1. Equilibrium Plasma Parameters Turbulent Wave Number Spectra
Microscopic Structure of Turbulence in the Torsatron TJ-K Carsten Lechte, HSX Plasma Laboratory, University of Wisconsin-Madison, USA Mirko Ramisch, Navid Mahdizadeh, Ulrich Stroth, IEAP, University Kiel, Germany
Motivation
Equilibrium Plasma Parameters
Turbulent Wave Number Spectra
Spectral Index
Energy Cascade in Fluids (3D)
Energy entered at large scales (Injection)
Total energy locally transferred to smaller scales by shearing (Inertial region)
Energy totally dissipated at smallest scales
 Power Spectrum ~ k-5/3
Spectrum of 2D-Turbulence
Kraichnan, Phys. Fluids, 1967
Enstrophy (conserved)
log( 1 / structure size)
log( energy density)
Injection
Floating potential (V)
Ion saturation current (mA)
Radial Tranport Profile
Motivation: turbulent transport in fusion plasmas
The experiment TJ-K: powerful turbulence diagnostics
Form and propagation of turbulent events
Spatial scales of fluctuations and transport
31 mm
3 mm
The Torsatron TJ-K
Krause, Lechte et. al., Rev. Sci. Instr. 2002
R = 0.6 m, a = 0.1 m
B < 0.25 T,
Te < 30 eV, ne < 51018 m-3
Heating: 2 kW Helicon (rf) or
Up to 6 kW ECRH (microwave)
Discharges up to 60 min
in H, He, Ar (variation of rs)
Langmuir probes employable
Everywhere
Formerly: TJ-IU, CIEMAT, Madrid
Conditional Averaging
TJ-K Spectra display broadband turbulence
Argon, rs = 31mm
Spectra shifted according to rs
spectral index -3  Enstrophy cascade
No space left for inverse energy cascade
Isat
rs-Scaling of Structure Sizes
Ffloat
Correlation length Lcorr
calculated by Fourier transform,
averaged over poloidal
Circumference increases with
drift scale
Turbulent Transport Scales
Power Spectrum
Probe Diagnostics
Isat
Argon 72 mT
rs = 31 mm
Helium 89 mT
rs = 10 mm
Hydrogen 96 mT
rs = 3 mm
Large quasi-coherent m=2 mode (2/7 rational), cross phase zero
Little radial propagation, mode appears in spectrum
Poloidal propagation determined by EB and diamagnetic drift
2D Movement
Stage for Probes
Equilibrium quantities
Correlation measurment: Structures
Transport G = n Eq / B
Helium, rs = 10mm
Lcorr
Lcorr
Lcorr
References and Acknowlegements
64 probes on flux surface: kq
Tilted view from above
Isat
[1] Lechte, C., Mahdizadeh, N., Ramisch, M., Stroth, U., Phys. Rev. Lett., submitted
[2] C. Lechte, S. Niedner, and U. Stroth, New J. Phys. 4, 34 (2002).
[3] Krause, N., Lechte, C., Niedner, S., Westphal, R., Stroth, U., Rev. Sci. Instrum. 73, 3474 (2002).
[4] S. Niedner, B. D. Scott, and U. Stroth, Plasma Phys. Controll. Fusion 44, (2002).
[5] B. Scott, Plasma Phys. Controll. Fusion 39, (1997).
We acknowledge financial support form Max-Planck Institut fuer Plasmaphysik. The TJ-K device was prodvided by CIEMAT, Madrid. We acknowledge A. Piel for support with the DAQ system.
Ffloat
H, He, Ar similar, Kolmogorov-like,
Transport maximum at correlation length of fluctuations
DAQ: A. Piel
Little radial propagation, cross phase zero, mode not in spectrum
Dipole structure, smaller than Argon
Cross Phases  0: Drift Waves in TJ-K
Measurement of all spatial scales at the same time
First time simultaneous n, F, G in fusion geometry
Argon
Hydrogen
Helium
Simulation with DALF3
MHD+Drift-Alfvén code
Highpass filtered data: smaller structures
Power Spectrum
Requests for Reprints
Ffloat (V)
Isat (mA)
Turbulent Mean EB Transport
Isat + -
Cross phase g governs mean transport