The Swiss Plasma Center seeks PhD students throughout the year and encourages candidates to apply at any time. PhD projects are discussed with the prospective thesis supervisor at SPC during the application phase, and can be tuned to the candidate’s interest. A non-exhaustive list of possible projects can be found below.
If you need more information on any proposal, send an e-mail to the corresponding contact person.
If you want to apply, please follow the procedure indicated on this page.
Thank you.
Experimental physics on the TCV tokamak
Experimental physics in the Basic Physics Plasma group
Experimental physics at the BioPlasmas Lab
Open positions in experimental physics on the TCV tokamak
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Motional-Stark spectroscopy for current distribution determination in the plasma core
Contact person: Dr. Dmytry Mykytchuk, Dr. MER Stefano Coda
Information on the current distribution of the current flowing, mostly toroidally, within the tokamak core is important in understanding the governing physics of impacting plasma instabilities and in seeking their mitigation. This information is also crucial to reliable plasma equilibrium reconstruction, particularly in scenarios where the current distribution is significantly changed by the electron cyclotron and/or neutral beam heating systems, both of which are exploited on TCV.
To obtain the current profile spectroscopically, a beam of fast, illuminating, neutral particles is injected into the plasma core. The polarization of emission resulting from these beam particles interacting with the plasma can be used to reveal the magnetic field direction at the emitting plasma location. The photon polarization is set by the direction of the electric field in the rest frame of a beam particle crossing the magnetic field, E=VxB (the effect of this electric field on the atomic energy levels is called Motional-Stark effect). A new spectroscopic system has been recently installed on TCV to measure the emission intensity distribution as a function of wavelength for Dα emission. The magnetic field is obtained by regressing the measured Dα intensity distribution to a model that considers both Motional-Stark and Zeeman effects, with the magnetic field as a variable. The current distribution is then obtained using Ampere’s law from the field measured at multiple radii across the core.
The PhD student will be expected to take responsibility for the remaining technical developments, namely: i) commissioning and calibration of the new spectroscopic system using dedicated discharge discharge scenarios operated on TCV, ii) development of the analysis workflow to regress measurements upon atomic model for Motional-Stark effect, iii) measurement of the current distribution in plasma scenarios with non-inductive current drive, iv) study of the plasma equilibrium reconstruction by the LIUQE code when constrained by these measurements of the core magnetic field. Points iii and iv will evolve into the more physics-based part of the thesis, which will be built around plasma regimes in which the details of the current profile play a key role: the so-called advanced scenario with flat or even hollow current profiles, featuring increased core confinement, is a very likely candidate – but more options will be available within the constantly shifting experimental program of TCV.
- Suprathermal electron physics in the TCV tokamak
Contact person: Dr. MER S. Coda, Dr. J. Decker
Highly energetic (“suprathermal”) electrons can be generated in a tokamak plasma by various mechanisms, including externally launched electromagnetic waves and internal magnetohydrodynamic (MHD) instabilities, possibly involving reconnection events. Invariably, these electrons hold the key to understanding the phenomena that generate them. In the case of electron cyclotron resonance heating (ECRH), a powerful auxiliary heating technique that is planned for instability control in future reactors and is the centerpiece of the TCV tokamak, the suprathermal electron population mediates the physics of heating and particularly current drive. In the case of MHD, strong electric fields associated with magnetic islands are responsible for accelerating electrons to high energies, and diagnosing these electrons is necessary to understand the dynamics of magnetic reconnection and island formation. Additionally, MHD modes can also be destabilized by the fast-electron population itself.
In very low-density plasmas or after a disruption, the inductive toroidal electric field can accelerate electrons to extremely high energies (in the MeV range). These so-called runaway electrons (RE) are a concern to a reactor since their sudden loss can inflict significant damage to the first wall.
Improving the description of fast electron dynamics is necessary to resolve important standing issues. ECCD is observed to be less efficient and less localized than expected from standard models. RE transport must be better described to calculate the effective critical field and provide quantitative predictions of RE population evolution. TCV is equipped with a state-of-the-art, 4-camera hard X-ray (HXR) tomographic spectrometer, a powerful and unequalled diagnostic for the study of fast electrons. This is complemented by high-field-side and vertical ECE systems and a soft X-ray spectrometer. On the modelling side, the main fast electron diagnostics (HXR and ECE) are available as synthetic diagnostics associated with the Fokker-Planck kinetic solver LUKE.
