Probing near-solid density plasmas using soft x-ray scattering

Journal of Physics B: Atomic, Molecular and Optical Physics 43 (2010)

S Toleikis, T Bornath, T Döppner, S Düsterer, RR Fäustlin, E Förster, C Fortmann, SH Glenzer, S Göde, G Gregori, R Irsig, T Laarmann, HJ Lee, B Li, KH Meiwes-Broer, J Mithen, B Nagler, A Przystawik, P Radcliffe, H Redlin, R Redmer, H Reinholz, G Röpke, F Tavella, R Thiele, J Tiggesbäumker, I Uschmann, SM Vinko, T Whitcher, U Zastrau, B Ziaja, B Ziaja, T Tschentscher

X-ray scattering using highly brilliant x-ray free-electron laser (FEL) radiation provides new access to probe free-electron density, temperature and ionization in near-solid density plasmas. First experiments at the soft x-ray FEL FLASH at DESY, Hamburg, show the capabilities of this technique. The ultrashort FEL pulses in particular can probe equilibration phenomena occurring after excitation of the plasma using ultrashort optical laser pumping. We have investigated liquid hydrogen and find that the interaction of very intense soft x-ray FEL radiation alone heats the sample volume. As the plasma establishes, photons from the same pulse undergo scattering, thus probing the transient, warm dense matter state. We find a free-electron density of (2.6 ± 0.2) × 1020 cm-3 and an electron temperature of 14 ± 3.5 eV. In pump-probe experiments, using intense optical laser pulses to generate more extreme states of matter, this interaction of the probe pulse has to be considered in the interpretation of scattering data. In this paper, we present details of the experimental setup at FLASH and the diagnostic methods used to quantitatively analyse the data. © 2010 IOP Publishing Ltd.

XUV emission from autoionizing hole states induced by intense XUV-FEL at intensities up to 1017 W/cm2

Journal of Physics: Conference Series 244 (2010)

FB Rosmej, FB Rosmej, E Galtier, D Riley, T Dzelzainis, P Heinmann, FY Khattak, RW Lee, B Nagler, A Nelson, T Tschentscher, SM Vinko, T Whitcher, S Toleikis, R Fäustlin, R Soberierski, L Juha, M Fajardo, JS Wark, J Chalupsky, V Hajkova, J Krzywinski, M Jurek, M Kozlova

Aluminium targets were irradiated with 92 eV radiation from FLASH Free Electron Laser at DESY at intensities up to 1017 W/cm2 by focussing the beam on target down to a spot size of ∼1 μm by means of a parabolic mirror. High resolution XUV spectroscopy was used to identify aluminium emission from complex hole-states. Simulations carried out with the MARIA code show that the emission characterizes the electron heating in the transition phase solid-atomic. The analysis allows constructing a simple model of electron heating via Auger electrons. © 2010 IOP Publishing Ltd.

Controlling implosion symmetry around a deuterium-tritium target

Science 327 (2010) 1208-1210

PA Norreys, PA Norreys

Fusion power is a step closer with the demonstration of control over the extreme thermal radiation pressure created by high-power laser beams within a cavity.

Observation of ultrafast nonequilibrium collective dynamics in warm dense hydrogen.

Phys Rev Lett 104 (2010) 125002-

RR Fäustlin, T Bornath, T Döppner, S Düsterer, E Förster, C Fortmann, SH Glenzer, S Göde, G Gregori, R Irsig, T Laarmann, HJ Lee, B Li, KH Meiwes-Broer, J Mithen, B Nagler, A Przystawik, H Redlin, R Redmer, H Reinholz, G Röpke, F Tavella, R Thiele, J Tiggesbäumker, S Toleikis, I Uschmann, SM Vinko, T Whitcher, U Zastrau, B Ziaja, T Tschentscher

We investigate ultrafast (fs) electron dynamics in a liquid hydrogen sample, isochorically and volumetrically heated to a moderately coupled plasma state. Thomson scattering measurements using 91.8 eV photons from the free-electron laser in Hamburg (FLASH at DESY) show that the hydrogen plasma has been driven to a nonthermal state with an electron temperature of 13 eV and an ion temperature below 0.1 eV, while the free-electron density is 2.8x10{20} cm{-3}. For dense plasmas, our experimental data strongly support a nonequilibrium kinetics model that uses impact ionization cross sections based on classical free-electron collisions.

