1. Main beam performance tests at FACET and at existing or future FELs (FELs based on Xband technology) Andrea Latina CLIC Workshop 2014 – Feb 3-7 2014 – CERN

2. Contents 1.Main beam beam dynamics challenges 2.Experimental program at FACET and main results 3.Experimental program to undertake 4.CLIC interest in X-band FEL 5.Summary 2

3. Main beam performance… Depends on: Low emittance preservation Energy spread control Longitudinal bunch compression Phase synchronization Under the effect of: Wakefields: geometric, resistive; short-range, long-range, … Multi-bunch beam breakup Coherent synchrotron radiation Incoherent synchrotron radiation Pre-Alignment, Coupling, Ground motion, vibrations, thermal stability, stray-fields, vacuum,.. Can be ensured by: Careful / robust design (strong focusing, BNS damping, … ) Design / Detuning of the accelerator structures Advanced computer codes / Monte Carlo simulations Beam-based techniques, model reconstruction techniques Innovative beam Instrumentation: fast, precise, non-destructive diagnostics Feed-back, feed-forward, control systems Tuning knobs: dispersion –, emittance –, wakefields –, coupling correction 3

4. CLIC-FACET Collaboration on Beam Physics Beam-based alignment – Excellent result, see next slides Collimator wake-field measurement – Very important! – But couldn’t happen: lack of funds – We need to revive interest in it! Measurement of short and long-range wake-fields in the CLIC Accelerator Structures – Very important! – But couldn’t happen: no positrons available at SLAC so far 4

5. Experiments at FACET FACET (Facility for Advanced Accelerator Experimental Tests) is a User Facility at SLAC National Accelerator Laboratory. The first User Run started in spring 2012 with 20 GeV, 3 nC electron beams. The facility is designed to provide short 20 μm bunches and small (20 μm wide) spot sizes Experiments at FACET: Plasma wake field acceleration, dielectric structure acceleration, Smith-Purcell radiation, magnetic switching, terahertz generation … E-211: Beam-Based Alignment 5

6. Results: SysID + Dispersion correction Focused on Sectors 04 through 08 (500 m of linac) Used 52 correctors in total (1h15 acquisition time) Measured orbit and dispersion (2h30 in total) Applied Orbit and DFS 6 Measured response matrix Corrected dispersion

7. Before correction After 3 iterations Incoming oscillation/dispersion is taken out and flattened; emittance in LI11 and emittance growth significantly reduced. After 1 iteration S19 phos, PR185 : Emittance Growth and Dispersion-Free Steering Emittance at LI11 (iteraton 1) X: 43.2 x 10 -5 m Y: 27.82 x 10 -5 m Emittance at LI11 (iteration 4) X: 3.71 x 10 -5 m Y: 0.87 x 10 -5 m 7

8. Wakefield-Free Steering (WFS) In DFS one measures the system response to a change in the energy In WFS one measures the system response to a change in the charge (for the test beam we used 80% of the nominal charge, i.e. ~2.6 nC) Recall: the DFS system of equations We propose: the WFS system of equations: The success is not obvious: DFS relies on an effect which affect the bunch as a whole; WFS relies on an effect with act within the same bunch. 8

9. Simulation of WFS at FACET Nominal beam: q=2e10 e - ; WFS test beam: q=1.6e10 e - 9 Simulation

10. Results: Measured Response Matrices 10 R0, Horizontal orbit response Corrs Bpms Corrs Bpms R1-R0, Horizontal Wakefield response 44 x-correctors, 43 y-correctors, 60 bpms Measured data! System Identification algorithm

11. SLC emittance Sectors 02-03 11 ε y [10 -5 m] Lower emittance achieved in S04! 1. We spoiled the emittance 2. We applied WFS Golden orbit: ε y =4.4 μm ε y =2.0 μm (before WFS)(after WFS) Δε y =2.4 ± 0.1 μm  Δε y = 0.0 ± 0.1 μm Emittance growth (before  after)

12. Conclusions from E-211 We demonstrated the proof of principle of a model-independent, global, automatic, dispersion-free correction algorithm, on 500 m of the SLC linac We demonstrated the performance of a machine system identification algorithm and its validity over hours and even days The DFS algorithm rapidly and robustly converged to a solution where the difference of a nominal and a dispersive orbit is minimized WFS was tested with very promising results We are going to integrate our tools into the SLAC control program 12

13. Main beam performance… Depends on: Low emittance preservation Energy spread control Longitudinal bunch compression Phase synchronization Under the effect of: Wakefields: geometric, resistive; short-range, long-range, … Multi-bunch beam breakup Coherent synchrotron radiation Incoherent synchrotron radiation Pre-Alignment, Coupling, Ground motion, vibrations, thermal stability, stray-fields, vacuum,.. Can be ensured by: Careful / robust design (strong focusing, BNS damping, … ) Design / Detuning of the accelerator structures Advanced computer codes / Monte Carlo Simulations Beam-based techniques, model reconstruction techniques Innovative beam Instrumentation: fast, precise, non-destructive diagnostics Feed-back, feed-forward, control systems Tuning knobs: dispersion –, emittance –, wakefields –, coupling correction 13

