Edge Localized Modes propagation and
fluctuations in the JET SOL region
presented by
Bruno Gonçalves
EURATOM/IST, Portugal
Contributors
C. Hidalgo, M.Pedrosa, B. Gonçalves*, C. Silva*, R. Balbín,
M. Hron**
Euratom-Ciemat, 28040 Madrid, Spain
*Euratom/IST, 1049-001 Lisbon, Portugal
**Euratom-IPP.CR, Prague, Czech Republic
A.Loarte
EFDA – Garching, Max-Planck-Institut für Plasmaphysik Germany
K. Erents, G. F. Matthews
Euratom-UKAEA, United Kingdom
Motivation
•Understanding the impact of ELMs induced particle and energy
fluxes in the divertor plates remains as one of the major concerns in
the fusion community for future devices like ITER.
•The possible link between the amplitude and the radial
propagation of ELMs might have an important consequence in the
extrapolation of ELMs impact in the divertor plates on future
devices.
•This work presents the investigation of the radial propagation of
ELMs in JET SOL region.
Experimental set-up
•The experimental set up consists of
arrays of Langmuir probes radially
separated 0.5 cm, allowing a unique
investigation of the propagation of
ELMs events and fluctuations with
good spatial ( 0.3 cm) and temporal
(2 s) resolution.
•Plasmas conditions:
B = 1 / 2.5,
Ip = 1 - 2.5 MA,
Ptotal = 2 – 13 MW
Radial profiles during ELMs in JET
Perturbations in ion saturation current and potential signals induced by the
appearance of ELMS are observed up to 7 cm beyond the LCFS.
This result implies that the ELMs convective SOL-width is much broader than
the typical SOL-width measured during time intervals between ELMs.
Radial propagation of ELMs: time delay measurements
•
The shape of ELMs as
measured by Langmuir
probes with high frequency
ADCs shows evidence of
high frequency structures.
•
Typical time delays are in
the range of 2 - 10 s for
sensors radially separated
0.5 cm. This implies a radial
velocity in the range of 1000
m / s.
Dynamical relation
between ExB turbulent transport
and gradients in ELMy discharges:
The radial effective velocity of ELMs
(a.u.)
JET #51115
0.4
Ha
0.2
0.2
in
(A)
0.0
19
2 -1
(10 m s )
out
Is -Is
1000
500
0
-500
GExB
50.02
50.04
time (s)
50.06
• Steep local gradients are
linked with ELMs radial
propagation
inner
outer
˜
˜
˜
 Is (t )  [ Is (t )  Is (t )]
• Experimental results show a
strong coupling between ExB
transport and ELMs.
GExB (t)  n˜ (t) E˜ (t) / B
Interplay between fluctuations in gradients and transport
in ELMy discharges
Radial velocity:
Radial local
gradient:
v eff   I˜s E˜   /I s BT
inner
outer
˜
˜
˜
 Is (t )  [ Is (t )  Is (t )]
What is the expected value of the radial velocity of ELMs
for a given density gradient (E[veff | r IS])?
Radial propagation of ELMs: influence of amplitude
JET #51115
JET #51115
0.5
(a)
0.2
0.2
0.0
46.53
46.54
46.55
46.56
0.5
46.57
(b)
Is (A)
Ha intensity
0.3
0.1
46.52
(a)
0.4
0.4
46.52
46.53
46.54
46.55
46.56
(b)
0.4
0.4
0.3
0.2
0.2
0.0
0.1
50.02
50.03
50.04
50.05
time (s)
50.06
50.07
50.02
46.57
50.03
50.04
50.05
50.06
time (s)
The influence of the size of ELM events (as measured by the
perturbations in local gradients) on the radial propagation have been
recently investigated in JET plasmas (B = 2.6 T, Ptotal=13 MW ).
50.07
JET #51115
t = 46 s
t = 50 s
-1
PDF (A )
10
1
0.1
-0.10
-0.05
0.00
0.05
out
Is -Is (A)
0.10
0.00
0.05
out
Is -Is (A)
0.10
in
The radial velocity is close
to 20 m/s for small
deviations
from
the
averaged gradient but
increases up to 2000 m/s
for large ELM transport
events.
JET #51115
eff
-1
E[ vr | gradr Is ] (ms )
2500
t = 46 s
t = 50 s
2000
1500
1000
500
0
-0.10
-0.05
in
Preliminary studies show that
the radial velocity of ELMs
increases with the ELM size
(.i.e. Size of perturbations in
local gradients).