There is huge potential for highly innovative thesis work breaking new ground in the physics of suprathermal electrons and associated phenomena, ranging from ECRH to MHD to runaway generation. The following specific subject is particularly envisioned:
Compare experimental measurements from several diagnostics with the corresponding modelled emission reconstructed from a common kinetic distribution. This multiply constrained model should help resolve some of the standing issues by simultaneously using the data of several diagnostics that are complementary in their multi-dimensional resolution. The work will require an intense modelling effort including theoretical developments and scientific programming. Additional experiments will likely be designed and conducted in order to refine the investigation.
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Divertor impurity distribution and compression studies
Contact persons: Prof. Christian Theiler ; Dr. Olivier Février; Dr. Artur Perek
It is widely recognized that in reactor conditions, impurity seeding will be needed for safe power exhaust. Key related, open questions are what divertor impurity concentrations will be required and to what extent impurities enter into the core plasma, diluting the fusion fuel. Divertor impurity concentrations and impurity compression (the ratio of divertor to core impurity density) are therefore key parameters. Understanding how these depend upon the divertor and core regimes, the level of divertor baffling, the divertor geometry and the seeding location become important. These key questions must be addressed for the upcoming Tightly-Baffled, Long-Legged Divertor (TBLLD) upgrade on TCV. They remain critical for exhaust studies in general, in particular for novel ‘ELM-free’ high-confinement modes and X-point radiator investigations.
A prerequisite for such studies is the detailed information on impurity distributions within the TCV boundary plasma, a task often requiring strong model assumptions than engender large uncertainties. The goal of this PhD project is to develop experimental techniques for nitrogen concentration measurements in TCV (the gas of most interest in extrinsically seeded detachment studies on TCV), validate them using numerical simulations and to investigate the required impurity concentrations for detachment and relate this to impurity compression as a function of divertor closure/configuration, seeding locations, and core plasma regime.
A measurement device, central to this work, is the multispectral imaging system MANTIS; an innovative imaging diagnostic providing ten, or more, filtered camera images for the same, tangential view of the TCV divertor with up to 800 Hz temporal resolution. The successful candidate will take operational responsibility for this system, learn how to tomographically invert the obtained, line-integrated, images and use line-ratio methods and absolute emission intensities, combined with collisional-radiative models, to infer plasma and impurity quantities across the divertor volume. This can be augmented by Charge-Exchange spectroscopic Nitrogen density measurements within the confined plasma core to obtain a complete view of the impurity transport and effect upon plasma discharge operations.
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Multi-diagnostic study of core turbulence
Contact person: Dr. Laurie Porte ; Dr. MER Stefano Coda
Energy and particle confinement in magnetised plasma is anomalous: it is not as good as classical theory predicts. Advances in measurement and computation now suggest that turbulence may be the root cause of anomalous heat and particle confinement. TCV is equipped with a set of diagnostics dedicated to measurement of both electron density and temperature turbulence. Ultra-fast reflectometry and tangential phase contrast imaging (T-PCI) are used to measure turbulence in electron density. Correlation electron cyclotron emission (CECE) is used to measure turbulence in electron temperature. A PhD thesis is proposed where core turbulence is studied using all of the above diagnostic systems. The first topic would be to make simultaneous measurements of electron density and temperature fluctuations in the same plasma volume and to extract the cross-phase between the two. This is motivated by the fact that gyrokinetic codes, that are used to simulate heat and particle transport that is driven by turbulence, provide estimates of cross-phase between density and temperature fluctuations. Direct comparison between experiment and computation is, therefore, possible. A second, equally important yet more demanding, thrust would be to explore the effect of magnetic islands on turbulence. Magnetic islands are associated with magnetohydrodynamic (MHD) instability in magnetically confined plasma. They modulate the local pressure profile and, as a result, modulate turbulence. The second thrust would be to explore, experimentally, the effect of islands on turbulence. The PhD candidate will be expected to be able to operate the diagnostics, in collaboration with experienced diagnostic operators, and to interact with the TCV experimental team to design and produce experimental scenarios that permit this study. In parallel the candidate will be expected to interact, very closely, with the theory group to ensure efficient and fruitful physics studies.
