This article reviews digital spectral analysis techniques that yield experimental insight into plasma turbulence. Methods to quantify the statistical properties of the fluctuations and to measure the particle and heat flux caused by electrostatic fluctuations are presented. Furthermore, analysis techniques to study the nonlinear coupling process of turbulence and the redistribution of energy among the different modes are discussed. The impact of the analysis techniques on fusion research is demonstrated with experimental results collected with Langmuir probes, heavy-ion beam probes, and laser scattering in the tokamak TEXT. Special emphasis is given to the characterization of the wavenumber distribution and the correlation lengths in all toroidal directions, including a first measurement of k∥ in a tokamak.

A quantitative comparison of the fluctuation-induced energy flux with the total energy flux has been made in the edge region of the TEXT tokamak using fluctuation measurements from Langmuir, heavyion-beam, and magnetic probes. At all but the lowest densities the convected energy flux due to electrostatic fluctuations dominates the energy losses caused by plasma transport. Energy loss through magnetic fluctuations is insignificant in the edge region. PACS numbers: 52.55.Fa, 52.25.Gj It is well known that the energy lost from tokamaks through transport processes is much larger than predicted by neoclassical theory (Refs. 1 and 2, and references therein). Plasma turbulence is generally invoked to account for the anomalous losses. Unlike neoclassical transport which depends on the mean plasma parameters and collisions, turbulent transport results from Auctuations in plasma parameters (electric and magnetic fields, density, temperature, etc.). Fluctuation-induced particle and energy Auxes have been measured in the edge region of several tokamaks.It has been established in the Texas Experimental Tokamak (TEXT) that the total particle flux in the edge plasma is primarily due to electrostatic fluctuations.In this work we investigate the role Auctuations play in the total edge energy transport.Specifically, we compare radial profiles of the energy Aux due to Auctuations with profiles of the total plasma energy flux in the edge of TEXT. The importance of the edge region is demonstrated by the improved global energy confinement in 0-mode discharges, TFTR supershots, and recent Ohmic discharges, in ASDEX. ' TEXT is a medium size tokamak with a major radius R of 1 m and a minor radius a of 0.26 m defined by a full poloidal limiter. The data presented here were taken in steady-state, Ohmically heated discharges with sawteeth and low Mirnov activity. The radial profiles were collected over a number of similar shots, with at least three shots for each radial position. The density, potential, and temperature fluctuation data were collected with Langmuir probes (LP) in the far edge region of the discharge and in the scrape-oA' layer (SOL) outside of the outermost closed flux surface (r/a-= 1). With a heavy-ion-beam probe'' (HIBP) the density and potential fluctuation data can be measured in the plasma interior. We use data in to r/a=0. 8. Magnetic fluctuation data were collected with magnetic probes (MP) located in the SOL. The Auctuation measurements of both the LP and the HIBP were taken approximately 180 away in the toroidal direction from the poloidal limiter; the MP was positioned about halfway between these diagnostics and the limiter. The fluctuation data were digi-0.8 CA 0.6 CD O 0 4 O V CD ) 0 2 C5 CD n n Te Te 0.0 0.8 0.9 r/a t 1.2FICs. I. Relative fluxuation levels of density n/n, plasma potential ep~~/ke T"electron temperature T,/T"and magnetic field 8,/8&, as functions of radius. Filled symbols represent data from Langmuir probes, and open symbols from the HIBP. tized with a 10-bit digitizer at a I-ps sampling in...

Externally applied resonant magnetic fields have been used on TEXT to modify the particle flux and the radial electric field near the plasma edge. Magnetic fields with primary mode numbers m/n = 7/3 and 7/2, and an average radial field amplitude <|b r |/B^> = 0.1% have been employed. This perturbation produces mixed islands and stochastic regions at the plasma edge