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Plasma is referred to as the fourth state of matter besides liquid, gas and solid. Plasma is typically an ionized gas meaning that at least one electron has been dissociated from, or added to, a proportion of the atoms or molecules. The free electric charges make the plasma electrically conductive so that it responds strongly to electromagnetic fields.
There exist different types of plasmas. In fact, more than 99% of the visible universe is in the plasma state, with the most wellknown example being our Sun. Life on Earth depends on the energy emitted by plasma produced during fusion reactions within the sun. Almost all the matter in the universe is very low density plasma: solids, liquids and gases are uncommon away from planetary bodies.
Closer to Earth, natural plasma manifests itself in the form of lightning, the Auroras, or SaintElmo’s fire. In addition, plasma can also artificially be created by supplying energy to a gas. A distinction can be made between fusion plasmas and gas discharge plasmas. Fusion plasmas operate at millions of degrees to mimic the conditions of the Sun in order to realize nuclear fusion as a future energy source. Gas discharge plasmas, on the other hand, operate at much lower temperature, even close to room temperature, and are created by
applying electrical energy to a gas. This explains why they are potentially interesting for use as renewable electricity.
Plasmas have many technological applications, from fluorescent lighting to plasma processing for semiconductor manufacture. The plasma torches are available commercially that can cut into materials for industrial use purposes; however, said torches currently only produce a plasma jet of several inches at most. The other example is the MARAUDER (Magnetically Accelerated Ring to Achieve Ultra-high Directed-Energy and Radiation) used the Shiva Star project (a high energy capacitor bank which provided the means to test weapons and other devices requiring brief and extremely large amounts of energy) to accelerate a toroid of plasma at a significant percentage of the speed of light. However, this device requires large amount of energy.
Militaries are increasingly demanding Directed-energy weapon (DEW) like laser and high power microwave that emits highly focused energy, transferring that energy to a target to damage it. These can be employed as personnel weapon systems, potential missile defense system, and the disabling of lightly armored vehicles such as cars, drones, watercraft, and electronic devices such as mobile phones. Plasma weapons are another type of directed energy weapon being researched that can fire a beam, bolt, or stream of plasma. These are predicted to enable future weapons like a plasma rifle that can cut through just about anything or a plasma shield that can instantly incinerate incoming ammunition and missiles.
For decades, the DoD has been researching a radical drag reduction technique for Hypersonic Vehicles that involves sheathing a vehicle in directed energy-induced plasma. By combining advanced directed energy technology with the latest in hypersonic vehicle design, researchers in private and Department of Defense (DoD) funded laboratories have laid the groundwork for systems designed to literally sheathe an entire vehicle in laser and/or microwave-induced plasma in order to drastically reduce drag. If successfully developed, this concept may someday lead to new frontiers in speed and radical new forms of aerodynamic control and aircraft design.
Plasma Technology: An Emerging Technology for Energy Storage
Plasma, i.e., ionized gas, has great potential for gas conversion applications because the energetic electrons can activate inert molecules, like CO2 and N2, enabling thermodynamically difficult reactions to occur at ambient conditions of temperature and pressure. Plasma is generated by electric power and can easily be switched on/off, making it, in principle, suitable for using intermittent renewable electricity.
In recent years, there is growing interest in the use of plasma for gas conversion applications. Two major application fields, which will be covered in this Perspective article, are (i) CO2 conversion into value-added chemicals or renewable fuels and (ii) N2 fixation from the air, to be used for the production of small building blocks for, e.g., mineral fertilizers. Plasma allows the activation of these stable molecules in an energy-efficient way. Indeed, the gas does not have to be heated as a whole. The applied electrical energy will selectively heat the electrons due to their small mass. Subsequently, these energetic electrons will collide with the gas molecules (e.g., CO2 or N2), causing excitation, ionization, and dissociation. The excited species, ions, and/or radicals will quickly react further, creating new molecules.
Plasma Jet propulsion
Most of that enormous rocket consisted of the fuel it burned to launch a tiny, crew-carrying space capsule into orbit. There, free of Earth’s gravity, small bursts from fuel-burning thrusters guided the Apollo space capsule to the moon and back. Since then, scientists have developed alternative thruster technologies that do not burn heavy fuels. Instead, these thrusters ionize stable gases like xenon and krypton, using electricity from solar cells to strip the electrons from the gas atoms to create a stream of positively charged ions, called a plasma. The spacecraft pushes this plasma out its exhaust to propel itself through the weightless void.
