T. Bornath - Academia.edu (original) (raw)
Papers by T. Bornath
Proceedings of SPIE - The International Society for Optical Engineering, 2009
We present collective Thomson scattering with soft x-ray free electron laser radiation as a metho... more 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 μm 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. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 10/11/2013 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 7451 74510D-2 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 10/11/2013 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 7451 74510D-5 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 10/11/2013 Terms of Use: http://spiedl.org/terms
The basic idea is to implement Thomson scattering with free electron laser (FEL) radiation at nea... more The basic idea is to implement Thomson scattering with free electron laser (FEL) radiation at near-solid density plasmas as a diagnostic method which allows the determination of plasma temperatures and densities in the warm dense matter (WDM) regime (free electron density of n{sub e} = 10²¹-10² cm³ with temperatures of several eV). The WDM regime [1] at near-solid density (n{sub
Phys. Rev. E, 2014
We investigate subpicosecond dynamics of warm dense hydrogen at the XUV free-electron laser facil... more 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 ≤ 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.
IEEE International Conference on Plasma Science, 2009
Summary form only given. A general overview of the potential for both warm and hot dense matter r... more Summary form only given. A general overview of the potential for both warm and hot dense matter research for the future will be presented. First, a discussion of the regime defined as relevant to warm dense matter will be attempted in terms of the underlying physical phenomena that define the field. Next a categorization of the facilities to be included in the perspective will be given. With this as background a series of schematic experiments will be discussed with respect to the facilities where they will be pursued. Comments on the interaction amongst the various experiments and between the various facilities will be outlined. Finally, a report will be given of the X-ray absorption of Warm Dense Matter experiment at the FLASH Free Electron Laser (FEL) facility at DESY. The FEL beam is used to produce Warm Dense Matter with soft X-ray absorption as the probe of electronic structure. A multilayer-coated parabolic mirror focuses the FEL radiation, to spot sizes as small as 0.3 mum in a ~15 fs pulse of containing >1012 photons at 13.5 nm wavelength, onto a thin sample. Silicon photodiodes measure the transmitted and reflected beams, while spectroscopy provides detailed measurement of the temperature of the sample. The goal is to measure over a range of intensities approaching 1018 W/cm2. Experimental results will be presented along with theoretical calculations.
Physical Review Letters, 2014
We report on the dynamics of ultrafast heating in cryogenic hydrogen initiated by a ≲300 fs, 92 e... more 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.
Physical Review Letters, 2010
The investigation of Warm Dense Matter (WDM) is one of the grand challenges of contemporary physi... more The investigation of Warm Dense Matter (WDM) is one of the grand challenges of contemporary physics . WDM is a plasma state characterized by moderate-to-strong inter-particle coupling which takes place at free electron temperatures of several eV and free electron densities around solid density . It is present in many physical environments, such as planetary interiors [3], gravitationally collapsing protostellar disks, laser matter interaction and particularly during the implosion of an inertial confinement fusion capsule . We investigate ultrafast (fs) electron dynamics in a liquid hydrogen sample, isochorically and volumetrically heated to a moderately coupled plasma state using 91.8 eV FLASH radiation . During the ∼40 fs heating process, a fraction of the radiation is Thomson scattered. The scattered radiation is recorded spectrally using a specially designed spectrograph . The spectral structure is dominated by two inelastically scattered peaks, the plasmons, from collective Thomson scattering. From their photon energy shift with respect to the incident radiation we can determine the plasma free electron density. The free electron temperature can be inferred from the intensity ratio of the two peaks via detailed balance. To determine these plasma parameters we fit the recorded spectrum with simulations ( ) and obtain a free electron temperature and density of 13 eV and 2.8 × 10 20 cm −3 , respectively. Furthermore, the measurements show that the hydrogen plasma has been driven to a non-thermal state with an ion temperature below 0.1 eV [5]. We have simulated [5, 7] the evolution of the electron kinetic energy distribution during and after the FEL irradiation and have compare these density and temperature trajectories with our measurements ( . In the simulation we can study the influence of different cross sections for impact ionization, which is the dominant mechanism on this time scale. We used the National Institute of Standards and Technology database for molecular hydrogen bases on the Binary Encounter Bethe (BEB) model as well as a classical expression based on free electron collisions. The models deviate up to a factor of four in the relevant electron energy range. Simulations with the classical model yield results which match our measurement significantly better than BEB ( . A possible interpretation is that the atomic structure (as treated in BEB) does not play a significant role in the context of dense plasmas where, due to screening and correlation effects, high lying atomic states are removed and the electron interaction is more properly described with a classical ionic background. This is an important step towards the investigation of strongly coupled plasmas which are within reach of current and future light sources such as LCLS and the European XFEL.