Experimental detection of post-soliton structures following high intensity laser interaction with a sub-critical gas jet

37th EPS Conference on Plasma Physics 2010, EPS 2010 3 (2010) 1960-1963

G Sarri, DK Singh, JR Davies, KL Lancaster, EL Clark, S Hassan, J Jiang, N Kageiwa, N Lopes, A Rehman, C Russo, RHH Scott, T Tanimoto, Z Najmudin, KA Tanaka, M Tatarakis, M Borghesi, P Norreys, P Norreys

Applications of the wave kinetic approach: From laser wakefields to drift wave turbulence

Journal of Plasma Physics 76 (2010) 903-914

RMGM Trines, R Bingham, LO Silva, JT Mendonça, PK Shukla, CD Murphy, MW Dunlop, JA Davies, R Bamford, A Vaivads, PA Norreys

Nonlinear wave-driven processes in plasmas are normally described by either a monochromatic pump wave that couples to other monochromatic waves, or as a random phase wave coupling to other random phase waves. An alternative approach involves a random or broadband pump coupling to monochromatic and/or coherent structures in the plasma. This approach can be implemented through the wave-kinetic model. In this model, the incoming pump wave is described by either a bunch (for coherent waves) or a sea (for random phase waves) of quasi-particles. This approach has been applied to both photon acceleration in laser wakefields and drift wave turbulence in magnetized plasma edge configurations. Numerical simulations have been compared to experiments, varying from photon acceleration to drift mode-zonal flow turbulence, and good qualitative correspondences have been found in all cases. © 2010 Cambridge University Press.

New developments in energy transfer and transport studies in relativistic laser-plasma interactions

Plasma Physics and Controlled Fusion 52 (2010)

PA Norreys, PA Norreys, JS Green, KL Lancaster, APL Robinson, RHH Scott, RHH Scott, F Perez, HP Schlenvoight, S Baton, S Hulin, B Vauzour, JJ Santos, DJ Adams, K Markey, B Ramakrishna, M Zepf, MN Quinn, XH Yuan, P McKenna, J Schreiber, J Schreiber, JR Davies, DP Higginson, DP Higginson, FN Beg, C Chen, T Ma, P Patel

Two critical issues related to the success of fast ignition inertial fusion have been vigorously investigated in a co-ordinated campaign in the European Union and the United States. These are the divergence of the fast electron beam generated in intense, PW laser-plasma interactions and the fast electron energy transport with the use of high intensity contrast ratio laser pulses. Proof is presented that resistivity gradient-induced magnetic fields can guide fast electrons over significant distances in (initially) cold metallic targets. Comparison of experiments undertaken in both France and the United States suggests that an important factor in obtaining efficient coupling into dense plasma is the irradiation with high intensity contrast ratio laser pulses, rather than the colour of the laser pulse itself. © 2010 IOP Publishing Ltd.

Hot electron generation and transport using Kα emission

Journal of Physics: Conference Series 244 (2010)

KU Akli, RB Stephens, MH Key, T Bartal, FN Beg, S Chawla, CD Chen, R Fedosejevs, RR Freeman, H Friesen, E Giraldez, JS Green, DS Hey, DP Higginson, J Hund, LC Jarrott, GE Kemp, JA King, A Kryger, K Lancaster, S Lepape, A Link, T Ma, AJ MacKinnon, AG MacPhee, HS McLean, C Murphy, PA Norreys, V Ovchinnikov, PK Patel, Y Ping, H Sawada, D Schumacher, W Theobald, YY Tsui, LD Van Woerkom, MS Wei, B Westover, T Yabuuchi

We have conducted experiments on both the Vulcan and Titan laser facilities to study hot electron generation and transport in the context of fast ignition. Cu wires attached to Al cones were used to investigate the effect on coupling efficiency of plasma surround and the pre-formed plasma inside the cone. We found that with thin cones 15% of laser energy is coupled to the 40μm diameter wire emulating a 40μm fast ignition spot. Thick cone walls, simulating plasma in fast ignition, reduce coupling by x4. An increase of pre-pulse level inside the cone by a factor of 50 reduces coupling by a factor of 3. © 2010 IOP Publishing Ltd.

