Publications


X-ray polarization measurements of dense plasmas heated by fast electrons

AIP Conference Proceedings 1228 (2010) 79-85

N Booth, RJ Clarke, P Gallegos, LA Gizzi, G Gregori, P Koester, L Labate, T Levato, B Li, M Makita, J Pasley, PP Rajeev, D Riley, E Wagenaars, JN Waugh, NC Woolsey

The detailed knowledge of fast electron energy transport following interaction with high-intensity, ultra-short laser pulses is a key area for secondary source generation for ELI. We demonstrate polarization spectroscopy at laser intensities up to 1021 Wcm-2. This is significant as it suggests that in situ emission spectroscopy may be used as an effective probe of fast electron velocity distributions in regimes relevant to electron transport in solid targets. Ly-α doublet emission of nickel (Z = 28) and sulphur (Z = 16) is observed to measure the degree of polarization from the Ly-α1 emission. Ly-α2 emission is unpolarized, and as such acts as a calibration source between spectrometers. The measured ratio of the X-ray σ-and π-polarization allows the possibility to infer the velocity distribution function of the fast electron beam. © 2010 American Institute of Physics.


Ultrafast melting of carbon induced by intense proton beams

Physical Review Letters 105 (2010)

A Pelka, G Gregori, DO Gericke, J Vorberger, SH Glenzer, MM Günther, K Harres, R Heathcote, AL Kritcher, NL Kugland, B Li, M Makita, J Mithen, D Neely, C Niemann, A Otten, D Riley, G Schaumann, M Schollmeier, A Tauschwitz, M Roth

Laser-produced proton beams have been used to achieve ultrafast volumetric heating of carbon samples at solid density. The isochoric melting of carbon was probed by a scattering of x rays from a secondary laser-produced plasma. From the scattering signal, we have deduced the fraction of the material that was melted by the inhomogeneous heating. The results are compared to different theoretical approaches for the equation of state which suggests modifications from standard models. © 2010 The American Physical Society.


Phonon instabilities in uniaxially compressed fcc metals as seen in molecular dynamics simulations

PHYSICAL REVIEW B 81 (2010) ARTN 092102

G Kimminau, P Erhart, EM Bringa, B Remington, JS Wark


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.


Bragg diffraction using a 100 ps 17.5 keV x-ray backlighter and the Bragg diffraction imager

REVIEW OF SCIENTIFIC INSTRUMENTS 81 (2010)

BR Maddox, H-S Park, J Hawreliak, A Elsholz, R Van Maren, BA Remington, A Comley, JS Wark


Relativistic quasimonoenergetic positron jets from intense laser-solid interactions.

Phys Rev Lett 105 (2010) 015003-

H Chen, SC Wilks, DD Meyerhofer, J Bonlie, CD Chen, SN Chen, C Courtois, L Elberson, G Gregori, W Kruer, O Landoas, J Mithen, J Myatt, CD Murphy, P Nilson, D Price, M Schneider, R Shepherd, C Stoeckl, M Tabak, R Tommasini, P Beiersdorfer

Detailed angle and energy resolved measurements of positrons ejected from the back of a gold target that was irradiated with an intense picosecond duration laser pulse reveal that the positrons are ejected in a collimated relativistic jet. The laser-positron energy conversion efficiency is ∼2×10{-4}. The jets have ∼20 degree angular divergence and the energy distributions are quasimonoenergetic with energy of 4 to 20 MeV and a beam temperature of ∼1  MeV. The sheath electric field on the surface of the target is shown to determine the positron energy. The positron angular and energy distribution is controlled by varying the sheath field, through the laser conditions and target geometry.