Physical Review E, 2010
The introduction of brilliant free-electron lasers enables new pump-probe experiments to characte... more The introduction of brilliant free-electron lasers enables new pump-probe experiments to characterize warm dense matter states. For instance, a short-pulse optical laser irradiates a liquid hydrogen jet that is subsequently probed with brilliant soft x-ray radiation. The strongly inhomogeneous plasma prepared by the optical laser is characterized with particle-in-cell simulations. The interaction of the soft x-ray probe radiation for different time delays between pump and probe with the inhomogeneous plasma is also taken into account via radiative hydrodynamic simulations. We calculate the respective scattering spectrum based on the Born-Mermin approximation for the dynamic structure factor considering the full density and temperature-dependent Thomson scattering cross section throughout the target. We can identify plasmon modes that are generated in different target regions and monitor their temporal evolution. Therefore, such pump-probe experiments are promising tools not only to measure the important plasma parameters density and temperature but also to gain valuable information about their time-dependent profile through the target. The method described here can be applied to various pump-probe scenarios by combining optical lasers and soft x ray, as well as x-ray sources.
Laser and Particle Beams, 2009
ABSTRACT With the advent of intense, coherent light sources in the XUV and soft X-ray regime, X-r... more ABSTRACT With the advent of intense, coherent light sources in the XUV and soft X-ray regime, X-ray Thomson scattering becomes a unique tool for the diagnostics of dense plasmas. The scattering spectrum gives direct access to plasma properties like density, temperature, and composition. In dense systems, collisions among constituents are of primary importance for the prediction and interpretation of the scattering signal. We present a systematic approach to the dynamical structure factor using the Born-Mermin ansatz to include collisions via the dynamical collision frequency. Calculations of the scattering spectrum are performed for X-ray scattering on solid and compressed beryllium targets as well as for XUV-photons scattering on hydrogen at near solid density.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2010
X-ray scattering using highly brilliant X-ray free-electron laser (FEL) radiation provides a new ... more X-ray scattering using highly brilliant X-ray free-electron laser (FEL) radiation provides a 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 20 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 analyze the data.
High Energy Density Physics, 2007
We propose a collective Thomson scattering experiment at the VUV free electron laser facility at ... more We propose a collective Thomson scattering experiment at the VUV free electron laser facility at DESY (FLASH) which aims to diagnose warm dense matter at near-solid density. The plasma region of interest marks the transition from an ideal plasma to a correlated and degenerate many-particle system and is of current interest, e.g. in ICF experiments or laboratory astrophysics. Plasma diagnostic of such plasmas is a longstanding issue. The collective electron plasma mode (plasmon) is revealed in a pump-probe scattering experiment using the high-brilliant radiation to probe the plasma. The distinctive scattering features allow to infer basic plasma properties. For plasmas in thermal equilibrium the electron density and temperature is determined from scattering off the plasmon mode.
Proceedings of SPIE - The International Society for Optical Engineering, 2009
We present collective Thomson scattering with soft x-ray free electron laser radiation as a metho... more 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 μm 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. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 10/11/2013 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 7451 74510D-2 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 10/11/2013 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 7451 74510D-5 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 10/11/2013 Terms of Use: http://spiedl.org/terms
The basic idea is to implement Thomson scattering with free electron laser (FEL) radiation at nea... more The basic idea is to implement Thomson scattering with free electron laser (FEL) radiation at near-solid density plasmas as a diagnostic method which allows the determination of plasma temperatures and densities in the warm dense matter (WDM) regime (free electron density of n{sub e} = 10²¹-10² cm³ with temperatures of several eV). The WDM regime [1] at near-solid density (n{sub
Phys. Rev. E, 2014
We investigate subpicosecond dynamics of warm dense hydrogen at the XUV free-electron laser facil... more 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 ≤ 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.
IEEE International Conference on Plasma Science, 2009
Summary form only given. A general overview of the potential for both warm and hot dense matter r... more Summary form only given. A general overview of the potential for both warm and hot dense matter research for the future will be presented. First, a discussion of the regime defined as relevant to warm dense matter will be attempted in terms of the underlying physical phenomena that define the field. Next a categorization of the facilities to be included in the perspective will be given. With this as background a series of schematic experiments will be discussed with respect to the facilities where they will be pursued. Comments on the interaction amongst the various experiments and between the various facilities will be outlined. Finally, a report will be given of the X-ray absorption of Warm Dense Matter experiment at the FLASH Free Electron Laser (FEL) facility at DESY. The FEL beam is used to produce Warm Dense Matter with soft X-ray absorption as the probe of electronic structure. A multilayer-coated parabolic mirror focuses the FEL radiation, to spot sizes as small as 0.3 mum in a ~15 fs pulse of containing >1012 photons at 13.5 nm wavelength, onto a thin sample. Silicon photodiodes measure the transmitted and reflected beams, while spectroscopy provides detailed measurement of the temperature of the sample. The goal is to measure over a range of intensities approaching 1018 W/cm2. Experimental results will be presented along with theoretical calculations.
Physical Review Letters, 2014
We report on the dynamics of ultrafast heating in cryogenic hydrogen initiated by a ≲300 fs, 92 e... more 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.
