AA Offenberger - Academia.edu (original) (raw)
Papers by AA Offenberger
HiPER technical report Version 1.0 3 1 Foreword This document provides technical details of the H... more HiPER technical report Version 1.0 3 1 Foreword This document provides technical details of the High Power laser Energy Research facility, HiPER. The content is the result of a 2-year design study by over 50 senior scientists from 12 of the 15 nations now associated with HiPER. The design is now sufficiently mature that a formal proposal has been made to the European Commission to prepare the case for construction as part of the European strategic facility roadmap process (ESFRI) and Framework Programme 7. HiPER is a multinational laser facility designed to allow Europe to take a leading position in the pursuit of Inertial Fusion Energy, whilst offering an internationally unique capability for science in extreme conditions. It will open up entirely new areas of research, providing access to physics regimes which cannot be explored on any other science facility. It has been formally endorsed by 7 European nations at the governmental or national funding agency level, 2 regional governments, over 20 scientific institutions and has direct involvement from industry. Inertial Fusion Energy (IFE) lies at the heart of the design of HiPER. Fusion is the holy grail of energy sources-combining abundant fuel with no greenhouse gas emissions, minimal waste products, and a scale that can meet mankind's long-term energy demands. Fusion combines hydrogen isotopes to create helium gas and a neutron which is captured to provide heat for a steam turbine. The IFE solution for fusion is a proven scientific concept. A laboratory demonstration of net energy production using lasers for IFE is now only 3 to 5 years away, marking the culmination of 40 years research. This will attract significant public and political attention, and so the HiPER project has been developed to provide a clear path forwards, based on a strong science mission. The project already stretches beyond the EU, involving coordination with work in Japan, China, South Korea, Canada, Russia and the USA. HiPER represents science with a strong societal goal.
The first stages in our study of nonadiabatic scattering have been completed. We have measured th... more The first stages in our study of nonadiabatic scattering have been completed. We have measured the lifetime of electrons subject to resonant perturbations in mirror and toroidal geometry. We have predicted the point at which first-order perturbation-theoretic estimates of velocity space diffusion fail and developed a new theory that is valid past this limit. We are now extending our experimental studies to very weak and to nearly resonant interactions. This should provide a sensitive test of certain facets of nonlinear plasma kinetic theory. We shall apply an earlier result to estimate the importance of nonlinear effects on the growth of ionospheric "whistlers."
Physical Review E, 1993
The formation and evolution of collisional structures in the coronas of laser-produced plasmas ha... more The formation and evolution of collisional structures in the coronas of laser-produced plasmas have been studied by irradiating multilayered targets with nonuniform laser beams. Spatially resolved x-ray emission patterns and spectra were recorded to infer the temperatures, ionization states, and timeintegrated hydrodynamic histories of plasmas originating from tracer layers embedded in the targets. The conditions of the experiment have been simulated using a two-dimensional single-Quid hydrodynamic code. The experimental results and code predictions are in good agreement, showing the stagnation of colliding plasmas in the nonirradiated regions.
Physical Review E, 1998
Efficient guiding of 1-ps infrared laser pulses with power exceeding 10 TW has been demonstrated ... more Efficient guiding of 1-ps infrared laser pulses with power exceeding 10 TW has been demonstrated through hollow capillary tubes with 40- and 100-mum internal diameters and lengths up to 10 mm, with transmission greater than 80% of the incident energy coupled into the capillary. The beam is guided via multiple reflections off a plasma formed on the walls of the
Contains research objectives. United States Atomic Energy Commission (Contract AT(30-1)-3285)
Optics Communications, 1987
We report here on an experimental study of reward energy transport m hlgh-Z gold plasma heated by... more We report here on an experimental study of reward energy transport m hlgh-Z gold plasma heated by 2 ns KrF laser pulses (2=0 248 nm) Gold coated plastic targets were wradmted m the intensity range of 10~2-10 ~3 W/cm 2 and measurements of heat penetratmn, soft X-ray emlssmn and plasma hydrodynamics were performed It is observed that the penetratmn depth for an 100 eV isotherm in gold is smaller than that predicted by a simple self-regulating model which excludes radmtmn transport It is also observed that plasma ablatmn at lower temperature occurs at greater depths in the plasUc substrate A significant role of reward radmtmn energy transport is inferred from the measured variation of parameters with gold overlayer thickness and laser intensity
Physical Review Letters, 1980
Efficient absorption of long-pulse C${\mathrm{O}}_{2}$-laser radiation is observed to follow a tr... more Efficient absorption of long-pulse C${\mathrm{O}}_{2}$-laser radiation is observed to follow a transient phase of stimulated Brillouin backscatter in critical density, laminar oxygen gas target irradiation experiments. Nearly complete energy absorption occurs for \ensuremath{\lesssim} 10 nsec following stimulated Brillouin backscatter after which target burnthrough and refraction dominate. Inverse bremsstrahlung and resonance absorption cannot account for the general features observed. Anomalous collisions due to strong ion turbulence produced by the incident laser radiation are postulated to account for the efficient absorption.
