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Miscellaneous publications


2017

V. Tympel, J. Golm, R. Neubert, P. Seidel, M. Schmelz, R. Stolz, V. Zakosarenko, F. Kurian, M. Schwickert, T. Sieber, and Th. Stöhlker
The Next Generation of Cryogenic Current Comparators for Beam Monitoring
Proceedings of the 5th International Beam Instrumentation Conference, IBIC 2016 (2017)

Abstract: A new Cryogenic Current Comparator with eXtended Dimensions (CCC-XD), compared to earlier versions built for GSI, is currently under development for a non-destructive, highly-sensitive monitoring of nA-intensities of beams for larger beamline diameters planned for the new FAIR accelerator facility at GSI. The CCC consists of a:
1) flux concentrator,
2) superconducting shield against external magnetic field and a
3) superconducting toroidal coil of niobium which is read out by a
4) Superconducting Quantum Interference Device (SQUID).
The new flux concentrator (1) comprises a specially designed highly-permeable core made of nano-crystalline material, in order to assure low-noise operation with high system bandwidth of up to 200 kHz. The superconducting shielding of niobium (2) is extended in its geometric dimensions compared to the predecessor CCC and thus will suppress (better -200 dB) disturbing magnetic fields of the beamline environment more effectively. For the CCD-XD readout, new SQUID sensors (4) with sub-μm Josephson junctions are used which enable the lowest possible noiselimited current resolution in combination with a good suppression of external disturbances. The CCC-XD system, together with a new dedicated cryostat, will be ready for testing in the CRYRING at GSI in spring 2017. For the application of a CCC in the antiproton storage ring at CERN a pulse shape correction has been developed and tested in parallel. Results from electrical measurements of two components (1 and 4) of the new CCC-XD setup will be presented in this work.

2016

D. Bernhardt, C. Brandau, Z. Harman, C. Kozhuharov, S. Böhm, F. Bosch, S. Fritzsche, J. Jacobi, S. Kieslich, H. Knopp, F. Nolden, W. Shi, Z. Stachura, M. Steck, Th. Stöhlker, S. Schippers, and A. Müller
Erratum: Electron-ion collision spectroscopy: Lithium-like xenon ions [Phys. Rev. A 91, 012710 (2015)]
Phyical Review A 94, 029903 (2016)

Abstract: *

F. Karbstein
The quantum vacuum in electromagnetic fields: From the Heisenberg-Euler effective action to vacuum birefringence
Lectures given at the Helmholtz International Summer School: "Quantum Field Theory at the Limits: from Strong Fields to Heavy Quarks", July 2016 (2016)

Abstract: The focus of these lectures is on the quantum vacuum subjected to classical electromagnetic fields. To this end we explicitly derive the renowned Heisenberg-Euler effective action in constant electromagnetic fields in a rather pedagogical and easy to conceive way. As an application, we use it to study vacuum birefringence constituting one of the most promising optical signatures of quantum vacuum nonlinearity.

2015

R. Loetzsch, A. Lübcke, F. Zamponi, T. Kämpfer, I. Uschmann, and E. Förster
Time-Resolved X-ray Diffraction of Cryogenic Samples Using a Laser Based Plasma Source
in: Davide Bleiner, John Costello, Francois Dortan, Gerry O'Sullivan, Ladislav Pina, Alan Michette (ed.): Short Wavelength Laboratory Sources : Principles and Practices (ESF (European Science Foundation)) (2015)

Abstract: In this chapter, the microscopic characteristics of a bright, short-pulsed source of Ti Kα radiation are studied. This x-ray emission is generated from fast electrons that are generated when a relativistically intense laser pulse interacts with a solid metal surface. The electrons have average energies significantly exceeding the ionization threshold of the K-shell (5 keV) and give rise to K-radiation when the K-shell recombines with a lifetime of a few femtoseconds only. Hence the duration of the Kα emission is dominantly determined by the time these fast electrons are present. But at the same time, the electrons also generate a solid-density plasma state at several tens of electronvolts temperature (e.g., several 100 000 K). This alters the emission probabilities of the Kα source, potentially effecting the brightness of the x-ray source. These mechanisms and possible optimizations are subject of this chapter.

