= Spalling and Sputtering Cascades=

The gap between the rotor and the containment tube will be evacuated, but the vacuum will not be perfect. A 5600km long, 7 cm diameter tube has an inner surface of 1.23 square kilometers, and the 5 cm rotor has an outer surface of 0.88 square kilometers. If that vast surface is graphite (layered-graphene hexagonal grid structured carbon, .142nm bonds, 3.8E-17 m2 unit cell), there are about 8E25 atoms exposed on a smooth surface, more on a rough surface. The tube plus rotor might have 1E26 atoms exposed. It is very unlikely that all those atoms are strongly attached - some will break loose, travel across the 1 cm gap, and impact the opposite side at rotor speed. If that process breaks loose even more atoms, then the population of the gap can grow exponentially. The gap will fill with hot plasma, and the rotor and track will disintegrate.

If the average velocity of the material in the gap is half of the rotor speed, and the thermal velocity variance around that average is also half of the rotor speed (WAG), then the thermal energy of a gas goes up as half the rotor velocity squared times the nuclear mass. For carbon, and a 14km/s rotor, the energy per nucleon is 0.5*12*70002/6.0221E26 = 4.9E-19J = 3.05eV = 12000K. The bond energy of carbon is 3.6eV, and the ionization energy of carbon is 11.3eV,

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