Dr James Mithen

Research Fellow

Email:
Phone: Work: 01483 68 6782
Room no: 24 BB 03

Further information

Biography

2012 - DPhil Physics, University of Oxford

2007 - MSci Mathematics and Physics, University of Bristol

Research Interests

My research interests are in the general area of computational statistical mechanics.  

For my DPhil (PhD), I studied the equilibrium dynamics of two simple systems that are ubiquitous in plasma physics.  This involved a detailed comparison of the results of molecular dynamics simulations with analytical models of the physical properties of these systems. The full story is in my DPhil thesis, available below.

In my current role, I am studying nucleation of crystal phases.  Nucleation, which is the first stage of crystallisation, is a problem in non-equilibrium statistical mechanics.  This already makes understanding nucleation rather tricky.  To complicate things even further, since nucleation involves overcoming an energy barrier, it is a 'rare event', and therefore difficult to observe directly in computer simulations.  This has led to the development of advanced simulation methods.  In my research, I use these methods to study nucleation in simple systems.

For more information about my research and other interests, see my personal webpage.

My DPhil thesis: jpmithen_thesis (2778.33KB - Requires Adobe Reader)

Publications

Highlights

  • Mithen JP, Daligault J, Gregori G. (2012) 'Comparative merits of the memory function and dynamic local-field correction of the classical one-component plasma'. PRE, 85 (5)
  • Mithen JP, Gregori G, Daligault J. (2012) 'Molecular Dynamics Simulations for the Shear Viscosity of the One-Component Plasma'. Contributions to Plasma Physics, 52 (1), pp. 58-61.

    Abstract

    We discuss two methods for determining the shear viscosity of a fluid of particles with Yukawa interaction potential (a one-component plasma). Both methods are based on computing the equilibrium dynamics using large-scale molecular dynamics (MD) simulations. Our MD results illustrate that the hydrodynamic method for computing the shear viscosity is feasible and therefore complements the more widely used method based on the Green-Kubo relation. We expect that in the future our shear viscosity calculations will be used to assist with the interpretation and analysis of x-ray scattering experiments, which could in principle measure this fundamental dynamical quantity. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • Mithen JP, Daligault J, Crowley BJB, Gregori G. (2011) 'Density fluctuations in the Yukawa one-component plasma: An accurate model for the dynamical structure factor'. PRE, 84 (4)
  • Mithen JP, Gregori G, Daligault J. (2011) 'Extent of validity of the hydrodynamic description of ions in dense plasmas'. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 83 (1)

    Abstract

    We show that the hydrodynamic description can be applied to modeling the ionic response in dense plasmas for a wide range of length scales that are experimentally accessible. Using numerical simulations for the Yukawa model, we find that the maximum wave number k at which the hydrodynamic description applies is independent of the coupling strength, given by k λ 0.43, where λ is the ionic screening length. Our results show that the hydrodynamic description can be used for interpreting x-ray scattering data from fourth generation light sources and high power lasers. In addition, our investigation sheds new light on how the domain of validity of the hydrodynamic description depends on both the microscopic properties and the thermodynamic state of fluids in general. © 2011 American Physical Society.

  • Mithen JP, Gregori G, Daligault J. (2011) 'Onset of negative dispersion in the one-component plasma'. AIP Conference Proceedings, 1421, pp. 68-72.

    Abstract

    We have carried out molecular dynamics (MD) simulations in order to investigate the onset of negative dispersion of the plasmon mode in the classical one-component plasma (OCP). We find that negative dispersion sets in at a Coulomb coupling strength of Γ∼9.5-10. A good quantitative agreement is obtained with an existing theoretical treatment of the dispersion relation that is based on a memory function approach to the dynamics of the OCP. © 2012 American Institute of Physics.

