Tokamak Definition and 9 Discussions

A tokamak (; Russian: Токамáк) 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 2021, it is the leading candidate for a practical fusion reactor.Tokamaks were initially conceptualized in the 1950s by Soviet physicists Igor Tamm and Andrei Sakharov, inspired by a letter by Oleg Lavrentiev. The first working tokamak was attributed to the work of Natan Yavlinsky on the T-1 in 1958. It had been demonstrated that a stable plasma equilibrium requires magnetic field lines that wind around the torus in a helix. Devices like the z-pinch and stellarator had attempted this, but demonstrated serious instabilities. It was the development of the concept now known as the safety factor (labelled q in mathematical notation) that guided tokamak development; by arranging the reactor so this critical factor q was always greater than 1, the tokamaks strongly suppressed the instabilities which plagued earlier designs.
By the mid-1960s, the tokamak designs began to show greatly improved performance. The initial results were released in 1965, but were ignored; Lyman Spitzer dismissed them out of hand after noting potential problems in their system for measuring temperatures. A second set of results was published in 1968, this time claiming performance far in advance of any other machine. When these were also met skeptically, the Soviets invited a delegation from the United Kingdom to make their own measurements. These confirmed the Soviet results, and their 1969 publication resulted in a stampede of tokamak construction.
By the mid-1970s, dozens of tokamaks were in use around the world. By the late 1970s, these machines had reached all of the conditions needed for practical fusion, although not at the same time nor in a single reactor. With the goal of breakeven (a fusion energy gain factor equal to 1) now in sight, a new series of machines were designed that would run on a fusion fuel of deuterium and tritium. These machines, notably the Joint European Torus (JET), Tokamak Fusion Test Reactor (TFTR), had the explicit goal of reaching breakeven.
Instead, these machines demonstrated new problems that limited their performance. Solving these would require a much larger and more expensive machine, beyond the abilities of any one country. After an initial agreement between Ronald Reagan and Mikhail Gorbachev in November 1985, the International Thermonuclear Experimental Reactor (ITER) effort emerged and remains the primary international effort to develop practical fusion power. Many smaller designs, and offshoots like the spherical tokamak, continue to be used to investigate performance parameters and other issues. As of 2020, JET remains the record holder for fusion output, reaching 16 MW of output for 24 MW of input heating power.

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  1. Shreya

    Electric field due to a Poloidal Magnetic Field in Toroidal Magnetic Confinement of a Plasma

    Please be kind to help. How is an electric field formed due to toroidal magnetic field? How does the introduction of a poloidal magnetic field confine the plasma? Please answer in the context of Nuclear Fusion Reactor (tokamak).
  2. JF001

    I How is the viscosity of a plasma produced?

    Summary: I'm interested in knowing more about instabilities within plasma. Is the viscosity of plasma produced by thermal, magnetic, or gravitational effects (or even something else)? I had the opportunity to talk with multiple Ph.D. students during the summer and was especially interested in...
  3. T

    New approach to stabilize fusion plasmas By applying more RF power to the unstable 'bubbles' that form in the plasmas.
  4. Jan Berkhout

    How is current induced in the plasma in a tokamak?

    For a Year 12 Assignment I have to do a seminar on how magnetic fields are involved with a certain topic. I chose nuclear fusion energy production and specifically the tokamak. I understand that a toroidal magnetic field is created when a current is sent through a solenoid wrapped in a torus...
  5. rebc

    Tokamaks and plasma confinement

    I have the fundamental understanding of how tokamaks work. Now, why is it not ideal to confine plasmas using a z- or theta- pinch configurations?
  6. J

    Tokamak News and Queries It appears that Stuart Prager is “stepping down” as director of PPPL. I wish him well. But in the announcement it refers to a “recent technical setback in the NSTX-U facility”. I had not heard previously of this set...
  7. U

    Plasma containment approaches

    I've been reading some about the ITER project, tokamaks, and other approaches to plasma containment. Why can't ion trapping approaches such as an orbitrap be used for fusion plasma containment?
  8. Teen4Ideas

    Is My Idea Valid? Nuclear Fusion Power

    So as we all know (or at least I assume) Global Warming is real and happening, I am a teen, 17, and not trying to get answers for homework or anything like that. I just want to know, is it possible to create fusion using the temperature found at active Geo-thermal sites to reach the temp...
  9. T

    Quick Tokamak questions

    HI, Some things I want to confirm, somethings I need to be reminded of: So what I remember is that Magnetostatics - stationary charges Electrostatics - constant or slow moving charges And that an accelerating charge makes a magnetic field, but you need a time varying field to move charges. So...