Nauka i Tehnika (Dec 2014)
CONDUCTIVE CHANNEL FOR ENERGY TRANSMISSION
Abstract
Laser spark obtained by using a conical optics is much more appropriate to form conducting channels in atmosphere. Only two types of lasers are actively considered to be used in forming high-conductivity channels in atmosphere, controlled by laser spark: pulsed sub-microsecond gas and chemical lasers (CO2, DF) and short pulse solid-state and UV lasers. Main advantage of short pulse lasers is their ability in forming of super long ionized channels with a characteristic diameter of ~100 µ in atmosphere along the beam propagation direction. At estimated electron densities below 10 ⋅ 16 cm–3 in these filaments and laser wavelengths in the range of 0,5–1,0 mm, the plasma barely absorbs laser radiation. In this case, the length of the track composed of many filaments is determined by the laser intensity and may reach many kilometers at a femtosecond pulse energy of ~100 mJ. However, these lasers could not be used to form high-conductivity long channels in atmosphere. The ohmic resistance of this type a conducting channels turned out to be very high, and the gas in the channels could not be strongly heated (< 1 J). An electric breakdown controlled by radiation of femtosecond solid-state laser was implemented in only at a length of 3 m with a voltage of 2 MV across the discharge gap (670 kV/m).Not so long ago scientific group from P. N. Lebedev has improved that result, the discharge gap – 1 m had been broken under KrF laser irradiation when switching high-voltage (up to 390 kV/m) electric discharge by 100-ns UV pulses. Our previous result – 16 m long conducting channel controlled by a laser spark at the voltage – 3 MV – was obtained more than 20 years ago in Russia and Japan by using pulsed CO2 laser with energy – 0,5 kJ. An average electric field strength was < 190 kV/m. It is still too much for efficient applications.
