Abstract/Details

## Microwave reflectometry on the Advanced Toroidal Facility to measure density fluctuations and their radial correlation lengths

Hanson, Gregory Richard.   Georgia Institute of Technology ProQuest Dissertations Publishing,  1991. 9206080.

### Abstract (summary)

A two-frequency correlation reflectometer has been designed, built, and operated on the Advanced Toroidal Facility (ATF) to measure plasma density fluctuations. This reflectometer uses quadrature phase detection to allow true phase measurement of the reflected microwave signal (probing beam). By measuring the phase fluctuations in the reflected probing beam, it is possible to estimate the amplitude of the density fluctuations. Simultaneous two-frequency operation makes it possible to measure the coherence between fluctuations at two radially separated cutoff layers, from which the radial correlation lengths and wave numbers can be estimated.

This reflectometer has been used to study the density fluctuations in the edge density gradient region in low-density ATF plasmas with electron cyclotron heating (ECH). These studies have revealed globally coherent turbulence having a radial correlation length $\sim$5 cm, a radial wave number k$\sb{r}$ $\sim$ 0 cm$\sp{-1}$, and a poloidal wave number k$\sb\theta$ $\sim$ 1 cm$\sp{-1}$. The fluctuation rms amplitude reaches a maximum ($\sim$5%) at the plasma edge and decreases with radius to a level of $\sbsp{\sim}{<}$1%. Simultaneous measurements with the reflectometer, heavy ion beam probe and fast reciprocating Langmuir probe, provided verification of the measured fluctuation amplitude.

A comparison of the results of these measurements with theoretical models shows that the pressure-gradient-driven resistive interchange instabilities are a likely cause of the observed turbulence.

### Indexing (details)

Subject
Fluid dynamics;
Gases;
Plasma physics
Classification
0759: Plasma physics
Identifier / keyword
Pure sciences
Title
Microwave reflectometry on the Advanced Toroidal Facility to measure density fluctuations and their radial correlation lengths
Author
Hanson, Gregory Richard
Number of pages
262
Degree date
1991
School code
0078
Source
DAI-B 52/09, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
979-8-207-54057-3
Thomas, C. E.
University/institution
Georgia Institute of Technology
University location
United States -- Georgia
Degree
Ph.D.
Source type
Dissertation or Thesis
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
9206080
ProQuest document ID
303924742