Institutskolloquium des IPP 2017

Plasma wakes, excited by short high-power laser pulses or short bunches of relativistic charged particles passing through the plasma, give rise to strong longitudinal electric fields which can be employed to accelerate electrons. The accelerating gradients achieved in a plasma wakefield can exceed those of accelerating structures typically used in state-of-the-art particle accelerators by three to four orders of magnitude. Since the scale of accelerator-driven research facilities drives their construction and operation cost on the one hand and limits their range of applications on the other, it appears extremely attractive to utilize plasma-wakefield accelerating techniques in future: one may dream of X-ray free electron lasers fitting into university laboratories and hospitals or of TeV electron-positron colliders less than one kilometer long instead of requiring a 50 to 100 kilometer long tunnel passing beneath the Lake Geneva. Therefore, since the first experimental demonstration of the acceleration of plasma background electrons in the so-called wave-breaking regime of laser wakefield acceleration in 2004 a steadily increasing R&D effort in laser, plasma and accelerator physics has been devoted to this topic.In my talk I will give a - non-exhaustive - review of the current status of laser wakefield electron accelerators and introduce the particular challenges one is facing if one intends to combine laser wakefield and "conventional" accelerator techniques in order to realize synchrotron light sources or even free electron lasers. I will present our ideas on how to possibly cope with some of these challenges. [mehr]

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It took about a century until the riddle of the origin of the Sun's energy was solved. The first theory based on energy conservation was suggested in the 1840s, to be transformed into the successful Helmholtz-Kelvin contraction theory a few decades later. This theory held the position as a standard theory for about 40 years, but was eventually challenged by theories based on radioactive decay. However, the Sun is not a radioactive machine and only in the late 1930s, after the emergence of nuclear physics, did a satisfactory explanation arrive with Bethe's celebrated theory of stellar energy production. The talk reviews the development in a historical perspective. [mehr]

The story of Jim Knopf und his friend Lukas, the engine driver, is probably the master piece of the book author Michael Ende. The thrilling story on magnetic mountains, mermaids, dragons, pirates und flying railway locomotives is embedded into a plethora of phenomena from practically all fields of physics, all charmingly distorted to be attractive for children. We will have a fresh look at the adventures of the two friends, connecting them to fields of modern physics, like quantum physics, particle physics, and cosmology. [mehr]

The possibility of magnetic confinement devices that have the same neoclassical transport properties as axisymmetric tokamaks was realised by Nührenberg and co-workers three decades ago. In quasi-axisymmetric stellarators, the magnetic strength is independent of the toroidal (Boozer) angle, the particle orbits are similar to those in a tokamak, and the drift kinetic equation is the same. In such devices, the particle orbits are thus well confined and the bootstrap current can contribute substantially to the rotational transform of the magnetic field. However, some of the rotational transform comes from external coils and the plasma is thus confined even in the absence of a toroidal plasma current. This opens the possibility for a device that is maximally similar to a tokamak but can operate in steady state, hopefully without disruptions.In this talk, I will review the theoretical background and describe the first steps that have been undertaken in Greifswald to design a new such device. [mehr]