Physical Review A, 1978
Two-plasmon decay has been observed in a C${\mathrm{O}}_{2}$-laser-gas-target-plasma interaction ... more Two-plasmon decay has been observed in a C${\mathrm{O}}_{2}$-laser-gas-target-plasma interaction experiment. The spectrum of frac32\frac{3}{2}frac32-harmonic radiation has been measured and the threshold intensity for decay determined. An experimental value of \ensuremath{\sim} 2 \ifmmode\times\else\texttimes\fi{} 1011{10}^{11}1011 W/${\mathrm{cm}}^{2}$ is in reasonable agreement with theoretical predictions for an inhomogeneous plasma.
Physics of Fluids, 1983
Threshold conditions are analyzed for stimulated Raman backscattering (SRS) from an underdense pl... more Threshold conditions are analyzed for stimulated Raman backscattering (SRS) from an underdense plasma in the presence of ion‐acoustic fluctuations. For typical ion‐acoustic spectra which could result from a Brillouin instability occurring simultaneously with SRS, a reduced collisional threshold due to induced bremsstrahlung is found for the Raman instability. Similarly, for inhomogeneous plasma the phase mismatch created by a density gradient can be compensated for by an inhomogeneity in the ion‐acoustic spectrum; as a consequence, the inhomogeneity threshold for absolute instability can be substantially reduced. Comparisons are made with experimental observations of stimulated Raman scattering in the presence of strong stimulated Brillouin scattering for CO2 laser‐plasma interaction. It is found theoretically that for fluctuation levels typical of that accompanying SBS, induced bremsstrahlung growth rates for Langmuir waves can be of the order of collisional damping rates.
Physics Letters A, 1975
Preliminary observations of stimulated baekscatter from CO2 laser produced plasma are reported. T... more Preliminary observations of stimulated baekscatter from CO2 laser produced plasma are reported. The scattered radiation has been spectrally resolved and the measured shift found to be consistent with that expected from ion acoustic waves. The change in wavelength shift when helium is substituted for hydrogen is in agreement with x/'m-i, where m i = ion mass.
Journal of Fusion Energy, 1998
A model of energy gain induced by fast ignition of thermonuclear burn in compressed deuteriumtrit... more A model of energy gain induced by fast ignition of thermonuclear burn in compressed deuteriumtritium fuel, is used to show the potential for 300X gain with a driver energy of 1 MJ, if the National Ignition Facility (NIF) were to be adapted for fast ignition. The physics of fast ignition has been studied using a petawatt laser facility at the Lawrence Livermore National Laboratory. Laser plasma interaction in a preformed plasma on a solid target leads to relativistic self-focusing evidenced by x-ray images. Absorption of the laser radiation transfers energy to an intense source of relativistic electrons. Good conversion efficiency into a wide angular distribution is reported. Heating by the electrons in solid density CD2 produces 0.5 to 1 keV temperature, inferred from the D-D thermonuclear neutron yield.
Review of Scientific Instruments, 1984
This investigation is concerned with the development of a low‐inductance, low‐jitter, electricall... more This investigation is concerned with the development of a low‐inductance, low‐jitter, electrically triggered, high‐voltage annular rail spark gap. Three trigger electrode geometries—blade, dull, and sawtooth edge—are tested for the effects of different field stresses on the spark gap switching performance. All possible polarity combinations are applied to the high‐voltage and trigger electrodes of the rail gap, and the switching inductance and jitter is measured for each case. Finally, the effects of photopreionization from bare sparks on the spark gap switching performance is explored. A switch inductance of 4 nH and jitter of 0.6 ns have been achieved. A practical application of the rail gap is also described.