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Study of Electron Cyclotron Emission (ECE) on TCV Tokamak
Contact person: Prof. Ambrogio Fasoli ; Dr. Laurie Porte
Electron Cyclotron Emission (ECE) is ubiquitous in magnetically confined plasma. It is generated by the acceleration of free electrons immersed in a magnetic field and, in the right conditions, can be used to determine the electron temperature of the plasma with high spatial and temporal resolution. By changing the line of sight, or in the presence of strong microwave heating, the frequency spectrum of ECE provides information on the electron energy distribution. This information provides information on the generation and the dynamics of ‘runaway’ electrons in tokamaks that are of sufficient energy to damage the vacuum vessel and are to be avoided. It also is important in the characterisation of electron cyclotron current drive efficiency which is a key parameter for future steady state tokamak designs. Now, by making very highly resolved measurements of the ECE spectrum and by making estimates of the statistical properties of the measured signal it is possible to infer the spatial distribution and spectral content of electron turbulence. This measurement is key in the understanding of energy and heat transport in tokamaks; a subject that is a dynamic area of tokamak research. TCV is equipped with a suite of heterodyne radiometers that permit detailed study of ECE on TCV. Making use of the numerous lines of sight available, measurements can be made of electron temperature, electron turbulence and of the dynamics of the electron energy distribution function in various plasma regimes. A PhD dissertation is proposed where the candidate is expected to contribute to the operation of the whole suite of ECE diagnostic systems on TCV. At the same time the candidate will be expected to develop new and robust means of calibration of the systems and to develop data analysis tools. The candidate will be free to contribute original work in collaboration with the TCV team, in any or all fields of research. This may include extensive modelling of ECE emission and its relation to non-thermal electron energy distributions or, indeed, the use of machine learning and Bayesian techniques for optimising diagnostic data analysis. The candidate may prefer more technical challenges like, for example but not limited to, implementing real-time control of filters and polarisers.
- Visible light 2D camera diagnostics of the TCV divertor
Contact person: Dr. MER B.P. Duval or Dr. MER H. Reimerdes
One of the outstanding problems that requires resolution for a functional Fusion reactor is that of Fusion power exhaust. In the most promising magnetic “bottle” fusion plasma configuration (the Tokamak such as the TCV device at the Swiss Plasma Center), plasma is directed to a special region called the divertor. Due to the high power exhaust of a fusion reactor, if unmitigated, the power density reaching the divertor would quickly damage the reactor vessel. For this reason, considerable research effort is dedicated to controlling this heat flux and changing the magnetic configuration (the “bottle” shape) and adding highly radiating impurities to the plasma edge that can reduce the heat flux to tolerable levels. To understand the plasma performance in these endeavours, we use plasma diagnostics. Plasmas in this divertor region, where the plasma is relatively cold (compared to the fusion core), emit a lot of power as visible light. Diagnostics using multiple visible cameras are used to monitor this light that, by using filters to isolate specific spectral lines, can be associated with the radiation from chosen impurity species. This PhD project aims at two such diagnostics. The first, called MANTIS, is a multi camera system that has been developed over the last 5 years to provide 2D plasma images with repetition rates up to 1kHz, of up to 10 separate spectral lines whose intensity distributions can be used to diagnose the plasma conditions as they vary through TCV’s plasma discharge. In the second, which shall be a new diagnostic for TCV, the doppler shift of the light from the plasma is cast as a set of fringes on the camera image. From this fringe pattern, the plasma flow across the whole divertor region can be tracked. This technique, known as Coherence Imaging Spectroscopy, or CIS, will be designed, built and operated on TCV with the collaboration of international experts. These are complex optical systems that will require an enthusiastic and practical minded candidate who enjoys working, and evolving, within a lively research group.
- Fast-ion deuterium alpha (FIDA) Spectroscopy
Contact person:Dr. MER B.P. Duval
Neutral heating beams are often used in thermonuclear devices to heat the plasma above that achievable by passing large currents through the plasma resistance (Ohmic Heating). The fast neutral atoms injected are well above thermal (called fast-ions) and must slow down in the plasma to efficiently heat the thermal plasma. FIDA spectroscopy takes the light emitted from the interaction of the fast ions/atoms within the plasma to analyse the spatial and velocity profiles of these ions from injection to thermalisation. These fast ions can be taken as a proxy for the fast Helium atoms created by particle fusion (the basic process of energy production concerned) and as they slow, they are subject to many interactions with the target plasma that can prematurely eject these fast ions, which could be catastrophic as their energy is used to keep the plasma hot and thus reactive. TCV has recently installed such a fast ion heating beam and preliminary FIDA spectroscopy shows a rich range of physical processes. This thesis will commence with the installation of two multi-chord spectroscopic systems to observe FIDA light. Many experimental probes on the effect of plasma shape and other parameters (density, temperature etc.) will follow. The student will use the FIDASIM program developed by a worldwide group to interpret the spectra together with detailed plasma transport modelling to diagnose the fast ion behaviour. This work will be part of a new and developing group at the SPC looking into fast ion behaviour on the TCV Tokamak.
