Simultaneous current ramping and application of lower hybrid heating and current drive (LHCD) have produced a region with zero current density within measurement errors in the core ( r/a< or =0.2) of JET tokamak optimized shear discharges. The reduction of core current density is consistent with a simple physical explanation and numerical simulations of radial current diffusion including the effects of LHCD. However, the core current density is clamped at zero, indicating the existence of a physical mechanism which prevents it from becoming negative.

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Analytical models of the penetration process focus on estimating depth of penetration based on target density, target strength (sometimes associated with the unconfined compressive strength of the target for geological targets), the areal density of the penetrator (W/A), and the impact velocity. In this paper, an expression for work is used in conjunction with thermodynamic considerations to devise a simple estimate for mass lost by a high velocity projectile during the penetration process. The result shows that the mass loss is directly proportional to the tunnel length and the target shear strength. The constant of proportionality is not easy to deduce, however, in that it contains an unusual factor from the work analysis. A method for estimating target shear under high pressure from penetration experiments is introduced.

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