11. B. Marchetti R. Assmann, U. Dorda, J. Grebenyuk, Y. Nie, J. Zhu Acknowledgements: C. Behrens, R. Brinkmann, K. Flöttmann, M. Hüning, H. Schlarb M. Ferrario, A. Bacci Status of the design of ARES (Accelerator Research Experiment at Sinbad)

12. ARES layout 12.9m 27.3m 18.3m REGAE-like RF gun 2.998 GHz Beam final energy~5MeV LINAC II –like Traveling wave 2.998 GHz To be used as RF compressor LINAC II –like Traveling wave 2.998 GHz Total av. Gradient~80MV/100MV Gun solenoid TW solenoids (preliminary design) Xband linearizer Standing wave 11.9942 GHz Total av. Gradient~5MV LINAC II –like Traveling wave 2.998 GHz Total av. Gradient~80MV/100MV Matching section + bunch compressor (containing a slit) R56= 0-30 mm Experiment area Diagnostic section Xband TDS 11.9942 GHz Total transverse voltage > 40MV

13. Beam parameters Goal parameters for external injection into plasma: E-bunch energy 100 MeV E-bunch length ≤ 1fs Arrival time jitter ≤ 10 fs Transverse position jitter ≤ few μm Energy upgrade: E-bunch energy 150-200 MeV Other e- beam parameters: Charge: 0.2-20 pC Energy spread: 0.1-0.4 % Transverse emittance < 0.5 mm*mrad

14. POSSIBLE COMPRESSION SETUPS

15. Mode 1– pure velocity bunching compression 5 MeV COMPRESSION + ACCELERATION ACCELERATION 25-30 MeV100-110 MeV Final bunch length Final peak current Low charge (0.2-0.5 pC) 1-7 fs ̴ 100 A Intermediate charge (20-50 pC) 10-100 fs ̴ 1000 A High charge (100-150 pC) < 1 ps> 1000 A

16. Mode 1– pure velocity bunching compression 5 MeV COMPRESSION + ACCELERATION ACCELERATION 25-30 MeV100-110 MeV Final bunch length Final peak current Low charge (0.2-0.5 pC) 1-7 fs ̴ 100 A Intermediate charge (20-50 pC) 10-100 fs ̴ 1000 A High charge (100-150 pC) < 1 ps> 1000 A In this presentation some preliminary simulations

17. Advantages: ◦ Relatively simple ◦ High currents can be reached Limits: ◦ 1 fs FWHM bunch length for Q=0.2-0.5 pC… Possible? ◦ Tolerances 5 MeV COMPRESSION + ACCELERATION ACCELERATION 25-30 MeV100-110 MeV Mode 1– pure velocity bunching compression

18. Mode 1b– hybrid compression: velocity bunching + chicane 5 MeV COMPRESSION + ACCELERATION ACCELERATION 25-30 MeV 100-110 MeV COMPENSATION OF THE SPACE CHARGE CHIRP OCCURRED DURING THE TRANSPORT Advantages: ◦ The beam can be re-compressed right in front of the target Limits: ◦ Bunch compressor with low charge: challenging. Not studied yet!

19. Mode 2– pure magnetic compression with cut 5 MeV ACCELERATION+ CHIRP 50 MeV CUT OF THE BEAM IN THE DISPERSIVE ARM

20. Preliminary! Slides by Jun Zhu

21. Preliminary! Slides by Jun Zhu

22. Preliminary! Slides by Jun Zhu

23. Mode 2– pure magnetic compression with cut 5 MeV ACCELERATION+ CHIRP 50 MeV CUT OF THE BEAM IN THE DISPERSIVE ARM Advantages: ◦ Most promising method to get bunches shorter than 1 fs ◦ Easy transport in the BC: the beam has high charge before the cut Limits: ◦ Destructive method: limit on the peak current achievable set by wake-fields. ACCELERATION+ CHIRP

24. Mode 3– compression of a train of bunches Laser on cathode

25. Mode 3– compression of a train of bunches E-bunch at the gun exit

26. Mode 3– compression of a train of bunches E-bunch at the linac exit See theoretical and experimental studies done at SPARC (INFN LnF, ITALY)

27. Mode 3– compression of a train of bunches

28. … Alternative way…

29. COMPRESSION USING PURE VELOCITY BUNCHING

30. Transverse beam envelope equation: Matching condition delivering constant envelope in the accelerator: (assumption I=I 0 * γ/ γ 0 ) PRL 104, 054801 (2010) k= e*B sol /(mc) γ΄~2E acc I A =17 kA SC External focusing Emittance pressure Valid for an ellipsoidal bunch distribution with a constant volume density charge. Adiabatic damping term In the transverse plane we want to control the emittance oscillations Mismatches between the space charge correlated forces and the external focusing gradient produce slice envelope oscillations that cause normalize emittance oscillations.

31. PRSTAB 8, 014401(2005) NIM A 740 (2014) β normalized velocity γ 0 ΄=eE acc /(m 0 c 2 ) Longitudinal laminarity parameter: In the longitudinal plane we want: The RF longitudinal focusing to be stronger than the longitudinal space charge force at the beginning of the compression The longitudinal space charge force to be strong enough to prevent slice crossover in the last part of the compression (i.e. we want to preserve the longitudinal laminarity of the beam) Longitudinal beam envelope equation: RF compression SC Emittance pressure The strength of the longitudinal space charge can be modulated by tuning the transverse spot size.

32. Preliminary simulations Gaussian longitudinal laser profile – not optimized at all No linearizing cavity

33. Q=0.5pC E=110 MeV DeltaE/E=1.4% zFWHM ~ 5 fs C.S parameters at the linac exit: Alpha=1 Beta=0.15 m

34. Q=0.5pC E=110 MeV DeltaE/E=1% zFWHM ~ 4.8 fs C.S parameters: Alpha=14 Beta=17 m

35. Q=0.5pC E=110 MeV DeltaE/E=0.8% zFWHM ~ 2.8 fs C.S parameters: Alpha=-163 Beta= 3488 m

36. DIAGNOSTICS - TDS

37. TDS Resolution Beam parameters: Ek=100*10^6; % eV nemitty=0.1*10^(-6); % pi*m*rad % Optics parameters ------------------------------------------------------ betays0=[0.1,1,5,10,50]; % beta twiss inside the cavity in m Dphiy=pi/2; % phase advance between the cavity and the screen in rad % RF cavity parameters --------------------------------------------------- Vy= [5:5:50]*10^6; % peak deflection voltage V freq=11.9920*10^9; % Hz