Review of UK HiPER relevant experiments

Kate Lancaster

Work presented here is part of HiPER WP10 which aims to de-risk some of the physics of HiPER through targeted experimental campaigns

There are two sets of work presented here:

Absorption as a function of scale length, LULI April 2008Channelling in under and near critical plasma, march 2009

Work here is new and still under analysis.....

R.H.H. Scott, J. J. Santos, K. L. Lancaster, J. R. Davies, S. D. Baton, F. Perez, F. Dorchies, C. Fourment, S. Hulin, J. Valente, J.-L. Feugeas, Ph. Nicola, M. Rabec Le Glohaec and P.A. Norreys

Critical SurfacePlasma ablated by ASE pedestalAl102550Cu 10Al1CH5w0 ps laser beam40J, 1ps (FWHM), 45 incidence10-13m diameter spot (f/4 OAP)2 - 5 x 1019W/cm2LULI 2008 absorption experiment

ASE width(ns)Energy contrast ratioType1.13x10-3best1.96x10-3median4.31x10-2worst

Heating was diagnosed time resolved rear side optical emission HISAC

3rd harmonic emission was used to diagnose scale length as in Watts et al, PRE 66

Cu-Kalpha was used to image rear surface transport pattern

Transverse probing was used to examine front surface expansionTarget plane2D Cu Ka imagerTo CCDshadowgraphyVisible emisson diagnosticPointing systemup and downLULI 2008 Experimental layout

2D Hydro simulations: match the experimental density profiles in the range 1019-1020cm-3 the density scale-length presents no variations near the critical density LULI 2008 Interferometry data

Best contrast FWHM = 21.28, Peak Wavelength = 350.24Medium contrastFWHM = 20.52 Peak Wavelength = 335.0Worst contrastFWHM = 25.08 Peak Wavelength = 343.03w Peaks correspond roughly to scale length of 6-8 microns (from Ian Watts paper, PRE 66, 2002)Peak signal and bandwidth dont change linearly with ASE. Fluctuation probably due to shot to shot fluctuation.

This supports the notion that the near critical density position did not change very much by varying the ASE duration.

LULI 2008 Harmonics measurements

25 half angle divergence was observed for all contrast levelsLULI 2008 Cu K-alpha measurements

LULI 2008 Cu K-alpha measurementsCurves were fitted to the k-alpha peak intensities as a function of thickness for each ASE level

Double heating pulse structure (40 ps delay independent of the propagation layer thickness) Factor 2 increase in intensity with longer pre-pulse, but effect appears to reach saturation for the thickest targetsLULI 2008 rear surface optical emission

Our data for the best contrast fit well with other data in literature

Quantitative agreement with hybrid simulations by J. Davies: - best contrast data well fitted by 15% laser energy absorption - worst contrast data well fitted by 30% laser energy absorption (but only for the thinnest targets)

LULI 2008 Discussion of HISAC data

CHANNEL FORMATION IN UNDERDENSE PLASMAS FOR FAST IGNITION INERTIAL FUSIONP.A. Norreys1,2, K.L. Lancaster1, M. Borghesi3, H. Chen4, E.L. Clark5, S. Hassan5, J. Jiang6, N. Kageiwa7, N. Lopes6, Z. Najmudin2, C. Russo6, G. Sarri3, R.H.H. Scott1,2, R. Ramis8, A. Rehman2, K.A. Tanaka7, M. Temporal8, T. Tanimoto7, R. Trines1, and J.R. Davies61. STFC Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK2. Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2BZ UK3. School of Mathematics and Physics, Queens University Belfast, Belfast BT7 1NN, UK4. Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA5. Technological Educational Institute of Crete, P.O. Box 1939 IRAKLIO, Crete, GR 710 04 Greece6. GoLP, Instituto de Plasmas e Fuso Nuclear, Instituto Superior Tcnico, 1049-001 Lisbon, Portugal7. Graduate School of Engineering, Osaka University, Osaka 565-0871, Japan8. ETSI Industriales, Universidad Politcnica de Madrid, Spain

Hole boring in fast ignitionHole-boring is an alternative to cone-shell geometry

Easier to implement (target fabrication) for inertial fusion energy

No debris issues

3D view of experiment layoutPhase 1:Interact 30ps, ~200J beam with gas jet to image channel at 1019 to 1021 cm-3

Phase 2:

Create plasma column with 800J, 1ns

Interact 30ps ~200J beam with plasma column

Top view of experiment layout

DiagnosticsElectron spectrometers

Optical forward scatter spectrometer 500 nm 1100 nm

Transverse optical probe interferometry and shadowgraphy

Transverse MeV proton probe

X-ray pinhole cameras

Thomson parabola

Ion pinhole imaging camera

Ar 1barAr 3barElectron spectraEvidence for relativistic self focusing

Temperature scalingElectron energy spectra close to 800 keV pulse experiences relativistic self focusing

No evidence for self modulationLaser pulse pushes plasma aside

Channels clearly seen in shadowgramDeuterium gas backing pressure 99 bar (~1020 electrons cm-3) 2 mmTiming +30 pslaser

Temporal evolution of channelDeuterium gas backing pressure 72 bar (~71019 electrons cm-3) 2 mmTiming +130 psTiming +30 psTiming 0 pslaserand decay into turbulence after pulse

4 MeV proton radiographDeuterium gas backing pressure 1 bar (~1018 electrons cm-3) Timing = 150 ps after interaction3 mmlaserDecay into turbulence is also density dependent

Deuterium gas backing pressure 10 bar (~1019 electrons cm-3) Timing = 150 ps after interaction3 mmlaser

Deuterium gas backing pressure 100 bar (~1020 electrons cm-3) Timing = 150 ps after interaction3 mmlaser

0.45 mm1.53 mmChannels also visible in X-ray images with Argon 100 bar ~1021 e- cm-3 10 bar ~1020 e- cm-3

800 J / ns laser800 J / ns laserX-ray pinhole imageShadowgramCharacterise large scalelength plasmaNeed to reduce intensity in next injection experiment to avoid thermal filamentation

Channel formation observed in X-ray images, proton radiographs and shadowgrams

Extend up to 2mm in length

Laser pulse simply pushes the plasma sideways no self-modulated forward scatter or high energy electrons

Laser pulse experiences relativistic self focusing

For absorption:Need to repeat the experiment looking near to the critical densityNeed also to repeat with high contrast using 2w

For channelling:Need to produce long scale length well characterised plasma in solids (without destroying optics!!) and repeat experiment under these conditionsFuture work