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The multi-rail concept of railguns, the so-called multi-turn railguns, has been considered and dependences of their main parameters such as accelerating force, current density distribution in rails and breech voltage upon bore sizes, number of turns and the launcher's scale are presented. The experimental designs of multi-turn railguns built in the TRINITI in 1995-1999 are described: a three-turn RBM-3-1 and MTR-3-1.3 railgun with a 5.6 [micro]H/m inductance gradient and two five-turn RBM-5-05 and RBM-5-2 railguns with 0.5 m and 2 m bore length, correspondingly and a 16.5 [micro]H/m inductance gradient both. The experimental design of the armature for these railguns is described as well. The results of tests of launching armatures with a 0.14-1.1 kg mass up to velocities of 800-1300 m/s and accelerations up to 8 [multiplied by] [10.sup.5] m/[s.sup.2] are given. Representative oscillograms of current and muzzle voltage of each rail pair are shown. Some methods of providing electrical strength for rail insulation in the bore and armature plates at metal contact fault are considered. Strengths and weaknesses of multi-turn launchers in comparison with conventional ones are discussed and an advantage of the former railguns at launching bodies with large volume and mass is shown. Index Terms--Armature, inductance gradient, multi-rail launcher, multi-turn railgun.

The concept of using multi-turn railguns as high-speed limiters of short-circuit current has been considered. The principle of similar devices is based on quickly bringing a large ballast impedance in the power supply circuit at a synchronic movement of several electric arcs along the insulated channels of the multi-turn launcher with its electrodes made of material with high specific resistance. Due to good magnetic coupling between the contours of the moving electric arc one can maintain a high velocity of the motion along the electrodes even at relatively weak currents. Limitation of the outside circuit current is basically achieved at the cost of electric energy dissipation in the rails. The advantages of the proposed device in comparison with existing analogs are as follows: * high-speed limitation of short-circuit current with its subsequent reduction to a level which is lower by several fold than nominal (at time less than 0.01 s) with low overvoltages in the interrupted circuit; * low cost-price of manufacturing and its high reliability; * high energy absorption (several MJ). The experimental data on the tests of the pilot model of the current limiter with five turns, 80 mm inter-electrode distance and 1.3 m rail length is given. The setup resistance gradient is 1.20hm/m and inductance gradient is 15 [micro]H/m. This model device efficiently limited and interrupted the direct current at voltage of 3 kV. The paper also considers a design of a current limiter for 200 MVA power systems. Index Terms--Arc launcher, ballast resistance, current limiter, multi-turn railgun, short-circuit.

Presents a developed experimental technique for the study of the current distribution in the rails and a moving metal armature. Experiments with a stationary armature; Discussion of the experimental set-up and measurements at the sliding contact; Restoration of current density in the contact area; Results of the experiment; Conclusions.