Supersonic gas-jet based beam profile monitor

Ions and in particular antiprotons, stored and cooled at low energies in a storage ring or at rest in traps, are highly desirable for the investigation of a large number of basic questions on fundamental interactions, on the static structure of exotic antiprotonic atomic systems or of (radioactive) nuclei as well as on the time-dependent quantum dynamics of correlated systems. Such low energy, low intensity beams pose, however, new challenges on beam instrumentation, as they require least intrusive diagnostics operating at ultra-high vacuum pressures of the order of 1

Holography and Optical Filtering

Holography and optical filtering techniques for structural analysis, material tests, and astronomical observation - conferenc

Design, Construction, and Application of an Electrostatic Quadrupole Doublet for Heavy Ion Nuclear Microprobe Research

A nuclear microprobe, typically consisting of 2 - 4 quadrupole magnetic lenses and apertures serving as objective and a collimating divergence slits, focuses MeV ions to approximately 1 x 1 μm for modification and analysis of materials. Although far less utilized, electrostatic quadrupole fields similarly afford strong focusing of ions and have the added benefit of doing so independent of ion mass. Instead, electrostatic quadrupole focusing exhibits energy dependence on focusing ions. A heavy ion microprobe could extend the spatial resolution of conventional microprobe techniques to masses untenable by quadrupole magnetic fields. An electrostatic quadrupole doublet focusing system has been designed and constructed using several non-conventional methods and materials for a wide range of microprobe applications. The system was modeled using the software package "Propagate Rays and Aberrations by Matrices" which quantifies system specific parameters such as demagnification and intrinsic aberrations. Direct experimental verification was obtained for several of the parameters associated with the system. Details of the project and with specific applications of the system are presented

Kinematically complete multiphoton ionization studies on optically trapped 6Li and 6Li_2 created by single-color photoassociation

In this work, a reaction microscope with a magneto-optical trap for 6Li atoms, was extended by an optical dipole trap in order to be able to investigate in detail laser-induced atomic and molecular ionization dynamics in a cold quantum gas. The optical dipole trap was operated at a full trap depth of 2.3 mK for 6Li atoms and about 1% of the atoms in the MOT could be transferred into the dipole trap, with 1/e storage times exceeding 5 s. The optically trapped ensemble of 6Li atoms was used as a target for ionisation with intensive and broadband femtosecond laser pulses (λ = 750−820 nm, P = 10^11−10^14 W/cm2, Δt = 30 fs) and allowed to perform kinematically complete experiments, in which 6Li+ ions as well as photoelectrons were measured coincidentically. As a first application, in this work, a series of association- and ionization mechanisms, which led to production of molecular 6Li2+ ions, were investigated with trapped lithium atoms. In photoassociative ionization, two atoms collide, which were previously lifted into the asymptotic 2p − 3s potential energy curve by ladder excitation. During the collision the atoms autoionize into the 12Σg+(6Li2+) groundstate of the molecular ion, since these two potential energy curves exhibit an avoided crossing. This process was observed when magneto-optically trapped atoms were illuminated with the femtosecond laser. In the dipole trap, using single-color photoassociation, excited state molecules were produced in high-lying vibrational states 11Σg+(ν = 65) and 13Σg+(v = 57) and spectroscopically investigated. A fraction of the excited state molecules decay via fluorescence into the molecular ground state. The 11Σg+(ν = 38)(6Li2) ground state molecules created via the singlet res- onance 11Σu+(ν = 65)(Li∗2) were detected via direct 3 photon ionisation. The momentum spectra show very low kinetic energies for the photo electrons of below 100 meV. Therefore in the molecular ion only vibrational states of Li2+ are getting populated, which are directly below the 3-photon transition energy. Finally, a stepwise ionization mechanism was identified, which leads into the continuum via an intermediate molecular state of 6Li2∗ after photoassociation. The starting point is a pho- toassociated excited state molecule 11Σu+(ν = 65)(6Li∗2), which absorbs two photons of the dipole trap laser (λ = 1070 nm ± 2 nm). This happens via an intermediate molecular state 31Σg+(2s + 3s), after which it leads into the 12Σg+(6Li2+) potential

