Forward modeling of collective Thomson scattering for Wendelstein 7-X plasmas: Electrostatic approximation

In this paper, we present a method for numerical computation of collective Thomson scattering (CTS). We developed a forward model, eCTS, in the electrostatic approximation and benchmarked it against a full electromagnetic model. Differences between the electrostatic and the electromagnetic models are discussed. The sensitivity of the results to the ion temperature and the plasma composition is demonstrated. We integrated the model into the Bayesian data analysis framework Minerva and used it for the analysis of noisy synthetic data sets produced by a full electromagnetic model. It is shown that eCTS can be used for the inference of the bulk ion temperature. The model has been used to infer the bulk ion temperature from the first CTS measurements on Wendelstein 7-X

Towards a new image processing system at Wendelstein 7-X: From spatial calibration to characterization of thermal events

Wendelstein 7-X (W7-X) is the most advanced fusion experiment in the stellarator line and is aimed at proving that the stellarator concept is suitable for a fusion reactor. One of the most important issues for fusion reactors is the monitoring of plasma facing components when exposed to very high heat loads, through the use of visible and infrared (IR) cameras. In this paper, a new image processing system for the analysis of the strike lines on the inboard limiters from the first W7-X experimental campaign is presented. This system builds a model of the IR cameras through the use of spatial calibration techniques, helping to characterize the strike lines by using the information given by real spatial coordinates of each pixel. The characterization of the strike lines is made in terms of position, size, and shape, after projecting the camera image in a 2D grid which tries to preserve the curvilinear surface distances between points. The description of the strike-line shape is made by means of the Fourier Descriptors

Algorithms for image reconstruction.

Three-dimensional (3D) imaging is becoming one of the most important applications of radioactive materials in medicine. It offers good spatial resolution, a 3D insight into the human body, and a high sensitivity in the picomolar range because markers for biological processes can be detected well when labeled with radioactive materials. In addition, the technical equipment has undergone many technological achievements. This is true for single-photon emission computed tomography (SPECT), positron emission tomography (PET), and X-ray computed tomography (CT), which is often used in connection with the nuclear medical imaging systems, as also described in chapter 5 about sources in nuclear medicine. As can be realized by the names of the systems, the imaging methodologies all generate the images using a computational process. This is necessary since in all types of CT the purpose is to generate a stack of two-dimensional slices (a 3D data set) that are reconstructed from various 'projections' along certain lines. This reconstruction process can be achieved by various different methods, which can be divided into so-called algebraic or iterative reconstruction methods and analytical methods. After a brief introduction to give an approach to the reconstruction task in general, we describe both kinds of algorithms

Tomographic imaging using poissonian detector data.

An image reconstruction method for reconstructing a tomographic image (f j ) of a region of investigation within an object (1), comprises the steps of providing detector data (y i ) comprising Poisson random values measured at an i-th of a plurality of different positions, e.g. i = (k,l) with pixel index k on a detector device and angular index l referring to both the angular position (a l ) and the rotation radius (r l ) of the detector device (10) relative to the object (1), providing a predetermined system matrix A ij assigning a j-th voxel of the object (1) to the i-th detector data (y i ), and reconstructing the tomographic image (f j ) based on the detector data (y i ), said reconstructing step including a procedure of minimizing a functional F(f) depending on the detector data (y i ) and the system matrix A ij and additionally including a sparse or compressive representation of the object (1) in an orthobasis T, wherein the tomographic image (f j ) represents the global minimum of the functional F(f). Furthermore, an imaging method and an imaging device using the image reconstruction method are described

Experimental investigation of a HOPG crystal fan for x-ray fluorescence molecular imaging.

