RELATIONSHIP BETWEEN MAGNETIC FIELD STRUCTURE AND PLASMA DENSITY PROFILE IN LHD EDGE REGION

H.Matsuura,S.Iguchi,T.Morisaki1),K.Tanaka1),A.Komori1),O.Motojima1),LHD Experimental Group1)

Osaka Prefecture University,Sakai,Osaka 599-8531,Japan
1)National Institute for Fusion Science, Toki, Gifu 509-5292, Japan

The last closed flux surface (LCFS), which define the boundary between nested magnetic surfaces and the so-called separatrix layer is one of the key parameters for the coil winding design of the helical experimental devices. Due to the complicated ergodic properties, however, its position is still unclear[1]. Moreover, this ergodicity is thought to change with the magnetic axis shift or the plasma beta effect.

In the 6th experimental campagin, detailed electron density profiles of the LHD edge region are measured with a 20keV lithium beam probe[2]. Especially in low density plasma, density profiles are thought to show some properties of the vacuum magnetic field ergodicity.

Various methods such as conection length, Kolmogorov entropy, and so on have been proposed and tried to study the helical magnetic field ergodicity. In this paper, we calculate the Poincare map of vacuum field lines and their Lyapunov exponents for various LHD magnetic configuration[3]. Luapunov exponents are the measure of the distance in the phase space between the reference orbit and the neighborhood point. The comparation of these calculation and density profiles is now under study. Its result will be shown in the conference.

References

[1]H.Akao,J.Phys.Soc.Jpn.,59(1990)1633
[2]T.Morisaki et al.,Proc. 30th EPS conf. on Cont. Fusion and Plasma Phys.,(2003,Saint Petersburg)
[3]H.Matsuura et al.,J.Plasma Fusion Res. SERIES,1(1998)213

This work is performed with the support and under the auspices of the NIFS Collaborative Research Program.