Creation of persistent, straight, 2 mm long laser driven channels in underdense plasmas

Physics of Plasmas 17 (2010)

G Sarri, KL Lancaster, R Trines, R Trines, EL Clark, S Hassan, J Jiang, N Kageiwa, N Lopes, R Ramis, A Rehman, X Ribeyre, C Russo, RHH Scott, RHH Scott, T Tanimoto, M Temporal, M Borghesi, JR Davies, Z Najmudin, KA Tanaka, M Tatarakis, PA Norreys, PA Norreys

The experimental study of the behavior of deuterium plasma with densities between 2× 1018 and 2× 1020 cm-3, subjected to a 6 TW, 30 ps, 3× 1018 W cm-2 laser pulse, is presented. Conclusive experimental proof that a single straight channel is generated when the laser pulse interacts with the lowest densities is provided. This channel shows no small-scale longitudinal density modulations, extends up to 2 mm in length and persists for up to 150 ps after the peak of the interaction. Bifurcation of the channel after 1 mm propagation distance is observed for the first time. For higher density interactions, above the relativistic self-focusing threshold, bubblelike structures are observed to form at late times. These observations have implications for both laser wakefield accelerators and fast ignition inertial fusion studies. © 2010 American Institute of Physics.

A proposal for testing subcritical vacuum pair production with high power lasers

ArXiv (2010)

G Gregori, DB Blaschke, PP Rajeev, H Chen, RJ Clarke, T Huffman, CD Murphy, AV Prozorkevich, CD Roberts, G Röpke, SM Schmidt, SA Smolyansky, S Wilks, R Bingham

We present a proposal for testing the prediction of non-equilibrium quantum field theory below the Schwinger limit. The proposed experiments should be able to detect a measurable number of gamma rays resulting from the annihilation of pairs in the focal spot of two opposing high intensity laser beams. We discuss the dependence of the expected number of gamma rays with the laser parameters and compare with the estimated background level of gamma hits for realistic laser conditions.

Measurement of the dynamic response of compressed hydrogen by inelastic X-ray scattering

Journal of Physics: Conference Series 244 (2010)

K Falk, AP Jephcoat, AP Jephcoat, BJB Crowley, BJB Crowley, RR Fäustlin, C Fortmann, FY Khattak, AK Kleppe, D Riley, D Riley, S Toleikis, J Wark, H Wilhelm, G Gregori

Measurement of the dynamic properties of hydrogen and helium under extreme pressures is a key to understanding the physics of planetary interiors. The inelastic scattering signal from statically compressed hydrogen inside diamond anvil cells at 2.8 GPa and 6.4 GPa was measured at the Diamond Light Source synchrotron facility in the UK. The first direct measurement of the local field correction to the Coulomb interactions in degenerate plasmas was obtained from spectral shifts in the scattering data and compared to predictions by the Utsumi-Ichimaru theory for degenerate electron liquids. © 2010 IOP Publishing Ltd.

Static ion structure factor for dense plasmas: Semi-classical and ab initio calculations

High Energy Density Physics 6 (2010) 305-310

V Schwarz, B Holst, T Bornath, C Fortmann, WD Kraeft, R Thiele, R Redmer, G Gregori, G Gregori, HJ Lee, T Döppner, SH Glenzer

We calculate the static structure factor of dense multi-component plasmas. Large scale ab initio finite-temperature DFT molecular dynamics simulations are performed in order to cover the region where a consistent quantum treatment for the electrons is inevitable. Especially, the behavior at small wave numbers k can be inferred from the relation to the isothermal compressibility. Alternatively, the static structure factor is obtained by solving the integral equations for the pair correlation functions within the hypernetted chain (HNC) scheme. For this purpose we derive new effective two-particle quantum potentials for the interactions between the charge carriers from the full two-particle Slater sum by accounting for bound states. Comparison to the ab initio molecular dynamics simulations enables us to determine the short-range behavior of the effective electron-ion quantum potentials. Results for the static structure factor are presented for beryllium plasmas at solid density and at threefold compression. © 2009 Elsevier B.V.

