Adam T. Drobot

Theory and Simulation of the Gyrotron Traveling Wave Amplifier Operating at Cyclotron Harmonics

An analytical expresion for the efficiency of the gyrotron traveling wave amplifier is derived for the case of nonfundamental cyclotron harmonic interaction. It scales the efficiency with respect to the modes and parameters of operation. This relation, together with a general linear dispersion relation, also derived in the present paper, gives the characteristics and optimum operation conditions of the gyrotron traveling wave amplifier.

Characteristics and Optimum Operating Parameters of a Gyrotron Traveling Wave Amplifier

Characteristics and optimum operating parameters are determined for a new type of high-power high-efficiency generator of millimeter waves known as a gyrotron traveling wave amplifier. In the example consided, wave amplification results from the interaction of a TE/sub 01/ waveguide mode with the fundamental cyclotron harmonic of an electron beam. The parameter optimization involves the determination of the point of maximum device efficiency as a function of beam density, beam energy, beam positioning, and external magnetic field for the output power required. An analytical linear theory and a numerical simulation code form the basis of theoretical calculations. As a result of the extensive survey in parameter space, the peak efficiency in the beam frame has been found to exceed 70 percent. This result has been applied to the specific design of a 35-GHz amplifier with output power ~340 kW, a power gain of 2 dB/cm, and a laboratory frame efficiency of 51 percent.

An investigation of a magnetron injection gun suitable for use in cyclotron resonance masers

The requirements of an electron-beam source suitable for use in cyclotron resonance masers are discussed. The beam source of preference, a magnetron injection gun with its emission temperature limited, is studied by use of a numerical simulation code. This computer code includes the effect of external magnetic fields, the beams azimuthal self-magnetic field, and space charge in a self-consistent manner. By use of this program, a prediction of gun operation, particularly as it affects gyrotron performance, can be made. Of particular interest are the effects of varying such control parameters as the magnitude of the electric and magnetic fields, the shape of the electric and magnetic fields, and the current. It is demonstrated that, for a particular optimized gun design, the gun operation is very sensitive to both the applied electric and magnetic fields at the cathode. However, the gun shows no strong dependence on other factors such as the temperature-limited beam current or the magnetic-field taper used to compress the beam.

Numerical simulation of a low‐density plasma erosion opening switch

Current conduction through a low density (∼1012 cm−3) collisionless plasma injected between two coaxial conducting cylinders is simulated using a 2 (1)/(2) ‐D, electromagnetic particle‐in‐cell code. Plasma is injected through the anode towards the cathode with flow velocity, VF, and is assumed to be azimuthally symmetric. Current is driven through the plasma so that the 100 kA level is reached in ≂5 nsec. The opening process, when current is diverted to a load, is also treated. Electrons are found to carry current in a narrow current channel across the plasma by E×B drift. A large electric field is established by charge separation in the plasma in order to provide the drift. The motion of the anode end of the current channel controls the time of opening and is found to be independent of VF and to depend strongly on density and length.

Gain, saturation, and bandwidth measurements of the NRL gyrotron travelling wave amplifier

Gyrotron travelling wave amplifier (gyro-TWA) experiments have been recently performed, demonstrating linear gains as high as 32 dB at 35.1 GHz for a 70 kv, 9 amp beam, and 24 dB for a 3 amp beam. The gyro-TWA operates in the TE01circular waveguide mode and at the fundamental electron cyclotron frequency. At present, it is a single stage device with no severs or stabilizing elements. The amplifier has been driven into saturation with a maximum observed output of 26 kW at 13 dB gain. Saturation begins at approximately 10 kW output with 30 dB gain. The best efficiency observed was 7.8 percent for a 3 amp beam and 20 dB gain. Linear bandwidth measurements show a -3 dB bandwidth of approximately 500 MHz for the peak gain of 24 dB with a 3 amp beam.

Spatial and Temporal Coherence of a 35-GHz Gyromonotron Using the TE/sub 01/ Circular Mode

The characteristics of a 35-GHz oscillator operating with the TE/sub 01/ circular waveguide mode are described. The device produced 147 kW, with an efficiency of 31 percent at 100 kW. The total radiated energy was 2 kJ/pulse. The spectral coherence appears to be equal to those of other high-quality microwave tubes. The mode purity is greater than 95 percent.

Computer simulation studies of strong proton rings

Results are reported from a numerical simulation study on the propagation of a rotating proton pulse and the formation and trapping of the resulting strong proton ring. It is observed that the self‐magnetic field has a very pronounced effect on the dynamics of such systems. In addition, it is observed that rings trapped in a magnetic mirror field are r, z stable for the entire confinement time tested of 550 nsec and suffer neither axial nor radial particle losses.