ilc bcd crossing angle issues g. a. blair royal holloway univ. london ecfa ilc workshop, vienna 14...

ILC BCD Crossing Angle Issues

G. A. Blair

Royal Holloway Univ. London

ECFA ILC Workshop, Vienna

14th November 2005

• Introduction• BCD Crossing Angle Rankings• Discussion

ECFA Workshop, Vienna G. Blair, RHUL 2

The sequence of beamline sections in the baseline optics is the following: Linac• beam emittance diagnostics and coupling correction section• tune-up and emergency extraction beamline,• beam switch yard, • upstream polarization diagnostics section, • betatron collimation, • energy collimation, • upstream energy spectrometer, • final focus proper with secondary clean-up collimation and with tail-folding octupoles, • the final doublet, • extraction beamline with downstream energy and polarization diagnostics, • beam dump.

Beam Delivery System: Base-line Configuration Document

A. Seryi et al.Discussion of version as of 11 Nov 2005


The baseline configuration for the case of two IRs consists of • two Beam Delivery Systems with crossing angle

20mrad and 2mrad• two detectors, • two independent and longitudinally separated IR halls

While the group has consensus on the baseline for the case of two IRs being 20/2mrad configuration, discussion for single IR case is ongoing.

Either 20mrad or 2mrad could be a candidate for a single IR.

Additional alternatives:Alternative1: 2 BDS, 20/2 mrad, 2 detectors

in single IR hall @ z=0Alternative2: 1 IR/BDS, 2 push-pull detectors


• 0 mrad (“head on”) • 2 mrad• 10-15 mrad• 20 mrad

Ranking of BDS Configurations

Rank 1 - directly affecting energy and luminosity reach, background, and precision measurements of beam properties

Rank 2 - may affect energy, luminosity and background indirectly, e.g. via reliability of operation (integrated luminosity):

Rank 3 - affecting only cost, difficulty of R&D and difficulty of the design:

Alternatives:


Detector Integrated Dipole

B

Anti-DID

DID

• DID ‘good’ for upstream polarimetry, ‘bad’ for downstream backgrounds


Rank 1• Luminosity reach (disrupted beam)

– best 14 and 20mr, worst 2mr and head on• Background (pairs)

– best head-on, 2mr and 14mr, worst 20mr • Flexibility of extraction optics and possibility of downstream diagnostics

- best 20 and 14mr, then 2mr, worst head-on • Hermeticity & min veto angle –

- best head-on and 2mr, then 14mr, worst 20mr • Losses and background conditions in downstream diagnostics

– best 20 and 14mr, then 2mr, worst head-on • Losses in extraction affecting IR background

– best 20 and 14mr, worst 2mr and head-on


Rank 2• Parasitic crossings

– best 20,14,2mr, worst head-on • Crab-crossing

– best head-on, then 2mr, then 14mr, worst 20mr

• Integration of fast feedback hardware into FD – best 20 and 14mr, then head-on, worst 2mr

• Vertical orbit correction in IP – best head on and 2mr, then 14mr, worst 20mr

• Tracking, in particular TPC operation and calibration – best head on and 2mr, worst 14 and 20mr


Rank 2 ctd

• Radiation in solenoid field – best head on and 2mr, then 14mr, worst 20mr

• Extraction line clearance for beamstrahlung photons

– best 20 and 14mr, worst head-on and 2mrad

•Photon losses (beam halo) in FD, direct sight to vertex – best 20,14 and head-on, worst 2mr

• Extraction devices affecting Machine Protection System – best 20,14, then 2mr, worst head on

• Extraction devices affecting collision stability – best 20,14 & 2mr, worst head-on


Rank 3

• Difficulty of final doublet magnets – best 20 and 14mr, then head-on, then 2mr

• Length of extraction line – best 20 and 14mrad, worst 2mr and head on

• Difficulty of final doublet integration in detector – best 20, 14mr and head on, worst 2mr

• Special extraction magnets – best 20 and 14, then head on, worst 2mr


Other physics programmes

• Compatibility with gamma-gamma – best 20mr, worst head-on, 2mr, 14mr

• Compatibility with e-e- – best 20 and 14mr, then head-on, worst 2mr

• Compatibility with multi-TeV– best 20mr and 14mr, worst head on and 2mr


The ILC BDSis being designed to be optimal up to 500GeV CM (1TeV CM in upgrade). Realizing that the question of multi-TeV upgrade goes much beyond the scope of the working group, the group suggests that serious consideration need to be given by the whole community to studying the advantages and disadvantages ofnot precluding the multi-TeV compatibility.

-- crossing angle about 20mrad required -- horizontal bend between high energy end on the linac and beam delivery should be less than 2mrad, zero for vertical -- strongly prefer laser straight linac tunnels -- provision to add tunnel alcoves every 600m to house a drive beam return loop and 2MW drive beam dump -- strongly prefer ground motion to be no worse than model A or B -- surface space 1200x250m in IP region to house the drive beam generation complex -- provision to connect to power grid with capacity 450MW -- main beam dumps for 20MW, very similar to ILC

Multi-TeV Issues


Also Addressed in the Document:

• Specific R&D required for the various options• Overview of the BDS and its subsystems• Overview of beam diagnostics systems

Report will be available from the www.linearcollider.orgwebsite


Questions:

• Is the DID an issue for the detector; field map etc.?• “High Lumi” options – energy spectrum vs. luminosity• What level of effective lumi-cut at low angle can we accept?• Compatibility with other programmes; will cost force us to 1 IR for much of the early ILC programme? If so, which crossing angle?• Note – most of the discussion has centred on machine issues; are there any other physics drivers we have forgotten?• Anything else?

Report will be available from the www.linearcollider.orgwebsite


Summary

• The BDS BCD document represents an enormous amount of work by a select and manpower-limited team• Optics design is now being complemented by full simulations• This work is just starting and the workload will increase• Although nothing is set in stone, if full CDR parameters are to be defined by end 2006, it is possible that teams may have to limit their scope in the near future.• It is important the physics community is fully involved in this key discussion.• The BCD will be finalised in GDE meeting 7-9 December; please input any comments now.• We need a base-line that we can all support and build on.

ilc bcd crossing angle issues g. a. blair royal holloway univ. london ecfa ilc workshop, vienna 14...

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