Journal articles

  • Zastrau U, Förster E, Hilbert V, Fletcher LB, Glenzer SH, Göde S, Lee HJ, Sperling P, Becker A, Bornath T, Bredow R, Fennel T, Holst B, Skruszewicz S, Tiggesbäumker J, Redmer R, Döppner T, Fortmann C, Ma T, Dziarzhytski S, Harmand M, Laarmann T, Przystawik A, Schulz M, Toleikis S, Gregori G, Mithen JP, Murphy CD, White T, Mitzner R, Roling S, Siemer B, Wöstmann M, Zacharias H, Nakatsutsumi M, Tschentscher T, Neumayer P. (2014) 'Equilibration dynamics and conductivity of warm dense hydrogen'. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 90 (1)

    Abstract

    We investigate subpicosecond dynamics of warm dense hydrogen at the XUV free-electron laser facility (FLASH) at DESY (Hamburg). Ultrafast impulsive electron heating is initiated by a â‰300-fs short x-ray burst of 92-eV photon energy. A second pulse probes the sample via x-ray scattering at jitter-free variable time delay. We show that the initial molecular structure dissociates within (0.9±0.2) ps, allowing us to infer the energy transfer rate between electrons and ions. We evaluate Saha and Thomas-Fermi ionization models in radiation hydrodynamics simulations, predicting plasma parameters that are subsequently used to calculate the static structure factor. A conductivity model for partially ionized plasma is validated by two-temperature density-functional theory coupled to molecular dynamic simulations and agrees with the experimental data. Our results provide important insights and the needed experimental data on transport properties of dense plasmas. © 2014 American Physical Society.

  • Zastrau U, Förster E, Hilbert V, Fletcher LB, Lee HJ, Glenzer SH, Sperling P, Becker A, Bornath T, Bredow R, Fennel T, Göde S, Holst B, Skruszewicz S, Tiggesbäumker J, Redmer R, Harmand M, Dziarzhytski S, Laarmann T, Przystawik A, Schulz M, Toleikis S, Gregori G, Mithen JP, Murphy CD, White T, Hochhaus D, Neumayer P, Ma T, Döppner T, Mitzner R, Roling S, Siemer B, Wöstmann M, Zacharias H, Nakatsutsumi M, Tschentscher T. (2014) 'Resolving ultrafast heating of dense cryogenic hydrogen'. Physical Review Letters, 112 (10)

    Abstract

    We report on the dynamics of ultrafast heating in cryogenic hydrogen initiated by a ≲300 fs, 92 eV free electron laser x-ray burst. The rise of the x-ray scattering amplitude from a second x-ray pulse probes the transition from dense cryogenic molecular hydrogen to a nearly uncorrelated plasmalike structure, indicating an electron-ion equilibration time of ∼0.9 ps. The rise time agrees with radiation hydrodynamics simulations based on a conductivity model for partially ionized plasma that is validated by two-temperature density-functional theory. © 2014 American Physical Society.

  • Mithen JP, Sear RP. (2014) 'Computer simulation of epitaxial nucleation of a crystal on a crystalline surface.'. J Chem Phys, United States: 140 (8)

    Abstract

    We present results of computer simulations of crystal nucleation on a crystalline surface, in the Lennard-Jones model. Motivated by the pioneering work of Turnbull and Vonnegut [Ind. Eng. Chem. 44, 1292 (1952)], we investigate the effects of a mismatch between the surface lattice constant and that of the bulk nucleating crystal. We find that the nucleation rate is maximum close to, but not exactly at, zero mismatch. The offset is due to the finite size of the nucleus. In agreement with a number of experiments, we find that even for large mismatches of 10% or more, the formation of the crystal can be epitaxial, meaning that the crystals that nucleate have a fixed orientation with respect to the surface lattice. However, nucleation is not always epitaxial, and loss of epitaxy does affect how the rate varies with mismatch. The surface lattice strongly influences the nucleation rate. We show that the epitaxy observed in our simulations can be predicted using calculations of the potential energy between the surface and the first layer of the nucleating crystal, in the spirit of simple approaches such as that of Hillier and Ward [Phys. Rev. B 54, 14037 (1996)].

  • Mithen JP. (2014) 'Transverse current fluctuations in the Yukawa one-component plasma'. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 89 (1)

    Abstract

    Using numerical simulations, we investigate the wave number and frequency dependent transverse current correlation function CT(k,ω) of a single-component fluid with Yukawa interaction potential, also known as the Yukawa one-component plasma. The transverse current correlation function is an important quantity because it contains the microscopic details of the viscoelastic behavior of the fluid. We show that, in the region of densities and temperatures in which shear waves do not propagate, the dynamics of the system are in striking agreement with a simple model of generalized hydrodynamics. As either the density is increased or the temperature decreased, the transverse current correlation function shows additional structure that the simple models fail to capture. © 2014 American Physical Society.

