Mechanical Design of the 10kW FEL Upgrade Optical Systems 121405

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Mechanical Designof the10kW FEL Upgrade Optical
Systems12/14/05
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OUTLINE

• Free Electron Laser (FEL)
• Why build it?
• How does it work?
• Overview of JLAB FEL Optical Systems
• Major components
• High Reflector (HR), wiggler, alignment viewers,
  output coupler (OC), insertable mirrors,
  collimator system, transport to labs
• IR Optical Cavity
• Specification, OC assembly, challenges,
  improvements
• IR Optical Transport
• Insertable mirrors and beam dump
• Collimator System
• Transport Turning Mirror Cassettes
• Introduction to UV Optical Cavity
• New challenges, design solutions
• Questions

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FREE ELECTRON LASER

• Why build it?
• Broad range of applications
• Potential defense applications if scaled to
  higher powers
• Polymer and metals surface processing
• Micromachining
• Potential applications in biological sciences
• Facility spin-off technology Terahertz light
• Applications in enhanced medical and security
  imaging
• How does it work?

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Overview of JLab FEL Optical Systems
Insertable Mirrors, Collimator
Source
Transport to Labs
Wiggler
Output Coupler
IR Optical Cavity 32.042m
LINAC
High Reflector
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IR Optical Cavity

• Highlights from Initial Specification
• Ability to switch between four mirrors in vacuo
  in 20 min
• Allows for operation at various wavelengths
• Optics must be cooled to remove absorbed heat
• High reflector backplane cooled
• Output coupler edge cooled
• High reflector optics must be deformable to
  optimize lasing and correct figure for thermally
  induced distortion
• Optics must be gimbaled to allow alignment in
  pitch and yaw
• Angular resolution required 200 nano-radians (
  0.000015 degrees )
• High reflector optics must be adjustable in the
  beam direction to allow changes in cavity length
• Cavity vessel design is constrained by electron
  beam height and upstream chicane

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IR Optical Cavity
Output Coupler Assembly
Bellows sealed rotary feedthrough driving
vertical translation stage
Purge port
Top hat
Access to de-couple rotary feedthrough
NEG pump port
27in wire seal flange
Transmitted photon beam
Viewports
Instrumentation Feedthroughs
Intra-cavity photon beam
Ion pump port
Fluid feedthrough
Roughing pump/ vac gauge port
Vessel Dimensions Diameter 24in Height 60 in
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IR Optical Cavity
Output Coupler Assembly Cont

• Foundation Alignment of Internals
• Internals are bolted to plates that are welded to
  the side of the vacuum vessel
• Simple 3 point scheme used for alignment
• Jacking bolts at base used to adjust in-plane
  rotation

Foundation plates
Jacking bolts
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IR Optical Cavity
Output Coupler Assembly Cont

• Internals
• Four mirrors independently mounted in pitch
  holders (two 4in, one 3in and one 2in)
• Single ganged yaw holder mounted on horizontal
  translation stage (The big C)

Flexible coupling
Vertical translation stage (Thomson rails with
stainless ball bushings)
Horizontal translation stage (Thomson rails with
stainless ball bushings)
Cooling line and instrumentation service chain
Lead screw and bearing block
Big C
Full step resolution of translation
stages Vertical 1.3?m Horizontal 27nm
Cooling lines
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IR Optical Cavity
Output Coupler Assembly Cont

• Mirror holder angular adjustment scheme

Yaw mounting holder
Pitch mounting holder
Micropusher with PZT mounted on tip produces
pitch rotation
Pitch flex pivot
Full step resolution of micropusher 27nm PZT
Resolution 0.01nm PZT Stroke 16?m Pusher
thrust 25lbf
LVDT position sensor with compression spring
mounted on tip to produce restoring force
Yaw flex pivot
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IR Optical Cavity
Output Coupler Assembly Cont

• Cooling water and instrumentation wire service to
  internals
• Commercial conveyer chain modified to support
  flexible cooling tubes and instrumentation wires
• Fittings are Swagelok VCR metal face seal
• Bellows used in cooling lines to reduce loads
  transmitted to optic

Cooling tube jumper
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IR Optical Cavity
Mirror Holders

• Output coupler
• Edge cooled optic holder
• Vacuum brazed assembly
• Optic brazed into holder
• Material chosen to closely match optic CTE to
  reduce distortion

Anti-twist VCR fittings
Bellows
Flow channel
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IR Optical Cavity
Mirror Holders

• High Reflector
• Deformable mirror holder
• Vacuum brazed assembly
• Optic bonded to face of deformer with vacuum
  grade conductive epoxy

VCR fittings
Radial flow diversion channels
Optic
Film heater bonded to back plate
Flow Inlet
Flow Outlet
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IR Optical Cavity
Output Coupler Assembly Cont

• Scattered light absorber
• Designed to reduce vacuum pressure spikes caused
  by stray light striking surfaces
• Also reduces mirror steering caused by absorption
  of scattered light

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IR Optical Cavity
High Reflector Assembly
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IR Optical Cavity
Output Coupler Assembly
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IR Optical Cavity
Output Coupler Assembly
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IR Optical Cavity
High Reflector Assembly
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IR Optical Cavity
High Reflector Assembly
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IR Optical Cavity
Performance
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IR Optical Cavity
Alignment Viewers

• Ultrviewer is used to align optical cavity
  mirrors
• Exceeds angular repeatability spec of 50?rad

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IR Optical Transport
Insertable Mirrors Beam Dump Collimator
assembly
Collimated laser transport to labs
Collimator can 2
Insertable mirror
Collimator can 1
Optical beam dump
Laser
Insertable mirror
Diagnostics breadboard
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IR Optical Transport
Collimator assembly

• Can1
• Eight elliptical backplane cooled mirrors mounted
  on translation stage
• Can2
• Four 4in deformable mirrors
• Design is very similar to the high reflector

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IR Optical Transport
Collimator can 1 assembly

• Internals
• Heavy duty drawer slides allow easy access to
  mirrors
• Three bushings on translation stage engage pins
  mounted in the vessel to provide position
  repeatability

Drawer slide
Alignment bushing
Access to motor driving translation stage
Cover flange
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IR Optical Transport
Collimator can 2 internals
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IR Optical Transport
Collimator can 1 assembly (Fabricated and
assembled by our machine shop)
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IR Optical Transport
Turning Mirror Cassettes

• Used to transport laser to experimental labs on
  2nd floor
• Design is similar to collimator can 1
• Includes gimbaled mirror holders

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Introduction to UV Optical Cavity
Source
Insertable Mirrors Collimator
LINAC
Transport to Labs
Output Coupler
UV Wiggler
UV Optical Cavity 32.042m
High Reflector
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UV Optical Cavity
Specification

• Requires a cryo cooled output coupler!

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UV Optical Cavity
UV Mirror Gimbal

• Initially designed to replace the troubled
  commercial kinematic mounts used in the demo
  machine and the IR upgrade temporary transport
  system (transport lite)

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UV Optical Cavity
UV Output Coupler

• Highlights
• Uses the same vessel (with a few mods) as the IR
  design
• Internals mounting scheme and translation stages
  are also consistent with the IR system
• Mirror holders required redesign to accommodate
  cryo cooled mirror mount
• New low inertia mirror mount is used to enable
  active stabilization (a must for the UV system)
• A Umbilical cord is used to reduce the gas load
  from wire insulation
• Eliminated long stroke micropushers

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UV Optical Cavity
UV Output Coupler

• Internals

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Questions??