Such thrusters, known as electric propulsion engines, or plasma thrusters, currently enable hundreds of GPS, military and communications satellites make tiny course corrections and maintain stable orbits. But now, scientists are developing a new generation of ion thrusters capable of sending spacecraft on long-distance missions throughout the solar system, such as the Deep Space 1 module that visited asteroid 9969 Braille and comet Borrelly, and the Dawn spacecraft that traveled to the asteroid belt between Mars and Jupiter.”Plasma thrusters represent the future of space exploration,” said Ken Hara, an assistant professor of aeronautics and astronautics, who is helping develop computer models to make ion engines more powerful, efficient and useful.
Hara says the plasma thrusters have a number of advantages over their predecessors. For starters, the ionized gases used as the propellants in plasma thrusters weigh less than the fuels burned by the thrusters of the Apollo era. Every pound the spacecraft saves by lessening its fuel load means more weight to carry a larger scientific payload. Moreover, once a plasma-powered craft is in space, it can accelerate over time in a way that fuel-burning craft can’t, ultimately giving these lightweight engines a speed advantage as well.
Understanding just why this is so involves a concept called exhaust velocity—the speed at which a propellant exits an engine. A traditional fuel-burning engine burns a huge volume of fuel but at a low exhaust velocity, a combination that produces tremendous thrust. Think about a rocket on the launch pad, moving slowly at first as it is lifted by a great billowing of flames, then accelerating as the tremendous thrust that is generated breaks the grip of gravity and hurls the rocket skyward.
By contrast, a plasma engine is designed for a different environment—propelling a spacecraft that is already in a low- or no-gravity environment. The plasma engine does this by emitting ionized particles at extremely high exhaust velocities, but very low volumes, propelling the spacecraft with what might be likened to puffs of breath. In the vacuum of space, with nothing to diminish the spacecraft’s forward momentum, these puffs of ionized thrust allow the vessel to pick up speed over time, going both faster and further than fuel-burning spacecraft.
China’s plasma drive
The Institute of Technological Science at Wuhan recently published a paper announcing the creation of a prototype ‘plasma drive’ that could lift a small steel ball across a one-inch quartz tube – the same level of thrust required to power a commercial aircraft engine, according to South China Morning Post. While this is only a prototype, the hope is that a larger version could pave a route forwards for a green alternative to the fossil-fuel hungry engines that power aircraft today. Unlike the ion thrusters that have been used in space travel which use propellants such as hydrogen, this concept uses air – a potentially unlimited source.
This design, says SCMP, uses pressurised air injected to a chamber where it’s then subjected to extremely high temperatures at over 1,000 degrees Celsius, as well as microwaves, creating an ionised plasma in the process – which is then expelled for the propulsion. “There is no need for fossil fuel with our design, and therefore, there is no carbon emission to cause a greenhouse effect or global warming,” lead author on the report at Wuhan University, professor Jau Tang, told the paper.
Tang, an acclaimed inventor and Wuhan University professor, and his Institute of Technological Sciences colleagues Dan Ye and Jun Li might be on the verge of revolutionizing jet and rocket engines, The process utilizes microwaves to energize compressed air into a plasma state and directing it outward as an expelled propellant similar to a jet engine. “Essentially, the goal of this technology is to try and use electricity and air to replace gasoline,” Tang told Futurism. “Global warming is a major threat to human civilization. Fossil fuel-free technology using microwave air plasma could be a solution. I think the jet engine is more efficient than the electric motor, you can drive a car at much faster speeds. That’s what I have in mind: to combine the plasma jet engine with a turbine to drive a car.”
This design, conceived and built by a team at the Institute of Technical Sciences at Wuhan University, uses only air and electricity, and appears to produce an impressive push that may see it become relevant to electric aircraft applications. The device works by ionizing air to create a low-temperature plasma, which is blown up a tube by an air compressor. Part way up the tube, the plasma is hit with a powerful microwave, which shakes the ions in the plasma about violently, crashing them against other non-ionized atoms and vastly increasing the temperature and pressure of the plasma. This temperature and pressure generates significant thrust up the tube.
