is a metric for plasma confinement quality. It is defined as the ratio of the energy confinement time to the confinement time predicted by the IPB98(y,2) scaling law.[1]

where


and
is the plasma current,
is the toroidal magnetic field at
,
is the average density,
is the loss power across the LCFS into the SOL,
is the geometric major radius (average of maximum and minimum
of the LCFS) of the plasma,
is the elongation, defined unusually in this case as
,
is the inverse aspect ratio,
is the ion mass,
is the minor radius,
is stored energy, and
is the input heating power.
For a basic, predictable H-mode scenario,
. L-mode will have
significantly below 1, and some regimes such as super H-mode can have
significantly above 1.0.