Imaging x-ray fluorescence generally generates a conflict between the best image quality or highest sensitivity and lowest possible radiation dose. Consequently many experimental studies investigating the feasibility of this molecular imaging method, deal with either monochromatic x-ray sources that are not practical in clinical environment or accept high x-ray doses in order to maintain the advantage of high sensitivity and producing high quality images. In this work we present a x-ray fluorescence imaging setup using a HOPG crystal fan construction consisting of a Bragg reflecting analyzer array together with a scatter reducing radial collimator. This method allows for the use of polychromatic x-ray tubes that are in general easily accessible in contrast to monochromatic x-ray sources such as synchrotron facilities. Moreover this energy-selecting device minimizes the amount of Compton scattered photons while simultaneously increasing the fluorescence signal yield, thus significantly reducing the signal to noise ratio. The aim is to show the feasibility of this approach by measuring the Bragg reflected Kα fluorescence signal of an object containing an iodine solution using a large area detector with moderate energy resolution. Contemplating the anisotropic energy distribution of background scattered x-rays we compare the detection sensitivity, applying two different detector angular configurations. Our results show that even for large area detectors with limited energy resolution, iodine concentrations of 0.12 % can be detected. However, the potentially large scan times and therefore high radiation dose need to be decreased in further investigations

Smartphones jetzt noch smarter? - Möglichkeit des Einsatzes als „Dosiswarner“.

Ziel: Die Möglichkeit, mit den in den Kameras von Smartphones verwendeten (CMOS-)Chips neben sichtbarem Licht auch andere elektromagnetische Strahlung zu registrieren, führte zu der Entwicklung von Apps zur Messung ionisierender Strahlung. Ziel der vorliegenden Studie war es, die Genauigkeit dieser Messmethode exemplarisch zu überprüfen und mögliche Anwendungsbereiche zu identifizieren. Material und Methoden: Es wurden 2 Apps auf 2 Hardwareplattformen im Vergleich zu einem geeichten Ionisationsmessgerät und einem elektronischen Personendosimeter getestet. Zur Erstellung der Kalibrierungskurve dienten Dosisraten zwischen 12 700 µSv/h und 5,7 µSv/h. Der Einsatz der Apps für die Messung der Streustrahlung eines C-Bogens erfolgte an einem Alderson-Rando-Phantom. Ergebnisse: Während eine App sich als unbrauchbar erwies, ergaben sich bei der anderen folgende Messwerte: Die seitlich am Phantom gemessene Streustrahlung lag mit 117 µSv/h (2 m Abstand) bis 5910 µSv/h (0,3 m Abstand) jeweils ca. um den Faktor 1,4 unterhalb der mit der Ionisationsmesskammer ermittelten Werte. Auf Höhe der Schilddrüse eines Untersuchers wurden 4200 - 4400 µSv/h gemessen. Bei geringem Abstand zum Phantom zeigte sich eine starke Winkelabhängigkeit der Messergebnisse. In 0,3 m Abstand war bei einem Abkippen des Smartphones um 45° nach unten eine Abnahme von 3000 µSv/h auf 972 µSv/h, nach oben eine Zunahme auf 5000 µSv/h zu verzeichnen. Im Abstand von 1 m war dieser Effekt deutlich schwächer. Schlussfolgerung: Es konnte gezeigt werden, dass ein Nachweis ionisierender Strahlung mit Smartphone-Kameras prinzipiell möglich ist. Trotz überraschend guter Messergebnisse ist die Genauigkeit aufgrund starker Winkelabhängigkeit für die Personendosimetrie nicht ausreichend. Eine qualitative Aussage im Sinne eines Dosiswarners ist jedoch möglich

Reduction of aliasing artifacts in tomographic images.

Refining the sampling geometry of a CT scanner is a standard approach used for reduction of aliasing artifacts in CT images. Although this leads to reduction of the artifacts, the principal problem of aliasing streaks artifacts remains unsolved. A different approach is proposed, which in some special cases can solve the problem very efficiently. It is shown that under certain specific conditions, the sum of images reconstructed from the data collected within different sampling geometries is free of aliasing. These conditions are studied and practical situations where they can be realized are discussed