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.
- 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 two following specific subjects are particularly envisioned.
1) Investigate the effects that may cause ECRH coupling to be less precise and localized than expected, a big concern for a reactor. Distinguishing between the two main possible effects, enhanced transport of suprathermals and refraction of the microwave beam by edge turbulence, will require tailored experiments and the application and refinement of modeling tools combining turbulence, wave propagation, and wave-particle coupling.
2) 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.
Multi-diagnostic study of core turbulenceEnergy 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.
Study of Electron Cyclotron Emission (ECE) on TCV Tokamak
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
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 applications
Contact 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.
Real Time Control of Tokamaks
Contact person: Dr Federico Felici
The SPC tokamak TCV is equipped with an advanced real-time control system, based on matlab-simulink and which allows rapid and flexible developments. In addition, we have developed a rapid tokamak transport simulator, RAPTOR, capable of simulating in real-time current density and kinetic profiles. This is a perfect environment for PhD thesis project related to real-time control of tokamaks, including magnetic control, plasma profile control, as well as advanced topics such as scenario control, monitoring and supervision.
Measurement of turbulence and modes driven by and interacting with the high-energy NBI ions in TCV
Contact person: Dr. Duccio Testa
Analysis of NBI-driven magnetic turbulence and modes in TCV, and interaction of MHD instabilities with the slowing-down NBI ions; develop and test mathematical tools for the magnetic turbulence analysis as needed; develop high-frequency magnetic sensors based on LTCC technology.
- Active spectroscopy in fusion relevant plasmas on the RAID device
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.
- Modelling and experimental investigation of plasma disruptions in the JET tokamak
Contact person: Dr. MER Jonathan Graves; Dr. Mengdi Kong
One of the crucial questions to be addressed for the normal operation of large tokamak devices like ITER is the plasma disruption. Accompanied by an abrupt loss of plasma confinement, disruptions lead to substantial thermal loads, electromagnetic forces and relativistic runaway electrons, posing a serious threat to the integrity of plasma facing components in future tokamak reactors. Extensive experimental studies have been carried out on the JET tokamak regarding the causes, characteristics, consequences and mitigation of disruptions. Being the largest operating tokamak in the world, JET provides valuable datasets for extrapolation to future tokamaks like ITER. Given the transient nature of plasma disruptions, coverage of diagnostics measuring the complex physics processes involved is limited. Hence, numerical modelling is needed to better interpret the experiments and clarify the underlying physics. The proposed thesis focuses on studying plasma disruptions on JET with the JOREK code, a 3D non-linear extended magneto-hydrodynamic (MHD) code for realistic tokamak geometries. One of the important topics is the mitigation of disruptions via the shattered pellet injection (SPI) technique that will also be applied to ITER. In particular, the effects of adding a small amount of impurities to the pellet on SPI assimilation and (pre-)thermal quench dynamics will be investigated in detail. Another topic is on the cause and dynamics of the unintended/natural disruptions observed on JET. The thesis work involves analyzing relevant experimental data on JET, performing interpretative numerical modelling with JOREK and collaborating with international experimental and modelling teams.
Measurement and interpretation of TAE in JET, including DT experiments.
Contact person: Dr. Duccio Testa
Analysis of the Toroidal Alfven Eigenmode (TAE) measurements obtained in JET using the upgraded TAE system, including real-time control applications, MHD spectroscopy, and in preparation of studies of alpha-driven TAEs during the DT experiment planned at JET for 2017-2018.
Note: the upgraded TAE system should become operational around the end of 2014 or early 2015.
Overall data analysis for JET also to include comparison with all fast ion diagnostics and other turbulence diagnostic.
- Gyrokinetic turbulence simulations with advanced numerical techniques
Contact person: Prof L. Villard
The SPC theory group has been active since many years in the field of numerical simulation of magnetized fusion-relevant plasmas by developing codes that are run on some of the currently most powerful High Performance Computing (HPC) platforms. In particular, the realistic description of low frequency turbulence from first principles using gyrokinetic theory, which remains a great simulation challenge, has been one of the group’s main research focus. The loss of heat and particles associated to this turbulence is a key limiting factor in achieving the conditions required in a fusion reactor. The architecture of the most powerful HPC platforms has been evolving towards more heterogenous systems (CPU+GPU or CPU+MIC) and there is therefore the need to adapt our physics application codes to this new type of machines. We are currently looking for a PhD candidate that is seriously motivated to deal with advanced numerical simulations of gyrokinetic turbulence and actively engage in the current effort to adapt our codes to the new generation platforms. The thesis will thus include both physical studies as well as technical aspects. The successful candidate will interact with our group at SPC and other institutions and laboratories.
- 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.
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.
Other available positions in fusion in Switzerland: