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This Ph. D. thesis with the title "Characterisation of laser-driven radiation beams: Gamma-ray dosimetry and Monte Carlo simulations of optimised target geometry for record-breaking efficiency of MeV gamma-sources" is dedicated to the study of the acceleration of electrons by intense sub-picosecond laser pulses propagating in a sub-millimeter plasma with near-critical electron density (NCD) and resulting generation of the gamma bremsstrahlung and positrons in the targets of different materials and thickness.
Laser-driven particle acceleration is an area of increasing scientific interest since the recent development of short pulse, high-intensity laser systems. The interaction of intense high-energy, short-pulse lasers with solid targets leads to the production of high-energy electrons in the relativistic laser intensity regime of more than 1018 W /cm2. These electrons play the leading role in the first stage of the interaction of laser with matter, which leads to the creation of laser sources of particles and radiation. Therefore, the optimisation of the electron beam parameters in the direction of increasing the effective temperature and beam charge, together with a slight divergence, plays a decisive role, especially for further detection and characterisation of laser-driven photon and positron beams.
In the context of this work, experiments were carried out at the PHELIX laser system (Petawatt High-Energy Laser for Heavy Ion eXperiments) at GSI Helmholtz Center for Heavy-Ion Research GmbH in Darmstadt, Germany. This thesis presents a thermoluminescence dosimetry (TLD) based method for the measurement of bremsstrahlung spectra in the energy range from 30 keV to 100 MeV. The results of the TLD measurements reinforced the observed tendency towards the strong increase of the mean electron energy and number of super-ponderomotive electrons. In the case of laser interaction with long-scale NCD-plasmas, the dose caused by the gamma-radiation measured in the direction of the laser pulse propagation showed a 1000-fold increase compared to the high contrast shots onto plane foils and doses measured perpendicular to the laser propagation direction for all used combinations of targets and laser parameters.
In this thesis I present novel characterisation method using a combination of TLD measurements and Monte Carlo FLUKA simulations applicable to laser-driven beams. The thermoluminescence detector-based spectrometry method for simultaneous detection of electrons and photons from relativistic laser-induced plasmas initially developed by Behrens et al. (Behrens et al., 2003) and further applied in experiments at PHELIX laser (Horst et al., 2015) delivered good spectral information from keV energies up to some MeV, but as it was presented in (Horst et al., 2015) this method was not really suitable to resolve the content of photon spectra above 10 MeV because of the dominant presence of electrons. Therefore, I created new evaluation method of the incident electron spectra from the readings of TLDs. For this purpose, by means of MatLab programming language an unfolding algorithm was written. It was based on a sequential enumeration of matching data series of the dose values measured by the dosimeters and calculated with of FLUKA-simulations. The significant advantage of this method is the ability to obtain the spectrum of incident electrons in the low energy range from 1 keV, which is very difficult to measure reliably using traditional electron spectrometers.
The results of the evaluation of the effective temperature of super-ponderomotive electrons retrieved from the measured TLD-doses by means of the Monte-Carlo simulations demonstrated, that application of low density polymer foam layers irradiated by the relativistic sub-ps laser pulse provided a strong increase of the electron effective temperature from 1.5 - 2 MeV in the case of the relativistic laser interaction with a metallic foil up to 13 MeV for the laser shots onto the pre-ionized foam and more than 10 times higher charge carried by relativistic electrons.
The progressive simulation method of whole electron spectra described with two -temperatures Maxwellian distribution function has been developed and the results of dose simulations were compared with the acquired experimental data. The advanced feature of this method, which distinguishes it from the results of the simulation of the photon spectrum using the interaction with the target of mono-energetic electron beams (Nilgün Demir, 2013; Nilgün Demir, 2019) or the initial electron spectrum expressed as a function of one electron temperature (Fiorini, 2012), is the ability to simulate the initial electron spectrum described by the Maxwellian distribution function with two temperatures.
The important objective of this thesis was dedicated to the study and characterisation of laser-driven photon beams. In addition to this, the positron beams were evaluated. The investigation of bremsstrahlung photons and positrons spectra from high Z targets by varying the target thickness from 10 µm to 4 mm in simulated models of the interactions of electron spectra with Maxwellian distribution functions allowed to define an optimal thickness when the fluences of photons and positrons are maximal. Furthermore based on the results of FLUKA simulations the gold material was found to be the most suitable for the future experiments as e − γ target because of its highest bremsstrahlung yield.
