We report recent results on the performance of FLASH (Free Electron Laser in Hamburg) operating at a wavelength of 13.7 nm where unprecedented peak and average powers for a coherent EUV radiation source have been measured. In the saturation regime the peak energy approached 170 µJ for individual pulses while the average energy per pulse reached 70 µJ. The pulse duration was in the region of 10 femtoseconds and peak

Distinctive steep‐sided flat‐topped domes have been discovered in the Magellan images of Venus. These domes have similar characteristics to terrestrial domes formed by viscous andesitic, dacitic, and rhyolitic lavas. A survey of more than 95% of the surface reveals 145 such features ranging from less than 10 km to almost 100 km in diameter, with a mean diameter of 23.8 km and a mean height of about 700 m. The domes are 10–100 times wider and have volumes (25–3400 km3) orders of magnitude larger than analogous terrestrial features. The morphology of many of the domes suggests that they were emplaced in a single continuous mode rather than episodically. The domes are widely distributed over the planet (including one near the Venera 8 site) and occur preferentially in association with coronae and in plains adjacent to regional occurrences of tessera. They show no strong correlation with latitude and longitude, but are preferentially concentrated at altitudes near and just below the mean planetary radius; this altitude concentration may be related to the preferential development of neutral buoyancy zones and magma reservoirs at intermediate to higher altitudes. The common association of domes with coronae appears to be an indication of the importance of magma upwelling and magma reservoirs in the formation of domes. The probability that magma reservoirs on Venus will grow to unusually large sizes favors large‐scale differentiation processes in such magma reservoirs. This suggests that production of large‐volume magma bodies by in situ processes such as fractional crystallization or volatile enhancement is entirely plausible. The association with tesserae may be related to ab initio processes of melting of preexisting crust of evolved composition by stalling of basaltic magma at neutral buoyancy zones, comparable to the environment on terrestrial continents. The resemblance of the Venus domes to terrestrial rhyolite and dacite domes provides possible evidence for the emplacement of high viscosity magma on Venus. The extremely large volumes of the domes and evidence for their emplacement in a continuous mode has led us to develop two models for the emplacement of the Venus domes. In the compositionally evolved magma model, the high apparent viscosity is due to differentiation and evolution of basaltic magma to produce silicic magmas. Magmas with such compositions and viscosities can be erupted on Venus through fissures of plausible widths and at rates comparable to those observed on Earth; terrestrial rhyolite flows with volumes of 200 km3 are known. A related possibility is that the domes are the undisrupted Venus equivalent of terrestrial ignimbrite‐producing eruptions. The second model is a basaltic bubble enhancement model, in which the high apparent viscosity is due to the extrusion of basaltic foams following volatile enhancement in the upper part of a magma reservoir. Large volumes and single eruptive phases are plausible because of low magma viscosity during ascent, high viscosity on the surface, and enhanced b...

We studied the relationship between altitude and microwave emissivity (the complement of power reflectivity) in 10 highland regions of Venus, using the Magellan data set. Above a critical altitude that ranges from 4.75 km on Maxwell Montes to 2.49 km on Sapas Mons, emissivity undergoes an abrupt decrease to values so low (<0.6) that the surface mineralogy on these mountaintops must differ from that at lower altitudes in such a way as to enhance the bulk dielectric constant of the highland surface material. This emissivity effect probably is produced not by basalt minerals but by a secondary, weathered mineral assemblage. We developed the phase diagrams descriptive of equilibrium secondary mineral assemblages on Venus, as a function of altitude and atmospheric redox state. The mineral responsible for low emissivity on mountaintops appears to be the electrical semiconductor pyrite (FeS2). Variation from one highland area to another in the altitude at which pyrite becomes the stable Fe mineral (as opposed to magnetite at lower altitudes) may be attributable to local modulation by topography of the atmospheric thermal profile. The altitudes at which the magnetite/pyrite phase boundary is encountered vary with the redox slate of the atmosphere, and observed values of this altitude can be used to estimate an oxygen fugacity at plains level of ∼10−21 bars. Maat Mons, a volcanic peak almost as lofty as Maxwell Montes, is the only high mountaintop on Venus that has not weathered to a low‐emissivity mineral assemblage. Presumably, this means flows at the highest altitudes are negligibly weathered and the volcano is relatively young.

Extreme-ultraviolet to x-ray free-electron lasers (FELs) in operation for scientific applications are up to now single-user facilities. While most FELs generate around 100 photon pulses per second, FLASH at DESY can deliver almost two orders of magnitude more pulses in this time span due to its superconducting accelerator technology. This makes the facility a prime candidate to realize the next step in FELs-dividing the electron pulse trains into several FEL lines and delivering photon pulses to several users at the same time. Hence, FLASH has been extended with a second undulator line and self-amplified spontaneous emission (SASE) is demonstrated in both FELs simultaneously. FLASH can now deliver MHz pulse trains to two user experiments in parallel with individually selected photon beam characteristics. First results of the capabilities of this extension are shown with emphasis on independent variation of wavelength, repetition rate, and photon pulse length.

No abstract