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Progress in Plasma Processing of Materials, 1999

ISBN Print: 1-56700-126-2



The simplest device for the EM acceleration is railgun - a system of two parallel electrodes with an electrically conductive strap sliding along them. When current flows through the system, the strap speeds-up under ponderomotive force action. At velocity ≥1 km/s a solid sliding contact works badly due to occurence of phase transition, so that the contact transfers into an arc mode. Then it becomes advantageous to launch dielectric bodies by virtue of pressure of a plasma armature (PA) formed usually of the matter eroded from the channel walls. At typical current ~600 kA and the channel cross-section of 1 cm × 1 cm the PA plasma is characterized by a pressure of ~5000 atm, temperature is ~20-40 kK, particle concentration is 1021 cm−3, while its magnetic field is ~40 T, so that electrons are magnetized (ωτ~1).
Regrettably, upon reaching ~6 km/s velocity, an efficiency of the body speeding-up drops and the further velocity growth ceases due to the PA degradation. The last manifests itself in the current density redistribution to the PA trailing part, that leads to the PA spreading along the barrel and its detaching from the body under acceleration. The current redistribution is due to the smaller value of inductive counter-emf in the slower moving trailing part of PA. By means of cooling and deionizing the PA trailing part we succeeded in compacting the PA and thus in overcoming this "6 km/s limit". As a result, in a channel of mere 56 cm long, lexan cube of 1 g mass was launched in a mode of a constant acceleration up to 7.1 km/s at total efficiency (kinetic energy of body/energy stored in a battery) as great as 10 %. Besides, with using the PA and imposing onto the railgun an augmented magnetic field fed from independent source, we pioneered in non-sabot launching a body as small as ~1 mm up to 5-6 km/s, which is more than three-fold in excess of existing achivements. By doing so, we've simultaneously demonstrated unambigous prospects for using the augmented magnetic field in railguns, what was frequently doubted hitherto.
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