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Device type | Stellarator |
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Location | Alabama, United States |
Affiliation | Auburn University |
Technical specifications | |
Major radius | 0.75 m (2 ft 6 in) |
Minor radius | 0.29 m (11 in) |
Plasma volume | 0.6 m3 |
Magnetic field | 0.4–0.7 T (4,000–7,000 G) |
Heating power | 10 kW (ECH) 100 kW (ohmic) |
History | |
Year(s) of operation | 2005–present |
Preceded by | Compact Auburn Torsatron |
The Compact Toroidal Hybrid (CTH) [1] is an experimental device at Auburn University that uses magnetic fields to confine high-temperature plasmas. [2] [3] CTH is a torsatron type of stellarator with an external, continuously wound helical coil that generates the bulk of the magnetic field for containing a plasma.
Toroidal magnetic confinement fusion devices create magnetic fields that lie in a torus. These magnetic fields consist of two components, one component points in the direction that goes the long way around the torus (the toroidal direction), while the other component points in the direction that is the short way around the torus (the poloidal direction). The combination of the two components creates a helically shaped field. (You might imagine taking a flexible stick of candy cane and connecting the two ends.) Stellarator type devices generate all required magnetic fields with external magnetic coils. This is different from tokamak devices where the toroidal magnetic field is generated by external coils and the poloidal magnetic field is produced by an electrical current flowing through the plasma.
The main magnetic field in CTH is generated by a continuously wound helical coil. An auxiliary set of ten coils produces a toroidal field much like that of a tokamak. This toroidal field is used to vary the rotational transform of the confining magnetic field structure. CTH typically operates at a magnetic field of 0.5 to 0.6 tesla at the center of the plasma. CTH can be operated as a pure stellarator, but also has ohmic heating transformer system to drive electrical current in the plasma. This current produces a poloidal magnetic field that, in addition to heating the plasma, changes the rotational transform of the magnetic field. CTH researchers study how well the plasma is confined while they vary the source of rotational transform from external coils to plasma current.
The CTH vacuum vessel is made of Inconel 625, which has a higher electrical resistance and lower magnetic permeability than stainless steel. Plasma formation and heating is achieved using 14 GHz, 10 kW electron cyclotron resonance heating (ECRH). A 200 kW gyrotron has recently been installed on CTH. Ohmic heating on CTH has an input power of 100 kW.
The following gives a list of subsystems needed for CTH operation.
The CTH has a large set of diagnostics to measure properties of plasma and magnetic fields. The following gives a list of major diagnostics.
V3FIT [5] is a code to reconstruct the equilibrium between the plasma and confining magnetic field in cases where the magnetic field is toroidal in nature, but not axisymmetric as is the case with tokamak equilibria. Because stellarators are non-axisymmetric, the CTH group uses the V3FIT and VMEC [6] codes for reconstructing equilibria. The V3FIT code uses as inputs the currents in the magnetic confinement coils, the plasma current, and data from the various diagnostics such as the Rogowski coils, SXR cameras, and interferometer. The output of the V3FIT code includes the structure of the magnetic field, and profiles of the plasma current, density, and SXR emissivity. Data from the CTH experiment was and continues to be used as a testbed for the V3FIT code which has also used for equilibrium reconstruction on the Helically Symmetric eXperiment (HSX), Large Helical Device (LHD), and Wendelstein 7-X (W7-X) stellarators, and the Reversed-Field eXperiment (RFX) and Madison Symmetric Torus (MST) reversed field pinches.