Electron trapping and acceleration on a downward density ramp: A two-stage approach

New Journal of Physics 12 (2010)

RMGM Trines, RMGM Trines, R Bingham, R Bingham, Z Najmudin, S Mangles, LO Silva, R Fonseca, R Fonseca, PA Norreys, PA Norreys

In a recent experiment at Lawrence Berkeley National Laboratory (Geddes et al 2008 Phys. Rev. Lett. 100 215004), electron bunches with about 1 MeV mean energy and small absolute energy spread (about 0.3 MeV) were produced by plasma wave breaking on a downward density ramp. It was then speculated that such a bunch might be accelerated further in a plasma of low constant density, while mostly preserving its small absolute energy spread. This would then lead to a bunch with a high mean energy and very low relative energy spread. In this paper, trapping of a low-energy, low-spread electron bunch on a downward density ramp, followed by acceleration in a constant-density plasma, has been explored through particle-in-cell simulations. It has been found that the scheme works best when it is used as a separate injection stage for a laserwakefield accelerator, where the injection and acceleration stages are separated by a vacuum gap. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Laser-driven fast electron collimation in targets with resistivity boundary

Physical Review Letters 105 (2010)

B Ramakrishna, S Kar, APL Robinson, DJ Adams, K Markey, MN Quinn, XH Yuan, P McKenna, KL Lancaster, JS Green, RHH Scott, RHH Scott, PA Norreys, J Schreiber, M Zepf

We demonstrate experimentally that the relativistic electron flow in a dense plasma can be efficiently confined and guided in targets exhibiting a high-resistivity-core-low-resistivity-cladding structure analogous to optical waveguides. The relativistic electron beam is shown to be confined to an area of the order of the core diameter (50μm), which has the potential to substantially enhance the coupling efficiency of electrons to the compressed fusion fuel in the Fast Ignitor fusion in full-scale fusion experiments. © 2010 The American Physical Society.

Micron-scale fast electron filaments and recirculation determined from rear-side optical emission in high-intensity laser-solid interactions

New Journal of Physics 12 (2010)

C Bellei, SR Nagel, S Kar, A Henig, A Henig, S Kneip, C Palmer, A Sävert, L Willingale, L Willingale, D Carroll, B Dromey, JS Green, JS Green, K Markey, P Simpson, RJ Clarke, H Lowe, D Neely, C Spindloe, M Tolley, MC Kaluza, MC Kaluza, SPD Mangles, P McKenna, PA Norreys, PA Norreys, J Schreiber, J Schreiber, J Schreiber, M Zepf, JR Davies, K Krushelnick, K Krushelnick, Z Najmudin

The transport of relativistic electrons generated in the interaction of petawatt class lasers with solid targets has been studied through measurements of the second harmonic optical emission from their rear surface. The high degree of polarization of the emission indicates that it is predominantly optical transition radiation (TR). A halo that surrounds the main region of emission is also polarized and is attributed to the effect of electron recirculation. The variation of the polarization state and intensity of radiation with the angle of observation indicates that the emission of TR is highly directional and provides evidence for the presence of μm-size filaments. A brief discussion on the possible causes of such a fine electron beam structure is given. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Plasma emission spectroscopy of solids irradiated by intense XUV pulses from a free electron laser

High Energy Density Physics 6 (2010) 109-112

TWJ Dzelzainis, J Chalupsky, M Fajardo, R Fäustlin, PA Heimann, V Hajkova, L Juha, M Jurek, FY Khattak, M Kozlova, J Krzywinski, RW Lee, B Nagler, AJ Nelson, FB Rosmej, R Soberierski, S Toleikis, T Tschentscher, SM Vinko, JS Wark, T Whitcher, D Riley

The FLASH XUV-free electron laser has been used to irradiate solid samples at intensities of the order 1016 W cm-2 at a wavelength of 13.5 nm. The subsequent time integrated XUV emission was observed with a grating spectrometer. The electron temperature inferred from plasma line ratios was in the range 5-8 eV with electron density in the range 1021-1022 cm-3. These results are consistent with the saturation of absorption through bleaching of the L-edge by intense photo-absorption reported in an earlier publication. © 2009 Elsevier B.V. All rights reserved.

