3.6M north10.pdf - Dean-O's Toy Box

More documents

Recommendations

Info

Cathode Pulsers: Hard-Tube Modulators (10) 187 Permarwntmagnets~ “T sourcegrid ~ ‘“’’”’gM 19 : ● . i cathode / \ \ C43rkr- ; . I Iiie I t I i 1. Shapeof sourceplasma Carrnaicanode insulator ~ Anode arm! :magnets rid ~ Hydrc@n.sarvoir l.- Mo~anum (cold)cathode Figure 10-29. Cross-section view of Crossatron odoff control switch. on. A negative pulse applied to the same grid will turn it off, much in the same fashion as a gate-turn-off (GTO) thyristor. The amount of current that can be gated off is unlikely to be as much as that which can be gated on, unless the grid construction of the tube is deliberately altered to optimize turn-off instead of turn-on. The ability of the device to emulate full-control+r at least 2/3 control, if one considers intrapulse-current-amplitude control as being worth l/3-derives horn the action of the crossed magnetic and electric fields. Figure 10-29 shows the cross section of a typical Crossatron. Its design is coaxial-cylindrical. It has an internal anode, its current flow is radial, and it has a cold molybdenum cathode and two grids. A continuous voltage is applied to the “source” grid, which stimulates a continuous “source” plasma. The magnets, which surround the tube, are radially magnetized. They produce alternating north and south poles that progress vertically up the tube and a magnetic field that matches the shape of the source plasma. A positive-going trigger pulse applied to the control grid attracts plasma into the region between control grid and anode and initiates full conduction between cathode and anode. A negative-going pulse applied to the control grid will reverse the process.
188 High-Power Microwave-Tube Transmitters \ / WI characferistlcof crossed-field amplifier(QK-522 Arnplifron) b \ AV/Al =200ohms (0.128xstatic resistance) \ 1/ I / \ VAcharacferistlc oflhar- \ 1+~$’!i!liae] . \ / . Above-the-kneeregbn of friode \ ortetrodeswitchtube AWAI-75 kohms \ ~ Linearresisfancaload AV/Al.1583dims ----- ---- \ \ , Operafiig point 50 kV, 32A (1583 ohms) Cuxka.he regionof trbde Loadiii of line-type a tefrode switch tube modulatormatckedto AWAI -300 OhlS operating-pointresistance I I . / . / \ o 20 40 80 80 100 voltage (w) Figure 10-30. Load-line representation of modulator/load interaction. If one of these devices is used to supplant a vacuum tube as the switch in a hard-tube modulator, external resistance must be provided to limit current in case of a shoot-through event. As with a gridded vacuum tube, the Crossatron is almost always more susceptible to damage than the diode-type microwave tube it is pulse modulating. For this reason, it determines the magnitude of the series resistance. The value of this resistance, in turn, often determines the usable output power from the switch because its resistance value can easily be greater than the ratio of conduction-tube drop and output current.
Page 1 and 2: 10. Cathode Pulsers: Hard-Tube Modu
Page 3 and 4: 148 High-Power Microwave-Tube Trans
Page 41: 186 High-Power Microwave-Tube Trans

3.6M north10.pdf - Dean-O's Toy Box

Create successful ePaper yourself

Delete template?

Save as template?