Kinematically complete multiphoton ionization studies on optically trapped ⁶Li and ⁶Li₂ created by single-color photoassociation

n this work, a reaction microscope with a magneto-optical trap for 6Li atoms, was extended by an optical dipole trap in order to be able to investigate in detail laser-induced atomic and molecular ionization dynamics in a cold quantum gas. The optical dipole trap was operated at a full trap depth of 2.3 mK for 6Li atoms and about 1% of the atoms in the MOT could be transferred into the dipole trap, with 1/e storage times exceeding 5 s. The optically trapped ensemble of 6Li atoms was used as a target for ionisation with intensive and broadband femtosecond laser pulses (λ = 750−820 nm, P = 10^11−10^14 W/cm2, Δt = 30 fs) and allowed to perform kinematically complete experiments, in which 6Li+ ions as well as photoelectrons were measured coincidentically. As a first application, in this work, a series of association- and ionization mechanisms, which led to production of molecular 6Li2+ ions, were investigated with trapped lithium atoms. In photoassociative ionization, two atoms collide, which were previously lifted into the asymptotic 2p − 3s potential energy curve by ladder excitation. During the collision the atoms autoionize into the 12Σg+(6Li2+) groundstate of the molecular ion, since these two potential energy curves exhibit an avoided crossing. This process was observed when magneto-optically trapped atoms were illuminated with the femtosecond laser. In the dipole trap, using single-color photoassociation, excited state molecules were produced in high-lying vibrational states 11Σg+(ν = 65) and 13Σg+(v = 57) and spectroscopically investigated. A fraction of the excited state molecules decay via fluorescence into the molecular ground state. The 11Σg+(ν = 38)(6Li2) ground state molecules created via the singlet res- onance 11Σu+(ν = 65)(Li∗2) were detected via direct 3 photon ionisation. The momentum spectra show very low kinetic energies for the photo electrons of below 100 meV. Therefore in the molecular ion only vibrational states of Li2+ are getting populated, which are directly below the 3-photon transition energy. Finally, a stepwise ionization mechanism was identified, which leads into the continuum via an intermediate molecular state of 6Li2∗ after photoassociation. The starting point is a pho- toassociated excited state molecule 11Σu+(ν = 65)(6Li∗2), which absorbs two photons of the dipole trap laser (λ = 1070 nm ± 2 nm). This happens via an intermediate molecular state 31Σg+(2s + 3s), after which it leads into the 12Σg+(6Li2+) potential

Dynamic fracture and fragmentation: studies in Ti-6Al-4V

This study concentrates on the development of experimental techniques that are of benefit to research into high strain rate fracture and fragmentation. Two main areas are pursued, namely the effect of the stress state in the sample and the initial temperature of the sample on the resulting fracture mechanism and fragmentation behaviour when under tensile loading at strain rates of 10^4 s^-1. Both areas use expanding rings and cylinders to achieve this. Experiments are designed and fielded on explosively loaded Ti-6Al-4V rings where the aspect ratio (sample wall thickness to height) is adjusted to create stress states ranging from uniaxial stress to plane strain with velocimetry and fragment recovery used to measure the expansion and failure processes. A transition to necking before failure under uniaxial stress was observed, as opposed to ductile tearing under shear loading in plane strain conditions. Intermediate geometries were found to undergo massive internal damage not seen in the other experiments, leading to premature failure and smaller fragments. Temperature dependence was investigated using a new gas gun driven expanding cylinder technique with Ti-6Al-4V cylinders 150 mm long, 50 mm inner diameter and 4 mm wall thick- ness reaching temperatures between 150 K and 800 K before expansion. The loading mechanism was found to be highly repeatable and independent of sample temperature, providing a robust platform for generating high strain rate tensile and failure test data at temperatures unob- tainable by other means. A full suite of velocimetry, high speed imaging, fragment recovery and microscopy techniques were used to fully characterise the material during and after defor- mation. At elevated temperatures adiabatic shear banding was found to be an active failure mechanism. The fragmentation toughness parameter Kf was found to be 101 ± 13 MPa m^1/2 under these conditions.Open Acces

Untersuchung der radialen Ionisationsdichteverteilung von schweren Ionen mit einer optischen Teilchenspurkammer und mit Monte-Carlo-Simulationen

