LIFE, Electron Beam SPARC Daniele Filippetto On behalf of SPARC team

LIFE, PC Laser SPARC LAYOUT

LIFE, e- beam detectors: 3 different types of screens: Optical Transition Radiation Best resolution, no saturation, Low Photon Yield in the visible region, need precise alignement Single Crystal Ce:Yag Good resolution, high photon yield centered on 500nm Saturation, multiple scattering can limit the resolution (thickness) Crom-ox powder High saturation level, only visible light emitted Poor resolution (depending on the grain size), 8-12 bit Firewire/ethernet digital camera used as detectors; Commercial Macro obj. used to image the screen on the CCD

LIFE, beam imaging: Screens Chosen screens: Yag:Ce single crystal with aluminum coating to assure Conduction ( the material itself is an insulator). The system resolution is a combination of all these causes: 1.Electron multiple scattering inside the screen; 2.Bremsstrahlung radiation creation, that generates x-rays causing scintillation 3.The lens diffraction; 4.The pixel size divide by the optical system magnification. We need to choose the screen thickness to assure the best resolution, but also the bigger signal possible (bulk effect) Yag:Ce single crystal has best resolution (that is dominated by the optical system).Linearity assured on the SPARC density range, saturation excluded. A saturation limit approx pC/um^2 for YAG:CE crystal has been found, while the maximum for the SPARC case is about 0.18 fC/um^2.

LIFE, e- beam Detectors: ICT Faraday cup High sensitivity; beam dump; Used just for low energy; sensitivity; beam position dependency error <10-4 3E6 particles resolution (about 500fC) Non intercepting; Both low and high energy; BPMs Resolution 100um Non intercepting;

LIFE, RF Deflector: 5 cells standing wave, TM110 mode, GHz Input power = 1MW Shunt Imp.=2.5 MΩ SPARC case: σ z_res = 65fs = 20um (hyp σ y_defl 100um)

LIFE, Gun diagnostics: Feedback on the RF phase and amplitude; ICT and Faraday cup; (Phase scan) Yag screen (beam centering, solenoid scan, th. emittance). 2 orthogonal slit systems (emittance) 2 bpm to control the positon of the beam injected in the LINAC; 2 screens Faraday cup ICT Slit mask BPMs

LIFE, Orbit control and correction: BPMs each setion entrance; H/V Corrector magnets each section entrance/exit; Envelope control for emittance minimization: “ Cromox” at each section exit, to image the beam. Rough estimate of RF kick, beam envelope all along the LINAC. Solenoids to compensate for the emittance growth (usefull expecially in the velocity bunching setup ). LINAC:

LIFE, TL: 3 points for beam imaging (2 different screens,OTR and Ce:Yag crystal) Quadruoles for beam matching in the undulator used to measured the projected emittance Dispersive section (dipole) used to measure energy and energy spread (14 degrees,1.07 m trj. radius) RF deflector: slice emittance, slice energy spread, longitudinal Trace Space. time ~7ps time energy ~750KeV (0.1% RMS) ~100KeV (0.013% RMS)

LIFE, NEXT FUTURE...

LIFE, Dipole modes are used for position detection, since their amplitude depends linearly on the beam position and is zero for a centered beam. The signals excited in the cavity are coupled into an external circuit, and the amplitude of this particular mode can be separated in the frequency domain. In principle, no additional subtraction is needed, the information about the position is given directly. High resolution because of the large signal per micron displacement. N =√Z0kT k Δf k is the Boltzmann’s constant, Tk the temperature in Kelvin Δf = f110/Qext Resolution down to nm Cavity BPM

LIFE, EO crystal /4 pol. Wollaston Prism Balanced Detector ++ -- fs laser e-beam b Electro-Optical Technique: Γ is the phase shift between the two polarization α is the angle between Ethz and the crystal axis Ea is the Thz field coming with the e-beam ZnTe or GaP Crystals are used (110 cut).

LIFE, EOS Single shot schemes SPECTRAL DECODING Simplest implementation Limited resolution>600fs. TEMPORAL DECODING Highest resolution demonstrated ~ 50 fs Needs complex amplified laser and laser transport SPATIAL ENCODING Resolution expected to be same as TD Low power laser sufficient: e.g. femtosecond fiber lasers

LIFE, Thanks to M.Veronese 14 Menlo Laser TC-780 Delay line nsec gated ICCD 75 COMPRESSOR /2 Pol /2 /4 Cube beamsplit lens mot mirror, Periscope CCD FAST DIODE Optical Enclosure box Diode- AUTO CORR Seed laser E-beam Fiber link etalon EO O 2 E conv.box (300x80x100) Mirror mirror Fiber receiver box (413x178x90) Cylindircal lens lens EO chamber concept by D.Fritz LCLS Stretcher BBO ICCD EO SPARC: SPARC-FERMI collaboration Longitudinal electron bunch shape Laser-electron beam jitter, with fs resolution (can be used to measure the FLAME-SPARC jitter) example of raw data for single shot measurement of short FLASH (temporal decoding)

LIFE, Absolute bunch length measurements by incoherent radiation fluctuation analysis A new method for bunch length measurement Photon radiation by charged particles is a stochastic process. (synchrotron radiation, transition radiation, Cherenkov radiation, …) The photons radiated by the electrons within a single mode adds coherently. By fixing a bandwidth  , we define a mode with coherence length:

LIFE, In this situation, the fluctuation of the energy radiated per pulse becomes (M combined Poisson processes): Possibility of absolute bunch length measurements ! In a bunch of length σ t and zero transverse size, there are M= σ t / σ tc independent modes radiating simultaneously. M ~ 10 Fluctuations as function of number of modes

LIFE, In order to minimize the experimental error is good to have no more than ~ 100 modes Shorter bunches relax the requirements on the bandwidth… No intrinsic limit in measuring shorter and shorter bunches! And because A step more toward shorter bunches measurements

LIFE, Measurement range Measured amplitude 20 mV/div 2 ns/div 1.9 GeV - I CS ~ 3.7 mA Nat. bunch length = 20.3 ps ALS - BL Sept. 22, 2006 Filter: nm, 1 nm FWHM Filter: nm, 1 nm FWHM APD: Perkin Elmer C30902S, Vbias = -238 V (G~100) APD: Perkin Elmer C30902S, Vbias = -238 V (G~100) AMP. Ortec VT 120 G ~ 200 AMP. Ortec VT 120 G ~ 200 First results:

LIFE, the actual Photo-injector diagnostic has been tested and optimized. All the parameters needed for the present machine goal can be measured with good accuracy. The accuracy decreases going toward shorter and bunches and lower currents; Conclusions: Going toward: More sensitive, precise and accurate tools; Non interceptive systems; Using noise may help.