Josef Pal

Josef Pal

Dr. rer. nat

About

35
Publications
3,488
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
211
Citations
Introduction
Skills and Expertise

Publications

Publications (35)
Article
Full-text available
The Czochralski (CZ) process is one of the most important techniques for the production of bulk single crystals. Various numerical models for CZ growth furnaces exist, however, a review of the recent literature demonstrates that their validation is often questionable due to missing in-situ measurement data. In this work, a new 2D open-source therma...
Article
Full-text available
The Czochralski (CZ) growth technique is widely applied in crystal growth, using both induction and resistance heaters. In this work, a novel model experiment platform with comprehensive in-situ measurement capability is introduced. Growth experiments with the model material tin applying both heating concepts are performed and analyzed, e.g., in te...
Presentation
Full-text available
Presentation at DKT 2021 Conference. File will be made available upon request.
Presentation
Full-text available
Presentations slides available on request.
Presentation
Full-text available
MODEL EXPERIMENTS FOR HEATER CONCEPTS IN CZOCHRALSKI CRYSTAL GROWTH PROCESSES Keywords: multiphysics, crystal growth, Czochralski method, model experiment, induction heater
Presentation
Full-text available
The NEMOCRYS project in the group “Model experiments” at the IKZ funded by an ERC Starting Grant aims at profoundly validated numerical models for crystal growth. These processes involve a variety of coupled physical phenomena such as heat transfer including radiation and phase change, electromagnetism, melt- and gas flows and thermal stresses. Num...
Presentation
Full-text available
The NEMOCRYS project in the group “Model experiments” at the IKZ develops an open-source-based framework for coupled multiphysics simulation in crystal growth. Currently, Gmsh for FEM mesh generation and Elmer to solve the heat transfer problem including inductive heating are applied. These tools are wrapped in an easy-to-use python interface that...
Presentation
Full-text available
Short presentation of the new Junior Research Group at the IKZ
Presentation
The NEMOCRYS project funded by an ERC Starting Grant aims at the development of profoundly validated numerical models for crystal growth processes using the Czochralski (CZ) and Floating Zone (FZ) methods. These growth processes usually involve very high temperatures and have high requirements on the degree of purity, which prevents in-depth measur...
Article
Full-text available
Within this paper we present a model experiment focusing on investigations of the flow field in a Czochralski puller. Low melting point liquid metals as GaInSn are an important tool to investigate the flow structure for such industrial processes. The topology of the prevailing thermally-driven convection might be very complex and is mainly determin...
Article
Full-text available
A novel, vertical Bridgman-type technique for growing multi-crystalline silicon ingots in an induction furnace is described. In contrast to conventional growth, a modified setup with a cone-shaped crucible and susceptor is used. A detailed numerical simulation of the setup is presented. It includes a global thermal simulation of the furnace and a l...
Article
This study addresses experimentally the heat transfer, the temperature azimuthal non-uniformity and the onset of oscillations in a low temperature physical model of a medium-sized Czochralski crystal growth process with a strong horizontal magnetic field (HMF). It is observed that under certain conditions the integral heat flux may decrease with in...
Article
Rayleigh-Benard convection is not only a classical problem in fluid dynamics but plays also an important role in many metallurgical and crystal growth applications. The measurement of the flow field and of the dynamics of the emerging large-scale circulation in liquid metals is a challenging task due to the opaqueness and the high temperature of th...
Article
A low temperature liquid metal model of the Czochralski (CZ) crystal growth process is considered experimentally for a high aspect ratio. Temperature fluctuations close to the edge of the model crystal are studied under the action of a rotating magnetic field (RMF) and/or rotation of the model crystal. A rotation of thermal structures is observed w...
Article
An experimental study of the buoyancy-induced flow in a model of a Czochralski crystal growth system was conducted. Ultrasonic velocimetry was used to measure fluid velocities. To approach the thermal boundary conditions in an industrial growth facility, a double-walled glass crucible flown through by a heating fluid was chosen to hold the fluid. S...
Article
A great deal of work with respect to both physical and numerical modelling of Czochralski crystal growth has been conducted in the generic Rayleigh-Bénard system. In order to come closer to the conditions in a real Czochralski puller, specific effects such as the influence of a rounded crucible bottom, deviations of the thermal boundary conditions...
Article
Alternating magnetic fields provide a comfortable means for non-intrusive flow control in conductive fluids. However, despite a long history of applications in metallurgy and crystal growth, detailed investigation of the practically important transitional and turbulent flow regimes has become possible only in the last dozen years. The present revie...
Article
Full-text available
A lot of the physical and the numerical modeling of Czochralski crystal growth is done on the generic Rayleigh-Bénard system. To better approximate the conditions in a Czochralski puller, the influences of a rounded crucible bottom, deviations of the thermal boundary conditions from the generic case, crucible and/or crystal rotation, and the influe...
Article
Full-text available
Four-wire electric potential difference probes are used to record time series of two local velocity components in a flow driven by a rotating magnetic field. It is demonstrated that statistical properties of turbulence in an electromagnetically driven flow can be extracted from the signals, although they are predominated by noise, disturbances main...
Article
With conventional methods the sound velocity c in fluids can be determined using the back wall echo. This paper proposes a novel technique, in which the signals reflected by scattering particles suspended in a fluid are analysed instead. The basic idea is that the particles generate the strongest echo signal when being located in the sound field ma...
Article
The sensitivity of a flow that is driven by a travelling magnetic field (TMF) with respect to a shift between the axes of the cylindrical liquid metal column and of the TMF was studied both experimentally and by numerical simulation. In the physical modelling, the TMF is generated by six equidistantly spaced cylindrical coils loaded with ac current...
Article
Full-text available
The shape of the solidification front and the related mono-crystalline growth in the Czochralski crystal growth process is thought of being strongly influenced by the ratio of the horizontal and the vertical temperature gradient r* = grad T_h / grad T_v at the triple point liquid--solid--atmosphere, which ratio desirably should be in the order of u...
Article
Full-text available
This work examines the induction heating of a metal sheet to be used for multiple instance melt extraction from the lower edge. The task formulation of heating the edge in first place while keeping the release of Joule heat along that edge as homogeneous as possible, i.e., the avoidance of end effects, is solved numerically with a parametric study....
Article
Liquid metal model experiments (LMME) are an important tool in metallurgy and crystal growth. They allow investigating the flow structure and the transport properties in industrial facilities on laboratory scale. Further, LMME provide a profound basis for the validation of numerical simulations. Physical modelling as well as up-scaling is ruled by...
Article
Full-text available
Flow visualization and velocity measurements in a liquid metal flow were performed in order to study the combined action of a rotating and a travelling magnetic field. The combination of both fields, which is not necessarily a linear superposition, may give rise to an inherent three-dimensional constituent of the electromagnetic force distribution....
Article
Full-text available
Velocity measurements in a liquid metal flow were performed in order to study the combined action of a rotating (RMF) and a traveling magnetic field (TMF). In a cylindrical container, a RMF alone, as well as a TMF alone, cause axisymmetric volume forces, which drive corresponding axisymmetric base flows. The combination of both fields gives rise to...
Article
Full-text available
Mit Hilfe magnetoakustischer Messmethoden wurde im Rahmen dieser Arbeit die Flusslinienverankerung im System des Hochtemperatursupraleiters YBCO untersucht. Die theoretischen Grundlagen lassen sich dabei, aufbauend auf das TAFF-Modell, mit Hilfe der Pankert'schen Theorie beschreiben. Durch die vielfältigen Orientierungsmöglichkeiten zwischen der Sc...
Article
Investigations on the temperature dependence in the range from 4 to 100K of the ultrasonic attenuation α(T, B) and the relative change Δv(T,B)/v of the sound velocity for various applied magnetic fields have been made. The ultrasonic attenuation α was measured by the pulse-echo technique and the relative change of the sound velocity Δv/v by a phase...
Article
Magnetostriction hysteresis data reveal the presence of the fishtail effect in isothermal scans between 72 and 80 K. Thermal cycles in a constant magnetic field show the behaviour of pinning of flux lines in the different phases. Ultrasonic attenuation and the relative change of the sound velocity for various magnetic fields were measured. The aim...
Article
On 10th December 1999, the European X-ray satellite XMM, now called XMM-Newton, was successfully put into orbit. After initial commissioning of the satellite's subsystems, the EPIC-pn camera was switched on and tested thoroughly in the period Jan./Febr. 2000. After refining of some of the parameter settings and the on-board pn-computer programs, we...
Conference Paper
Full-text available
On 10th December 1999, the European X-ray satellite XMM, now called XMM-Newton, was successfully put into orbit. After initial commissioning of the satellite's subsystems, the EPIC-pn camera was switched on and tested thoroughly in the period Jan./Febr. 2000. After refining of some of the parameter settings and the on-board pn-computer programs, we...
Article
The European X-ray satellite XMM will be launched in December 1999. One of the focal plane instruments of the European Photon Imaging Camera (EPIC) on board XMM is equipped with a monolithic pn-CCD consisting of 12 individual CCDs with 200 X 64 pixels each. In order to exploit the god intrinsic energy resolution of the pn-CCD, the charge transfer e...
Conference Paper
In the near future the European x-ray satellite XMM will be launched into orbit. The satellite is equipped with a PN-CCD camera with a sensitive area of 60 mm X 60 mm, integrated on a single silicon wafer. The same camera is on board of the German x-ray satellite ABRIXAS. The main feature of this camera type is the very good quantum efficiency of m...
Article
Cottbus, Techn. Univ., Diss., 2004 Langzeitarchivierung in Der Deutschen Bibliothek gewährleistet