2014

C. Spielmann
Electrons take the fast track through silicon
Science 346, 1293 (2014)

Abstract: The photoelectric effect, the emission of electrons from a metal surface after absorbing light, was explained by Einstein's model, where light particles (photons) must have a minimum energy (frequency) to ionize atoms. The number of excited atoms is proportional to the intensity (the number of photons delivered). However, when the light is supplied by very intense, very fast pulses from lasers, the number of ionized atoms will depend on the electric field strength - the amplitude of the light seen as an electromagnetic wave. This change occurs because ionization occurs via quantum tunneling through the relevant energy barrier during a short time window near the maxima of the electric field. Isolated attosecond pulses recently enabled studies of the dynamics of tunneling ionization of atoms in gases. On page 1348 of this issue, Schultze et al. experimentally show that atoms in a solid are also excited via the tunneling process.

M. Kaluza
Surfen auf der Plasmawelle
Physik in unserer Zeit 45, 274 (2014)

Abstract: Hochleistungslaser ermöglichen es inzwischen, relativistische Elektronenpulse mit bemerkenswerten Eigenschaften zu erzeugen. Neben der äußerst kurzen Beschleunigungslänge sind vor allem die kleine Quellgröße und auch die kurze Pulsdauer interessant. Mit diesen Elektronenpulsen lässt sich zudem elektromagnetische Sekundärstrahlung im Kiloelektronenvolt-Bereich erzeugen. Mit dieser Röntgenstrahlung würden auch Universitäten relativ kompakte Röntgenquellen zur Verfügung stehen, mit denen sich Effekte beobachten lassen, die auf äußerst kurzen räumlichen und zeitlichen Skalen ablaufen. Momentan ist diese Art von Forschung nur an großen, konventionellen Synchrotron-Beschleunigern möglich.

M. Zürch, S. Foertsch, M. Matzas, K. Pachmann, R. Kuth, and C. Spielmann
Apparatus and fast method for cancer cell classification based on high harmonic coherent diffraction imaging in reflection geometry
Proceedings of SPIE 9033, 1 (2014)

Abstract: In cancer treatment it is highly desirable to identify and /or classify individual cancer cells in real time. Nowadays, the standard method is PCR which is costly and time-consuming. Here we present a different approach to rapidly classify cell types: we measure the pattern of coherently diffracted extreme ultraviolet radiation (XUV radiation at 38nm wavelength), allowing to distinguish different single breast cancer cell types. The output of our laser driven XUV light source is focused onto a single unstained and unlabeled cancer cell, and the resulting diffraction pattern is measured in reflection geometry. As we will further show, the outer shape of the object can be retrieved from the diffraction pattern with sub-micron resolution. For classification it is often not necessary to retrieve the image, it is only necessary to compare the diffraction patterns which can be regarded as a spatial fingerprint of the specimen. For a proof-of-principle experiment MCF7 and SKBR3 breast cancer cells were pipetted on gold-coated silica slides. From illuminating each single cell and measuring a diffraction pattern we could distinguish between them. Owing to the short bursts of coherent soft x-ray light, one could also image temporal changes of the specimen, i.e. studying changes upon drug application once the desired specimen is found by the classification method. Using a more powerful laser, even classifying circulating tumor cells (CTC) at a high throughput seems possible. This lab-sized equipment will allow fast classification of any kind of cells, bacteria or even viruses in the near future.

