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Microwave Vacuum Devices
Published in Jerry C. Whitaker, The RF Transmission Systems Handbook, 2017
If the electron gun of the gyrotron is moved to the side of the waveguide and microwave power is extracted from the waveguide opening in proximity to the electron gun, as shown in Fig. 8.39, then the device is termed a gyrotron backward oscillator.9 The principle involved is similar to the backward wave oscillator, and the process of velocity modulation, drifting, bunching, and catching is similar to that of the klystron. Microwave energy induced in the waveguide travels in both directions but the circuit is adjusted to emphasize the waves traveling in a backward direction. The backward waves become the output of the tube and, at the same time, carry the positive feedback energy to the electrons just emitted and to be velocity-modulated. The system thus goes into oscillation.
Introduction to microwave sources
Published in R A Cairns, A D R Phelps, P Osborne, Generation and Application of High Power Microwaves, 2020
Finally as an example of some specific interaction processes Figure 2 shows some of the different microwave sources that can be created by interaction of the cyclotron wave on an electron beam with a waveguide mode. The four examples shown are of a gyrotron, gyro-TWT, CARM and gyro-BWO. The gyrotron is the source which is the basis of many of the present applications of high power microwaves to plasma heating The gyrotron is associated implicitly or explicitly with several of the chapters in this book and we are very fortunate that one of the original co-inventors of the gyrotron, namely Michael Petelin, is an author of one of these chapters.
Biological Effects of Millimeter and Submillimeter Waves
Published in Ben Greenebaum, Frank Barnes, Biological and Medical Aspects of Electromagnetic Fields, 2018
Stanislav I. Alekseev, Marvin C. Ziskin
Millimeter wave generators use different sources of oscillators. Vacuum tube based sources include backward wave oscillators (BWO), orotrons (high-power BWO), magnetrons, gyrotrons, gyro-klystrons, and gyro-traveling wave tubes (gyro-TWT). Solid-state sources include widely used Gunn diodes and impact ionization avalanche transit-time (IMPATT) diodes. Magnetrons, gyrotrons, gyro-klystrons, and gyro-TWT are used in high output power generators. Pulse magnetrons operate in the frequency range up to 220 GHz with peak power of 30 kW. Gyrotrons depending on cooling conditions can generate power at fixed frequencies up to 20 kW. Gyro-klystrons operate at fixed frequencies with output power up to 340 kW. Gyro-TWT can generate peak power up to 180 kW. The low output generators commonly used in biological experiments have oscillators such as BWO, Gunn diodes, and IMPATT diodes. These sources of mm waves cover the frequency range of 30–178 GHz at maximum output power up to 400 mW. Generators based on BWO operate at frequencies from 36 to 178 GHz with output powers up to 80 mW. BWO are the most wide-banded sources with electronic control of frequency. Cavity stabilized Gunn oscillators generate from 40 to 140 GHz with maximum CW power at lower frequencies up to 200 mW, which drops at higher frequencies to 30 mW. CW IMPATT diodes are used for oscillators and amplifiers. They operate in the frequency range of 30–140 GHz with output power up to 400 mW. IMPATT diodes are used in noise generators. Some generators use frequency synthesizers. A frequency synthesizer is an electronic circuit for generating any of a range of frequencies from a single fixed oscillator. A frequency synthesizer uses the techniques of frequency multiplication, frequency division, direct digital synthesis, and frequency mixing (photomixing) to generate new frequencies, which have the same stability and accuracy as the master oscillator. Commercially available synthesizers cover the frequency ranges from 36 to 1250 GHz and 0.45 to 2.85 THz.
Prospects for Disruption Handling in a Tokamak-Based Fusion Reactor
Published in Fusion Science and Technology, 2021
The availability of high-power (>1 MW), long-pulse, or continuous-wave microwave sources for active ECCD stabilization of NTMs becomes problematic for a high-field reactor unless it operates at low normalized pressure where NTMs are unlikely to be an issue. Development of suitable gyrotrons in the 230- to 240-GHz range represents the state of the art.27 Extension of microwave sources to higher frequencies to provide ECCD at higher fields (e.g., SPARC at BT = 12.2 T or ARC at BT = 9.2 T) (Refs. 6 and 7) will become increasingly difficult. Development of the free-electron maser shows promise as an alternate to the gyrotron for development of submillimeter, high-power microwave sources.28
High power millimeter-wave TE03 to TM11 mode converters
Published in International Journal of Electronics, 2019
Amit Patel, Riddhi Goswami, Keyur Mahant, Pujita Bhatt, Hiren Mewada, Alpesh Vala, Sathyanarayana K, Sanjay Kulkarni
Nowadays, gyrotron plays a vital role in the generation of millimetre-wave power source for communication, controlled thermonuclear fusion system and phased array radio detection and ranging (RADAR) system (Kumrić & Thumm, 1986). However, power generated by gyrotron is in TE0n unpolarised mode and for efficient heating of plasma in a thermonuclear fusion requires axis-symmetric linearly polarised gaussian narrow pencil beam (Fu, Liao, He, Niu, & Yu, 2017; Singh et al., 2013). The gyrotron is currently in an advanced stage of testing and commissioning at Institute for Plasma Research (IPR)-India (Singh et al., 2010, 2013). The microwave power from the gyrotron can be pulsed for a duration of 1msecs to a maximum duration of 3secs. This is done by pulsing the anode modulator power supply. The duty cycle of gyrotron pulsing is 1 pulse every 100 s. The desired mode purity of the gyrotron in TE03 mode is approximately 87%. The microwave power of 200kW at 42 GHz is extracted axially from the gyrotron. The gyrotron output mode is unpolarised, and it is not having an internal mode converter system which can convert this unpolarised mode into the polarised mode. Efficient plasma heating requires a narrow, axis-symmetric, gaussian pencil-like beam with linearly polarised radiation pattern (Fu et al., 2017). The required type of characteristics exists in HE11 (hybrid) mode with large isolation from cross polarisation components. Several techniques have been developed for transforming TE0n mode into a HE11 mode (Thumm, 1986; Thumm et al., 1985). One of the approaches is to design a set of axis-symmetric TE0n-TE01 mode converters followed by TE01-TE11 wriggle converter and TE11-HE11 mode conversion system to launch HE11 microwave power into the plasma chamber (Lyneis et al., 2014; Patel et al., 2018; Singh et al., 2010; Thumm, 1986; Thumm et al., 1985). Another approach is to design a TE01-TM11 bend converter followed by TM11-HE11 mode converter (Miller, 1952). These two conversion sequences are possible (Thumm et al., 1985): TE0n-TE01-TE11-HE11TE0n-TE01-TM11-HE11