AAWSAP DIRD, Advanced Nuclear Propulsion for Manned Deep Space Missions, March 2010

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UNCLASSIFIED//FOR OFFl@IAL 148E OHL¥
To erect the Super Marx, its capacitors C are switched into series by circular spark gap
switches S. The capacitors of the Super Marx are magnetically levitated inside an
evacuated tunnel and magnetically insulated against the wall of the tunnel by an axial
magnetic field B, generated by superconducting external magnetic field coils M. The
magnetic insulation criterion requires that B > E, where B is measured in gauss and E
in electrostatic cgs units. If B = 3x 104 G, for example, magnetic insulation is possible up
to E = 3xl04 esu ~ 107 Vjcm, at the limit of electron field emission. To withstand a
voltage of 109 volts between the outer positively charged surface of the capacitors in
series and the tunnel wall then requires a distance somewhat greater than 1 meter.
The capacitance of one co-axial capacitor with the inner and outer radius Ro and R1 of
length / and filled with a dielectric of dielectric constant E is
I
C = c
(
) [cm]
(34)
21n R) R0
Assuming a breakdown strength of the dielectric larger than 3 x 104 V/cm and a
potential difference of 107 volts between the inner and outer conductor, the smallest
distance of separation d between both conductors has to be d = R, - Ro =3 x 102 cm. If,
for example, l = 1.6 x 103 cm, R, = l/2 =8 x 102 cm, and & =10 , one finds that
C =2xl04 cm. For these numbers, the energy e stored in the capacitor
(V =l07 volts =3xl04 esu) is
(35)
which for the 100 capacitors of the Super Marx add up to e - 10'5 erg. About 10 times
more energy can be stored if the radius of the capacitor is about 3 times larger, if there
is a larger dielectric constant, or if a combination of these conditions exists. This means
that for about 100 capacitors, energy 1016 erg = 1 GJ can be stored in the mile-long
Super Marx.
Another idea, proposed by Fuelling (Reference 19), is to place the ordinary Marx
generators of the first stage inside the coaxial capacitors of the Super Marx. The
advantage of this configuration is that it does not require disconnection of the Marx
generators from the capacitors of the Super Marx prior to its firing. Because the
charging and discharging of the Super Marx can be done very fast, one can use
compact water capacitors where & =80 . And instead of magnetic insulation of the
capacitors of the Super Marx against the outer wall, one can perhaps use transformer
oil for the insulation. Giving each inner segment of the Super Marx enough buoyancy,
for example by adding air chambers, these segments can be suspended in the
transformer oil. There the outer radius of the co-axial capacitors is much larger. This
permits storage of gigajoule energies in the Super Marx.
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