CTH has made and continues to make fundamental contributions to the physics of current carrying stellarators. [7] [8] [9] CTH researchers have studied disruption limits and characterizations as a function of the externally applied rotational transform (due to external magnet coils) for:
CTH students and staff work on a number of experimental and computational research projects. Some of these are solely in house while others are in collaboration with other universities and national laboratories in the United States and abroad. Current research projects include:
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Device type | Stellarator |
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Location | Alabama, United States |
Affiliation | Auburn University |
Technical specifications | |
Major radius | 0.58 m (1 ft 11 in) |
Minor radius | 0.14 m (5.5 in) |
Magnetic field | < 0.2 T (2,000 G) |
History | |
Year(s) of operation | 1983–1990 |
Succeeded by | Compact Auburn Torsatron |
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Device type | Stellarator |
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Location | Alabama, United States |
Affiliation | Auburn University |
Technical specifications | |
Major radius | 0.53 m (1 ft 9 in) |
Minor radius | 0.11 m (4.3 in) |
Plasma volume | 0.12 m3 |
Magnetic field | 0.1 T (1,000 G) |
History | |
Year(s) of operation | 1990–2000 |
Preceded by | Auburn Torsatron |
Succeeded by | Compact Toroidal Hybrid |
CTH is the third torsatron device to be built at Auburn University. Previous Magnetic Confinement Devices built at the university were:
The Auburn Torsatron had an l=2, m=10 helical coil. The vacuum vessel had a major radius was Ro = 0.58 m with a minor radius of av=0.14 m. The magnetic field strength was |B| ≤ 0.2 T and plasmas were formed with ECRH using a 2.45 GHz magnetron taken from a microwave oven. The Auburn Torsatron was used to study basic plasma physics and diagnostics, and magnetic surface mapping techniques [12] [13]
The Compact Auburn Torsatron (CAT) had two helical coils, an l=1,m=5 and an l=2,m=5 whose currents could be controlled independently. [14] Varying the relative currents between the helical coils modified the rotational transform. The vacuum vessel major radius was Ro = 0.53 m with a plasma minor radius of av=0.11 m. The steady state magnetic field strength was |B| 0.1 T. CAT plasmas were formed with ECRH using a low ripple, 6 kW, 2.45 GHz magnetron source. CAT was used to study magnetic islands, [15] magnetic island minimization, [16] and driven plasma rotations [17]
Below is a list of other Stellarators in the US and around the world:
A stellarator is a device that confines plasma using external magnets. Scientists researching magnetic confinement fusion aim to use stellarator devices as a vessel for nuclear fusion reactions. The name refers to stars as fusion also occurs in stars such as the Sun. It is one of the earliest fusion power devices, along with the z-pinch and magnetic mirror.
A tokamak is a device which uses a powerful magnetic field generated by external magnets to confine plasma in the shape of an axially-symmetrical torus. The tokamak is one of several types of magnetic confinement devices being developed to produce controlled thermonuclear fusion power. The tokamak concept is currently one of the leading candidates for a practical fusion reactor.
In plasma physics, plasma stability concerns the stability properties of a plasma in equilibrium and its behavior under small perturbations. The stability of the system determines if the perturbations will grow, oscillate, or be damped out. It is an important consideration in topics such as nuclear fusion and astrophysical plasma.
The Large Helical Device (LHD) is a fusion research device located in Toki, Gifu, Japan. It is operated by the National Institute for Fusion Science, and is the world's second-largest superconducting stellarator, after Wendelstein 7-X. The LHD employs a heliotron magnetic field originally developed in Japan.
Magnetic confinement fusion (MCF) is an approach to generate thermonuclear fusion power that uses magnetic fields to confine fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of controlled fusion research, along with inertial confinement fusion.
A field-reversed configuration (FRC) is a type of plasma device studied as a means of producing nuclear fusion. It confines a plasma on closed magnetic field lines without a central penetration. In an FRC, the plasma has the form of a self-stable torus, similar to a smoke ring.
A spheromak is an arrangement of plasma formed into a toroidal shape similar to a smoke ring. The spheromak contains large internal electric currents and their associated magnetic fields arranged so the magnetohydrodynamic forces within the spheromak are nearly balanced, resulting in long-lived (microsecond) confinement times without external fields. Spheromaks belong to a type of plasma configuration referred to as the compact toroids. A spheromak can be made and sustained using magnetic flux injection, leading to a dynomak.
