200-kW Gyrotron Research Articles

Development of 42-GHz, 200-kW Gyrotron for Indian Tokamak System Tested in the Regime of Short Pulselength

A 42-GHz, 200-kW gyrotron was developed and tested for the Indian plasma fusion system. The gyrotron was designed for the TE0,3 operating mode. The configuration of the triode-type magnetron injection gun (MIG) with the linear RF output, undepressed collector, and face-cooled double disk window was adopted in this gyrotron because of the first development experience. The complete tube was developed and processed at Central Electronics Engineering Research Institute (CEERI), Pilani, India. The RF testing of the gyrotron was performed at the participating institute, Institute of Plasma Research (IPR), Gandhinagar, India. Due to some cooling issues in the collector region, the tube was tested by a resistive capacitor network-based power supply for a very short pulse in place of a long pulse, high voltage power supply. The tube was tested up to the beam voltage of 51 kV and a beam current of 12 A at the cavity magnetic field of 1.61 T for the short pulse of 500 μs. The tube was inserted into the magnet system consisting of a main electromagnet, auxiliary gun coils, and collector magnets. The multi-hole and single hole couplers were used to measure the RF power in the TE0,3 mode and the overall power, respectively. The measured results were also compared with the simulated results and a close agreement of the results was found. The short pulse testing confirms the electrical design and the development approach for the 42-GHz gyrotron tube.

Tapered Cavity Measurement for 42-GHz, 200-kW Gyrotron

The 42-GHz gyrotron cavity had three sections in its final design: down-taper section, up-taper section, and uniform middle section. The design of the cavity depends on the RF mode and desired power growth. The finalized design parameters of down-taper and up-taper angles are 2° and 3°, respectively, with respect to the middle section of gyrotron cavity. This cavity consists of these poorly tapered sections at both the ends of midsection. The combination of all three sections results into a complex cavity structure which is complicated and challenging to fabricate. An additional challenge in fabrication is to achieve desired designed parameters. Therefore, design realization through fabrication clearly needs dimensional measurement. The dimensional parameters of cavities such as down-and up-taper angles, uniform section diameter, taper lengths, and surface roughness measurement have their own significance and importance. This paper presents the destructive and the nondestructive methods to measure the dimensional parameters of a complex cavity structure. Further, a computational analysis is also done to represent the comparisons between the design and measured values in terms of ohmic quality factor and efficiency and reported the effects of geometrical changes.

Long Duration Operational Characteristics of the First Indian 42-GHz, 200-kW Gyrotron

Institute for Plasma Research (IPR) has indigenously developed the magnet system appropriate for a 42.2-GHz 200-kW continuous-wave/long-pulse gyrotron in a multi-institutional collaboration sponsored by the Department of Science & Technology, Government of India. The Gyrotron Magnet System (GMS) consists of a resistive gun magnet coil, superconducting cavity magnet coil, and three resistive collector magnet coils. The experimental validations of performance and stability of the magnet system in long-term operational scenarios has been elaborated in this paper. The Gun Magnet and the Collector magnets are fabricated from OFHC copper strands and oil/air cooled, whereas the cavity magnet is NbTi strand wound and helium bath cooled inside a low loss cryostat. The entire magnet system has been charged to their nominal transport current values and validated for long duration operation both in normal and off-normal scenarios. The desired field homogeneity and optimized positioning of individual magnets have been established from these experiments. The field at various radial positions is established within ±5% along the z-direction. GMS has been further successfully validated toward its performance with respect to the gyrotron beam guiding requirements.

Development of Face-Cooled Tunable Double-Disk Sapphire Window for 42-GHz 200-kW Gyrotron

Window happens to be the most critical and vulnerable component in high-power gyrotrons. A face-cooled tunable double-disk sapphire window has been developed primarily for a 42-GHz 200-kW gyrotron. The critical issues like: sapphire-to-metal joining, electrical simulation, thermal analysis, structural analysis of the window, and its low-power characterizations in TE03 mode have been discussed. The return loss and insertion loss have been measured to be -29 and -0.12 dB, respectively. The window has been attached to the first Indian gyrotron and vacuum processed successfully.

Design of 42 GHz gyrotron for Indian fusion tokamak system

In this paper, the complete design of a 42GHz, 200kW gyrotron at first harmonic operation for Indian tokamak system is presented. The gyrotron is designed for TE0,3 operating mode. Un-depressed collector and axial output system for RF power is selected just due to the sake of simplicity in the actual fabrication of the device as it is the first design and development experience. Various commercially available design tools as well as in-house developed computer codes are used in the design process. The experimental results of cold cavity analysis are also presented in this manuscript. The rigorous design simulations confirm more than 200kW RF power generation in TE0,3 mode at 42GHz frequency.

