Presented at the 15th International Symposium on

1
Short Pulse Laser Generated Ion Beams for Fast
Ignition
TU Darmstadt

• Presented at the 15th International Symposium on
• Heavy Ion Driven Inertial Confinement Fusion
• in Princeton, June 7, 2004
• by
• Matthias Geissel1,2, Markus Roth2,
• M. Allen3, P. Audebert4, M. Basko5, A. Blaževic2,
  E. Brambrink2,
• J. Cobble6, T.E. Cowan7, M. Cuneo1, J.C.
  Fernández6,
• J. Fuchs4,7, J.-C. Gauthier4, M. Hegelich6, S.
  Karsch8

UN Reno
1Sandia National Laboratories, Albuquerque
5Inst. for Theor. and Exp. Physics, Moscow
2Darmstadt University of Technology GSI,
Darmstadt
6Los Alamos National Laboratory
7University of Nevada, Reno GA, San Diego
3University of California, Berkeley
4LULI École Polytechnique, Palaiseau
8Rutherford Appleton Laboratory
Sandia is a multiprogram laboratory operated by
Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energys
National Nuclear Security Administration under
contract DE-AC04-94AL85000
2

1. Intro Combining Lasers and Ion Drivers
2. Concept How Does It Work?
3. Experiments Probing the Models
4. Fast Ignition Some Considerations
5. New Projects Perspectives at SNL

3
Heavy Ion Drivers
Laser Drivers
hohlraum
fuel pellet
FAST IGNITOR
PROTON

• Relieved compression requirements
• Problematic energy transport from critical
• density layer to core via hot electrons

• Low Driver Efficiency
• Low Repetition Rate

• Lower Power
• Lower Focusability

• High Power Densities
• Good Pulse Shaping

• High Efficiency
• Beam-Target Coupling
• High rep-Rate

4
Mechanism
TNSA Target Normal Sheath Acceleration
TNSA Target Normal Sheath Acceleration
pre-plasma
1012 V/m
-

MAIN PULSE _at_ gt1019 W/cm2
protons
electron cloud

• Acceleration of surface contaminants
• Influence of sheath formation(bulk
  material/conductivity)
• Influence of rear surface(roughness/features/curv
  ature)

gold foil
5
Experimental Issues

• Target
• Investigation of different materials
• Investigation of foil curvatures
• Investigation of surface structures
• Beam
• Spatial distribution
• Emittance
• Energy distribution

6
Setup of the Experiment
20-30J _at_ 300-400fs 50-100TW
ion spectrometer and / or Thomson parabola
RCF
protons
radiochromic film
_at_ 0 or 13
7
Conductivity

• high conductivity
• well established e--sheath
• intense, collimated protons
• smooth proton beam

• no conductivity
• filamented e and proton beams
• low proton intensity

gold
plastic
laser
laser
8
1D Defocusing
apertures for ion spectrometers
RCF
RCF
protons
protons
laser
laser
60µm gold wire
9
Rear Surface Features
Example Line Pattern
false color picture of the RCF response (beam
imprint)
interpretation

• proton source size 60µm
• emittance lt 0.01 mm mrad

laser
for protons gt 10 MeV source size lt 15µm eN lt
0.002 mm mrad
10
Proton Energy Spectra
Tayloring the energy spectrum of laser generated
protons is an important issue to be
solved (mono-energetic ions for FI).
11
Fast Ignitor Scenario

• Conversion efficiency 1-10 so far
• (increasing with laser performance).
• Need for a Multi-Beam-Ignitor.
• Conversion window as concave multi-lenslets.

Multiple (Multi-) PW Beams

• Production Target Issues
• Cold rear surface
• Acceleration vacuum gap
• Proximity to the hohlraum/capsule
• Thin shield must protect from driver-
• induced soft X-rays

Radiation Shields
12
Production Target Stability Planar Gold Wall
Response on Driver Radiation (M. Basko)
IGNITION
15µm
2nd shield
30µm
50µm
50µm
15µm
30µm

• a 50µm shield is displaced by 230µm at the
  time of ignition (maximum compression)
• the shield is heated up to 2-3 eV at the time
  of ignition

13
Conclusion

• Ultra intense lasers can generate ion beams of
  superior beam quality
• TNSA is the primary process
• Spatial distribution and divergence ca be
  taylored
• Fast Ignition
• Multiple PW laser necessary
• Sophistically shaped p-production target
• Careful heat shielding essential
• Complex but feasible scenario

14
Sandia Multi-TW Facilities OPCPA at High
Energies

• General Atomics custom design OPCPA front end
  30mJ _at_ 10Hz.
• Ndglass (phosphate) rod amplifiers push to 4J
  _at_ 1 shot / 15 min.
• Ndglass (phosphate) slab amplifier (Beamlet
  design) push to 40-400 J (depending on
  available gratings and compressor design).

Sandia is a multiprogram laboratory operated by
Sandia Corporation, a Lockheed Martin Company,
for the United States Department of Energys
National Nuclear Security Administration under
contract DE-AC04-94AL85000
15
The ZBL Laser Complex
Z-Beamlet
Control Room
100 TW Laser
Optics Support Facility
100TW Target Area
16
10TW Experiments Small Scale 15 min. Rep-Rate
compressor target chamber
CCDLDM, HeNe
17
100TW Project Status
18
Petawatt Experiments Fast Ignition Experiments
on Z
100 TW Target Area
Petawatt Target Area