Output Cavity Research Articles

Present status of a 17.1-GHz four-cavity frequency-doubling coaxial gyroklystron design

A design of a Ku-band 17.1-GHz four-cavity coaxial gyroklystron amplifier for driving future linear colliders is presented. The X-band input cavity operates in the TE/sub 0.11/ mode, whereas the remaining three cavities (buncher, penultimate, and output) operate in the TE/sub 021/ mode, doubling the frequency of the input signal. The electron beam parameters are the following: current of 540 A, voltage of 460 kV, perpendicular-to-parallel velocity ratio of 1.5, and a parallel velocity spread of 6.4%. The output cavity has been simulated as (1) zero-drive unstable with Q-factor of 320 and (2) zero-drive stable with Q-factor of 250. The simulations show that the maximum efficiency in the first case is 37.4%, and in the second one is 34.4%. In both cases, a high gain of 60 dB at a 100-MW output power level can be realized.

Design of a 34-GHz second-harmonic coaxial gyroklystron experiment for accelerator applications

Presents the complete design of a 34-GHz, four-cavity coaxial gyroklystron experiment. The 500-kV, 300-A beam is produced by a double anode magnetron injection gun (MIGc) with an average perpendicular-to-parallel velocity ratio of 1.5 and a parallel velocity spread of less than 5%. The microwave circuit has a first-harmonic TE/sub 011/ input cavity that is driven at 17.135 GHz. It has buncher, penultimate, and output cavities that operate In the TE/sub 021/-mode and are resonant near the second harmonic of the gyrofrequency. A peak power of 55 MW is obtained with a 47-46 gain and 36.5% efficiency. A complete description of the system is presented. We also present scaled circuit designs at 17 GHz and 91 GHz.

Design of a frequency-doubling, 35-GHz, 1-MW gyroklystron

Presents a design of a 1-MV, frequency-doubling, four-cavity gyroklystron. The input cavity is driven by a 17.5-GHz driver and operates in the transverse electric (TE)/sub 011/ mode at the fundamental cyclotron resonance, while the buncher, penultimate, and output cavities operate in the TE/sub 021/ mode at twice the signal frequency at the second cyclotron harmonic. The device exhibits about 40% efficiency and 40-dB gain at 1-MW power level with a fractional bandwidth exceeding 0.1%. The power-bandwidth product for this device is on the same order as that of Ka-band gyroklystrons without the frequency doubling feature.

Dynamic simulation of mode-selective interaction cavity for wide-band high-power gyrotron applications

A stretched particle-in-cell (PIC) code was used to carry out dynamic simulations of a mode-selective extended-interaction gyrotron oscillator. Simulation results show that using the same interaction length, increasing the number of coupled cavities tends to force the peak of the electric-field profile closer to the output plane. As a result, the radiation becomes easier to leak out and the cavity Q is reduced. Using three coupled cavities (TE/sub 02//TE/sub 03//TE/sub 04/) with 10.6-cm total interaction length, the cavity Q of 260% and 25% efficiency can be attained in a second harmonic (31 GHz) gyrotron oscillator. Using the proposed cavity as the output cavity of an inverted gyrotwystron, the bandwidth without resistive loading attains 0.6%.

State Preparation by Photon Filtering

We propose a setup capable of generating Fock states of a single mode radiation field. The scheme is based on coupling the signal field to a ring cavity through cross-Kerr phase modulation, and on conditional ON-OFF photodetection at the output cavity mode. The same setup allows to prepare selected superpositions of Fock states and entangled two-mode states. Remarkably, the detector's quantum efficiency does not affect the reliability of the state synthesis.

State Preparation by Photon Filtering

We propose a setup capable of generating Fock states of a single mode radiation field. The scheme is based on coupling the signal field to a ring cavity through cross-Kerr phase modulation, and on conditional ON-OFF photodetection at the output cavity mode. The same setup allows to prepare selected superpositions of Fock states and entangled two-mode states. Remarkably, the detector's quantum efficiency does not affect the reliability of the state synthesis.