Effect of cavity geometry on the performance of a gyrotron

The effect of interaction cavity geometry on the gyrotron performance in terms of cold cavity parameters (Q value and axial electric field profile), Ohmic wall loss, start oscillation current and interaction efficiency are analyzed in detail in this article. The measurement of Q value and axial electric field profile is also performed for the cavities with different geometries by using non-destructive and perturbation techniques, respectively. Scattering matrix code is used for the computation of Q value and axial electric field profile and results are compared with the experimental data. A Particle-in-Cell code and a specific beam–wave interaction computation code based on generalized non-linear theory are used in the efficiency calculations. For all numerical and experimental analyses, the case of 42GHz, 200kW gyrotron is considered here.

Thermal Design of RF Window for High-Power Gyrotron

In this paper, thermal and structural analyses of an RF window for a 42-GHz 200-kW gyrotron have been carried out using ANSYS software and discussed in this paper. The evaluation of the thermal and structural aspects of the window for the 42-GHz gyrotron during an extreme case of operation, i.e., at saturation, has been carried out. Temperature profiles have been obtained for different values of dielectric loss. The temperature range on the sapphire disk surface has been found to be 30°C -68°C. The window performance has been found satisfactory.

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.

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.

Comparative EGUN and TRAK simulation studies on the design of the magnetron injection gun of a 200kW, 42GHz gyrotron

A triode-type magnetron injection gun (MIG) for a 42 GHz, 200 kW gyrotron was designed by two commercial codes: EGUN and TRAK. An in-house code MIGANS was used as the p ost-processor of the EGUN. Some basic equations relevant to the problem available in literature were used while using the EGUN code for the purpose. The results on the design output parameters obtained by these two codes were found to be in close agreement. The gyrotron is a device to generate high powers at high frequencies. In this device, the source of electrons is a magnetron injection gun (MIG) which forms a beam of electrons in which the electrons execute the small cyclotron orbits at a frequency required for the cyclotron resonance interaction with RF waves in the device (1,2). The MIG is placed in an axially symmetrical magnetic field at the magnetic field strength determined by the magnetic compression ratio . The initial electron motion occurs in the crossed electric and magnetic fields so that the electron s follow the helical trajectories around the magnetic field lines. The gun anode accelerates the beam to th e final beam energy. Downstream from the gun, the magnetic field increases smoothly in the magneti c compression region to the required peak value at the interaction region. The magnetic field compress ion reduces the radius of the beam and results in an increase of the velocity component perpendicular to the magnetic field. Since the total energy is constant, the drift velocity is correspondingly reduced. In India, an activity related to the design and development of 42GHz, 200kW gyrotron has been started. The operating mode has been selected as TE03 with the second maximum of the transverse-plane field pattern of the cylindrical interaction cavity as the be am launching position for the fundamental beam-mode operation. For the better performances of the gyrotron and the gyro-devices, an electron beam of good quality is required (1-6). The triode-type MIG has been designed having the beam voltage V0 = 65kV, the beam current I0 = 10A and the transverse-to-axial beam velocity ratio � = 1.26. The

Three-Dimensional Simulation of MIG for 42-GHz 200-kW Gyrotron

This paper presents a three-dimensional (3-D) simulation of a triode-type magnetron injection gun (MIG) for a 42-GHz 200-kW gyrotron with a transverse-to-axial velocity ratio of the electron beam at 1.22 and a maximum transverse-velocity spread of 3.2%. The operating mode of the gyrotron is TE_03, and it is operated in the fundamental harmonic. The MIG has been designed by using some tradeoff equations and the 3-D particle-tracing code (computer simulation technology). The simulated results have been validated with the results obtained using the 3-D code OPERA Vector Fields and the two-dimensional trajectory codes EGUN and TRAK.

Design of a 42-GHz 200-kW Gyrotron Operating at the Second Harmonic

The design of a 42-GHz 200-kW continuous-wave gyrotron operating in the TE/sub 4,2/ mode at the second cyclotron harmonic is presented. This study includes mode selection, cavity design, and interaction calculations for power and efficiency as a function of various parameters, as well as preliminary design of the beam optical system, launcher, and window. This device is intended to serve as a heating source for a small experimental steady-state Tokamak, which requires microwave power, preferably in the form of a Gaussian beam.