This revolutionary device is comprised of a microwave power supply, an air compressor, a compressed microwave waveguide, and a flame ignitor. Their findings were recently published in the online scientific journal AIP Advances. Tang’s ambitious belief is that his plasma jet technology could be harnessed to propel drones and within a decade be employed in powering automobiles, projectile weapons, speedboats, commercial and military aircraft, and even an ultra-modern kitchen stove that utilizes a microwave air plasma torch.
Part of the secret sauce here is in the flattened waveguide through which the microwaves are fired. Generated by a 1-kW, 2.45-Gh magnetron, the microwaves are sent down a waveguide that’s squeezed down to half its height as it approaches the plasma tube. This is done to boost its electric field strength and impart as much heat and pressure to the plasma as possible.
The researchers noticed that, keeping the air flow from the compressor steady, the flame jet in the tube appeared to lengthen when the microwave power was increased. They set about trying to measure how much thrust was being produced, which proved difficult since the thousand-degree plasma jet would destroy a regular barometer. Instead, they settled on balancing a hollow steel ball on top of the tube, which could be filled with smaller steel beads to change its weight. At a certain weight, the thrust would counteract the gravitational forces pulling the ball down and begin lifting it off the tube, causing it to move and jump about, and the researchers used these measurements, minus the thrust contributed by the air compressor, to work out how hard their new plasma thruster was pushing.
In efficiency terms, the propulsion force at 400 W and 1.45 cubic meters of air per hour was 11 Newtons, representing a conversion of power into thrust at a rate of 28 N/kW. One of the greatest hurdles for Tang’s jet engine is that his team’s prototype currently provides a mere 10 newtons of thrusts, which is the equivalent of an average-sized Estes hobby rocket. For this machine to lift an entire airplane, its output would have to be boosted exponentially. For example, the current Air Force One 747-200B jet’s four engines deliver nearly 240,000 newtons of thrust, making the amount of electricity generating batteries to produce this type of power using Tang’s novel approach impossible with today’s technology. “The steps toward realization of a full plasma jet engine would cost lots of money, time and energy,” Tang added. “Such investment is beyond our present resources. Such tasks should be taken by aerospace industries or governmental agencies.”
Assuming linear extrapolation, the team speculated it could take a Tesla Model S battery capable of outputting 310 kW and turn that into something like an 8,500-N propulsive thrust force. By means of comparison, the Airbus E-Fan electric airplane uses a pair of 30-kW electric ducted fans, which combine to produce 1,500 N of thrust. That would imply an efficiency of 25 N/kW, which is not quite as good as the first prototype assembled in this lab. The researchers say this thrust efficiency is already “comparable to those of commercial airplane jet engines.”
The researchers say they’re working on ditching their steel ball testing method for something more reliable and accurate, as well as trying to increase the efficiency of the design. But things certainly look promising for this new plasma thruster idea in electric aircraft propulsion, with a few important caveats.
Blasting The Air In Front Of Hypersonic Vehicles With Lasers Could Unlock Unprecedented Speeds
As with all hypersonic systems, drag and the resulting thermal stresses of extremely high-speed flight are two of the biggest hurdles faced by these vehicles. Even with advanced geometry, extreme levels of heat are generated by friction on the skin of high-speed craft, which can potentially degrade the structural integrity of the airframe and damage internal components, potentially even in a catastrophic fashion.
One of the ways of mitigating that heat buildup is to add shielding to the external surfaces of an airframe. That can increase a craft’s weight and may, therefore, decrease its range, maneuverability, and top speed. Thermal shielding requirements can also be very restrictive for aerospace designers that are looking to push the limits of inter-atmospheric speed.
Tweaking a vehicle’s geometry can mitigate drag, which can also help to reduce heat buildup. However, due to the limitations of materials science and the need to include various subsystems and payloads inside of hypersonic craft, there are restrictions on just how much the geometry can be altered. Thus, there is a pressing need for other drag reduction methods to be used in conjunction with airframe geometry. Like in many other areas of cutting-edge defense and aerospace research today, that’s where breakthroughs in directed energy may be able to lend a hand.
Hypersonic vehicles Drag Reduction Through Directed Energy Deposition
Alongside the ongoing hypersonic revolution, the Department of Defense has been investing vast sums in directed energy systems. Many huge leaps in power and miniaturization have occurred in the last decade as solid-state systems have rapidly matured, enabling them to be used for new applications.
