Interest of thick-target bremsstrahlung for an innovating compact X-ray source

A compact plasma source (1 dm3 ) has been built at the Ecole Polytechnique, called ECR-X. The plasma is confined in a simple magnetic bottle with permanent magnets and heated by 2.45 GHz waves with a standard magnetron. A hot electron ring has been observed in the mid-plane and described previously. These hot electrons are taken advantage of to produce an important X-ray emission, and the specific features of thick-target bremsstrahlung in comparison with thin-target bremsstrahlung are exploited. The emission from the lateral walls of the chamber and the emission from a solid target located inside the plasma are recorded. The comparisons provide information on the confinement of the hot electrons in the 10-150 keV range, and recent diagnostics based on thick-target bremsstrahlung are applied. More importantly, when a well designed solid target is judiciously inserted into the electron ring, a punctual and intense X-ray source is achieved. The amplification of the emission in comparison with the plain plasma emission is accounted for by calculations involving the energy distribution of the free electrons. The characteristics of the source are indicated (brightness, perspectives for medical imaging utilizing the photons around 20 keV). (author)