Modeling Ion Extraction from First Toroidal Electron-Cyclotron-Resonance Ion Source

This project will use computational modeling to test the feasibility of a novel source of ions for particle accelerators, one of the most ubiquitous tools within the scientific community, with uses ranging from fundamental research to applications to cancer therapy, materials science, and nanofabrication. Several particle accelerators worldwide accelerate ions to very high velocities, approaching the speed of light. For example, the Large Hadron Collider at CERN accelerates ions of lead; the Relativistic Heavy Ion Collider at Brookhaven collided ions of gold to recreate and study the physics of the first 10 microseconds after the Big Bang. All require a source of ions. They also require the ions to have high charge, that is, to be stripped from as many electrons as possible. And they require many ions per unit time. The new concept proposed here builds on a type of ion source called an Electron Cyclotron Resonance Ion Source, but in a new doughnut-shaped geometry inspired by nuclear fusion experiments. Such a source, investigated within this project, would have greatly improved characteristics over those presently available.

There have been attempts over the years to increase the density, temperature and confinement-time of Electron Cyclotron Resonance Ion Source (ECRIS) plasmas, resulting in ions of higher charge. In fusion plasmas there is a push to increase the 'triple product' of nearly the same quantities for the sake of increasing the fusion reactivity. Inspired by this analogy, this project will numerically explore the ion-source-relevance of toroidal confinement, and compare it with the linear ECRIS paradigm, a magnetic mirror combined with an hexapolar field. At a first glance, the toroidal geometry is highly attractive. It makes a better use of the magnetic field, where toroidal ECRIS could be heated and confined at the same field. On the other hand, ion extraction will not be as straightforward as from a linear ECRIS. This project will numerically address this aspect by comparing magnetostatic, electrostatic and drift-based extraction techniques. The second aspect to investigate is how transport and confinement compare in a linear and a toroidal ECRIS: while hot ions of H, D and T are well-known from fusion research to be better confined in toroidal devices than linear ones, the same is not guaranteed for cold collisional ions of heavy species. Both problems will be addressed by numerically tracing the orbits of several 'test ions', by means of symplectic integrators, and by letting these ions undergo collisions - according to a distribution function - with each other and with ions and electrons from the background plasma.