Stable transport in proton driven fast ignition

Proton beam transport in the context of proton driven fast ignition is usually assumed to be stable due to proton high inertia, but an analytical analysis of the process is still lacking. The stability of a charge and current neutralized proton beam passing through a plasma is therefore conducted here, for typical proton driven fast ignition parameters. In the cold regime, two fast growing modes are found, with an inverse growth rate much smaller than the beam time of flight to the target core. The stability issue is thus not so obvious, and kinetic effects are investigated. One unstable mode is found stabilized by the background plasma proton and electron temperatures. The second mode is also damped, providing the proton beam thermal spread is larger than similar to 10 keV. In fusion conditions, the beam propagation should therefore be stable. (C) 2009 American Institute of Physics. [doi:10.1063/1.3213098]