Applications of Laser Plasma Radiation, 1994
We report results of Thomson scattering measurements of optically ionized gases produced using 12... more We report results of Thomson scattering measurements of optically ionized gases produced using 12 psec pulses from a KrF-pumped Raman laser at intensities of 3 X 1017 W cm-2. Electron densities and temperatures are determined from the scattered Thomson spectra in both He and Ne (static and gas jet targets) at pressures of 10-3 - 1 bar. The central, low frequency region of the spectra from low pressure shots clearly shows an enhanced intensity above that given by the Salpeter approximation, and is indicative of a high electron-to-ion temperature ratios of at least 10 - 20. These observations are consistent with the long electron-ion collision time relative to the pulse length.
International Conference on Plasma Sciences (ICOPS), 1993
Summary form only given. The authors report on studies of optical ionization of gases produced by... more Summary form only given. The authors report on studies of optical ionization of gases produced by 12-ps pulses of focused Raman-shifted KrF laser radiation (γ=268 nm) at intensities of 3×1017 W/cm2. Measurements of Thomson, stimulated Raman, and stimulated Brillouin scattering have been used to determine the electron energy distribution and temperature in He and Ne (static and pulsed gas jet targets) at pressures of 10-3 to 1 bar and to investigate the role of parametric instabilities in the laser/plasma interaction. The electron velocity distribution evolves from a multiphoton (tunnel) ionization spectrum at low pressure to a thermal electron distribution at moderate pressure. The ion determined portion of the Thomson-scattered spectrum is highly nonthermal for pressures greater than a few mbar. At high pressure, significant Raman and Brillouin backscattering is observed. Inverse bremsstrahlung absorption is shown to dominate heating from p>10-2 bar except at the highest pressures where stimulated Raman scattering may also be important
Physical Review Letters, 1993
Thomson scattering measurements have been used to determine the electron energy distribution in U... more Thomson scattering measurements have been used to determine the electron energy distribution in UV optically ionized He and Ne at pressures up to j bar irradiated at 3x 10 17 W/cm 2 in 12 ps. The electrons evolve from a multiphoton ionization spectrum to a thermal distribution with increasing pressure. The low frequency part of the scattered spectrum clearly shows the "zero-damped" ion acoustic mode for high values of ZT e /Tt. Experimental and modeling results indicate that nonlinear inverse bremsstrahlung heating and radial conduction cooling dominate the electron energy balance.
Review of Scientific Instruments, 1975
A CO2 laser energy detector is described which uses the pressure rise generated in a vaccum cell ... more A CO2 laser energy detector is described which uses the pressure rise generated in a vaccum cell by gaseous infrared absorption to provide linear energy detection over many decades, good responsivity, wide aperture, and in-line beam monitoring. Nonadiabatic pressure measurements resulting when the beam size is less than the cell aperture are discussed.
Review of Scientific Instruments, 1997
We report on the first plasma experiments with the 100 TW laser at LLNL. We have experimentally i... more We report on the first plasma experiments with the 100 TW laser at LLNL. We have experimentally investigated the interaction of 1 μm, 40 J, 400 fs, 5×1019 W/cm2 laser pulses with multilayer solid targets. Various diagnostics were used to characterize this interaction. An x-ray pinhole camera monitored laser spot size and plasma location on target. Part of the laser
Review of Scientific Instruments, 1997
ABSTRACT We report on experiments using the 100 TW laser at LLNL (40J, 400 fs, 5×1019 W/cm2 focal... more ABSTRACT We report on experiments using the 100 TW laser at LLNL (40J, 400 fs, 5×1019 W/cm2 focal intensity) and planar multilayer targets (Mo/Sn) to study the generation and transport of electrons with MeV energies. Such fast electrons are of prime importance to many proposed applications, e.g., the fast ignitor fusion concept. X-ray emission spectroscopy is used to study the electron transport. Characteristic K α photon emission produced by the fast electrons in the front (Mo) and rear (Sn) layers of the target is measured with a charge-coupled device detector (single photon counting mode) to infer the electron energy deposition. The electron energy spectrum is measured by varying the thickness of the Mo layer to attenuate the electrons by different amounts. Penumbral imaging of the K α emission is used to give information about the angular distribution of the fast electron emission. Details of the measurement techniques and experimental results will be discussed and compared with modeling calculations.