B. Zielbauer, B. Ecker, P. Neumayer, K. Cassou, S. Daboussi, O. Guilbaud, S. Kazamias, D. Ros, T. Kuehl, U. Eisenbarth, S. Goette, D. Winters, V. Bagnoud, and Th. Stöhlker
Heavy-Ion Spectroscopy with X-Ray Lasers at GSI
X-Ray Lasers 2012 - Proceedings of the 13th International Conference on X-Ray Lasers, Springer Proceedings in Physics (2014)

Abstract: Different pumping schemes for soft X-ray lasers have been investigated at the PHELIX laser facility, including a double-target seeding approach at 18.9 nm. A technical feasibility study of using a Mo XRL beam of several μJ as an excitation source for heavy-ion spectroscopy in a storage ring has been carried out. XRL photon numbers and the beam transport under ultra-high vacuum conditions over almost 30 m are the major challenges.

2013

J. Körner, J. Hein, H. Liebetrau, M. Kahle, R. Seifert, D. Klöpfel, and M. C. Kaluza
Diode-pumped, cryogenically cooled, femtosecond burst mode laser
Proceedings of SPIE 8780, 878008 (2013)

Abstract: We present a novel approach for the construction of a high energy, high power burst mode laser system, based on diode pumped cryogenically cooled Yb:CaF2. The system consists of a frontend producing pulses of 300 fs duration with 1 MHz. Bursts of 1000 subsequent pulses are cut from the continuous train by an electro optical modulator. Afterwards the duration of the individual pulses is stretched to 50 ps.

The amplifier system consists of two amplifiers. Both amplifiers utilize mirror based relay imaging schemes to allow for a sufficient number of extraction passes for achieving efficient energy extraction. The goal parameters of the system are to achieve a total energy of 5 J per burst with a repetition rate of 10Hz.

Amplification results for the first of two amplifiers are demonstrated. A total output energy of 480 mJ was achieved corresponding to an optical to optical efficiency from absorbed pump energy to extracted energy of more than 17%. Single pulse energies of up to 7.5mJ are generated when changing to less pulses per burst.

To achieve a constant energy from pulse to pulse during the burst we present a technique based on the modulation of the laser diode current during one pulse. With this technique the gain variation during the burst was than 5% peak to peak.

S. Keppler, C. Wandt, M. Hornung, R. Bödefeld, A. Kessler, A. Sävert, M. Hellwing, F. Schorcht, J. Hein, and M. C. Kaluza
Multipass amplifiers of POLARIS
Proceedings of SPIE 8780, 87800I (2013)

Abstract: Advanced high intensity laser matter interaction experiments always call for optimized laser performance. In order to further enhance the POLARIS laser system, operational at the University of Jena and the Helmholtz-Institute Jena, in particular its energy, bandwidth and focusability, new amplifier technologies have been developed and are reported here. Additionally, existing sections were considerably improved. A new multi-pass amplification stage, which is able to replace two currently used ones, was developed in close collaboration with the MPQ (Garching). The new basic elements of this amplifier are well homogenized pump modules and the application of a successive imaging principle. By operating the amplifier under vacuum conditions a top hat beam profile with an output energy of up to 1.5 J per pulse is foreseen. The already implemented POLARIS amplifier A4 was further improved by adapting an advanced method for the homogenization of the multi-spot composed pump profile. The new method comprises a computer-based evolutionary algorithm which optimizes the position of the different spots regarding its individual size, shape and intensity. The latter allowed a better homogenization of the POLARIS near field profile.

R. Geithner, W. Vodel, R. Neubert, P. Seidel, F. Kurian, H. Reeg, and M. Schwickert
A Cryogenic Current Comparator for FAIR with Improved Resolution
Proceedings of the 2nd International Beam Instrumentation Conference (IBIC2013), p. 590 (2013)

Abstract: A Cryogenic Current Comparator is a highly sensitive tool for the non-destructive online monitoring of continuous as well as bunched beams of very low intensities. The noise-limited current resolution of such a device depends on the ferromagnetic material embedded in the pickup coil of the CCC. Therefore, the main focus of research was on the low temperature properties of ferromagnetic core materials. In this contribution we present first results of the completed Cryogenic Current Comparator for FAIR working in a laboratory environment, regarding the improvements in resolution due to the use of suitable ferromagnetic core materials.

