Local regions of high-pressure plasma in a vacuum spark

The formation of local regions of high-temperature, high-pressure plasma, 'hot-spots' in a vacuum spark is studied using X-ray spectroscopy and holography. Measurements of the dimensions of the hot-spots, of the absolute flux of radiation and of the spectral composition of the X-ray emission, have been analyzed to give order-of-magnitude values for the local electron density, temperature and plasma lifetime. It appears that the plasma pressure is approximately 10,000,000 atm and that the formation of the hot spots requires intense heating rates more commonly associated with focused laser beams, i.e. approximately 10 to the 15th W/cu cm. It is probable that in the vacuum spark electron beams are responsible for plasma heating. Possible mechanisms for concentrating energy deposition in localized regions are discussed.