Podcasts about asdex upgrade

Fusion plasmas contain impurities, either intrinsic originating from the wall, or injected willfully with the aim of reducing power loads on machine components by converting heat flux into radiation. The understanding and the prediction of the effects of these impurities and their radiation on plasma performances is crucial in order to retain good confinement. In addition, it is important to understand the impact of pellet injection on plasma performance since this technique allows higher core densities which are required to maximise the fusion power. This thesis contributes to these efforts through both experimental investigations and modelling. Experiments were conducted at ASDEX Upgrade which has a full-W wall. Impurity seeding was applied to H-modes by injecting nitrogen and also medium-Z impurities such as Kr and Ar to assess the impact of both edge and central radiation on confinement. A database of about 25 discharges has been collected and analysed. A wide range of plasma parameters was achieved up to ITER relevant values such as high Greenwald and high radiation fractions. Transport analyses taking into account the radiation distribution reveal that edge localised radiation losses do not significantly impact confinement as long as the H-mode pedestal is sustained. N seeding induces higher pedestal pressure which is propagated to the core via profile stiffness. Central radiation must be limited and controlled to avoid confinement degradation. This requires reliable control of the impurity concentration but also possibilities to act on the ELM frequency which must be kept high enough to avoid an irreversible impurity accumulation in the centre and the consequent radiation collapse. The key role of the ELM frequency is confirmed also by the analysis of N+He discharges. Non-coronal effects affect the radiation of low-Z impurities at the plasma edge. Due to the radial transport, the steep temperature gradients and the ELM flush out, a local equilibrium cannot be establish an the radiation increases in this region. To account for these effects, an empirical non-coronal model was developed which takes the impurity residence time at the pedestal into account. The validity of this assumption was verified by modelling the evolution of the impurities and radiation for ASDEX Upgrade H-modes with nitrogen seeding by coupling the ASTRA transport code with STRAHL. The time-dependent simulations include impurity radiation due to nitrogen and tungsten and the transport effects induced at the edge by the ELMs. The modelling results have been validated against the experimental data. The modelled radiation profiles show a very good agreement with the measured ones over both radius and time. In particular, the strong enhancement of the nitrogen radiation caused by non-coronal effects through the ELM-induced transport is well reproduced. The radiation properties of tungsten are very weakly influenced by non-coronal effects due to the faster equilibration. W radiation, which is highly dependent on the Elm frequency, strongly increases when this is decreased, due to the lack of sufficiently strong flush out of this impurity. This is in agreement with the experimental observations and indicates that maintaining high ELM frequency is essential for the stability and performance of the discharges. Analyses of the high density scenario with pellets indicate that several processes take place when pellets are injected into the plasma. In particular, due to their cooling effect, the temperature drops as soon as pellets are injected. This is compensated by an increase in density. These processes occur mainly at the edge and are propagated to the core via stiffness. This explains why the confinement stays approximately constant during the whole discharge. Both experiments and transport calculations reveal that the energy confinement time is independent of the density indicating that the currently used scaling is not valid in this regime. The results of this thesis will contribute towards an extension of the confinement scaling which is currently being undertaken.

