Hasina Khatun

Numerical Simulation of Magnetron Injection Gun for 1mw 120 GHz Gyrotron

A 40A triode-type magnetron injection gun for a 1MW, 120GHz gyrotron has been designed. The preliminary design has been obtained by using some trade-ofi equations. Computer simulation has been performed by using the commercially available code EGUN and the in-house developed code MIGANS. The operating voltages of the modulating anode and the accelerating anode are 60kV and 80kV, respectively. The electron beam with a low transverse velocity spread (-fl?max = 3:3%) and velocity ratio, fi = 1:38 at beam current = 40A is obtained. The simulated results of the MIG obtained with the EGUN code have been validated with another trajectory code TRAK. The results on the design output parameters obtained by these two codes were found to be in close agreement. The sensitivity study has been carried out by changing the difierent gun parameters to decide the fabrication tolerance.

DESIGN OF 35 GHZ GYROTRON FOR MATERIAL PROCESSING APPLICATIONS

The complete design of 35GHz, 200kW gyrotron for various material processing and heating applications is presented in this article. The components of the device, such as Magnetron Injection Gun, interaction cavity, collector and RF window, are designed for the TE03 mode. Various in-house developed codes (GCOMS, MIGSYN and MIGANS) and commercially available codes (MAGIC, EGUN and CST-MS) are used for the design purpose. A thorough sensitivity analysis of the gyrotron components is also carried out. The designed device shows the capability to generate more than 200kW of output power with more than 40% of e-ciency.

On the Design of a High-Efficiency Double-Beam Gyrotron

The gyrotron that operates with a double electron beam is designed and presented. The design of a 42-GHz 200-kW gyrotron at TE03 mode has been done and presented elsewhere. To enhance the RF power without losing the interaction efficiency of the 42-GHz gyrotron, double electron beams are launched into the cavity. The beam-wave interaction calculations and power and frequency growth estimation are performed and compared with the single-beam operation results. In the design of the gyrotron, in-house developed codes, GCOMS, MIGSYN, and MIGANS, as well as commercially available codes MAGIC and EGUN are used. The results show that more than 400 kW of power is not possible by single-beam operation while the double-beam operation shows this amount of power with the same mode. To achieve the double electron beams of the desired parameters at the cavity region, the double-beam magnetron injection gun (MIG) is designed. The results of the interaction cavity and MIG show the feasibility of the double-beam gyrotron for high-power and high-efficiency operation.

Discharge analysis and electrical modeling for the development of efficient dielectric barrier discharge

Dielectric-barrier discharges (DBDs) are characterized by the presence of at least one insulating layer in contact with the discharge between two planar or cylindrical electrodes connected to an AC/pulse power supply. The dielectric layers covering the electrodes act as current limiters and prevent the transition to an arc discharge. DBDs exist usually in filamentary mode, based on the streamer nature of the discharges. The main advantage of this type of electrical discharges is that nonequilibrium and non-thermal plasma conditions can be established at atmospheric pressure. VUV/UV sources based on DBDs are considered as promising alternatives of conventional mercury-based discharge plasmas, producing highly efficient VUV/UV radiation. The experiments have been performed using two coaxial quartz double barrier DBD tubes, which are filled with Xe/Ar at different pressures. A sinusoidal voltage up to 2.4 kV peak with frequencies from 20 to 100 kHz has been applied to the discharge electrodes for the generation of microdischarges. A stable and uniform discharge is produced in the gas gap between the dielectric barrier electrodes. By comparisons of visual images and electrical waveforms, the filamentary discharges for Ar tube while homogeneous discharge for Xe tube at the same conditions have been confirmed. The electrical modeling has been carried out to understand DBD phenomenon in variation of applied voltage waveforms. The simulated discharge characteristics have been validated by the experimental results.

Experimental study of low-pressure nitrogen dielectric barrier discharge

The electrical and spectral characteristics of a dielectric barrier discharge (DBD) are experimentally investigated in a sealed off coaxial cylinder filled with nitrogen at a pressure of 10 mbar. The discharge is a transient diffused glow at low frequency alternating voltage (60 Hz) and changes to a filamentary mode at high frequency alternating voltage (35 kHz). In case of pulsed voltage, the discharge is always transient diffused glow at any frequency. The intensity of a second positive system (SPS) of the nitrogen molecule has been also measured to characterize the discharge excitation. The effective vibrational temperature is estimated from the SPS vibrational band, Δv = -2. It is concluded that the intensity of the SPS of the nitrogen and the effective vibrational temperature depends upon the reduced electric field and the energy consumed per cycle by the device.

