1

Hybrid Illinois Device for Research & Applications (HIDRA)P. Delaney1 1 Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois, Urbana, IL 61801, USA

Abstract

The Hybrid Illinois Device for Research and Applications (HIDRA), formally known as WEGA (Wendelstein Experiment in Greifswald für die Ausbildung) in Germany, will take the capabilities of the Nuclear, Plasma, and Radiological Engineering department and the College of Engineering to new levels and increase the university’s profile amongst the world. HIDRA is a hybrid device, which can operate as a tokamak as well as a stellarator that makes this device unique among the world’s fusion device.

What is fusion?

Nuclear fusion is a process in which two light nuclei combine to create a heavier nucleus such as helium. For a nuclear fusion reaction to occur, both protons and neutrons will have to be placed at temperatures that could potentially reach up to 100 million Kelvins. The nuclear reaction releases excess energy from the reaction from the binding energies of the atoms involved in the reactions, which a fusion reaction releases much higher energies levels than fission reactions. There are multiple types of methods that are used to achieve a fusion reaction. Thermonuclear fusion is the process where if the matter is sufficiently heated (hence being plasma), the fusion reaction may occur due to collisions with extreme thermal kinetic energies of the particles. In the form of thermonuclear weapons, thermonuclear fusion is the only fusion technique so far to yield undeniably large amounts of useful fusion energy. Usable amounts of thermonuclear fusion energy released in a controlled manner have yet to be achieved” [11]. Inertial confinement fusion is a type of fusion energy that “research that attempts to initiate nuclear fusion reactions by heating and compressing a fuel target, typically in the form of a pellet that most often contains a mixture of deuterium and tritium” [11]. Muon-catalyzed fusion (μCF) is a process allowing nuclear fusion to take place at temperatures significantly lower than the temperatures required for thermonuclear fusion, even at room temperature or lower [12]. The most common used nuclear fusion reaction (Thermonuclear fusion) is deuterium and tritium, which are isotopes of hydrogen with one and two extra neutrons. As these two isotopes of helium, deuterium and tritium, have become fused at a relatively high speed, nuclear arrangement reacts to become more stable where kinetic energy has been released. Once these two isotopes, deuterium and tritium, are fused together to create a nucleus of helium, a neutron, and 17.6 MeV of energy, which will

Figure 1:The sun is an example of a nuclear fusionCredit: Nuclear Fusion

2

surround the plasma. The neutrons and the heat from the plasma can be collected and used to heat water surrounding the reaction, which turns to steam to drive turbines that produce electricity [8]. Deuterium can be directly extracted from seawater where it exists in a relatively high concentration naturally, and tritium can be made when lithium combines with a neutron in a nuclear reactor [8]. Additionally, the helium that is produced as a waste product in a fusion reaction does not pose environmental risks because it is not radioactive and, when it is released into the air, it floats to the top of the atmosphere and disappears into space [8]. A device that uses this nuclear fusion reaction is known as the International Thermonuclear Experimental Reactor (ITER, which is the first viable nuclear fusion reactor. ITER is an international project to design and build an experimental fusion reactor based on the "tokamak" concept. A Stanford student, Fedja Kadribasic, described the components in the ITER.

“Fusion reactors such as the International Thermonuclear Experimental Reactor ITER use a tokamak, which is a combination of magnets that make a toroidal field and poloidal field. The toroidal field has the shape of a torus that surrounds the plasma, and the poloidal field moves in circles around the plasma. The result is a magnetic field that has a similar shape to the toroidal plasma it is trying to confine and surrounds it on all sides, thereby trapping it. The reason it works in the first place is that the plasma is a gas of ionized atoms and electrons, so, like any collection of charged particles, can be deflected and confined by a magnetic field. Despite the fact that the magnetic field does a very good job of confining the plasma, it cannot do so for much longer than a few seconds because instabilities in the plasma accumulate that eventually make fusion impossible and containment very difficult. Consequently, a fusion reaction in such a device only lasts for a very short time, so the containment chamber does not need to be exposed to the extreme conditions for very long” [8]

As scientists and Engineers continue to study for the advancement of nuclear fusion, physicist Steven Cowley, the director of the Culham Center for Fusion Energy, has declared that, "fusion is in many respects the perfect energy source.”

