CLIC Rebaselining at 380 GeV and Staging Considerations D. Schulte for the CLIC Team D. Schulte et al., CLIC Staging, LCWS, October 2017

D. Schulte et al., CLIC Staging, LCWS, October 2017 CLIC Staged Scenario Lots of good physics at 380 GeV: HZ, WW fusion, top asymmetry Stage design Implementation in stages Integration at CERN Central complex on Prevessin site Design goals for CLIC team Optimised 380 GeV stage With upgrade path Alternative first stage with klystrons Upgrade with drive beam D. Schulte et al., CLIC Staging, LCWS, October 2017

D. Schulte et al., CLIC Staging, LCWS, October 2017 CLIC 3 TeV Design D. Schulte et al., CLIC Staging, LCWS, October 2017

D. Schulte et al., CLIC Staging, LCWS, October 2017 CLIC 380 GeV Design D. Schulte et al., CLIC Staging, LCWS, October 2017

D. Schulte et al., CLIC Staging, LCWS, October 2017 CLIC 380 GeV Design Same decelerator length = same RF pulse length Parameter Unit 380 GeV 3 TeV Centre-of-mass energy TeV 0.38 3 Total luminosity 1034cm-2s-1 1.5 6 Luminosity above 99% √s 0.9 2 Repetition rate Hz 50 Bunches per train 352 312 Bunch separation ns 0.5 Bunch charge 109 5.2 3.7 Gradient MV/m 72 100/72 Site length km 11 D. Schulte et al., CLIC Staging, LCWS, October 2017

For Reference: Basic Parameters Based on CDR study results and SLC experiences D. Schulte et al., CLIC Staging, LCWS, October 2017

Choice of 380 GeV Parameters Optimisation for performance, cost and power, but considering further energy stages Luminosity goal 1.5x1034cm-2s-1, 60% of luminosity in the peak Using already demonstrated structure performance Includes all our knowledge on system design limits (RF structures, beam-beam, damping ring, beam delivery system, stabilisation, magnets, …) CERN-2016-004 D. Schulte et al., CLIC Staging, LCWS, October 2017

D. Schulte et al., CLIC Staging, LCWS, October 2017 Upgrade Strategies Use same structure at 380 GeV and 3 TeV would prevent us from learning in the future Also not enough luminosity at 380 GeV Replace the structures of the 380 GeV stage would cost more (but can always be done) Use a structure optimised for 380 GeV and upgrade with different structure 380 GeV structures must accelerate 3 TeV beam D. Schulte et al., CLIC Staging, LCWS, October 2017

RF and Beam Pulses at 3TeV Right: RF pulse lengths and bunch number for G=100 MV/m Around 250 ns and 300+ bunches Below: Optimistic 120 MV/m Still around 250ns and 300+ bunches Numbers go slightly down CDR 3 TeV values are good prediction Use beam parameters from CDR for 3 TeV Strategy is to require τRF = 244 ns nb ≥ 312, N ≥ 4x109 D. Schulte et al., CLIC Staging, LCWS, October 2017

D. Schulte et al., CLIC Staging, LCWS, October 2017 Impact on Cost at 380GeV Cost as a function of RF pulse length and number of bunches L=1.5x1034cm-2s-1 Minimum cost (structure DB) Ready for upgrade structures Structure DB244 Our baseline Constraint of τRF=244ns nb ≥ 312 causes limited additional cost (50 MCHF) Used choice consistent with energy upgrade D. Schulte et al., CLIC Staging, LCWS, October 2017

Baseline Structure Choice D. Schulte et al., CLIC Staging, LCWS, October 2017

D. Schulte et al., CLIC Staging, LCWS, October 2017 Ongoing Work Design and optimisation of 380 GeV stage ongoing right now, e.g. Review of injector design (significant cost) Update of damping rings, main linac, drive beam complex, … Technical systems such as main linac module, klystrons, … … Ensure consistency with further energy stages Will focus on main linac D. Schulte et al., CLIC Staging, LCWS, October 2017

Main Linac Lattice Design for 380 GeV Main linac is build from modules of constant length Eff. structure length from 230 mm => 271.6 mm Module length 2010 mm => 2343 mm New quadrupole magnetic lengths are 430 mm and 1010 mm CDR design D. Schulte et al., CLIC Staging, LCWS, October 2017

Reviewed Optimisation Beam jitter Many lattice generated and tested for performance RF phase of 6° is the preferred Optimum choice f(0) = 1.5 m, L (0)= 2.2 m agrees with rebaselining assumption BPM misalignment Structure misalignment D. Schulte et al., CLIC Staging, LCWS, October 2017

D. Schulte et al., CLIC Staging, LCWS, October 2017 Tentative Design The best solution has been chosen L(0)=2.2m and f(0)=1.5m Last sector could be merge with previous on Tentative numbers per linac: 356 girders with short quadrupoles 218 girders with long quadrupoles 914 girders with structures 5160 (double) structures Filling factor 80%, after adding decelerator ends 79% D. Schulte et al., CLIC Staging, LCWS, October 2017

Note: Tolerances and Specifications Scaled maintaining beam stability Most imperfection affect the beam less at 380GeV than at 3TeV Structure misalignment leads to 0.3 nm vs 0.54 nm emittance growth Could relax tolerance by 40% BPM misalignment leads to 4.4 times less emittance growth Quadrupole jitter leads to 6 times less emittance growth We maintain specifications Ready for energy upgrade Less risk or better performance in first stage But review impact of specifications on technology choice/cost reduction Also preparing ultimate parameter set Will take advantage of smaller emittance growth And more aggressive tuning D. Schulte et al., CLIC Staging, LCWS, October 2017