The standard model in cavity quantum electrodynamics. II. Coupling constants and atom field interaction

Specific forms of the travelling and trapped vector mode functions for a three-dimensional Fabry-Perot cavity are developed from the general results of the preceding paper, with parameters describing the output cavity mirror chosen for a typical high Q cavity case. Cavity and external quasi-mode functions associated with the quasi-mode theory of macroscopic canonical quantization are then obtained via an idealized choice of output mirror parameters. The coupling constants describing photon exchange processes between the single cavity quasi-mode associated with each Fabry-Perot resonance and various external quasi-modes are calculated, and their slow dependence on the external quasi-mode frequency shows that the conditions for irreversible Markovian damping of the cavity quasi-mode are satisfied. For radiative atoms placed in the cavity the coupling constants for energy exchange processes with sideways travelling external quasi-modes also vary slowely, so that Markovian spontaneous emission damping occurs for the radiative atoms. However, their coupling with the isolated cavity quasi-modes is associated with reversible photon exchanges as represented via one photon Rabi frequencies. The standard model in cavity quantum electrodynamics, in which the basic processes are described by a cavity damping rate, a radiative atom spontaneous decay rate and an atom-cavity mode coupling constant has now been justified in terms of the quasi-mode theory of macroscopic canonical quantization.

Measurements of intrinsic shot noise in a 35 GHz gyroklystron

Experimental measurements of electron beam shot noise in a 35 GHz, 225 kW, three-cavity gyroklystron have been obtained from both the input and output cavities. This intrinsic noise was studied in the absence of an applied carrier (i.e., at zero drive power). The spectrum of the noise emitted by the input cavity is found to have a Lorentzian shape, with peak noise power densities from the input cavity typically reaching 6.3×10−15 W/Hz (−112 dBm/Hz), and typical 3 dB bandwidths of 160 MHz. The output cavity noise spectrum is found to be equal to the input cavity noise spectrum multiplied by the measured linear frequency response of the gyroklystron. The measured noise levels at the input cavity are 0–5 dB lower than theoretical predictions for shot noise unaltered by collective effects. Furthermore, the input cavity noise power exhibits complex variations as a function of beam current, beam velocity ratio, and circuit magnetic field that are not predicted by present theory. Noise-to-carrier ratios expected in the input cavity during full power amplifier operation are inferred from the noise measurements and known values of drive power required to saturate the gyroklystron. The noise-to-carrier ratio, with typical values of −90 to −80 dBc, is found to be a strong function of the operating parameters.

Design of a 7 MW, 95 GHz, three-cavity gyroklystron

In this paper we present a three-cavity design of a gyroklystron amplifier at 95 GHz. We present the design of the magnetron injection gun (MIG), the magnetic field coils, and the three-cavity microwave circuit. The MIG produces a 500 kV, 45 A small orbit annular beam with an average perpendicular-to-parallel velocity ratio of 1.5 and a parallel velocity spread below 5% (RMS). The MIG requires a control anode with a voltage of about 65 kV, a magnetic compression of about 30, and a cathode loading near 10 A/cm/sup 2/. The circuit magnetic field is about 28.7 kG. The microwave circuit has a first-harmonic TE/sub 011/ input cavity which is driven at 47.5 GHz, and second-harmonic TE/sub 021/ buncher and output cavities which are resonant at 95 GHz. A peak power of 7.56 MW is obtained with 51.6 dB gain and 33.6% efficiency. A complete description of the system is presented along with a systematic study of the sensitivity of the device to parametric variations.

High efficiency, phase-locked operation of the harmonic-multiplying inverted gyrotwystron oscillator

The inverted gyrotwystron (phigtron) is a millimeter wave frequency-doubling amplifier that has been demonstrated to produce over 300 kW peak power at twice the input frequency (centered at f/sub in/=16.85 GHz and f/sub out/=33.7 GHz) over a 0.5% bandwidth with a saturated gain of 30 dB and efficiency greater than 35%. The device has also been studied both theoretically and experimentally in a different operating regime where frequency-doubled, phase-locked oscillation is possible. A signal, injected via a fundamental gyro-traveling wave tube input section, modulated a 55 kV, 10 A electron beam. After transit through a drift section, the prebunched electron beam produced phase-locked, second harmonic oscillations in a TE/sub 03/ mode output cavity. RF output centered at either of two frequencies, 34.42 and 34.62 GHz, with a maximum output power of 180 kW, an efficiency of 32% and a locked signal gain of 35 dB was measured. A theoretical prediction of locking bandwidth, a design overview, and the experimental results are presented followed by a summary and discussion of the results.

