Magnetrons are high-powered vacuum tubes used to generate microwave signals. There are many types of products. Examples include cavity magnetrons, cylindrical magnetrons, circular magnetrons, rectangular magnetrons, and sputtering magnetrons. Applications for magnetrons include radar, microwave ovens, and lighting systems. In radar devices, magnetrons use very short pulses of applied voltage. In microwave ovens, a waveguide leads to a port in the cooking chamber. In lighting systems such as sulphur lamps and metal halide lamps, magnetrons also produce a microwave field. Cavity magnetrons use a high-voltage DC power supply to bring a hot-filament cathode to a high negative potential. Permanent magnets located next to the filament produce a magnetic field that causes electrons to spiral outward instead of moving directly toward the anode. Cylindrical cavities that are spaced around the rim of the magnetron chamber induce a resonant, high-frequency field. In turn, this causes the electrons to accumulate in groups. An antenna connected to a waveguide extracts a portion of this radio frequency (RF) field, and the waveguide directs the RF energy to the load. Circular magnetrons carry product specifications for maximum sputtering power, cooling requirements, target, mounting style, maximum temperature, source-to-substrate distance, and materials. There are five parameters for maximum sputtering power: direct current (DC), radio frequency (RF), cathode voltage, discharge current, and operating pressure. Cooling requirements include flow rate at maximum power, maximum input temperature, and open drain. Form, diameter, thickness, and cooling method are target parameters. Materials of construction for magnetrons include copper and stainless steel. Rectangular magnetrons are well-suited for coating broad substrates and achieving very high throughputs. Like circular magnetrons, rectangular magnetrons may use profiled magnets and turbulent water flow. Some rectangular magnetrons are designed for aerospace, decorative coating, defense, dental, medical, optical, or packaging applications. Other rectangular magnetrons are used in the production of architectural glass, flat panel displays (FPDs), magnetic storage media, semiconductors, and wear-resistant coatings. Magnetron suppliers may provide custom magnetrons as well as sputtering targets and materials. Custom magnetrons are designed for specialized applications. They are available as complete systems, and include components such as mounting hardware, shutter assemblies, and gas manifolds. Sputtering targets and materials are available as either prefabricated or bulk-form products. They are produced via processes such as hot pressing, vacuum sintering, and vacuum melting. Sputtering materials cover a range of metals and alloys.