe technology for recirculating laser pulses which will be critical to achieve a cost effectivesolution for the photon linear collider.Current MeV gamma-ray sources include the ThomX [5] machine at LAL, the LUCX [6]machine at KEK and the T-REX [7] machine at LLNL. The MightyLaser collaboration is de-veloping a four mirror recirculating cavity for the demonstration of Compton backscatteringat ATF [8].4 Future ProspectsThe technology of Compton backscattering and recirculating cavities is being developedfor the applications of MeV light sources, polarized positron sources and beam diagnostics.High average power, short-pulse lasers are being developed for the application of InertialConfinement Fusion. All of these efforts push forward the technical feasibility of a photonlinear collider. While the photon linear collider has always been envisioned as a secondstage to the basic linear collider program there may be advantages to considering it as afirst stage. The photon collider requires an electron linear collider to drive it but it doesnot require positrons and it does not require flat electron beams at the Interaction Point inorder to reduce the beamsstrahlung. This opens up the possibility of creating a first stagelinear collider without a positron source. The creation of a low-emittance RF electron gunLCWS11 2might also create the possibility of eliminating the damping rings in the first stage. Bothwould provide major cost savings. If the Higgs is discovered at LHC and its mass is low itmight also be worthwhile to create a lower energy dedicated photon collider Higgs factoryas a first stage to the linear collider program.References[1] F. Bechtel et al. Nucl. Instrum. Meth. A564 (2006) 243-261.[2] I.F Ginzburg, G.L. Kotkin, V.G. Serbo, and V.I. Telnov JETP Lett. 34 (1981) 491-495.[3] ECFA/DESY Photon Collider Working Group, B. Badelek et al., “TESLA Technical Design Report,Part VI, Chapter 1: Photon collider at TESLA.”, DESY-01-011E.[4] I. Will, T. Quast, H. Redlin and W. Sandner, Nucl. Instrum. Meth. A472, (2001) 79.[5] A. Variola, “The ThomX Project”, Proceedings of IPAC11,http://accelconf.web.cern.ch/AccelConf/IPAC2011/papers/weoaa01.pdf[6] M.K. Fukuda et al., “Status and Future Plan of the Accelerator for Laser Undulator Compact X-raySource (LUCX)”, Proceedings of IPAC10,http://accelconf.web.cern.ch/AccelConf/IPAC10/papers/tupd089.pdf[7] F.V. Hartemann et al. “Overview of Mono-energetic Gamma-ray Sources and Applications”, Proceed-ings of IPAC10,http://accelconf.web.cern.ch/AccelConf/IPAC10/papers/tupd098.pdf[8] N. Delerue et al., “High Flux Polarized Gamma Rays Production: First Measurements with a Four-mirror Cavity at the ATF”, Proceedings of IPAC11,http://accelconf.web.cern.ch/AccelConf/IPAC2011/papers/tupo002.pdf3 LCWS11

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