Benefits of Nuclear Fusion

Nuclear fusion is important because it is a sustainable, yet a high power energy source that could fuel the world’s rising population. Most organisms that reside on the planet Earth receive its’ energy from the sun, which the sun consumes its’ energy through nuclear fusion. Because fossil fuels are being used faster than they are produced, the amount of fossil fuel available will decrease or the price of fossil fuels can increase allowing society to not be able to afford it. As the world’s population continues to increase, the demand for energy will continue increase that will lead to an Energy Gap that would be nearly impossible to fulfill it with fossil fuels. If we continue without making any significant improvements in efficiency then we will need more

3

than 80% more energy by 2020 and even with efficiency improvements at the limit of technology we would still need 40% more energy [17]. Nuclear fusion is can become the main supply of the nation's energy because of the variety of benefits it can offer as an energy source. Using nuclear energy as a main source, we can reduce the amount of fossil fuels (coal, natural gas, oil) used, which would lower the greenhouse gas emissions. By reducing the usage of fossil fuels, we would improve the quality of the air affecting human’s health. Because of the easier access of fuel, the currently proposed research reactors and demonstration power plants will use a mixture of deuterium and tritium gases (forms of hydrogen) [15]. Deuterium is extracted from seawater and tritium can be manufactured inside the reactor from lithium, a readily available metal [15]. According to the website, Nuclear-Energy, “another advantage is the required amount of fuel: less fuel offers more energy. It represents a significant save on raw materials but also in transport, handling and extraction of nuclear fuel. The cost of nuclear fuel (overall uranium) is 20% of the cost of energy generated. The production of electric energy is also continuous. A nuclear power plant is generating electricity for almost 90% of annual time. It reduces the price volatility of other fuels such as petrol” [9]. The benefits of nuclear fusion are an unlimited fuel supply, no long-lived radioactive waste, and no air pollution. Opposed to a fission plant, fusion is much safer because there is no runaway reaction that could occur. The entire reactor vessel (about 840 m3 for ITER) contains less than a gram of fuel at any time and the plasma exists in such a delicate and carefully controlled state that any disturbance or disruption will simply cause it to hit the walls of the reactor rapidly to the point where fusion is no longer possible [15]. The technology that would be fueled by fusion could help to improve the quality of the nation's energy. According to the research conducted by scientists at Oak Ridge National Laboratory, the technology fuel by fusion could,

“Provides an environmentally acceptable alternative to fossil fuel combustion, and help ensure continued economic growth through reliable electricity supply. Advanced research and development in fusion energy could provide high-technology spin-offs in such areas as superconducting magnets; high speed computing; high power lasers; electronic diagnostic equipment; and high power, high frequency radio.”

Magnetic confinement fusion

Tokamak

In 1951, two Soviet physicists, Igor Tamm and Andrei Sakharov, were inspired by an idea that was thought of by Oleg Lavrentiev. Oleg Lavrentiev’s idea led Igor Tamm and Andrei Sakharov to propose an idea to create a device known as the tokamak. The term tokamak is originated from the Russian words “toroidalnaya kamera magnitnaya katushka (toroidal chamber magnetic coil).

4

The objective of the tokamak was to confine extremely hot ionized plasma by torus shaped magnetic fields for controlling nuclear fusion [1]. The tokamak has been considered to be the most developed magnetic confinement system and is the basis for the design of future fusion reactors using this method [2]. The tokamak is a useful plasma confinement device because of the high degree of symmetry. The most productive method to heat the plasma in a tokamak is by passing through it a current induced by the primary coil [9]. This coil is the primary circuit of a transformer in which the plasma ring constitutes the secondary circuit [9]. For example, a tokamak would function like a heater because of the current and the resistance of the plasma that would depend on the amount of energy produced. The tokamak is axially symmetric that depends on a 2D shaping, which fulfills its rotational transform, “motion of the magnetic field lines the short way around the torus while they are also wrapping the long way around the torus” [4], through internal plasma currents that flows around the torus. The axis-symmetry of a tokamak makes it a much easier system to build and analyze, as opposed to a stellarator, which requires the ability to build and analyze a 3D system. Basically a tokamak does NOT need the optimization of a stellarator.

