Magnetron theory
- Science Application International Corporation, McLean, Virginia 22102 (United States)
A guiding center fluid theory is applied to model steady-state, single mode, high-power magnetron operation. A hub of uniform, prescribed density, feeds the current spokes. The spoke charge follows from the continuity equation and the incompressibility of the guiding center flow. Included are the spoke self-fields (DC and AC), obtained by an expansion around the unperturbed (zero-spoke charge) flow in powers of {nu}/{ital V}{sub 1}, {nu}, and {ital V}{sub 1} being the effective charge density and AC amplitude. The spoke current is obtained as a nonlinear function of the detuning from the synchronous (Buneman{endash}Hartree, BH) voltage {ital V}{sub {ital s}}; the spoke charge is included in the self-consistent definition of {ital V}{sub {ital s}}. It is shown that there is a DC voltage region of width {parallel}{ital V}{minus}{ital V}{sub {ital s}}{parallel}{approximately}{ital V}{sub 1}, where the spoke width is constant and the spoke current is simply proportional to the AC voltage. The magnetron characteristic curves are {open_quotes} flat{close_quotes} in that range, and are approximated by a linear expansion around {ital V}{sub {ital s}}. The derived formulas differ from earlier results [J. F. Hull, in {ital Cross} {ital Field} {ital Microwave} {ital Devices}] in (a) there is no current cutoff at synchronism; the tube operates well below as well above the BH voltage; (b) the characteristics are single valued within the synchronous voltage range; (c) the hub top is not treated as virtual cathode; and (d) the hub density is not equal to the Brillouin density; comparisons with tube measurements show the best agreement for hub density near half the Brillouin density. It is also shown that at low space charge and low power the gain curve is symmetric relative to the voltage (frequency) detuning. While symmetry is broken at high-power/high space charge magnetron operation, the BH voltage remains between the current cutoff voltages. (Abstract Truncated)
- OSTI ID:
- 459848
- Journal Information:
- Physics of Plasmas, Vol. 3, Issue 3; Other Information: PBD: Mar 1996
- Country of Publication:
- United States
- Language:
- English
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