On April 16th I arrived in Lausanne to begin my internship at the Swiss Plasma Center (SPC) at the EPFL, and thanks to FuseNet, my internship had been partially funded. At SPC, I had the opportunity to work with wonderful and bright researchers about developing a database for ELMy H-Mode plasmas for TCV.
H-Mode is a type of plasma confinement regime, achieved when a threshold value of injected power is reached, which possess interesting improvements to the general properties of a plasma, such as density, temperature and pressure, by the arising of a transport barrier at the edge of the plasma. As a consequence, there is an improvement in the energy confiment time (which doubles in value with respect to another regime of confinement at lower power, the L-Mode), thus increasing the overall probability that two nuclei inside the plasma will undergo nuclear fusion reactions.
However, in H-Mode plasmas instabilities can arise, the most important ones being the Edge Localized Modes (or ELMs), characterized by ejections of plasma after a certain MHD instability is reached. Several types of ELMs have been observed, but the Type I ELMs are the most dangerous ones because of their high energy and the high and pulsed thermal load on Plasma-Facing Components (PFCs), such as the divertor.
Database for TCV
Because of this deleterious effect on these components, prediction and control of the ELMs’ behavior are some of the goals when designing future tokamaks, with particular regards of ITER and, later, DEMO. Thus, Eurofusion endorsed the creation of an international database, from different machines, which will gather useful data to obtain empyrical formulae and scaling laws.
My work at SPC was to start implementing such database for TCV. During my six months of internship at SPC, I gained some insight to H-Mode plasmas and the development of ELMs, as well as general knowledge of plasma physics; after that, I began implementing the database by selecting the most promising plasma shots in the TCV database, under the simplifying requirement of stationariety of plasma density, external power supplied and plasma current, as well as fuelling and seeding injections; the data concerning the density and temperature profiles have been provided by the Thomson scattering diagnostics at TCV, which have then been corrected by using CHEASE, a code which iteratively solves the self-consistent problem given by the Grad-Shafranov equation, while the data that did not require knowledge of equilibrium have been taken from the older TCV database, LIUQE. Lastly, I tried to interpret the gathered data, trying to derive some behaviors and scaling laws represented in the EPED1 model.
Life at Lausanne
Lausanne left me a very good impression. Since my internship went from Spring to the end of Summer, I found a very warm and comfortable climate. It is a quiet city, especially during nighttime, even though the Lausanne-Flon district is always bursting with life since the majority of discos and pubs are there. The EPFL, where I spent most of my time, is an astounding university, its people being kind and hospitable, and the pubs located in the university are always full, and they are perfect places to hang out and drink a beer with your colleagues at the end of the week.
Overall, I had an astounding experience, and I hope to come back at Lausanne again, possibly for a Ph.D.
- Edoardo Rovere