Langmuir oblique solitons in ''free motion'' regime

For the first time in magnetized collisionless plasma on the wave branch with the Traivelpiece-Gold linear dispersion detected experimentally the Langmuir slow ( almost motionless relative to plasma) oblique solitons with HF filling. They result from modulation instability (self-compression) of nonlinear waves. Their evolution is investigated in the ''free path'' mode, i.e. after the cutting-off of electron ''pumping beam''. The experiments were carried out with the following parameters: plasma density n=(3-4)x109 cm-3; 2x103 Oe longitudinal magnetic field; 10-20 eV electron temperature; residual gas (hydrogen) pressure p0 < or approximately 5x10-6 Hg; approximately 200 cm plasma filament length; (2-6)x106 cmxs-1 plasma motion velocity. Typical beam parameters are: 2-2.5 keV electron energy; 2-2.5 A current intensity; 0.1-0.2 n beam density; approximately 20 μs beam pulse duration. Plasma motion velocity was determined from time shift of saturation ion currents to cellular probes (with approximately 95% transparency) located in different places of plasma filament. Wave distribution velocity was measured by the same probes. A quarter-wave resonator was used to measure plasma density wells and plasmoids (as well as time dependence of density itself). Solitons detected differ from a known fast soliton existing in the same wave mode: the fast soliton moves quicker by several orders, represents potential hump without HF filling and arises not as a result of modulation instability but due to the Korteveg-de Vries mechanism - the same way as a shallow water soliton or ion sound soliton