A J H Donn

A V Gorshkov

A V Sushkov

G M D Hogeweij

H J Van Der Meiden

I S Bel&apos

K A Razumova

S K Varshney

T Oyevaar

V F Andreev

V I Poznyak

V V Sannikov

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Investigation of internal transport barrier in OH mode with sawtooth oscillation 
and in discharges where sawtooth are suppressed by off -axis ECRH. 
I.S.Bel’bas1, V.F.Andreev1, A.V.Gorshkov1, V.I.Poznyak1, K.A.Razumova1, V.V.Sannikov1, 
A.V.Sushkov1, A.J.H.Donn 2, G.M.D.Hogeweij2, H.J. van der Meiden2,T. Oyevaar2, 
S.K.Varshney2. 
1. RRC ” Kurchatov  institute” , Moscow, Russia. 
2. FOM Institute for Plasma Physics, Nieuwegein, Netherlands. 
 
In this paper certain aspects of ITB physics in OH and ECRH plasmas in the T-10 tokamak are described.  
 
Introduction 
The formation and evolution of internal transport barriers (ITB, i.e. local regions with 
decreased heat and particle transport coeff icients or heat and particle flows) has been the 
subject of many studies over the last decade. The underlying mechanism(s) of ITBs are still 
not full y understood. Therefore core plasma diagnostics are being modernized, while new 
ones are being developed to resolve this problem [1, 2]. These efforts bring out on a new 
higher level understanding of the processes which lead to formation and existence of ITB. 
In this paper measurements are aimed at resolving the characteristic features of ITBs 
as well as their relation with rational values of the safety factor (q). This is done in T-10 
tokamak discharges with ohmic heating (OH), central and non central electron cyclotron 
resonance heating (ECRH). In the latter experiments sawtooth oscillations have been 
stabili zed. The experiments were carried out with the aid of electron cyclotron heating waves 
from two gyrotrons: 130 GHz (550 kW) and 140 GHz (900 kW) in the T-10 tokamak 
(R=1.5m, a = 0.3m, B#2.4 T, I # 150 k∃, ne#1.4&2*10
19 m-3).  The ECRH waves were 
launched into stationary OH plasmas, perpendicular to toroidal magnetic field. The cold 
resonance zone was placed on the plasma axis (for 130 GHz) or at half radius at the high 
magnetic field side (for 140 GHz). 
  The following diagnostics were used: a 21-channel radiometer using the 2nd 
harmonic X-mode of the electron-cyclotron emission (ECE, ∆r = 2&3 cm, ∆t = 0.02 ms), a 
single pulse Thomson scattering system (TS, ∆r = 0.6-1.2 cm), a semiconductor soft x-ray 
pulse height analysis system (PHA, Te(r = 0), ∆t = 50ms) for electron temperature (Te) 
measurements.  The PHA system was mainly used for the absolute calibration of ECE in the 
point r = 0, with a successive relative calibration of all  other channels on the known Te 
distribution in the OH stage. The soft x-ray emission (SXR) was also registered by a multi-
wire proportional detector (∆r =1–1.5 cm and ∆t = 0.05 ms). These chordal measurements  
32nd EPS Conference on Plasma Phys. Tarragona, 27 June - 1 July 2005 ECA Vol.29C, P-5.066  (2005)
-20 -10 0 10 20
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
T-10, #39470, on axis ECRH switching on
 
 
T
e,
ke
V
R-R0,cm
 δt = 0. ms
 δt = 1. ms
 δt = 2.2 ms
 δt = 4.4 ms
545 550 555 560
 
 
Ie
ce
,[
a.
u
.]
t,ms
#39470
 ECE27 h-1.37
-30 -20 -10 0 10 20 30
0,0
0,5
1,0
1,5
2,0
2,5
 
 
S
X
R
,[
a.
u
.]
R-R
0
,cm
  δτ = 0. ms
  δτ =0.7ms
  δτ =1.7ms
  δτ =2.7ms
  δτ =3.5ms
T-10, #39470, on axis ECRH switching on
546.93 550.77 554.61 558.45
 
Is
xr
,[
a.
u]
t,ms
#39470,SXR
 HWBD34,h0
were less noisy and more sensiti ve to Te changes in the core plasma, and have been used in 
non-abelized form. 
Results 
 To check hypothesis of ITB existence, central ECRH was switched on in the stable 
phase of an OH discharge, and the response on Te profile, measured by ECE and SXR, was 
studied. 
 
 
 
 
 
 
 
 
Fig.1. Time evolution of SXR radial distribution, after switching on central ECRH. 
The SXR signal increases after ECRH switch-on during ≈1.5 ms. This occurs only 
inside the radius limited by -7cm and 7cm (shot # 32913, <ne> = 1.4*10
19m-3), see fig.1. The 
radius of +/- 7 cm corresponds to the calculated q=1 radius. In pulses li ke #39470 (<ne> = 
2.*1019m-3) the SXR signal increases inside the zone -5 <r<+7.5 cm within a time interval ∆t 
≈ 4.5 ms. The sawtooth inversion radius (rrs) is -5 and +5.5 cm according to the SXR data. 
 