Poloidal electric fields and effective radial velocity
JET #51115
2000
1500
1000
500
0
-0.10
JET #51115
t = 46 s
t = 50 s
E[ E | gradr Is ] (V/m)
eff
-1
E[ vr | gradr Is ] (ms )
2500
4000
-0.05
0.00
0.05
out
Is -Is (A)
in
0.10
3000
t = 46 s
t = 50 s
2000
1000
0
-1000
-0.10
BT = 2.6 T
-0.05
0.00
out
Is -Is (A)
0.05
0.10
in
The effective radial velocity is consistent with the ExB drift velocity.
Radial and poloidal electric fields during ELMs
propagation
JET #51115
3000
4000
t = 46 s
t = 50 s
2000
1000
0
-1000
-0.10
BT = 2.6 T
-0.05
0.00
in
out
Is -Is (A)
0.05
0.10
E[ Er | gradr Is ] (V/m)
E[ E | gradr Is ] (V/m)
4000
JET #51115
t = 46 s
t = 50 s
3000
2000
1000
0
-1000
-0.10
-0.05
0.00
0.05
out
Is -Is (A)
in
0.10
ErxB radial propagation is larger than ExB poloidal propagation
0.2 r-rLCFS = 2 cm
0.0
JET #51116
0.2 r-rLCFS = 2 cm
0.0
JET #51115
0.2 r-rLCFS = 4 cm
0.0
JET #51113
0.2 r-rLCFS = 6 cm
0.0
JET #51112
50.02
50.03
50.04
time (s)
50.05
50.06
50.07
1500
-1
JET #51117
eff
0.2 r-rLCFS = 1 cm
0.0
E[ vr | gradr Is ] (ms )
Is (A)
Radial propagation versus radius in the SOL
1000
#51117 (50 s)
#51116 (50 s)
#51115 (50 s)
#51113 (50 s)
#51112 (50 s)
500
0
-0.10
-0.05
0.00
0.05
out
Is -Is (A)
in
The maximum radial speed of ELMs seems to be independent
of the distance to the LCFS.
0.10
1000
4000
#51117 (50 s)
#51116 (50 s)
#51115 (50 s)
#51113 (50 s)
#51112 (50 s)
E[ E | gradr Is ] (V/m)
eff
-1
E[ vr | gradr Is ] (ms )
1500
500
0
-0.10
-0.05
0.00
0.05
in
out
Is -Is (A)
0.10
#51117
#51116
#51115
#51113
#51112
3000
2000
1000
0
-1000
-0.10
-0.05
0.00
0.05
out
Is -Is (A)
in
0.10
The maximum poloidal electric field linked to ELMs seems to be
independent of the distance to the LCFS
ELMs versus large turbulent transport events
L-mode
1500
1500
H-mode
t = 46 s
t = 50 s
-1
-1
E[ vr | gradr Is ] (ms )
#54008
#53983
E[ vr | gradr Is ] (ms )
JET #51115
1000
500
eff
eff
500
1000
0
-0.15 -0.10 -0.05 0.00 0.05
in
out
Is -Is (A)
0.10
0.15
0
-0.15 -0.10 -0.05 0.00 0.05
in
out
Is -Is (A)
0.10
0.15
Large transport events in L-mode plasmas have radial velocities rather similar
to ELMs radial speed.
The dynamical link between fluctuations in gradients and turbulent transport
is affected by heating power and sheared radial electric fields, in L-mode
plasmas.
C. Hidalgo, B. Gonçalves, M.A. Pedrosa et al. IAEA, Oct. 2002
Radial versus parallel propagation
ELMs arrival time to the plasma wall can be comparable to, or even
smaller than, the characteristic time of transport to the divertor plates (in
the range of 0.1 – 0.5 ms).
In these circumstances we have to consider the competition between
parallel and radial transport of ELMs to explain and predict particle and
energy fluxes onto the divertor plates in ITER.
The large radial speed of ELMs might explain experimental results
showing that only about 60 % of the energy losses due to large type I
ELMs arrives to the divertor plates.
ELMs and Mach probe measurements
During the appearance of ELMs, perturbations in the ion saturation current
are larger (about a factor of 3) in the probe facing the outer divertor (e.g.
region of bad curvature) than in the probe facing the inner divertor (e.g.
region of good curvature). This result implies that ELMs have strong
ballooning character.
Conclusions
•
ELMs propagate radially with an effective velocity in the range of
1000 m/s.
•
ELMs arrival time to the plasma wall can be comparable to, or
even smaller than, the characteristic time of transport to the
divertor plates (in the range of (0.1 – 0.5 ms); in these
circumstances we have to consider the competition between
parallel and radial transport of ELMs to explain and predict
particle and energy fluxes onto the divertor plates in ITER.
•
Experimental results suggest a link between the radial velocity and
the size of ELMs transport events. This result might have an
important consequence in the extrapolation of the impact of ELM
in the divertor plates on future devices.