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PROBLEM: Determination of optimal compression of BC1 and BC2 and longitudinal feedback system. PROPOSED SOLUTION: Power monitor of CSR emitted from compressors.

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Presentation on theme: "PROBLEM: Determination of optimal compression of BC1 and BC2 and longitudinal feedback system. PROPOSED SOLUTION: Power monitor of CSR emitted from compressors."— Presentation transcript:

1 PROBLEM: Determination of optimal compression of BC1 and BC2 and longitudinal feedback system. PROPOSED SOLUTION: Power monitor of CSR emitted from compressors Pyroelectric detector measures the CSR power in THz region. The emitted power increases as the bunch gets shorter. RF accelerating phases before compressor are changed to find the optimal compression. Applications to longitudinal feedback system References: TTF2 Linac- Y.Kim et al. FEL2005 pg 518 LCLS Linac - J.Wu et al.SLAC-PUB and11276 May, 2005 M.Veronese, M.Ferianis

2 Radiation sources for diagnostic purposes: signals evaluation for FERMI + COHERENT RADIATION EMISSION Short Bunches Synchrotron Radiation Transition radiation Diffraction Radiation I  N particles I  N 2 particles d 2 I/d  d  tot = [N+N(N-1)|F| 2 ] d 2 I/d  d  single e– |F| 2 = |  dr  (r)e -irk | 2 Coherence enhancement factor: |Fourrier Transform of longitudinal electron distribution| 2 M.Veronese, M.Ferianis

3 Medium Bunch Long Bunch S. Di Mitri simualtions after BC1 after BC2 at LINAC end

4 Enhancement factors: medium bunch long bunch M.Veronese, M.Ferianis

5 Comparison between step function and expected bunch The peaks enhance high frequencies M.Veronese, M.Ferianis

6 Synchrotron Radiation angular spectral distribution References: H.Wiedemann “Particle Accelerator Physics” SV, NY 1993 O.Grimm single electron synchrotron radiation emission from TTF2-BC2 Integrating over the solid angle: M.Veronese, M.Ferianis

7 Incoherent Synchrotron spectrum for medium and long bunches M.Veronese, M.Ferianis

8 CSR spectra for expected MEDIUM gaussian VISIBLE M.Veronese, M.Ferianis

9 gaussian CSR distributions for expected LONG VISIBLE M.Veronese, M.Ferianis

10 Vacuum Chamber low frequency cut-off Warnock PAC1991 pg1824: 2 Parallel perfectly conducting planes cutoff =2*h 3/2 /R 1/2 shielding function Dohlus and Limberg NIMPR-A v407 pg278 y1998 M.Veronese, M.Ferianis

11 CSR shield from 2 Perfect conduct. planes: cutoff < < bunch, cutoff =2*h 3/2 /R 1/2 bunch =2*  *  z (  z =rms bunch length)-gaussian approximation location/ bunch type R[m]h[m] cutoff / cutoff bunch / bunch RMS L B [m] exit BC1 medium [mm]-0.41[THz] 2.08[mm]-0.14 [THz] 3.8[mm] [THz] 2[mm]-0.144[THz]1.1 [ps] 0.33 [mm] exit BC1 long [mm]-0.41 [THz] 2.08[mm]-0.14 [THz] 3.8[mm] [THz] 4.5[mm] [THz]2.4 [ps] 0.71 [mm] exit BC2 medium [mm]-0.46 [THz] 1.85[mm]-0.16 [THz] 3.4[mm] [THz] 0.59[mm] [THz] 0.31 [ps] [mm] exit BC2 long [mm]-0.37 [THz] 2.30[mm]-0.13 [THz] 4.2[mm] [THz] 1.5[mm] [THz]0.8 [ps] 0.24 [mm] M.Veronese, M.Ferianis

12 Proposed layout for BC1/BC2 CSR THz extraction TTF2 design adapted to FERMI BC1: -bigger chamber height -> 30 mm -CSR detection ->no transport line -> as near as possible pyroelectric detector to avoid water absorption -angle of extraction 0.045rad M.Veronese, M.Ferianis

13 Angular distribution for CSR extraction from BC1 e BC2. For low frequencies  <<  c the angular distribution becomes wider. The critical angle at which the SR decrease by 1/e is q c: Example at: BC1: R=7.38m and cuoff =0.07 THz then   c =65 mrad BC2: R=6.17m and cuoff =0.07 THz then   c =69 mrad Considering extraction of Thz radiation after 1m one gets: chamber width = at least 65-69mm !! Note that average opening angle: q =1/  BC1[E=0.22GeV]  =2.33mrad BC2[E=0.6GeV]  =0.85mrad  c =(3*c/  R) 1/3 where R is the bending radius. M.Veronese, M.Ferianis

