1. ILC BDS Collimation Optimisation and PLACET simulations Adina Toader School of Physics and Astronomy, University of Manchester & Cockcroft Institute, Daresbury Laboratory The University of Manchester Outline of talk Introduction to collimation optimisation PLACET Introduction & Capabilities Examples: CLIC BDS Relevance to collimation Results with PLACET Future plans

2. Collaborators Roger Barlow University of Manchester Roger Jones Adriana Bungau Deepa Angal-Kalinin Daresbury Laboratory, ASTEC Frank Jackson Jonny Smith Lancaster University Daniel Schulte CERN Geneva Andrea Latina Giovanni Rumolo

3. WP1 BDS Lattice Design and Simulation Began using PLACET as general tool for collimation- related simulations Recently used to complement collimation lattice optimisation by Frank Jackson Preliminary results with PLACET Background

4. ILC BDS collimation performance not good compared to NLC. - phase advances not correct and bandwidth poor Tighter apertures to compensate for poor performance  increased wakefields, emittance dilution. Adjust matching of collimation and final focus optics. - open collimators to reduce wakefields Collimation Lattice Optimisation

5. Phase advance 2006e2006e optimised SP4- SPEX x: 0.38 y: 0.59 x: 0.5 y: 1.0 SP4-IPx: 2.76 y: 2.34 x: 2.75 y: 3.25 2006e Original 2006e Optimised matching quadrupoles SP4 SPEX SP2 Use matching quadrupoles to restore correct phase advances between SP4, SPEX and IP. Multiple solutions available. Choose solution with the best lattice bandwidth. Collimation Optimisation

6. MERLIN BDS halo tracking, “black” spoilers set at nominal collimation depth, uniform halo dimension 50% larger than nominal collimation depth. Clearly improved performance in new lattice. Original 2006e PerformanceNew Performance Plot shows halo profile at Final Double Entrance. The black square is the nominal collimation depth (same population in both halos at FD). 2006 Optimised Performance Tracking Results

7. PLACET Introduction & Capabilities: The program PLACET (Program for Linear Accelerator Correction Efficiency Tests) was initially developed by Daniel Schulte and currently updated by Andrea Latina (CERN) for CLIC (Compact Linear Collider). It is a tracking code for linear colliders which implements: wakefileds, synchrotron radiation emission, single or multibunch effects, lattice errors, ground motion, the earth’s magnetic field and beam jitter. Interfaced in PLACET there is GUINEA-PIG – a beam-beam interaction code to simulate beam-beam collisions and calculates the luminosity.

8. Example of PLACET tracking along the CLIC BDS Horizontal (left) and vertical (right) phase space portraits at the end of BDS including or not including the collimator wakefields in the tracking *. CLIC Luminosity reduction curves versus vertical collimator offset *. *EUROTeV-Report-2006-026

9. Relevance of PLACET to collimation optimisation Collimation modifications disturb lattice and may make luminosity more sensitive to errors in quadrupole strength and alignment. Can easily introduce quadrupole strength errors and offsets to check luminosity sensitivity in PLACET.

10. Results with PLACET Wakefield results: The y kick varies with the position along the bunch - the tail is more affected than the head. Plots show qualitative agreement with MERLIN.

11. Results with PLACET Tracking original ILC2006e lattice: Plots of beam size at IP in x, x’, y, y’ agreeing with designed values (top) and of beam distributions in x and y (bottom). x (µm)y (µm) y’ (µrad)x’ (µrad) Designed values PLACET values σ x’ (nrad) σ y’ (nrad) σ x (nm) σ y (nm) 31.2 14.3 655 5.72 31.2 14.3 655 5.72 Number of particle

12. Future Plans Collimation optimisation led to improved halo tracking performance. Use PLACET to check optimised lattice sensitivity to magnet errors. Also we can study the effect of the collimator wakefields. PLACET is useful to calculate the luminosity deterioration due to these effects.