The Plasma Facing Components (PFC) will play a crucial role in future deuterium-tritium magnetically confined fusion power plants, since they will be subject to high energy and particle loads, but at the same time have to ensure long lifetimes and a low tritium retention. These requirements will most probably necessitate the use of high-Z materials such as tungsten for the wall materials, since their erosion properties are very benign and, unlike carbon, capture only little tritium. The drawback with high-Z materials is, that they emit strong line radiation in the core plasma, which acts as a powerful energy loss mechanism. Thus, the concentration of these high-Z materials has to be controlled and kept at low levels in order to achieve a burning plasma. Understanding the transport processes in the plasma edge is essential for applying the proper impurity control mechanisms. This control can be exerted either by enhancing the outflux, e.g. by Edge Localized Modes (ELM), since they are known to expell impurities from the main plasma, or by reducing the influx, e.g. minimizing the tungsten erosion or increasing the shielding effect of the Scrape Off Layer (SOL). ASDEX Upgrade (AUG) has been successfully operating with a full tungsten wall for several years now and offers the possibility to investigate these edge transport processes for tungsten. This study focused on the disentanglement of the frequency of type-I ELMs and the main chamber gas injection rate, two parameters which are usually linked in H-mode discharges. Such a separation allowed for the first time the direct assessment of the impact of each parameter on the tungsten concentration. The control of the ELM frequency was performed by adjusting the shape of the plasma, i.e. the upper triangularity. The radial tungsten transport was investigated by implementing a modulated tungsten source. To create this modulated source, the linear dependence of the tungsten erosion rate at the Ion Cyclotron Resonance Heating (ICRH) limiters on the injected ICRH power was used. The phase and amplitude of the inwardly propagating tungsten signal was then observed at the erosion site and at three radial positions in the main plasma, from which two were identified in the course of this work by a thorough investigation of the tungsten radiation features in the Vacuum Ultra-Violet (VUV) spectral range . The newly found observation sites are located right in the steep gradient region, close to the Edge Transport Barrier (ETB) and slightly further inside at the pedestal top of AUG H-mode discharges. Futhermore, the parallel flows in the SOL have been monitored by spectroscopical means and Langmuir probes. The experimental results were quite unexpected, since the ELM frequency had no influence on the tungsten concentration, and the sole actuator on this quantity was the gas injection rate. The evaluation of the modulated tungsten signal revealed that neither gas puffing nor plasma shape had an measureable influence on the radial tungsten transport processes. In addition, the tungsten erosion sources were only partially responsible for the observed tungsten behavior. These observations inspired a simple model, which balanced the tungsten outflux with the tungsten influx. In this model the impurity exauhst by ELMs is not diffusive, but turbulent and linked to the ELM size. The model predicted a linear dependence between the tungsten concentration and the parallel velocity in the SOL. This linear dependence was confirmed by the spectroscopical evaluation of the SOL parallel flows.

This works deals with the Ion Cyclotron Emission (ICE), a plasma instability that takes place both in astrophysical plasmas and in fusion energy facilities like Tokamaks and Stellarators, when a population of high energetic ions is present. These fast ions can interact with the waves which propagate in the background thermal plasma and excite instabilities in the Mega-Hertz range. This emission can be measured in a non-intrusive way with radio-frequency probes and provide information on the characteristics of the fast ions. The hope of a new diagnostic sparked many studies in the years 1992-2002 but, in spite of the theoretical and experimental progresses, no practical instrumentation was achieved. There are indeed two main difficulties: first, the ICE involves many different types of plasma phenomena: waves propagation, resonances, conversion and absorption in complex geometries, core and edge plasma modelling, fast ion creation and trajectories; all these aspects are entangled. Therefore, accurate data both in time and frequency domains and a theory that covers these physics fields are necessary to distinguish the impact of these different phenomena. Second, there are technical difficulties in measuring high-frequency signals with a sufficient Signal-to-Noise Ratio to discriminate it from the background noise. The purpose of this study is to address these issues with the use of the latest acquisition technologies and an improved ICE theory, which can relate in a new light the properties of the fast ions to the characteristics of the emission.

Mon, 16 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16485/ https://edoc.ub.uni-muenchen.de/16485/1/Burckhart_Andreas.pdf Burckhart, Andreas ddc:530, ddc:500, Fakultät für Phy

Mon, 16 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16483/ https://edoc.ub.uni-muenchen.de/16483/1/Fietz_Sina.pdf Fietz, Sina ddc:530, ddc:500, Fakultät