14 Suitable window materials for Far infrared (and visible) z-cut Quartz MaterialVacuum EnvironmentSpectral Range z-cut quartz:UHV0.15

15 Other diagnostics usable radiation sources: CTR - Coherent Transition Radiation destructive simple has useful intense optical emission mature experience in diagnostics CDR - Coherent Diffraction Radiation non destructive !! weak optical emission less mature but promising Transition Radiation = lim (h->0) of Diffraction Radiation Same detection scheme for both CTR and CDR M.Veronese, M.Ferianis

16 TR and DR angular spectral distribution References: Castellano et. al. PRST-AB 1 pg (1998) Murokh et al. NIMPR-A 410 pg452 (1998) Rule et al. NIMPR-B 173 pg 67 (2001) a slit of height “h” between infinite perfectly conducting semi-planes Transition radiation spectral distrib: approx. constant for >200nm DR less intense than TR in visible spectral region Coherent Enhancement factor is the same for both CTR and CDR. R=h /(  *  X=  x  Y=  y  M.Veronese, M.Ferianis

17 Diffraction Radiation Far field X,Y angular distributions Transition radition    R=2 R=0.5 R=2 R=h /(  *    orthogonal polarization parallel polarization M.Veronese, M.Ferianis

18 CDR-CTR Targets design Castellano group design for TTF Variable height rectangular slit at 45° Very flexible but complex OTR + fixed DR slits TR-screen e - beam 1 mm slit 2 mm slit Less flexible Simple extension of TR- screen M.Veronese, M.Ferianis

19 EOS bunch arrival monitor diagnostics: A non destructive shot-to-shot bunch arrival time in needed It will be placed at the end of linac (E=1.2GeV) Desired time resolution 100 fsec Time window ps Our choice is EOS sampling based diagnostics M.Veronese, M.Ferianis

20 Spectral distribution function: dI/d  =k*|Ey(  )| 2 where Ey(  )=F(E y t (z))= F(E y (z))*F(  (z))with E y t (z)=E y (z)*  (z) Typical Electric Field frequencies for FERMI less than 1 THz  Phonon frequency of EO crystal (about 5.3THz ZnTe,11THz GaP) 4  0 e ( x 2+ y 2 +  2 z 2 ) xx Ex=Ex= 4  0 e ( x 2+ y 2 +  2 z 2 ) zz Ez=Ez= 4  0 e ( x 2+ y 2 +  2 z 2 ) zz Ey=Ey= Transverse electric field of electron bunch z y b fs laser EO crystal e - bunch E x =0 4  0 e ( b 2 +  2 z 2 ) zz Ez=Ez= 4  0 e ( b 2 +  2 z 2 ) bb Ey=Ey= on-axis References: A.Cavalieri et al. PRL 94, (2005) S. Casalbuoni et al. TESLA Report J.D.Jackson “Classical Elctrodynamics” M.Veronese, M.Ferianis

21 Estimated EOS signal EO crystal /4 pol. Wollaston Prism Balanced Detector e-beam EO Signal=|A1| 2 -|A2| 2 =sin(  ) where  = (  d/ 0 )n 0 3 r 41 E a sqrt(1+3cos 2 (  )) M.Veronese, M.Ferianis

22 Transverse Electric field intensity (Gaussian) Medium Bunch Long Bunch M.Veronese, M.Ferianis

23 Bunch arrival EOS Layout We need a single shot EO scheme ->, two main options: BBO EO 20ps 30fs CCD TEMPORAL DECODING CCD fs-laser EO 20ps 30fs SPATIAL DECODING fs-laser Spatial decoding (SPPS,VUV-FEL-proposed) Temporal decoding (FELIX,TTF2): Needs high power laser Appealing if seed laser branch could be used No need of high power laser Pre-compensated fiber transmission from MLO M.Veronese, M.Ferianis

24 Future work: CSR/CTR/CDR: Transverse beam size, Low frequency cutoffs (vucuum chamber) simulations Impact of optics and detector on the signal Comparison of available detectors (Diode, Golay cells, Pyroelectric) Feasibility of CDR Evaluation of CTR EO autocorrelator for single shot measurements Evaluation of single shot polychromator EOS: Study effect of simulated bunch profile on EOS Simulation of THz and Laser propagation through the optics. Re-scaling of single shot scheme of SLAC to our case. COTR: as bunching intra- undulator diagnostics has to be evaluated Instrumentation: Choice of Laser for EO operation diags (800nm-30fsec): independent phase locked laser or MLO derived pulses. Set-up of laser test bench at Elettra including 800 nm, 30fs pulsed laser (Ti:Sa or Fiber Laser), FROG, GaAs THz wide area source,etc. M.Veronese, M.Ferianis

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