Additionally Monte Carlo simulations were performed applying the obtained electron beam parameters from the electron acceleration process in laser-plasma interactions simulated with particle-in-cell (PIC) code for two laser energies of 20 J and 200 J. The corresponding electron spectra were imported into a Monte Carlo code FLUKA to simulate the production process of bremsstrahlung photons and positrons in Au converter. FLUKA simulations showed the record conversion of efficiency in MeV gammas can reach 10%, which reinforces the generation of positrons. The obtained results demonstrate the advantages of long-scale plasmas of near critical density (NCD) to increase the parameters of MeV particles and photon beams generated in relativistic laser-plasma interaction. The efficiency of the laser-driven generation of MeV electrons and photons by application of low-density polymer foams is essentially enhanced.
In dieser Arbeit wurden thermodynamische Eigenschaften eines chiralen Quark Meson Modelles untersucht. Das chirale Quark Meson Model beschreibt die starke Wechselwirkung über den Austausch von Mesonen und zudem die thermische und dichteabhängige Entwicklung der Quarkmassen im Medium über die chirale Symmetrie.Im SU(2) Model wurde zunächst in mean field approximation gearbeitet, um im Anschluss den divergenten Vakuumterm mit einzubeziehen. Nach eingehender Untersuchung der Ergebnisse, wurden dann die thermischen Mesonenfluktuationen studiert. In beiden Ansätzen verschiebt die Nullpunktsenergie den chiralen Phasenübergang zu höheren Temperaturen, wodurch die Massen bei höheren Temperaturen entarten. Beide Ansätze wurden dann zu einem gemeinsamen Modell kombiniert, um den Einfluss der Mesonenfluktuationen auf Ordnungsparameter, Massen und thermodynamische Grössen zu untersuchen. Als Fazit der Studie kann behauptet werden, dass sich der Einfluss der Mesonenfluktuationen in grösserem Maÿ auf die Thermodynamik, als auf den Ordnungsparameter und die Massen auswirkt. Im SU(3) Modell wurden ebenfalls regularisiert und zudem Vektormesonen mitberücksichtigt, welche die Repulsion zwischen den einzelnen Freiheitsgraden modelliert. Die Zustandsgleichung wird durch den Vakuum Term etwas softer und zeigt ein ähnliches Verhalten im niederen Energiebereich. Untersucht wurde neben der Temperatur T, die Elektron Baryon Rate Ye, die Sigma Meson Masse noch der Einfluss der Vektorkopplung. Aus der Zustandsgleichung konntendann Isentropen im T-mu Phasendiagramm errechnet werden, welche in naher Zukunft Aufschluss über eine dritte Familie von kompakten Sternen in Zusammenhang mit der entsprechenden Supernova Explosion geben könnte. Um die Existenz von kompakten Sternen genauer zu analysieren, wurde das chiraleSU(3) Quark Meson Modell bei T = 0 benutzt, um über die aus dem Formalismusgewonnenen Grössen Druck und Energiedichte die Tolmann-Oppenheimer-Volkoff zu lösen. Diese stellen die Masse-Radius Beziehungen kompakter Objekte dar. Auf der Suche nach Twin Stern Lösungen aus dem chiralen SU(3) Quark Meson Model wurde zunächst ein Modell für Hybridsterne entwickelt. Im untersuchten Parameterbereich fanden wir Hybrid Stern Lösungen, bei welchen der Einfluss der Quarkmaterie auf die Stabilität des Sternes untersucht wurde, denn das Einsetzen des Phasenüberganges übt einen zusätzlichen gravitativen Zug auf die hadronische Kruste aus. Der Stern ist stabil, wenn der Druck der Quarkmaterie diesem zusätzlichen Zug standzuhalten vermag. Für einen zu grossen Sprung in der Energiedichte werden die Lösungen jedoch instabil. Zwillingssterne waren nicht unter den Lösungen, da der Übergangsdruck relativklein sein muss, während der Energiedichtesprung eher gross sein sollte. Das Auftreten zweier stabiler Äste in der Masse Radius Relation kann allerdingsmit dem SU(3) Modell und entsprechendem chiralen Phasenübergang modelliert werden. Für einen gewissen Parameterbereich einhergehend mit kleinem Wert des Vakuum Druckes B konnten Nicht-Linearitäten in der Zustangsgleichungzur Lösung der TOV Gleichung beitragen. Im Weitern ist das Zusammenspiel der Vektorkopplung und der Sigma Mesonen Masse einflussreich auf die Lösungen, welche auf Kausalität, Stabilität und neben der 2 Sonnenmassen Bedingung noch auf Restriktionen vom millisecond pulsar PSR J1748-2446ad untersucht wurden.Mit Weltraummissionen wie etwa NICER (Neutron star Interior CompositionExploreR) sollte die Radiusbestimmung kompakter Objekte in Zukunft bis auf einen Kilometer genau bestimmt werden können. Die Entdeckung von zweiSternen mit der gleichen Masse und unterschiedlichen Radien wäre in der Tat ein Beweis für die Existenz von Zwillingssternen, welche dann die Theorie des Phasenüberganges in dichter Materie untermauern würde. Das Kollaps-Szenario eines Zwillingssternes würde weiteren Aufschluss über Neutrino-Emmissivität, Gamma-ray burster und Gravitationswellen Signale geben können. Dynamische Simulationen in allgemein relativistischem Kontext für compact star merger mit den hier diskutierten Zustandsgleichungen sind bereits in Planung, um Eigenschaftenwie beispielsweise das Temperatur- und Dichteprofil solcher Objekte genauer zu analysieren.