Stellarator

In 1952, astrophysicist Lyman Spitzer Jr. proposed to the United States of America Atomic Energy Commission a project to try to contain and harness the nuclear burning of hydrogen at temperatures exceeding those found on the sun, terming the machine a “stellarator,” which would be “designed to obtain power from the thermonuclear reactions between deuterium and either deuterium or tritium” [3]. Lyman Spitzer's innovation was a change in geometry because he suggested extending the torus with straight sections to form a racetrack shape, and then twisting one end by 180 degrees to produce a figure-8 shaped device [13]. When a particle is on the outside of the center on one of the curved sections, by the time it flows through the straight area and into the other curved section it is now on the inside of center, which means that the upward drift on one side is counteracted by the downward drift on the other [13]. As plasma is electrically charged, and thus magnetic, it can be confined by an appropriate arrangement of magnetic fields by understanding that it is a solenoid, which consist of a helix of wire wrapped around a cylindrical support [13]. Plasma inside the solenoid will experience an inward force that would confine it in the center of the helix, which would see no force along the long axis, and would rapidly flow out the ends of the solenoid and escape [13] The purpose for the stellarator is to restrain very high

Figure 4:A photo of a “tokamak”Credit: Euronuclear

Figure 5:A photo of a stellarator Credit: Euronuclear

5

temperature plasmas at a high-density rate with a manageable time frame so it can turn into fusion power production. This can be related to the Lawson Criterion.

“The Lawson criterion, first derived by John D. Lawson in 1957, is an important general measure of a system that defines the conditions needed for a fusion reactor to reach ignition, that is, that the heating of the plasma by the products of the fusion reactions is sufficient to maintain the temperature of the plasma against all losses without external power input. As originally formulated the Lawson criterion gives a minimum required value for the product of the plasma (electron) density ne and the "energy confinement time" τ. Later analyses suggested that a more useful figure of merit is the "triple product" of density, confinement time, and plasma temperature T. The triple product also has a minimum required value, and the name "Lawson criterion" often refers to this inequality [14].

HIDRA

In 1975, WEGA was built in Grenoble, France where the hybrid device was mainly operating as a tokamak during the device tenure in Germany. WEGA is a 1,200 square foot, 70-ton plasma/fusion advanced physics testing device that was created to be a hybrid experiment for studies of lower hybrid heating scenarios as both a tokamak and a stellarator configuration within the framework of the German-French-Belgian project. In 1982, the WEGA was moved from Grenoble, France to the Institut für Physik at the University of Stuttgart who operated the hybrid device as a stellarator for nearly 20 years. During WEGAs tenure in Grenoble, France and the Institut für Physik at the University of Stuttgart, the device was used to research the development of low hybrid heating. WEGA provided much of the new personnel of the branch institute, established in 1994, with their first experience of a plasma experiment. In 2001, WEGA had then been relocated from the University of Stuttgart to operate at Max Planck Institute of Plasma Physics in Greifswald (IPP). During 2001 to 2013, (IPP) used WEGA as a traditional stellarator for educational purposes; basic research on plasma fusion, and testing of a new diagnostics for the new W7-X optimized stellarator, which was a new stellarator in the process of being built for over one billion dollars. In 2014, IPP and the University of Illinois at Urbana-Champaign (UIUC) had made an agreement that WEGA will be relocated and given to the University of Illinois at no cost. After the University of Illinois gain ownership of the Hybrid tokamak/stellarator device, the device was renamed to HIDRA (Hybrid Illinois Device for Research and Applications). At the University of Illinois, HIDRA will be dedicated to the study of plasma material interactions (PMI).

How does the HIDRA Heat Plasma?

