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Electric field and flows at the edge of toroidal fusion plasmas (Abstract/Comunicazione in atti di convegno)
- Type
- Label
- Electric field and flows at the edge of toroidal fusion plasmas (Abstract/Comunicazione in atti di convegno) (literal)
- Anno
- 2013-01-01T00:00:00+01:00 (literal)
- Alternative label
G. Spizzo (2013)
Electric field and flows at the edge of toroidal fusion plasmas
in Joint 19th ISHW and 16th IEA-RFP workshop, Padova, Italy, September 16-20, 2013
(literal)
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- http://www.igi.cnr.it/ish_rfp_ws2013/sites/default/files/attachments/02_Detailed%20programme_chair.pdf; Invited IL17 30 min. (literal)
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- http://www.igi.cnr.it/ish_rfp_ws2013/sites/default/files/attachments/12_BookOfAbstracts.pdf (literal)
- Note
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- Consorzio RFX, Euratom-ENEA Association, Corso Stati Uniti, 4 35127 Padova - Italy (literal)
- Titolo
- Electric field and flows at the edge of toroidal fusion plasmas (literal)
- Abstract
- A series of issues in plasma physics, such as the presence of the Greenwald limit in
Tokamaks and reversed-field pinches (RFP) [
1
], the restriction of the collisionality window for
the application of the resonant magnetic perturbations (RMPs) in Tokamaks (in particular
linked to the role of X-points of edge islands, e.g. in TEXTOR [
2
]), and again the presence
of edge islands interacting with the bootstrap current in stellarators [
3
], seem to share the
same physical mechanism, namely, 3D flows generated by edge islands interacting with the
wall and embedded in a chaotic magnetic field.
Detailed measurements in the RFX-mod device (
a
= 0
.
46 m,
R
= 2 m) show that the 2D
map of the edge electric field response to the magnetic perturbation,
E
r
(
r
=
a,?,?
), exhibits
a ripple consistent with the helicity of the perturbation. In fact, using an appropriate helical
angle
u
=
m?
-
n?
+
?
m,n
, maps of
E
r
show a sinusoidal dependence,
E
r
=
?
E
r
sin
u
, or
equivalently,
E
r
is constant on helical flux surfaces [
4
]. The ripple of
E
r
is associated with a
huge convective cell with
v
(
a
)
6
= 0 which, in RFX and near the Greenwald limit, determines
a stagnation point for density and a reversal of the sign of
E
r
[
1
]. Similar reversal of
E
r
at
high collisionality is found also in Alcator C-mod [
5
].
From a theoretical point of view, the problem is how a perturbed toroidal flux of symmetry
m/n
the form
?
=
?
0
+
?
?
sin
u
gives rise to an ambipolar potential ? =
?
?sin
u
. On the
basis of a model developed with the guiding center code
Orbit
[
6
] and applied to RFX
and TEXTOR, we will show that, without perturbations, the canonical toroidal momentum
given by the guiding-center Lagrangian (Boozer coordinates) is conserved,
?
P
?
= 0. The
presence of a
m/n
perturbation
in any kind of device
breakes the simmetry,
?
P
?
?
?B
2
cos
u
,
and the resulting drift is proportional to the gyroradius
?
, so it is larger for ions (
?
i
?
e
).
Immediately an ambipolar potential arises to balance the drifts, and
will possess the same
symmetry as the original perturbation
. The residual dependence on
?
i/e
makes the potential
extremely sensitive to particle energy, ratio
T
e
/T
i
, and collisions, which seems to fit well-
established results in RFPs, Tokamaks and Stellarators. (literal)
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