Terahertz (THz) radiation lies between the micro and far-infrared range in the electromagnetic spectrum. Compared with microwave and millimeter waves, it has a larger signal bandwidth and extremely narrow antenna beam. Thus, it is easier to achieve high-resolution for imaging and detection applications. The unique properties, such as penetration for majority non-polar materials, non-ionizing characteristic and the spectral fingerprint of materials, makes THz imaging an appealing artifice in the military, biomedical, astronomical communications, and other areas. However, THz radiation’s current low power level and detection sensitivity block THz imaging system from including fewer optical elements than the visible or infrared range. This leads to imaging resolution, contrast, and imaging field of view degenerate and makes the aberration more serious. THz imaging based on the space Fourier spectrum detection is developed in this thesis to achieve high-quality imaging. The main concept of Fourier imaging is by recording the field distribution in the Fourier plane (focal plane) of the imaging system; the information of the target is obtained. The numerical processing method is needed to extract the amplitude and phase information of the imaged target. With additional process, three-dimensional (3D) information can be obtained based on the phase information. The novel recording and reconstructing ways of the Fourier imaging system enables it to have a higher resolution, better contrast, and broader field of view than conventional imaging systems such as microscopy and plane to plane telescopic imaging system.
The work presented in this thesis consists of two imaging systems, one is working at 300 GHz based on the fundamental heterodyne detection of the THz radiation, the other is operated at 600 GHz by utilizing the sub harmonic heterodyne detection technique. The realization and test of the heterodyne detection are based on the THz antenna-coupled field-effect transistor (TeraFET) detector developed by Dr. Alvydas Lisauskas. Both systems use two synchronized electronic multiplier chains to radiate the THz waves. One radiation works as the local oscillator (LO), the other works as illumination with a slight frequency shift, the radiations are mixed on the detector scanning in the Fourier plane to record the complex Fourier spectrum of the imaged target. The LO has the same frequency range as the illuminating radiation for fundamental heterodyne detection but half the frequency range for the sub-harmonic heterodyne detection. The 2-mm resolution, 60-dB contrast, and 5.5-cm diameter imaging area at 300 GHz and the of 500-μm resolution, 40-dB contrast, and 3.5-cm diameter imaging area at 600 GHz are achieved (the 300-GHz illuminating radiation has the approximate power of 600 μW , the 600-GHz illuminating radiation has the approximate power of 60 μW ).
The thesis consists of 6 parts. After the introduction, the second chapter expands on the topic of Fourier optics from a theoretical point of view and the simulations of the Fourier imaging system. First, the theory of the electromagnetic field propagation in free space and through an optical system are investigated to elicit the Fourier transform function of the imaging system. The simulation is used for theoretical considerations and the implementation of a Fourier optic script that allows for numerical investigations on reconstruction. The preliminary imaging field of view and resolution are also demonstrated. The third chapter describes the Fourier imaging system at 300 GHz based on the fundamental heterodyne detection, including the experimental setup, the 2D, and 3D imaging results. The following fourth chapter reports the integration of the TeraFET detector with two substrate lenses (one is a Si lens on the back-side Si substrate, the other is a wax/PTFE lens on the front side containing the bonding wires) for sub-harmonic heterodyne detection at 600 GHz. The characteristic of the wax/PTFE lens at THz range is presented. After that, the compared imaging results between the detector with and without the wax/PTFE lens are shown. The fifth chapter extends the demonstration on the lateral and depth resolution of the Fourier imaging system in detail and uses the experimental results at 600 GHz to validate the analytical predictions. The comparison of the resolution between the Fourier imaging system and the conventional microscopy system proves that the Fourier imaging system has better imaging quality under the same system configuration. The last chapter in this thesis concludes on the findings of the THz Fourier imaging and gives an outlook for the enhancement of the Fourier imaging system at THz range.
