1. Turbulence wave number spectra reconstruction
from radial correlation reflectometry data at Tore Supra and FT-2 tokamaks
N. Kosolapova1,2,4, A. Altukhov1,4, A. Gurchenko1,4, E. Gusakov1,4, S. Heuraux2, R. Sabot3, F. Clairet3
1Ioffe Physical-Technical Institute of the Russian Academy of Sciences, Saint-Petersburg, Russia; 2Institut Jean Lamour, 7198 UMR CNRS, Nancy, France
3CEA, IRFM, F-13108, Saint Paul Les Durance, France; 4Saint-Petersburg State Polytechnical University, RLPAT, Saint-Petersburg, Russia
Scope
In this work we study plasma turbulence properties in a tokamak using radial correlation reflectometry (RCR). We aim to reconstruct the turbulence radial wave number spectrum, radial correlation length and turbulence spatial cross correlation function (CCF) from RCR measurements. This poster shows the preliminary results obtained at Tore Supra and FT-2 tokamaks.
Tore Supra
We have held RCR measurements using D-band ( GHz) X-mode reflectometer in equatorial plane from low field side of the Tore Supra tokamak (R=2.25m, a=0.72m).
Plasma density profile, shot #47669 (t=7s, Bt=3.8T, Ip=0.9MA, Te=2.3keV ) :
FT-2
We present results of two RCR measurements held from the high field side of the FT-2 tokamak (R=50cm, a=8cm),
I. O-mode probing in Ka-band (27-40 GHz) in equatorial plane of the torus (Bt=2.1T, Ip=19kA, Te=200eV). Plasma density profile (t=32ms) :
Conclusions
We have estimated plasma turbulence parameters at large Tore Supra and small FT-2 tokamaks. These RCR experiments are preliminary and allow us to determine the experimental parameters for future attempts.
RCR measurement in both equatorial plane of the tokamak and with a small shift give information on turbulence spectrum behavior and the scale of correlation length.
Theoretical approach has been developed for O-mode probing of linear profile and tested in case of close to experimental profile [3] therefore can be applied for X-mode probing presented here.
Equidistant spatial probing step is preferable to exponentially growing one which introduces difficulties into fast Fourier transform of the RCR CCF.
RCR diagnostic provides more precise measurements for smaller values of wavenumbers than e.g. Doppler reflectometry.
reflectometer
HFS
LFS
Introduction
Drift wave micro-turbulence is considered nowadays to be the main source of anomalous transport of heat and particles in magnetic fusion devices [1]. RCR is a microwave scattering technique for measuring the properties of electron density fluctuations in tokamaks [2].
Principle of RCR :
Correlation between RCR signals :
reflectometer
HFS
LFS
Plasma density evolution in time, r/a=0.31 :
Experimental RCR CCF :
Spectrum reconstruction :
n(r)
- reference frequency
- sweeping frequency
Future plans
We plan to study micro turbulence on JET machine in case of H-mode flat plasma density profiles and L-mode profiles knowing the required experimental parameters from simulations and previous experiments.
Simulations of the RCR experiments are planned for typical ITER plasma density profiles in various regimes.
- distance between cut offs
- signal from plasma
at reference frequency
- signal from plasma
at sweeping frequency r
Number of points within a window :
II. X-mode probing in V-band (50-75 GHz), antenna set shifted out of equatorial plane by 15mm. Plasma density profile (t=32ms) :
- averaging samples
- turbulence frequency
resolution
- probing frequencies
63 GHz
57GHz
reflectometer
Theoretical background
Signal RCR CCF
and turbulence CCF
(1D simulations in
Born approximation [3]) :
- turbulence correlation length;
- signal correlation length
Relation between radial wave number spectrum and RCR CCF for linear plasma density profile [4] :
- fluctuation wave number;
- conjugate error function.
Numerically reconstructed
radial wave number spectrum [3].
Synthetic Gaussian spectrum:
where
References
[1] B. Carreras, IEEE Trans. Plasma Sci. 24 (1997) 1281
[2] N. Bretz, Physical Fluids B4(8) (1992) 2414
[3] N. Kosolapova et al., Plasma Phys. Control. Fusion 54 (2012)
[4] E. Gusakov, N. Kosolapova, Plasma Phys. Control. Fusion 53 (2011)
[5] L. Vermare et al., C R Physique (2011)
[6] A. Altukhov et al., 39th EPS Conf. on Plasma Physics, Stockholm (2012)
HFS
LFS
Turbulence radial wave number spectrum reconstruction :
Doppler shift :
Experimental CCF coherence :
Turbulence spectrum :
Contacts
Natalia Kosolapova
Example of wavenumber spectrum measured
on Tore Supra, Doppler reflectometry,
shot #45511 [5].
Acknowledgements
This work is partly supported by Centre-of-Excellence grant , RF government grant 11.G and RFBR grants and , by the Saint-Petersburg Government, the French Government and Carnot ICEEL program, Russian Government Grant according to Ordinance No. 220 under Agreement No. 11.G with Ministry of Education and Science of Russia.
Turbulence CCF,
ELMFIRE fullwave modeling [6] :
Turbulence CCF reconstruction : Radial correlation length :
Turbulence CCF :
shot #47669
at r/a=0.31
shots #
at 0.3<r/a<0.8
on Tore Supra
Radial correlation length :
at r/a= on FT-2