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

Cathode Pulsers: Hard-Tube Modulators (10) 187
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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.