Shape evolution of imploding shocks and shells and its effects on burn wave propagations in magnetized implosions for high yield

Spherically symmetric shocks imploding in the imposed B field always evolve into an ellipsoidal shape. After bouncing from the center, the outgoing shock front induces an uneven radial velocity field, which is further enhanced by the oblate shape of the imploding shell in late time. This radial velocity field delays the impediment of burn wave propagation by the compressed B field, and this effect is the determining factor in the feasibility of achieving high yields in magnetized implosions. The uneven radial velocity field is further enhanced in late time as the spherical imploding shell evolves into an oblate shape because of the magnetic pressure inside the shell. This uneven velocity field expands the plasma in the central region along the perpendicular direction and limits the strength of the compressed B field. Thus, the B field in the central region is weak enough to allow burn wave propagation while strong enough to enhance the energy deposition of the alpha particles into the hotspot. The imploding shock and the shell are spherical in the hypothetical magnetized situation where the jB force is absent. The compressed B field in the central hotspot region can then be strong enough to impede the propagation of burn waves, and the thermonuclear yield is substantially reduced. Simulations of the magnetized N210808 with the jB force show that the B field amplifies the yield if the imposed field is 60T, while without this force, the B field does not enhance the yield effectively because a strong central B field impedes the burn wave propagation.