Laser weapons have been developed and tested for use aboard Naval vessels and even aircraft, while other forms of directed energy systems, such as high-powered microwaves, have been designed for power-beaming concepts, close-in defense systems, and anti-satellite technologies. While most discussions of directed energy focus on the potential to revolutionize anti-aircraft systems, missile defenses, or anti-satellite systems, it turns out directed energy could revolutionize high-speed aerospace propulsion and airframe design just as significantly.
Since at least the 1980s, many leading aerospace laboratories have explored the concept of “energy deposition” in order to reduce drag. This concept involves beaming energy in the form of laser filaments, electric arcs, or microwave radiation along the leading edges or just in front of an aircraft in order to condition the air to be more conducive to high-speed flight. Similar concepts have been tested in the past for different purposes, including an electron gun aboard the Lockheed A-12 designed to reduce the aircraft’s radar signature.
In a 1983 NASA-funded study conducted by the BDM Corporation and authored by Leik Myrabo, pioneer of the laser lightcraft propulsion concept, Myrabo proposed using lasers to literally explode the air in front of a high-speed craft. Myrabo’s initial concept centered on small lightcraft propelled by ground-based lasers focused on their aft section. These proposed craft would also employ internal mirrored optics to then redirect those beams forward to create a “laser-supported detonation” or “LSD wave” in front of the craft.
This LSD wave would create a detached shockwave “at some distance in advance of the leading edge,” which would theoretically “do the work of pushing the atmosphere out of the way and thereby suppress the formation of a strong bow shock and the associated wave drag.” The hot, pressurized gases created by the LSD wave would also theoretically then be used by the craft’s air-breathing engine, thus reducing the amount of energy required for combustion.
Myrabo updated the concept throughout the 1990s in response to the limitations of high-powered lasers at the time. In a 1995 Popular Mechanics article by Gregory Pope, Myrabo claimed that pulsed microwave energy beamed from an overhead satellite could be focused in front of a craft to “blast air into plasma,” which could then be focused downward by powerful superconducting magnets circling the craft in order to create propulsion. As Pope’s article points out, “NASA officials see promise in some of the component technologies, but envision no short-term payoff.” Myrabo’s radical concept appears to have never left the ground.
Other researchers continued exploring similar concepts, however. In 1999, Australia-based aerospace researcher H. David Froning conducted a study published by AIAA titled “Influence of EM Discharges on Hypersonic Vehicle Lift, Drag, and Airbreathing Thrust” that investigated creating “plasma formations by electric arcs or by laser or microwave radiation.” Using computational fluid dynamics, Froning found that “electric or electromagnetic discharges from hypersonic vehicles’ nose sections propagate downstream over the entire extent of the vehicles and through their engines – affecting not only nose drag, but temperatures, pressures, and total vehicle thrust, drag, and lift.” These were only computational studies, but they established a theoretical framework for developing these systems in the future.
Throughout the last two decades, researchers in Brazil and the Rensselaer Polytechnic Institute in Rochester, New York have built upon this theoretical research and designed experiments to test energy deposition in hypersonic wind tunnels. This concept became known as the Laser-Supported Directed Energy Air Spike, or DEAS. Leik Myrabo was once again involved with the research, this time alongside a team of Brazilian researchers. In 2005, Myrabo and Brazilian researchers testing the DEAS concept in hypersonic wind tunnels concluded that “the laser-supported DEAS was able to generate a decrease in the surface pressure over the new model tested and, therefore, a considerable decrease in the aerodynamic drag” experienced by a hemispherical test model. By 2011, Myrabo’s team was researching the DEAS concept in cooperation with the Brazilian Air Force and the U.S. Air Force Research Laboratory.
Myrabo’s concept seemed to have attracted the attention of several top laboratories. In 2010, the Journal of Propulsion and Power published the article “Review: Laser-Ablation Propulsion” which features input from personnel at the USAF Office of Scientific Research (AFOSR), Los Alamos National Laboratory, and academic institutions worldwide. The review notes that at that time, Brazilian researchers had shown that “hypersonic drag can be cut by as much as 40%” and cites cooperation between American, Brazilian, and Australian researchers on the subject of laser-aided propulsion. Similar energy deposition concepts have been explored by researchers at Johns Hopkins University Applied Physics Laboratory (Van Wie 2004), Rutgers University (Knight 2008; Anderson & Knight 2012), the Laboratory of Optics Applications in France (Elias 2018), and the Russian Academy of Sciences (Fomin 2004), among many other laboratories.