The high confinement mode (H-mode) is the operational scenario foreseen for ITER, DEMO and future fusion power plants. At high densities, which are favourable in order to maximize the fusion power, a back transition from the H-mode to the low confinement mode (L-mode) is observed. This H-mode density limit (HDL) occurs at densities on the order of, but below, the Greenwald density. In this thesis, the HDL is revisited in the fully tungsten walled ASDEX Upgrade tokamak (AUG). In AUG discharges, four distinct operational phases were identified in the approach towards the HDL. First, there is a stable H-mode, where the plasma density increases at steady confinement, followed by a degrading H-mode, where the core electron density is fixed and the confinement, expressed as the energy confinement time, reduces. In the third phase, the breakdown of the H-mode and transition to the L-mode, the overall electron density is fixed and the confinement decreases further, leading, finally, to an L-mode, where the density increases again at a steady confinement at typical L-mode values until the disruptive Greenwald limit is reached. These four phases are reproducible, quasi-stable plasma regimes and provide a framework in which the HDL can be further analysed. Radiation losses and several other mechanisms, that were proposed as explanations for the HDL, are ruled out for the current set of AUG experiments with tungsten walls. In addition, a threshold of the radial electric field or of the power flux into the divertor appears to be responsible for the final transition back to L-mode, however, it does not determine the onset of the HDL. The observation of the four phases is explained by the combination of two mechanisms: a fueling limit due to an outward shift of the ionization profile and an additional energy loss channel, which decreases the confinement. The latter is most likely created by an increased radial convective transport at the edge of the plasma. It is shown that the four phases occur due to a coupling of these two mechanisms. These observations are in line with studies made at AUG with carbon walls, although in those discharges the energy loss was most likely caused by the full detachment of the divertor. The density of the HDL depends only weakly on the plasma current, unlike the Greenwald limit, and can be increased by high heating power, again unlike the Greenwald limit. The triangularity of the plasma has no influence on the density of the HDL, though improves the performance of the plasma, since the onset of the degrading H-mode phase occurs at higher densities. It is explicitly shown that the HDL and also the L-mode density limit are determined by edge parameters. Using pellet fueling, centrally elevated density profiles above the Greenwald limit can be achieved in stable H-modes at a moderate confinement. Future tokamaks will have intrinsic density peaking. Consequently, they will most likely operate in H-modes above the Greenwald limit.

The ratio of heating power going to electrons and ions will undergo a transition from mixed electron and ion heating as it is in current fusion experiments to dominant electron heating in future experiments and reactors. In order to make valid projections towards future devices the connected changes in plasma response and performance are important to be study and understand: Do electron heated plasmas behave systematically different or is the change of heated species fully compensated by heat exchange from electrons to ions? How does particle transport influence the density profile? Is the energy confinement and the H-mode pedestal reduced with reduced torque input? Does the turbulent transport regime change fundamentally? The unique capabilities of the ECRH system at ASDEX Upgrade enable this change of heated species by replacing NBI with ECRH power and thereby offer the possibility to discuss these and other questions. For low heating powers corresponding to high collisionalities the transition from mixed electron and ion heating to pure electron heating showed next to no degradation of the global plasma parameters and no change of the edge values of kinetic profiles. The electron density shows an increased central peaking with increased ECRH power. The central electron temperature stays constant while the ion temperature decreases slightly. The toroidal rotation decreases with reduced NBI fraction, but does not influence the profile stability. The power balance analysis shows a large energy transfer from electrons to ions, so that the electron heat flux approaches zero at the edge whereas the ion heat flux is independent of heating mix. The ion heat diffusivity exceeds the electron one. For high power, low collisionality discharges global plasma parameters show a slight degradation with increasing electron heating. The density profile shows a strong peaking which remains unchanged when modifying the heating mix. The electron temperature profile is unchanged whereas the central ion temperature decreases significantly with increasing ECRH fraction. The relative contribution of the heat exchange is smaller so that the electrons still carry a substantial fraction of heat at the edge. The ion heat flux is still independent of the heating mix and the ion heat diffusivity exceeds the electron one. The radial electrical field does not show any variation with changing heating mix. The analysis of the whole database of discharges shows a degradation of the ion temperature gradient with increasing Te/Ti and a steepening with increasing gradient of the toroidal rotation. These findings complement previous studies. The electron density, and the electron and ion temperatures were modelled with a first principle code. The applied sawtooth model could reproduce the experimental observations. The profile shapes, the changing Te/Ti and the peaking of the density and temperature profiles agree very well with the experimental data. Linear gyrokinetic calculations found the ion temperature gradient mode to be the dominant candidate for heat transport. The investigations can explain the observed phenomena in the experiment, like the different degree of increase of ion heat flux or density peaking for various collisionalities. The results presented in this work show a consistent picture of the observed phenomena and the understanding of the main underlying physics. They allow a correct implementation in the applied computer codes and a reliable prediction of the performance of future fusion devices.