  • Mithen JP, Sear RP. (2014) 'Epitaxial nucleation of a crystal on a crystalline surface'. EPL, 105 (1)

    Abstract

    We consider the nucleation of a crystal phase, on a crystalline surface of a different substance. Sixty years ago, Turnbull and Vonnegut predicted that a crystalline surface is best at inducing nucleation of another crystal when there is a perfect epitaxial match between the two bulk lattices. We use computer simulation to show that this is not quite right. In fact, the crystal lattice of a finite nucleus is strained from that in the bulk, and nucleation is fastest when the surface matches this strained lattice. We also find that the approach of Hillier and Ward predicts when nucleation is epitaxial. © Copyright EPLA, 2014.

  • Chen H, Tommasini R, Seely J, Szabo CI, Feldman U, Pereira N, Gregori G, Falk K, Mithen J, Murphy CD. (2012) 'Measuring electron-positron annihilation radiation from laser plasma interactions.'. Rev Sci Instrum, United States: 83 (10)

    Abstract

    We investigated various diagnostic techniques to measure the 511 keV annihilation radiations. These include step-wedge filters, transmission crystal spectroscopy, single-hit CCD detectors, and streaked scintillating detection. While none of the diagnostics recorded conclusive results, the step-wedge filter that is sensitive to the energy range between 100 keV and 700 keV shows a signal around 500 keV that is clearly departing from a pure Bremsstrahlung spectrum and that we ascribe to annihilation radiation.

  • Mithen JP, Daligault J, Gregori G. (2012) 'Comparative merits of the memory function and dynamic local-field correction of the classical one-component plasma'. PRE, 85 (5)
  • Gregori G, Murphy CD, Schaar K, Baird A, Bell AR, Edwards M, Lau W, Mithen J, Reville B, Yang S, Bingham R, Robinson APL, Ravasio A, Benuzzi-Mounaix A, Koenig M, Constantin C, Everson ET, Niemann C, Drake RP, Gregory CD, Woolsey NC, Kuramitsu Y, Sakawa Y, Park H-S, Remington BA, Ryutov DD, Miniati F. (2012) 'Generation of scaled protogalactic seed magnetic fields in laser-produced shock waves'. Nature, 481 (7382), pp. 480-483.

    Abstract

    The standard model for the origin of galactic magnetic fields is through the amplification of seed fields via dynamo or turbulent processes to the level consistent with present observations. Although other mechanisms may also operate, currents from misaligned pressure and temperature gradients (the Biermann battery process) inevitably accompany the formation of galaxies in the absence of a primordial field. Driven by geometrical asymmetries in shocks associated with the collapse of protogalactic structures, the Biermann battery is believed to generate tiny seed fields to a level of about 10 gauss (refs 7, 8). With the advent of high-power laser systems in the past two decades, a new area of research has opened in which, using simple scaling relations, astrophysical environments can effectively be reproduced in the laboratory. Here we report the results of an experiment that produced seed magnetic fields by the Biermann battery effect. We show that these results can be scaled to the intergalactic medium, where turbulence, acting on timescales of around 700 million years, can amplify the seed fields sufficiently to affect galaxy evolution. © 2012 Macmillan Publishers Limited. All rights reserved.

  • Schmidt R, Crowley BJB, Mithen J, Gregori G. (2012) 'Quantum hydrodynamics of strongly coupled electron fluids'. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 85 (4)

    Abstract

    We have extended the classical hydrodynamics formalism to include nonlocal quantum behavior via the phenomenological Bohm potential. We have then solved the quantum hydrodynamics equations to derive an expression for the dynamical structure factor, which describes the density-density correlations in the system. This formalism can be applied to high density strongly coupled electron fluids in the long wavelength domain. We show that at densities above 7×1025 cm 3 there are significant differences in the dispersion relation. Future experiments at large laser facilities could provide an experimental test of the theory. © 2012 American Physical Society.

  • Mithen JP, Gregori G, Daligault J. (2012) 'Molecular Dynamics Simulations for the Shear Viscosity of the One-Component Plasma'. Contributions to Plasma Physics, 52 (1), pp. 58-61.