Thomson scattering data analysis for real-time applicationsContact person: Dr. P. Blanchard
On the TCV tokamak, reliable electron temperature and density profiles are routinely obtained from Thomson Scattering (TS) measurements. In 2013-2014, the TS diagnostic has undergone a substantial upgrade which is opening the road to real-time (RT) applications of such parameters.
In the frame of a PhD, algorithms for RT analysis of TS signals should be first developed and tested along with the implementation of a new DAQ system. The availability of electron temperature and density profiles in RT could then be used for TCV scenario development and actuator control like microwave heating system as well as inputs for RT transport code like RAPTOR.
Open positions in experimental physics in the Basic Plasma Physics group
- Active spectroscopy in fusion relevant plasmas on the RAID device
Contact person: Prof. Ivo Furno, Dr. Marcelo Baquero
Active spectroscopy encompasses several techniques to diagnose plasmas using light or, more generally, electromagnetic radiation from the deep ultraviolet to the infrared. This allows probing the plasmas in non-perturbing ways and in conditions and/or locations out of reach to other techniques such as those based on insertion of material probes.
In the Resonant Antenna Ion Device (RAID), we have in recent years developed significant expertise in the use of active spectroscopy using lasers. RAID is a basic plasma physics experiment located here at SPC in which RF waves are used to produce high density helicon plasmas that can reproduce plasma conditions similar to the ones found in tokamak divertors and scrape-off layers, such as in TCV. RAID is therefore an ideal platform to study laser spectroscopy techniques of direct relevance to tokamak physics and fusion.
Of particular interest to us has been laser induced fluorescence (LIF), in which absorption of an injected laser of known wavelength leads to the very selective excitation of a species (atom, ion or molecule) of interest within the plasma. Detection of the photons arising from the decay of the excited species can then be used to determine their density and temperature and, sometimes, characteristics of the plasma itself.
We seek a PhD candidate to continue these developments. The candidate will in particular tackle two-photon LIF measurements of atomic hydrogen and deuterium in RAID. They will study possible new calibration methods, as well as the role of competing atomic processes both in laser absorption and fluorescence in a dense plasma. These investigations will include theory as well as experiments, and may involve collaborations with other groups within SPC, but also at EPFL and abroad, providing a unique opportunity to develop competences at the intersection of several fields in science and engineering including plasma and tokamak physics, atomic physics, ultrafast processes, electronics, control systems and simulations.
Plasma Physics Theory
- Simulation of the plasma dynamics at the tokamak edge
Contact person: Prof P. Ricci
The understanding turbulence in the edge of magnetic confinement device is an outstanding open issue in magnetic fusion. The physics of this region determines the boundary conditions of the whole plasma by controlling the plasma refueling, heat losses, and impurity dynamics. Edge dynamics regulates the heat load on the tokamak vessel; this is considered among the most crucial open problems for ITER and future fusion reactors. Since a few years, a project has been initiated at the SPC with the goal of improving the understanding of edge physics. This effort has significantly advanced our grasp of plasma turbulence in the edge of a relatively simple configuration, the circular limited tokamak, and we are now exploring the physics of diverted configurations. Ph.D. theses are proposed with the goal of advancing the simulation and the understanding of edge turbulence in reactor relevant conditions, in particular to consider improved plasma models and advanced exhaust configurations.
Open positions in experimental physics at the BioPlasmas Lab
A virtual tour of the BioPlasmas Lab can be found here:
https://www.epfl.ch/research/domains/swiss-plasma-center/virtual-tours/
The interest in Cold Atmospheric Plasmas (CAPs) is constantly growing for a wide number of applications, from medical treatments, to sterilization of bacteria, viruses, as well as fungii (plasma-agriculture). The high-energy electron population obtained with CAP results in a complex chemistry featuring a variety of Reactive Oxygen and Nitrogen Species (RONS), which have a key role in affecting the biological sample, but keeping a low ambient temperature during the process, thanks to the low energy of ions and atmospheric gas molecules.
At the BioPlamas Lab of the SPC, this interdisciplinary topic where physics, chemistry, and biology are strongly connected is explored on several projects, with a two-fold challenge: on the one hand, CAPs are developed for industrial applications to have a short-medium term impact on the society, on the other hand, the mechanism underlying the biological effects of CAPs is investigated to increase the current understanding of CAP applications, as well as to fine tune the target process.