Measurement of fast electrons spectra generated by interaction between solid target and peta watt laser

Journal of Physics: Conference Series 244 (2010)

T Tanimoto, H Habara, KA Tanaka, R Kodama, M Nakatsutsumi, KL Lancaster, JS Green, RHH Scott, RHH Scott, M Sherlock, M Sherlock, PA Norreys, PA Norreys, RG Evans, MG Haines, S Kar, M Zepf, J King, T Ma, MS Wei, T Yabuuchi, FN Beg, MH Key, P Nilson, RB Stephens, H Azechi, K Nagai, T Norimatsu, K Takeda, J Valente, JR Davies

Fast electron energy spectra have been measured for a range of intensities between 1018 Wcm-2 and 1021 Wcm-2 and for different target materials using electron spectrometers. Several experimental campaigns were conducted on peta watt laser facilities at the Rutherford Appleton Laboratory and Osaka University. In these experimental campaigns, the pulse duration was varied from 0.5 ps to 5 ps. The laser incident angle was also changed from normal incidence to 40° in p-polarized. The results show a reduction from the ponderomotive scaling on fast electrons over 1020 Wcm-2. © 2010 IOP Publishing Ltd.

Design of the 10 PW OPCPA facility for the Vulcan laser

Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010)

I Musgrave, O Chekhlov, J Collier, R Clarke, A Dunne, S Hancock, R Heathcote, C Hernandez-Gomez, M Galimberti, A Lyachev, P Matousek, D Neely, P Norreys, I Ross, Y Tang, T Winstone, G New

We present the progress made in developing IOPW OPCPA facility for the Vulcan laser to produce pulses with focused intensities >1023 Wcm-2. This power level will be delivered by generating pulses with >300J in 30fs. These pulses will be delivered to two target areas: in one target area they will be combined with the existing Vulcan Petawatt beamline and a new target area will be created for high intensity interactions. © 2010 Optical Society of America.

Design of the 10 PW OPCPA facility for the vulcan laser

Optics InfoBase Conference Papers (2010)

I Musgrave, O Chekhlov, J Collier, R Clarke, A Dunne, S Hancock, R Heathcote, C Hernandez-Gomez, M Galimberti, A Lyachev, P Matousek, D Neely, P Norreys, I Ross, Y Tang, T Winstone, G New

We present the progress made in developing 10PW OPCPA facility for the Vulcan laser to produce pulses with focused intensities >1023 Wcm-2. This power level will be delivered by generating pulses with >300J in 30fs. These pulses will be delivered to two target areas: in one target area they will be combined with the existing Vulcan Petawatt beamline and a new target area will be created for high intensity interactions. © 2010 Optical Society of America.

Electronic structure of an XUV photogenerated solid-density aluminum plasma.

Phys Rev Lett 104 (2010) 225001-

SM Vinko, U Zastrau, S Mazevet, J Andreasson, S Bajt, T Burian, J Chalupsky, HN Chapman, J Cihelka, D Doria, T Döppner, S Düsterer, T Dzelzainis, RR Fäustlin, C Fortmann, E Förster, E Galtier, SH Glenzer, S Göde, G Gregori, J Hajdu, V Hajkova, PA Heimann, R Irsig, L Juha, M Jurek, J Krzywinski, T Laarmann, HJ Lee, RW Lee, B Li, KH Meiwes-Broer, JP Mithen, B Nagler, AJ Nelson, A Przystawik, R Redmer, D Riley, F Rosmej, R Sobierajski, F Tavella, R Thiele, J Tiggesbäumker, S Toleikis, T Tschentscher, L Vysin, TJ Whitcher, S White, JS Wark

By use of high intensity XUV radiation from the FLASH free-electron laser at DESY, we have created highly excited exotic states of matter in solid-density aluminum samples. The XUV intensity is sufficiently high to excite an inner-shell electron from a large fraction of the atoms in the focal region. We show that soft-x-ray emission spectroscopy measurements reveal the electronic temperature and density of this highly excited system immediately after the excitation pulse, with detailed calculations of the electronic structure, based on finite-temperature density functional theory, in good agreement with the experimental results.