    Abstract

    We discuss two methods for determining the shear viscosity of a fluid of particles with Yukawa interaction potential (a one-component plasma). Both methods are based on computing the equilibrium dynamics using large-scale molecular dynamics (MD) simulations. Our MD results illustrate that the hydrodynamic method for computing the shear viscosity is feasible and therefore complements the more widely used method based on the Green-Kubo relation. We expect that in the future our shear viscosity calculations will be used to assist with the interpretation and analysis of x-ray scattering experiments, which could in principle measure this fundamental dynamical quantity. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • Mithen JP, Daligault J, Crowley BJB, Gregori G. (2011) 'Density fluctuations in the Yukawa one-component plasma: An accurate model for the dynamical structure factor'. PRE, 84 (4)
  • Mithen JP, Gregori G, Daligault J. (2011) 'Onset of negative dispersion in the one-component plasma'. AIP Conference Proceedings, 1421, pp. 68-72.

    Abstract

    We have carried out molecular dynamics (MD) simulations in order to investigate the onset of negative dispersion of the plasmon mode in the classical one-component plasma (OCP). We find that negative dispersion sets in at a Coulomb coupling strength of Γ∼9.5-10. A good quantitative agreement is obtained with an existing theoretical treatment of the dispersion relation that is based on a memory function approach to the dynamics of the OCP. © 2012 American Institute of Physics.

  • Koester P, Cecchetti CA, Labate L, Gizzia LA, Booth N, Woolsey N, Chen H, Evans RG, Gregori G, Li B, Mithen J, Murphy C, Levato T, Makita M, Riley D, Notley M, Pattathil R. (2011) 'High resolution X-ray spectroscopy in fast electron transport studies'. Proceedings of SPIE - The International Society for Optical Engineering, 8080

    Abstract

    A detailed knowledge of the physical phenomena underlying the generation and the transport of fast electrons generated in high-intensity laser-matter interactions is of fundamental importance for the fast ignition scheme for inertial confinement fusion. Here we report on an experiment carried out with the VULCAN Petawatt beam and aimed at investigating the role of collisional return currents in the dynamics of the fast electron beam. To that scope, in the experiment counter-propagating electron beams were generated by double-sided irradiation of layered target foils containing a Ti layer. The experimental results were obtained for different time delays between the two laser beams as well as for single-sided irradiation of the target foils. The main diagnostics consisted of two bent mica crystal spectrometers placed at either side of the target foil. High-resolution X-ray spectra of the Ti emission lines in the range from the Lyα to the Kα line were recorded. In addition, 2D X-ray images with spectral resolution were obtained by means of a novel diagnostic technique, the energy-encoded pin-hole camera, based on the use of a pin-hole array equipped with a CCD detector working in single-photon regime. The spectroscopic measurements suggest a higher target temperature for well-aligned laser beams and a precise timing between the two beams. The experimental results are presented and compared to simulation results. © 2011 SPIE.

  • Mithen JP, Gregori G, Daligault J. (2011) 'Extent of validity of the hydrodynamic description of ions in dense plasmas'. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 83 (1)

    Abstract

    We show that the hydrodynamic description can be applied to modeling the ionic response in dense plasmas for a wide range of length scales that are experimentally accessible. Using numerical simulations for the Yukawa model, we find that the maximum wave number k at which the hydrodynamic description applies is independent of the coupling strength, given by k λ 0.43, where λ is the ionic screening length. Our results show that the hydrodynamic description can be used for interpreting x-ray scattering data from fourth generation light sources and high power lasers. In addition, our investigation sheds new light on how the domain of validity of the hydrodynamic description depends on both the microscopic properties and the thermodynamic state of fluids in general. © 2011 American Physical Society.

  • Pelka A, Günther MM, Harres K, Otten A, Schaumann G, Schollmeier M, Roth M, Gregori G, Mithen J, Heathcote R, Li B, Neely D, Gericke DO, Vorberger J, Glenzer SH, Kritcher AL, Kugland NL, Niemann C, Makita M, Riley D, Tauschwitz A. (2010) 'Ultrafast melting of carbon induced by intense proton beams'. Physical Review Letters, 105 (26)

    Abstract

    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.

  • Chen H, Wilks SC, Bonlie J, Chen CD, Chen SN, Elberson L, Kruer W, Price D, Schneider M, Shepherd R, Tabak M, Tommasini R, Beiersdorfer P, Meyerhofer DD, Myatt J, Nilson P, Stoeckl C, Courtois C, Landoas O, Gregori G, Mithen J, Murphy CD. (2010) 'Relativistic quasimonoenergetic positron jets from intense laser-solid interactions'. Physical Review Letters, 105 (1)

    Abstract

    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 ∼2×104. 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 ∼1MeV. 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. © 2010 The American Physical Society.