Understanding and control of the plasma edge behaviour are essential for the success of ITER and future fusion plants. This requires the availability of suitable methods for assessing the edge parameters and reliable techniques to handle edge phenomena, e.g. to mitigate 'Edge Localized Modes' (ELMs) --- a potentially harmful plasma edge instability. This thesis introduces a new method for the estimation of accurate edge electron temperature profiles by forward modelling of the electron cyclotron radiation transport and demonstrates its successful application to investigate the impact of Magnetic Perturbation (MP) fields used for ELM mitigation on the edge kinetic data. While for ASDEX Upgrade bulk plasmas, straightforward analysis of the measured electron cyclotron intensity spectrum based on the optically thick plasma approximation is usually justified, reasonable analysis of the steep and optically thin edge region relies on full treatment of the radiation transport considering broadened emission and absorption profiles. This is realized in the framework of integrated data analysis which applies Bayesian probability theory for joint analysis of the electron density and temperature with data of different independent and complementary diagnostics. The method reveals that in regimes with improved confinement ('High-confinement modes' (H-modes)) the edge gradient of the electron temperature can be several times higher than that of the radiation temperature. Furthermore, the model is able to reproduce the 'shine-through' peak --- the observation of increased radiation temperatures at frequencies with cold resonance outside the confined plasma region. This phenomenon is caused by strongly down-shifted radiation of Maxwellian tail electrons located in the H-mode edge region and, therefore, contains valuable information about the electron temperature edge gradient. The accurate knowledge about the edge profiles and gradients of the electron temperature and --- including the density information --- the electron pressure allows a detailed study of plasma edge phenomena like ELMs or the transition from 'Low-confinement mode' (L-mode) to H-mode. It is shown how the application of non-axisymmetric MP fields acts on the edge profiles of electron temperature, density and pressure in H-modes with type-I and mitigated ELMs and during the L-H transition. Compared to type-I ELMs, mitigated ELMs tend to occur at higher edge densities, lower edge temperatures and reduced edge pressure gradients. This parameter regime can be achieved by strong gas fuelling. MP fields might support ELM mitigation by shifting the threshold between type-I and small ELMs towards slightly higher edge temperatures. The application of MPs in L-modes results in a degradation of the pressure gradient due to increased heat transport. At the L-H transition, the pressure gradient and the radial electric field shearing seem to exhibit the same value with and without MPs, while its required heating power is increased in the presence of MPs.

Fri, 25 Jan 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/15367/ https://edoc.ub.uni-muenchen.de/15367/1/Geiger_Benedikt.pdf Geiger, Benedikt ddc:530, ddc:500, Fakultät fü

The most direct way to avoid the formation of a relativistic electron beam under the influence of an electric field in a highly conducting plasma, is to increase the electron density to a value, where the retarding collisional force balances the accelerating one. In a disruptive tokamak plasma, rapid cooling induces a high electric field, which could easily violate the force balance and push electrons into the relativistic regime. Such relativistic electrons, the so-called runaways, accumulate many MeV's and can cause substantial damage when they hit the wall. This thesis is based on the principle of rapidly fueling the plasma for holding the force balance even under the influence of high electric fields typical for disruptions. The method of injecting high amounts of noble gas particles into the plasma from a close distance is put into practice in the ASDEX Upgrade fusion test facility. In the framework of this thesis, a multi-channel photometer system based on 144 AXUV detectors in a toroidal stereo measurement setup was built. It kept its promise to provide new insights into the transport mechanisms in a disruptive plasma under the influence of strong radiative interaction dynamics between injected matter and the hot plasma.

