The 23rd Academic Exchange Seminar Between Shanghai Jiao Tong University and Osaka University
Shinsuke Fujioka
(Institute of Laser Engineering, Osaka University)
ABSTRACT
Inertial confinement fusion (ICF) is created by imploding a spherical target to achieve high compression of the fuel and generate a high temperature hot-spark to trigger ignition and maximize the thermonuclear energy gain. The current central ignition scheme has not yet reached the ignition condition. Hot-spark mixing with the cold dense fuel hampers fusion ignition mainly due to the significant growth of Rayleigh-Taylor (RT) instabilities during the compression. An alternate approach is to accept that perturbations are unavoidable in ICF experiments and instead reduce hot-spark cooling through the application of an external magnetic field. Ablative RT instability growth was investigated to elucidate the fundamental physics of thermal conduction suppression in a magnetic field. Experiments found that unstable modulation growth is faster in an external magnetic field. This result was reproduced by a magnetohydrodynamic simulation based on a Babinskii model of electron thermal transport. An external magnetic field reduces the electron thermal conduction across the magnetic field lines because the Larmor radius of the thermal electrons in the field is much shorter than the temperature scale length. Thermal conduction suppression leads to spatially nonuniform pressure and reduced thermal ablative stabilization, which in turn increases the growth of ablative RT instability. We also obtain the condition that the magnetic field can affect the ablative RT instability. The stronger the magnetic field, the higher the modes of RT growth affected. In other words, by reducing the thermal transport at the instability growth front, the magnetization allows higher modes of RT instability to grow.