A 2004 report commissioned by the Air Force Research Laboratory (AFRL) studied “plasmas generated by electron beams and high-voltage nanosecond pulses” and explored “aerodynamic steering using plasma energy addition” using a “microwave-driven supersonic plasma wind tunnel.” As in many exotic aerospace studies, the authors note that “Of course, fundamental issues have to be resolved prior to any practical applications.” That doesn’t mean the DOD stopped trying to resolve those issues. In 2009, the AFRL published another study titled “Lines of Energy Deposition for Supersonic/Hypersonic Temperature/ Drag-Reduction and Vehicle Control.” The report was authored by Kevin Kremeyer, Vice President of Research at Physics, Materials, and Applied Mathematics Research (PM&AM) in Tucson, AZ. Kremeyer holds numerous patents for systems designed to reduce drag through the use of directed energy.
NASA even conducted a study in 2017 at the Langley Research Center into the “experimental determination of the drag reduction and energetic efficiency” of laser discharges ahead of simulated aircraft traveling at high speeds, and the Department of Energy (DOE) has looked into the same concept for increasing the performance of wind turbines. In a 2019 patent, PM&AM’s Kremeyer claims that his system can reduce drag, aid propulsion, and reduce the thermal effects an aircraft experiences by ionizing and heating the air immediately around the vehicle with short laser pulses. Microwave energy is then pulsed into that laser-induced plasma to further heat the air in front of the vehicle:
Plasma Stealth
Plasmas can interact strongly with electromagnetic radiation: this is why plasmas might plausibly be used to conceal an aircraft from radar by modifying an object’s radar signature. The Journal of Electronic Defense reported that in 2002, the Russians tested a plasma-stealth device on board an SU27 and the radar cross-section (RCS) of the aircraft was decreased by a factor of 100.7.
The principle of plasma stealth is to generate an ionized “layer” at nose/ leading edge that surrounds the aircraft. When the plasma cloud interacts with electromagnetic waves radiated by enemy radar several phenomena result. First, absorption of electromagnetic energy occurs because of its interaction with plasma charged particles, which pass onto them a portion of its energy. Second, due to specific physical processes, electromagnetic wave tends to pass around plasma cloud. Both of these phenomena results in dramatic decrease of the reflected signal and reduction in the radar cross-section (RCS) of an aircraft.
Plasma is capable of absorbing/spreading a wide range of radar frequencies, angles, polarizations, and power densities. However, Plasma stealth technology also faces various technical problems. For example, the plasma itself emits EM radiation, fortunately this is usually weak and noise-like in spectrum. Also, it takes some time for plasma to be re-absorbed by the atmosphere and a trail of ionized air would be created behind the moving aircraft, but at present there is no method to detect this kind of plasma trail at long distance. Thirdly, plasmas (like glow discharges or fluorescent lights) tend to emit a visible glow: this is not compatible with overall low observability concept. However, present optical detection devices like FLIR has a shorter range than radar, so Plasma Stealth still has an operational range space.
Plasma Weapons
The primary damage mechanism of these fictional weapons is usually thermal transfer; it typically causes serious burns, and often immediate death of living creatures, and melts or evaporates other materials. In certain fiction, plasma weapons may also have a significant kinetic energy component, that is to say the ionized material is projected with sufficient momentum to cause some secondary impact damage in addition to causing high thermal damage. In some fictions, like Star Wars, plasma is highly effective against mechanical targets such as droids. The ionized gas disrupts their systems.
Plasma railgun
Rail guns work by delivering a high power electric pulse to a pair of conductive rails, which in turn generates a magnetic field and rapidly accelerates the bullet situated between them. A plasma railgun is a linear accelerator which, like a projectile railgun, uses two long parallel electrodes to accelerate a “sliding short” armature. However, in a plasma railgun, the armature and ejected projectile consists of plasma, or hot, ionized, gas-like particles, instead of a solid slug of material.