Tue, 20 Jul 2010 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/11921/ https://edoc.ub.uni-muenchen.de/11921/1/Mlynek_Alexander.pdf Mlynek, Alexander ddc:530, ddc:500, Fakultät für Physik

Tue, 20 Jul 2010 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/12056/ https://edoc.ub.uni-muenchen.de/12056/1/Sertoli_Marco.pdf Sertoli, Marco ddc:530, ddc:500, Fakultät für Physik

This episode covers my visit to the Max Plack Institut for Plasmaphysik where I spent a couple of hours with Matthias Reich talking about nuclear fusion. The episode has three parts. In part one we talk about the scienfic and physical basics of nuclear fusion. Part two covers some of the ways the MPI facilities work, and part three discusses the ASDEX Upgrade experiment at IPP in Garching.

Mon, 27 Jul 2009 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/10626/ https://edoc.ub.uni-muenchen.de/10626/1/Urso_Laura_1.pdf Urso, Laura ddc:530, ddc:500, Fakultät für Physik

The Tokamak configuration is a promising concept for magnetic confinement fusion. Cross-field transport in the plasma core leads to a plasma flux across the separatrix into the scrape-off layer, where it is guided along field lines towards the divertor targets. A return flux of neutral particles after plasma-wall interaction is directed towards the plasma chamber. Each discharge scenario is accompanied by a characteristic recycling pattern. The dominant mechanisms of neutralplasma interaction are ionisation and atom-ion charge exchange. The impact of neutrals on the particle-, momentum- and energy-balance of the plasma is relevant for the understanding of the properties of the edge plasma and the state of the divertor plasma. Neutrals may cause energyand momentum-detachment, a state of reduced power and particle fluxes, at the targets, which is a prerequisite for acceptable wall loads under reactor conditions. The distribution of neutral particles in the plasma chamber can be determined by the analysis of line emission. Parameters of neutrals have been available so far only from localised measurements and it is therefore desired to extend the observation area. At the ASDEX Upgrade Tokamak, two cameras are installed to record the Deuterium Balmer-alpha (D_alpha) emission with high spatial resolution and dynamic range in the divertor and midplane regions. Two methods for data deconvolution are presented. A simple profile-fit is used to resolve the radial profile of emission at the low and high field sides for low and medium density discharges. This emission profile is translated to neutral parameters by comparison to the results obtained from kinetic modelling of neutral penetration (KN1D). An algorithm for tomographic reconstruction is applied to image data of the divertor region. In general, radiance data recorded is blurred due to the impact of diffuse reflection from surfaces of the plasma facing components in the all-Tungsten machine. Therefore, the tomographic algorithm has been extended by a model for reflection based on a solid angle resolved measurement. The sensitivity of the procedures is proven by the accurate analysis of different edge plasma configurations. Poloidally resolved neutral flux densities at the plasma edge and corresponding core fuelling rates are presented for the high field side. Underlying estimates of plasma parameters indicate a drop of static plasma pressure along the magnetic field towards the inner target. Changes of the poloidal flux density profile during a radial shift of the plasma column, indicate a correlation of plasma-wall gap and scrape-off layer parameters at the high field side. From the deconvolution of divertor view data separate emission patterns have been resolved. Besides the character of emission at the strike zones which can give a hint on the level of detachment, the occurrence of radiation above the inner target indicates that the distribution of plasma parameters is probably more complex than expected from simple radial decay lengths. The experimental emission profiles and inferred neutral parameters display an important boundary condition for complex 2D edge modelling codes like SOLPS. The comparison of experimental and code results question the applicability of the standard recipe (concerning code settings) for arbitrary plasma scenarios. An interface to theory is required to reasonably exploit the experimental data on neutral penetration. The essential result of this thesis is a reference frame for the quantitative analysis of video diagnostics data recorded on a Tokamak plasma, including the impact of reflecting plasma facing components.

