A. N. Karpushov

B. P. Duval

Ch. Schlatter

Hans-Jürgen Hartfuss

Jozef Musielok

Marek J. Sadowski

Michel Dudeck

English

Crossref

 1
Ion Temperature Fluctuations in ELMy H-mode of the X3 
EC-heated Plasmas on TCV 
A.N.Karpushov, B.P.Duval, Ch.Schlatter 
Ecole Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas, 
Association Euratom-Confédération Suisse, CH-1015 Lausanne, Switzerland 
Abstract. This paper focuses on interpreting variations in the NPA measured energy distribution of neutral fluxes from 
the TCV high density H-mode plasma discharges with strong third harmonic electron cyclotron heating (PX3>PΩ). Two 
quasi-stationary regimes: ELMy H-mode and ELM-free H-mode, routinely and reproducibly obtained in TCV, with a 
plasma density 5-10×1019 m-3, electron temperature 2-3 keV and ion temperature of 0.7-1.0 keV. The ELMy X3-heated 
H-mode plasma on TCV is significantly perturbed by ELMs, sawteeth activity and modes. In X3-heated plasmas ELMs 
are characterised by increased amplitudes and lower frequencies than are typical in ohmic H-modes with strong sawteeth 
synchronised with ELM cycle. The energy losses per ELM can exceed the 15% of the total stored energy and the plasma 
density and electron temperature profiles were resolved during the ELM cycle. NPA measurements in the presence of 
ELMs and sawteeth cannot be explained with the classical theory of two-body Coulomb electron-ion collisions alone. 
Additional effects (such as a modification of the ion temperature radial profile and/or ion redistribution in the coordinate 
and velocity space due to plasma perturbations) must be considered. 
Keywords: Tokamak plasma, H-mode, ELMs, Neural particle analyser, Ion 
temperature. 
PACS: 52.55.Fa, 52.70.Nc, 52.25.Xz, 52.35.Py, 52.50.Sw 
INTRODUCTION 
The Tokamak à Configuration Variable (TCV) [1,2] is a medium-sized 
tokamak (R=0.88 m, a=0.25 m, Ip < 1 MA, BT < 1.45 T, plasma 
elongation 1-2.8) able to produce a plasma with the central electron 
density 0.5-15×1019 m-3, an electron temperature over 10 keV (with X2 
ECH heating) and bulk central ion temperatures of 0.25-1.0 keV. TCV 
is equipped with 3 MW of electron cyclotron heating (ECH) power at 
the second harmonic (X2: X-mode; 87.4 GHz, 6 gyrotrons, low field 
side launch) and 1.5 MW of a third harmonic ECH system (X3: X-
mode, 118 GHz, 3 gyrotrons, top launch).  
The operational domain of the H-mode plasma with and without 
edge localised modes (ELMs) has already been reported in [3]. The 
low-density (ne~4.2×1019 m−3) cut-off of X2 waves, prohibits exploring 
H-modes with X2 heating, where the working density is often too high. 
The higher cut-off density for X3 waves, ne~11×1019 m−3, permits the 
study of auxiliary heated H-modes on TCV. In the contrast with limited 
electron and ion temperatures coupling in low density X2 heated TCV 
plasmas (Te/Ti in the range of 5-30) X3 ECH heated discharges show 
increases in both (electron and ion temperatures) from ~1.0/0.5 keV to 
2-3/0.7-1.0 keV, respectively [4,5]. 
0.6 0.8 1 1.2
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
TCV #33654 @1.0s
Ip=-335kA,q=0.97/2.5/4.1
CNPA viewline
5-
ch
. N
PA
 v
ie
w
lin
e
 
