  Recent studies have shown direct ion heating (vashistha2020new,Juneja_2023)
by lasers EM (Electromagnetic) wave interacting with a plasma threaded by an
external uniform magnetic field. The EM wave frequency was near the lower
hybrid (LH) resonance frequency. The LH resonance occurs at the edge of the
pass band of the magnetized dispersion relation. The group speed of the wave is
negligible at resonance. In these studies, the energy absorption remains
essentially confined at the plasma surface. However, to heat the ions in the
bulk plasma and at a desired location, a tailored inhomogeneous external
magnetic field profile has been chosen here. The strength of the magnetic field
at the plasma edge is such that the EM wave frequency lies inside the pass
band, where the group velocity has a significant value. It enables the wave to
enter the bulk plasma. The external magnetic field is then spatially tailored
appropriately to have the LH resonance at a desired spatial location inside the
plasma. The Particle-In-Cell (PIC) simulations using the OSIRIS4.0 platform
have been carried out, which demonstrates that the EM wave pulse comes to a
standstill at the location of the resonance. The wave pulse is observed to
break down subsequently, and the energy consequently goes dominantly to the
local plasma ions. The absorption is significantly enhanced compared to the
case in which the magnetic field profile was homogeneous. The dependence of
absorption on the choice of magnetic field profile, the laser intensity, etc.,
has also been carried out.
