Advanced Collimator Schemes for the NLC

1
Advanced Collimator Schemes for the NLC

• Josef Frisch, Knut Skarpaas, Tom Markiewicz

Josef Frisch
2
Motivation for Advanced Collimators

• The beam in the Linac downstream of the damping
  rings has sufficient energy density to destroy
  any physical object.
• Damage from direct interception / energy loss
• Damage without interception from wall current
  heating
• The collimation system must either greatly
  magnify the beam, or use an advanced
  collimation system.
• Large magnifications generally require tight
  component tolerances and large system sizes.
• Advanced collimators would ease technological
  constraints, and reduce costs for the collimation
  system.

3
Types of collimators

• Standard Solid metal jaws which cannot be
  re-used after damage.
• Consumable Can be re-used a limited number of
  times after damage
• Rotating Wheels, Moving jaws, Metal tapes
• Repairable Can be repaired in situ after damage
• In vacuum collimator factory solidifying metal
• (primary focus of this talk)
• Indestructible Cannot be damaged by the beam
• Liquid metal jets, Lasers.
• Nonlinear Optics Use Octopoles to remove tails
• Can be combined with any of the above schemes

4
Spoiler / Absorber Scheme

• Spoilers
• Thin, lt 1 radiation length
• Greatly increase phase space of beam tails
• Absorbers
• Thick, water cooled structures
• Absorb spoiled beam tails
• Handle high deposited energy, but lower energy
  density

5
Advanced Collimator Technologies

• The spoilers are the most difficult part of the
  system due to the high beam energy densities
• Consumable Will be discussed next in this talk
• Repairable Will be discussed later in this talk
• Liquid metal jets
• Some work at Budker Institute of Technology
  (Russia)
• Primary problem is meeting micron level jet
  surface stability
• Laser collimation
• Required laser power is much too expensive
  (gt100M each spoiler) with present day technology

6
Consumable Collimators

• Design collimation system so that normal beam
  halo is not damaging, but errant pulses can
  damage the spoilers
• When the spoiler is damaged, move to a new
  undamaged location
• Various mechanical configurations
• Wheels, bars, tapes
• Key technologies High precision (micron)
  mechanicals under conditions of
• Ultra high vacuum
• High radiation levels MRad/Hour
• Primary use Protection collimation.
• Collimator will only be damaged by occasional
  errant pulses.
• Damaged portion of collimator is moved away from
  beam

7
Consumable Collimator Concepts
8
Repairable Collimator (Solidifying Metal)

• Essentially a collimator factory in the beam
  line.
• Freeze liquid metal onto a rotating wheel.
• Roll the surface flat with rollers.
• The solidified surface is destroyed by the beam,
  and then reformed
• Primary technical issues
• Surface quality of rolled surface
• Adherence of solidified metal to wheel and
  rollers
• Corrosion by the liquid metal
• Liquid metal outgassing in UHV
• Temperature control of rotating devices in UHV
• Idea is rather Rube Goldberg in nature
• If it works, it greatly simplifies the
  collimation system

9
Materials for Solidifying Metal Collimator

• Want to use pure elements to avoid complex phase
  changes during solidification (could result in a
  poor surface)
• Want materials with low melting points (lt350ºC)
• Need materials with low vapor pressure at their
  melting point. (System is being used in UHV)
• Want materials with relatively short radiation
  lengths
• Want materials which are ductile when solid
• Elements which meet these requirements
• Indium Best ductility, lowest melting point,
  possible adherence problems
• Tin Good ductility, better adherence properties
  than Indium
• Lead Much industrial experience with liquid lead
• Bismuth Similar properties to Lead, lower
  melting point

10
Solidifying Collimator Concept
11
Advanced Collimator RD Plan

• Test materials damage limits
• Electron beam coupon tests (underway)
• Laser multi-shot damage tests material fatigue
  issues
• Tests done 5/01 85K(Special Projects) 300K
  (Beam delivery)
• Test rotating consumable collimator
• Construct UHV mechanicals, Measure surface
  position stability
• Prototype 5/01 184K (Beam delivery)
• Test solidifying metal repairable collimator
• Initial tests in an inert atmosphere (to simplify
  mechanical design)
• Measure smoothness of solidified, rolled surface.
• Determine potential of this technology
• Technology demonstration by 8/01, 150K RD
  budget (special projects)
• Conceptual design of final collimation system
  11/01

12
Advanced Collimators Summary

• Materials damage constrains the design of the
  collimation system
• Cost and complexity could be reduced by using
  consumable or repairable collimators
• RD will be done during CDR to test various
  advanced collimator designs.