Overcoming the Child-Langmuir law via the magnetic mirror effect
  The maximum current in a vacuum tube prescribed by the classical Child-Langmuir law can be overcome, when the space-charge effect of the induced potential is mitigated by the mirror effect in a spatially varying magnetic field. The current could exceed the Child-Langmuir value by as much as a few factors. The regime of practical interest is examined. 
S. Son and Sung Joon Moon
physics.plasm-ph physics.class-ph physics.flu-dyn