The gridded electromagnet probe

We attempted to measure the anisotropy in the electron distribution function in magnetized plasma by exploiting the adiabatic invariance of the electron's magnetic moment with a probe comprising a grid, a collector, and an inertially cooled electromagnet. The electric mirror force of the grid, which is located at the electromagnet throat, reduces the demand on the magnetic mirror force and thereby on the electromagnet current, which then allows for the construction of a compact probe that can be inserted inside the plasma chamber. An analysis of the effects of space charge inside the grid-collector cavity revealed that the size of the probe's entrance aperture, b, which gives the size of the plasma beam inside the probe, should be chosen to be within a factor of ten of the electron Debye-length [lambda][sub]De. In addition, an analysis of the discrete structure of the grid showed that the mesh wire spacing d should be chosen to be much less than [lambda][sub]De. Also, the wire thickness t should be chosen to be much less than d . We built a probe with a grid of tungsten wires with dimensions, t = 5,[mu]m and d = 200[mu]m . We then tested this probe in a hydrogen plasma immersed in a background magnetic field of B [approximately] 1kG. The plasma was heated by microwaves via the electron cyclotron resonance. It was characterized by a density and temperature equal to n[sub]e [approximately] 10¹⁰ cm⁻³ and T[sub]e [approximately] 10eV, respectively, which gave [lambda][sub]De [approximately] 300[mu]m. The collector's current-voltage characteristic demonstrated the interaction between the electric barrier at the collector and the hybrid electric-magnetic barrier at the grid, thereby establishing the basic principles of the probe.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Nuclear Engineering

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2003

Author dc:creator

• Shadman, K. (Khashayar), 1972-

Advisor dc:contributor.advisor

• Jeffrey P. Freidberg.

• Nuclear Engineering.

Statement dc:rights

• 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.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/17041

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/17041