regimes of the LHD stellarator [28]. As an example in Fig. 9.7 one can see such selfsustained oscillations found in L-mode discharges on JET tokamak [27], which were
explained based on the theory developed in [29, 30].
The main idea of [29, 30], which we also will use for the analysis of tokamak
divertor plasma detachment, is based on the properties of the high recycling regime
of divertor operation. In these regimes, the neutral ionization mean-free path near the
targets becomes very small, smaller than the corresponding width of the SOL.
Therefore, the SOL can be considered as an ensemble of weakly interacting magnetic flux tubes filled with plasma and neutrals. The redistribution of plasma ions and
neutrals along the magnetic field in the flux tube occurs rather quickly (characteristic
time scales of ion and neutral redistribution are determined by the sound speed and
inverse ionization frequency respectively, which we will consider being much
smaller than the particle exchange time between different flux tubes). As a result,
in a steady-state conditions, total pressure (including contributions from both plasma
and neutrals) in a flux tube, P
tot
ft , can be considered constant (except rather narrow
region near the target where neutral friction with the target cannot be ignored)
whereas the distributions of plasma and neutral gas parameters along the flux tube
are determined by plasma and neutral transport processes and such input parameters
as the heat flux propagating through the flux tube to the target, q ft , and averaged
density of neutrals and ions, N
tot
ft , in the flux tube. For simplicity, we ignore, for now,
the effects of impurities.
We will be looking for the solution for the distributions of plasma and neutral gas
parameters along the flux tube as well as for the plasma flux to the target. To
elucidate the physics of the variation of plasma and neutral gas parameters, it
17.2
0
5
10
17.4
17.6
Pulse No: 34154
n –
e
P rad
div
P neut
div
div
P neut
PFR
P neut
D α
D α (out)
div
D α (in)
B exp
State
A exp
State
17.8
Time (s)
(10 21
ph m –2
s –1
)
(10 19
m –3
)
2
0.04
0.02
0
3
4
8
7
6
(mbar)
(MW)
18.0
18.2
JG99,106/1c/m
Fig. 9.7 Self-sustained
oscillations of (from top to
bottom) averaged density,
divertor radiation, neutral
density in inner divertor and
private region, and inner/
outer D α emission observed
in the JET tokamak.
(Reproduced with
permission from [27],
© American Physical
Society 1999)
9.2 Self-Sustained Divertor Plasma Oscillations
235
explained based on the theory developed in [29, 30].
The main idea of [29, 30], which we also will use for the analysis of tokamak
divertor plasma detachment, is based on the properties of the high recycling regime
of divertor operation. In these regimes, the neutral ionization mean-free path near the
targets becomes very small, smaller than the corresponding width of the SOL.
Therefore, the SOL can be considered as an ensemble of weakly interacting magnetic flux tubes filled with plasma and neutrals. The redistribution of plasma ions and
neutrals along the magnetic field in the flux tube occurs rather quickly (characteristic
time scales of ion and neutral redistribution are determined by the sound speed and
inverse ionization frequency respectively, which we will consider being much
smaller than the particle exchange time between different flux tubes). As a result,
in a steady-state conditions, total pressure (including contributions from both plasma
and neutrals) in a flux tube, P
tot
ft , can be considered constant (except rather narrow
region near the target where neutral friction with the target cannot be ignored)
whereas the distributions of plasma and neutral gas parameters along the flux tube
are determined by plasma and neutral transport processes and such input parameters
as the heat flux propagating through the flux tube to the target, q ft , and averaged
density of neutrals and ions, N
tot
ft , in the flux tube. For simplicity, we ignore, for now,
the effects of impurities.
We will be looking for the solution for the distributions of plasma and neutral gas
parameters along the flux tube as well as for the plasma flux to the target. To
elucidate the physics of the variation of plasma and neutral gas parameters, it
17.2
0
5
10
17.4
17.6
Pulse No: 34154
n –
e
P rad
div
P neut
div
div
P neut
PFR
P neut
D α
D α (out)
div
D α (in)
B exp
State
A exp
State
17.8
Time (s)
(10 21
ph m –2
s –1
)
(10 19
m –3
)
2
0.04
0.02
0
3
4
8
7
6
(mbar)
(MW)
18.0
18.2
JG99,106/1c/m
Fig. 9.7 Self-sustained
oscillations of (from top to
bottom) averaged density,
divertor radiation, neutral
density in inner divertor and
private region, and inner/
outer D α emission observed
in the JET tokamak.
(Reproduced with
permission from [27],
© American Physical
Society 1999)
9.2 Self-Sustained Divertor Plasma Oscillations
235