The plasma channel for the transmission of energy at a distance, which was once said the famous engineer Nikola Tesla, is not fiction. Scientists from the Institute of Physics. PN Lebedev Physical Institute learned to create a plasma microwave waveguides directly along the corridor of their work. A new way to transport the microwave signal in the sliding mode, developed by LPI, will reach a record distance — at least 1 km.
Krypton-Fluoride laser amplifier and optics to form a ring beam of ultraviolet used to create a plasma microwave waveguide.
Creating extended plasma structures became possible after the discovery at the end of the last century filamentary plasma traces of powerful ultrashort laser pulses. These plasma filaments or filaments are formed by the self-focusing of high-intensity radiation and ionization of the gas medium (eg, air), and the process of their formation is called filamentation. Using this laser beam to effect the annular section (it is obtained by means of special conical lenses — axicons or AO) of the filaments can create hollow cylindrical waveguide plasma. If the diameter of the waveguide is comparable to the wavelength of the transmitted microwave radiation, it is similar to conventional metal waveguide spatial modes, wherein the propagation of signals provided by a high conductivity walls. However, the conductivity of the plasma is much less than the metal and microwave waves decay in a plasma waveguide is only a few meters. Addressing range can be found on the basis of employee ideas LPI Gourgen Askar’yan, back in the 60s of the last century has offered to create an ultraviolet laser waveguide in which microwave radiation is reflected from the walls of the plasma at grazing angles of incidence. However, UV lasers powerful enough to implement the idea at that time did not exist.
"The effect of total internal reflection works, for example, in optical fibers, when the laser pulse passes lossless many tens or even hundreds of kilometers by the fact that the refractive index of the outer portion of the fiber slightly smaller than at its center. In the plasma waveguide refractive index no ionized air at the center is slightly larger than in the surrounding plasma. And there is also a limit angle at which the microwave radiation reflected from the walls, without departing from the waveguide, although some loss due to absorption of the plasma there are still"- The head of the leading researcher LPI Candidate of Physics and Mathematics Vladimir Zworykin.
"For waveguide experiments, — Continues Vladimir Zworykin — We used our UV-krypton laser Fluoride Harpoon. This powerful laser system with radiation energy of about 100 Joules and a pulse duration of 100 ns at a wavelength of 248 nm. This radiation ionizes the air is good, because it has higher energy photons — about 5 eV. As a result, the first time we were able to demonstrate the capture and distribution of microwave radiation with a wavelength of 8.5 mm in the moving plasma wave at a distance of several tens of meters. "
However, a few tens of meters — is not the limit. It found a senior fellow LPI, the candidate of physical and mathematical sciences Igor Smets, The detailed theoretical analysis, to a sliding plasma waveguide to transmit microwave radiation at 2.1 kilometers, it is necessary to perform two conditions — first, to maintain a certain concentration of electrons — at least 1012-1013 cm-3, and second , the diameter of the waveguide to withstand at least ten times larger than the wavelength of the transmitted microwave radiation.
In order to reduce energy costs in much the waveguide extended plasma in the air, it was suggested to use a train ("package") ultrashort pulse laser UV.
"In order to obtain a greater concentration of electrons, — Says another member of, an associate researcher LPI Alexey Levchenko, — necessary to increase the laser radiation intensity. We went by reducing the duration of the laser pulse. In order to maintain long-lived plasma waveguide, given the limited lifetime of a free electron in the air, the cycle time in the train must be less than 10 ns. "
To set such tasks Krypton Fluoride-lasers are ideal — a short recovery time gain in the active medium allows them to receive trains of pulses with a repetition period of about 2 ns. Besides, except for "developments" new photoelectrons by a train of pulses can be accumulated electrons taking them from electronegative oxygen molecules.
The use of microwave plasma waveguides and horns can significantly improve the accuracy and range of the radar devices. Among other practical applications can be mentioned active lightning protection system based on the management capabilities of lightning discharges by creating an atmosphere of extended conductive plasma channels.
The work was supported by the Company "New Energy Technologies"