Prototyping Liquid Argon Dark Matter Detector

The aim of the project is to build a small ion chamber serving as a prototype of a much larger dark matter detector to be built in the future. This is a brand-new project at Fermilab; my task would be to come up with the prototype ion chamber and a first set of measurements. To start with, the small chamber is going to be filled with Argon extracted from the air, i.e. predominantly 40Ar and traces of the radioactive 39Ar isotope. The Argon will be in its gaseous phase when introduced in the chamber. Some properties of the inside volume are being recorded (electric field configuration, voltage output etc.). Subsequently, we will make use of Argon extracted from underground gas wells, which contains smaller concentrations of decaying 39Ar. The beta-decay of 39Ar must be well monitored, because it is the main background source for WIMP dark matter searches. Also, the chamber is put under high voltage by sending a current through an iron rod placed along the horizontal axis of the cylindrical chamber. After the passing of a highly energetic particle, the electric field separates the newly formed positive ions and negatively charged electrons. After data taking and analysis of this configuration, the next step consists in replacing the gaseous Argon with liquid Argon and take new data samples to be compared with the previous ones. The project combines aspects of cryogenic design, work with low-radioactivity material and data analysis. Furthermore, the CERN-software Garfield allows us to simulate the electric field configuration inside the chamber. In fact, the exact field configuration in three dimensions is not known for most drift chamber geometries. In addition, the geometry can become highly complicated locally (the shapes of the electrodes, for instance). The knowledge of the field configuration is of particular importance,