FIGURE 1. Poloidal cross section of the TCV 
Plasma configuration. 
 2
The EC power deposition and current drive profiles are 
calculated using the TORAY ray-tracing code with magnetic 
equilibrium obtained from the LIUQE reconstruction code 
using measured Thomson scattering (TS) electron temperature 
and density profiles [6]. The total plasma energy content on 
TCV was calculated from a diamagnetic loop diagnostic. 
Two Neutral Particle Analysers (NPAs) are used on the 
TCV to obtain energy spectra of energetic neutrals escaping 
plasma resulting from the charge exchange of plasma ions with 
neutrals in the plasma. A "Five-Channel Energy Analyser of 
Atomic Particles" (5-ch.NPA) [7], operated on TCV in double 
electrical analysis mode, detects particles without atomic mass 
discrimination in the energy range 0.6-6.5 keV, with a time 
resolution up to 50 µs. A 28-channel "Compact Neutral Particle 
Analyser" (CNPA) [7] with mass and energy separation in E||B 
field simultaneously detects two mass species (11 channels for 
hydrogen and 17 for deuterium) in the 0.5-50 keV energy range 
with a time resolution in the 0.5-4.0 ms range. The DOUBLE-
TCV numerical code is used to model the energy spectra of 
neutrals leaving the plasma and entering the NPAs [8]. The 
main carbon impurity CVI ion temperature radial profiles were 
available from the CXRS [9] diagnostic. To improve the 
statistical accuracy, a coherent averaging technique [10] over 
several ELM events is been used in the analysis. 
X3-HEATED ELMY H-MODE PLASMA 
An Ohmic ELMy H-mode plasma in single null down 
diverted magnetic configuration (Fig.1), with ~220 kW of OH 
power and electron density of 5-7×1019 m−3, was used as 
target for X3 heating. 700-800 kW (two gyrotrons) of X3 EC 
power was used to sustain quasi-stationary plasma conditions, 
where an increase of the X3 power typically provokes a 
transition to an ELM-free regime [5]. The plasma current was 
300-350 kA and the electron temperature 1.9-2.1 keV before 
an ELM (and sawteeth crash) falling to 1.2-1.6 keV 
afterwards. Figure 2 shows some of the main plasma 
0
1
2
3
4
D
α
 (a
.u
.)
Overview of #33654
2
3
4
5
n e
L,
 1
01
9  m
-2
5
10
15
20
25
W
D
M
L
 (k
J)
1
1.5
2
Te
 (k
eV
)
0.2 0.4 0.6 0.8 1 1.2 1.4
0.5
1
1.5
2
Time (sec)
β t
or
 (%
)
750 kW delivered X3 power
Quasi-Stationary
ELMy H-mode
 
FIGURE 2. Overview of TCV shot 33654 with quasi-
stationary ELMy H-mode with X3 ECH. From top to 
bottom: the Dα light, line integrated density (vertical 
view line), the stored energy (magnetic – DML), 
electron temperature (Soft X-ray foil absorption flux – 
lines, Thomson scattering – dots) and βtor. 
0
500
1000
1500
2000
T e
 (e
V)
TS n
e
&T
e
 vs ELM phase #33654 @0.92-1.35s
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0
2
4
6
8
x 1019
ρ
n e
 (m
-3
)
ELM phase:0.03-0.25
ELM phase:0.70-0.95
ELM phase:0.03-0.25
ELM phase:0.70-0.95
 
FIGURE 3. Variation of electron temperature and density 
profiles during the ELM phase 
 
1400
1500
1600
1700
1800
1900
2000
Te
, e
V
#33654 @0.92-1.35s
-0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25
380
390
400
410
420
430
440
450
460
470
480
490
ELM phase
T iN
P
A
 (e
V)
NPA 1.55-3.47keV
Coulomb collisions
D-alpha
TS max
axis (fit)
Te Soft-X
A)
B)
 
