Some CLIC Critical Issues

1. Some CLIC Critical Issues H. Braun and D. Schulte

2. List of Systems • Magnet systems • Vacuum systems • Klystrons and modulators • RF structures (main linac not in CTC) • RF distribution and control • Dumps and collimators • Alignment and stabilisation • Instrumentation • Detector infrastructure • Conventional facilities

3. Categories • Feasibility demonstration • Needed to show that the key machine parameters are not unrealistic. In particular, a proof of existance of the basic critical constituents of the machine. • Performance issue • Issues that need to be adressed to finalise design choices and ensure performance and reliability of the machine. Validate the machine design. • Cost issues • Issues related to the cost of the project. • Separation of categories are not always clear cut

4. Stabilisation and Alignment • Stabilisation specifications are beyond state of the art • Alignment specifications are beyond state of the art • Integration of both systems is needed • A performance and cost issue • Problem is dealt with in a specific working group • Not further discussed this time

5. Beam Instrumentation • BPM specifications are very tight • Phase monitors are crucial • Beam size monitors are critical • E.g. laser wire • Luminosity instrumentation is critical • Slow luminosity measurement implies slow convergence of tuning procedures • In dynamic machine tuning procedures could even fail if they are too slow • Instrumentation for commissioning/debugging • Machine protection instrumentation • Loss monitors • Important performance issue • Review in preparation

6. Machine Detector Interface • Important integration issue with cost and performance impact • Working group will address that • Some discussion in CLIC physics report • No further discussion here

7. Operations and Reliability • Commissioning strategy • Staging of commissioning and construction • Schedule and cost issue • Availability • Performance and cost issue • Large component counts • E.g. drive beam decelerator quadrupoles • Machine protection • Cost and performance issue

8. Magnets • Damping ring wiggler • Performance, including ecloud mitigation • Final focus doublet • Only old permanent magnet design exists • Performance • Main linac quadrupoles and correctors • Part of module working group • Cost, in part performance • Drive beam quadrupoles and correctors • Cost • Extraction kickers, DR and turn-around • Performance • Orbit corrector performance • General review • E.g. damping ring (too tight cell), BDS (multipoles etc), spent beam line (large apertures) • Cost and performance (reliability)

9. Vacuum • Damping ring • Very good vacuum quality is required (0.1ntorr) • Synchrotron radiation • Small beam pipe likely required • Cell design is at limit space integration of vacuum equipment can impact lattice design • Hence, an important performance and cost issue • Electron cloud in the damping ring is serious limitation • Very low secondary electron yield required • Electron cloud mitigation is important • Grooved surfaces, coatings etc • An important performance issue • Also a problem for ILC • Addressed in that context as one of the main issues

10. Vacuum II • Drive beam accelerator • Mainly a cost issue • Tranfer lines • Very good vacuum required (0.1ntorr) • Mainly a cost issue • Main Linac/drive beam decelerator • Vacuum in RF structure needs to be understood • Important performance and cost issue • Part of module working group • BDS • Probably 0.1ntorr required • Certainly cost maybe performance issue • Space constraints in some magnets

11. Klystrons and Modulators • Drive beam accelerator • Klystrons and modulators are a major cost item • RF phase stability has a significant impact on performance • Interaction with low-level RF control • Systems have a significant impact on reliability and power efficiency • Other klystrons • Bunch compressor / booster linac phase stability • Other systems also require klystrons, e.g. the booster linac, the damping ring, RF deflectors • But should be conventional systems

12. RF Structures • Main linac accelerating structures and PETS are not part of the CTC • Drive beam accelerator structures • No up to date design exists • Important to have for report • Cost and performance issue • Booster linac structures • No up to date design exists • Potential performance issue • Other missing designs • Pre-injector accelerating structures • Damping ring accelerating cavities • May be do not need a real design

13. RF Structures II • RF deflectors • Critically impact the performance • Design needed • Drive beam feedback kicker for phase correction • This feedback is our last line of defence against RF phase jitter • Performance issue

14. Low Level RF Control and Timing • Drive beam induced main linac RF phase jitter is a potentially severe problem • Typical tolerance is 0.2 degree at 12GHz • All drive beam phase jitter at 1GHz is amplified by factor 12 at 12GHz • Control of drive beam accelerator RF is important • Need an RF phase feedback • Distributed phase reference • Based on beam (local oscillator) • Or coupled oscillators • Has impact on the performance • Synergies with XFEL exist

15. Collimators and Beam Dumps • BDS • Collimator survival at limit with full beam impact • Synergy with ILC/LHC exists • Serious performance issue • Drive beam dumps • Need about 50, hence potentially significant cost issue • Low cost design can impact the performance • Need to understand trade-offs • Main beam dumps • Total power not too different from ILC • Mainly a cost and safety issue • Tune-up dumps • Drive and main beam (to be defined) • Positron target • Needs to be reviewed, some importance for cost

16. Overall Feedback Design • Large part of the machine is controlled with a single MIMO feedback • Pulse-to-pulse and intra-pulse response required • Latency budgets • Consistency of hardware with latency and precision requirement for feedback • Close collaboration with beam dynamics to define/optimise algorithms