Ultrafast Laser-Driven Plasma for Space Propulsion Terry Kammash , K. Flippo † , T. Lin, A. Maksimchuk, M. Rever, S. Banerjee, D. Umstadter FOCUS Center / Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, MI 48109-2099, USA Y. Sentoku General Atomics, San Diego, CA V. Yu. Bychenkov P. N. Lebedev Physics Institute, Russian Academy of Science, 117924 Moscow, Russia Lasers supported by the National Science Foundation FOCUS Center and the U of M Center for Ultrafast Optical Science, and funding from NASA Institute For Advanced Concepts
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Ultrafast Laser-Driven Plasma for Space
PropulsionTerry Kammash, K. Flippo†, T. Lin,
A. Maksimchuk, M. Rever,S. Banerjee, D. Umstadter
FOCUS Center / Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, MI 48109-2099, USA
Y. SentokuGeneral Atomics, San Diego, CA
V. Yu. BychenkovP. N. Lebedev Physics Institute, Russian Academy of Science, 117924 Moscow, Russia
Lasers supported by the National Science Foundation FOCUS Centerand the U of M Center for Ultrafast Optical Science, and funding from NASA Institute For Advanced Concepts
Accelerator SetupProton Beam
CUOS T3 Laser Parameters:• Ti:Sapphire / Nd:Glass• 1.053 mm (ωo),
527nm (2 ωo)• up to ~12 TW • 5 J• 400 fs• Contrast: 10-5:1 @ ωo,
10-7:1 @2 ωo• 2x1018 - 2x1019 W/cm2
Target Normal Forward Direction
Laser Forward Direction
CR-39 Detector
FWHM = 4.3 um
Incident Laser Spot
Front Surface Deuteron Acceleration
•Activation of 10B to 11C is achieved only by illuminating deuterons on the front surface. •No activation when deuterons were on the back surface, or without deuterons (i.e. no production of 11C detected from 11B (p,n)11C reaction).•Deuterons have about ½ the Emax of the measured protons
10
100
1000
0 10 20 30 40 50 60 70
Cou
nts
/2 m
in
Time after shot (min)
Decay for 11C
Ilas=6x1018 W/cm2
Detection efficiency 15%
10B(d,n)11C reaction
Boronsample
Laser
Mylar filmCD
11C10BDeuterons
n
K. Nemoto, S. Banerjee, K. Flippo , A. Maksimchuk, D. Umstadter App. Phys. Lett, 78, 595 (2001)
RCF (a,c,e,g) / CR-39 (b,d,f,h) detector stack images for 13µm Mylar, 10 µm silicon, 12.5 µm aluminum, and 12.5 µm copper targets. All pairs are single shot except (c) and (d) which were two separate shots. RCF records protons between ~0.2 and ~2 MeV, CR-39 records protons between ~2.5- ~4 MeV. Except (d) which recorded between ~1.2 MeV and 3 MeV
Call out: White arrows point to beam filamentation, most likely a manifestation of the Weibel, instability.
Comparison with Simulation
Images: Contrast enhanced RCF images of proton beam profiles after a drift of 5 cm from target exit from experiments with 13 microns of Mylar (a) top left, and 12.5 microns of aluminum (b) bottom left. Compare an electron beam profile from a simulation (c) by L. Gremillet, et al. [Phys. Plasmas 9, 941(2002)], showing the transverse electron profile jb/enc at 20 microns inside a silica target for a propagating monoenergetic electron beam of energy 500 keV, after 405 fs of propagation, which is also the beam duration. Image reproduced with permission.
SilicaObserved profiles e-beam simulation
Magnetic Field from Simulation vs. Proton Beam Profile
E field configuration plot from the simulation at 405 fs. Notice the similarities in the simulation slices to proton beam images in row (I) of the previous slide.
e-beam induced B field evolution is very similar to that of the proton beam profile seen from Mylar previously.
And as shown byM. Honda, J. Meyer-ter-Vehn and A. Pukov, PRL 85 2128 (2000) the ions can follow the electron filaments in as little as 60 fs.
Electron Distribution From Al Target
ProtonsX-ray Film
laser
Target
Top View
Target Holder Shadow
X-ray Film Line Out
X-ray Film
Holder0°
Protons From Front Surface
0
2
4
6
8
10
12
14
16
0 50 100 150 200
Target Thickness [microns]
Max
imum
Pro
ton
Ene
rgy
[MeV
]
Ei max ~ 13 µm
Simulation of proton beam
Sentoku’s[1] recent 1-D PIC simulations predict a 5 MeV beam from the front surface for a 400fs laser pulse, with about 13 MeV from the rear. This agrees well with the observed 4 MeV trend, and a maximum of about 12 MeV.
