S. Casalbuoni

Coronal plumes and the expansion of pressure‐balanced structures in the fast solar wind

The expansion of a coronal hole filled with a discrete number of higher density filaments (plumes) in overall pressure balance with the ambient medium is described within the thin flux tube approximation. The resulting solar wind model extends the results of Parker [1964] and Velli et al. [1994] to nonisothermal temperature profiles and includes a flux of Alfven waves propagating both inside and outside the structures. Remote sensing and solar wind in situ observations are used to constrain the parameter range of our study. Close to the Sun, the precise plasma parameters are fundamental in determining the relative position of the critical points, which are found by means of an iterative procedure because the flows from the two regions are coupled. At greater distances the filling factor of the higher-density regions may vary largely, and streams which are either faster or slower than the wind arising from the ambient hole may result, depending on the temperature differences and on the flux of Alfven waves assumed in the two regions. Velocity differences of the order of ∼50 km s−1, such as those found in microstreams in the high-speed solar wind, might be thus easily explained by reasonable fluctuation amplitudes at the Sun, although the natural candidates for plumes at large heliocentric distances are more likely to be the so-called pressure-balanced structures.

Numerical Studies on the Electro-Optic Sampling of Relativistic Electron Bunches

Ultraviolet and X ray free electron lasers require sub-picosecond electron bunches of high charge density. Electro-optic sampling (EOS) is a suitable diagnostic tool for resolving the time structure of these ultrashort bunches. The transient electric field of the relativistic bunch induces a polarization anisotropy in a nonlinear crystal which is sampled by femtosecond laser pulses. In this paper, the EOS process is studied in detailed numerical calculations. The THz and the laser pulses are treated as wave packets which are propagated through the zinc telluride resp. gallium phosphide crystals. The effects of signal broadening and distortion are taken into account. The time resolution is severely limited by transverse optical (TO) lattice oscillations (5.3 THz in ZnTe, 11 THz in GaP). The shortest bunch length which can be resolved with moderate distortion is about 200 fs (FWHM) in ZnTe and 100 fs in GaP.

Training and Magnetic Field Measurements of the ANKA Superconducting Undulator

In this contribution we report the results of the training and of the local field measurements performed in a liquid helium bath of the ANKA superconducting undulator. The period length is 15 mm and the coils are 1.5 m long. The key specifications of the system are an undulator parameter K higher than 2 (for a magnetic gap of 5 mm) and a phase error smaller than 3.5 degrees. The superconducting undulator is planned to be installed in the ANKA storage ring by the beginning of 2011 to be the light source of the new beamline NANO for high resolution X-ray diffraction..

The New Conduction-Cooled Superconducting Undulator for ANKA

Babcock Noell GmbH (BNG) is completing the fabrication of a 1.5 m long superconducting insertion device for the Karlsruhe Institute of Technology (KIT). The unit is planned to be installed in the ANKA storage ring at the end of 2010 to become the light source of the new beamline NANO for high resolution X-ray diffraction. The period length of the device is 15 mm for a total of 100.5 full periods plus an additional matching period at each end. The key specifications of the system are: a K value higher than 2 for a magnetic gap of 5 mm, the capability of withstanding a 4 W beam heat load and a phase error smaller than 3.5 degrees. The superconducting coils have been qualified by means of a vertical test in liquid helium at CERN and are ready to be installed in the cryostat. This paper describes the main features of the system.

CASPER- A magnetic measurement facility for superconducting undulators

For a given gap and a given period length superconductive cold-bore undulators have a higher field strength compared to permanent magnet undulators. The measurement of the field and the field quality in the cold bore is demanding since the position of the Hall-probes have to be precise within a few microns over a distance of one to two meters. At the Forschungszentrum Karlsruhe two measuring facilities are under construction which allow to measure short mock-ups and undulators with a length of up to two meters. In this paper the two devices called CASPER (ChAracterization Setup for Phase Error Reduction) are described.

Instrumentation for Local and Integral Field Measurements of Superconducting Undulator Coils

Accurate magnetic field measurements are a prerequisite for the characterization and optimization of undulators. The precision for measuring the magnetic properties of conventional, i.e., permanent magnet based insertion devices, has undergone tremendous improvements over the past 10 to 15 years initiating a new era in synchrotron light sources worldwide; a similar break through is now necessary in the field of superconducting insertion devices. In this contribution we describe the planned instrumentation needed to perform magnetic measurements of the local field, and field integrals, of up to 2 m length superconducting undulator coils while in a cold-in-vacuum (helium free) environment.

Magnetic Field Test Facility for Superconductive Undulator Coils

Superconducting undulators and wigglers are developed for synchrotron light sources, damping rings for linear colliders and polarized positron sources. In an undulator the emitted photons along the trajectory have to interfere. In order to do so the magnetic field in all periods has to be almost identical. The field strength over one or several hundred periods is not allowed to deviate by more than 1%. Translated into mechanical accuracy the position of the wire and the poles has to be more accurate than about 5 over 1 to 2 m. High quality measurement of the field is an essential requirement. In this paper we present two field measuring systems, one is under construction and another one is under design phase at the Forschungszentrum Karlsruhe.

Development of Superconducting Undulators at ANKA

In order to produce synchrotron radiation of the highest brilliance, third generation synchrotron sources make use of insertion devices (IDs). The state of the art available today for IDs is the permanent magnet technology with magnet blocks placed inside the vacuum (IVU) of the storage ring. Following an initial proposal at SPring-8 [1], the concept of Cryogenic Permanent Magnet Undulators (CPMU) is presently considered as a possible future evolution of in-vacuum undulators [2–5]. Superconducting undulators (SCUs) can reach, for the same gap and period length, even higher fields than CPMU devices, allowing increases in the spectral range and the brilliance. At ANKA we are running a research and development program to develop superconducting IDs. The proof of principle of SCU technology application in a storage ring has been demonstrated at ANKA with a device developed together with the company ACCEL Instr. GmbH and installed in the ANKA storage ring since March 2005 [6].

The ORPHEUS dark matter experiment

Abstract The ORPHEUS dark matter experiment iis being built and most of it is already installed at our underground facility in Bern (70 m.w.e). The detector relies in an initial phase on 0.45 kg (1.6 kg maximum capacity) superheated superconducting tin granules (SSG) to measure recoils from weakly interacting massive particles (WIMPs). The actual status of the installation as well as parallel ongoing studies are presented.

First Experimental Demonstration of Period Length Switching for Superconducting Insertion Devices

Superconducting insertion devices (IDs) are very attractive for synchrotron light sources since they offer the possibility to enhance the tuning range and functionality significantly by period length switching. Period length switching can be achieved by employing two or more individually powerable subsets of superconducting coils and reverse the current in a part of the windings. In this contribution we report the first experimental test of this principle demonstrated on a 70 mm NbTi mock-up coil with period tripling, allowing to switch between a 15 mm period length undulator and a 45 mm wiggler (SCUW 15/45).