Transcript NLC
NLC - The Next Linear Collider Project Interaction Region Optical and Optomechanical Design Ken Skulina/LLNL Snowmass 2001 – The Future of Particle Physics Snowmass CO, 6 July 2001 Contributors: David Asner, Steve Boege, Paul Bloom, John Crane, Jim Early, Jeff Gronberg, Scott Lerner, Steve Mills, Lynn Seppala 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. NLC - The Next Linear Collider Project Agenda: •Introduction to the optical system •Optomechanical packaging into the Interaction region •Engineering issues The conceptual design is a “snapshot in time”. It is meant to help further detailed design and define interfaces NLC - The Next Linear Collider Project Lets understand where we are in the system: Ti-sapphire oscillator EO switch Grating Stretcher OPA Pre-amp Beam Steering and Transport Detector Interaction Region Mercury Amplifiers Grating Compressor Controls Timing Diagnostics Accelerator Interface NLC - The Next Linear Collider Project All Laser light generation occurs remotely from the IR NLC - The Next Linear Collider Project The laser light and charged particles collide at 15 mrad NLC - The Next Linear Collider Project Optical Design Requirements •Two foci, separated by 1 cm. •~1 times diffraction limited. •Ability to handle high peak power laser light. •Near co-linear laser and electron beam propagation. •Spot size 10 m diameter. •Pathlength control on return leg. •Ability to rotate polarization on return leg. These requirements are met using: •Two Schwarzchild focusing systems. •All reflective optics (except waveplate). NLC - The Next Linear Collider Project The interaction region is at the center of all detectors Hadron calorimeter Magnet EM calorimeter Muon chambers Tracker IR (including vertex detector) NLC - The Next Linear Collider Project The IR is surrounded by other detector subsystems s Exploded views help determine physical interfaces and assembly methods NLC - The Next Linear Collider Project We Will Be Packaging the Following Optical Train 15:47:27 Optics & beampath Optics only Side view of optics and beampath NLC - The Next Linear Collider Project Several competing requirements for the focusing optics must be met •Laser beam must be nearly co-linear with the electron beam •Electron beam must pass through the final focusing optic •Conversion efficiency goal determines photon number density •laser pulse energy then proportional to spot size ~(f#)2 •want minimum f# on focusing optic •Laser beam and electrons must simultaneously be at conversion point •Length of laser pulse (2ps) must be similar to electron pulse •Depth of field ~(2f#) as long as laser pulse gives minimum f# Optimum f# for optics ~f7 NLC - The Next Linear Collider Project The first packaging task is to accommodate the electron beam paths Electron beams go through The focusing optics NLC - The Next Linear Collider Project A central hole in the two end mirrors allows charged particle and background transport •Final focusing optic must be closely aligned to the electron beams •beam must pass through center of optic •Hole in primary optic for electron beams also allows passage of most of the background particles Incoming electron beam Exiting electron beam NLC - The Next Linear Collider Project A wireframe model lets us see the laser light and electron beam paths. Focusing optic with Central hole Electron beam entrance and exit NLC - The Next Linear Collider Project 2D IR Region Layout (incoming leg) 1 micron laser transport IR beampipe Vacuum enclosure(s) mask QD0 NLC - The Next Linear Collider Project 2D IR Region Layout (reflected leg) Silicon plate detectors QD0 mask Vacuum enclosure beampipe NLC - The Next Linear Collider Project Polarization options •The polarization of the laser beams can be controlled to allow either parallel of crossed polarization in the collisions •Straight reflection of the linear polarized laser beam to interact with the second electron beam results in parallel polarizations •For crossed polarization a waveplate is placed in the beampath of the reflected laser beam •Insertion of a waveplate is a quick, remotely controlled operation. NLC - The Next Linear Collider Project Modeled Optical Performance Figure of Merit ( X , Y ) WAVEFRONT ABERRATION NLC Laser Focusing Optics, Tilted Schwa Waves 0.0000 -0.125 120 m < 13 m (1.6 TDL) > 0.93 < /4 @ 1053 nm Rayleigh Depth of focus Beam diameter at focus Strehl ratio P-V wavefront error Y-FAN 0.25 1.00, 1.00 RELATIVE FIELD ( 0.06 O, 0.06)O X-FAN 0.25 1 -0.250 Field = (0.0573,0.0573) Degrees Wavelength = 1064.0 nm Defocusing = 0.000000 mm -0.25 -0.25 Worst case P-V wavefront error at focus is /4 (=1053nm) NLC - The Next Linear Collider Project Several features are unique to a collider IR •Cylindrical carbon fiber outer tube •Vacuum boundary with transition from thick cylinder to thin beampipe. •Sections of “strongback” for optical support •Thermal Management NLC - The Next Linear Collider Project Finite Element Analysis shows a benign mechanical environment Max Static sag ~50 microns Static sag at focus ~25 microns 1st fund freq ~70Hz Anticipated vibration < .05 m rms at focus @ 10-10 g2/Hz 1-200 Hz NLC - The Next Linear Collider Project Optical Train-IR buildup contained within the carbon fiber-honeycomb tube The design intent was to have the IR self-contained (assembled and rough aligned) within a low z tube. NLC - The Next Linear Collider Project The entire carbon fiber tube is inserted on a rail-pillow block system Carbon fiber tube rail Pillow-block NLC - The Next Linear Collider Project Thermal management •Absorbed 1 micron light will be re-radiated. •Use thermally stabilized optical strongbacks •Use chill plates behind optical mounts. •Constant temperature water (+-0.1C) can supply this thermal control NLC - The Next Linear Collider Project Current applications will be modified to use UHV inchworm actuators Waveplate rotation stage Tip/tilt mirror stage •A vendor has been identified that can deliver motor operation in a ultra-high vacuum, 3T environment NLC - The Next Linear Collider Project Optomechanical Design Drivers/Requirements/Constraints Drivers/Requirements/Constraints Result 1 micron laser pulses, 1.8 ps wide, 1.4 nsec spacing, 100 pulses per train (120 Hz) Vacuum transport. Optical coatings at ~1J/cm2 damage threshold, 99.95% reflectance. High quality coatings Optical system of ~f/7.5 Optical train located within IR; Structure must also act as an optical “strongback” Laser Beam retroreflected for two passes in two conversion points Independent alignment Independent polarization control of either laser beam. Added waveplate on return leg 10-9 torr at conversion points Vacuum pumping near IR (not unique to ) 3 Tesla (baseline) Magnetic Field (design to 5 Telsa) Limited to piezoelectric inchworm motors Minimize material between IR and first detector surfaces Transition from area containing optics to IR. NLC - The Next Linear Collider Project The control system still needs to be designed •Pointing and centering required •Diagnostic for collision with electrons NLC - The Next Linear Collider Project Conclusions •Current Mercury Laser Technology can meet Gamma-Gamma collider needs. •All major Interaction Region design requirements can be met.