Cryo-electron tomography (CET) is a unique technique to visualize biological objects under near-to-native conditions at near-atomic resolution. CET provides three-dimensional (3D) snapshots of the cellular proteome, in which the spatial relations between macromolecular complexes in their near native cellular context can be explored. Due to the limitation of the electron dose applicable on biological samples, the achievable resolution of a tomogram is restricted to a few nanometers, higher resolution can be achieved by averaging of structures occurring in multiples. For this purpose, computational techniques such as template matching, sub-tomogram averaging and classification are essential for a meaningful processing of CET data.
This thesis introduces the techniques of template matching and sub-tomogram averaging and their applications on real biological data sets. Subsequently, the problem of reference bias, which restricts the applicability of those techniques, is addressed. Two methods that estimate the reference bias in Fourier and real space are demonstrated. The real space method, which we have named the “M-free” score, provides a reliable estimation of the reference bias, which gives access to the reliability of the template matching or sub-tomogram averaging process. Thus, the “M-free” score makes those approaches more applicable to structural biology. Furthermore, a classification algorithm based on Neural Networks (NN) called “KerDenSOM3D” is introduced, which is implemented in 3D and compensates for the missing-wedge. This approach helps extracting different structural states of macromolecular complexes or increasing the class purity of data sets by eliminating outliers. A comprehensive comparison with other classification methods shows superior performance of KerDenSOM3D.
In the present work, the problem of protein folding is addressed from the point of view of equilibrium thermodynamics. The conformation of a globular protein in solution at common temperatures is quite complicated without any geometrical symmetry, but it is an ordered state in the sense of its biological activity. This complicated conformation of a single protein molecule is destroyed upon increasing the temperature or by the addition of appropriate chemical agents, as is revealed by the loss of its activity and change of the physical properties, and so on. Once the complicated native structures having biological activity are lost, it would be natural to suppose that the native structure could hardly be restored. Nevertheless, pioneers, such as Anson and Mirsky, recognized as early as in 1925 that this was not always the case. If one defines the folded and unfolded states of a protein as two distinct phases of a system, then under the variation of temperature the system is transformed from one phase state into another and vice versa. The process of protein folding is accompanied by the release or absorption of a certain amount of energy, corresponding to the first-oder-type phase transitions in the bulk. Knowing the partition function of the system one can evaluate its energy and heat capacity under different temperatures. This task was performed in this work. The results of the developed statistical mechanics model were compared with the results of molecular dynamic simulations of alanine poylpeptides. In particular, the dependencies on temperature of the total energy of the system and heat capacity were compared for alanine polypeptides consisting of 21, 30, 40, 50 and 100 amino acids. The good correspondence of the results of the theoretical model with the results of molecular dynamics simulations allowed to validate the assumptions made about the system and to establish the accuracy range of the theory. In order to perform the comparison of the results of theoretical model and the molecular dynamics simulations it is necessary to perform the efficient analysis of the results of molecular dynamics simulations. This task was also addressed in the present work. In particular, different ways to obtain dependence of the heat capacity on temperature from molecular dynamics simulations are discussed and the most efficient one is proposed. The present thesis reports the result of molecular dynamic simulations for not only alanine polypeptides by also for valine and leucine polypeptides. In valine and leucine polypeptides, it is also possible to observe the helix↔random coil transitions with the increase of temperature. The current thesis presents a work that starts with the investigation of the fundamental degrees of freedom in polypeptides that are responsible for the conformational transitions. Then this knowledge is applied for the statistical mechanics description of helix↔coil transitions in polypeptides. Finally, the theoretical formalism is generalized for the case of proteins in water environment and the comparison of the results of the statistical mechanics model with the experimental measurements of the heat capacity on temperature dependencies for two globular proteins is performed. The presented formalism is based on fundamental physical properties of the system and provides the possibility to describe the folding↔unfolding transitions quantitatively. The combination of these two facts is the major novelty of the presented approach in comparison to the existing ones. The “transparent” physical nature of the formalism provides a possibility to further apply it to a large variety of systems and processes. For instance, it can be used for investigation of the influence of the mutations in the proteins on their stability. This task is of primary importance for design of novel proteins and drug delivering molecules in medicine. It can provide further insights into the problem of protein aggregation and formation of amyloids. The problem of protein aggregation is closely associated with various illnesses such as Alzheimer and mad cow disease. With certain modifications, the presented theoretical method can be applied to the description of the protein crystallization process, which is important for the determination of the structure of proteins with X-Rays. There many other possible applications of the ideas described in the thesis. For instance, the similar formalism can be developed for the description of melting and unzipping of DNA, growth of nanotubes, formation of fullerenes, etc.
Charge states and energy loss of heavy ions after passing an inductively coupled plasma target
(2019)
In various kinds of fields such as accelerator physics, warm dense matter, high energy density physics, and inertial confinement fusion, heavy ions beam-plasma interaction plays an important role, and abundant investigations have been and are being carried out. Taking advantage of a good level of understanding on the interaction between a swift heavy ions beam and a hydrogen gas discharge plasma, an engineering application of a spherical theta-pinch device as a plasma stripper for FAIR (facility for antiproton and ion research) and a scientific application of a swift heavy ions beam as a novel plasma diagnostic tool are proposed and investigated.
The spherical theta-pinch device is manufactured, improved, and comprehensively tested for its application as a plasma stripper. The device is mainly composed of an evacuated glass vessel that can be filled with gas (for example: hydrogen) and a LRC circuit including a capacitors bank and a set of coils. Discharging the device at an initial hydrogen pressure in the glass vessel and an operation voltage for the capacitors bank, a circuit current oscillates in the LRC circuit. The oscillating circuit current in the set of coils induces a corresponding alternating magnetic field inside the glass vessel to ignite and maintain a hydrogen plasma.
Based on the built setup of circuit and plasma diagnostics, the measurements of circuit current, plasma light emission, plasma shape, and hydrogen Balmer series are carried out. The recorded signals of the circuit current and the plasma light emission of many consecutively repetitive discharges overlap perfectly, which indicate a very good reproducibility of the parameters of the LRC circuit during discharge and the generated plasma. From the measured circuit current, a real energy transfer efficiency is calculated by our proposed new model, which shows its overall tendency varying with the hydrogen pressure and the operation voltage, including the maximum value of 25% occurring at an initial hydrogen pressure of around 25 Pa and a maximum operation voltage of 14 kV. So, the discharge at an initial hydrogen pressure of 20 Pa and an operation voltage of 14 ...
Conclusion Scale Integration Based on the results of spike-field coherence, the underlying process of shortterm memory seems to involve networks of different sizes within and, most probably, beyond prefrontal cortex. Spikes, which were generated by single neurons, cooperate with local field potentials, which were the slower fluctuations of the environment. Although differences among behavioral conditions appear to be based on rather few instances of phase-locked spikes, the task-related effects on spike-field coherence are highly reliable and cannot be explained by chance, as the comparison of results from experimental and simulated data shows. The differential locking of prefrontal neuron populations with two different frequency bands in their input signals suggests that neuronal activity underlying short-term memory in prefrontal cortex transiently engages cortical circuits on different spatial scales, probably in order to coordinate distributed processes. NeuroXidence method and Synchronizedfiring Based on the results of the calibration datasets, for bi- and multi-variate cases, the extension of NeuroXidence remains its sensitivity and reliability of detecting coordinate firing events for different processes. Based on this extension of NeuroXidence, we demonstrated that in monkey’s prefrontal cortex during short-term memory task, encoding and maintenance of the information rely on the formation of neuronal assemblies characterized by precise and reliable synchronization of spiking activity on a millisecond time scale, which is consistent with the results from spike-spike coherence. The task and performance dependent modulation of synchrony reflects the dynamic formation of group of neurons has large effect on short-term-memory.
Light scalar mesons can be understood as dynamically generated resonances. They arise as 'companion poles' in the propagators of quark-antiquark seed states when accounting for hadronic loop contributions to the self-energies of the latter. Such a mechanism may explain the overpopulation in the scalar sector - there exist more resonances with total spin J=0 than can be described within a quark model.
Along this line, we study an effective Lagrangian approach where the isovector state a_{0}(1450) couples via both non-derivative and derivative interactions to pseudoscalar mesons. It is demonstrated that the propagator has two poles: a companion pole corresponding to a_{0}(980) and a pole of the seed state a_{0}(1450). The positions of these poles are in quantitative agreement with experimental data. Besides that, we investigate similar models for the isodoublet state K_{0}^{*}(1430) by performing a fit to pion-kaon phase shift data in the I=1/2, J=0 channel. We show that, in order to fit the data accurately, a companion pole for the K_{0}^{*}(800), that is, the light kappa resonance, is required. A large-N_{c} study confirms that both resonances below 1 GeV are predominantly four-quark states, while the heavy states are quarkonia.
