Anomalous intense driver (AID) concept Page: 12 of 56
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with a pulse width of approximately 100 ns. The overall electrical efficiency
for such a generator would be 40 to 45%. If the energy remaining in the Marx
generator is recovered, the energy efficiency of such a generator would be 80
to 90%.
As shown in Fig. 11, high-impedance generators are composed of five basic
components. A dc charging system is used to charge the Marx generator, which
is the primary energy storage component. The Marx generator consists of a
large number of stages which are charged in parallel and discharged in series
using spark gap switches. A typical Marx stage consists of two capacitors con-
nected in series with a center ground to allow positive and negative dc charg-
ing;; see Fig. 12a.
The Marx generator is then used to charge a Blumlein. A Blumlein is essen-
tially two coaxial transmission lines connected in series with the diode imped-
ance Z^; see Fig. 12b. Physically, the Blumlein appears as three concentric,
annular conductors. This folded configuration is used to reduce the spatial
dimension of the Blumlein. In operation, the center conductor is charged
through an inductor Lc which appears as a short. Once charged, the switch Sq
connecting the center and intermediate conductors is closed, and the inner
transmission line begins to discharge with a pulse propagating toward the diode.
When the pulse hits the impedance discontinuity, a voltage appears across the
diode. As opposed to the shorted inner transmission line, which has an imped-
ance Zj, the outer transmission line, with impedance ZQ, is open. Thus, for a
properly matched configuration (ZQ = - Z^/2) a voltage equal to charge
voltage on the inner conductor appears across the diode for a period twice the
propagation time down the transmission line. The inductor Lc appears as an
open circuit during the Blumlein discharge. For high voltages the Blumlein uses
transformer oil as a dielectric.
Due to the physical configuration of the Blumlein, it is difficult to
design the inner and outer transmission lines such than Z^ = Z^. Thus, there
is typically a very small, but noneligible, voltage that appears across the
diode during the Blumlein charge. From the standpoint of proper operation of a
high-current density diode, this so-called prepulse must be suppressed. Signif-
icant progress in prepulse suppression has occurred in the past few years.
Through the use of prepulse switches combined with careful design of the feed
and diode region, a prepulse of less than 50 kV has been demonstrated for a 9
37
MV Blumlein charge. With this advance in prepulse suppression beam particle
10
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Thode, L.E. Anomalous intense driver (AID) concept, report, March 1, 1980; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1093537/m1/12/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.