  We present a theoretical model of electromagnetic pulse emission and nozzle
damage from high-power laser interactions with gas jets. As hot electrons are
accelerated beyond the laser channel, they produce a positively-charged plasma
that expands into the ambient gas until it reaches the gas jet nozzle. A strong
plasma potential leads to electrical breakdown that ionises the gas even faster
than the expanding plasma ions. When contact is made between the plasma and the
conducting nozzle surface, a discharge current propagates to ground and an
electromagnetic pulse is radiated via an antenna emission mechanism. Damage to
gas jet nozzles is caused by heating from plasma ions rather than Ohmic heating
via a discharge current. Our model agrees with experimental data from
experiments on proton acceleration in near-critical plasmas at the Vulcan and
VEGA-3 lasers.
