No abstract

We report on recent experimental results deploying a continuous cryogenic hydrogen jet as a debris-free, renewable laser-driven source of pure proton beams generated at the 150 TW ultrashort pulse laser Draco. Efficient proton acceleration reaching cut-off energies of up to 20 MeV with particle numbers exceeding 109 particles per MeV per steradian is demonstrated, showing for the first time that the acceleration performance is comparable to solid foil targets with thicknesses in the micrometer range. Two different target geometries are presented and their proton beam deliverance characterized: cylindrical (∅ 5 μm) and planar (20 μm × 2 μm). In both cases typical Target Normal Sheath Acceleration emission patterns with exponential proton energy spectra are detected. Significantly higher proton numbers in laser-forward direction are observed when deploying the planar jet as compared to the cylindrical jet case. This is confirmed by two-dimensional Particle-in-Cell (2D3V PIC) simulations, which demonstrate that the planar jet proves favorable as its geometry leads to more optimized acceleration conditions.

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Extreme field gradients intrinsic to relativistic laser-interactions with thin solid targets enable compact MeV proton accelerators with unique bunch characteristics. Yet, direct control of the proton beam profile is usually not possible. Here we present a readily applicable all-optical approach to imprint detailed spatial information from the driving laser pulse onto the proton bunch. In a series of experiments, counter-intuitively, the spatial profile of the energetic proton bunch was found to exhibit identical structures as the fraction of the laser pulse passing around a target of limited size. Such information transfer between the laser pulse and the naturally delayed proton bunch is attributed to the formation of quasi-static electric fields in the beam path by ionization of residual gas. Essentially acting as a programmable memory, these fields provide access to a higher level of proton beam manipulation.

No abstract

ASPECTS score ≥ 8 within 24 hours and S100β protein < 140.5 ng/L at 48 hours predict better upper limb functioning, while advanced age predicts worse upper limb functioning 12 weeks after stroke.

The ESA (European Space Agency) is currently pursuing the development of the e.Deorbit mission that will remove a large defunct satellite from Earth orbit: ENVISAT. To fulfil the mission autonomy requirements, ESA has decided to embed in the GNC (Guidance, Navigation, Control) software, fault tolerance capacities against actuator faults. The aim of this paper is to present the development and validation of a model-based fault diagnosis and tolerant control solution for such faults. The proposed solution is based on a new class of nonlinear unknown input observers, optimal in the L2-gain sense, and a modified version of the nonlinear inverse pseudo control allocation technique. An intensive simulation campaign conducted within a high-fidelity nonlinear industrial simulator, demonstrates the efficiency of the approach.

One of the main issues of the international space programs is the identification and the design of a more flexible and possibly reusable manned space vehicle, able to re-enter from space missions and safely land on earth. Several re-entry strategies are feasible -from classical, direct capsule re-entry (APOLLO, SOYUZ) over a skip re-entry (ZOND, ORION) to aerocapture/aerobraking with a following orbital re-entry (Space Shuttle). But to achieve the objectives mentioned above, vehicles with a high lift-over-drag (L/D) ratio are necessary. A concept for this high L/D earth re-entry vehicle is the PHOEBUS (Plane-shaped Hypersonic Orbital Re-entry BUS) of the OHB-Team. This concept of a high L/D vehicle was studied within a framework of an ESA study and performs long duration re-entry trajectories with large down-and crossrange and good maneuverability by proper utilization of the lift forces. This paper presents an overview of the PHOEBUS vehicle design which is based on the OHB SpacePlane LR-L. Here the characteristic of a high L/D vehicle with a hot structure concept is described, using state-of-the-Art materials and an innovative design to permit low-risk re-entry flights with lower aerothermal -and deceleration loads. Furthermore, the flexibility to fly very large re-entry trajectories by the use of innovative entry strategies -as well as the limits for such strategies is described.A first iteration of the system performance related to the aerodynamic -and aerothermodynamic aspects as well as the downrange -and crossrange capabilities of the PHOEBUS vehicle are shown. The significantly larger performance of PHOEBUS will be illustrated by comparison of these parameters with conventional re-entry vehicles.