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FRENCH ARE ALSO DEVELOPING PLASMA STEALTH
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Towards greater discretion through the plasma
Research engineer at the Electromagnetism and Radar Department (DEMR), Gerard Bobillot is responsible for mission "stealth radar" with the director of this department. Working at ONERA for thirty years, radar operator is interested in the topic of stealth since the year 1982/83. Today, the work of DEMR in this area include, among others, on plasmas whose work was initiated during 2002. First applications in 2020.
By 2003, this line of plasmas applied to stealth became a reality with the launch of a Federator Research Project (FRP), which involves teams of the departments Physical Measurements (DMPH), Information processing and modeling (DTIM ) and those of DEMR working on so-called "plasma mirror". "The radar antennas are" soft ", real reflectors, which have the theoretical advantage of being oriented very quickly. Today, this activity continues in Toulouse and Palaiseau," explains Gerard Bobillot. The objective of this work is to achieve direct beams of electromagnetic waves through a plasma, not through reflection, but refraction, this by modifying its parameters.
Antenna protection
As part of the PRF, further research is to design plasma inside the micro-capillaries, stacked one upon another, would yield meta-materials or materials known as "photon band "whose propagation properties are extremely interesting. "Typically, these metamaterials are designed either with metal rods, or with glass rods. But there it is filled with plasma glass capillaries, which will allow switching by changing the properties of this structure, "said the engineer at Onera Palaiseau. In the future, these materials could be used to create protection systems switchable antenna. Thus, when the antenna does not work, the plasma is put in place to protect against electromagnetic attacks. There has been abroad several attempts to design antenna reflectors with tubes of this type, but larger diameter, that is to say, one centimeter against a few millimeters or less for microcapillary . "It performs research paper on this subject in close liaison with the Centre for Plasma Physics and Applications of Toulouse (CPAT) that has acquired significant technical on these tubes," he says.
Meanwhile, Onera researchers interested in the use of plasmas to increase the stealth of some systems such as radomes. Two studies are underway. Created in collaboration with CPAT, the study focuses on the ability to protect the nose of a fighter aircraft. "For this, we must develop the plasma inside the radome, which implies that the plasma fills the interior volume," said Gerard Bobillot. The objective is to achieve a device that can switch very brief. "On the plasmas used, we have the choice of gas and pressure. So do we want to play with these settings to try to come to switch a few microseconds."
Two air discharges very different
If Onera is interested in confined plasmas, its teams are also developing plasmas in air. "Certainly, the idea is not new. This is indeed making a stealth aircraft by surrounding it with a plasma ball. The only problem is that the energy required to achieve this is huge," Gerard summarizes Bobillot. That's why Onera teams have opted for a more reasonable goal in treating only certain points local "shiny" device, which involves producing a stable plasma. A literature survey and a series of tests conducted by Serge Larigaldie, Senior Fellow in the Optical Diagnostics and plasma unit (DOP) DMPH and plasma specialist at Palaiseau Center, have revealed two stable discharges in the air.
Purple, the first of these discharges is cold and wind resistant. It remains stable in the presence of air flowing at a speed of 80 m / s. In addition, it consumes only a few tens of watts. His only fault is to measure only 8 mm. "We varied the different parameters without managing to increase the length of the discharge. The only solution is to lower the pressure by a factor of ten which then allows to extend the discharge substantially. This means that it could be used at high altitude, "said the engineer. Why not imagine in the future ramps, designed with these plasmas, to equip certain moving parts of an airplane, just in places where there are slots? By giving them a continuum of plasma, it would be probably possible to hide them.
Preparation of experience on the bench discharge Cyprus
Produced over a length of 30 cm, in an experiment run in 2004 on the bench Cyprus, the second discharge, which consumes only a few hundred watts, is likely quite different from the first, even if the device for producing always consists of a point and a plane, the tip being anodic and cathodic terms as opposed to the device used for the first discharge. Researchers have begun to show interest, there are about ten years, as part of work focused on the cleanup. "The electron densities were one hundred times lower than those that allow us today to uptake," says Gerard Bobillot. Stable and beaming little light, this discharge plasma absorbs about 3 dB. Also Onera researchers will they try to produce more in order to achieve an absorption of about ten dB. However, this discharge has a major flaw, that of not being stable in the wind. "So we decided to let it develop, trying to regenerate constantly so you always have a sufficient volume of electrons". This work is conducted as part of a thesis launched in November 2004.
Discharge plasma flow in the vein of the bench Cyprus
First applications: between ten and fifteen years
At what horizon the first applications of these plasmas could they emerge? "It all depends on what we're talking about plasmas," replied Gerard Bobillot. "Regarding confined plasmas can protect antennas, this horizon is located about ten years. For plasmas in air, it will take longer, at least 15 years. Many problems are not solved. Currently we're only getting very small plasmas. So we have to work hard to hope for treating the air inlet of a fighter plane and have an operational solution, "said the engineer DEMR.
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