  Fast isochoric laser heating is a scheme to heat a matter with
relativistic-intensity ($>$ 10$^{18}$ W/cm$^2$) laser pulse or X-ray free
electron laser pulse. The fast isochoric laser heating has been studied for
creating efficiently ultra-high-energy-density (UHED) state. We demonstrate an
fast isochoric heating of an imploded dense plasma using a multi-picosecond
kJ-class petawatt laser with an assistance of externally applied kilo-tesla
magnetic fields for guiding fast electrons to the dense plasma.The UHED state
with 2.2 Peta-Pascal is achieved experimentally with 4.6 kJ of total laser
energy that is one order of magnitude lower than the energy used in the
conventional implosion scheme. A two-dimensional particle-in-cell simulation
reveals that diffusive heating from a laser-plasma interaction zone to the
dense plasma plays an essential role to the efficient creation of the UHED
state.

Plasma Physics