During the early investigation of the high‐energy, low‐pressure mode of a coaxial hydromagnetic gun, a second mode of action was established for large gas fillings. This particular mode, previously reported was found to lead to a high‐density plasma focus situated at a distance ∼1–1.5 cm beyond the face of the center electrode. The plasma focus has the following properties; particle density ρ ∼ 2–3 × 1019/cm3, temperature T ∼ 1–3 keV, time duration t ∼ 0.2–0.3 μsec, and volume ∼15 mm3. Neutron yields >1010/burst and soft x rays are observed. These results are remarkably similar to those reported by Petrov et al. and Filippov et al. of the USSR using a metal wall pinch tube apparatus. The average velocity vz of the current sheath in the gun proper is found to depend on the fourth root of the applied voltage squares, divided by the mass density according to the simple ``snowplow'' ``M'' theory. The current sheath is found to be nonplanar and mass pickup by the advancing sheath is nonlinear with radius. The sudden collapse of the radial current sheath toward the axis at the center electrode end is most likely caused by the rapid conversion of stored magnetic energy into radial sheath motion (v̄r ∼ 3.5 × 107 cm/sec) forming in essence a super dense pinch effect.

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