1. A. Cianchi University of Rome Tor Vergata and INFN on behalf of SPARC Lab Diagnostic group 1

2. The SPARC LAB Plasma acceleration Relevant parameters for particle beams diagnostic Problems with the definition of the emittance Proposed solutions Conclusions? 2nd International Conference Frontiers in Diagnostic Technologies 2

3. D. Alesini, P. Antici, A. Bacci, M. Bellaveglia, M. Castellano, E. Chiadroni, A. Cianchi, G. Di Pirro, A. Drago, R. Faccini, M. Ferrario, A. Gallo, C. Gatti, G. Gatti, A. Ghigo, D. Giulietti, L. Gizzi, L. Labate, T. Levato, A. Mostacci, E. Pace, R. Pompili, A. R. Rossi, L. Serafini, C. Ronsivalle, C. Vaccarezza, P. Valente 2nd International Conference Frontiers in Diagnostic Technologies 3

4. THz source FEL source Thompson source Plasma acceleration R&D on advanced beam dynamics R&D on advanced beam dynamics R&D on FEL radiation R&D on FEL radiation Developing a THz source Developing a THz source Developing a Thomson source Developing a Thomson source R&D on plasma acceleration R&D on plasma acceleration Photoinjector 2nd International Conference Frontiers in Diagnostic Technologies 4

5. 5

6. In LWFA, the ponderomotive force of a laser pulse traveling through underdense plasma can excite a plasma wave with longitudinal electric fields larger than 10 GV/m. These fields may be utilized to accelerate electrons to ultrarelativistic energies on a centimeter scale As the laser pulse pass trough, the electrons are pulled back toward the centre by the ions that did not move. As they "fall" into this positive area they pick up speed, so when they reach the centre they "pile up“. Laser beam Electron beam 1 mm 2nd International Conference Frontiers in Diagnostic Technologies 6

7. * Two-beams or more beams, co-linear, plasma-based accelerator * Plasma wave/wake excited by relativistic particle bunch * Deceleration, acceleration, focusing by plasma * Typical: n e ≈10 17 cm -3, λ p ≈100 µm, E>10 GV/m * High-gradient, high-efficiency energy transformer 2nd International Conference Frontiers in Diagnostic Technologies 7

8. SPARC COMB beam 2nd International Conference Frontiers in Diagnostic Technologies 8 To be submitted

9. Charge Energy Energy spread Emittance Bunch length Wide range of energy 50 MeV–1GeV Large energy spread: the best is few % Low charge and repetition rate Poor shot to shot reproducibility Huge background Difficulties in modeling the phenomena Lack of simulations Few experiments, no status of the art Transition between proof of principle to production of “real” beams 2nd International Conference Frontiers in Diagnostic Technologies 9

10. Phase space (x,p x ;y,p y ; z,p z ) area occupied by the beam Under the conditions of the Liouville theorem is an motion invariant 2nd International Conference Frontiers in Diagnostic Technologies 10

11. 2nd International Conference Frontiers in Diagnostic Technologies 11

12. 2nd International Conference Frontiers in Diagnostic Technologies 12

13. For the accelerator community the normalized emittance is one of the main parameter because is constant For such a beam, due to the large energy spread and huge angular divergence, it is not true anymore P. Antici, A. Bacci, C. Benedetti, E. Chiadroni, M. Migliorati, A. Mostacci, L. Palumbo, A.R. Rossi, L. Serafini, to be published 2nd International Conference Frontiers in Diagnostic Technologies 13

14. To measure the emittance for a space charge dominated beam the used technique is the well known 1-D pepper-pot The emittance can be reconstructed from the second momentum of the distribution C. Lejeune and J. Aubert, Adv. Electron. Electron Phys. Suppl. A 13, 159 (1980) 2nd International Conference Frontiers in Diagnostic Technologies 14

15. The contribution of the slit width to the size of the beamlet profile should be negligible The material thickness (usually tungsten) must be long enough to stop or heavily scatter beam at large angle (critical issue at high energy) The angular acceptance of the slit cannot be smaller of the expected angular divergence of the beam 2nd International Conference Frontiers in Diagnostic Technologies 15

16. No considerations about S/N ratio – Detector – Multiple scattering – Background Mask thickness neglected 2nd International Conference Frontiers in Diagnostic Technologies 16

17. All beams have  n =1 mm-mrad z=0.6 m  =0.1 m means 10  m on the source  =0.001 m means 1  m on the source 5 MeV  =1 m 500 MeV  =0.1 m 500 MeV  =0.001 m 2nd International Conference Frontiers in Diagnostic Technologies 17

18. D2=1m %error=1% 5 slits 50  m size 500  m distance D1= 0.6 m D2=2m %error=37% 9 slits 25  m size 50  m distance D1 0.6 m 5 MeV  =1 m500 MeV  =.1 m D1 D2 2nd International Conference Frontiers in Diagnostic Technologies 18

19. The phase space is so thin that the sampling is very inefficient D2=2m %error=1800% 13 slits 50  m size 300  m distance D1 0.6 m 2nd International Conference Frontiers in Diagnostic Technologies 19

