Irregular waveguides as open resonators

1981

An analytic theory has been derived for determining the eigenfrequencies, RF-field distribution and Q of the TE modes of a gyrotron mpq resonator consisting of a circular cylinder joined to a slowly tapered section. Explicit results are obtained for a linear taper. The cavity modes are found to have an RF-field distribution which is useful for prebunching the electron beam and enhancing efficiency. For high Q cavities, the cavity Q depends on axial mode number q as q-2 , which is important for mode discrimination. Proper selection of taper length is found to reduce the Q of high q modes, also aiding in mode discrimination.The present approach may be applied to other forms of weakly irregular cavities, such as cavities with nonlinear tapers.

Section: Discussionsupporting

confidence: 83%

Analytic theory of a tapered gyrotron resonator

1981

“…It can be shown that Eqs. (8) and (9) also apply to cavities with weakly irregular features at the ends for output coupling, or with slowly tapered cross sections, if we allow k 1 , k 1 l , and T to become functions of z (11,211. The dependence of T on z will be relatively weak for these cavities, and can be neglected.…”

Section: General Theorymentioning

confidence: 99%

Linear theory of an electron cyclotron maser operating at the fundamental

Kreischer

1980

“…Although Eq. (4) indicates that the highest gain for this device should be achieved at x = -1, nonlinear theory shows that the optimum efficiency occurs at a somewhat smaller value of x, usually in the range -3.0 : x -1.5.…”

Section: A Basic Theorymentioning

confidence: 99%

“…Since ,a standing wave can be decomposed into waves travelling in both the forward and backward directions, a gyrotron oscillator can, in principle, be excited at both the (+) and (-) resonances of Eq. (4).…”

Section: A Basic Theorymentioning

confidence: 99%

“…(6) is first solved to obtain the oscillation frequency w, and this value is used in Eq. (4) to calculate wc and subsequently the magnetic field. Although this simple analysis allows one to quickly determine the major excitation regions of a gyrotron, it is not accurate enough for a quantitative analysis, as will be shown in the next section.…”

Section: A Basic Theorymentioning

confidence: 99%

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Mode excitation in a gyrotron operating at the fundamental

Kreischer

1981

A simplified formalism has been developed for calculating the minimum starting currents of gyrotron modes, as well as the sequence of gyrotron modes excited as a function of resonator magnetic field. Unlike treatments ihich assume that modes are excited at the Doppler-shifted cyclotron frequency, this analysis is in good agreement with the exact solution of gyrotron linear theory. It is shown that each TEmpq mode is characterized by q strong excitation branches, and of these branches two predominate for q > 2. For the case of q = 1, only a single branch at the Doppler down-shifted frequency is strong. 'The cyclotron frequencies at which these branches are excited are found to vary with q, but their minimum starting currents are roughly independent of q if Q does not depend on q. A simple technique for constructing mode spectra is presented, and examples are given for the TE 0 3 1 and TE521 modes. In addition the effect of the time-varying gun voltages on the mode excitation spectra during the turn-on phase of a pulsed gyrotron has been investigated. The method in which the cathode and control anode voltages of the gun are increased to their final operating values can significantly affect which modes are excited in a gyrotron. Of the two startup procedures analyzed in detail, it was found that holding the cathode voltage steady at its final value while ramping-up the anode voltage helped to minimize the appearance of parasitic