Beam Dynamics in Curved ILC Main Linac (following earth curvature) 2006.02.08 K.KUBO This presentation is a summary of two reports in ILC-Asia Note: http://lcdev.kek.jp/ILCAsiaNotes/2005/ILCAsia2005-23.pdf http://lcdev.kek.jp/ILCAsiaNotes/2005/ILCAsia2005-25.pdf

Design and simulation of curved ILC Main Linac All Quad-magnets are aligned along the earth curvature, and accelerating cavities are aligned along the straight lines between quads. (Coordinate change at the middle of each quad) Thin (zero-length) steering magnet is inserted at the middle of each quad. Used SAD for optics calculations, SAD and SLEPT for tracking simulations.

Simulated Two Solutions Strength of steering magnets are set (a) Eliminating beam offset and dispersion at center of every vertically defocusing quad. (b) Making the beam goes through the centers of the all quad-magnets. The initial dispersion ( and ’) is adjusted to minimize the final ‘Linear Dispersion Corrected emittance’

Optics: Old. Not ILC baseline, but not too different Optics: Old. Not ILC baseline, but not too different. FODO Beam energy: From 5 GeV to 250 GeV Acc. cavity: 35 MV/m, 10 cavities/module from 5 GeV to 125 GeV: 2 modules/quad from 125GeV to 250 GeV: 3 modules/quad

“Design” orbit and dispersion of (a) Offset from the curvature.

“Design” orbit and dispersion of (a), near the beginning of linac. The curvature and design orbit. Offset from the curvature. Dispersion

Result of simulation without errors in case (a), using SLEPT. Projected emittance along the linac. Initial vertical emittance: 0=2E-8 m, Initial energy spread: 2.8%, TESLA-TDR wake.

Dispersion along the linac in the case (b) (Initial dispersion is optimized to minimize the emittance growth.)

Projected emittance along the linac. ‘Linear Dispersion corrected’ emittance along the linac.

Definition of Projected emittance and Linear Dispersion Corrected emittance

Simulation including alignment errors and orbit (Kick Minimum) correction Initial normalized vertical emittance: 2E-8 m Initial energy spread: 2.8% Random unknown offset of BPM with respect to quad: 10 micron Random error of BPM(resolution): 5 micron Every quad has a BPM and a steering at its middle. Correction: Steering correction. Minimize additional offset and additional kick” at quads.

Distribution of final projected-normalized emittance. Misalignment of quads and cavities: 300 micron (Total 100 random seeds in each case.) Left: Following Earth Curvature, case (a) Right: Laser Straight Curved (a) Laser straight

Distribution of Linear Dispersion Corrected emittance Misalignment of quads and cavities: 200 micron Left: Following Earth Curvature, case (b) Right: Laser Straight

Vertical position change due to magnet strength error. Calculated by SAD, 100 random seeds. Relative magnet strength error 0.01% (sigma). Relative error of a quad and steering magnet at its middle was set to be the same. Errors of magnets at different locations were set independently. Distribution of y/y of the same data. To make the rms of y/y less than 0.14, the strength error should be less than 0.0025%. (Random 0.14  offset of each beam will make average position offset 0.2  between two beams at IP, which will decrease luminosity about 3%, without beam-beam force.) Required stability: order of 10-5. Very tight but, Relevant only for fast jitter, faster than orbit feedback

Required stability: order of 10-3. Emittance increase due to magnet strength error. Simulated by SLEPT, 100 random seeds. Relative magnet strength error 0.1% (sigma). Relative error of a quad and steering magnet at its middle was set to be the same. Errors of magnets at different locations were set independently. To make the average of /0 less than 0.063, the strength error should be less than 0.17%. (Emittance increase by 0.063 will decrease luminosity about 3%, without beam-beam force.) Required stability: order of 10-3.

Summary-1 Simulations were done for 250 GeV beam energy linac, all Quad-magnets are aligned along the earth curvature and accelerating cavities are aligned along the straight lines between quads. Two cases: (a) Zero dispersion at every defocusing quad (b) Zero orbit every where, tuned initial dispersion Emittance increase was small without errors. Emittance increase with misalignments and orbit correction in the curved linac and the straight linac were almost the same.

Summary-2 Tolerance of random magnet strength jitters (magnet by magnet independent) For beam offset less than 0.14  (3% Lunimosity reduction from simple calc.) 0.0025% (case (a)) and 0.0017%(case (b)) For emittance increase less than 0.063 0 (3% Lunimosity reduction from simple calc.) 0.17% (case (a)) and 0.4% (case (b)) The results suggests: Curved Linac (following earth curvature) will be OK, if magnet strength can be stable enough.