Lithium Tokamak Experiment | |
---|---|
Device type | Tokamak |
Location | Princeton, New Jersey, United States |
Affiliation | Princeton Plasma Physics Laboratory |
History | |
Date(s) of construction | 2000 (as CDX-U) |
Year(s) of operation | 2008–present |
Preceded by | Current Drive Experiment-Upgrade (CDX-U) |
Links | |
Website | The Lithium Tokamak Experiment (LTX) |
The Lithium Tokamak Experiment (LTX), and its predecessor, the Current Drive Experiment-Upgrade (CDX-U), are devices dedicated to the study of liquid lithium as a plasma-facing component (PFC) at Princeton Plasma Physics Laboratory.
One of the ongoing research issues for commercial fusion power development is the choice of material for the plasma-facing portions of the reactor vessel, also known as the first wall. Most reactors operate at the equivalent of a high vacuum and thus demand high-strength materials to resists the inward pressure of the magnets against the empty interior. Typical materials are those used in other chemical and atomic processes, like various steel alloys.
Unfortunately, these same materials have a number of disadvantages when used in fusion reactors. One major problem is that when escaped fusion fuel hits the material it cools, returning to the fuel mass at a lower temperature and cooling the fuel as a whole. This is known as "recycling". The other is that these reactions can also spall off metal atoms, and due to their high atomic mass, or "high-Z", when they are heated they give off copious amounts of X-rays which also cools the plasma fuel.
One of the attractive features of a liquid lithium PFC is that it virtually eliminates recycling. This is because lithium has a high chemical reactivity with atomic hydrogen, which is then retained in the PFC. In addition, lithium has a low atomic number, Z. This gives the lowest possible energy loss by radiation from PFC material that may end up in the plasma, because radiation increases strongly with increasing Z. Finally, flowing liquid lithium can also potentially handle the high power densities expected on reactor walls.
All major tokamaks have obtained their best performance under low recycling conditions. If a fully non-recycling wall can be achieved, theory predicts that the basic nature of magnetic confinement will be changed.[ citation needed ] The temperature and density profiles, and plasma current distributions, would potentially eliminate deleterious plasma instabilities. Furthermore, the transport mechanisms causing the loss of energy and particles would be reduced, and plasmas with higher energy confinement could result.[ citation needed ]
Operated at PPPL from 2000 to 2005. [1]
As the first test of large area liquid lithium PFC, CDX-U had a toroidal tray on the bottom of the vacuum chamber to contain the lithium. Even with this partial non-recycling PFC, major improvements in plasma performance were obtained. Impurities were reduced, and a dramatic improvement (x6) in energy confinement was observed in 2005. [1]
To achieve more a complete non-recycling PFC, the CDX-U vacuum vessel was disassembled for the installation of a heated inner shell inside it. This was a major step for the conversion of CDX-U to LTX.
LTX had its first plasma in 2008, and first run with lithium wall coatings in 2010. [1]
The shell was fabricated out of 3/8” copper sheets, which had a stainless steel liner explosively bonded to it. The stainless steel plasma-facing surface of the inner LTX shell will be coated with lithium between shots, using an electron beam evaporator. By keeping the shell temperature above the melting point of lithium, 90% of the LTX PFC area (~5 m2) will consist of non-recycling liquid lithium.
From 2016 to 2019 LTX was upgraded to become LTX-β. [2] The upgrade increased the magnetic field by about two thirds, and added 500 kW of neutral beam injector heating. [2] First results from the upgraded facility were reported in August 2020. [3]
A stellarator is a plasma device that relies primarily on external magnets to confine a plasma. Scientists researching magnetic confinement fusion aim to use stellarator devices as a vessel for nuclear fusion reactions. The name refers to the possibility of harnessing the power source of the 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 to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being developed to produce controlled thermonuclear fusion power. As of 2016, it was the leading candidate for a practical fusion reactor.
Princeton Plasma Physics Laboratory (PPPL) is a United States Department of Energy national laboratory for plasma physics and nuclear fusion science. Its primary mission is research into and development of fusion as an energy source. It is known in particular for the development of the stellarator and tokamak designs, along with numerous fundamental advances in plasma physics and the exploration of many other plasma confinement concepts.
Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices designed to harness this energy are known as fusion reactors. Research into fusion reactors began in the 1940s, but to date, no design has produced more fusion power output than the electrical power input.
This timeline of nuclear fusion is an incomplete chronological summary of significant events in the study and use of nuclear fusion.