  • Fäustlin RR, Düsterer S, Laarmann T, Redlin H, Tavella F, Toleikis S, Bornath T, Göde S, Irsig R, Meiwes-Broer K-H, Przystawik A, Redmer R, Reinholz H, Röpke G, Thiele R, Tiggesbäumker J, Döppner T, Glenzer SH, Förster E, Uschmann I, Zastrau U, Fortmann C, Gregori G, Mithen J, Nagler B, Vinko SM, Whitcher T, Lee HJ, Li B, Ziaja B, Tschentscher T. (2010) 'Observation of ultrafast nonequilibrium collective dynamics in warm dense hydrogen'. Physical Review Letters, 104 (12)

    Abstract

    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 2.8×1020cm3. For dense plasmas, our experimental data strongly support a nonequilibrium kinetics model that uses impact ionization cross sections based on classical free-electron collisions. © 2010 The American Physical Society.

  • Toleikis S, Fäustlin RR, Düsterer S, Laarmann T, Radcliffe P, Tavella F, Cao L, Förster E, Uschmann I, Zastrau U, Döppner T, Glenzer SH, Fortmann C, Göde S, Irsig R, Meiwes-Broer K-H, Przystawik A, Redmer R, Thiele R, Tiggesbäumker J, Truong NX, Gregori G, Mithen J, Lee HJ, Tschentscher T, Li B. (2010) 'Soft X-ray scattering using FEL radiation for probing near-solid density plasmas at few electron volt temperatures'. High Energy Density Physics, 6 (1), pp. 15-20.

    Abstract

    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.

  • Roth M, Alber I, Günther M, Harres K, Nürnberg F, Otten A, Pelka A, Schollmeier M, Schütrumpf J, Bagnoud V, Tauschwitz A, Brown C, Gregori G, Mithen J, Clarke R, Heathcote R, Li B, Schaumann G, Daido H, Tampo M, Fernandez J, Flippo K, Gaillard S, Gauthier C, Offermann D, Glenzer S, Kritcher A, Kugland N, Lepape S, Makita M, Riley D, Niemann C, Tauschwitz AN. (2010) 'Transport of laser accelerated proton beams and isochoric heating of matter'. Journal of Physics: Conference Series, 244 (PART 1)

    Abstract

    The acceleration of intense proton and ion beams by ultra-intense lasers has matured to a point where applications in basic research and technology are being developed. Crucial for harvesting the unmatched beam parameters driven by the relativistic electron sheath is the precise control of the beam. We report on recent experiments using the PHELIX laser at GSI, the VULCAN laser at RAL and the TRIDENT laser at LANL to control and use laser accelerated proton beams for applications in high energy density research. We demonstrate efficient collimation of the proton beam using high field pulsed solenoid magnets, a prerequisite to capture and transport the beam for applications. Furthermore we report on two campaigns to use intense, short proton bunches to isochorically heat solid targets up to the warm dense matter state. The temporal profile of the proton beam allows for rapid heating of the target, much faster than the hydrodynamic response time thereby creating a strongly coupled plasma at solid density. The target parameters are then probed by X-ray Thomson scattering (XRTS) to reveal the density and temperature of the heated volume. This combination of two powerful techniques developed during the past few years allows for the generation and investigation of macroscopic samples of matter in states present in giant planets or the interior of the earth. © 2010 IOP Publishing Ltd.

  • Toleikis S, Düsterer S, Fäustlin RR, Laarmann T, Redlin H, Tavella F, Bornath T, Göde S, Irsig R, Meiwes-Broer K-H, Przystawik A, Redmer R, Reinholz H, Röpke G, Thiele R, Tiggesbäumker J, Döppner T, Glenzer SH, Förster E, Uschmann I, Zastrau U, Fortmann C, Gregori G, Vinko SM, Whitcher T, Lee HJ, Mithen J, Nagler B, Li B, Radcliffe P, Tschentscher T, Ziaja B. (2010) 'Probing near-solid density plasmas using soft x-ray scattering'. Journal of Physics B: Atomic, Molecular and Optical Physics, 43 (19)

    Abstract

    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) × 10 cm 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.

