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Register a new userModeling Intense-Electron-Beam Generated Plasmas Using a Rigid-Beam Approximation
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A model of an electron-beam-plasma system is introduced to model the electrical breakdown physics of low-pressure nitrogen irradiated by an intense pulsed electron beam. The rapidly rising beam current induces an electric field which drives a return current in the plasma. The rigid-beam model is a reduction of the problem geometry to cylindrical coordinates and simplifications to Maxwells equations that are driven by a prescribed electron beam current density. The model is convenient for comparing various reductions of the plasma dynamics and plasma chemistry while maintaining a good approximation to the overall magnitude of the beam-created electric field. The usefulness of this model is demonstrated by coupling the rigid-beam model to a fluid plasma model and a simplified nitrogen plasma chemistry. The dynamics of this coupled system are computed for a range of background gas pressures, and the results are compared with experimental measurements. At pressures 1 Torr and above, the simulated line-integrated electron densities are within a factor of two of measurements, and show the same trend with pressure as observed in experiment.
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A method of slicing of high-energy electron beams following their interaction with the transverse component of the wakefield left in a plasma behind a high intensity ultra short laser pulse is proposed. The transverse component of the wakefield focuses a portion of the electron bunch, which experiences betatron oscillations. The length of the focused part of the electron bunch can be made substantially less than the wakefield wavelength.
A non-equilibrium model for laser-induced plasmas is used to describe how nano-second temporal mode-beating affects plasma kernel formation and growth in quiescent air. The chemically reactive Navier-Stokes equations describe the hydrodynamics, and non-equilibrium effects are modeled based on a two-temperature model. Inverse Bremsstrahlung and multiphoton ionization are self-consistently taken into account via a coupled solution of the equations governing plasma dynamics and beam propagation and attenuation (i.e., Radiative Transfer Equation). This strategy, despite the additional challenges it may bring, allows to minimize empiricism and enables for more accurate simulations since it does not require an artificial plasma seed to trigger breakdown. The benefits of this methodology are demonstrated by the good agreement between the predicted and the experimental plasma boundary evolution and absorbed energy. The same goes for the periodic plasma kernel structures which, as suggested by experiments and confirmed by the simulations discussed here, are linked to the modulating frequency.
Here, we demonstrate the radiative polarization of high-energy electron beams in collisions with ultrashort pulsed bi-chromatic laser fields. Employing a Boltzmann kinetic approach for the electron distribution allows us to simulate the beam polarization over a wide range of parameters and determine the optimum conditions for maximum radiative polarization. Those results are contrasted with a Monte-Carlo algorithm where photon emission and associated spin effects are treated fully quantum mechanically using spin-dependent photon emission rates. The latter method includes realistic focusing laser fields, which allows us to simulate a near-term experimentally feasible scenario of a 8 GeV electron beam scattering from a 1 PW laser pulse and provide a measurement that would verify the ultrafast radiative polarization in high-intensity laser pulses that we predict. Aspects of spin dependent radiation reaction are also discussed, with spin polarization leading to a measurable (5%) splitting of the energies of spin-up and spin-down electrons.
One of the main diagnostic tools for measuring electron density profiles and the characteristics of long wavelength turbulent wave structures in fusion plasmas is Beam Emission Spectroscopy (BES). The increasing number of BES systems necessitated an accurate and comprehensive simulation of BES diagnostics, which in turn motivated the development of the RENATE simulation code that is the topic of this paper. RENATE is a modular, fully three-dimensional code incorporating all key features of BES systems from the atomic physics to the observation, including an advanced modeling of the optics. Thus RENATE can be used both in the interpretation of measured signals and the development of new BES systems. The most important components of the code have been successfully benchmarked against other simulation codes. The primary results have been validated against experimental data from the KSTAR tokamak.
Interaction of an intense electron beam with a finite-length, inhomogeneous plasma is investigated numerically. The plasma density profile is maximal in the middle and decays towards the plasma edges. Two regimes of the two-stream instability are observed. In one regime, the frequency of the instability is the plasma frequency at the density maximum and plasma waves are excited in the middle of the plasma. In the other regime, the frequency of the instability matches the local plasma frequency near the edges of the plasma and the intense plasma oscillations occur near plasma boundaries. The latter regime appears sporadically and only for strong electron beam currents. This instability generates copious amount of suprathermal electrons. The energy transfer to suprathermal electrons is the saturation mechanism of the instability.
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