Tue, 5 Aug 2008 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/9015/ https://edoc.ub.uni-muenchen.de/9015/1/troester_carolin_helma.pdf Tröster, Carolin Helma

In fusion plasma devices, fast particles i.e. suprathermal ions generated by heating systems and fusion born a particles must be well confined, until they have transferred their energy to the plasma bulk. Signicant loss of these ions may reduce drastically the heating eficiency and, in addition, may cause damage to plasma facing components in the vacuum vessel, if it is suficiently intense and localized. A detailed knowledge of the underlying physics in particular in the presence of magnetohydrodynamic (MHD) instabilities is of crucial importance, since these instabilities can lead to an enhancement of the outwards fast ion radial drift. The development of a new diagnostic for the study of fast particle-wave interactions in the ASDEX Upgrade tokamak as well as the interpretation of the rst measurements have been the aim of this thesis. The design is based on similar diagnostics that have been operated in the TFTR tokamak and the W7-AS stellerator. The fast ion loss detector acts as a magnetic spectrometer, dispersing fast ions onto a scintillator, with the strike point depending on their gyroradius (energy) and pitch angle (angle between ion velocity and magnetic eld line). The emitted light pattern allows particle identification in the phase space with a high time resolution. The major new development for the diagnostic used on ASDEX Upgrade is the use of a very fast scintillator material that allows sampling rates up to 1 MHz, adequate to study time resolved interactions between MHD modes and fast particles. Fast Ion Losses (FIL) were found in the presence of different kinds of MHD instabilities: time resolved FIL due to Edge Localized Modes (ELMs) have been directly observed. They show a complex behavior of a great variety, depending on the ELM substructure. The influence of ELMs on escaping fast particles is appreciable in the whole lost particle phase space independent of the fast ion source. FIL could be measured in the presence of Toroidal Alfv´en Eigenmodes (TAEs) in ICRH heated discharges. Both species, fast hydrogen and deuterium ions are affected in a similar way by TAEs. A resonant process between the TAE frequency and the precession frequency of the lost ions has been identied by comparisons with HAGIS simulations as the loss mechanism. A new MHD perturbation has been observed for the first time during this thesis by means of its strong influence on the energetic deuterium ion population. The mode is localized deeply in the plasma core and dominates the uxes of lost fast deuterium ions in ICRH heated discharges. Finally, bursts of fast deuterium ions ejected by Neoclassical Tearing Modes have been detected in discharges with different heating systems. In pure NBI heated discharges, these ions have energies approximately equal to the full NBI injection energy and pitch angles corresponding to ions on passing orbits. A detailed study of the FIL signal together with Mirnov coil signals revealed that the losses are due to a diffusive process. According to this, simulations with the ORBIT code have proven that orbit stochasticity is a good candidate for the mechanism that causes the losses of these, in principle well confined, passing ions. These results revealed the high diagnostic potential of this method, opening new ways towards a better understanding of the fast ion physics and therefore will help to predict the behavior of fast ions in the presence of MHD instabilities for ITER.