  • Vinko SM, Gregori G, Li B, Mithen JP, Whitcher TJ, Wark JS, Zastrau U, Förster E, Mazevet S, Andreasson J, Hajdu J, Bajt S, Düsterer S, Fäustlin RR, Laarmann T, Tavella F, Toleikis S, Burian T, Chalupsky J, Cihelka J, Hajkova V, Juha L, Vysin L, Chapman HN, Doria D, Dzelzainis T, Riley D, White S, Döppner T, Fortmann C, Glenzer SH, Lee RW, Nelson AJ, Galtier E, Rosmej F, Göde S, Irsig R, Meiwes-Broer K-H, Przystawik A, Redmer R, Thiele R, Tiggesbäumker J, Heimann PA, Jurek M, Sobierajski R, Krzywinski J, Lee HJ, Nagler B, Tschentscher T. (2010) 'Electronic Structure of an XUV Photogenerated Solid-Density Aluminum Plasma'. Physical Review Letters, 104 (22)

    Abstract

    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. © 2010 The American Physical Society.

  • Fäustlin RR, Toleikis S, Düsterer S, Laarmann T, Redlin H, Tavella F, Tschentscher T, Bornath T, Fortmann C, Göde S, Irsig R, Meiwes-Broer K-H, Przystawik A, Redmer R, Reinholz H, Röpke G, Thiele R, Tiggesbäumker J, Förster E, Uschmann I, Zastrau U, Döppner T, Glenzer SH, Gregori G, Mithen J, Lee HJ, Li B. (2009) 'Soft X-Ray Thomson scattering in warm dense hydrogen at FLASH'. Proceedings of SPIE - The International Society for Optical Engineering, 7451

    Abstract

    We present collective Thomson scattering with soft x-ray free electron laser radiation as a method to track the evolution of warm dense matter plasmas with ∼200 fs time resolution. In a pump-probe scheme an 800 nm laser heats a 20 ∼m hydrogen droplet to the plasma state. After a variable time delay in the order of ps the plasma is probed by an x-ray ultra violet (XUV) pulse which scatters from the target and is recorded spectrally. Alternatively, in a self-Thomson scattering experiment, a single XUV pulse heats the target while a portion of its photons are being scattered probing the target. From such inelastic x-ray scattering spectra free electron temperature and density can be inferred giving insight on relaxation time scales in plasmas as well as the equation of state. We prove the feasibility of this method in the XUV range utilizing the free electron laser facility in Hamburg, FLASH. We recorded Thomson scattering spectra for hydrogen plasma, both in the self-scattering and in the pump-probe mode using optical laser heating. © 2009 SPIE-.

  • Roth M, Alber I, Günther M, Harres K, Nürnberg F, Otten A, Pelka A, Schaumann G, Schollmeier M, Schütrumpf J, Bagnoud V, Tauschwitz A, Brown CRD, Clarke R, Heathcote R, Li B, Daido H, Tampo M, Fernandez J, Flippo K, Gaillard S, Gauthier C, Offermann D, Geissel M, Glenzer S, Kritcher A, Kugland N, Lepape S, Gregori G, Mithen J, Makita M, Riley D, Niemann C. (2009) 'Proton acceleration experiments and warm dense matter research using high power lasers'. Plasma Physics and Controlled Fusion, 51 (12)

    Abstract

    The acceleration of intense proton and ion beams by ultra-intense lasers has matured to a point where applications in basic research and technology are being developed. Crucial for harvesting the unmatched beam parameters driven by the relativistic electron sheath is the precise control of the beam. In this paper we report on recent experiments using the PHELIX laser at GSI, the VULCAN laser at RAL and the TRIDENT laser at LANL to control and use laser accelerated proton beams for applications in high energy density research. We demonstrate efficient collimation of the proton beam using high field pulsed solenoid magnets, a prerequisite to capture and transport the beam for applications. Furthermore, we report on two campaigns to use intense, short proton bunches to isochorically heat solid targets up to the warm dense matter state. The temporal profile of the proton beam allows for rapid heating of the target, much faster than the hydrodynamic response time thereby creating a strongly coupled plasma at solid density. The target parameters are then probed by x-ray Thomson scattering to reveal the density and temperature of the heated volume. This combination of two powerful techniques developed during the past few years allows for the generation and investigation of macroscopic samples of matter in states present in giant planets or the interior of the earth. © 2009 IOP Publishing Ltd.

Teaching

At present, I teach small group tutorials which cover all topics in the 1st year undergraduate physics course.

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