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 Ecole Polytechnique
Motivation: Investigation of acceleration potential and
electron energy distribution 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
Motivation: Acceleration potential and electron energies
in the RPA-regime
displaced electrons due to pressure impact
(laser accelerates electrons)
balance
IL
c
~ oE
Laser
2
s
restoring (electrostatic) force
due to ion background
e0 E
relativistically
a0 
normalized
m ec L
laser
vector potential
balance condition
2
IL 
a0
L
a0 ~
1 . 37  10
18
W m
cm
ne d
nc L

2
2
2
critical
 0 m e L
electron n c 
2
e0
density
normalized areal electron density
Motivation: optimum ion acceleration
in 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)
Laser parameters : I  5  10 19 W / cm 2 t L  45 fs d L  6  m
C-target parmeters : l f  0.6 nm
n i  6  10 cm
22
3
Electron density distribution function at
t=17 fs
Circular polarization
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
electron signal on film (arb.u.)
Look back: laser driven mass-limited droplet targets
simple electron spectrometer with dosimetric film
1
scanned film data
(relative absorption)
smoothed
0.1
Electron confinement
in the spherical plasma
is visible in the emitted
electron spectrum
from a single droplet.
1x10
charged
particle
burst
exponential slope:
exp(-E/kTe-hot)
with
kTe-hot ~ 600 keV
6
ponderomotive
potential at 1019 W/cm2
~ 640 keV
2x10
6
3x10
6
energy (eV)
B = 0.27 T
electrons
GAF-chromic HD810-film
~ integration of 104 pulses
S. Busch et al., APL (2003)
Look back: laser driven mass-limited droplet targets
imaging MCP for electron detection
Laser
~ 2 mm aperture
at about 35 cm distance
B-, Efields
imaging
MCP
for ion
detection
advantage:
- single pulse, online detection
disadvantage:
- small detection range for electron energies
- large aperture to achieve reasonable electron signal gave low resolution
Look back: laser driven mass-limited droplet targets
cutoff deuteron energy (keV)
Dependance of ion cutoff energies on maximum observed
electron energies in correlated detection indicate a
sensitive influence of energetic electrons on ion acceleration.
800
600
400
200
1400
1500
1600
1700
maximum electron energy (keV)
S. Ter-Avetisyan et al., PRL 2004
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
Separate ion and electron measurements
in acceleration measurements with ultra-thin foils
A glimpse of
the
experiment
Separate ion and electron measurements
in acceleration measurements with ultra-thin foils
to achieve of electron blow out
red glowing
3nm DLC
transition from
optimum ion acceleration
to electron blow out
Prad  2 I / c  Pes  ( en 0 D ) / 2
2
proton cutoff energy (MeV)
22
10
2
intensity (W/cm )
21
10
protons
12
10
DLC
Al
Ti
8
6
4
2
0
1
10
100
1000
foil thickness (nm)
20
10
19
10
electrons
18
10
0
5
10
15
20
target thickness (nm)
25
D. Kiefer, et al., in preparation
 D  3 nm
14
500
µm
Attempts with a wide angle
multi-pinhole magnetic spectrometer setup
ion phase space
angle
2°
0°
-2°
energy
angle
detection limit
electron phase space
5°
advantage
0°
- correlated ion and electron detection
with angular emission (phase space)
information
disadvantage
-20°
- strong inhomogeneous B-field requires
extensive 3D-tracking and numerical
data analysis
- no E-field for ion TP, blurring and background, requires MCP gating
S. Ter-Avetisyan et al. POP 16, 043108 (2009), D. Jung et al. RSI 82, 043301 (2011)
energy
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
data evaluation
in progress
D. Kiefer MPQ
electron energies
0.5 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
detected electron signal level is low:
0.4 mm pinhole at 80 cm source distance
1
4 7 10
31 MeV
10
2
1
0.1 T + E- field
MeV
scintillator screen
inside B-field
test experiments
with 5 micron Ti - foil
proton , C4+
trace
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
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 )
High Field Laser Laboratory at Max-Born-Institute
Thank you for your attention !