Investigation of the High-Energy Acceleration Mode in the Coaxial Gun

Abstract

The amount of deuterium gas admitted to a short center electrode (1 cm) coaxial plasma gun delineates two regions of operation, depending on whether the gas is localized near the inlet port or allowed to diffuse throughout the gun length. In the former, fast deuterium ions with energy in excess of the applied voltage (V₀ = 15 kV) emerge from the gun muzzle whereas in the latter, the accelerated plasma which initially starts at the breech end reaches an axial velocity of ∼2.5 × 10⁷ cm/sec at the muzzle end and forms a high‐density plasma focus on the axis in front of the central electrode. Neutron measurements show that this dense plasma is not in contact with the electrode and is most probably stagnated by the high ambient gas pressure downstream. Particle momentum analysis of the fast ion (> V₀) distribution and neutron measurements downstream of the gun suggest two accelerated groups of fast ions, (1) a group of ∼10¹⁶ particles which diverge from the gun muzzle and (2) a group of ∼10¹⁴ particles which stream primarily along the axis with a radial distribution of ∼3 cm width. Multiple probes (B_θ) show an asymmetric angular distribution of the discharge current that varies as a function of time during a given discharge. A sharp break in the total gas current is accompanied by large inductive voltages. In the high‐energy mode, inductive voltages up to 7V₀ have been recorded at the breech end.