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Isabella Mario - Master Thesis at IPP Garching

Master Thesis at the Max-Planck Institute - Garching, Germany
Reported by Isabella Mario. Powered by FuseNet.

My name is Isabella Mario and I am a student from the University of Padova in Italy. I am 24 years old and I have completed my master degree in Physics on the 28th of September in 2016.

My interest in Neutral Beam Injectors

Nuclear Fusion is one of my main interests, because it promisses to provide the world a possibility for a safe and environmentally friendly energy source. The ITER-reactor, which is the most advanced experiment in nuclear fusion, is very important in this regard, since it aims to prove the feasibility of fusion for civil use. In order to reach the required plasma temperatures and currents, ITER partially relies on neutral beam injectors (NBI) to provide the heating and current drive (two NBI systems of 16.5 MW each will be installed in ITER).

My interest in thermonuclear fusion, NBI systems and, in particular, the development of diagnostics related to the characterisation of neutral beams, arose 2 years ago during my bachelor thesis, during which I started working in this field. After the positive experiences of my bachelor thesis, I decided that I wanted to continue working on neutral beam injectors. However, for my master thesis I wanted to do that in a laboratory abroad: the Max-Planck Institut für Plasmaphysik (IPP) in Garching, Germany.

ELISE: a step towards the ITER NBI system.

In March 2016 I started my adventure at IPP, working on infrared thermography analysis of the powerful hydrogen beam at ELISE, which stands for Extraction from a Large Ion Source Experiment. As such, ELISE is inteded to bridge the gap between small-scale prototypes and the full-sized ITER NBI source. The NBI uses a negative ion source with an extraction and acceleration system up to 60 kV. During my thesis, I have characterised the beam properties of ELISE for different operational conditions by means of an infrared analysis of the beam profile on a diagnostic calorimeter. Properties of interest were, for example, the beam width and the beam deflection.

NBI-beam characterisation

In order to analyse the beam, an IR camera was installed outside the tank of the experiment, which was used to observe a diagnostic calorimeter through one of the diagnostic ports in the vessel. Immediately after exposing the calorimeter to the NBI-beam, the beam imprint is measured by the IR camera, which allowed me to locally measure the heat deposited by the beam. To make local measurements easier and to avoid transversal heat conduction, the surface of the calorimeter consisted of a grid of 30 x 30 small blocks with a size of 3.8 cm. Using this procedure, the beam imprint on the calorimeter could be described by a 30 x 30 matrix. Subsequently, by fitting a convolution of Gaussian functions to the acquired imprint, the beam deflection and the beam width could respectively be determined from the positions and widths of the Gaussians fit-functions.


The diagnostic system for ELISE and an IR image of the caloriemeter [Courtesy of IPP].

Repeating this experiment for several combinations of set-up parameters, has allowed me to study these two beam-characteristic parameters as a function of the set-up parameters of the experiment, such as the extraction and acceleration potential, the filtering magnetic field, the gas pressure and so on. The results of these measurements were all automatically collected in a database, which now contains information for all beams of the last two years. The reliability and the robustness of the diagnostic were tested by means of an initial cross-check with other beam diagnostics. Finally, the results of my work will contribute to understand the physics behind beam parameter variations.

Adapting diagnostics to give quantitive information

During my project, I was able to collaborate with the other researchers in the group. Moreover, I have learnt how to use VISUAL BASIC, MATLAB and, at the end, I was able to create a database for the diagnostic calorimeter of ELISE that is easily accessible. Due to my work, the diagnostic calorimeter can now be used to give quantitative information on the beam with a precision of about 1 cm, whereas it had previously only been used for a qualitative analysis.

I found my work at IPP a very exciting and satisfying experience, not just because of the work that I have done, but also for the persons that I have met. I would like to thank FuseNet, the European fusion education network, for enabling me to do this by providing me with a solid fund.