The seemingly impossible combination can help us master the controllable nuclear fusion technology.
In the very short time after the big bang, the universe was filled with something very special. It is very hot and has a “self-destructive tendency.” It contains both positive and antimatter. This kind of thing is called “electron-positron plasma”, which is a perfect blend of equal amounts of electrons and positrons. But within a few seconds, it disappears: electrons and positrons annihilate each other after contact, and their mass is completely converted into energy.
But since then, many of the dramatic astronomical events that have occurred in the universe have produced electron-positron plasmas. Now, scientists are beginning to learn to produce this plasma in the laboratory, hoping to understand the scientific principles behind the dramatic astronomical events. In addition, understanding this plasma can help us master the controllable nuclear fusion technology.
It seems that the electron-positron plasma is really amazing. Below, let’s take a look at it.
Dramatic astronomical event can produce it
Einstein’s famous equation E = mc2 tells us that mass and energy are equivalent, they can be converted to each other, to produce electronic universe – positive power electron plasma on from this. After the big bang, the universe was filled with energy in the form of photons. As long as the energy of the photon is greater than the sum of the energy of the electron and the positron, the photon has the ability to transform into an electron and a positron pair, and vice versa.
The electron-positron plasmas produced after the big bang did not exist for too long. They cooled rapidly as the universe expanded and then annihilated into photons. In the past decade or so, astronomers have increasingly believed that many violent astronomical events can produce this plasma, even though the amount produced is much less than that produced by the big bang itself.
An example is the gamma ray burst, which is a phenomenon in which the intensity of gamma rays from a certain direction in the sky suddenly increases in a short period of time and then rapidly weakens. However, besides these, astronomers don’t know much about gamma-ray bursts, and the cause is still a mystery. A popular view is that gamma-ray bursts are produced when massive stars become supernovae. However, regardless of the truth, an electron-positron plasma is thought to be related to the cause of a gamma ray burst, whether it is rotating in a magnetic field or colliding with interstellar medium, in many cases, It can produce a lot of gamma rays.
In addition, pulsars and fast radio bursts are also associated with electron-positron plasmas. A pulsar is a neutron star that produces a pulsed signal. The neutron star is small in volume, fast in rotation, and has a strong magnetic field. Electromagnetic radiation can only radiate out along the magnetic axis. If the magnetic axis and the rotation axis do not coincide, the electromagnetic radiation will periodically sweep through the surrounding space like a lighthouse, and a flashing pulse signal will be observed on the earth, so such a neutron star is called a pulsar.
A fast radio storm is a very high-intensity radio wave pulse that lasts only a few milliseconds in one direction in the sky. Observations show that the source of the explosion should be a celestial body with a very strong magnetic field. As for the specificity of this celestial body, it is also a mystery. At present, the hypotheses proposed by astronomers include neutron stars with super-strong magnetic fields, neutron stars or black holes in mergers, and super-supernova explosions.
Astronomers speculate that electron-positron plasmas may be produced in these astronomical events. The high-intensity magnetic field will limit it to the vicinity of the magnetic pole, and some will also be injected into the space along the magnetic axis to form a plasma stream, and the radio wave pulse we receive may be generated when the plasma flow is quenched.
It is manufactured in the lab
these dramatic astronomical event locations are very far away from us. To better understand them, researchers from around the world began experimenting with making electron-positron plasmas in the lab.
Researchers know that ultra-short laser pulses can strike electrons in a sparse array of atoms, making them a bunch of electrons that move forward at speeds close to the speed of light. If the electron beam hits the metal block, the energy of the electron is converted into a pile of high-energy photons. Researchers believe that in this collision, some high-energy photons can also be converted into a bundle of electron-positron pairs. An electron-positron plasma can be formed by generating enough electron-positron pairs.
In 2012, researchers at the University of Michigan conducted the first attempt with a laser device, but only half of it succeeded: a positron beam appeared, but the amount produced was too small and no plasma was formed. Researchers believe that more powerful laser equipment is needed.
Three years later, the Rutherford Appleton Laboratory in the United Kingdom produced the same number of electrons and positrons with a superb laser device, forming an electron-positron plasma. The researchers also observed a filamentous structure produced by the plasma in the experiment, which is generated when the plasma interacts with itself. After a while, the electrons and positrons inside will be annihilated and become photons.
Researchers at the Rutherford Appleton Laboratory in the UK are also preparing to validate an idea that gamma rays are primarily high-energy photons produced by electron-positron plasmas in collisions with interstellar media and in the form of a shock wave. Erupted out. In August 2017, the researchers let the electron-positron plasma strike the simulant of the interstellar medium, and it seems to have detected some signs of shock waves. They are working with multiple laboratories to further test this process.
It needs to master controlled nuclear fusion
research electron – positron plasma, there is a more practical reason. After all, the electron-positron plasma is still a plasma. In life, neon, fluorescent, and television screens have artificial plasmas. In addition, in those huge controllable nuclear fusion reactors, there is also a plasma.
Since the 1950s, scientists around the world have been studying controlled nuclear fusion, which can bring almost inexhaustible clean energy to humans. To achieve controlled nuclear fusion, a plasma consisting of electrons and positively charged nuclei is required in the reactor. When the plasma is hot enough, the nucleus will fuse and release a large amount of nuclear energy. However, research on controlled nuclear fusion has progressed very slowly. For example, in the European Union of Circular Reactors in the United Kingdom, fusion produces only 70% of the input energy. The International Thermonuclear Experimental Reactor in France is planned to achieve an output energy greater than the input energy by around 2030. It can be seen that it is still a distant matter to realize the commercialization of controlled nuclear fusion.
Because the gap between electron mass and nuclear mass is very large, this makes the theoretical formula of plasma physics in the fusion reactor very bloated and complicated, and researchers often cannot theoretically predict the behavior of the plasma. For example, many times, keeping the number of digits after the decimal point is not enough, or ignoring some physical quantities, the theoretical predictions made by researchers have failed. This problem is actually one of the reasons why the research progress of controlled nuclear fusion is too slow.
As for the electron-positron plasma, since the masses of electrons and positrons are equal, the theory describing them is relatively simple. It can be said that it is the simplest kind of plasma. If researchers can observe electron-positron plasmas in experiments and compare them theoretically, they can improve current plasma physics and ultimately improve the understanding of plasma in fusion reactors.
It trapped magnetic field
in order to more easily observed electron – positron plasma, Institute of Plasma Physics under the Max Planck Institute in Germany has been trying to build a container can store it. They used the technique used to study traditional plasma, which is magnetic confinement. If you can design the magnetic field in the right way, leaving the electrons and positrons away from the container wall, they can exist in the container for a long time.
It sounds simple, but the researchers found that after loading a certain amount of electrons and positrons into the container, new particles could no longer be loaded because the magnetic field would repel more particles into the container. Researchers are trying a way to get new electrons and positrons into the container. In the latest experiments, they found that by applying a stable voltage inside the container, new electrons and positrons can be slowly added to the container.
Their experiments are still going on, hoping to get a perfect electron-positron plasma soon. If successful, one of the key questions researchers hope to answer is how long the plasma will survive and then annihilate. The current theory tells us that it should last for a few minutes. However, if it is more unstable or stable than our theoretical predictions, then there is still a significant problem with our current plasma physics, and theorists need to revisit the theory. In this case, many theories related to controllable fusion also need to be rewritten.
The general plasma means that atoms in a gas are ionized under high temperature or strong electromagnetic field, and become a gaseous substance composed of charged particles.
The seemingly impossible combination can help us master the controllable nuclear fusion technology.