[1] Y. Sentoku Phys. Plasmas 10 2009 (2003)
Deuteron AccelerationPreliminary Results
Deuteron coating No deuteron coating
p+d+p+
Where do highest energy deuterons come from?1. The BACK of 12.5um Al2. The FRONT of 6 um Mylar3. The FRONT of 13 um Mylar4. The FRONT of 12.5 um Al5. The BACK of 13 um Mylar
Proton Energy Scaling with Pulse Duration and Intensity
From Y. Sentoku, T. E. Cowan, A. Kemp, and H. RuhlPhysics of Plasmas 10, 2009 (2003)
14.5 MeV
> 30 MeV
Current T-cubed System
Future HERCULES System
Peak Proton Energy vs. Spot Size
E = 190.87d 1.7404
0
1000
2000
3000
4000
5000
6000
3 3.5 4 4.5 5 5.5 6 6.5 7
Spot size diameter [microns]
Peak
Pro
ton
Ener
gy [k
eV]
f/3.3 off-axis parabola
f/1.5 off-axis parabola
Power Scaling Fit
For intensities of ~ 1.4 x 1019 W/cm2
For intensities of ~ 2.5 x 1019 W/cm2
E =190.87 x d 1.704
Spot Size Comparison
Total Intensity vs. Diameter for f/1.5 Paraboloid 4.3 FWHM Spot Size
Material Effects on Plume ProfileProton Beam Images Using a CCD
Laser Propagation
Direction
TargetPlane
Dark Side
IlluminatedSide
4 Al Target, 4MeV beamNo backfilled
gas,200 mTorr ambient
4 um Al Target with 2 Torr H2
25 um Mylar Target
25 um Mylar Target
with 2.4 Torr He
25 um Al Target
Proton Beam isEmitted Normal to Target
Plume Evolution in 1 Torr H2Ambient Backfill
12.5 mm Al
+4 ms +1 ms +4 ms +14 ms
3.069 cm
25 mm Mylar
2.138 cm
~31000 m/s
2.222cm
3.194 cm
~32000 m/s
1 cm
+ 65.5us+1 ms
Target Geometry
>1.4 MeV, 55º div.@ 1.5x1019 W/cm2
>2 MeV, 38º div.@ 1.2x1019 W/cm2
> 1.4 MeV, 44º div.@ 1.6x1019 W/cm2
> 3 MeV, 28º div.@ 1.2x1019 W/cm2
Laser
Protons
Target
TargetHolder
Curved TargetGeometry 25 µm AlRadius of
curvature ~ 0.2 mm
Radius of curvature ~ 0.5 mm
Target Geometry
~100 Micron Half Wire Cross-sectionsFocus on
flat surfaceFocus on
round surface
Wire orientation:
Protons
Laser
ProtonsProtons
Laser
Wire position
CR-39
Flat Round
laser
laser
Beam Images:Focusing on flat surface
(840) creates an ion beam, while focusing on the round side produces a cylindrical-like spray
Target Surface Geometry
Electron Microscopyof LaserBlack™
Results:•30 mm Laserblack target ~ 8.2 MeV•Enhancement in the number of maximum energy protons•Beam profile does not suffer, regardless of which surface has been coated, i.e. no imprinting even from rear-side
100 µm
2 µm
Murnane et al. APL 62 (1993) used gratings and clusters,Kulcsar et al. PRL 84 (2000) used metallic “velvet”.
Both showed enhanced X-ray yield from enhance electron heating from efficient coupling.
LaserBlack® is > 96% absorptive at 1 mm.
Laser Spot Size ~ 6 microns
Use a material which will “trap” the laser light, to enhance the generation of hot electrons.
>1.3MeV31º div.
T-cube Laser
Thin Film Target
Mesh Radiochromic Film
51.8 lines high
Proton Radiography
The possibility exists to use the laser produced proton beam for very small scale imaging or even lithography.
The image on the left is a 5x magnified proton radiograph captured on RCF of a mesh with 10 micron wires and 30 micron grid spacing.
Accomplishments Thus Far1. Generate a Relativistically Consistent
Mathematical Expression for the energy of the ejected ion as a function of laser and target parameters, i.e.
Ei =z √ηIRλwhere
z = ion chargeη = energy conversion efficiencyR = radius of focal spotλ = laser wave length
Accomplishments Thus Far
2. Experimentally validatedEi~ √IEi~ √λ
3. Indirectly established relationships relating Ei to R and dependence on η. More work is needed in this area!
Just purchased 5 parabolic mirrors to investigate thoroughly dependence of Ei and total number of ejected particles on R.
Accomplishments Thus Far4. Experimentally established dependence of
Ei on target thickness “t”, optimized t≈10λ5. Experimentally established conditions for
filamentation instabilityP =5Pc=5[17(ωo/ωp)2 GW]
4Tc/ωpa0≤2R
c = speed of lighta0=8.5×10-10 λ [µm] I1/2[W/cm2]ωp=plasma frequencyR= radius of focal spot
Accomplishments Thus Far
4. Experimentally established energy of ions ejected from front and rear surfaces of target which appear to agree well with simulations
5. Established dependence of proton beam profiles on materials, surface conditions and geometry
6. Carried out designs of space Nuclear Reactor for use in LAPPS. Likely candidates are gas-cooled Cermet reactors using Uranium, Plutonium or Americium as fuel.