Heavy ion beam target coronal physics

Numerical calculations of the heavy ion beam interaction with the low density plasma (corona) surrounding a small fusion pellet are discussed. As heavy ions enter the coronal plasma, they lose some of their electrons, and these stripped electrons, called 'drop-offs', constitute an electron beam with approximately the velocity of the ions. The interaction among the heavy ions, the drop-off electrons and the background electrons is investigated. The coronal density and temperature profiles are determined from one-dimensional hydrodynamic calculations, assuming classical ion deposition. The electron-electron and ion-electron cold two-stream instabilities are examined with one-dimensional particle-in-cell calculations. The results suggest that a strong coupling among the heavy ions, the drop-off electrons and the background electrons can exist; this leads to the creation of a non-Maxwellian electron plasma and significant electron heating. The ion beam energy loss is sensitive to the emittance of the beam, to the saturation level of the electric fields generated and to the background density scale length; these effects are discussed. Estimates of ion energy coupling to the corona are made, including the possible impact of target charge buildup; also, the coronal coupling effect on target physics is addressed.