Metal deformation and phase transitions at extremely high strain rates

MRS BULLETIN 35 (2010) 999-1006

RE Rudd, TC Germann, BA Remington, JS Wark


Soft X-ray scattering using FEL radiation for probing near-solid density plasmas at few electron volt temperatures

High Energy Density Physics 6 (2010) 15-20

S Toleikis, RR Fäustlin, L Cao, T Döppner, S Düsterer, E Förster, C Fortmann, SH Glenzer, S Göde, G Gregori, R Irsig, T Laarmann, HJ Lee, B Li, J Mithen, K-H Meiwes-Broer, A Przystawik, P Radcliffe, R Redmer, F Tavella, R Thiele, J Tiggesbäumker, NX Truong, I Uschmann, U Zastrau, T Tschentscher

We report on soft X-ray scattering experiments on cryogenic hydrogen and simple metal samples. As a source of intense, ultrashort soft X-ray pulses we have used free-electron laser radiation at 92 eV photon energy from FLASH at DESY, Hamburg. X-ray pulses with energies up to 150 μJ and durations 15-50 fs provide interaction with the sample leading simultaneously to plasma formation and scattering. Experiments exploiting both of these interactions have been carried out, using the same experimental setup. Firstly, recording of soft X-ray inelastic scattering from near-solid density hydrogen plasmas at few electron volt temperatures confirms the feasibility of this diagnostics technique. Secondly, the soft X-ray excitation of few electron volt solid-density plasmas in bulk metal samples could be studied by recording soft X-ray line and continuum emission integrated over emission times from fs to ns. © 2009 Elsevier B.V.


Magnetic collimation of petawatt driven fast electron beam for prospective fast ignition studies

Journal of Physics: Conference Series 244 (2010)

S Kar, D Adams, M Borghesi, K Markey, B Ramakrishna, M Zepf, K Lancaster, P Norreys, APL Robinson, DC Carroll, P McKenna, M Quinn, X Yuan, C Bellei, J Schreiber

Collimated transport of fast electron beam through solid density matter is one of the key issues behind the success of the fast ignition scheme by means of which the required amount of ignition energy can be delivered to the hot spot region of the compressed fuel. Here we report on a hot electron beam collimation scheme in solids by tactfully using the strong magnetic fields generated by an electrical resistivity gradient according to Faraday's law. This was accomplished by appropriately fabricating the targets in such a way that the electron beam is directed to flow in a metal which is embedded in a much lower resistivity and atomic number metal. Experimental results showed guided transport of hot electron beam over hundreds of microns length inside solid density plasma, which were obtained from two experiments examining the scheme for petawatt laser driven hot electron beam while employing various target configurations. © 2010 IOP Publishing Ltd.


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, K-H 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, 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.


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


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

Plasma Physics and Controlled Fusion 52 (2010)

PA Norreys, JS Green, KL Lancaster, APL Robinson, RHH Scott, F Perez, H-P 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, JR Davies, 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.


Observation of postsoliton expansion following laser propagation through an underdense plasma

Physical Review Letters 105 (2010)

G Sarri, DK Singh, JR Davies, F Fiuza, 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, PA Norreys

The expansion of electromagnetic postsolitons emerging from the interaction of a 30? ps, 3×1018Wcm⊃-2 laser pulse with an underdense deuterium plasma has been observed up to 100? ps after the pulse propagation, when large numbers of postsolitons were seen to remain in the plasma. The temporal evolution of the postsolitons has been accurately characterized with a high spatial and temporal resolution. The observed expansion is compared to analytical models and three-dimensional particle-in-cell results, revealing a polarization dependence of the postsoliton dynamics. © 2010 The American Physical Society.


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


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, M Sherlock, 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.


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.


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.


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

New Journal of Physics 12 (2010)

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


The Vulcan 10 PW project

Journal of Physics: Conference Series 244 (2010)

C Hernandez-Gomez, SP Blake, O Chekhlov, RJ Clarke, AM Dunne, M Galimberti, S Hancock, R Heathcote, P Holligan, A Lyachev, P Matousek, IO Musgrave, D Neely, PA Norreys, I Ross, Y Tang, TB Winstone, BE Wyborn, J Collier

The aim of this project is to establish a 10 PW facility on the Vulcan laser system capable of being focussed to intensities of at least 10 23 Wcm-2 and integrate this into a flexible and unique user facility This paper will present progress made in Phase one developing the 10PW Front End as well as the concept for the new Vulcan 10 PW facility. The new facility will be configured in a unique way to maximise the scientific opportunities presented through a combination with the existing capabilities already established on Vulcan. This ground breaking development will open up a range of new scientific opportunities. © 2010 IOP Publishing Ltd.


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.