14. Impact of Wake-monitors on BBA 14 D. Schulte et al. Single machine shown With no wakemonitors With wakemonitors Goal is to keep emittance growth due to wakefields below 1nm Average emittance growth with no wakemonitor is about 40nm Sensitive to prealignment, girder accuracy, structure accuracy etc. With wakemonitor we find about 0.5nm Only sensitive to accuracy of structure and on electronics

15. Wakefield measurements 70 o phase acceptance 65 ps Laser with photo-injector offers great flexibility (as proven by phase coding) Objective: to generate 2 successive bunches at different energies and with variable spacing. (ex. using 2 pulse picker units and an optical delay line) Interesting challenge for the laserists Gun bunch charge as function of phase 3 GHz Accelerating field First bunch second bunch N x 333 + variable delay(0-65) ps 15 W. Farabolini Use of CALIFES for Wakefield tests

16. The University of Oslo has established a project for further investigating linear collider emittance preservation, both by simulations, experimental tests at FACET/ATF2 and by experimental tests of Wake Field Monitors (WFM) WFMs could also be used for FEL emittance preservation One of the key challenge is demonstrate WFM as a reliable means to ensure CLIC main linac emittance preservation (  ny of 10 nm) A crucial test is to prove experimentally that the required WFM beam position resolution of ~3 um can be achieved in a realistic test environment (rf + beam) F. Peauger et al. "Wakefield monitor development for CLIC accelerating structure", Proceedings of LINAC'10 (2010) Ideal test-bed for WFM: Califes in CTF3, with TBTS or Xbox power. Strongly desired to keep e- beam test-cabilities at CERN, also after 2016 E. Adli 16

17. Proposal for Single-Bunch Collimator Wakefield Measurements 17 J. Resta-Lopez et al. New diagnostics required

18. ATF2: visible charge-dependent effect 18 Jochem Snuverink at ATF2 Topical Meeting – July 5-8, 2013 WFS should work wherever a change in the bunch charge impacts the orbit This wakefield effect is a limiting factor for ATF2: charge is currently reduced by a factor 10 to limit this effect (consequences on BPMs, Shintake monitor … )

19. ATF2: fisrt simulations of WFS 19 J. Snuverink et al. New proposal being written! Will be presented next week at ATF2 project meeting

20. 20 14 ground motion sensors have been installed (K. Artoos, A. Jeremie, Y. Renier, ATF2 team) Measurements are available: (PSD and correlation) Goal 1: predict ground motion effects on the beam using GM sensors Compare with BPM readings Could relax stabilisation tolerances for CLIC quadrupoles Ground-motion feed-forward at ATF2 J. Pfinsgstner et al.

21. Report from design/parameter CLIC FEL Working Group Avni Aksoy, Daniel Schulte, Andrea Latina, Zafer Nergiz, Gerardo D‘Auria, Simone Di Mitri, Walter Wuensch, Mark Boland, Qiang Gu, Mustafa Doğan, Evangelos Gazis, Anastasios Charitonidis, Francesca Cubris, Wencheng Fang, Jonathan Mckinlay I need to mention:

22. Benefits of FELs from X-band technology Use of X-band in FELs in other labs would help CLIC for a number of tasks – Further technical developments with industry Will create the industrial basis – Performance studies of accelerator parts and systems From components up to large scale main linac system test Other laboratories would get support from CERN about RF instrumentation, alignment, test stands, industrial contacts … … XBOX2 @CERN XBOX1 @ CERN CLIC Module @ CERN W. Wuensch 22

23. Bunch length evolution σ z = 7.0 µm E = 6.0 GeV dE/E = 0.028 % dE/E slice = 0.004 % Total S-band RF active length = 28 meters Total X-band RF active length = 93 meters Linearizing X-band = 0.75 m L1 = 17.25 m L2 = 75 m Compare with other C-band FEL: L ~ 500m A. Latina Many beam dynamics challenges! 23

24. Transverse Stability Stability of beam with initial jitter requires to stay above red line 24 (Strong) CLIC lattice and simplified wakefield Emittance growth with 100um tolerances: We need dispersion free steering or CLIC-style alignment for FEL D. Schulte

25. User Requirements; time structure (150 ns RF train) Option 1: (Baseline) – 50 Hz Rf repetition – Single Bunch  Option 2:  500 Hz Rf repetition  Single Bunch  Option 3:  50 Hz Rf repetition  Few Bunches  Option 4:  500 Hz Rf repetition  Few Bunches  Option 5: 50 Hz Rf repetition with ns bunch spacing A. Aksoy 25

26. 26 Emittance preservation (longitudinal and transverse) Misalignments, dynamic effects, ISR, CSR Beam-based alignment: DFS, WFS, …, tuning bumps Bunch-to-bunch effects Stray fields Diagnostics Fast transverse and longitudinal bunch measurements Feed-back and feed-forward loops Fast orbit, dispersion, wake-fields correction Phase-energy stabilization: LL-RF but not only Ground-motion counteraction Performance tests of accelerator components and technologies X-band RF, industrialization, test stands, … Beam Physics challenges at X-band XFEL

27. Summary Beam physics challenges in the main beam are many More tests should be foreseen: techniques, systems, components Diagnostics R&D is vital and crucial CLIC-FACET witnessed a tremendous successful example of mutual cooperation: we have learned a great lesson (DFS works; we can do better than DFS e.g. WFS) – mutual benefit XFEL X-band is an exciting field – Similar challenges, cutting edge technology R&D, – reliability of components Lot of interesting work ahead! 27