Manchester Christmas meeting 2006:The ILC interaction region and beyond

Rob Appleby

Happy New Year everyone!

This is my first Christmas meeting…

• I spend a large fraction of my time working on the International Linear Collider (ILC) [What else? Theoretical beam dynamics, LHC]

• The UK is heavily involved in the beam delivery system, which starts from the end of the linac and finishes at the dumps

• A lot of work has been done on the layout of the beam interaction regions (IRs), where the two beams collide…

ILC baseline layout

e- e+

• Baseline (supported by the GDE)

– two BDSs, 20/2mrad, 2 detectors, 2 longitudinally separated IR halls

The baseline design of the IRs

• The baseline design consists of two independent interaction regions, with two independent detectors

• BUT, there is considerable pressure to reduce this to a single IR layout

• Hence, the baseline specifies two alternatives• two BDSs, 20/2mrad, 2 detectors in a single IR hall @ z=0•Single IR/BDS, collider hall long enough for two push-pull detectors

• The next couple of slides take a closer look at the IRs and extraction lines of the two baseline crossing angles

Design features of 20mrad extraction line

Key design featureIncoming and outgoing beams do not see the same magnets

l*=3.51m

9m

optical transfer

SC QD (r 35mm)215 T/m

warm QF (r ~ 10mm)150 T/m

2 mrad

~ 6-7 mrad

to beam diagnostics

2mrad Extraction Line

Key design featureIncoming and outgoing beams share the same magnets. This is a direct consequence of the small crossing angle

• SC super septum quadrupole and Panofsky septum quadrupole designs under study for the first extraction magnets where horizontal separation is limited.

Super Septum QuadrupoleB. Parker

Warm : Panofsky QuadrupoleC. Spencer

What else could we do?

• The choice of 2mrad and 20mrad has emerged from a long (and ongoing) debate

• Other alternatives are– Colliding the beams head-on (tried for the TESLA

project…very hard but not dead yet!)– Pushing the 20mrad down, but still having separate

magnets…gives you 14mrad (this is under study and favoured by our US colleagues)

– 7mrad, 25mrad….all have some advantages

• Finally, if we drop to 1 IR…what do we choose?

Once the beam has been extracted, the show is not quite over1!

1: This is not generally appreciated, even among accelerator physicists!

How do you dump a 20MW particle beam?

A water dump was used at the SLC. It was rated to 2MW but onlyever used to 800kW. This jump to 20MW is considerable

Summary

• The ILC IR baseline has taken a long time to reach the current point, and there is a long way to go.

• Currently the configuration is 2mrad and 20mrad, but the number of IRs and the choice of crossing angle may chance, and is a very contentious point

• Finally, we also need to worry about dumping the charged particle beam – the UK is now taking a strong lead in this aspect of the ILC