Manipulating Electromagnetic Waves in Magnetized Plasmas: Compression, Frequency Shifting, and Release

A new approach to manipulating the duration and frequency of microwave pulses using magnetized plasmas is demonstrated. The plasma accomplishes two functions: (i) slowing down and spatially compressing the incident wave, and (ii) modifying the propagation properties (group velocity and frequency) of the wave in the plasma during a uniform in space adiabatic in time variation of the magnitude and/or direction of the magnetic field. The increase in the group velocity results in the shortening of the temporal pulse duration. Depending on the plasma parameters, the frequency of the outgoing compressed pulse can either change or remain unchanged. Such dynamic manipulation of radiation in plasma opens new avenues for manipulating high power microwave pulses.

Figure 1

Schematic of pulse compression in magnetized plasma. Radiation pulse with initial frequency ${\omega }_0$ and duration $T$ slows down in the plasma to a group velocity $v_{g0}\ll c$. USAT variation of the magnetic field changes the radiation frequency to ${\omega }_1$ and increases the group velocity to $v_{g1}\gg v_{g0}$ of the radiation in the plasma. The emerging pulse is compressed to $T_1=T{v}_{g0}/v_{g1}$. One-dimensional (a) and waveguide (b) implementations.

Figure 2

The dispersion relation of a plane wave propagating at an angle $\theta$ to a static magnetic field. (a),(b) four propagation branches for ${\Omega }_0=1.5{\omega }_p$, with $\theta =0$ in (a) and $\theta =0.1$ in (b). (c),(d) dispersion curves for the second branch for different values of ${\Omega }_0$ and $\theta$, where in (c) $\theta =0.1$ and ${\Omega }_0$ is variable, and in (d) ${\Omega }_0=1.5{\omega }_p$ and $\theta$ is variable.

Figure 3

Evolution of the longitudinal ${\mathit{E}}_{\parallel }=\mathit{n}·\mathit{E}$ and transverse ${\mathit{E}}_{\perp }=\mathit{n}\times \mathit{E}$ electric fields upon changing the magnetic field angle $\theta (t)={\theta }_0+\Delta \theta f(t)$ [(a) and (b)] and amplitude ${\Omega }_0(t)={\Omega }_0(0)+\Delta {\Omega }_{0}f(t)$ [(c) and (d)], where $f(t)=(1+\tanh [\pi (t-t_0)/\tau ])/2$ with $t_0/T_0=480$, $\tau /T_0=160$, and $T_0=2\pi /{\omega }_0$. Initial radiation frequency ${\omega }_0={\omega }_p$ [(a) and (c)] and ${\omega }_0=1.1{\omega }_p$ [(b) and (d)]. Dashed lines: radiation frequency variation $\omega (t)$. Magnetic field parameters: ${\theta }_0=0.1$, $\Delta \theta =1.4$, ${\Omega }_0(0)=1.5{\omega }_p$, and $\Delta {\Omega }_0=13.5{\omega }_p$.

Figure 4

(a) Dispersion curves (for various values of ${\Omega }_0$) and (b) electric field profiles (for $\omega ={\omega }_p$ and ${\Omega }_0=1.5{\omega }_p$) of the slow mode of a plasma-filled waveguide of width $L=5\pi c/{\omega }_p$.

Figure 5

Time evolution of the slow mode of the MPMW ($L=5\pi c/{\omega }_p$) during the variation of the magnetic field: $1.5<{\Omega }_0/{\omega }_p<15$. Left column [(a),(c), and (e)]: ${\omega }_0={\omega }_p$, right column [(b),(d) and (f)]: ${\omega }_0=1.1{\omega }_p$. Group velocities calculated numerically from the Poynting flux.