Detached plasma was observed on many tokamaks in ohmic plasmas and with
relatively low auxiliary heating (e.g. see [8, 22–24] and the review papers [10, 25]).
Similar to the MARFE case, the formation of the radiative mantle can be accompanied by strong fluctuations of plasma parameters. For example, ~100% D α signal
fluctuations at the frequencies ~100 Hz were observed in the FT tokamak [22] (see
Fig. 9.6), which shows a strong variation of the plasma recycling process. However,
the physics of these fluctuations of plasma recycling is not known.
In addition, preliminary spectral measurements in detached plasma in C-Mod
indicate that plasma recombination can be the major plasma sink.
9.2 Self-Sustained Divertor Plasma Oscillations
As we have described in the previous section, such macroscopic phenomena as
MARFE and detached plasma in limiter discharges are accompanied by the fluctuations of plasma parameters which look as self-sustained oscillations (e.g. see
Fig. 9.6).
Actually, taking into account complexity and non-linearity of edge plasma
processes, in particular, those where strong energy radiation losses play an important
role, it is not surprising that edge plasma can exhibit regimes with self-sustained
oscillations. Among other tokamak processes resulting in self-sustained oscillations,
we can mention sawtooth oscillations and ELMs. However, these oscillations are
closely related to MHD phenomena.
Somewhat similar to oscillations in MARFE and detached plasma self-sustainedlike oscillations of plasma parameters were also found in the discharges with
poloidal divertors (e.g. see [26, 27]). Typical frequencies of these oscillations are
about 100 Hz, which is close to the oscillation frequencies observed in MARFE and
detached plasmas. Oscillations with similar frequencies were observed in detached
Fig. 9.6 From the top to
bottom: sawtooth
oscillations and time
variation of loop voltage and
the D α signal from the
detached plasma of the FT
tokamak. (Reproduced with
permission from [22],
© Elsevier 1982)
234
9 Physics of Some Edge Plasma Phenomena
relatively low auxiliary heating (e.g. see [8, 22–24] and the review papers [10, 25]).
Similar to the MARFE case, the formation of the radiative mantle can be accompanied by strong fluctuations of plasma parameters. For example, ~100% D α signal
fluctuations at the frequencies ~100 Hz were observed in the FT tokamak [22] (see
Fig. 9.6), which shows a strong variation of the plasma recycling process. However,
the physics of these fluctuations of plasma recycling is not known.
In addition, preliminary spectral measurements in detached plasma in C-Mod
indicate that plasma recombination can be the major plasma sink.
9.2 Self-Sustained Divertor Plasma Oscillations
As we have described in the previous section, such macroscopic phenomena as
MARFE and detached plasma in limiter discharges are accompanied by the fluctuations of plasma parameters which look as self-sustained oscillations (e.g. see
Fig. 9.6).
Actually, taking into account complexity and non-linearity of edge plasma
processes, in particular, those where strong energy radiation losses play an important
role, it is not surprising that edge plasma can exhibit regimes with self-sustained
oscillations. Among other tokamak processes resulting in self-sustained oscillations,
we can mention sawtooth oscillations and ELMs. However, these oscillations are
closely related to MHD phenomena.
Somewhat similar to oscillations in MARFE and detached plasma self-sustainedlike oscillations of plasma parameters were also found in the discharges with
poloidal divertors (e.g. see [26, 27]). Typical frequencies of these oscillations are
about 100 Hz, which is close to the oscillation frequencies observed in MARFE and
detached plasmas. Oscillations with similar frequencies were observed in detached
Fig. 9.6 From the top to
bottom: sawtooth
oscillations and time
variation of loop voltage and
the D α signal from the
detached plasma of the FT
tokamak. (Reproduced with
permission from [22],
© Elsevier 1982)
234
9 Physics of Some Edge Plasma Phenomena