seeking for combined electron/ion spectrometer in laser ion acceleration experiments
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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
cIbalance
LecmEea
00 2
0
20
emn Le
c
Lc
e dnna ~0
relativistically normalizedlaser vector potential
critical electron density
normalized areal electron density
2
218
20 1037.1
cmmWaI
LL
balance condition
Laser
LecmEea
00
20
20
emn 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 ~ optimum ion acceleration a0 > 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 polarization electron 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
el
ectro
n si
gnal
on
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-
fieldsadvantage:- 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
deut
eron
ene
rgy
(keV
)
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
nsity
(W/c
m2 )
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
prot
on c
utof
f ene
rgy
(MeV
)
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 !
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