Injector Optimization at the Superconducting Darmstadt Linear Electron Accelerator S-DALINAC

The former 5-cell capture cavity of the S-DALINAC injector was insufficiently adapted to the beam energies provided by the electron sources. This led to an inefficient energy gain and a deterioration of the beam quality in this acceleration structure. In order to optimize the performance of the injector, especially with regard to an accelerator operation in the energy-recovery mode, it was therefore necessary to replace the 5-cell cavity with a dedicated β-adapted capture structure. This project was implemented within the scope of this dissertation. A new β-reduced 6-cell structure was manufactured, tested and installed at the accelerator. Tuner frame components had to be adapted to the novel geometry and mechanical features of the cavity. To achieve an exchange of the cavities within a regular maintenance shutdown, full compatibility with the existing cryostat was prioritized during the design of the modified cryomodule components. In addition, a beam diagnostic setup was conceptualized, installed and commissioned upstream of the capture cavity. This setup was used to characterize momentum spreads of the beam along the normal-conducting injector section with a relative uncertainty of ±2 %. Furthermore, parameters of the beam entering the superconducting injector section, which have a significant influence on the achievable injector beam quality, could be optimized. After the cool-down of the installed capture cavity, full functionality of the upgraded cryomodule was shown. First beam parameter studies were conducted at the optimized injector. The results were benchmarked against the former injector setup. Besides a reduction of the momentum spread by a factor of around four, a substantially improved energy gain of up to 1.4 MeV was achieved in the new capture structure for an incident beam energy of 250 keV. Furthermore, a decreased bunch length was observed at the injector beam, which had already proven beneficial for the overall S-DALINAC performance during ERL experiments following the commissioning. The optimized injector is fully operational and is now available for further beam operation at the S-DALINAC

Mycorrhizas and biomass crops: opportunities for future sustainable development

Central to soil health and plant productivity in natural ecosystems are in situ soil microbial communities, of which mycorrhizal fungi are an integral component, regulating nutrient transfer between plants and the surrounding soil via extensive mycelial networks. Such networks are supported by plant-derived carbon and are likely to be enhanced under coppiced biomass plantations, a forestry practice that has been highlighted recently as a viable means of providing an alternative source of energy to fossil fuels, with potentially favourable consequences for carbon mitigation. Here, we explore ways in which biomass forestry, in conjunction with mycorrhizal fungi, can offer a more holistic approach to addressing several topical environmental issues, including ‘carbon-neutral’ energy, ecologically sustainable land management and CO2 sequestration

Contributions of a global network of tree diversity experiments to sustainable forest plantations

status: publishe

Preconditioning-induced ischemic tolerance: a window into endogenous gearing for cerebroprotection

Ischemic tolerance defines transient resistance to lethal ischemia gained by a prior sublethal noxious stimulus (i.e., preconditioning). This adaptive response is thought to be an evolutionarily conserved defense mechanism, observed in a wide variety of species. Preconditioning confers ischemic tolerance if not in all, in most organ systems, including the heart, kidney, liver, and small intestine. Since the first landmark experimental demonstration of ischemic tolerance in the gerbil brain in early 1990's, basic scientific knowledge on the mechanisms of cerebral ischemic tolerance increased substantially. Various noxious stimuli can precondition the brain, presumably through a common mechanism, genomic reprogramming. Ischemic tolerance occurs in two temporally distinct windows. Early tolerance can be achieved within minutes, but wanes also rapidly, within hours. Delayed tolerance develops in hours and lasts for days. The main mechanism involved in early tolerance is adaptation of membrane receptors, whereas gene activation with subsequent de novo protein synthesis dominates delayed tolerance. Ischemic preconditioning is associated with robust cerebroprotection in animals. In humans, transient ischemic attacks may be the clinical correlate of preconditioning leading to ischemic tolerance. Mimicking the mechanisms of this unique endogenous protection process is therefore a potential strategy for stroke prevention. Perhaps new remedies for stroke are very close, right in our cells

Rank signaling links the development of invariant γδ T cell progenitors and Aire(+) medullary epithelium

The thymic medulla provides a specialized microenvironment for the negative selection of T cells, with the presence of autoimmune regulator (Aire)-expressing medullary thymic epithelial cells (mTECs) during the embryonic-neonatal period being both necessary and sufficient to establish long-lasting tolerance. Here we showed that emergence of the first cohorts of Aire(+) mTECs at this key developmental stage, prior to αβ T cell repertoire selection, was jointly directed by Rankl(+) lymphoid tissue inducer cells and invariant Vγ5(+) dendritic epidermal T cell (DETC) progenitors that are the first thymocytes to express the products of gene rearrangement. In turn, generation of Aire(+) mTECs then fostered Skint-1-dependent, but Aire-independent, DETC progenitor maturation and the emergence of an invariant DETC repertoire. Hence, our data attributed a functional importance to the temporal development of Vγ5(+) γδ T cells during thymus medulla formation for αβ T cell tolerance induction and demonstrated a Rank-mediated reciprocal link between DETC and Aire(+) mTEC maturation

Data set for the Twofold Energy-Recovery Mode at S-DALINAC

This data set belongs to the twofold energy-recovery mode realized at the Darmstadt electron accelerator S-DALINAC in August 2021. It contains measurements for different acceleration modes at different beam currents. This data set can be used under the Creative Commons Attribution 4.0 International (CC BY 4.0) license