Seeking for combined electron/ion spectrometerin laser ion acceleration experiments

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

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 GarchingD. Kiefer, P. Hilz., C. Kreuzer, K. Allinger, J. Schreiber

Instrumentation for Diagnostics and Control of Laser-Accelerated Proton (Ion) Beams: Second Workshop, 2012 June 7-8 at Ecole Polytechnique

Motivation: Investigation of acceleration potential andelectron energy distribution in the TNSA-regime

TNSA scheme

precursor electrons

which leave the targetand 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

Motivation: Acceleration potential and electron energies in the RPA-regime

displaced electrons due to pressure impact (laser accelerates electrons)

restoring (electrostatic) force due to ion background

2~ soL E

c

I

balance

Lecm

Eea

0

0 20

20

e

mn Le

c

Lc

e d

n

na ~0

relativistically normalizedlaser vector potential

critical electron density

normalized areal electron density

2

218

20 1037.1

cm

mWaI

LL

balance condition

Laser

Lecm

Eea

0

0 20

20

e

mn Le

c

Motivation: optimum ion accelerationin the RPA-regime and beyond – electron blow out

different cases for laser intensity IL in relation to target thickness d :c

a0 ~ s optimum ion acceleration a0 > s electron blow out

Motivation: investigation of electron blow out – perspective of flying electron mirror

2D PIC simulations (A.A. Andreev)

Electron density distribution function at

t=17 fs 33fs

19 25 10 /I W cm 45Lt fs 6Ld m22 36 10in cm 0.6fl nm

Laser parameters :

C-target parmeters :

Circular polarizationelectron mirror moves with 0,92 c0

with g ~ 2.55 possible frequency up shiftof reflected light by a factor 4 g2 ~ 26

1x106 2x106 3x106

0.1

1

ele

ctro

n s

ignal o

n film

(arb

.u.)

energy (eV)

scanned film data (relative absorption)

smoothed

Electron confinement in the spherical plasma is visible in the emitted electron spectrum from a single droplet.

chargedparticleburst

GAF-chromic HD810-film~ integration of 104 pulses

electrons

B = 0.27 T

exponential slope:exp(-E/kTe-hot)

withkTe-hot ~ 600 keV

ponderomotivepotential at 1019 W/cm2

~ 640 keV

S. Busch et al., APL (2003)

Look back: laser driven mass-limited droplet targetssimple electron spectrometer with dosimetric film

Look back: laser driven mass-limited droplet targets

Laser

imaging MCP for electron detection

imagingMCP for iondetection

~ 2 mm apertureat about 35 cm distance

B-, E- fields

advantage:- single pulse, online detectiondisadvantage:- small detection range for electron energies- large aperture to achieve reasonable electron signal gave low resolution

1400 1500 1600 1700

200

400

600

800

cu

toff d

eute

ron e

nerg

y (k

eV

)

maximum electron energy (keV)

Look back: laser driven mass-limited droplet targets

Dependance of ion cutoff energies on maximum observedelectron energies in correlated detection indicate a sensitive influence of energetic electrons on ion acceleration.

S. Ter-Avetisyan et al., PRL 2004

Separate ion and electron measurements in acceleration measurements with ultra-thin foils

~ 2 mm apertureat about 40 cm distance from source

design (D.Kiefer MPQ) of a magnet spectrometer for electronssuitable for a range 1 MeV … 10 MeV

LANEX screen approx. 25 cm long

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

A glimpse of the

experiment

Separate ion and electron measurements in acceleration measurements with ultra-thin foils

Separate ion and electron measurements in acceleration measurements with ultra-thin foils

nmD 3

to achieve of electron blow out

2/)(/2 20DenPcIP esrad

red glowing 3nm DLC

500 µm

electron blow-out condition

0 5 10 15 20 251018

1019

1020

1021

1022

inte

nsit

y (W

/cm2 )

target thickness (nm)

D. K

iefer, et al., in preparation

transition from optimum ion accelerationto electron blow out

1 10 100 10000

2

4

6

8

10

12

14

TiAlDLC

pro

ton

cu

toff

en

erg

y (M

eV

)

foil thickness (nm)

protons

electrons

S. Ter-Avetisyan et al. POP 16, 043108 (2009), D. Jung et al. RSI 82, 043301 (2011)

advantage - correlated ion and electron detection with angular emission (phase space) informationdisadvantage - strong inhomogeneous B-field requires extensive 3D-tracking and numerical data analysis - no E-field for ion TP, blurring and background, requires MCP gating

energy

ion phase space

energy

electron phase space

0°

2°

-2°

0°

5°

-20°

angl

ean

gle

detection limit

Attempts with a wide angle multi-pinhole magnetic spectrometer setup

Angular resolved electron emission from laser (3x1019W/cm2 @ 40 fs) irradiated 100 nm CH-foil

principle potential of the spectrometer is clearly visiblea more homogeneous 3D B-field geometry should be possiblewhich provides better manageable data evaluation

B-field along spectrometer axis of used setup

data evaluationin progressD. Kiefer MPQ

electron energies0.5 1 2 5 MeV

Design, test of a single channel electron/ion spectrometer

design goals:- to avoid influence of fringe fields and large inhomogeneous fields- reasonable resolution

scintillator screen inside B-field

0.1 T + E- field

proton , C4+

trace

test experimentswith 5 micron Ti - foil

detected electron signal level is low:0.4 mm pinhole at 80 cm source distance

1 4 7 10 31 MeV

1021

MeV

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

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 )

Credits

High Field Laser Laboratory at Max-Born-Institute

Thank you for your attention !