Thermal stability of a moderately large Tokamak proto-reactor Page: 1 of 4
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E IIR-IrIL STABILITY OF A 1,1ODEBATIELY LkAGE TOKAAK PjROTO -iEA TOR
R. A. Dory, J. T. hogan and 14. M. Widner
Oak Ridge Rational Laboratory, . Oak Ridge, Tennessee 37830 U.S.A.
An operating procedure is given, which uses feedback control of the external
energy input source (injection of energetic neutral particles) to give therm-
ally stable operation near but below the ignition temperature T . For higher
temperatures, thermonuclear reactions give enough energy to the plasma to over-
balance the energy loss mechanisms now known and (because the thermonuclear rates
rise more steeply with temperature) lead to thermal runaway.2'
The consequences of thenrial runaway are not known well, but the thermonuclear
rates are limited only when the ion temperature approaches 100 keV, where (high P)
equilibrium and stability problems are predicted theoretically. For example, we
show here that for devices of the size now being discussed for studies in the late
1970's thermal runaway leads very quickly to values of poloidal beta (p0 = 8nnkT/
Be, B = I/5a, I = plasma current, a = minor radius of the plasma discharge, B =
major radius) in excess of critical value (R/a) at which theory has predicted
disruption of equilibrium by currents associated with trapped particles.
It is noted here that feedback control of the neutral injection heating sys-
ten will pe:[rit experimental approach to and investigation of the critical regimes
in test devices. Shnilar work by our colleagues has shown that careful control
of energy and fuel injection rates leads to acceptable operating schemes for full
scale reactor devices.
In this note, we use a previously developed space (minor radius r) and time
resolved computer code to follow the evolution of a single discharge; incorporat-
ing the toroidal ion energy transport coefficients ("neoclassical") given by
Galeev and Sagdeev (coefficients adjusted to incorporate data from more recent
calculations by Hinton and Rosenbluth). Electron thermal transport is assumed to
follow the law proposed by Arts imovich. We include synchrotron radiation follow-
ing Trubnikov,9 and brcmsstrahltung losses and electron-ion energy transfer after
Machine parameters are patterned after those being discussed at ORFNL under
the device name SCORE. These are: . = 600 cm, a = 75 cm, I.= 10 Amp, and
B = 50 kG. We assume operation at 8x1015 cm-5 with pulse tames ~2.5 sec, and
find that very large injected power is required to heat the plasma from the point
( 1 k1M) of falloff of effec'ivencss of Ohmic heating to temperatures ." 10 kcV
DISTIDUT)ON OlF W'IS DflCLNA* I i5 UjNLBwalE~
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Dory, R.A.; Hogan, J.T. & Widner, M.M. Thermal stability of a moderately large Tokamak proto-reactor, article, October 31, 1973; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc1036058/m1/1/: accessed June 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.