HiPER technical report Version 1.0 3 1 Foreword This document provides technical details of the H... more HiPER technical report Version 1.0 3 1 Foreword This document provides technical details of the High Power laser Energy Research facility, HiPER. The content is the result of a 2-year design study by over 50 senior scientists from 12 of the 15 nations now associated with HiPER. The design is now sufficiently mature that a formal proposal has been made to the European Commission to prepare the case for construction as part of the European strategic facility roadmap process (ESFRI) and Framework Programme 7. HiPER is a multinational laser facility designed to allow Europe to take a leading position in the pursuit of Inertial Fusion Energy, whilst offering an internationally unique capability for science in extreme conditions. It will open up entirely new areas of research, providing access to physics regimes which cannot be explored on any other science facility. It has been formally endorsed by 7 European nations at the governmental or national funding agency level, 2 regional governments, over 20 scientific institutions and has direct involvement from industry. Inertial Fusion Energy (IFE) lies at the heart of the design of HiPER. Fusion is the holy grail of energy sources-combining abundant fuel with no greenhouse gas emissions, minimal waste products, and a scale that can meet mankind's long-term energy demands. Fusion combines hydrogen isotopes to create helium gas and a neutron which is captured to provide heat for a steam turbine. The IFE solution for fusion is a proven scientific concept. A laboratory demonstration of net energy production using lasers for IFE is now only 3 to 5 years away, marking the culmination of 40 years research. This will attract significant public and political attention, and so the HiPER project has been developed to provide a clear path forwards, based on a strong science mission. The project already stretches beyond the EU, involving coordination with work in Japan, China, South Korea, Canada, Russia and the USA. HiPER represents science with a strong societal goal.
The first stages in our study of nonadiabatic scattering have been completed. We have measured th... more The first stages in our study of nonadiabatic scattering have been completed. We have measured the lifetime of electrons subject to resonant perturbations in mirror and toroidal geometry. We have predicted the point at which first-order perturbation-theoretic estimates of velocity space diffusion fail and developed a new theory that is valid past this limit. We are now extending our experimental studies to very weak and to nearly resonant interactions. This should provide a sensitive test of certain facets of nonlinear plasma kinetic theory. We shall apply an earlier result to estimate the importance of nonlinear effects on the growth of ionospheric "whistlers."
Physical Review E, 1993
The formation and evolution of collisional structures in the coronas of laser-produced plasmas ha... more The formation and evolution of collisional structures in the coronas of laser-produced plasmas have been studied by irradiating multilayered targets with nonuniform laser beams. Spatially resolved x-ray emission patterns and spectra were recorded to infer the temperatures, ionization states, and timeintegrated hydrodynamic histories of plasmas originating from tracer layers embedded in the targets. The conditions of the experiment have been simulated using a two-dimensional single-Quid hydrodynamic code. The experimental results and code predictions are in good agreement, showing the stagnation of colliding plasmas in the nonirradiated regions.
Physical Review E, 1998
Efficient guiding of 1-ps infrared laser pulses with power exceeding 10 TW has been demonstrated ... more Efficient guiding of 1-ps infrared laser pulses with power exceeding 10 TW has been demonstrated through hollow capillary tubes with 40- and 100-mum internal diameters and lengths up to 10 mm, with transmission greater than 80% of the incident energy coupled into the capillary. The beam is guided via multiple reflections off a plasma formed on the walls of the
Contains research objectives. United States Atomic Energy Commission (Contract AT(30-1)-3285)
Optics Communications, 1987
We report here on an experimental study of reward energy transport m hlgh-Z gold plasma heated by... more We report here on an experimental study of reward energy transport m hlgh-Z gold plasma heated by 2 ns KrF laser pulses (2=0 248 nm) Gold coated plastic targets were wradmted m the intensity range of 10~2-10 ~3 W/cm 2 and measurements of heat penetratmn, soft X-ray emlssmn and plasma hydrodynamics were performed It is observed that the penetratmn depth for an 100 eV isotherm in gold is smaller than that predicted by a simple self-regulating model which excludes radmtmn transport It is also observed that plasma ablatmn at lower temperature occurs at greater depths in the plasUc substrate A significant role of reward radmtmn energy transport is inferred from the measured variation of parameters with gold overlayer thickness and laser intensity
Physical Review Letters, 1980
Efficient absorption of long-pulse C${\mathrm{O}}_{2}$-laser radiation is observed to follow a tr... more Efficient absorption of long-pulse C${\mathrm{O}}_{2}$-laser radiation is observed to follow a transient phase of stimulated Brillouin backscatter in critical density, laminar oxygen gas target irradiation experiments. Nearly complete energy absorption occurs for \ensuremath{\lesssim} 10 nsec following stimulated Brillouin backscatter after which target burnthrough and refraction dominate. Inverse bremsstrahlung and resonance absorption cannot account for the general features observed. Anomalous collisions due to strong ion turbulence produced by the incident laser radiation are postulated to account for the efficient absorption.