 
 
 
 
 
 
 
Fig.2 Te evolution after switch-on of central ECRH in the OH phase in two shots.
       The electron temperature measured by ECE showed a similar behavior (fig.2): during ∆t 
≈1.5 ms after switch-on of on-axis ECRH, the electron temperature increases by a factor ~1.7.  
32nd EPS 2005; I.S.BelBas et al. : Investigation of internal transport barrier in OH mode with sawtooth oscil... 2 of 4
-150 -100 -50 0 50 100 150
0
1
2
3
4
 
 
11.9cm
39470,555s
550 ms switch on-axis ECRH 
 T
e
(r), TS
T
e,
ke
V
z,mm
7.1cm
-200 -150 -100 -50 0 50 100 150 200
1
2
3
 
 
Te
,k
eV
z,mm
                 OH 
   39467
(4-6)ms  on-axis ECRH
 39474
-20 -15 -10 -5 0 5 10 15 20
 
 
Is
xr
-<
Is
xr
>
(5
55
-5
59
,m
s)
,[
a.
u
.]
R-R
0
,cm
#39470,555ms,SXR
 HWBD_1
 HWBD_2
8,cm
 This happens only in the region between -6.0cm and 10.4cm (# 32913). The temperature 
gradient increased approximately by a factor of 5-6 times in this shot (fig.2). 
      Estimations for the thermal conductivity in the barrier region (4&10 cm) yielded χeff ~0.03-
0.10 m2/sec. In discharge #39470 a similar Te increase is observed between -6cm and 13cm 
during ∆t ≈ 4.5 ms (~ one sawtooth period) after on-axis ECRH switch on. In this shot the 
electron temperature increased by a factor of ~1.4; its gradient approximately by a factor of 3. 
 
 
 
 
 
 
 
 
Fig.3 Te (TS) in OH and 4 ms after on-axis ECRH. fig.4 Te (TS) at 5ms after switch-on of on-axis ECRH. 
Thomson scattering was applied in discharges with <ne> = 2*10
19m-3 to obtain the Te 
profile in the OH stage and during the first ms of central ECRH. The existence of a zone with 
high dTe/dr (ITB) is apparent in fig.3. but growing temperature scope in first ms restricted 
within -10cm< z <6cm.( a systematic  Te (TS) excess over Te (ECE) is observed: ~400 eV in 
OH and ~600eV in ECRH plasmas, but  it doesn’t affect our conclusions on ITBs).   
Fig.5 Odd mode SXR oscillation, period ~500 µs. 
Non-monotonous Te(r) profiles were 
distinctly seen within the ITB zone in OH and 
ECRH discharges. The typical radial position of 
local Te peaks (“ears” ) is around r = rRS, while 
islands on SXR signals were present on r< rrs inside 
the barrier (fig.4,5).Under off-axis ECR heating the 
∋e profile becomes more flat but conserves typical 
for OH and on-axis ECRH appearance (also “ears” 
near ECRH deposition radius), see figure.6.  
32nd EPS 2005; I.S.BelBas et al. : Investigation of internal transport barrier in OH mode with sawtooth oscil... 3 of 4
-200 -150 -100 -50 0 50 100 150 200
0
1
2
3
Te
,k
eV
z,mm
T-10,    
OH
   39467
35 ms off axis  ECRH
    39469
q(r) ≈ 1
-0,4 -0,2 0,0 0,2 0,4
0,0
0,4
0,8
1,2
1,6
 
45+τ ms  after ECRH on
 0ms
 0.4
 0.8
 1.2
 1.6
 2.0
TEXTOR,
#97223 
off-axis ECRH
T e
 ,k
eV
τ
ECRH
ColdResonans
R-R0,m
 A similar picture was observed on TEXTOR [3], fig.7. In this case the Te profile is 
hollow in the centre with two maxima near the deposition zone of off-axis ECRH (#700kW, 
140 GHz near q(r)>#1, on 45 ms after the start of ECRH). 
 
 
 
 
 
 
 
 
 
 
Fig.6 Te (TS, T-10) in OH and steady-state off-axis 
ECRH. 
Fig.7 Hollow Te profiles (TS, Textor) averaged over 
two pulses and four spatial points. 
Conclusions 
During the first few ms (~one sawtooth period) of on-axis ECRH the temperature 
increases only inside q # 1, outside this radius Te rise starts after this time lag. Three different 
diagnostics have measured a clear electron temperature increase inside the sawtooth inversion 
radius during this time interval. The Thomson scattering displays non monotonous behavior 
Te(r) inside the region limited approximately r = rrs in OH and on-axis ECRH. Traces of such 
Te(r) behaviour are also observed on SXR (in OH and on-axis ECRH mode) and ECE signals. 
The explanation for this could be the presence of MHD islands. Analysis of the transient 
process after off-axis ECRH switch-on indicates that immediately outside the resonance 
surface q=1 a zone with reduced heat transport exist. The estimations of the heat conductivity 
coeff icient result in an inference: χeff has minimum in this region immediately after ECRH 
switch-on in OH mode. 
This work is done under assistance of grants NWO 047.016.015, RFFI 04-02-17562, 
INTAS 2001-2056. 
[1] A.V.Gorshkov, C.J.Barth et al., Abstracts of 11th Inter.Symp. on LAPD, Les-Houshes, 
France (2004), p.57. 
[2] H.J. van der Meiden et al., Rev.Sci.Instruments, 75, 3849(2004) 
[3] S.K. Varshney, Abstracts of 32 EPS Conf. on Plasma Physics,Tarragona,Spain (2005) 
32nd EPS 2005; I.S.BelBas et al. : Investigation of internal transport barrier in OH mode with sawtooth oscil... 4 of 4


Investigation of internal transport barrier in OH mode with sawtooth oscillation and in discharges where sawtooth are suppressed by off-axis ECRH

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Investigation of internal transport barrier in OH mode with sawtooth oscillation and in discharges where sawtooth are suppressed by off-axis ECRH

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