Cavity magnetron

A cross-sectional diagram of a resonant cavity magnetron. The magnetic field is perpendicular to the plane of the diagram. 

Resonant cavity magnetron high-power high-frequency oscillator... 

Cavity magnetron (Hemy Boot and John Randall) Boot and Randall develop the cavity magnetron, which advances radar technology. 

This chapter provides a detailed description of the various commercially available microwave reactors that are dedicated for microwave-assisted organic synthesis. A comprehensive coverage of microwave oven design, applicator theory, and a description of waveguides, magnetrons, and microwave cavities lies beyond the scope of this book. Excellent coverage of these topics can be found elsewhere [1—4]. An overview of experimental, non-commercial microwave reactors has recently been presented by Stuerga and Delmotte [4],... 

Based on their microwave digestion system, Milestone offers the MicroSYNTH labstation (also known as ETHOS series) multimode instrument (Fig. 3.4 and Table 3.1), which is available with various accessories. Two magnetrons deliver 1000 W microwave output power and a patented pyramid-shaped microwave diffuser ensures homogeneous microwave distribution within the cavity [12]. 

When microwaves travel along a waveguide terminated by the microwave heating application (for example a resonant cavity loaded by the object to be heated) a reflected wave travels back towards the source. The wave traveling towards the termination is called the incident wave and the wave traveling back to the magnetron is... 

Fig. 10.1 Microwave batch reactor 1. micro-wave cavity, 2. magnetron, 3. stirring bar, 4. alir minum plate, 5. magnetic stirrer, 6. IR pyrometer, 7. switch on/off, 8. watercooler.

Fig. 14.5 A modified MW oven for microwave photochemistry experiments. A. magnetron, B. reaction mixture with the EDL and a magnetic stir bar, C. aluminum plate, D. magnetic stirrer, E. infrared pyrometer, F. circulating water in a glass tube, G. dummy load inside the oven cavity [88]. With permission from Elsevier Science.

Figure 9.1 Schematic diagram of the MBR65.1, Reaction vessel 2, top flange 3, cold-finger 4, pressure meter 5, magnetron 6, forward/reverse power meters 7, magnetron power supply 8, magnetic stirrer 9, computer 10, optic fibre thermometer 11, load matching device 12, waveguide 13, multi-modal cavity (applicator).

Figure 3.5. Multi-mode microwave reactor 1 - magnetron, 2 - rotating deflector, 3 -multi-mode cavity, 4 - reaction vessel, A - non-regular shape of electromagnetic waves as a superposition of a number of waves.

The difference between the magnetron and other vacuum tubes is that the electron flow passes along a spiral this route is created by an external magnetic field B (Fig. 3.4). The electron cloud produces resonance cavities several times in its trip to the anode. These cavities work as Helmholtz resonators and produce oscillations of fixed frequency, determined by the cavity dimensions small cavities produce higher frequencies, large cavities smaller frequencies. The antenna in the right zone collects the oscillations. 

The basic components of a microwave system include a microwave generator (magnetron), a waveguide for transmission, a resonant cavity, and a power supply. For safety and other reasons, domestic microwave ovens are not suitable for laboratory use. There are two types of laboratory microwave units. One uses closed extraction vessels under elevated pressure the other uses open vessels under atmospheric pressure. Table 3.12 lists the features of some commercial MAE systems. 

Microwaves can be produced by four types of macroscopic cavity resonators that use the ballistic motion of electrons across a cavity opening the klystron, the magnetron, the traveling-wave tube (TWT), and the gyrotron. They can also be generated by field-effect transistors at low frequencies, by Gunn42 diodes, and by IMP ATT diodes. 

The size of the cavities determines the resonant frequency of both klystrons and magnetrons, thereby determining the frequency of emitted microwaves. The frequency of magnetrons is not precisely controllable where... 

The magnetron is the device that generates the microwaves. Wave guides direct these waves to the oven cavity. 

Resonant eavities they have been built into the anode. Random noise in the electron swarm causes occasional electrons to strike these eavities are such that most radiation frequencies die out. Microwave frequencies, on the other hand, bounce around the cavities and tend to grow, thus getting their energy from the magnetron, passes through the wave guides, and enters the cavity. 

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