FIGURE 4. Electron temperature (A) and TiNPA (B) 
variation during ELM-phase: “0” on x-axis – ELM, 
maximum of Dα emission; -1 – previous ELM; 1 – next 
ELM, ~20.5 ms. 
 3
parameters in a TCV discharge with a quasi-stationary ELMy H-mode phase (0.92-1.35 sec). Strong sawteeth 
activity together with ELMs with a period of 20.5±2.6 ms result in a loss of ~15-20 % of the total plasma energy per 
ELM (values in the range 4-5 % being typical for ohmic H-mode ELMs). According to TS [6] measurement (Fig.3) 
ELMs leads to a small (<15%) decrease of electron density at intermediates plasma radii (0.3<ρ<0.9) and to a fast 
(~2 ms) decrease of core electron temperature from 1.8-2.0 to ~1.5 keV followed by a relatively slow (~10 ms) 
recovery time (Fig.4-A). The edge electron temperature profiles do not change significantly (Fig.3).  
NPA MEASUREMENT 
The technique described in [7], and references within, has been used for interpretation of the NPA data. In this paper 
we use a “CX spectra” defined as  
))(/()()( EEEJEF cxdc ×= σ ,     (1) 
where σcx is the cross-section for charge exchange. The energy spectra of the passive atomic flux J(E) emitted from 
the plasma into the NPA is the sum of fluxes in the plasma column along the view line of the analyser : 
dzvvEfnnSEJ
a
a
iaiacxiia ⋅⋅⋅⋅⋅⋅⋅⋅Ω= ∫
−
γσ )()()( ,     (2) 
J(E) is proportional to the number of pulses detected by a given NPA channel (count-rate) N(E): 
))(/()()( det EEtENEJ α⋅∆⋅∆= . The temporal evolution of NPAs count-rates at several energies in quasi-
stationary ELMy phase are shown in Fig.5. Fast ELM-driven (<1 ms) flux-spikes are clearly distinguishable from 
the 5-ch. NPA followed by decrease in the count-rates with a few ms decay time to below pre-ELM values. The 
increase of neutral density caused by the ELM related transient increase in the plasma-wall interaction is sufficient 
to explain these temporal flux-spikes. 
For low density plasmas with a Maxwellian ion energy distribution, the ion temperature should be proportional to 
the logarithm of the Fdc slope; in most situations, including ELMy H-mode on the TCV, the plasma does not exhibit 
a single ion temperature and since attenuation may not be neglected the ion temperature, inferred from the slope of 
(Fdc), depends on the neutrals’ energy:  
dEFdET dc
NPA
i /)ln()(/1 =   (3) 
TiNPA from the NPA CX spectrum, with TCV plasma 
conditions typical for ELMy H-mode, is 1.5-2 times 
lower than core ion temperature (Fig.6). There is a 
significantly larger variation of the neutral fluxes at high 
energy (>2.5 keV) than for lower energies (characterised 
by TiNPA) during an ELM cycle (Fig.5, 4-B). 
0
2
4
6
8
10
12
5-
ch
.N
PA
 c
ou
nt
ra
te
s 
(M
H
z)
NPAs in #33654
0
0.05
0.1
0.15
0.2
C
N
PA
 c
ou
nt
ra
te
s 
(M
H
z)
0.95 1 1.05 1.1
300
350
400
450
500
Time (sec)
T iN
P
A
 (e
V)
#33654
0.86keV
1.14keV
1.66keV
2.33keV
3.21keV
D-alpha
0.57keV
1.06keV
1.58keV
2.12keV
2.71keV
3.36keV
4.24keV
D-alpha
NPA 0.85,1.13,1.65keV
NPA 1.13,1.65,2.34keV
NPA 1.65,2.34,3.20keV
CNPA 1.1-3.4keV
~100% variation
during ELM cycle
 
FIGURE 5. Variation of NPAs count-rates and TiNPA during 
a quasi-stationary ELMy phase. 
1000 1500 2000 2500 3000
1025
1026
1027
Energy (eV)
C
X-
flu
x 
/((
E)
1/
2 x
<s
ig
m
a 
v>
cx
) [
m
-5
 e
V-
1.
5 ]
5-ch.NPA energy spectrum #33654@0.92-1.35s
376eV@-7...-5ms
416eV@0.5...1m s
367eV@5...7ms
 
