Characterization of low-frequency electric potential oscillations near the edge of a plasma confined by a levitated magnetic dipole
Name
535773556-MIT.pdf
Description
Full printable version
Size
34.57 MB
Format
Adobe PDF
Checksum (MD5)
71565ec99ff845bf3381b5ec7a6b3d6e
Author(s)
Bergmann, Ryan M
Advisor(s)
Jay Kesner and Darren T. Garnier.
Date Issued
2009
Publisher
Massachusetts Institute of Technology
Abstract
A vertically adjustable electrostatic probe array was made to observe the previously seen low-frequency angular oscillations in LDX and identify if they are related to computationally expected convective cells. The array rests one meter from the centerline and measures edge fluctuations at field lines near the separatrix. It spans ninety degrees and has 24 probes mounted on it for total probe tip separation of 6.8cm. Bispectral analysis of the fluctuations show that that an inverse cascade of energy is present at times in LDX. The cascade transfers energy from small spatial scale structures to large scale structures. The wavenumber spectrum is xc k-1.4 to cx k-25 at high wavenumbers, which encompasses the inverse energy cascade regime of c k-5/3. The plasma also has a linear dispersion relation which gives a phase velocity of 2-16 k. This phase velocity is inversely correlated with neutral gas pressure in the vessel. The velocity also has a local maximum at 5 pTorr which is the pressure that produces maximum plasma density. The radial E x B drift velocities are observed to have a mean near zero, which indicates a closed structure like a convective cell. The instantaneous radial drift velocities are on the order of the ion sound speed, which is 35 km/s.
Description
Thesis (S.M. and S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 95-96).
Subjects
Nuclear Science and Engineering.
MIT Department
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
Terms of Use
M.I.T. theses are protected by
copyright. They may be viewed from this source for any purpose, but
reproduction or distribution in any format is prohibited without written
permission. See provided URL for inquiries about permission.
copyright. They may be viewed from this source for any purpose, but
reproduction or distribution in any format is prohibited without written
permission. See provided URL for inquiries about permission.
Persistent DSpace Link