Solid state dye lasers based on 2-hydroxyethyl methacrylate and methyl methacrylate co-polymers

The laser performance of a range of solid state dye lasers based on rhodamine 590-doped co-polymers of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) has been investigated. The optimisation of preparation conditions, including polymerisation initiator and solvent for dye delivery is discussed in detail. Laser efficiency is compared for different polymeric hosts and dye concentrations with a range of output couplers, cavity lengths and repetition rates. Passive and dynamic loss have been determined for each host medium. Laser efficiencies of optimised polymers are among the highest reported for rhodamine 590-doped solid state dye lasers under these operating conditions. Highest slope efficiency of 35% and lowest threshold fluence of 0.06 J cm −2 were obtained with dimethyl sulphoxide (DMSO) additive in MPMMA at 10 Hz repetition rate.

Theory of multibeam stagger-tuned gyroklystrons

An analytical theory describing the tradeoff in the bandwidth and gain in multibeam stagger-tuned gyroklystrons (GKLs) is developed. A two stage multibeam configuration (i.e., the device consisting only of input and output cavities) is considered in detail. The analysis of two-, three- and four-beam configurations allows one to evaluate the increase in bandwidth due to multibeam configuration and the tradeoff in the bandwidth and gain due to the stagger tuning.

Operation of a high performance, harmonic-multiplying, inverted gyrotwystron

Experiment on a new type of high-power, millimeter wave amplifier, (a harmonic-multiplying, inverted gyrotwystron), are reported. Superior stability resulted from two factors: (1) interaction between a relatively low order waveguide mode (TE/sub 22/) and the beam wave at the fundamental cyclotron frequency in the traveling wave input section; (2) an internal mode filter in the highly overmoded (TE/sub 42p/), second harmonic output cavity. Bandwidth was 1.3% with saturated gain of 33 dB around 31.8 GHz. The gain-band width performance represents a significant advance for gyrotron amplifiers operating in such high order modes, and is thought to be due in part to operation of the long output cavity in several modes with different axial eigennumber (p=3, 4, 5) but with overlapping spectral regions.

Theory of the inverted gyrotwystron

The theory of the inverted gyrotwystron, a gyrodevice consisting of the input waveguide and output cavity separated by the drift section, is developed. The case of frequency doubling when the input waveguide operates at the fundamental cyclotron resonance and the output cavity operates at the second cyclotron harmonic is analyzed. It is shown that the electron prebunching in the input waveguide provides a better harmonic content in the electron current density than a standard ballistic bunching occurring in gyroklystrons with a short input cavity followed by a long drift section. The dependence of the efficiency and locking bandwidth on the input power and the lengths of input waveguide and drift section is studied. The effect of the electron velocity spread on the locking bandwidth and the electronic efficiency is analyzed.

Operation of a Highly Overmoded, Harmonic-Multiplying, Wideband Gyrotron Amplifier

Experiments on a unique, high-power, millimeter wave amplifier (a phase-coherent, harmonic-multiplying, inverted gyrotwystron) are reported. Superior stability resulted from two factors: (1) interaction between a relatively low order waveguide mode $({\mathrm{TE}}_{22})$ and the beam wave at the fundamental cyclotron frequency in the input section, and (2) an internal mode filter in the highly overmoded $({\mathrm{TE}}_{42})$, second harmonic output cavity. Bandwidth was 1.3% with peak gain of 33 dB around 31.8 GHz. The gain-bandwidth performance is a significant advance for gyrotron amplifiers operating in such high order modes.

Analysis for the new type long-pulsed and high efficient microwave amplifier—magnicon

This paper begins with the cylindrical cavity field expression of the rotating TMn10 mode in magnicon, and obtains its dissipated power, cold quality formula and so on, which are different from those in the static state TMn10. Furthermore starting from the dynamics equations, the passive deflect cavity electron velocity and position solution, as well as the interact instantaneous power solution between electron and wave have been solved. The cylindrical coordinate electron energy dynamics equation in the output cavity, and the modification of terminal parameter formula for relativity have also been discussed.