Note: Impact on Drive Beam Same decelerator length = same RF pulse length Drive beam current same as for 3 TeV Structures are longer (33 vs 28 cells) Fewer PETS per decelerator Slightly lower impedance PETS to reduce power from 61.3 MW to 59.5 Drive beam energy reduced from 2.4 GeV to 2.0 GeV Simply use fewer RF units in drive beam accelerator (446 vs. 540) D. Schulte et al., CLIC Staging, LCWS, October 2017

Klystron-Based Alternative Alternative to drive beam scheme Faster implementation: Avoids drive beam complex for reception tests Many recent improvements (not yet in cost) Upgrade to higher energies with drive beam Continue to use klystron structures Note: cost estimate is more uncertain than for drive beam Also study alternative 380 GeV stage with klystrons Develop novel high efficiency klystrons Novel pulse compressors Optimised structure Drive beam Klystrons BDS Detector D. Schulte et al., CLIC Staging, LCWS, October 2017

Further Upgrade Considerations Hardware will be modified, but try to minimise changes At high energy smaller number of bunches and bunch charge Should be acceptable in most systems But have to allow for longer pulses Upgrade of injector and RTML RF systems Example: BDS takes energy stages into account D. Schulte et al., CLIC Staging, LCWS, October 2017

Klystron-Based Alternative Alternative to drive beam scheme Faster implementation: Avoids drive beam complex for reception tests Many recent improvements (not yet in cost) Upgrade to higher energies with drive beam Continue to use klystron structures Note: cost estimate is more uncertain than for drive beam Also study alternative 380 GeV stage with klystrons Develop novel high efficiency klystrons Novel pulse compressors Optimised structure Large tunnel Drive beam Klystrons BDS Detector D. Schulte et al., CLIC Staging, LCWS, October 2017

Klystron-based Design Structure Choice Additional extra cost if we use klystrons instead of drive beam D. Schulte et al., CLIC Staging, LCWS, October 2017

Klystron-based Design Structure Choice Cheapest klystron design with a structure that can be used with drive beam or klystrons A bit better D. Schulte et al., CLIC Staging, LCWS, October 2017

Klystron-based Design Structure Choice Significantly better cost for structure that is optimised for klystron-based design For the upgrade cannot use this design with drive beam But can still use it with klystrons Our baseline D. Schulte et al., CLIC Staging, LCWS, October 2017

Selected 380 GeV Beam Parameters for K N 109 3.87 nb 485 frep Hz 50 ex/ey mm/nm 0.66/30 bx/by mm/mm 8.2/0.1 sx/sy nm/nm 120/2.9 sz mm -- Ltotal 1034cm-2s-1 1.5 L0.01 0.9 ng dE % The emittances are nominal values at the IP Draft values for emittances targets are Exit of damping ring ex < 500nm, ex < 5nm Exit of RTML ex < 600nm, ex < 10nm Exit of ML ex < 630nm, ex < 20nm A limited flexibility exists for the collision parameters O(10%) since the beam size is larger than the minimum that could be achieved Also the waist shift allows to gain a few percent D. Schulte et al., CLIC Staging, LCWS, October 2017

Tentative Klystron Lattice Always 8 structure per module, length of 201 cm Quadrupoles are on separate supports, including BPM 20 cm longer than quadrupole More flexibility in choosing quadrupole lengths and scalings Scaled from L = 2 m and f = 1.5 m Tentative numbers per linac: 362 short quadrupoles (40 cm) 226 long quadrupoles (65 cm) 1466 girders with structures 5864 (double) structures Filling factor 80.4% D. Schulte et al., CLIC Staging, LCWS, October 2017

D. Schulte et al., CLIC Staging, LCWS, October 2017 Conclusion Preliminary version of new main beam main linac lattice is ready Keep the same logic as before, but dimensions change slightly Performance matches expectations Tolerances changed as expected But will not change specifications Upgrade should be straightforward for main linac Can add new structures (and move existing ones) Tolerances are maintained Same drive beam current First lattice for klystron-based design is ready Same accelerator girders as before Quadrupoles are independent Also consistent with energy upgrade (some modifications to move quadrupoles but leave structures in place) Thanks to the CLIC team D. Schulte et al., CLIC Staging, LCWS, October 2017

D. Schulte et al., CLIC Staging, LCWS, October 2017 Reserve D. Schulte et al., CLIC Staging, LCWS, October 2017

D. Schulte et al., CLIC Staging, LCWS, October 2017 Real Lattice Design Follow scaling but use modules Form sectors with equal quadrupole length and spacing Number of girders between quadrupoles chosen to be close to ideal L(s) Type of quadrupole chosen to be shortest that is consistent with K(s) Optics functions are periodic in each sector Match optics functions from one sector to the next using 7 quadrupoles CDR 3TeV lattice D. Schulte et al., CLIC Staging, LCWS, October 2017

D. Schulte et al., CLIC Staging, LCWS, October 2017 Note on RF Phases Need to operated off-crest in main linac to compensate wakefield induced energy spread Goal is 1% full width (0.35% RMS) energy spread Average phase is 12° (part of the optimisation) Example with 6° in sectors 1 and 2 11.5° in sector 3, 30° in sector 4 Can operate at different phases in each decelerator, will adjust in real life as required Choose phase of first three/two Use last/last two to compensate Different phases lead to different energy spread in linac, but not at end Different beam dynamics D. Schulte et al., CLIC Staging, LCWS, October 2017