Network

Cited By

Projects

Project (1)
Project
*** NEMOCRYS: Next Generation Multiphysical Models for Crystal Growth Processes *** Crystalline materials are indispensable for the contemporary world and silicon crystals in particular have enabled the technological progress from first transistors to quantum computers. Such crystals are produced in high-temperature processes with a permanent demand to improve both material quality and efficiency of mass production. The high complexity of the growth processes involving various physical phenomena from electromagnetism to fluid dynamics as well as the limited possibilities of direct measurements make process optimization very challenging. Numerical simulation is often used, but due to limited accuracy of the models, experimental trial-and-error still dominates in practice as I have directly experienced while developing crystal growth methods both on research and industrial scales for more than a decade. There is a series of fundamental assumptions in multiphysical models that have been used for many crystal growth processes of various materials but have never been thoroughly validated. I propose to build a general experimental platform (MultiValidator) to address these challenges and, for the first time, to consider the complete physical complexity of a real growth process. A unique crystal growth setup will be developed for a model material (e.g., Ga) to enable low working temperatures, relaxed vacuum-sealing requirements and easy experimental access for various measurement techniques simultaneously (e.g., flow velocity and thermal stress fields). In this way, a new level of physical understanding and a new generation of multiphysical models for crystal growth processes will be established. The following paradigm change in the way how we observe, describe and develop crystal growth processes and similar complex multiphysical systems will minimize the necessary experimental cycles and open new horizons for a scientific analysis as well as for smart process control, for example, within the Industry 4.0 initiative. *** This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 851768). ***