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

2. 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

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

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

5. 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

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

7. 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
D. Schulte et al., CLIC Staging, LCWS, October 2017

8. 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

9. 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

10. 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

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

12. 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

13. Main Linac Lattice Design for 380 GeV
Main linac is build from modules of constant length
Eff. structure length from 230 mm => 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. Selected 380 GeV Beam Parameters for KN
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

25. 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

26. 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

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

28. 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

29. 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