Seeking for combined electron/ion spectrometer in laser ion acceleration experiments

1. Seeking for combined electron/ion spectrometer in laser ion acceleration experiments M. Schnürer, S. Steinke, F. Abicht, J. Bränzel, A.A. Andreev, W. Sandner Max Born Institute, Max Born Str. 2a, D-12489 Berlin, Germany schnuerer@mbi-berlin.de TR-18 collaboration LMU-MPQ Garching D. Kiefer, P. Hilz., C. Kreuzer, K. Allinger, J. Schreiber • Outline • Motivation • Look back: laser driven mass-limited droplet targets • Separate ion and electron measurements • in acceleration measurements with ultra-thin foils • Attempts with a wide angle magnetic spectrometer setup • Design, test of a single channel electron/ion spectrometer • Conclusion and Summary Instrumentation for Diagnostics and Control of Laser-Accelerated Proton (Ion) Beams: Second Workshop, 2012 June 7-8 at EcolePolytechnique

2. Motivation: Investigation of acceleration potential and electronenergydistribution in the TNSA-regime TNSA scheme • precursor electrons • which leave the target • and built up the potential wall • their energy distribution gives information about: • ponderomotive potential of • laser field (and thus acting • laser intensity) or additional • electron acceleration • mechanism • - acceleration potential (wall) in • electron – ion sheath

3. Motivation: Acceleration potential and electronenergies in the RPA-regime displaced electrons due to pressure impact (laser accelerates electrons) Laser restoring (electrostatic) force due to ion background critical electron density relativistically normalized laser vector potential balance condition normalized areal electron density

4. Motivation: optimumionacceleration in the RPA-regime andbeyond – electronblow out different cases for laser intensity IL in relation to target thickness d :c a0 ~ s optimum ion acceleration a0 > s electron blow out

5. Motivation: investigationofelectronblow out – perspectiveofflyingelectronmirror 2D PIC simulations (A.A. Andreev) Laser parameters : C-targetparmeters : Electron densitydistribution functionat t=17 fs 33fs electron mirror moves with 0,92 c0 with g ~ 2.55 possible frequency up shift of reflected light by a factor 4 g2 ~ 26 Circularpolarization

6. Look back: laser driven mass-limited droplet targets simple electron spectrometer with dosimetric film exponential slope: exp(-E/kTe-hot) with kTe-hot ~ 600 keV ponderomotive potential at 1019 W/cm2 ~ 640 keV Electronconfinement in thesphericalplasma isvisiblein theemitted electronspectrum froma singledroplet. charged particle burst B = 0.27 T electrons GAF-chromicHD810-film ~ integrationof 104pulses S. Busch et al., APL (2003)

7. Look back: laser driven mass-limited droplet targets imaging MCP for electron detection imaging MCP for ion detection Laser ~ 2 mm aperture at about 35 cm distance B-, E- fields • advantage: • single pulse, online detection • disadvantage: • small detection range for electron energies • large aperture to achieve reasonable electron signal gave low resolution

8. Look back: laser driven mass-limited droplet targets Dependance of ion cutoff energies on maximum observed electron energies in correlated detection indicate a sensitive influence of energetic electrons on ion acceleration. S. Ter-Avetisyanet al., PRL 2004

9. Separate ion and electron measurements in acceleration measurements with ultra-thin foils design (D.Kiefer MPQ) of a magnet spectrometer for electrons suitable for a range 1 MeV … 10 MeV LANEX screen approx. 25 cm long ~ 2 mm aperture at about 40 cm distance from source advantages - reasonable energy resolution - single pulse, low - but detectable signals - calibration data of fluorescent screen material available disadvantages - fringe fields of magnet introduce beam focusing and defocusing ( try with stronger magnet and electron MCP-detection failed) - setup hardly combinable with 80 mm MCP for ion detection for reasonable energy range and resolution

10. Separate ion and electron measurements in acceleration measurements with ultra-thin foils A glimpse of the experiment

11. red glowing 3nm DLC 500 µm electron blow-out condition Separate ion and electron measurements in acceleration measurements with ultra-thin foils transition from optimum ion acceleration to electron blow out to achieve of electron blow out protons D. Kiefer, et al., in preparation electrons

12. Attempts with a wide angle multi-pinhole magnetic spectrometer setup 2° 0° angle ion phase space -2° energy 5° advantage - correlated ion and electron detection with angular emission (phase space) information disadvantage - strong inhomogeneous B-field requires extensive 3D-tracking and numerical data analysis - no E-field for ion TP, blurring and background, requires MCP gating 0° angle electron phase space detection limit -20° energy S. Ter-Avetisyan et al. POP 16, 043108 (2009), D. Jung et al. RSI 82, 043301 (2011)

13. Angular resolved electron emission from laser (3x1019W/cm2 @ 40 fs) irradiated 100 nm CH-foil principle potential of the spectrometer is clearly visible a more homogeneous 3D B-field geometry should be possible which provides better manageable data evaluation B-field along spectrometer axis of used setup electron energies 0.5 1 2 5 MeV data evaluation in progress D. Kiefer MPQ

14. Design, test of a single channel electron/ion spectrometer • design goals: • to avoid influence of fringe fields and large inhomogeneous fields • reasonable resolution detected electron signal level is low: 0.4 mm pinhole at 80 cm source distance 1 4 7 10 31 MeV 10 2 1 MeV 0.1 T + E- field scintillator screen inside B-field test experiments with 5 micron Ti - foil proton , C4+ trace

15. Summary and Conclusion • several experiments in laser ion acceleration showed the usefulness • of correlated electron/ion data to explore acceleration mechanisms • upcoming experiments to access the flying electron mirror regime • underline the need of combined electron spectrometer • the limited electron flux from laser driven thin foils • forces spectrometer solutions with relative small distances • between source and entrance aperture + dispersion unit • while keeping a reasonable resolution for both electrons and ions • and taking size restrictions • as well as thresholds of imaging detectors into account • separated slit apertures and separated B- , E- fields, • specific field configurations, • MCP-gating and/or other electron, ion detectors (semiconductor based) • offer further and interesting design possibilities

16. Credits A.A. Andreev (also VSI St. Petersburg), F. Abicht, J. Bränzel, W. Sandner T. Sokollik (presently LBNL), S. Steinke (presently LBNL), T. Paasch-Colberg (now MPQ), P.V. Nickles (GIST Korea), Laser+HFL: L. Ehrentraut, G. Priebe, M.P. Kalashnikov, G. Kommol (MBI) Transregio 18 collaboration: MPQ / LMU Munic: J. Schreiber, D. Kiefer , P. Hilz, K. Allinger, C. Kreuzer T. Tajima, J. Meyer-ter-Vehn, D. Habs, A. Henig, R. Hörlein, X. Q. Yan, D. Jung, M. Hegelich (LANL) HHU Düsseldorf, FSU Jena S. Ter-Avetisyan(MBI, QUB, now ELI – beam lines Prague )

17. High Field Laser Laboratory at Max-Born-Institute Thank you for your attention !