The Joint European Torus, or JET, is an operational magnetically confined plasma physics experiment, located at Culham Centre for Fusion Energy in Oxfordshire, UK. Based on a tokamak design, the fusion research facility is a joint European project with a main purpose of opening the way to future nuclear fusion grid energy. At the time of its design JET was larger than any comparable machine.
ITER is an international nuclear fusion research and engineering megaproject aimed at creating energy by replicating, on Earth, the fusion processes of the Sun. Upon completion of construction of the main reactor and first plasma, planned for late 2025, it will be the world's largest magnetic confinement plasma physics experiment and the largest experimental tokamak nuclear fusion reactor. It is being built next to the Cadarache facility in southern France. ITER will be the largest of more than 100 fusion reactors built since the 1950s, with ten times the plasma volume of any other tokamak operating today.
The Tokamak Fusion Test Reactor (TFTR) was an experimental tokamak built at Princeton Plasma Physics Laboratory (PPPL) circa 1980 and entering service in 1982. TFTR was designed with the explicit goal of reaching scientific breakeven, the point where the heat being released from the fusion reactions in the plasma is equal or greater than the heating being supplied to the plasma by external devices to warm it up.
Magnetic confinement fusion 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 fusion energy research, along with inertial confinement fusion. The magnetic approach began in the 1940s and absorbed the majority of subsequent development.
DEMO refers to a proposed class of nuclear fusion experimental reactors that are intended to demonstrate the net production of electric power from nuclear fusion. Most of the ITER partners have plans for their own DEMO-class reactors. With the possible exception of the EU and Japan, there are no plans for international collaboration as there was with ITER.
DIII-D is a tokamak that has been operated since the late 1980s by General Atomics (GA) in San Diego, USA, for the U.S. Department of Energy. The DIII-D National Fusion Facility is part of the ongoing effort to achieve magnetically confined fusion. The mission of the DIII-D Research Program is to establish the scientific basis for the optimization of the tokamak approach to fusion energy production.
The National Spherical Torus Experiment (NSTX) is a magnetic fusion device based on the spherical tokamak concept. It was constructed by the Princeton Plasma Physics Laboratory (PPPL) in collaboration with the Oak Ridge National Laboratory, Columbia University, and the University of Washington at Seattle. It entered service in 1999. In 2012 it was shut down as part of an upgrade program and became NSTX-U, for Upgrade.
The beta of a plasma, symbolized by β, is the ratio of the plasma pressure to the magnetic pressure. The term is commonly used in studies of the Sun and Earth's magnetic field, and in the field of fusion power designs.
Magnetized Target Fusion (MTF) is a fusion power concept that combines features of magnetic confinement fusion (MCF) and inertial confinement fusion (ICF). Like the magnetic approach, the fusion fuel is confined at lower density by magnetic fields while it is heated into a plasma. As with the inertial approach, fusion is initiated by rapidly squeezing the target to greatly increase fuel density and temperature. Although the resulting density is far lower than in ICF, it is thought that the combination of longer confinement times and better heat retention will let MTF operate, yet be easier to build. The term magneto-inertial fusion (MIF) is similar, but encompasses a wider variety of arrangements. The two terms are often applied interchangeably to experiments.
A spherical tokamak is a type of fusion power device based on the tokamak principle. It is notable for its very narrow profile, or aspect ratio. A traditional tokamak has a toroidal confinement area that gives it an overall shape similar to a donut, complete with a large hole in the middle. The spherical tokamak reduces the size of the hole as much as possible, resulting in a plasma shape that is almost spherical, often compared with a cored apple. The spherical tokamak is sometimes referred to as a spherical torus and often shortened to ST.
In nuclear fusion power research, the plasma-facing material (PFM) is any material used to construct the plasma-facing components (PFC), those components exposed to the plasma within which nuclear fusion occurs, and particularly the material used for the lining the first wall or divertor region of the reactor vessel.
In nuclear fusion power research, a divertor is a device within a tokamak or a stellarator that allows the online removal of waste material from the plasma while the reactor is still operating. This allows control over the buildup of fusion products in the fuel, and removes impurities in the plasma that have entered into it from the vessel lining.
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 ARC fusion reactor is a design for a compact fusion reactor developed by the Massachusetts Institute of Technology (MIT) Plasma Science and Fusion Center (PSFC). ARC aims to achieve an engineering breakeven of three. The key technical innovation is to use high-temperature superconducting magnets in place of ITER's low-temperature superconducting magnets. The proposed device would be about half the diameter of the ITER reactor and cheaper to build.
The Linus program was an experimental fusion power project developed by the United States Naval Research Laboratory (NRL) starting in 1971. The goal of the project was to produce a controlled fusion reaction by compressing plasma inside a metal liner. The basic concept is today known as magnetized target fusion.