Results 1 - 10 of 17
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[en] Electromagnetic radiation emitted by electron bunches in accelerators is usually incoherent. However, when the bunch length becomes shorter than the wavelength of the emitted radiation, the waves of the individual electrons interfere constructively. As a result, the intensity of this coherent radiation is enhanced by several orders of magnitude at this wavelength. On one hand, this allows for intense radiation. On the other hand, coherent radiation can act as a ''magnifying glass'', which allows one to study the electron bunch structure. I give a brief derivation of the basic equation for coherent radiation and discuss its properties for a simple Gaussian bunch as well as more complex bunches.
[en] We discuss the postulate that the U(1) gauge group describing photon propagation results from a dynamically broken SU(2) gauge theory. In the context of Yang-Mills thermodynamics such a symmetry breaking occurs via the non-trivial ground state. As a result of the interaction with the quasi particles of the theory the photon acquires an effective, temperature and momentum dependent, mass. We explain how this leads to modified black body spectra at temperatures of about 5 K. Furthermore, we discuss the properties and effects of an emergent longitudinal polarization.
[en] We discuss the constraints on energy-momentum transfers in local vertices in the effective theory for the deconfining phase of SU(2) Yang-Mills thermodynamics. Subsequently, we apply these constraints to the computation of the polarization tensor of the massless mode on the one-loop level. The resulting gap equation for the sought-after screening function is solved numerically. We discuss and interpret our results.
[en] One possible result of a theory of quantum gravity is that spacetime might have a ''foamy'' and topologically nontrivial structure on small scales. Since there is no complete theory of quantum gravity yet, we investigate classical models with nontrivial spacetime topology. One of these is an SO(3)-Skyrme model interacting with gravity on spacetimes of topology R x SO(3). This particular class of spacetimes can be realized by cutting a ball of radius b out of Minkowski spacetime and identifying antipodal points. To prevent a spacetime with such a defect from collapsing, an SO(3)-valued scalar field together with a Skyrme Lagrangian is added. The resulting Einstein-SO(3)-Skyrme model admits classical solutions where the SO(3)-Skyrme field has integer winding number. For odd winding numbers there exists a nonzero radius b that minimizes the mass of the spacetime. This means that we have found a potentially stable spacetime with nontrivial topology. We briefly discuss similarities to and differences from the Einstein-SU(2)-Skyrme model.
[en] Operating with short electron bunches at Synchrotron Light Sources can induce micro-structures inside the bunches, which intensify the emission of Coherent Synchrotron Radiation (CSR) in the wavelength range comparable to the size of the micro-structures. Dynamic variations of these micro-structures, however, lead to fluctuations in the intensity of the emitted CSR. Such phenomena have been observed at various facilities including ANKA, KIT. Using the in-house developed simulation code, Inovesa, the dynamics of the micro-structures in the longitudinal profiles have been investigated with the help of machine learning techniques. In this contribution we present possible categorization of these micro-structures and their correlations to the CSR intensity.
[en] FLUTE is a linac-based THz-source being constructed at the Karlsruhe Institute of Technology (KIT). One of the goals of the FLUTE project is the generation of femtosecond electron-bunches. In order to study the various effects influencing the final bunch length, data-acquisition and storage systems that allow correlation of parameters on a per-pulse basis are required. We are planning to use an EPICS-based control system that employs special techniques for pulse-synchronous data-acquisition. In this talk we present the current design concept for this system.
[en] The usage of electro-optical measurement techniques allows precise and single-shot measurements of the length and shape of an electron bunch. At the ANKA storage ring such a setup for near-field measurements has recently been installed. The installation of such a setup changes the impedance of the storage ring and the corresponding effects have to be studied carefully. By using numerical codes it is possible to simulate the wakefields induced by the setup. In this presentation, first results obtained with the wakefield solver implemented in the CST studio suite are shown.
[en] A setup for precise electro-optical bunch length measurements at the ANKA storage ring is currently assembled. It is based on the principle of spectral decoding and consists of a GaP-crystal and an Yb fiber laser. As the impedance is changed by introducing the crystal in the beam pipe the resulting wake fields have to be taken into account. In this talk we present the current status of the project and the first simulation results.
[en] We present the effects of the filling pattern structure in multi-bunch mode on the beam spectrum. This effects can be seen by all detectors whose resolution is better than the RF frequency, ranging from stripline and Schottky measurements to high resolution synchrotron radiation measurements. Our heterodyne measurements of the emitted coherent synchrotron radiation at 270 GHz reveal the discrete frequency harmonics around the 100'000 revolution harmonic of ANKA, the synchrotron radiation facility in Karlsruhe, Germany. Significant effects of bunch spacing, gaps between bunch trains and variations in individual bunch currents on the emitted CSR spectrum are described by theory and supported by observations.