Electron impact ionization of neutral and ionized fusion plasma constituents

In this project we determined and studied data and reactions important for applications in plasma physics (in particular fusion plasma technology), plasma chemistry and radiotherapy. We used apparatus and techniques developed in our institute in the framework of various international cooperations thus allowing us to obtain qualitative and quantitative information about electron impact ionization and electron attachment to atoms, molecules and clusters (aerosols). In addition we were able to study properties of these ions for instance prompt and delayed unimolecular decay reactions (including electron-induced decay ) and the reactive interaction of these ions with surfaces exhibiting in some cases novel type of reaction mechanisms. During the project period from 1999-2002 a total of 83 publications in international journals have been published and 42 invited and 111 poster contributions at international conferences have been presented. Especially interesting results include (i) the accurate determination of the production probability for H- ions from H2 via dissociative electron attachment (important for the heating of the plasma in a fusion tokamak), (ii) the first evidence for the occurrence of a liquid-gas like phase transition in a finite system (cluster) by measuring the caloric curve and other critical phenomena (here we discovered a paradox phenomenon: if small particles are heated their temperature decreases!!!)and (iii) the discovery that building blocks of life (such as uracil) can be destroyed by interaction with electrons having no kinetic energy (this has far reaching consequences for radiation damage in living cells for e.g. cancer therapy etc.). In addition we were able for the first time to analyse in detail the ionisation of water molecules and nucleic acids (uracil) by proton and hydrogen impact also taking into account the fate of the projectile in terms of its charge state, this gives valuable information for the interpretation of the Bragg peak which is essential in radiotherapy.