Design of a low-voltage, axially modulated, cusp-injected, third harmonic, X-band gyrotron amplifier experiment

We present the design of a prebunched, third harmonic small-orbit gyrotron experiment that utilizes a 45 kV, 8 A beam to produce over 185 kW of amplified power at 9.9 GHz in a 1.23 kG magnetic field. We detail the design of the electron gun, which produces a moderately compressed axially streaming annular beam. The beam is velocity modulated by a short TM/sub 010/ coaxial input cavity and energy is extracted in a right-circular TE/sub 021/ output cavity. Perpendicular energy is imparted to the beam via a nonadiabatic magnetic transition at the end of a 23 cm drift region between the two cavities. A nonlinear single particle code is used to predict an electronic efficiency of 52% and a large signal gain of 25.5 dB. This code generates the cavity field profiles via a scattering matrix formalism and uses the output from the electron gun code to model the beam. This improved model allows the potentially important effects of leakage fields and finite beam thickness and spread to be investigated.

Design and operation of a two-cavity third harmonic Ka-band gyroklystron

We present the operating characteristics of a two-cavity third harmonic gyroklystron experiment. The input cavity utilizes a 9.854 GHz TE011 mode which is driven by a 100 kW magnetron. The TE031 output cavity has a resonant frequency of 29.57 GHz. The nominal beam voltage and current are 435 kV and 210 A, respectively. The pulse length is about 1 μs and the average ratio of parallel to perpendicular velocity is near one. Peak powers above 1.8 MW are achieved with an efficiency of about 2% and a gain of 14 dB. The theoretical simulations are in good agreement with the experimental results.

Mode competition in fourth-harmonic magnicon amplifiers

In the magnicon RF amplifier, the drive and gain cavities are cylindrical deflection cavities which operate in a rotating TM/sub 110/-mode and spin up an electron beam to high transverse momentum. As a result of the rotating-mode interaction, the electron beam entry point into the output cavity rotates about the axis at the drive frequency. The gyrotron-like output cavity can be operated at m times the drive frequency by using a mode with an azimuthal index of m, as this mode rotates at m/sup -1/ times its RF frequency, thus maintaining synchronism with the electron beam. Previous frequency-multiplying magnicons have used m=2; in this paper it is shown that magnicons with m=4 may be practical, provided one also operates the output cavity at the m/2 harmonic of the cyclotron frequency. Operation at higher harmonics lowers the frequency of the deflection cavities allowing lower RF fields, reducing cavity breakdown problems; lower magnetic fields, reducing magnet cast and complexity; and a larger electron beam, relaxing beam quality constraints. On the other hand, higher order azimuthal-index magnicon modes interacting at higher order cyclotron interactions are subject to competition with nonsynchronous (gyrotron) modes and are more sensitive to electron beam scanning angle spread. A time-dependent multimode gyrotron code has been modified to examine competition in the output cavity between the phase-synchronous operating mode and other nonsynchronous modes which interact via the conventional gyrotron interaction. Calculations have been carried out for fourth-harmonic magnicons with TM/sub 410/ and TE/sub 411/ mode output cavities and include the effects of mode competition with nonsynchronous modes as well as a spread in entry-point angles of the scanning electron beam.

Design of an efficient, low voltage, third harmonic, large-orbit gyrotron amplifier with a vane-resonator output cavity

We present the design of a 100 kW, J-band, third harmonic large-orbit gyrotron amplifier which utilizes the interaction between a 45 kV, 4 A beam and a vane resonator output cavity operating in the /spl pi/-mode. An efficiency of 55% is predicted with a large signal gain near 20 dB by a single particle code which takes into account nonideal effects associated with finite beam thickness and finite magnetic field transition widths. High efficiency is achieved by velocity modulation of an axially-streaming annular beam via a short TM/sub 310/ drive cavity. Ballistically created axial bunches are converted into azimuthal bunches when the beam encounters a nonadiabatic, balanced magnetic field reversal at the end of a 30 cm drift region. The design of this tube is presented and its performance is completely characterized before the prospects for the operation of this low voltage configuration at other harmonics are explored.