The H-1NF was a research institute of the H-1 heliac, a large stellarator device located in the ANU Research School of Physics at Canberra, Australia. It was established when the H-1 heliac was promoted to a national facility in 1996, adopting H-1NF as its facility name. In 2022 the H-1 heliac was disassembled before being shipped to its new home in China.
The National Compact Stellarator Experiment, NCSX in short, was a magnetic fusion energy experiment based on the stellarator design being constructed at the Princeton Plasma Physics Laboratory (PPPL).
The Wendelstein 7-X reactor is an experimental stellarator built in Greifswald, Germany, by the Max Planck Institute for Plasma Physics (IPP), and completed in October 2015. Its purpose is to advance stellarator technology: though this experimental reactor will not produce electricity, it is used to evaluate the main components of a future fusion power plant; it was developed based on the predecessor Wendelstein 7-AS experimental reactor.
The Helically Symmetric Experiment, is an experimental plasma confinement device at the University of Wisconsin–Madison, with design principles that are intended to be incorporated into a fusion reactor. The HSX is a modular coil stellarator which is a toroid-shaped pressure vessel with external electromagnets which generate a magnetic field for the purpose of containing a plasma. It began operation in 1999.
Trisops was an experimental machine for the study of magnetic confinement of plasmas with the ultimate goal of producing fusion power. The configuration was a variation of a compact toroid, a toroidal (doughnut-shaped) structure of plasma and magnetic fields with no coils penetrating the center. It lost funding in its original form in 1978.
The Hybrid Illinois Device for Research and Applications (HIDRA) is a medium-sized toroidal magnetic fusion device housed in the Nuclear Radiation Laboratory and operated by the Center for Plasma-Material Interactions (CPMI) within the Department of Nuclear, Plasma and Radiological Engineering at the University of Illinois at Urbana–Champaign, United States. HIDRA had its first plasma at the end of April 2016 and started experimental campaigns by December of that year. HIDRA is the former WEGA classical stellarator that was operated at the Max Planck Institute for Plasma Physics in Greifswald Germany from 2001 to 2013.
The Model C stellarator was the first large-scale stellarator to be built, during the early stages of fusion power research. Planned since 1952, construction began in 1961 at what is today the Princeton Plasma Physics Laboratory (PPPL). The Model C followed the table-top sized Model A, and a series of Model B machines that refined the stellarator concept and provided the basis for the Model C, which intended to reach break-even conditions. Model C ultimately failed to reach this goal, producing electron temperatures of 400 eV when about 100,000 were needed. In 1969, after UK researchers confirmed that the USSR's T-3 tokamak was reaching 1000 eV, the Model C was converted to the Symmetrical Tokamak, and stellarator development at PPPL ended.
TJ-II is a flexible Heliac installed at Spain's National Fusion Laboratory.
Uragan-2M is a stellarator installed at the Institute of Plasma Physics National Science Center, which is part of the Kharkiv Institute of Physics and Technology in Kharkiv, Ukraine. It was the largest stellarator (torsatron) in Europe until the construction of Wendelstein 7-X.
Wendelstein 7-AS was an experimental stellarator which was in operation from 1988 to 2002 by the Max Planck Institute for Plasma Physics (IPP) in Garching. It was the first of a new class of advanced stellarators with modular coils, designed with the goal of developing a nuclear fusion reactor to generate electricity.
Omnigeneity is a property of a magnetic field inside a magnetic confinement fusion reactor. Such a magnetic field is called omnigenous if the path a single particle takes does not drift radially inwards or outwards on average. A particle is then confined to stay on a flux surface. All tokamaks are exactly omnigenous by virtue of their axisymmetry, and conversely an unoptimized stellarator is generally not omnigenous.
A quasi-isodynamic (QI) stellarator is a type of stellarator that satisfies the property of omnigeneity, avoids the potentially hazardous toroidal bootstrap current, and has minimal neoclassical transport in the collisionless regime.
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