Pseudospark switch development for pulse power modulators

The Pseudospark switch is able to control high voltage and high current discharges and operates at low pressure like thyratron but much simpler in construction and does not suffer in electrodes wear. This switch is bipolar and has 100 % reverse current capability, much faster than thyratron and has applications in pulse power modulators, linear accelerators, laser systems etc. Such switch has been developed at CEERI Pilani and tested in a demountable setup. Switching behavior has been observed at 22 kV and 7 kA in hydrogen atmosphere (13 Pa). Electrodes shaping and high voltage gap has been simulated in ESTAT and designed accordingly. For this switch, as a cold cathode, a ferroelectric trigger source has also been developed and characterized. High dielectric material has been opted for such a source. The hold off voltage can be doubled if the gap of the electrodes is stacked to two single stage gaps. Such stack of two single stage switches has also been fabricated in a demountable setup. Switching behavior has been observed up to 40 kV and 2.9 kA. High voltage conditioning and characterization is still in progress. In this paper design of the electrodes, ferroelectric source, description of the demountable set up, fabrication, processing of the Pseudospark switch and switching behavior have been presented and discussed.

Discharge Characteristics of Dielectric Barrier Discharge (DBD) based VUV/UV Sources

Dielectric-barrier discharges (DBDs) are characterized by the presence of at least one insulating layer in contact with the discharge between two planar or cylindrical electrodes connected to an AC/pulse power supply. The dielectric layers covering the electrodes act as current limiters and prevent the transition to an arc discharge. DBDs exist usually in filamentary mode, based on the streamer nature of the discharges. The main advantage of this type of electrical discharges is that nonequilibrium and non-thermal plasma conditions can be established at atmospheric pressure. VUV/UV sources based on DBDs are considered as promising alternatives of conventional mercury-based discharge plasmas, producing highly efficient VUV/UV radiation. The experiments have been performed using coaxial and planar geometry of DBD (gas gap: 1–3 mm) made of quartz with N2/Ar/Xe gas at different pressures. A proper ultra high vacuum system and gas filing system has been made for the processing & characterization of DBD tubes. A RF generator (20-100 kHz, 0-2.4 kV peak) is used for discharges in DBD tube. A stable and uniform discharge is produced in the gas gap between the dielectric barrier electrodes. The discharge characteristics have been analyzed by V-I characteristics & Lissajous figure and found that the spatial discharge processes varies strongly according to the applied voltage waveform, pressure of filled gas and geometry of tube.

Design of interaction cavity for 42 GHz, 200 kW CW/long pulse gyrotron

A weakly tapered interaction cavity has been designed to excite TE03 operation mode at the fundamental harmonic number for 42 GHz, 200 kW gyrotron. A software code GCAVSYN has been developed to synthesize cavity geometry and selection of operating mode. The cold cavity analysis and beam-wave interaction were carried out using commercially available PIC code MAGIC. An axial output power above 200 kW has been achieved at guiding cavity magnetic field 1.61 T.

P3-1: Design of 42 GHz, 200 kW Gyrotron

The design of 42 GHz, 200 kW Gyrotron has been carried out using in-house and commercially available softwares. A triode type MIG has been designed using EGUN code and three in house developed codes MIGSYN, GINTMESH and MIGANS respectively. A weakly tapered interaction cavity has been designed to excite TE03 operation mode. A software GCAVSYN has been developed to synthesize the cavity geometry and selection of the operating mode. The cold cavity analysis was carried out using commercially available PIC code MAGIC. An axial output power above 200 kW has been obtained at the guiding magnetic field 1.60T–1.65T. The behavior of generated rf power in beam tunnel has been simulated using the CST Microwave Studio and Ansoft HFSS. The different lossy ceramics have been studied for reflection, transmission and absorption. A good agreement has been found in the simulated results from both the software. The design of collector has been optimized to achieve the maximum beam spread.

Optimization of magnetic field for maximum output power of a 42 GHz CW/Long pulse Gyrotron

A starting current analysis has been carried out to optimize the magnetic field of a 42 GHz Gyrotron. The simulated output power at the optimized magnetic field of 1.62 T is above 200 kW. At an operating mode of TE03, the strong mode competition has been analyzed through coupling coefficient and starting current.