W. Vodel, R. Neubert, R. Geithner, P. Seidel, H. Reeg, M. Schwickert, K. Knaack, K. Wittenburg, and A. Peters
20 Years of Developments of SQUID-based Cryogenic Current Comparators for Beam Diagnostics
4th International Particle Accelerator Conference (IPAC13), p. 499 (2013)

Abstract: An absolute and exact measurement of the intensity of charged particle beams - extracted from an accelerator or circulating in a Storage Ring - is one of the major problems of beam diagnostics. Also the measurement of socalled dark currents, generated by superconductive RF accelerator cavities at high voltage gradients to characterize the quality of these components becomes more and more important for the commissioning of new accelerators (XFEL at DESY). The Cryogenic Current Comparator (CCC) based on high precision LTS SQUIDs is an excellent tool to solve these problems.

2012

R. Geithner, W. Vodel, R. Neubert, P. Seidel, F. Kurian, H. Reeg, and M. Schwickert
An Improved Cryogenic Current Comparator For FAIR
3rd International Particle Accelerator Conference IPAC'12, p. 824 (2012)

Abstract: Online monitoring of low intensity (below 1 μA) charged particle beams without disturbing the beam and its environment is crucial for any accelerator facility. For the upcoming FAIR project a beam monitor based on the Cryogenic Current Comparator principle with an enhanced resolution was developed. The main focus of research was on the low temperature properties of the ferromagnetic core material of the superconducting pickup coil. The pick-up coil transforms the magnetic field of the beam into a current that is detected by a high performance low temperature dc Superconducting QUantum Interference Device (LTS-DC-SQUID). The penetration of the pick-up coil by interfering magnetic fields is highly attenuated by a meander shaped superconducting shielding. The Cryogenic Current Comparator is able to measure DC beam currents, e.g. as required for slow extraction from a synchrotron, as well as bunched beams. In this contribution we present first results of the improved Cryogenic Current Comparator working up to now in a laboratory environment.

V. P. Shevelko, M. S. Litsarev, Th. Stöhlker, H. Tawara, I. Y. Tolstikhina, and G. Weber
Electron Loss and Capture Processes in Collisions of Heavy Many-Electron Ions with Neutral Atoms
in: V. Shevelko and H. Tawara (ed.): Atomic Processes in Basic and Applied Physics (Springer Berlin Heidelberg) (2012)

Abstract: The present status and properties of charge-changing processes—electron capture and electron loss—are considered for heavy many-electron ions colliding with neutral atoms over a wide energy range E = 10 keV/u–100 GeV/u. The role of single- and multiple-electron charge-changing processes is discussed, and a brief description of available computer codes for calculation of the corresponding cross sections is presented. Experimental data for electron-loss and capture cross sections for germanium, xenon, lead, and uranium ions colliding with H, N, Ne, Ar, and Xe targets are given in comparison with numerical calculations applying different theoretical models as well as semiempirical formulae.

2011

S. Keppler, R. Bödefeld, M. Hornung, A. Sävert, J. Hein, and M. C. Kaluza
Contrast improvement by prepulse suppression in cascaded amplifier cavities
Proc. SPIE (2011)

Abstract: We introduce a method to suppress prepulses of pulse picking systems due to the limited extinction ratio of polarization gating systems. By matching the round trip times of the oscillator and the subsequent regenerative amplifiers, leaking pulses are hidden below the temporal intensity pedestal of the main pulse. With this method, prepulses at the temporal position equal to the time difference of the round trip times of the cavities could be suppressed completely.

2010

A. Tünnermann
Laser – das besondere Licht
Physik in unserer Zeit 41, 211 (2010)

Abstract: -

M. C. Kaluza
Laser-Based Particle Acceleration
Optik & Photonik 5, 56 (2010)

Abstract: Using state-of-the-art high-power laser systems, we are able to routinely generate extreme energy densities and focused light intensities in a controlled laboratory environment. During the interaction of these laser pulses with matter a plasma is generated that can both sustain and support huge electric fields. These can be used as a novel type of accelerator structure for electrons and ions having properties favorable for a large number of future applications.