Figure 6:A photo of the HIDRACredit: NPRE.Illinois

6

HIDRA uses a significant amount of power in order to create these magnetic fields and currents and to heat the plasma, while not being able to reach a certain temperature in order for the fusion to happen, it does heat the plasma sufficiently to do confinement studies and relevant plasma material studies for fusion devices. Usually, the maximum temperature that can be achieved in tokamaks by resistive heating (or ohmic heating) method is about 3×107 K, twice the temperature in the center of the sun but less than needed to startup a reactor, about 108 Kelvins [10]. In tokamak experiments auxiliary heating is used to reach temperatures currently as high as 5×108 K (more than 30 times the temperature at the sun-center) [10]. HIDRA has the capabilities to have two microwave heating systems at a frequency of 2.45 GHz and 28GHz. In 2006, a new 28 GHz Electron Cyclotron Resonance Heating (ECRH) System performing at 0.5 T magnetic fields was installed in the HIDRA for plasma heating. The ECRH system generates centrally peaked plasma density and temperature profiles that are required for basic plasma physics studies and for evaluation of a new Heavy Ion Beam Probe diagnostic [6]. When HIDRA starts the process of confining the plasma, it is stored in the vacuum vessel. The vacuum vessel is a donut-shaped chamber that the plasma is being spiraled continuously around while the hot part of the plasma does not touch the walls of the vacuum vessel. In the HIDRA, the two half-tori vacuum vessels have the measurements of R = 0.72 m and a = 0.19 m. As the plasma is continuously being spiral around the vacuum vessel, the plasma is getting developed through a small amount of gas, which is then heated up by the current. In HIDRA, the 2.45 GHz has the ability to heat up the plasma at 20 + 6KW magnetrons, and the 28 GHz has the ability to heat up the plasma at 10 kW gyrotions. The plasma can also heated through a neutral beam injection. A neutral beam injection is a process when the “neutral hydrogen atoms are injected at high speed into the plasma, ionized and trapped by the magnetic field. As they are slowed down, they transfer their energy to the plasma and heat it.” HIDRA can also use another source, which heats the ions that known as radiofrequency heating. Radiofrequency heating is when “a high-frequency oscillating currents are induced in the plasma by external coils or waveguides. The frequencies are chosen to match regions where the energy absorption is very high (resonances). In this way, large amounts of power may be transferred to the plasma.” The two most common methods to heat plasma are inertial and magnetic confinement. Inertial confinement uses very powerful lasers to heat and pressurize a tiny amount of fussionable material [8]. Magnetic confinement uses magnets to confine the plasma into a toroid where the nuclear reactions take place [8]. The magnetic field coils is the force that that is used to keep the plasma from touching the walls. In HIDRA, there are 40 toroidal field coils which can operate up to Bmax (cw) = 0.5 T with the configurations of poloidal field coil l = 2 and the magnetic toroidal field coil m = 5 help develops a field going in either horizontal or vertical that is used as a contained to maintain and to develop the plasma. In a traditional tokamak, the coils create a magnetic field in either vertical or horizontal of the torus oppose to the traditional stellarator who creates a magnetic field on the currents that are in helical coil.

The triple product diagram stellarators also use a rotational transform that produced a 3D shaping to help improve the plasmas confinements and stability properties. There are many different types of stellarator configurations that can be categorized by the form of symmetry, which each form of symmetry are trying to achieve in the magnetic field variation. The three types of magnetic field symmetry are helical (the magnetic field isobars form a helical pattern on the plasma surface), toroidal (the magnetic field isobars form bands running the long way around the plasma surface), and poloidal (the magnetic field isobars form bands running the short way

7

around the plasma surface). The torsatron is characterized by its magnetic coil structure, which consists of helical twisting coils that wrap around the plasma [4]. As stellarators continue to evolve, the Wendelstein 7-X will be the world's largest fusion device of the stellarator type. Located at the Max Planck Institute of Plasma Physics in Greifswald, the Wendelstein 7-X is a fusion reactor with modular superconducting coils, which enable steady state plasma operation in order to explore the reactor relevance of this concept [16]. W7-X will have its first plasma in the spring of 2015.

Conclusion

In conclusion, nuclear power is the most prominent renewable electricity generation method with today’s current technological era [17]. Because of nuclear fusions past scientific research, safety features, and an economical promise for the future, Nuclear energy is a clean, safe, reliable and competitive energy source that contributes to the energy of the future. [17] With the fusion technology such as the HIDRA, we can continue to have advancements on learning new scientific researches about plasma fusion.

Reference:[1] http://en.wikipedia.org/wiki/Andrei_Sakharov[3] http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/spitzer-lyman.pdf[4] http://web.ornl.gov/sci/fed/Theory/stci/FAQ.html[6] http://epsppd.epfl.ch/Roma/pdf/P2_122.pdf[8] http://large.stanford.edu/courses/2013/ph241/kadribasic2/[9] http://www.iter.org[10] http://www.plasma.inpe.br/LAP_Portal/LAP_Site/Text/Tokamaks.htm[11] http://nuclear--fusion.weebly.com/1/category/all/1.html[12] http://www.snipview.com/q/Muon-catalyzed%20fusion[13] http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Stellarator.html[14] http://dictionary.reference.com/browse/lawson+criterion[15] http://www.answers.com/Q/Advantages_and_disadvantages_of_nuclear_fusion[16] https://www.ipp.mpg.de/16900/w7x[17] https://www.iop.org/activity/groups/subject/env/prize/file_52570.pdf