Abstract
The investigation of the hot electron fraction is a crucial topic for high energy density laser driven plasmas: first, energy losses and radiative properties depend strongly on the hot electron fraction and, second, in ICF hohlraums suprathermal electrons preheat the D-T-capsule and seriously reduce the fusion performance. In the present work we present our first experimental and theoretical studies to analyze single shot space resolved hot electron fractions inside dense plasmas via optically thin X-ray line transitions from autoionizing states. The benchmark experiment has been carried out at an X-pinch in order to create a dense, localized plasma with a well defined symmetry axis of hot electron propagation. Simultaneous high spatial and spectral resolution in the X-ray spectral range has been obtained with a spherically bent quartz Bragg crystal. The high performance of the X-ray diagnostics allowed to identify space resolved hot electron fractions via the X-ray spectral distribution of multiple excited states.
Highlights
INTRODUCTIONNon-equilibrium electron statistics (or non-Maxwellian energy distribution functions) are at the center of worldwide research because they play an exceptional role for fusion research [1,2,3,4,5]: a) in the indirect drive scheme (hohlraum) of inertial fusion, hot electron production may lead to a preheat of the DT capsule and hinder subsequent compression above solid density to obtain ignition, b) in the direct drive scheme (fast ignition), hot electrons are created purposely by a PetaWatt laser via “hole boring” to initiate burn in the DT capsule, c) in atomic physics, suprathermal electrons lead to strong changes of almost all radiative properties like, e.g., ion charge state distributions, radiative losses, line intensities and line ratios
In the present work we present our first experimental and theoretical studies to analyze single shot space resolved hot electron fractions inside dense plasmas via optically thin X-ray line transitions from autoionizing states
Non-equilibrium electron statistics are at the center of worldwide research because they play an exceptional role for fusion research [1,2,3,4,5]: a) in the indirect drive scheme of inertial fusion, hot electron production may lead to a preheat of the DT capsule and hinder subsequent compression above solid density to obtain ignition, b) in the direct drive scheme, hot electrons are created purposely by a PetaWatt laser via “hole boring” to initiate burn in the DT capsule, c) in atomic physics, suprathermal electrons lead to strong changes of almost all radiative properties like, e.g., ion charge state distributions, radiative losses, line intensities and line ratios
Summary
Non-equilibrium electron statistics (or non-Maxwellian energy distribution functions) are at the center of worldwide research because they play an exceptional role for fusion research [1,2,3,4,5]: a) in the indirect drive scheme (hohlraum) of inertial fusion, hot electron production may lead to a preheat of the DT capsule and hinder subsequent compression above solid density to obtain ignition, b) in the direct drive scheme (fast ignition), hot electrons are created purposely by a PetaWatt laser via “hole boring” to initiate burn in the DT capsule, c) in atomic physics, suprathermal electrons lead to strong changes of almost all radiative properties like, e.g., ion charge state distributions, radiative losses, line intensities and line ratios. As high-resolution X-ray spectroscopy can provide a unique characterization of hot electrons [5], benchmark experiments are requested to validate non-Maxwellian atomic physics codes. An essential point of well characterized experiments is to have a well defined symmetry axis of hot electron propagation in dense plasmas. This is difficult to achieve in laser produced plasmas but can be quite well realized in X-pinch experiments.
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