G.S. Park

Electron prebunching in microwave magnetron by electric priming using anode shape modification

Electric priming is proposed for electron prebunching in a microwave magnetron and is demonstrated using a particle-in-cell code. When the N∕2-fold perturbation of the radial electric field using an anode shape modification is imposed in the interaction space of the N-cavity magnetron along the azimuthal direction, the electrons initially develop into the desired π-mode resulting in rapid startup. The startup is hastened from 3.2 to 1.2 ns when the radial variation of the protrusion and recession is 6.5% of the anode radius with the angular width of 6°.

Nonstationary behavior in a delayed feedback traveling wave tube folded waveguide oscillator

Folded waveguide traveling-wave tubes (FW TWT) are among the most promising candidates for powerful compact amplifiers and oscillators in millimeter and submillimeter wave bands. In this paper, the nonstationary behavior of a FW TWT oscillator with delayed feedback is investigated. Starting conditions of the oscillations are derived analytically. Results of numerical simulation of single-frequency, self-modulation (multifrequency) and chaotic generation regimes are presented. Mode competition phenomena, multistability and hysteresis are discussed.

Theoretical analysis of cross-talking signals between counter-streaming electron beams in a vacuum tube oscillator

The basic theory of cross-talking signals between counter-streaming electron beams in a vacuum tube oscillator consisting of two two-cavity klystron amplifiers reversely coupled through input/output slots is theoretically investigated. Application of Kirchhoff’s laws to the coupled equivalent RLC circuit model of the device provides four nonlinear coupled equations, which are the first-order time-delayed differential equations. Analytical solutions obtained through linearization of the equations provide oscillation frequencies and thresholds of four fundamental eigenstates, symmetric/antisymmetric 0∕π modes. Time-dependent output signals are numerically analyzed with variation of the beam current, and a self-modulation mechanism and transition to chaos scenario are examined. The oscillator shows a much stronger multistability compared to a delayed feedback klystron oscillator owing to the competitions among more diverse eigenmodes. A fully developed chaos region also appears at a relatively lower beam cur...

Experimental verification of low-velocity spread axis-encircling electron beam

We have experimentally demonstrated a low-velocity spread, axis-encircling electron beam using a comparatively simple Pierce-type electron gun and single cusp magnetic field based on a recent theory [Jeon et al., Appl. Phys. Lett. 80, 3703 (2002)] developed with the assumption of small orbit gyration before the magnetic cusp, in which every physical property has been analyzed and the possibility of zero percent axial velocity spread was concluded. The velocity ratio and the axial velocity spread were measured to compare the theory with varied operation conditions of the electron gun. These results agree well with our hypothesis.

Theory of the microelectronic traveling wave klystron amplifier with field-emission cathode array

A nonlinear theory is developed to predict the gain of a distributed vacuum amplifier employed with field-emitter arrays. Contrary to conventional expectation, it is shown that density modulation of the electrons in the emitting structure is limited by high resistive losses and electronic damping. Therefore, a modified schematic is suggested with the high-frequency modulator separated from the emitter that only dc bias voltage is applied to. Small-signal calculation shows that 15–25dB gain (with 3dB bandwidth over 200GHz) at 100–400GHz frequency band can be obtained within 1–2cm drift space length with currently available parameters of field emitters and microstrip transmission lines. Nonlinear calculations predict promising performances of good linearity and 13–20dBm saturated output power. The suggested distributed vacuum amplifier fully based on microelectromechanical systems technologies would open a new era for the devices operating at the border of millimeter and submillimeter bands.

Enhancement of backward-wave interaction by external feedback

Enhancement of backward-wave interaction by additional feedback was experimentally demonstrated adopting an external energy recovery scheme. The experimental observation was confirmed by particle-in-cell simulation. Measured efficiency improved in accordance with the strength of external feedback at the optimal phase, which is attributed universally to the increase of the normalized current defined by the ratio of the beam current to the start-oscillation current, regardless of each assigned feedback power level. This is a promising aspect to overcome the practical problems of low available current concomitant with the scaling of dimensions for generation of extremely high frequencies.

Design of a portable ammonia detector for supporting gas safety fields

In this paper, we proposed a design of the field-supported portable ammonia detector. Ammonia gases are toxic gases so they stimulate nose and throat and cause many diseases. So, we designed the detector for detecting the ammonia gases more safely. The structure of this detector is a detachable structure. Its detection part and display part can be separated. It has algorithms of an accuracy improvement using least square method and Neville interpolation. Also, it can use Bluetooth communication. Bluetooth communication is used when the display part and detection part is separated. So, it can check, adjust, and transmit the measured data when it is separated. Furthermore, the measured data of concentration of ammonia gases can be transmitted to the smart devices using Bluetooth communication and can be manage the data in the smart devices.

Third harmonic frequency multiplication of a two-stage tapered gyro-TWT amplifier

The third harmonic frequency multiplication is experimentally verified using a two-stage tapered gyrotron traveling-wave tube amplifier in low-power operation. The third harmonic frequency multiplication is predicted and investigated using a self-consistent large-signal theory and a particle-in-cell code simulation. Both results show a good agreement in frequency multiplication and power amplification. The interaction between a 30 kV axis-encircling electron beam with a drive signal in the tapered waveguide of the input stage modulates the electron beam at the fundamental cyclotron harmonic, then the third harmonic component of the modulated beam current is chosen to be extracted in the tapered output stage. In the proof-of-principle experiment, X-band drive signals from 10.6 to 12 GHz are multiplied by three times to be Ka-band output frequencies from 31.8 to 36 GHz, showing consistent results with theoretical predictions when a 30 kV, 160 mA electron beam is used.

MAGIC 2D simulation of nonstationary and chaotic processes in a relativistic backward wave oscillator

In this paper, we present the results of numerical modeling of transition to chaos in the relativistic BWO using 2D MAGIC particle-in-cell code. We compare the results with those of numerical and experimental studies. MAGIC allows simulating slow wave structures with realistic geometry and naturally takes into account such important phenomena as effects of transverse electron motion, frequency dependence of the end reflections and interaction with a non-synchronous forward wave reflected from the cutoff neck.

Design and Implementation of Concentration Calculation Algorithm for the Infrared Combustible Gas Detector

Recently, we can find news about toxic and combustible gas accident. So, we have to develop gas detector that can measure gas at dangerous area for preventing gas accidents. In this paper, we calculate a approximation function from sensors output using the linear regressiong. And we develop software algorithm using Nevilles algorithm for measuring gas concentration. Finally, we compare our algorithm with combustible gas detectors that are already developed, by using standard gas samples manufactured Korea Gas Safety. As a result of this experiment, we confirm that performance of our algorithm is more improved than performance of already developed combustible gas detectors. In the future, well research how to improve reliability from using count, temperature and humidity. And well design hardware applied explosion proof for safety.