In this thesis, a novel 257 kHz chopper device was numerically developed, technically designed and experimentally commissioned; a 4-solenoid, low-energy ion beam transport line was numerically investigated, installed and experimentally commissioned; and a novel massless beam-separation system was numerically developed.
The chopper combines a pulsed electric field with a static magnetic field in an ExB or Wien-filter type field configuration. Chopped beam pulses with a 257 kHz repetition rate and rise times of 110 ns were experimentally achieved using a 14 keV helium beam.
Due to the achieved results, the complete LEBT line for the future Frankfurt Neutron Source FRANZ is ready to deliver a dc or a pulsed beam. At the same time, the LEBT section represents an attractive test stand for the study of low-energy ion beams. It combines magnetic lenses, which allow space-charge compensated beam transport, and a chopper system capable of producing short beam pulses in the hundred nanosecond range. Since these beam pulses are transported onwards, their longitudinal and transverse properties can be analyzed. The pulse duration and time of flight are well below the rise time for the space-charge compensation through residual gas ionization. This opens the possibility for dedicated investigations of the transport of short, low-energy beam pulses including longitudinal and transverse space-charge effects and of relevant issues like the dynamics of space-charge compensation and electron effects in short pulses.
ALICE (A Large Ion Collider Experiment), is the dedicated heavy-ion experiment at the Large Hadron Collider (LHC) at CERN. It is optimised to reconstruct and identify the particles created in a lead-lead collision with a centre of mass energy of 5.5TeV. The main tracking detector is a large-volume time-projection chamber (TPC). With an active volume of about 88m^3 and a total readout area of 32.5m^2 it is the most challenging TPC ever build. A central electrode divides the 5m long detector into two drift regions. Each readout side is subdivided into 18 inner and 18 outer multi-wire proportional read-out chambers. The readout area is subdivide into 557568 pads, where each pad is read out by and electronics chanin. A complex calibration is needed in order to reach the design position-resolution of the reconstructed particle tracks of about 200um. One part of the calibration lies in understanding the electronic-response. The work at hand presents results of the pedestal and noise behaviour of the front-end electronics (FEE), measurements of the pulse-shaping properties of the FEE using results obtained with a calibration pulser and measurements performed with the laser-calibration system. The data concerned were taken during two phases of the TPC commissioning. First measurements were performed in the clean room where the TPC was built. After the TPC was moved underground and built into the experiment, a second round of commissioning took place. Noise measurements in the clean room revealed a very large fraction of pads with noise values larger than the design specifications. The unexpected high noise values could be explained by the 'ground bounce' effect. Two modifications helped to reduce this effect: A desynchronisation in the the start of the readout of groups of channels and a modification in the grounding scheme of the FEE. Further noise measurements were carried out after the TPC has been moved to the experimental area underground. Here even a larger fraction of channels showed too large noise values. This could be traced back to a common mode current injected by the electronics power supplies. To study the shaping properties of the FEE a calibration pulser was used. To generate signals in the FEE a pulse is injected to the cathode wires of the read-out chambers. Due to manufacturing tolerances slight channel-by-channel variations of the shaping properties are expected. This effects the determination of the arrival time as well as the measured integral signal of the induced charge and has to be corrected. The measured arrival time variations follow a Gaussian distribution with a width (sigma) of 6.2ns. This corresponds to an error of the cluster position of about 170um. The charge variations are on the level of 2.8%. In order to reach the intrinsic resolution on the measurement of the specific energy loss of the particles (6%) those variations have to be taken into account. The photons of the laser-calibration system are energetic enough to emit photo electrons off metallic surfaces. Most interesting for the detector calibration are photo electrons from the central electrode. The laser light is intense enough to get a signal in all readout channels of the TPC. Since the central electrode is a smooth surface, differences in the arrival time between sectors reveal mechanical displacements of the readout sectors and can be used to correct for this effect. In addition the measurements can be used to determine the electron drift velocity in the TPC gas. The drift velocity measurements have shown a vertical as well as a radial gradient. The first can be explained by the temperature gradient, which naturally builds up in the 5m high detector. The second gradient is most probably caused by a relative conical deformation of the readout plane and the central electrode.