Physical Review A, 1978
Two-plasmon decay has been observed in a C${\mathrm{O}}_{2}$-laser-gas-target-plasma interaction ... more Two-plasmon decay has been observed in a C${\mathrm{O}}_{2}$-laser-gas-target-plasma interaction experiment. The spectrum of frac32\frac{3}{2}frac32-harmonic radiation has been measured and the threshold intensity for decay determined. An experimental value of \ensuremath{\sim} 2 \ifmmode\times\else\texttimes\fi{} 1011{10}^{11}1011 W/${\mathrm{cm}}^{2}$ is in reasonable agreement with theoretical predictions for an inhomogeneous plasma.
Physics of Fluids, 1983
Threshold conditions are analyzed for stimulated Raman backscattering (SRS) from an underdense pl... more Threshold conditions are analyzed for stimulated Raman backscattering (SRS) from an underdense plasma in the presence of ion‐acoustic fluctuations. For typical ion‐acoustic spectra which could result from a Brillouin instability occurring simultaneously with SRS, a reduced collisional threshold due to induced bremsstrahlung is found for the Raman instability. Similarly, for inhomogeneous plasma the phase mismatch created by a density gradient can be compensated for by an inhomogeneity in the ion‐acoustic spectrum; as a consequence, the inhomogeneity threshold for absolute instability can be substantially reduced. Comparisons are made with experimental observations of stimulated Raman scattering in the presence of strong stimulated Brillouin scattering for CO2 laser‐plasma interaction. It is found theoretically that for fluctuation levels typical of that accompanying SBS, induced bremsstrahlung growth rates for Langmuir waves can be of the order of collisional damping rates.
Physics Letters A, 1975
Preliminary observations of stimulated baekscatter from CO2 laser produced plasma are reported. T... more Preliminary observations of stimulated baekscatter from CO2 laser produced plasma are reported. The scattered radiation has been spectrally resolved and the measured shift found to be consistent with that expected from ion acoustic waves. The change in wavelength shift when helium is substituted for hydrogen is in agreement with x/'m-i, where m i = ion mass.
Journal of Fusion Energy, 1998
A model of energy gain induced by fast ignition of thermonuclear burn in compressed deuteriumtrit... more A model of energy gain induced by fast ignition of thermonuclear burn in compressed deuteriumtritium fuel, is used to show the potential for 300X gain with a driver energy of 1 MJ, if the National Ignition Facility (NIF) were to be adapted for fast ignition. The physics of fast ignition has been studied using a petawatt laser facility at the Lawrence Livermore National Laboratory. Laser plasma interaction in a preformed plasma on a solid target leads to relativistic self-focusing evidenced by x-ray images. Absorption of the laser radiation transfers energy to an intense source of relativistic electrons. Good conversion efficiency into a wide angular distribution is reported. Heating by the electrons in solid density CD2 produces 0.5 to 1 keV temperature, inferred from the D-D thermonuclear neutron yield.
Review of Scientific Instruments, 1984
This investigation is concerned with the development of a low‐inductance, low‐jitter, electricall... more This investigation is concerned with the development of a low‐inductance, low‐jitter, electrically triggered, high‐voltage annular rail spark gap. Three trigger electrode geometries—blade, dull, and sawtooth edge—are tested for the effects of different field stresses on the spark gap switching performance. All possible polarity combinations are applied to the high‐voltage and trigger electrodes of the rail gap, and the switching inductance and jitter is measured for each case. Finally, the effects of photopreionization from bare sparks on the spark gap switching performance is explored. A switch inductance of 4 nH and jitter of 0.6 ns have been achieved. A practical application of the rail gap is also described.
