Collimators for the NLC

Special Projects Group and Beam Delivery Group

The NLC requires collimation of very high peak and average current electron beams. The (kilometer scale) length of the collimation system could be substantially reduced if material damage were not an issue. Two basic ideas are being pursued:

• Consumable collimators: These have jaws which can be moved to a new position after damage. This would allow continued operation after damage by an errant beam pulse. Typically the systems are designed to allow 1000 damage locations before requiring replacement.

• Repairable collimators: These use liquid metal or similar technology jaws that can be continuously repaired during operation. This allows use under conditions where the jaws were damaged on every beam pulse. They are considered to be more speculative than the "consumable collimators".

Prototypes of both types of collimators have been constructed, and are being tested. Initial results are promising. 

Spoiler / Absorber scheme: 

Use a "spoiler and absorber" design. The spoiler jaws are thin (< 1 radiation length) and are located close to the beam axis (~50um). Beam halo which hits the spoiler will be given a large transverse energy spread and stopped by the large aperture (~1mm) downstream absorber. Very little average power (few watts) is dissipated on the spoiler, however the high beam intensities can cause damage. High average powers (KW) are dissipated on the absorber but the beam density is too low to cause damage.

Consumable Spoilers

The Bar collimator is too space inefficient, and is no longer being considered. The tape collimator is mechanically complex and physically large. It will only be considered if there is a clear need for a collimator which can tolerate more damage locations. 

Repairable Spoilers

Several concepts for repairable spoilers are being considered. At the present time, the most promising designs use liquid metal films which are continuously re-formed in the vacuum system.

The design uses a rotating drum partially immersed in liquid metal. As the drum rotates it picks up a film of liquid metal. This film solidifies on the (cooled) drum. The surface finish is improved by a secondary finishing roller. Rollers are used in pairs (only one side shown):

Collimator slides from a meeting in May 2003  collimator5_3.pdf collimator 5_3.sxi   (Note sxi is in Open Office Write format).

Mac Meeting Talk Mac_collimator_2000.pdf

Talk on liquid metal collimator work as of 1/11/2000. Talk.pdf

Talk at Daresbury lab 6/30/00 Talk.pdf Talk.fm 

Old Documents:

Power point presentation collimation.ppt

Outline of collimation R+D plan: AllCollimator.pdf

Collimator CD1 talk collimatorcd1.ppt

Ideas for simulations to be done at LLNL LLNLsims.pdf    LLNLsims.fm

Description of work to be done at SLAC and at the Budker institute for Nuclear Physics in Novosibirsk Russia (collimatortasks.pdf).

Talk, 10/29/99   CollimatorTalk.pdf    CollimatorTalk.fm

Talk May 30, 2000 at fermilab  talk.pdf talk.fm

Page last updated 05/09/2003 Josef Frisch frisch@slac.stanford.edu