In short - particle accelerators

While the accelerators that exist today cover an area of ​​tens of kilometers, the size of such a device will not exceed tens of meters.

What will happen if we focus all the sunlight that reaches the earth on one square millimeter of material? We will get a material with a very high energy density, which is in the fourth state of aggregation and is called plasma - a cloud of particles carrying an electric charge. Different types of plasma - differing from each other in their composition, density and temperature - make up more than 99% of the visible matter in the universe. So, for example, the core of the sun is made of very compressed plasma, the temperature of which reaches ten million degrees or more. Under these conditions, a process of nuclear fusion takes place, which is the source of the sun's energy - four hydrogen nuclei fuse in a complex process into one helium nucleus, emitting a huge amount of energy: calculations show that the fusion of one gram of hydrogen provides the amount of energy produced by burning about ten tons of oil . Many scientists in different parts of the world are trying to deeply understand the properties of plasma, with the hope that such knowledge will help in the future, among other things, to develop nuclear fusion reactors.

How is "tamed" plasma produced in the laboratory? One option is through the transfer of a strong electric current (over a million amperes) in a very short time - less than a millionth of a second. The magnetic field of the current compresses the charged material, and at the end of the process a dense and hot plasma is obtained. Such a system is called a Z-pinch. Another option is to use laser devices that produce strong light in a short period of time and over a small area of ​​a few microns. The material obtained in such a system has properties between hot solid matter and those of hot plasma, and is similar in properties to that found in the cores of giant planets such as Jupiter and Saturn. In both ways, dense and high-energy plasma clouds are obtained, emitting a large amount of light. This light emission opens an important - and in fact a unique - opening to study the properties of the plasma without affecting and interfering with what is happening inside it, using spectroscopic methods. "The spectrum emitted from the plasma makes it possible to obtain a lot of information: temperature, density, electric and magnetic fields, particle speed and more," explains fellow Dr. Yevgeny Stambolchik, from the plasma laboratory in the department of particle physics and astrophysics at the Weizmann Institute of Science. The laboratory, headed by Prof. Yitzhak Maron, focuses on high-density and high-energy plasma spectroscopy, and the development of modeling methods for data processing.

For these studies, the plasma laboratory has developed unique methods for diagnosing fine details in the spectrum, including changes that occur in short periods of time from one thousandth of a second to one thousandth of a second. In contrast to the astrophysical plasmas, which exist for a very long time and therefore usually reach equilibrium, the plasmas created in the laboratory have a very short lifetime - one thousandth of a millionth of a second, at best, and even less in plasmas created by laser.

The properties of these plasmas are not uniform - which makes the measurements and data analysis difficult. For example, the plasma temperature - which is one of the most important indicators for its understanding - actually consists of a collection of data: the ion temperature is different from the electron temperature, and both are different from the radiation temperature, and also change according to the location of the particles and their movement.

In the plasma laboratory, methods are being developed that make it possible to distinguish between such phenomena, based on the spectrum of the light emitted from the plasma. These methods are also used to measure extreme conditions in plasmas, such as, for example, electric fields of a billion volts per meter, and magnetic fields of a million gauss.

One of the biggest difficulties in the study of high-density and high-energy plasmas is that most of the radiation emitted from the plasma core is absorbed within it - something that prevents the possibility of studying the conditions prevailing in the core. Recently, the plasma laboratory developed methods for determining the temperature in different locations within the core at a level of sensitivity that has not been achieved so far. The methods are based on the fact that in the plasmas produced by a laser, a special type of ionization takes place, in which the electrons are torn from the inner layers of the atoms, and not from the outer layers. Following this, electrons from the outer layers "jump" in to fill the "hole", releasing a characteristic spectrum of light, which is very sensitive to temperature and is not absorbed by the plasma. With its help, it is possible to determine - at a resolution level of ten microns - the temperature of the electrons "floating" in the plasma. These experiments were conducted with the help of extremely short and powerful laser pulses, in research laboratories in Germany and France, with the participation of the colleague Dr. Eyal Krupp, who was accompanied by the group's chief technician, Pesach Meiri. The analysis of the spectral lines was done by Dr. Stambolchik and Dr. Vladimir Bernstam in the plasma laboratory.

In another study, conducted in plasmas produced in the plasma laboratory using an electric current (Z-Pinch), the scientists were able to "extract" radiation from the plasma core, using the simultaneous jump of two electrons in the plasma ions. In this way, they were able to distinguish between the temperature of the ions and that of the electrons, and between the random movement of the particles (thermal movement), and non-thermal movement (macroscopic), through the use of two methods: one based on the Doppler phenomenon, and the other on a model describing changes in the electric field. The thermal motion, in contrast to the macroscopic motion, produces changes in the electric field, because the particles move relative to each other. Therefore, subtracting these data from each other makes it possible to isolate the macroscopic movement. This experiment, in which Dr. Eyal Krupp, and research students Dror Alomat and Guy Rosenzweig are participating, is being carried out within the framework of the University Center of Excellence of the US Department of Energy, which includes Cornell University, the Weizmann Institute of Science and Imperial College in London.

These days, plasma laboratory scientists are trying to harness a method used to create plasma for a surprising purpose - a compact particle accelerator. The idea is based on the fact that when a laser beam is focused on a plasma with certain properties, a strong electric field is created that moves almost at the speed of light, and "carries" the electrons with it. In fact, it is a particle accelerator. However, while the accelerators that exist today cover an area of ​​tens of kilometers, the size of such a device will not exceed tens of meters.

Several research groups in the world are trying to do this using plasma produced in a system of fine tubes, but this cannot be reused for a long time. The plasma laboratory at the institute collaborates with groups from Germany in order to try to implement a different method, using the Z-pinch system, in which there is no limit to the number of repeated experiments that can be performed. These days, after the joint work of research students Dimitri Mikitchuk and Christine Stuhlbarg, initial achievements have been made in preparing a plasma that is uniform in length and has a special density profile. Later, in collaboration with groups in Germany and France, they will try to produce the first particle accelerator of its kind.

personal

Dr. Yevgeny Stambolchik recently won the prize for scientific achievements on behalf of the plasma research committee in the American Society for Electrical and Electronics Engineering (IEEE), which is awarded to young researchers for achievements at the beginning of their scientific career. The award was given to him "for his extraordinary contribution to theory and modeling in the field of spectrum line broadening, which includes the development of quantitative methods and their application to unique approaches in plasma research".

Yevgeny Stumbulchik completed his undergraduate studies in physics at Novosibirsk University in Russia. In 1991 he immigrated to Israel, arrived in Rehovot, and joined Prof. Yitzhak Maron's group, where he completed his master's and master's degrees.