Applications of Laser Plasma Radiation, 1994
We report results of Thomson scattering measurements of optically ionized gases produced using 12... more We report results of Thomson scattering measurements of optically ionized gases produced using 12 psec pulses from a KrF-pumped Raman laser at intensities of 3 X 1017 W cm-2. Electron densities and temperatures are determined from the scattered Thomson spectra in both He and Ne (static and gas jet targets) at pressures of 10-3 - 1 bar. The central, low frequency region of the spectra from low pressure shots clearly shows an enhanced intensity above that given by the Salpeter approximation, and is indicative of a high electron-to-ion temperature ratios of at least 10 - 20. These observations are consistent with the long electron-ion collision time relative to the pulse length.
International Conference on Plasma Sciences (ICOPS), 1993
Summary form only given. The authors report on studies of optical ionization of gases produced by... more Summary form only given. The authors report on studies of optical ionization of gases produced by 12-ps pulses of focused Raman-shifted KrF laser radiation (γ=268 nm) at intensities of 3×1017 W/cm2. Measurements of Thomson, stimulated Raman, and stimulated Brillouin scattering have been used to determine the electron energy distribution and temperature in He and Ne (static and pulsed gas jet targets) at pressures of 10-3 to 1 bar and to investigate the role of parametric instabilities in the laser/plasma interaction. The electron velocity distribution evolves from a multiphoton (tunnel) ionization spectrum at low pressure to a thermal electron distribution at moderate pressure. The ion determined portion of the Thomson-scattered spectrum is highly nonthermal for pressures greater than a few mbar. At high pressure, significant Raman and Brillouin backscattering is observed. Inverse bremsstrahlung absorption is shown to dominate heating from p>10-2 bar except at the highest pressures where stimulated Raman scattering may also be important
Physical Review Letters, 1993
Thomson scattering measurements have been used to determine the electron energy distribution in U... more Thomson scattering measurements have been used to determine the electron energy distribution in UV optically ionized He and Ne at pressures up to j bar irradiated at 3x 10 17 W/cm 2 in 12 ps. The electrons evolve from a multiphoton ionization spectrum to a thermal distribution with increasing pressure. The low frequency part of the scattered spectrum clearly shows the "zero-damped" ion acoustic mode for high values of ZT e /Tt. Experimental and modeling results indicate that nonlinear inverse bremsstrahlung heating and radial conduction cooling dominate the electron energy balance.
Review of Scientific Instruments, 1975
A CO2 laser energy detector is described which uses the pressure rise generated in a vaccum cell ... more A CO2 laser energy detector is described which uses the pressure rise generated in a vaccum cell by gaseous infrared absorption to provide linear energy detection over many decades, good responsivity, wide aperture, and in-line beam monitoring. Nonadiabatic pressure measurements resulting when the beam size is less than the cell aperture are discussed.
Review of Scientific Instruments, 1997
We report on the first plasma experiments with the 100 TW laser at LLNL. We have experimentally i... more We report on the first plasma experiments with the 100 TW laser at LLNL. We have experimentally investigated the interaction of 1 μm, 40 J, 400 fs, 5×1019 W/cm2 laser pulses with multilayer solid targets. Various diagnostics were used to characterize this interaction. An x-ray pinhole camera monitored laser spot size and plasma location on target. Part of the laser
Review of Scientific Instruments, 1997
ABSTRACT We report on experiments using the 100 TW laser at LLNL (40J, 400 fs, 5×1019 W/cm2 focal... more ABSTRACT We report on experiments using the 100 TW laser at LLNL (40J, 400 fs, 5×1019 W/cm2 focal intensity) and planar multilayer targets (Mo/Sn) to study the generation and transport of electrons with MeV energies. Such fast electrons are of prime importance to many proposed applications, e.g., the fast ignitor fusion concept. X-ray emission spectroscopy is used to study the electron transport. Characteristic K α photon emission produced by the fast electrons in the front (Mo) and rear (Sn) layers of the target is measured with a charge-coupled device detector (single photon counting mode) to infer the electron energy deposition. The electron energy spectrum is measured by varying the thickness of the Mo layer to attenuate the electrons by different amounts. Penumbral imaging of the K α emission is used to give information about the angular distribution of the fast electron emission. Details of the measurement techniques and experimental results will be discussed and compared with modeling calculations.