In the present work we applied the Optically read out PArticle track Chamber, OPAC, for the measurement of radial dose distributions, d(r), around tracks of heavy ions passing through the gas-filled sensitive volume of the chamber. The measured data were compared with d(r) functions derived from data calculated with the Monte Carlo particle transport code, TRAX – which is used for the heavy ion therapy planning at GSI. To measure this quantity we have used here an optically read out time projection chamber (OPAC) with a parallel-drift field and one or several electron and light amplification stages. The two dimensional projection of the three dimensional ionization pattern caused by the ionizing particle passing through the chamber is captured by an image intensified CCD camera. The work is motivated by the role the radial dose distribution plays in the estimation of the relative biological effectiveness (RBE) of heavy ions, e.g. in radiation therapy and in radiation protection. The most successful model for high-dose irradiation with ions (applicable e.g. for heavy ion therapy) is found to be the local effect model (LEM). The present work intends to deliver measured data for one of the basic physical parameters which serve as input for the application of the local effect model: the radial dose distribution, d(r). The first goal of our measurement program was the measurement of d(r) distributions around carbon ions of different energies from 400 MeV/u down to the Bragg peak regions. We found an excellent agreement between the measured and simulated distributions at all carbon energies for the r–range in which the measurements deliver useful results. The lower limit of this range is about 100 nm and the upper limit is 6000 nm at a resolution of down to 33 nm - if scaled to water density. Despite the simplifications in the TRAX code (e.g. binary encounter theory for the emission ionization electrons), the discrepancies between the simulated and measured d(r) distributions are found to be lower than the measurement uncertainties at most measured carbon ion energies in almost the whole observed r-range. Hence, within the limitations of our measurements we can conclude that the precision of TRAX is sufficient to simulate the d(r) distributions around carbon ions to serve as input parameter for therapy planning. However, this conclusion is only valid for larger radial distances (r >100 nm). For smaller radial distances the measured data are dominated by the diffusion. Apart from carbon ion tracks, tracks of very heavy ions (40Ar, 84Kr and 238U) were also measured with OPAC. The simulated d(r) values were typically slightly or significantly higher than the measured data in the 100 nm < r < 5000 nm region. The experience has shown: the heavier or the faster the ion, the higher the discrepancies. On the one hand, we found a surprisingly good agreement between measurements and simulations if the ions had energies of around 50 MeV/u (i.e. relatively low energy). On the other hand, at higher energies, simulated data underestimate the measured ones by up to a factor of two in the region of 100 nm < r < 1000 nm for 84Kr (E = 650 MeV/u) or in the region of 100 nm < r < 6000 nm for 238U (E = 1 GeV/u). A possible reason for these discrepancies is that the BEA model, used in TRAX for the production ionization electrons, is not adequate for very heavy projectiles. The energy values of the very heavy ions were selected with the aim of comparing the track structures - and namely the d(r) distributions - of ions with largely different atomic mass but similar LET values. From the Z-dependency of the stopping power we know that for heavier ions a higher specific ion energy (expressed in MeV/u) is required to provide the same LET. For example the common LET of 315 keV/micro-m was achieved at largely different specific energy levels of 4,4 MeV/u for 12C, 65 MeV/u for 40Ar and 650 MeV/u for 84Kr ions. The difference in the track structures was expected mainly due to the different ion velocities and thus e.g. different ranges of d-electrons. This expectation could be confirmed by the measurements. The reason why - in line with the simulations - no strong differences could be observed in the d(r) distributions of the argon and krypton ions is the relatively small difference in the velocities of the both ion types in conjunction with the limited range in r, where the data can be compared. In contrary, the d(r) function of the carbon ion shows a qualitatively different behavior than the heavier ions inside the observable radius-range - in agreement with the simulations.Therapie mit schweren geladenen Teilchen wie Protonen und schwere Ionen ist eine überlegene Alternative zur konventionellen