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Investigating via active and passive spectroscopy the chemistry of cold atmospheric plasmas for biological applications
Contact person: Prof. Ivo Furno, Dr. Fabio Avino
To shed light on the mechanism underlying CAP effect on biological samples, a key step consists in obtaining a detailed spatial and temporal mapping of the RONS produced in the proximity of a plasma source. To address this challenge, the Bio-plasmas lab is equipped with a variety of active and passive spectroscopic methods, such as a picosecond laser to perform laser induced fluorescence spectroscopy and other laser-based measurements, such as E-FISH. The laser can be coupled to an in-house developed nanosecond-pulse power supply used to power our plasma sources as an alternative to commercial AC power supplies that are also available in the lab. Complementary CAP application to biological samplesare envisaged.
The PhD candidate will be responsible for the experimental activity, including, but not limited to, laser-based measurements, which will advance the current understanding of the RONS generated by our plasma sources. Numerical modelling could complement the Ph.D. activities. Collaborations with other laboratories sharing and complementing the SPC-Bio-plasmas lab expertise will likely be accessible.
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Investigating the underlying mechanisms responsible for Plasma Activated Water biocidal activity
Contact person: Prof. Ivo Furno, Dr. Fabio Avino
The production and application of Plasma Activated Water (PAW) is one of the investigated research topics at the BioPlasmas Lab, as an indirect plasma treatment of non-pathogen E. Coli: deionized water is firstly treated with a dedicated plasma source (surface dielectric barrier discharge), which enriches it with a variety of RONS, and secondly is applied on E. Coli testing its biocidal properties. The main challenge consists in understanding the details of the mechanisms responsible for the biocidal effects of PAW.
Within this framework, we are looking for a Ph.D. to pursue this experimental activity, coupling the know-how in plasma physics of the SPC, with several biological tools (e.g Flow Cytometry, Proteomics, RNA sequencing, single cell fluorescent time-lapse microscopy) that are mostly available either in the Biolab, or in other groups/laboratories on the EPFL campus. The BioPlasmas Lab is fully equipped with all the necessary for standard wet-lab activities as well as a brand-new Nikon time-lapse microscope, PCR, Q-PCR, and a novel device for single cell impedance measurement. This project will follow a previous Ph.D. project oriented on E.coli inactivation mechanism investigation by PAW. Comparisons of PAW inactivation effectiveness with other microorganisms (e.g. gram positive) will be performed during the PhD.
This project will provide the unique opportunity to acquire skills and experience on a topic joining physics, biology and chemistry.
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Development of a plasma-based prototype for tool sterilization and biohazardous material decontamination.
Contact person: Prof. Ivo Furno, Dr. Fabio Avino
To exploit the biocidal properties of CAP, an EPFL project has been launched by the SPC, together with the SV-IN facilities, to develop a plasma-based device with the aim of sterilizing tools, devices, and media, and/or decontaminate biosafety-level 2 materials (solids and liquids). This would allow to reduce the current usage of autoclaves, with the consequent reduction of electricity and water.
Within this framework, we are looking for a Ph.D. to bridge the SPC activity with the SV-IN facilities, where the final prototype would be implemented. The candidate will team up with two Post-Docs, having plasma physics and biology backgrounds. To optimize the process, the applied goal of developing a sterilization/decontamination tool will go along deeper investigations of the mechanisms responsible for the biocidal properties of CAP.
This project will provide the unique opportunity to acquire skills and experience on a topic joining physics, biology and chemistry, as well as being on a campus where both the know-hows of a plasma physics lab. and biosafety level 2,3 labs are present and can work in close collaboration.
Open positions in superconductivity for fusion
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Applied Superconductivity – R&D on Nb3Sn Superconducting Magnets
Contact Person: Dr. Xabier Sarasola, email: [email protected] .
We are looking for a motivated PhD candidate with a solid background in physics, interested in the R&D program of high-field dipole magnets suitable for constructing superconducting test facilities and accelerator magnets. The magnets are based on an innovative type of two-stage cable made of high Jc, Nb3Sn strands. The challenging project has a potential to open a new avenue towards the next generation of the accelerator-type magnets.
The successful candidate will prepare a short section of the high Jc cable with the support of an industrial partner, and characterize it in the SPC laboratory. The focus of the work is on the design, construction and test of a small prototype coil, retaining basic characteristics of a high field dipole magnet. The student will present his/her work in international conferences and report the results and findings in scientific journals. Experience in applied superconductivity or cryogenics is a valuable asset, though not a mandatory requirement. The place of work is Villigen PSI, close to Zurich.