Defense Intelligence Reference Document Pulsed High-Power Microwave Source Technology

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Figure 2 shows an example of a Marx generator circuit.
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Figure 2. Example of Marx Generator Circuit
TRANSFORMER BASED GENERATORS
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Transformer-based pulse generators have also been used for many years as prime
power for HPM sources. Transformers with ferrite cores have been used successfully in
sources with multigigawatt output powers at kilohertz repetition rates. Ferrite
development is an area where substantial gains could be made in HPM sources.
Typically, programs are under time or budget constraints and do not give adequate
attention to this research. As a result, little or no progress in new ferrite materials for
pulsed operation has been made. Ferrites with increased frequency ranges and
increased saturation flux density are needed. Air core transformers are used at higher
flux densities and are often of the resonant variety because of their decreased coupling
levels. Resonant transformers develop peak voltages after multiple cycles owing to
coupling effects. Dual-resonant air core pulse transformers are prevalent and require
coupling coefficients of 0.8, producing peak secondary voltage and maximum energy
transfer after an initial reverse voltage swing. In dual-resonant designs, two
frequencies or resonant modes are generated, and the output is the superposition of
the two modes. Transformer systems generally require the primary circuit to be
matched or tuned to the secondary, or vice versa.
EXPLOSIVELY DRIVEN GENERATORS
Explosively driven generators, also called flux compression generators (FCGs), work by
setting up a strong magnetic field between two conductors, usually by discharging a
capacitor bank charged to high voltage through an inductive coil. A conducting hollow
cylinder filled with high explosives is placed in the center of the coil, filling the region
between the two conductors with magnetic flux. The explosives are then used to
compress the initial magnetic flux by driving the conducting cylinder surface, which
contains the flux, outward into the current carrying coil. Work done by the conductors
moving against the magnetic field results in a huge increase in the EM energy. The
additional energy comes from chemical energy stored in the explosives. Thus, FCGs
essentially convert a portion of the chemical explosive energy into EM energy. The
explosively driven conductor is called an armature, and the nondriven inductive coil of
the generator is called the stator. Miniaturizing the generators and fine-tuning the
magnetohydrodynamic aspects takes years and is still an area of intense research.
Material properties under the enormous forces involved are also required for success.
Many hours of research and computer code writing and testing go into the selection of
every single material used. One problem with this form of HPM source is that of
coupling the energy to the load. Attempts to energize the load by direct generation
often result in the development of excessive internal generator voltages and
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