1. Laser-driven ion acceleration Matteo Passoni Dipartimento di Energia – Politecnico di Milano matteo.passoni@polimi.it - www.nanolab.polimi.it 2nd International Conference on “Frontiers in Diagnostic Technologies” Laboratori Nazionali di Frascati, 28-30 November 2011

2. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 2 Outline - I NTRODUCTION: ultraintense ultrashort (UU) laser pulse interaction with matter - C HARGED PARTICLE ACCELERATION IN PLASMAS: electrons, protons, heavy ions - L ASER-ION ACCELERATION: main experimental evidences, potential applications - P HYSICS OF THE LASER-BASED ION ACCELERATION: Present theoretical understanding. Ion acceleration mechanisms: TNSA, RPA. - M ATERIAL SCIENCE FOR LASER-ION ACCELERATION an example: multi-layered targets with ultra-low density layers - C ONCLUSIONS

3. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 3 Introduction: laser-matter interaction “Optics in the relativistic regime” G. Mourou, T. Tajima, S.V. Bulanov, Rev. Mod. Phys. 78, 309 (2006) Introduction of Chirped Pulsed Amplification (CPA) in 1985 determined a true revolution in the field …long story, started after the invention of lasers… Basic principle of CPA:

4. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 4 Typical laser parameters with CPA Laser wavelength (  m): ≈ 1 (Nd-Yag), 0.8 (Ti-Sa), ≈ 10 (CO 2 ) Intensity (power per unit area): > few times 10 18 W/cm 2 (max about 10 21 W/cm 2 ) Power: ≈ 100 TW - few PW (PW lines at LLNL and ILE) Pulse duration: ≈ 10 - 10 3 fs (at = 1  m,  = c/ = 3.3 fs) Spot size at focus: down to diffraction limit  typically ø < 10  m Critical density (  P =  )  : relativistic factor of the electron population

5. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 5 Electric field associated to the laser pulse: from Physical fields vs. laser intensity - atomic field - “relativistic” field - limit for e - -e + equilibrium [T e,hot ≈ 20 m e c 2, BKZS limit in H: G.S. Bisnovaty, et al., Sov. Astr. Journal 15, 17 (1971)] - Schwinger limit [Vacuum break-down: J. Schwinger, Phys. Rev. 82, 664 (1951)] [M. Lontano, M. Passoni, “Ultraintense electromagnetic radiation in plasmas”, Progress in Ultrafast Intense Laser Science, Springer's review book series, Vol I, (2006)]

6. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 6 Physical regimes achievable - 1 D. Umstadter, Relativistic laser-plasma interactions, J. Phys. D: Appl. Phys. 36, R151 (2006) today I ≤ 10 21 W/cm 2 room temperature first lasers photoionization Coulomb binding energy vaporization of molecules CPA relativistic electrons Electron positron plasma thermal pressure of Sun’s core fusion pion production relativistic protons Uranium atom fully stripped 10 5 10 10 15 10 20 10 25 Intensity (W/cm 2 )

7. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 7 Accelerating fields due to laser-driven charge separation + + + + + + + + - - - - - - - - - - - - - - - + + + + + + + 10 - 100 fs high-intensity laser pulse causes strong charge separation huge quasi-stationary electric (and magnetic) fields are produced E L ≈ E acc ≈ tens GV/cm  efficient charged particle acceleration ELEL E acc “electric field rectification” (  1  m = 3 fs)

8. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 8 Laser based electron acceleration - compact electron accelerators laser pulse into an underdense plasma  laser wakefield accelerator -maximum s.s. electric field A.I. Akhiezer, R.V. Polovin, Sov. Phys. JETP 30, 915 (1956) @ n e = 10 18 cm -3, =1  m  E M ≈ 8 GV/cm GeV regime experimentally approached! T. Tajima, J. Dawson, Phys. Rev. Lett. 43, 262 (1979) J.M. Dawson, Plasma Phys. Contr. Fus. 34, 2039 (1992) C. Joshi, Th. Katsouleas, Physics Today 6, 47 (2003) radiation pressure expels electrons longitudinal E field effective negative bullet

9. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 9 Laser-driven ion acceleration in solid targets Typical physical parameters of the accelerating system: Laser – energy: 0,1-1000 J, pulse duration: 10-1000 fs, intensity: 10 18 -10 21 W/cm 2 solid target – type: conductors, insulators, thickness: 0,01-100  m accelerated ions – protons in usual conditions, other ions in proper conditions If an ultraintense and ultrashort laser pulse hits the surface of a thin solid film, intense and energetic (Multi- MeV!) ion “beams” are effectively produced E. L. Clark et al. Phys. Rev. Lett. 84, 670 (2000) A. Maksimchuk, et al., ibid. 84, 4108 (2000) R. Snavely et al. ibid. 85, 2945 (2000)

10. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 10 Characteristics of ion emission: “front” vs. “rear” emission - 1 Y. Murakami, et al., Phys. Plasmas 8, 4138 (2001) E.L. Clark, et al., Phys. Rev. Lett. 85, 1654 (2000) M. Zepf, et al., Phys. Plasmas 8, 2323 (2001) P. McKenna, et al., Phys.Rev. E 70, 036405 (2004) I. Spencer, et al., Phys. Rev. E 67, 046402 (2003) …typical experimental setups to diagnose ion acceleration…from both sides of the target

11. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 11 Characteristics of ion emission: “front” vs. “rear” emission - 4 Many indications that energetic ions come from the rear surface (usually protons from contaminants!) Mackinnon, et al., Phys. Rev. Lett. 86, 1769 (2001) (Vulcan-Nd:glass-RAL) Allen, et al., Phys. Rev. Lett. 93, 265004 (2004) (JanUSP-Ti:Sa-LLNL)

12. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 12 Characteristics of ion emission: direction, maximum energy Laser: Nova (Nd:Glass)-LLNL. Parameters: = 1.053  m,  p ≈ 1 ps, E < 700 J,  ≈ 8-9  m, I ≈ 3  10 20 W/cm 2 Au, CH targets, 50-125  m thick laser  hot electrons (  l,e ≈ 40-50 %) T hot ≈ 5-6 MeV laser  protons (  l,pr ≈ 7 %) 3  10 13 prs.(>1 MeV), T pr ≈ 6 MeV  max ≈ 58 MeV from RC filmsfrom magn. deflection spectrometer high energy cut-off [ S.P. Hatchett, et al., Phys. Plasmas 7, 2076 (2000) R.A. Snavely, et al., Phys. Rev. Lett. 85, 2945 (2000)] beam Direction: target normal!!

13. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 13 Characteristics of ion emission: ion energy spectra “thermal”+ high energy cut-off + plateau (sometimes…) plateau high energy cut-off A.J. Mackinnon, et al., P.R.L. 88, 215006 (2002) Y. Murakami, et al., Ph. Pl. 8, 4138 (2001) GEKKO MII CPA LLNL-Ti:Sa VULCAN-RAL CRIEPI-Kanagawa A. Fukumi, et al., Ph. Pl. 12, 100701 (2005)E.L. Clark, et al., P.R.L. 85, 1654 (2000) Ti:Sa/Nd:Ph-CUOS A. Maksimchuk, et al., P.R.L. 84, 4108 (2000)

14. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 14 Characteristics of ion emission: dependence on laser parameters - 1 K. Krushelnick, et al., Plasma Phys. Contr. Fus. 47, B451 (2005) A large number of experiments have been performed to study the dependence of the accelerated ion properties on the laser parameters (rear side acceleration) M. Borghesi et al., Plasma Phys. Contr. Fus. 50, 024140 (2008)...collection of published data...

15. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 15 Characteristics of ion emission: dependence on laser parameters - 2 Experiments show that in general ion properties depend on - intensity - energy - pulse duration - contrast ratio (ASE/pedestal) - polarization: linear vs circular In particular some quite general features can be established: - Maximum ion energy mainly depends on laser intensity: E max ~ I 1/2 (…I?) - Energetic spectrum and maximum energy depend also on laser energy - Total number of ions increases with laser energy and pulse duration - Total number with short pulses (10-50 fs) can be increased exploiting higher repetition rate (Hz)

16. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 16 Characteristics of ion emission: dependence on target thickness - 1 several target thicknesses explored, from less than  m (~ ) to hundreds  m… indication of an “optimal” thickness depending on pulse properties - mainly pre-pulse pedestal level/contrast ratio - for a given target composition M. Kaluza, et al., Phys.Rev.Lett. 93, 045003 (2004) (ATLAS-MPQ) Spencer, et al., Phys. Rev. E 67, 046402 (2003) (Astra-Ti:SA-RAL) Thickness normalized to areal density

17. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 17 Characteristics of ion emission: dependence on target thickness - 2 Ultrathin targets (down to few tens nm) investigated (using ultrahigh contrast pulses!) - maximum ion energy can significantly increase reducing thickness - Symmetric acceleration: back/front vs forward/rear T. Ceccotti, et al., Phys.Rev.Lett. 99, 185002 (2007) (UHI100-Ti:Sa-CEA Saclay) A. Henig, et al., Phys.Rev.Lett. 103, 045002 (2009) (TRIDENT-Nd:glass-LANL)

18. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 18 Characteristics of ion emission: summary of the main exp. results - Ions can be effectively accelerated in laser-solid interaction - Protons are mainly accelerated (from surface contaminants), unless the target is properly cleaned - Ions are accelerated both at the front and at the rear surface - In usual conditions, ions from the rear surface present better properties: - total number (depending on conditions, 10 9 – 10 13 protons) - maximum energy (uo to several tens MeV for protons) - energetic spectrum (wide spectrum with sharp cut -off) - beam properties (ultralow-emittance 10 -3 mm mrad ps bunches) - There is a dependence on the target conditions - target thickness, transverse extension, density - more protons from CH (i.e. H rich) targets - much better properties from metallic targets (role of el. transport)

19. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 19 Potential applications  diagnostics for laser plasmas (proton imaging)  “fast ignitors” for inertial nuclear fusion (electron- or proton-driven)  laser-induced nuclear physics: isotope production, …  medical applications (PET, hadrontherapy)  injectors for larger accelerators …many applications are foreseen… …this is true especially for laser-accelerated ions! …in most cases, beam quality is definitely not enough yet… …A LOT of research is still required to reach real feasibility

20. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 20 Potential applications: “proton imaging” - 1 [M. Borghesi, et al., Phys. Plasmas. 9, 2214 (2002)] [M. Borghesi, et al., Phys. Rev. Lett. 88, 135002 (2002)] Vulcan- RAL Relativistic Electromagnetic Soliton ? e.g.: ultrafast measure of localized transient electric fields

21. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 21 Potential applications: “proton imaging” - 2 Example? diagnostic of the accelerating electric field on the rear side! [L. Romagnani, et al., Phys. Rev. Lett. 95, 195001 (2005)] LULI Palaiseau interaction CPA 1 I ≈ 3.5  10 18 W/cm 2  ≈ 1.5 ps 1 - 40  m, Al, Au bent foils diagnostic CPA 2 I ≈ 2  10 19 W/cm 2  ≈ 300 fs 10  m, Au foil T e ≈ 500 keV  int ≈ 6-7 MeV E ≈ 3  10 10 V/m CPA Set-Up

22. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 22 Ion acceleration mechanism - 1 There is common agreement on the fact that in most of the experiments protons are accelerated by the electrostatic field set up by fast electrons propagating into or leaving the target. Laser Pulse Target Electrons ++++++++++++ N p << N hot Light ions (protons)

23. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni Ion acceleration mechanism - 2 23 1 2 3 Laser pulse solid target front surface rear surface 1: laser pulse-front surface interaction - radiation pressure-driven charge separation (& resulting ion acceleration) - possible generation of energetic e - population - role of pulse properties (intensity, energy, prepulse, polarization) - role of target properties (density, profile, thickness, mass) 2: electron propagation in the target - role of electron properties (max. energy, spectrum, temperature) - role of target properties - return current 3: effective charge separation - generation of intense electric fields - resulting ion acceleration pre-plasma (underdense) Light ion layer relativistic e - current return current main pulse pre-pulse SOME CRUCIAL ISSUES:

24. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni Ion acceleration mechanisms: TNSA – RPA IF THE e - POPULATION IS DOMINATED BY A THERMAL SPECTRUM… (quite “natural” experimentally…) Target Normal Sheath Acceleration mechanism (TNSA) IF THE ROLE OF THE THERMAL e - POPULATION IS “SUPPRESSED” (superhigh intensity or CP+normal...is it “feasible” experimentally…?) Radiation Pressure Acceleration mechanism (RPA) …accelerating field due to strong charge separation between hot electrons expanding in vacuum and the bulk target …accelerating field due charge separation induced by the balance between radiation pressure and electrostatic force [S.C. Wilks, et al., Phys. Plasmas 8, 542 (2001)] [S.C. Esirkepov, et al., Phys. Rev. Lett. 92, 175003 (2004) A. Macchi et al., Phys. Rev. Lett. 94, 165003 (2005)] 24

25. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 25 TNSA ion acceleration mechanism Let us simply estimate the field at the rear surface: order of magnitude of electron energy ~ T e order of magnitude of el. cloud extention ~ de From quasineutral (QN) plasma expansion: E ~E ~ E QN ~ Estimate of T e : ponderomotive potential is the main mechanism of electron heating (see before) [S.C. Wilks, et al., Phys. Plasmas 8, 542 (2001)] If charge separation is relevant (L n =c s t << d )…

26. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 26 TNSA ion acceleration mechanism For ultraintense ultrashort laser pulses (I > 10 18 W/cm 2,  1  m, n e  n c  10 21 cm -3 ) we have T e ~ MeV, de ~  m (<< L n ) E ~ >>> E QN such fields can accelerate ions up to several MeV on a micrometer scale length!! It is the TNSA field!

27. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 27 TNSA: some other theoretical References TNSA as plasma expansion into vacuum P. Mora, Phys. Rev. Lett. 90, 185002 (2003) V.F. Kovalev, et al., JETP, 95, 226 (2002) V. Yu. Bychenkov et al., Phys. Plasmas, 11, 3242 (2004) V. T. Tikhonchuk, et al., Plasma Phys. Controlled Fusion 47, B869 (2005) P. Mora, Phys. Rev. E 72, 056401 (2005); Phys. Pl. 12, 112102 (2005) S. Betti, et al., Pl. Phys. Contr. Fus. 47, 521 (2005) Quasi-static TNSA models M.Passoni, M.Lontano, Laser Part. Beams 22, 171 (2004) M. Lontano, M. Passoni, Phys.Plasmas 13,042102 (2006) J. Schreiber, et al., Phys. Rev. Lett. 97, 045005 (2006) M. Passoni, M. Lontano, Phys. Rev. Lett. 101, 115001 (2008) B.J. Albright, et al., Phys. Rev. Lett. 97, 115002 (2006) A.P. Robinson, et al., Phys. Rev. Lett. 96, 035005 (2006) M. Passoni et al, New J. Phys. 12, 045012 (2010) [refs therein for more References]

28. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni Other than TNSA? Radiation Pressure Acceleration 28 - if pulse intensity increases beyond 10 22 W/cm 2 PIC simulations show that RPA becomes competitive, and above 10 23 W/cm 2 is the dominant acceleration process (so-called RPDA...) [ T. Esirkepov et al., Phys. Rev. Lett. 92, 175003 (2004); ibid. 96 105001 (2006) ] - if fast heated e - are “switched off”, TNSA can be suppressed, leaving only RPA “in action”: achieved using normal incidence and CP [A. Macchi et al. Phys. Rev. Lett. 94, 165003 (2005) ] Is it possible to achieve processes other than TNSA? In principle, yes, exploiting “directly” the pulse radiation pressure Radiation Pressure Acceleration (RPA) How?

29. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni RPA: general remarks 29 [A. Macchi et al. Phys. Rev. Lett. 94, 165003 (2005) ] - radiation pressure pushes e - inwards “depletion”, “compression” layers develop - balance between radiation and electrostatic pressure - acceleration of ions in the compression layer - in principle with this process we can have high conv. efficiency + monoenergetic ions

30. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni RPA with “thick targets”: “hole boring” RPA regime 30 - For solid-densities only a few MeV energies may be obtained (maybe not sufficient even to cross the target), but high density bunches - with respect to “Light Sail” (requiring ultrathin targets, see next slide) the scheme seems more robust and less prone to, e.g., prepulse effects - HB works in “preplasma”: lower densities boost ion energy If the target is thicker than the depletion+compression layer, the ion bunch is “simply” injected in the solid and crosses it Estimate of the maximum energy the hole boring regime: [A.P.L.Robinson et al, Plasma Phys. Contr. Fusion 51 024004 (2009)] where [A. Macchi et al. Phys. Rev. Lett. 94, 165003 (2005) ]

31. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni RPA with ultrathin targets: “light sail” RPA regime 31 [ G.Marx, Nature 211, 22 (1966) J.F.L.Simmons & C.R.McInnes, Am.J.Phys. 61, 205 (1993) ] …still a lot to be properly understood… Simple model: a perfectly reflecting, rigid mirror boosted by a light wave (pre-dates laser-ion acceleration era!!) In a ultrathin target, with thickness up to the compression layer (nm range), repeated acceleration of the ion layer by the laser (via e - !) can occur The whole target (even with multi-species ions) is accelerated in this way (…as a sail…) (reflectivity R = 1)

32. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni RPDA: Pressure Dominated Regime 32 If pulse intensity > 10 23 W/cm 2 (still to come experimentally!) PIC simulations show that RPA becomes the dominant acceleration process: - the pulse acts as a “relativistic piston”, efficiently accelerating ions - new phenomena, like Rayleigh-Taylor instability & Radiation friction can play a role T. Esirkepov et al., Phys. Rev. Lett. 92, 175003 (2004); ibid. 96 105001 (2006)

33. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 33 RPA: recent theoretical references Hole Boring RPA T.V.Liseikina & A.Macchi, Appl.Phys.Lett. 94, 165003 (2007) N.Naumova et al, Phys.Rev.Lett. 102, 025002 (2009) A.P.L.Robinson et al, Plasma Phys.Contr.Fus. 51, 024004 (2009). Light sail RPA X.Zhang et al, Phys. Plasmas 14, 073101 & 123108 (2007) A.P.L.Robinson et al, New J. Phys. 10, 013201 (2008) O.Klimo et al, Phys. Rev. ST-AB 11, 031301 (2008) X.Q.Yan et al, Phys. Rev. Lett. 100, 135003 (2008) B.Qiao et al, Phys. Rev. Lett. 102, 145002 (2009) V.K.Tripathi et al, Plasma Phys. Contr. Fus. 51, 024014 (2009) A. Macchi et al, Phys. Rev. Lett. 102, 085003 (2009) RPDA F. Pegoraro & S.V. Bulanov, Phys. Rev. Lett. 99, 065002 (2007); Laser Phys. 19, 222 (2009) M. Tamburini et al., New J. Phys. 12, 123005 (2010)

34. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni RPA: first experimental evidences 34 Henig, et al., Phys. Rev. Lett. 103, 245003 (2009) (JanUSP -Ti:Sa- LLNL) “Light Sail” Target: 5 nm DLC foils Palmer, et al., Phys. Rev. Lett. 106, 014801 (2011) (ATF- CO 2 - BNL) “Hole Boring” Target: H gas jet

35. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni A road towards enhanced TNSA: materials science for novel targets - Evident interest in “intermediate” conditions n e ~n c Motivation - Scalings predicting more efficient absorption and fast electron generation [L.Willingale et al. Phys. Rev. Lett 96, 245002 (2006)] [S.S.Bulanov et al. Phys. Plasmas 17, 044105 (2010)] Possibility to reach an “advanced” TNSA regime with multilayered targets: thin solid foil + low-density layer Parameter scan of target properties (foam thickness, density..) given a laser configuration Multilayered target manufacturing (not easy controlling density, adhesion to solid..) -Open problems- Foam layer Solid foil [L.Willingale et al. Phys. Rev. Lett 102, 125002 (2009)] 35

36. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni Fabrication tecnique: Pulsed Laser Deposition (PLD) Configuration under study at Nanolab@Politecnico di Milano: low-density Carbon foam low-density Carbon foam attached onto a solid substrate HV: 10 -3 Pa Nd:YAG pulsed laser lens/mirror target vacuum system substrate He/ Ar QC- Microbalance Main advantages: Large choice of materials and substrates Good adhesion properties possibility in obtaining controlled nanostructures Deposition parameters: Wavelength: 532 nm Ar pressure: 0 - 1000 Pa Target-substrate distance: 8,5 cm Fluence: 0,8 J/cm 2 Target: Graphite Substrates: Si[100] -> test depositions for characterization Al (10µm) -> target fabrication PLD 36

37. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni Carbon “foam” characterization Carbon foam morphology: SEM analysis 10 µm 30 Pa100 Pa300 Pa 10 µm 1 µm Structure at high magnification is clearly very open and porous mesoscale On a mesoscale these structures can arrange in different ways by simply varying one process parameter: Ar pressure 37

38. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni Conclusions 38 - U LTRAINTENSE ULTRASHORT (UU) LASER PULSE INTERACTION WITH MATTER - It is an exciting and growing area of reaserch! - L ASER-DRIVEN ION ACCELERATION IS OF PARTICULAR INTEREST - P HENOMENOLOGY OF THE LASER-ION ACCELERATION: - many experimental data available - ion spectrum depends on pulse properties (energy, intensity, pre-pulse) - ion spectrum depends on target properties (composition, thickness) - A NUMBER OF SIGNIFICANT APPLICATIONS ARE FORESEEN - diagnostic of ultrafast EM phenomena (proton imaging) - ion-driven inertial fusion - medical applications (PET, hadrontherapy) - P HYSICS OF THE LASER-BASED ION ACCELERATION: - ion acceleration mechanism relies on laser-induced strong charge separation - need of theoretical understanding…

39. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni That’s all!...but, if you want more information and material......a comprehensive and updated review is under preparation... A. Macchi, M. Borghesi, M. Passoni “Ion Acceleration by Superintense Laser Pulses: from Classic Problems to Advanced Applications” Reviews of Modern Physics (under review, 2012) THE END THANK YOU! 39

40. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni BACKUP SLIDES

41. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni ALaDyn PIC code [C. Benedetti et al. IEEE Trans. Plasma Sci. 36/4, 1790 (2008)] Pulse design: p-polarized “clean” pulse (λ=0.8 µm) Gaussian spatial profile: w=3 µm Temporal cos 4 profile: FWHM=25 fs Peak intensity: a 0 =10  I≈ 2x10 20 W/cm 2 Power content: P=32 TW Target design Ideal non-collisional ionized plasma MainMain “solid” foil: l m =0.5 µm ; n m =80n c ; Z/A=1/3 (Al 9+ ) ContaminantContaminant layer (rear): l r =50 nm ; n r =9n c ; Z/A=1 (H + ) Low-density “foam”Low-density “foam” layer (front): l f =0.5  12µm ; n f =1  4n c ; Z/A=1/2 (C 6+ ) Proton peak energy gain is found to be ~2.3! 2D-PIC: Overestimation of maximum proton energy BUT qualitative agreement Numerical results (I) 41 Explorative 3D simulations Full 3D and 2D runs were performed in the same conditions: with without foam with and without foam 2D3D

42. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 42 Numerical results (II) Maximum proton energy (2D-PIC) Dynamic energy balance @ n f =n c : Absorption increases with foam thickness, reflection decreases up to 60% energy absorbed by particles at optimum thickness (red) Without foam (black) absorption is 10 times smaller! Laser energy conversion (2D-PIC) Parameter scan with foam thickness and density optimum thickness area is broader at decreasing density Dashed line Dashed line: EM energy Solid lines Solid lines: total particle energy

43. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 43 Numerical results (III) First physical interpretation of the results stronger electric field Larger proton energies are justified by a stronger electric field 2 contributions to the longitudinal field: charge displacement  “ordinary” TNSA  electrons from the foam “inductive” component due to transient magnetic fields inside the foam [S.V. Bulanov et al. Phys. Rev. Lett 98 049503 (2007)] Between the electrostatic contributions, the one due to foam electrons dominates

44. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni Comparison among TNSA models 44 C. Perego, et al., Nucl. Instr. and Meth. A (2011), doi:10.1016/j.nima.2011.01.100 Quasi static models appear to be the most effective tools to describe, simply but effectively, TNSA

45. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 45 Pulse energy – intensity plane: TNSA beyond 10 21 W/cm 2 : ? M. Passoni et al, New J. Phys. 12, 045012 (2010) Example : 100 MeV protons with Ti:Sa ( =800 nm); I = 4x10 21 W/cm 2 ; E L = 5 J

46. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 46 Predictions for applications: hadrontherapy with TNSA? Possible path to reach 250 MeV protons and 10 nA current with “usual” TNSA: Ti:Sa ( =800 nm); I = 1x10 22 W/cm 2 ; E L = 50 J;  = 15 fs (focal=4 µm) (3 PW system); Rep. rate 5 Hz (with 10 10 protons/pulse in the selected energy interval) …these requirements could be even less demanding if “improved” schemes of TNSA (mass limited, ultralow thickness, etc) can be adopted at these laser parameters

47. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 47 Experiments with reduced wavelength and different spot size Spot size (FWHM) ~ 4.4  m 3m3m Spot size (FWHM) ~ 0.9  m 3m3m - Wavelength: 528 nm (2  ) - Pulse width: 400 fs - Max intensity (I 2 ): ~4.8*10 18 Wcm -2  m² - Temporal contrast: >10 10 - Use of Ellipsoidal Plasma mirror (EPM) to tight focus 1/5 spot From J. Fuchs presentations at ULIS ’09 and COULOMB ’09 conferences

48. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 48 Experiments with reduced wavelength and different spot size Theoretical interpretation of these experiments… (For a discussion on this subject: M. Passoni et al., NIMA 620, 46 (2010)) - General trend well reproduced - Underling physics seems to be nicely captured

49. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 49 Characteristics of ion emission: dependence on target structure LOW-DENSITY TARGETS L. Willingale, et al., Phys.Rev.Lett. 102, 125002 (2009) (Vulcan-Nd:glass-RAL) MASS LIMITED TARGETS S. Buffechoux, et al., Phys.Rev.Lett. 105, 015005 (2010) (100TW-Nd:glass-LULI) MICROSTRUCTURED TARGETS H. Schwoerer, et al., Nature 439, 445 (2006) (JETI-Ti:Sa-Jena)

50. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 50 Ion spectra: Comparison with experiments - 2 - our model C 5+ ions estimated layer thickness: < 5 nm Quasi-monoenergetic MeV carbon beams [B. M. Hegelich et al., Nature 439, 441 (2006)] […on this issue see also H. Schwoerer et al. ibid. 439, 445 (2006) ] - our model electron energy distribution (PIC) [T. Ceccotti et al, Phys. Rev. Lett. 99, 185002 (2007)] Use of Ultrahigh-Contrast Laser Pulses and thin targets No fitting parameters used!

51. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 51 Dependence on intensity: comparison with experiments Linear dependence confirmed by exp. parametric investigation: Experimental data from: - T. Ceccotti et al, Phys. Rev. Lett. 99, 185002 (2007) (UHI100-Ti:Sa-CEA Saclay) - K. Zeil et al., New J. Phys. 12, 045015 (2010) (Draco-Ti:Sa-Dresden) In both cases, fixed pulse duration (25 fs) and focal spot with UHC M. Passoni et al., AIP Conf. Proc. 1153, 159 (2009) A. Zani, Nucl. Instr. and Meth. A (2011), doi:10.1016/j.nima.2011.01.074

52. Frontiers in Diagnostic technologies, 29.11.2011 Matteo Passoni 52 Dependence on intensity: comparison with experiments [ From M. Borghesi et al., Plasma Phys. Contr. Fus. 50, 024140 (2008)] Effective linear dependence on I L resulting from combined variation of pulse energy & intensity! M. Passoni et al, New J. Phys. 12 045012, (2010)