20. This is the best measurement ever, well documented, a lot of details Energy 125 MeV, energy spread 1% 125  m mask thick Charge in the order of few pC Normalized emittance in the order of mm-mrad 2nd International Conference Frontiers in Diagnostic Technologies 20

21. 25  m diameter 150  m spaced Assuming  =0.025 and neglecting any other source of noise the error coming from undersampling is about 47% in my calculation Just increasing the drift up to 2 meter would reduce it to 27% If  =0.001 m (1  m) the overestimation is in the order of a factor 20. 2nd International Conference Frontiers in Diagnostic Technologies 21

22. Successfully holes array have been produced. The thickness of the material can be as large as 100 times the hole diameter 2nd International Conference Frontiers in Diagnostic Technologies 22

23. There are 3 unknown quantities  i,11 is the rms beam size squared C i and S i are the element of the transport matrix We need 3 measurements in 3 different positions to evaluate the emittance 2nd International Conference Frontiers in Diagnostic Technologies 23

24. C. Thomas, N. Delerue and R. Bartolini “Single shot transverse emittance measurement from OTR screens in a drift transport section”, 2011 JINST 6 P07004 In their case (3GeV) the multiple scattering is not a factor for thin (5  m) screens It is possible to produce even 1  m aluminum screen This system seems not feasible for beams with energy in the range of hundreds of MeV 2nd International Conference Frontiers in Diagnostic Technologies 24

25. Changing the strength of a magnetic lens is possible to measure the beam size With a least 3 different measurements is possible to retrieve the elements of the sigma matrix that are related with the emittance Multi shot measurement Beam Schermo Quadrupole k1k1 k2k2 k3k3 P1P1 P2P2 2nd International Conference Frontiers in Diagnostic Technologies 25

26. drift Quadrupole chromatic effect on the geometrical emittance (e.g. affecting emittance meas. for high energy spread beams). quadrupole Assuming the particle energy uncorrelated from its transverse position/divergence 2nd International Conference Frontiers in Diagnostic Technologies 26 E. Chiadroni, A. Cianchi, M. Ferrario, D. Filippetto, A. Mostacci, C. Ronsivalle, Chromatic effects in quadrupole scan technique, SPARC-EBD- 11/002

27. CASE 2: Large spot size ≈ 1.7 mmCASE 1: Moderate spot size ≈ 0.3 mm From the experience at SPARC, we learnt that a 1.7 mm spot size at the quadrupole, with 1% energy spread, produces an error of 50% on the emittance. E. Chiadroni, A. Mostacci, C. Ronsivalle 2nd International Conference Frontiers in Diagnostic Technologies 27

28. It is a single shot measurement. Both energy, energy spread and bunch length The limiting resolution is mainly due to the deflecting voltage Increasing the energy also the device length must be increased to have resolution in the order of tens of fs 2nd International Conference Frontiers in Diagnostic Technologies 28 Using with a dipole it gives the longitudinal phase space single shot DIPOLE

29. The longitudinal diagnostic for the injected beam must be non intercepting and single shot Two main candidates, coherent radiation, like CDR or Smith Purcell, or Electro Optical Sampling Coherent radiation:. Longitudinal diagnostic Plasma interaction Transverse and longitudinal diagnostic I tot (  )=I sp (  )[N+N*(N-1) F(  )] 2nd International Conference Frontiers in Diagnostic Technologies 29

30. B. Steffen, “Electro-optic time profile monitors for femtosecond electron bunches at the soft x-ray free-electron laser FLASH“, Phys. Rev. ST Accel. Beams 12, 032802 (2009) The short gate pulse overlaps with different temporal slices of the EO pulse at different spatial positions of the BBO crystal. Thus the temporal modulation of the EO pulse is transferred to spatial distribution of the SHG light. 2nd International Conference Frontiers in Diagnostic Technologies 30

31. 2nd International Conference Frontiers in Diagnostic Technologies 31

32. Temporal resolution on the order of 50-100 of femtoseconds Room-temperature operation Single-shot capabilities Measures relative timing to other pump/probe beams Yields exact charge profile Q(t), and not just |Q(  )| No experiments on multi bunch structure! 2nd International Conference Frontiers in Diagnostic Technologies 32

33. Beams produced by laser plasma acceleration are a challenging task for the diagnostics The few number of experiments, especially in external injection scheme, together with related difficulties to produce fast and reliable simulations are a big problem Several techniques have been proposed and they need to be validated on the field 2nd International Conference Frontiers in Diagnostic Technologies 33

34. 2nd International Conference Frontiers in Diagnostic Technologies 34

35. The most used techniques for emittance measurements are quadrupole scan and multiple monitors 2nd International Conference Frontiers in Diagnostic Technologies 35

36. Twiss parameters 2nd International Conference Frontiers in Diagnostic Technologies 36

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38. Quadrupole scan emittance measurement – multi-shot Large statistical error due to shot-to-shot fluctuations, however multi shot stability need to be solved for future applications – chromatic effects Under certain conditions, e.g. large transverse beam size, large angular divergence and large energy spread, the emittance of the beam might be overestimated – space charge Even at high energy (≈ GeV),  might be much greater than 1: peak current ≈ kA and large  x,y 2nd International Conference Frontiers in Diagnostic Technologies 38