Strahlentherapie für die Therapie tief liegender Tumore die zunehmend auch in Deutschland Verbreitung findet. Ein wichtiger Parameter bei der Bestrahlungsplanung ist die Relative Biologische Wirksamkeit (RBW) der verwendeten Strahlung. Um den biologischen Effekt von Schwerionen für die Zelltötung relativ zu dem von Photonen zu quantifizieren, wurde bei der GSI das “Local Effect Model“ (LEM) entwickelt. Das LEM basiert auf der Annahme, dass der zu erwartende biologische Effekt der Bestrahlung auf eine Zelle nicht direkt mit der über den Zellkern gemittelten "makroskopischen" Dosis zusammenhängt sondern stattdessen aus dem über das makroskopische Volumen gemittelten lokalen biologischen Effekt abgeleitet werden kann. Dabei hängen die lokalen biologischen Effekte wiederum von der mikroskopischen Dosis in wenigen Nanometer - großen Volumina ab. Bei der Bestimmung der mikroskopischen Dosis werden meist Monte Carlo Programme eingesetzt - bei der GSI der Code TRAX. Ein wichtiger Parameter im LEM ist dabei die radiale Ionsisationdichteverteilung, d(r), entlang der Spur eines Ions, die wesentlich vom Spektrum der Ionisationselektronen bestimmt wird. Messungen von d(r) direkt in biologisch relevanter kondensierter Materie (wie Gewebe oder Wasser) sind nicht möglich: die benötigte räumliche Auflösung in der Größenordnung von nm bis einige mikro-m ist nicht erreichbar mit den zur Verfügung stehenden Meßmethoden. Stattdessen wird es versucht, die erforderlichen Auflösungen durch Messungen in einem wesentlich größeren gasgefüllten Volumen zu erreichen. Die Längenskala wird dann entsprechend dem Verhältnis der Dichten vom Gas und kondensierter Materie skaliert. In der vorliegenden Arbeit werden experimentelle Messungen zur radialen Ionisationsverteilung schwerer Ionen mit einer optisch ausgelesenen Teilchenspurkammer (OPAC) vorgestellt. Die experimentellen Ergebnisse werden mit Monte Carlo Simulationen verglichen. OPAC ist eine optisch ausgelesene Zeitprojektionskammer (TPC) mit einem parallelen Driftfeld und mit einer oder mehreren Ladungs- und Lichtverstärkungsstufen. Die zweidimensionale Projektion der dreidimensionalen Verteilung der nach dem Durchdringen des ionisierenden Teilchens durch das Gas der Kammer entstehenden Ionisationselektronen wird von einer CCD Kamera mit gegatetem Bildverstärker ausgelesen. In dieser Arbeit wurden radiale Dosisverteilungsfunktionen, d(r), von Kohlenstoffionen und verschiedenen noch schwereren Ionen gemessen. Zeil der Experimente war es, die von TRAX vorausgesagte radiale Ionsisationsdichteverteilung zu verifizieren. Eine von OPAC gemessene Spur ist eine komplexe Konvolution von verschiedenen physikalischen Prozessen. Neben den zu messenden Ionisationen und Streuungen von Ionen und Ionisationselektronen spielen für die Bildentstehung auch die physikalischen Vorgänge beim Detektionsprozess und die Detektoreigenschaften eine wichtige Rolle. Eine komplexe Datenanalyse ist deshalb erforderlich, um quantitative Informationen, z.B. die d(r) Funktionen, aus den Rohbildern zu erhalten. In der zweiten Hälfte der Arbeit werden die Ergebnisse der Messungen mit OPAC bei der GSI im Vergleich mit den entsprechenden simulierten Daten gezeigt. Die erste Zielstellung des Messprogramms war die Durchführung systematischer Messungen von Spuren von Kohlenstoffionen mit Energien von 400 MeV/u bis hinunter zu Bragg Peak Energien (motiviert von der Therapie mit Kohlenstoffionen bei der GSI). Der Vergleich der gemessenen d(r) Funktionen mit den entsprechenden simulierten Daten zeigt eine sehr gute Übereinstimmung bei allen Kohlenstoff – Energien über den gesamten sinnvoll messbaren r Bereich (100 nm < r < 6000 nm). Trotz der unvermeidbaren Vereinfachungen im Simulationscode sind die Abweichungen zwischen den gemessenen und simulierten d(r) Funktionen für jede Ionenenergie fast im gesamten gemessenen r Bereich kleiner als die geschätzten Messunsicherheiten. Abgesehen von den Kohlenstoffionen wurden auch Spuren von schwereren Ionen (40Ar, 84Kr und 238U) im Rahmen des aktuellen Messprogramms mit OPAC gemessen. Die simulierten d(r) Daten liegen hier im gesamten r Bereich typischerweise etwas (teils auch signifikant: bis zu einem Faktor zwei) über den entsprechenden gemessenen Daten. Eine mögliche Erklärung für diese Abweichungen ist, dass das die bei TRAX angewandte „Binary Encounter Approximation“ für die Simulation der d-Elektronen Produktion bei sehr schweren Projektilen zu starke Vereinfachungen enthält. Die kinetischen Energien der gemessenen sehr schweren Ionen wurden so ausgewählt, dass die Ionen trotz stark unterschiedlichen Ordnungszahlen ähnliche LET-Werte in der Kammer aufwiesen. Die erwarteten Abweichungen in den Spurstrukturen konnten von den Messungen bestätigt werden