One of the major goals of the tokamak fusion program is the understanding and control of plasma turbulence. Turbulence causes additional radial transport of heat and particles to the tokamak vessel walls, thereby degrading the overall confinement of the plasma. Diagnostics for the study of tokamak turbulence are unfortunately scarce and limited in what they can measure. A new diagnostic technique, Doppler reflectometry, has been developed for measurements of plasma rotation profiles and turbulence properties. It is a type of microwave radar technique which uses the back-scatter of microwaves from a radial position in the plasma where the refractive index equals zero. In this thesis work, the technique is extended for turbulence correlation measurements by adding a second Doppler reflectometer channel where two microwave beams are launched into the plasma with a small frequency difference. A radial correlation Doppler reflectometer system can provide simultaneous measurements of the plasma radial electric field Er and its shear (both parameters are believed to be fundamental for suppressing turbulence) together with measurements of the properties of the plasma turbulence, such as the radial correlation length of the turbulence Lr. These measurements are explored in this thesis work for a wide range of plasma conditions. It was found that Er and its associated shear are indeed linked to plasma confinement. Their absolute values increase with confinement at the plasma edge. An increase in the absolute value of Er shear was also detected at the same plasma edge region where a decrease in radial correlation lengths of the turbulence was measured. This observation is in agreement with theoretical models which predict that an increase in the absolute shear suppresses turbulent fluctuations in the plasma, leading to a reduction in Lr. Measurements of Lr versus the perpendicular wavenumber of the turbulence were also obtained, which prompted an investigation of the correlation Doppler reflectometer response function using a 2-dimensional finite difference time domain (FDTD) code. The simulation results show that the magnitude of the measured Lr is dependent on the radial, poloidal and perpendicular wavenumbers of the turbulence.

This thesis work investigates the measurement of ion temperatures at the edge of a magnetically confined plasma used for fusion research at the ASDEX Upgrade tokamak operated by Max-Planck-Institut für Plasmaphysik in Garching. The tokamak is the most advanced concept in toroidal magnetic confinement fusion. The H-mode plasma regime, default scenario of the next step experiment ITER, is characterized by an edge transport barrier, which is not yet fully explained by theory. Experimentally measured edge ion temperature profiles will help to test and develop models for these barriers. Transport theory on a basic level is introduced as background and motivation for the new diagnostic. The standard model for an edge plasma instability named "edge localized mode" (ELM) observed in H-mode is described. The implementation of a new diagnostic for ion temperature measurements with high spatial resolution in the plasma edge region, its commissioning and the validation of the measurements comprises the main part of this work. The emission of line radiation induced by charge exchange processes between lithium atoms injected by a beam source and fully ionized impurities (of C and He) is observed with a detection system consisting of spectrometers and fast cameras. Due to the narrow beam (1 cm) and closely staggered optical fibers (6 mm), unprecedented spatial resolution of edge ion temperatures in all major plasma regimes of the ASDEX Upgrade tokamak was achieved. The spectral width of the line radiation (He II at 468.5 nm and C VI at 529.0 nm) contains information about the local ion temperature from thermal Doppler-broadening, which is the dominant broadening mechanism for these lines. The charge-exchange contribution to the total line radiation locally generated by the lithium is determined by gating the beam. Fitting a Gaussian model function to the local line radiation results in absolute line widths which can be directly converted into a temperature. The equilibration of impurities with the main plasma is fast enough that the assumption of nearly identical temperatures as the main plasma is justified. Corrections for systematic line broadening effects from collisional mixing and Zeeman broadening are incorporated by model calculations using existing routines for the involved atomic physics. Time resolution of the diagnostic is still not suffcient to resolve ELM events, but measuring between ELMs is possible if their frequency is low. L-mode plasmas with and without additional heating can be reliably diagnosed with a time resolution depending on the lithium beam intensity and plasma density, in best cases down to 100 ms. It was shown that diagnostic He puffing can be used to enhance the signal-to-noise ratio. Results from L-mode plasmas with electron heating show that ion temperatures can be significantly different from electron temperatures at the edge. For the verification of the new ion temperatures, comparison with data from already established diagnostics was done. In neutral beam heated L-mode and various H-mode plasmas the ion temperatures agree with those from a similar diagnostic measuring in the core using heating beams where both diagnostics overlap. They can be combined to form a complete ion temperature profile over the whole plasma radius. In a first application, transport coefficients have been determined by interpretative modeling for an ohmic plasma. In summary, a new method for measuring ion temperatures in the edge of a magnetically confined fusion plasma has been established. The results provide an important input to further understanding of transport in these plasmas.