Use of fewcycle laser pulses for fast ignition research

1
Use of few-cycle laser pulses for fast ignition
research
8th Fast Ignitor Workshop, Tarragona, June 30,
2005

• J. Meyer-ter-Vehn, M. Geissler,
• S. Karsch, F. Krausz, G. Tsakiris, W. Witte
• Max-Planck-Institute for Quantum Optics,
• Garching, Germany
• and
• J. Honrubia
• ETSII, Universidad Politecnica, Madrid, Spain

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Outline

• Cone-guided ILE experiments (Nature 2002)
  indicate more fuel heating than predicted by
  theory. Laser-generated electrons gain more
  energy (T 5 20 MeV) than can be stopped in
  fuel by Coulomb and resistive mechanisms.
• We take this as an indication for anomalous
  stopping due to small-scale (sub-mm, fs)
  instabilities in strongly driven (I/IAlfven gtgt
  1000), high-gradient plasma.
• This calls for pump-probe diagnostics of
  instability growth on sub-mm, fs scales.
  Few-cycle PW-range laser pulses now being
  developed at MPQ may provide the tools.

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Atzeni DT ignition conditions for r/r0130024
kJ, 24 ps, 1 PW
Atzeni, MtV (Oxford Univ.Press 2004) The Physics
of Inertial Fusion
ltEgt1.8 MeV (Il2/13.7 GW)1/2
Pukhov, Sheng, MtV, Phys.Plas. 6, 2847 (1999)
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Alfven limit, return currents, filamentation
In vacuum, beam-generated B-fields limit electron
transport to
IA (mc3/e) bg 17 kA bg Alfven current
In plasma, beam-generated return currents
compensate beam current, but
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Linear growth ratesTransverse beam temperature
stabilizes Weibel filamentation
L. Silva et al. Phys. Plasmas 9, 2458 (2002)
Instability grows on femtosecond timescale and
less wp-1 1 fs - 10 as
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Nonlinear evolution shows filament coalescence
and anomalous beam stopping
2D PIC (nb/np 0.1) Honda, MtV, Pukhov,
PRL 85, 2128 (2000)
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Plasma resistivity acts on return currents and
filamentation, leads to longitudinal E-fields and
beam stopping. 3D-PIC simulations reveal
anomalous resistivity
Sentoku, Mima, Kaw, Nishikawa, PRL 90, 155001
(2003)
1000x enhanced stopping anomalous
resistivity heff 4p wc/wp2
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Resistive filamentation has been studied by
hybrid models (beam by PIC, plasma as fluid)
Davies, Bell, Haines, Guerin, PRE 56, 7193
(1997) Gremillet, Bonnaud, Amiranoff, Phys.
Plasmas 9, 941 (2002) D.R. Welch et al., NIM
A464, 134 (2001) Taguchi, Antonsen, Liu, Mima,
PRL 86, 5055 (2001) CPC 164, 269 (2004) Honrubia
et al., Phys. Plasmas 12, 052708 (2005)
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Filamentation of a 1PW, 1 GA electron beam in a
DT density profile
100 g/cm3
1 GA
Beam parameters 1 MeV, T-120 keV, 12 mm spot
(FWHM)
2
60
j
30
y (mm)
0
60
4.5
log10 T (eV)
30
y (mm)
2.3
0
0
25
50
distance to front surface (mm)
10
p.567
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Few-cycle PW-range laser pulses may drive
ultra-bright fs electron, ion, X-ray sources for
pump-probe diagnostics
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Attosecond flash-lights
Gordienko, Pukhov, et al. PRL 93 (2004)
Lichters, MtV, Pukhov, Phys.Plas.3 (1997)
Tsakiris, MPQ (2005)
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Filamentation pump-probe diagnostics
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Conclusions

• Cone-guided ILE experiments (Nature 2002)
  indicate more fuel heating than predicted by
  theory. Laser-generated electrons gain more
  energy (T 5 20 MeV) than can be stopped in
  fuel by Coulomb and resistive mechanisms.
• We take this as an indication for anomalous
  stopping due to small-scale (sub-mm, fs)
  instabiluties in strongly driven (I/IAlfven gtgt
  1000), high-gradient plasma.
• This calls for pump-probe diagnostics of
  instability growth on sub-mm, fs scales.
  Few-cycle PW-range laser pulses now being
  developed at MPQ may provide the tools.

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Dependence of the linear growth rates on the
electron beam and plasma parameters
velocity spread
resistivity
total energy
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Cylindrical beam filamentation
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Filaments devour each other accompanied by
dramatic transverse heating
M. Honda, J. Meyer-ter-Vehn, A. Pukhov, PRL 85,
2128 (2000)
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Filamentation general phenomenon, here for 1017
W/cm2
3D PIC simulation, Pukhov (2000, unpublished), 7
keV electron spectrum
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Example of resistive filamentation
current density
constant resistivity h 10-6 W m
longitudinal cuts at x 0
transversal cuts at z 9 mm
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9mm
100 fs
jz
5.61012 A/cm2
1.4 MA g 2 T- 0
y (mm)
0
12mm
9mm
0
-15
15
200 fs
jz
5.61012 A/cm2
30mm
beam power vs. depth
y (mm)
0
0
-15
15
300 fs
jz
5.61012 A/cm2
y (mm)
0
0
-15
0
15
30
0
15
-15
z (mm)
x (mm)
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DT heating by fast electrons
3D hybrid simulation for DT (J. Honrubia, June
2005, unpublished)
DT at 1 g /cm3
2 MA g 4 dfocus 12 mm T- 100 keV
9.5 mm
32 mm
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