Localized absorption of laser energy in X-mode configuration of magnetized plasma

Abstract

The heating of ions via lower hybrid (LH) waves has been observed in several astrophysical as well as laboratory plasmas. We have conducted particle-in-cell simulations to demonstrate absorption of the incident laser pulse at a chosen localized point in the plasma target by manipulating its density profile. We show that a part of the incident laser propagates inside the plasma target when its frequency lies below the LH resonance frequency. Thereafter, as it experiences a negative density gradient, it approaches the resonance point where its group velocity approaches zero. This is where the electromagnetic (EM) energy prominently gets converted into the electrostatic and eventually the kinetic energy of ions. Thus, by tailoring the plasma density profile one can have the absorption of incident EM wave energy at a designated location inside the plasma. This may be important in various applications where energy deposition/heating of plasma in a localized region is desirable.