[Lex Computer & Tech Group/LCTG] One of the world's most complex machines

[Ted Kochanski]

All,

Both Stelllerators and Tokamaks were attempts to configure magnetic fields
in an endless form after the initial problems with what was called a pinch
experiment in the immediate Post WWII period
Pinches seemed the obvious approach --squeeze the plasma in a toroidal
magnetic configuration -- but they suffered from two problems:
a macroscopic catastrophic instability known as the Kink leading to total
loss of the plasma-- partial solution lower the plasma pressure
a microscopic problem of anomalous particle diffusion leading to
inability to get very hot [due to the gradient in curvature of the field
lines across the minor radius]

Tokamaks [invented by Lev Artsimovich in Russia] attempted to solve the
problems by combining a strong toroidal magnetic field [external coils]
with a weaker "poloidal" magnetic field due to current in the plasma [this
current was limited by the kink instability]
the current passing through the plasma also provided the basic heating of
the  plasma through "ohmic Dissipation"

Stererators [invented by Lyman Spitzer in Princeton] used a number of
different external coils to produce a mostly toroidal magnetic field with
twists to average out the diffusion problem [the initial approach was
essentially to use a figure 8 shaped vacuum chamber -- on view at the
Smithsonian]
all heating in a Sterator  -- and later added as auxiliary heating in
tokamak ---  was provided by either external neutral atom beams
[collisional transfer] or radio frequency wave absorption

Tokamaks have by far the greater body of experience and much data over a
wide range of parameters -- but there are still "true believers" in
Stellerators [considered more beautiful theoretically]


a bit of a preview  of my soon to be offered talk on the Tokamak
Renaissance and finally delivering on the promise of Controlled
Thermonuclear Fusion


Ted
tedpk at alum.mit.edu




On Fri, May 6, 2022 at 10:39 AM L Wittig <9423lew at gmail.com> wrote:

> This is the W7X stellarator at the Max Planck Institute for Plasmaphysics.
> It is a working machine that has achieved some useful results, but it will
> not exceed breakeven (that is more power out than in). Stellarators
> actually predated Tokamaks but now have fallen somewhat out of favor
> compared to Tokamaks and other designs.
> Max-Planck-Institute for Plasma Physics
> https://www.youtube.com/watch?v=lyqt6u5_sHA
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