Duan Zejia, He Zhefeng, Xiong Zhuozi
With the development of science and technology, more and more conceptual principles have entered the ever-changing battlefield from academic theories. The world has set off an upsurge of research on innovative practices in the military field, and various countries are scrambling to engage in a fierce arms race, in which high-tech products such as ballistic missiles with 100 shots, strategic nuclear submarines that turn the tide of war, and laser gyroscopes for precise measurement and control have emerged one after another, covering all aspects from weapons to defense support. Plasma is part of this whole research trend.
First, the first understanding of plasma
Understanding the use of plasma in the military requires an understanding of its basic concepts. The plasma state, also known as the supergaseous state, is the fourth largest state of matter independent of the solid, liquid, and gaseous states. Under high temperature and strong electromagnetic field, the gas will become plasma, and in this state, the atoms in the gas will have more or fewer electrons than normal, thus forming anions and cations, so the plasma has a high electrical conductivity. Plasma sounds mysterious and untouchable, but it's all around us. The common lightning in life is a natural plasma, and artificially created plasma is also present in household lamps and fusion reactors.
Fig. 1 The parametric space in which plasma exists
Unlike the fake science fiction weapons in fiction, plasma has existed in military affairs since ancient times. Flames produced by various combustion systems, from ancient flaming arrows to modern flamethrowers, are essentially low-temperature plasma, so plasma is not an unattainable scientific concept.
2. Mass Killing: Application in scenarios based on the purpose of killing
The principle of lethality of weapons based on plasma. Plasma generally has a fairly high energy and tends to transfer it to the surrounding material, causing the latter to ignite or explode for destruction. One of the most striking examples is the flash of a nuclear explosion. The enormous energy released during the fission or fusion of atomic nuclei can turn matter into a gaseous state and ionize to form a plasma cloud, which produces optical radiation with enough power to cause damage to a large area of objects centered on the explosion point.
Fig. 2 The plasma produced by a nuclear explosion exudes a lethal glow
Of course, plasma will not all kill as violently as a nuclear explosion. Its killing intensity is closely related to its temperature, concentration and other conditions, to make the plasma achieve the degree of damage like a nuclear explosion, the conditions and costs required are relatively high, therefore, under normal circumstances, plasma is still mostly used in the research and development of non-lethal weapons, to interfere with and delay the target effect.
In the past, the U.S. military has proposed plans for the research and development of non-lethal plasma weapons. An attempt was made to obtain plasma by a laser of sufficient frequency and used to inflict limited and controllable damage on the target. Based on this concept, since 1990, many related weapons such as Pulsed Kill Laser (PIKL), Pulsed Chemical Laser (PCL), and Pulsed Energy Bomb (PEP) have been developed, although they use specific pulses that do not cause direct damage and damage, but the plasma produced by the ionization of the air by the pulse will cause the target to suffer from vertigo, disorientation, paralysis and skin cold burns through radiation. However, this type of non-lethal plasma weapon still does not go beyond testing in the laboratory or test site, but when the technology of this weapon matures, it can have unpredictable effects on warfare.
Figure 3: Experimental, non-lethal laser complex PEP
3. Mature and full of possibilities - non-lethal applications of plasma
At the same time, plasma research is a wonderful field of physics, and its military application is not completely limited to the manufacture of lethal weapons, based on the diverse military scenarios in reality, other properties of plasma can also play a huge role where needed. It has to be mentioned that the application of plasma in space technology is also the most mature and common example of plasma technology.
In the 50s of the last century, countries made initial attempts to develop rocket engines using ionized gas, and after decades of efforts, plasma thrusters slowly became common and are still used today. The principle of plasma thruster is also very simple, that is, under the action of a set of magnets and electrical equipment, the gaseous working fluid is heated and ionized, and high-speed plasma is obtained to provide propulsion for the aircraft. After understanding the principle of plasma thruster, it is not difficult to find that plasma propulsion converts electrical energy into kinetic energy, compared with traditional chemical fuel propulsion, its jet speed is increased by several orders of magnitude, and at the same time, it can greatly reduce the fuel mass of the aircraft, so as to improve the payload of the aircraft, reduce the launch quality, and save costs. Boeing has used the XIPS-25 thruster instead of traditional chemical propulsion technology to achieve satellite orbit transfer and position maintenance after orbit, through the replacement of the thruster, the mass of a single satellite has been reduced by nearly half, and the launch cost has also been reduced by nearly 60 million US dollars. To this day, research on plasma engines is still in full swing, and it is also widely used in various spacecraft and military equipment.
Fig. 4 LIPS-200 ion thruster and HET-70 Hall thruster developed using plasma technology
The other is to use the shielding effect of plasma to help the aircraft stealth technology. Plasma stealth technology, that is, by placing some plasma generators in certain parts of the aircraft. During the flight, a plasma stream is released to form a plasma electromagnetic shield around the aircraft, which "shields" the aircraft and makes it impossible for radar to detect.
Schematic diagram of the plasma stealth scheme of the F-26STALMA fighter
Compared with the traditional design method of stealth aircraft with absorbing coatings, the outstanding advantage of plasma stealth is that it hardly requires any structural and performance changes to the aircraft. In other words, stealth can no longer be considered as the primary consideration in the design of modern aircraft, and for fighter jets, the design considerations of stealth, speed and maneuverability can be simplified to speed and maneuverability. In addition, plasma stealth also has the advantages of absorption frequency bandwidth, good absorption effect, easy use, low maintenance cost, etc., and this technology can also be used to achieve infrared stealth. At present, the methods that have been publicly reported to achieve plasma stealth include the independent plasma generator method and the atmospheric pressure local discharge method. The former has high power requirements, high energy consumption, low flexibility and difficulty in completing large-area coverage, while the latter has the advantages of easy control and implementation, but it is difficult to develop and there are few relevant test reports. At the same time, due to the large weight and volume of the plasma generator itself, the large power consumption, and the inability of the generator itself to carry out radar stealth and the plasma to the material has a certain corrosiveness, these problems lead to the plasma stealth technology is still in the experimental stage, and there is still a long way to go before it is fully practical.
Fourth, it is not a road - a challenge that has to be faced
In the military field, plasma certainly has some potential advantages, but there are also many disadvantages and challenges. First, plasma requires a lot of energy to generate and maintain, which can greatly limit its feasibility in military applications, especially in special battlefield environments, where energy supply can become an important issue. Secondly, the plasma itself has low stability and is easy to change or disappear due to external environmental influences, so maintaining the stability and durability of the plasma will also be a major challenge in practical applications. In addition, the use of plasma technology will produce electromagnetic radiation and gas release, which will have a bad impact on the human body and the environment in non-lethal scenarios. In addition, the development and application of plasma technology is difficult, time-consuming, and requires a large investment of money and resources, which can cause a serious economic burden on the military.
In general, plasma has set off a wave of research in the military field and has given rise to a series of related results. It has great potential advantages and good development prospects, however, the difficulty of turning theory into reality, the cost of funds, and the large time span of research have also become difficult problems that must be faced. Although the research on plasma-based weapons and equipment is still in the laboratory and test ground, time will see the day when it shines in the military field.