Speaker
Oleg Krutkin
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1009.pdf
Nonlinear Doppler reflectometry power response.
O. L. Krutkin1,2, E. Z. Gusakov1, S Heuraux2, C Lechte3
1
Ioffe Institute, St Petersburg, Russia
2
Institut Jean Lamour UMR 7198 CNRS, Université de Lorraine, 54000 Nancy, France
3
Institute of Interfacial Process Eng. and Plasma Technology, 70569 Stuttgart, Germany
Understanding and control of plasma turbulence is one of the major goals of fusion
research, since the turbulent transport plays a key role in plasma confinement. One of the
tools used for turbulence characterization is Doppler reflectometry, which utilizes a
microwave beam to probe the plasma at oblique incidence with respect to the magnetic
surface. The backscattered signal can provide turbulence "poloidal" wavenumber spectrum
and its Doppler shift, which is connected to poloidal velocity of plasma. However,
interpretation of experimental measurements is not always straightforward.
In case of small turbulence level, when Born approximation over the turbulence
amplitude is applicable, the diagnostic response was extensively studied both analytically [1]
and numerically [2]. In the case of strong turbulence, when multiple forward scattering is
dominant, analytical predictions have been made [3] and nonlinear effects were observed in
full-wave simulations [4, 5]. Recently, intermediate regime with power of scattering signal
enhanced due to high order nonlinear scattering effects was observed numerically in full-wave
computations utilizing IPF-FD3D code [4] and interpreted using physical optics model [6].
While simple and effective, this model possesses a limited domain of validity because it only
takes into account plasma-wave interaction in the very vicinity of the cutoff.
To overcome this limitation, transition from linear regime to regime with enhanced
power is studied in the present paper analytically using the first (Born) and the second order
of approximation over the turbulence amplitude. Transition criteria are derived and their
discrepancies from the physical optics model predictions are discussed. To confirm analytical
results, full-wave numerical modeling with IPF-FD3D code [4] is performed.
The research was supported by RSF grant 17-12-01110, Verdansly scholarship for PhD
students and by the Ioffe institute.
[1] E Z Gusakov and A V Surkov Plasma Phys. Control. Fusion 46 (2004)1143
[2] Hirsch M, Holzhauer E, Baldzuhn J, Kurzan B and Scott B Plasma Phys. Control. Fusion 43 (2001)1641
[3] E Z Gusakov, A.V. Surkov, and A Yu Popov Plasma Phys. Control. Fusion 47 (2005) 959
[4] C Lechte et al Plasma Phys. Control. Fusion 59 (2017) 075006
[5] O. L. Krutkin, A.B. Altukhov, A.D. Gurchenko, et al. Proc. 44th EPS Conf. on Contr. Fusion and Plasma
Physics (Belfast) ECA vol. 41F (2017) P2.108
[6] J R Pinzón et al Plasma Phys. Control. Fusion 59 (2017) 035005
