Resistive field generation in intense proton beam interaction with solid targets

The Brown-Preston-Singleton(BPS)stopping power model is added to our previously developed hybrid code to model ion beam-plasma interaction.Hybrid simulations show that both resistive field and ion scattering effects are important for proton beam transport in a solid target,in which they compete with each other.When the target is not completely ionized,the self-generated resistive field effect dominates over the ion scattering effect.However,when the target is completely ionized,this situation is reversed.Moreover,it is found that Ohmic heating is important for higher current densities and materials with high resistivity.The energy fraction deposited as Ohmic heating can be as high as 20%-30%.Typical ion divergences with half-angles of about 5°-10°will modify the proton energy deposition substantially and should be taken into account.

Hybrid PIC–fluid simulations for fast electron transport in a silicon target

Ultra-intense laser-driven fast electron beam propagation in a silicon target is studied by three-dimensional hybrid particle-in-cell–fluid simulations.It is found that the transverse spatial profile of the fast electron beam has a significant influence on the propagation of the fast electrons.In the case of a steep spatial profile(e.g.,a super-Gaussian profile),a tight fast electron beam is produced,and this excites more intense resistive magnetic fields,which pinch the electron beam strongly,leading to strong filamentation of the beam.By contrast,as the gradient of the spatial profile becomes more gentle(e.g.,in the case of a Lorentzian profile),the resistive magnetic field and filamentation become weaker.This indicates that fast electron propagation in a solid target can be controlled by modulating the spatial gradient of the laser pulse edge.

Transport of ultraintense laser-driven relativistic electrons in dielectric targets

Ultraintense laser-driven relativistic electrons provide a way of heating matter to high energy density states related to many applications. However, the transport of relativistic electrons in solid targets has not been understood well yet,especially in dielectric targets. We present the first detailed two-dimensional particle-in-cell simulations of relativistic electron transport in a silicon target by including the field ionization and collisional ionization processes. An ionization wave is found propagating in the insulator, with a velocity dependent on laser intensity and slower than the relativistic electron velocity. Widely spread electric fields in front of the sheath fields are observed due to the collective effect of free electrons and ions. The electric fields are much weaker than the threshold electric field of field ionization. Two-stream instability behind the ionization front arises for the cases with laser intensity greater than 5 × 1019W/cm^2 that produce high relativistic electron current densities.