Rutherford Appleton Laboratory

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Vulcan Front End OPCPA System
Rutherford Appleton Laboratory
Pump Laser
Stage 1 - BBO
Stage 2 - BBO
Stage 3 - LBO
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OPCPA Test Bandwidth
Rutherford Appleton Laboratory

• Theoretical bandwidth for this system is gt 250 nm
  (_at_ 1053 nm
• In previous tests (limited by bandwidth of
  optics) we demonstrated 50 nm

• Actually require just 16 nm
• So far first 2 stages tested (unsaturated gain of
  106)
• Need the 3rd stage for saturation and stability

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PW Scheme
Rutherford Appleton Laboratory
Rutherford Appleton Laboratory
Oscillator 5 nJ 100fs TiSa
Existing Building
New Target Area
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The Vulcan PW Facility
Rutherford Appleton Laboratory
Computer Schematic - 2000
Vulcan PW Facility - 2002
Energy on target 500J Pulse duration 500
fsec Intensity on target 1021 Wcm-2
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Single electron motion
Rutherford Appleton Laboratory
A single electron in the laser field exhibits a
figure of eight motion due to the vxB term in
the Lorentz force F -e(EvxB) Twice every
laser cycle, electrons are accelerated in the
direction of k The kinetic energy the electron
acquires is roughly proportional to the
ponderomotive potential
E
k
B
At 1021 Wcm-2, kT ? 10 MeV.
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Self-modulated wakefield, classical wakefield and
beatwave accelerators studies on the VULCAN PW
facility
Rutherford Appleton Laboratory
Rutherford Appleton Laboratory

• CPA beatwave schemes also possible and will be
  investigated on the PW facility

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Accelerated electrons observed at energies up to
120 MeV
Rutherford Appleton Laboratory
Rutherford Appleton Laboratory

• In the self modulated wakefield, stimulated
  Raman scatter arises from noise - generating an
  electron plasma wave and a down-shifted
  electromagnetic wave. This em wave beats with
  the incident laser pulse, and the increased
  intensity in the beat-wave pattern enhances the
  plasma wave. Gradients of 1 GeV/cm have been
  measured. Eventually, the plasma wave breaks,
  generating a wide energy spread shown here.
• In the classical wakefield, the laser intensity
  and plasma density are reduced below the
  threshold for stimulated Raman scatter. In this
  case, the ponderomotive force expels electrons
  from the focus, but space charge requires that
  they return

MIK Santala et al. Phys. Rev. Lett, 86, 1227
(2001)
after the laser pulse has passed. This sets up a
large amplitude (GeV/cm) oscillating longitudinal
electric field that can accelerate low emittance
electron bunches - provided the plasma wakefield
is quasi - 1 dimensional - requires PW -class
lasers with long focal lengths optics.

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Beat-wave accelerators
Rutherford Appleton Laboratory

• Beatwave accelerators were the first to be
  studied in the 1980s
• Two laser pulses of different frequencies are
  focused into a plasma gas. At a resonant density,
  the ponderomotive force of the induced beat
  pattern amplifies small density fluctuations
  arising from noise - and a large amplitude
  longitudinal electric field is set up.
• Nd glass operating at 1mm is better than CO2
  (10.6mm) as higher plasma densities are required
  - hence larger electric fields.
• However, if the laser pulse duration is too
  long, the modulation instability limits the
  amplitude of the plasma waves that can be
  generated.
• With chirped pulse, picosecond laser pulses, a
  beat-wave pattern can be induced by spectral
  shaping the laser pulse. The pulse duration is
  sufficiently short to amplify the plasma waves
  before the modulational instability can grow to
  disrupt the process.
• The VULCAN PW laser will be used to study this
  beat-wave accelerator process.

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Astra laser hall
Rutherford Appleton Laboratory
Astra is extremely compact, driving physics at up
to 1019Wcm-2 at 10Hz with table top scale
The final amplifier will be upgraded next year to
enable full energy to be delivered to TA2
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Astra high intensity target area
Rutherford Appleton Laboratory