Strong Longitudinal Compression Research Articles

Octupole based current horn suppression in multistage bunch compression with emittance growth correction

High brightness electron beams are critical for x-ray free-electron laser performance. To achieve higher peak current, strong longitudinal compression often produces electron beams with peaks in the head and/or tail of the current profile. These current horns are formed after bunch compression due to nonlinear correlations in the longitudinal phase space and the higher order optics of the compressor. It has been suggested that this higher order compression can be corrected by inserting an octupole magnet near the center of a bunch compressor. However, this scheme provides a correlated transverse kick leading to growth of the projected emittance. We present here a method whereby octupole magnets are inserted into two sequential bunch compressors. By tuning a $\ensuremath{\pi}$ betatron phase advance between the two octupoles, the correlated transverse kick from the first octupole can be corrected by the second, while providing a cummulative adjustment of the higher order compression.

Some features of bending of a rod under a strong longitudinal compression

Considered typical processes of rod bending under strong longitudinal compression. The dynamic equation of bending correspponds to a perturbation of the two- dimensional Laplace equation. It is established that, for these processes, expanding of do- mains of rapid increasing of bending begins in small neighborhoods of singularity points of solutions of the limiting Laplace's equation. The initial stages of these increases are described using the Hardy integral.

Origin, evolution and dynamic context of a Neoglacial lateral–frontal moraine at Austre Lovénbreen, Svalbard

Moraines marking the Neoglacial limits in Svalbard are commonly ice cored. Investigating the nature of this relict ice is important because it can aid our understanding of former glacier dynamics. This paper examines the composition of the lateral–frontal moraine associated with the Neoglacial limit at Austre Lovénbreen and assesses the likely geomorphological evolution. The moraine was investigated using ground-penetrating radar (GPR), with context being provided by structural mapping of the glacier based on an oblique aerial image from 1936 and vertical aerial imagery from 2003. Multiple up-glacier dipping reflectors and syncline structures are found in the GPR surveys. The reflectors are most clearly defined in lateral positions, where the moraine is substantially composed of ice. The frontal area of the moraine is dominantly composed of debris. The core of the lateral part of the moraine is likely to consist of stacked sequences of basal ice that have been deformed by strong longitudinal compression. The long term preservation potential of the ice-dominated lateral moraine is negligible, whereas the preservation of the debris-dominated frontal moraine is high. A glacier surface bulge, identified on the 1936 aerial imagery, provides evidence that Austre Lovénbreen has previously displayed surge activity, although it is highly unlikely to do so in the near future in its current state. This research shows the value of relict buried ice that is preserved in landforms to aiding our understanding of former glacier characteristics.

Concertina eskers, Brúarjökull, Iceland: An indicator of surge-type glacier behaviour

Brúarjökull is a surging outlet lobe of Vatnajökull in SE Iceland. Geological evidence indicates that during quiescent phases, water drainage takes place in ice-walled and ice-roofed channels. As the glacier retreats, the courses of these channels are represented by eskers. Eskers which were englacial prior to surges become deformed during a surge. The deformation of eskers reflects strong longitudinal compression of the ice in the terminal zone. The wavelength of one of the compressed eskers indicates that ice in a 4 km wide margin was compressed by 50% of its original length. Compressed, or concertina eskers, date from the 1963–1964 and the 1890 surges of Brúarjökull. They have not been found from the 1810 surge, indicating that they may not survive if overrun by subsequent surges.

The influence of stress and strain in the early development of shaft bones

In chick embryos from stage 23 to stage 27 the whole presumptive zeugopod - or its pre-axial (tibial) portion only - was proximodistally and dorsoventrally inverted by turning it 180 degrees round the anteroposterior axis of the limb bud. Development of the reoriented blastema of the tibia was consistently retarded and variously reduced: this skeletal piece appeared shorter and relatively thicker than the controlateral normal tibia. Chondrification, progress of differentiation of the cartilaginous model, onset and gradual spreading of the ossification processes were considerably delayed. Often the diminutive tibia underwent a degree of bending or angulation of up to 90 degrees - 100 degrees in the sagittal plane. In these bent tibiae - obviously developing under abnormal conditions of intrinsic and extrinsic mechanical stresses - cell hypertrophy appeared greatly retarded or hindered in sites of the diaphysial cartilaginous core which were presumably subjected to strong longitudinal compression. No rigorous temporal and topographical relationships were observed between chondrocyte hypertrophy and onset of perichondral osteogenesis. Apparently, a direct contact between hypertrophic cartilage and perichondrial cells was not strictly required to prompt osteogenesis; this process, in fact, often involved areas of the perichondrium enveloping parvicellular cartilage. Radial pressures exerted by the over-stretched outer layer of the perichondrium, or periosteum, on the subjacent prospective osteogenous layer reduced or prevented the deposition of bone. Conversely, radial stretching of the inner layer of the perichondrium, or periosteum, considerably enhanced cell proliferation, blood vessel formation, differentiation of osteoblasts and formation of bone matrix.

Telescoping Beams for Heavy Ion Fusion

In addition to the strong longitudinal compression and multiple beams now used in all designs for heavy ion fusion drivers, attaining the required beam power could be helped by telescoping bunches of different ion species. Telescoping is here defined as the overtaking and interpenetration of bunches consisting of ions of different species but whose velocity, mass, and charge state have been selected so that the typical ions in the various bunches have the same ratio of momentum to charge, or magnetic rigidity, and, therefore, the same single particle dynamics in transport and focussing lines. With velocities differing by 10% or more, the highest powers would only arise close to the end of the transport lines. Telescoping also increases the total available phase space of the different species. This can be translated to a smaller final momentum spread or a means to accommodate greater phase space dilution.

Foliation Pattern of Gulkana Glacier, Alaska Range, Alaska

AbstractGulkana Glacier, consisting of three major ice streams and two prominent ice falls, displays a complex foliation pattern. In the western ice stream, below Gabriel Ice Fall, the foliation is transverse, developing gradually down-glacier into a distinct series of nested arcs. The arcs are concave up-glacier with the foliation dipping steeply toward the inside of the arc. A similar pattern is displayed in the eastern ice stream but there the pattern is less distinct with the arcs evolving into a series of nested semi-arcs. The central ice stream is characterized by vertical layers of foliation with a longitudinal strike. Apparently, longitudinal foliation will form in areas with strong compression and shear caused by differential flow velocity such as where two ice streams unite. The foliation that ultimately displays arcuate (or semi-arcuate) patterns originates principally at the base of an ice fall where strong longitudinal compression is present due to the decrease of gradient.

Foliation Pattern of Gulkana Glacier, Alaska Range, Alaska

AbstractGulkana Glacier, consisting of three major ice streams and two prominent ice falls, displays a complex foliation pattern. In the western ice stream, below Gabriel Ice Fall, the foliation is transverse, developing gradually down-glacier into a distinct series of nested arcs. The arcs are concave up-glacier with the foliation dipping steeply toward the inside of the arc. A similar pattern is displayed in the eastern ice stream but there the pattern is less distinct with the arcs evolving into a series of nested semi-arcs. The central ice stream is characterized by vertical layers of foliation with a longitudinal strike. Apparently, longitudinal foliation will form in areas with strong compression and shear caused by differential flow velocity such as where two ice streams unite. The foliation that ultimately displays arcuate (or semi-arcuate) patterns originates principally at the base of an ice fall where strong longitudinal compression is present due to the decrease of gradient.