FIGURE 6. Measured energy distribution function (”NPA 
CX-spectra”) before (-7…-5 ms), during (0.5…1 ms) and 
after (5…7 ms) ELM.
 4
DISCUSSION 
The correlation of the neutral flux (J(E), eq.2) with 
ELMs could be caused by a several plasma effects: (a) 
increase of neutral density (na) due to ELM related 
transient increase of plasma-wall interaction; (b) plasma 
density (ni) variation; (c) variation of ion temperature 
(Ti) due to variation of electron temperature and power 
exchange between electrons and ions (Coulomb 
collisions); (d) modification of ion energy distribution 
function (fi(v3,ρ)) due to ion redistribution in coordinate 
and/or velocity space. DOUBLE-TCV simulations [8] 
show that for TCV ELMy H-mode discharges neutral 
fluxes with low (<1 keV) energies originate from the 
plasma edge (emissivity function have a maximum at 
ρ⊆[0.85…1.0]), whereas high energy fluxes originate 
from the plasma core (intermediate plasma radii, 
ρ⊆[0.75…0.85] for 3 keV). The transient increase of neutralisation probability should result in a stronger and faster 
increase of the neutral fluxes at lower energies (whereas experimental observations are opposite) and can thus not 
explain the increase of TiNPA during ELM cycle and the dependence of temporal variation of neutral fluxes with 
different energies (Fig.5,7). A plasma density variation of 10-15% is not sufficient to explain the observed increase 
in the neutral flux from decreased attenuation of the escaping plasma neutrals (increase of probability, γ). An 
analysis of the temporal behaviour of the Coulomb collisional electron-ion power balance indicates only a 2-3 % 
change of ion temperature mainly due the electron temperature variation (Fig.4). The variation of the TiNPA during 
ELM cycle (Fig.4,5) is much stronger corresponding to a 10-15 % increase in Ti.  
An ELM (or/and sawteeth) induced redistribution of ion remains the only considered candidate to explain NPA 
observations in the TCV ELMy H-mode plasma. Sawteeth crashes and ELMs are accompanied by a variation of the 
axial safety factor (q0) around 1 and plasma vertical and radial displacements of a few mm. Modes excitation could 
then result in strong ion mixing, especially of trapped ions. A set of experiments with NPA observations at different 
toroidal angles of view line, various q-profiles, etc. is planned for the upcoming TCV experimental campaign. 
ACKNOWLEDGMENTS 
The authors are grateful to Y.Martin and L.Porte for coordination of the TCV experimental program on “X3 
heated H-mode plasma”, and R.Behn for support in analysis of Thomson scattering data.  
This work was partly supported by the Swiss National Science Foundation. 
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1. F. Hofmann et al., Plasma Phys. Controlled Fusion 36, B277-B287 (1994). 
2. T. Goodman et al., Nucl. Fusion 43, 1619-1631 (2003). 
3. A.W. Degeling, et al., Plasma Phys. Control. Fusion 43, 1671-1698 (2001) 
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5. L. Porte and the TCV Team, Proc. 17th Topical Conference on Radio Frequency Power in Plasmas, Clearwater (Florida) 
2007, AIP Conference Proceedings, Volume 933, pp.385-392 (2007) 
6. R.Behn et al,. Plasma Phys. Control. Fusion 49, 1289-1308 (2007) 
7. A.N. Karpushov, et al., Rev. Sci. Instrum 77, 033504 (2006) 
8. Ch. Schlatter, B.P. Duval and A.N. Karpushov, Plasma Phys. Control. Fusion 48, 1765–1785(2006) 
9. P. Bosshard, et al.,, Proc. 29th EPS Conference on Controlled Fusion and Plasma Physics, Montreux, Switzerland, June 
2002, ECA Vol. 26B, P-4.120 (2002)  
10. H.F. Tammen, et.al., Rev. Sci. Instrum 66(1), 327-329 (1995) 
 
-100 0 100 200 300 400
0
1
2
3
4
5
6
Tim e (rel.to ELM) (µs)
5-
ch
.N
PA
 c
ou
nt
ra
te
s 
(M
H
z)
NPA #34187@0.5-0.7s, counting time 50µs
0.86 keV
1.14 keV
1.66 keV
2.33 keV
3.21 keV
 
FIGURE 7. 5-ch. NPA count-rates in Ohmic ELMy H-mode 
with a 50µs time resolution 


Ion Temperature Fluctuations in ELMy H-mode of the X3 EC-heated Plasmas on TCV

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Ion Temperature Fluctuations in ELMy H-mode of the X3 EC-heated Plasmas on TCV

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