Plasma railguns appear in two principle topologies, linear and coaxial. Linear railguns consist of two flat plate electrodes separated by insulating spacers and accelerate sheet armatures. Coaxial railguns accelerate toroidal plasma armatures using a hollow outer conductor and a central, concentric, inner conductor. Alex Smyth has developed “phased plasma” gun doesn’t just fire normal projectiles. “The projectiles I made for this to fire are 10 by 60 millimeter,” Smyth explains. “What they are is a glass vacuum tube that’s full of neon gas, with a copper sleeve around it. The electromagnetic fields created by the rails will ionize the gas to create plasma, which will be released when the glass projectile breaks on impact.
Rather than using straight rails, his build features a pair of rails that are twisted to form a double helix. According to Smyth, this gives the projectile some spin and extra stability, just like the rifling on a firearm barrel would provide for a normal bullet. The only difference is that, in lieu of a regular metal projectile, Smyth’s gun is designed to fire. Scientific plasma railguns are typically operated in vacuum and not at air pressure. They are of value because they produce muzzle velocities of up to several hundreds of kilometers per second. Because of this, these devices have applications in Magnetic confinement fusion (MCF), Magneto-inertial fusion (MIF), High Energy Density Physics research (HEDP), laboratory astrophysics, and as a Plasma propulsion engine for spacecraft.
Plasma Acoustic Shield System
Stellar Photonics has already demonstrated the Plasma Acoustic Shield System, or PASS, the device that creates a “mid-air plasma ball” that “basically ignites the air in front of the person…It creates fireworks right in front of you.” Its low power would mean that it would be unable to do significant damage to a specific enemy. However, it is able to disorient an enemy using a series of mid-air explosions, and may also use “high-power speakers for hailing or warning, and a dazzler light source”.
“It uses a programmed pattern of rapid plasma events to create a sort of wall of bright lights and reports (bangs) over the coverage area,” says Keith Braun of the US Army’s Advanced Energy Armaments Systems Division at Picatinny Arsenal in New Jersey, US. Braun puts the maximum range of the system at around a hundred meters. But he says the PASS laser is unlikely to be used as a weapon, in its current format, since it lacks sufficient power. Unlike other high-power lasers which burn a target, the DPD relies on a shockwave. Braun says it would take several minutes to burn through a piece of paper using the laser.
The PASS uses Synchronized Photo-pulse Detonation (SPD), a technology developed by Stellar Photonics wherein two short but powerful laser pulses first create a ball of plasma, then a supersonic shockwave creates a flash and a loud bang. Pass is the first functioning SPD weapon system, and it may lead to the construction of a “man-portable tuneable laser weapon that could be used in both non-lethal and lethal modes”.
The PASS is part of a project supervised by the United States Army Armament Research, Development and Engineering Center. The company received a $2.7 million contract from the U.S. Government to build the PASS. The laser was first tested in 2008, and will continue to be tested into 2009, with the testing of turret-mounted PASS.
University of Missouri engineer Randy Curry builds a plasma device that launches a ring of plasma through the air as far as two feet.
Plasma technologies are also predicted to build inexpensive fusion generators and revolutionize energy generation and storage. In 2013, University of Missouri engineer Randy Curry and his team developed a method of creating and controlling plasma that could revolutionize American energy generation and storage. Curry’s device launches a ring of plasma as far as two feet. The plasma doesn’t emit radiation, and it is completely safe for humans to be in the same room with it, although the plasma reaches a temperature hotter than the surface of the sun.
The key to Curry’s success was developing a way to make the plasma form its own self-magnetic field, which holds it together while it travels through the air. According to Curry, his tech breakthrough can generate 6 inch plasma rings using “very little energy” – “4,000 to 20,000 joules” However, Curry warns that without federal funding of basic research, America will lose the race to develop new plasma energy technologies. The basic research program was originally funded by the Office of Naval Research, but continued research has been funded by MU.
Reference and Resources also include:
http://news.softpedia.com/news/U-S-Army-Is-Developing-Plasma-Weapons-53296.shtml
https://en.wikipedia.org/wiki/Plasma_Acoustic_Shield_System
http://www.digitaltrends.com/cool-tech/homemade-rail-gun-phased-plasma-bullets/
https://www.syfy.com/syfywire/proposed-plasma-jet-technology-might-change-space-travel
https://phys.org/news/2020-02-propulsion-space-exploration.html
