8 research outputs found
Approaching Petavolts per meter plasmonics using structured semiconductors
A new class of strongly excited plasmonic modes that open access to
unprecedented Petavolts per meter electromagnetic fields promise wide-ranging,
transformative impact. These modes are constituted by large amplitude
oscillations of the ultradense, delocalized free electron Fermi gas which is
inherent in conductive media. Here structured semiconductors with appropriate
concentration of n-type dopant are introduced to tune the properties of the
Fermi gas for matched excitation of an electrostatic, surface "crunch-in"
plasmon using readily available electron beams of ten micron overall dimensions
and hundreds of picoCoulomb charge launched inside a tube. Strong excitation
made possible by matching results in relativistic oscillations of the Fermi
electron gas and uncovers unique phenomena. Relativistically induced ballistic
electron transport comes about due to relativistic multifold increase in the
mean free path. Acquired ballistic transport also leads to unconventional heat
deposition beyond the Ohm's law. This explains the absence of observed damage
or solid-plasma formation in experiments on interaction of conductive samples
with electron bunches shorter than . Furthermore,
relativistic momentum leads to copious tunneling of electron gas allowing it to
traverse the surface and crunch inside the tube. Relativistic effects along
with large, localized variation of Fermi gas density underlying these modes
necessitate the kinetic approach coupled with particle-in-cell simulations.
Experimental verification of acceleration and focusing of electron beams
modeled here using tens of Gigavolts per meter fields excited in semiconductors
with free electron density will pave the way for Petavolts
per meter plasmonics.Comment: 16 pages, 10 figure
Enhanced electron density and plasma dynamics on nanosecond time scales in Helium plasma discharges
Enhanced electron density and plasma dynamics are investigated for Helium discharges on nanosecond timescales with Particle-In-Cell simulations. The plasma discharges are driven between planar electrodes with DC, single pulses, and dynamic frequency square waves. It is assumed that the DC and pulse discharges operate in the glow regime. It is shown that as pressure increases with narrowing gap distance, the peak transient electron density rises. This is in contrast to what is observed under a constant pressure-gap (pd) and electric field reduced by neutral density (E/N) values at saturation time. It is shown that although the pd and E/N values and therefore the breakdown voltage are the same across cases, the plasma kinetics are different due to a change in the energy relaxation lengths. The cross-points between the sheath length and energy relaxation length move to higher electron energies at higher pressure. This facilitates high-energy electrons to undergo inelastic collisions and produces different rates of increasing electron density and temperature at nanosecond timescales. Moreover, using a plasma frequency-dependent square wave, the electron density can be increased to 50 times higher over that of the DC case because of a reverse electric field. The electron kinetics on nanosecond time scales can be exploited for high electron density and fast ionization applications
Finite difference modeling of coherent wave amplification in the Earth's radiation belts
Cyclotron Acceleration of Relativistic Electrons Through Landau Resonance With Obliquely Propagating WhistlerâMode Chorus Emissions
Efficient acceleration of relativistic electrons at Landau resonance with obliquely propagating whistlerâmode chorus emissions is confirmed by theory, simulation, and observation. The acceleration is due to the perpendicular component of the wave electric field. We first review theoretical analysis of nonlinear motion of resonant electrons interacting with obliquely propagating whistlerâmode chorus. We have derived formulae of inhomogeneity factors for Landau and cyclotron resonances to analyze nonlinear wave trapping of energetic electrons by an obliquely propagating chorus element. We performed test particle simulations to confirm that nonlinear wave trapping by both Landau and cyclotron resonances can take place for a wide range of energies. For an element of large amplitude chorus waves observed by the Van Allen Probes, we have performed detailed analyses of the wave form data based on theoretical framework of nonlinear trapping of resonant electrons. We compare the efficiencies of accelerations by cyclotron and Landau resonances. We find significant acceleration can take place both in Landau and cyclotron resonances. What controls the dynamics of relativistic electrons in the Landau resonance is the perpendicular field components rather than the parallel electric field of the oblique chorus wave. In evaluating the efficiency of nonlinear trapping, we have taken into account variation of the wave trapping potential structure controlled by the inhomogeneity factors
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Magnetospheric chorus wave simulation with the TRISTAN-MP PIC code
We present the results of particle-in-cell simulations of the whistler anisotropy instability that results in magnetospheric chorus wave excitation. The simulations were carried out using, for the first time for this problem, the 2D TRISTAN-massively parallelized code, widely used before in the modeling of astrophysical shocks. The code has been modified to allow for two populations of electrons: cold electrons (which maintain the wave propagation) and hot electrons (which provide the wave growth). For the hot electrons, the anisotropic form of the relativistic Maxwell-JĂŒttner distribution is implemented. We adopt the standard approximation of a parabolic magnetic field to simulate the Earth's magnetic field close to the equator. Simulations with different background magnetic field inhomogeneity strengths demonstrate that higher inhomogeneity yields lower frequency chirping rates and, eventually, it suppresses chorus generation. The results are in agreement with other numerical simulations and the theoretical predictions for the frequency chirping rates