Physical Review Letters, 2010
The investigation of Warm Dense Matter (WDM) is one of the grand challenges of contemporary physi... more The investigation of Warm Dense Matter (WDM) is one of the grand challenges of contemporary physics . WDM is a plasma state characterized by moderate-to-strong inter-particle coupling which takes place at free electron temperatures of several eV and free electron densities around solid density . It is present in many physical environments, such as planetary interiors [3], gravitationally collapsing protostellar disks, laser matter interaction and particularly during the implosion of an inertial confinement fusion capsule . We investigate ultrafast (fs) electron dynamics in a liquid hydrogen sample, isochorically and volumetrically heated to a moderately coupled plasma state using 91.8 eV FLASH radiation . During the ∼40 fs heating process, a fraction of the radiation is Thomson scattered. The scattered radiation is recorded spectrally using a specially designed spectrograph . The spectral structure is dominated by two inelastically scattered peaks, the plasmons, from collective Thomson scattering. From their photon energy shift with respect to the incident radiation we can determine the plasma free electron density. The free electron temperature can be inferred from the intensity ratio of the two peaks via detailed balance. To determine these plasma parameters we fit the recorded spectrum with simulations ( ) and obtain a free electron temperature and density of 13 eV and 2.8 × 10 20 cm −3 , respectively. Furthermore, the measurements show that the hydrogen plasma has been driven to a non-thermal state with an ion temperature below 0.1 eV [5]. We have simulated [5, 7] the evolution of the electron kinetic energy distribution during and after the FEL irradiation and have compare these density and temperature trajectories with our measurements ( . In the simulation we can study the influence of different cross sections for impact ionization, which is the dominant mechanism on this time scale. We used the National Institute of Standards and Technology database for molecular hydrogen bases on the Binary Encounter Bethe (BEB) model as well as a classical expression based on free electron collisions. The models deviate up to a factor of four in the relevant electron energy range. Simulations with the classical model yield results which match our measurement significantly better than BEB ( . A possible interpretation is that the atomic structure (as treated in BEB) does not play a significant role in the context of dense plasmas where, due to screening and correlation effects, high lying atomic states are removed and the electron interaction is more properly described with a classical ionic background. This is an important step towards the investigation of strongly coupled plasmas which are within reach of current and future light sources such as LCLS and the European XFEL.
Physical Review E, 2010
The introduction of brilliant free-electron lasers enables new pump-probe experiments to characte... more The introduction of brilliant free-electron lasers enables new pump-probe experiments to characterize warm dense matter states. For instance, a short-pulse optical laser irradiates a liquid hydrogen jet that is subsequently probed with brilliant soft x-ray radiation. The strongly inhomogeneous plasma prepared by the optical laser is characterized with particle-in-cell simulations. The interaction of the soft x-ray probe radiation for different time delays between pump and probe with the inhomogeneous plasma is also taken into account via radiative hydrodynamic simulations. We calculate the respective scattering spectrum based on the Born-Mermin approximation for the dynamic structure factor considering the full density and temperature-dependent Thomson scattering cross section throughout the target. We can identify plasmon modes that are generated in different target regions and monitor their temporal evolution. Therefore, such pump-probe experiments are promising tools not only to measure the important plasma parameters density and temperature but also to gain valuable information about their time-dependent profile through the target. The method described here can be applied to various pump-probe scenarios by combining optical lasers and soft x ray, as well as x-ray sources.
Laser and Particle Beams, 2009
ABSTRACT With the advent of intense, coherent light sources in the XUV and soft X-ray regime, X-r... more ABSTRACT With the advent of intense, coherent light sources in the XUV and soft X-ray regime, X-ray Thomson scattering becomes a unique tool for the diagnostics of dense plasmas. The scattering spectrum gives direct access to plasma properties like density, temperature, and composition. In dense systems, collisions among constituents are of primary importance for the prediction and interpretation of the scattering signal. We present a systematic approach to the dynamical structure factor using the Born-Mermin ansatz to include collisions via the dynamical collision frequency. Calculations of the scattering spectrum are performed for X-ray scattering on solid and compressed beryllium targets as well as for XUV-photons scattering on hydrogen at near solid density.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2010
X-ray scattering using highly brilliant X-ray free-electron laser (FEL) radiation provides a new ... more X-ray scattering using highly brilliant X-ray free-electron laser (FEL) radiation provides a 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 20 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 analyze the data.
High Energy Density Physics, 2007
We propose a collective Thomson scattering experiment at the VUV free electron laser facility at ... more We propose a collective Thomson scattering experiment at the VUV free electron laser facility at DESY (FLASH) which aims to diagnose warm dense matter at near-solid density. The plasma region of interest marks the transition from an ideal plasma to a correlated and degenerate many-particle system and is of current interest, e.g. in ICF experiments or laboratory astrophysics. Plasma diagnostic of such plasmas is a longstanding issue. The collective electron plasma mode (plasmon) is revealed in a pump-probe scattering experiment using the high-brilliant radiation to probe the plasma. The distinctive scattering features allow to infer basic plasma properties. For plasmas in thermal equilibrium the electron density and temperature is determined from scattering off the plasmon mode.