113457568
CLARA - A Proposed New FEL Test Facility for the UK
A Free Electron Laser (FEL) test facility, CLARA (Compact Linear Advanced Research Accelerator), is proposed to be constructed at Daresbury Laboratory in the UK. The aim of CLARA is to develop a normal conducting test accelerator able to generate longitudinally and transversely bright electron bunches and to use these bunches in the experimental production of stable, synchronised, ultra short photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation of light source facilities. In addition the facility will be an ideal test bed for demonstrating innovative technologies such as high repetition rate normal conducting RF linacs and advanced undulator designs. This paper will describe the design of CLARA, pointing out the flexible features that will be incorporated to allow multiple novel FEL schemes to be proven.
114544071
DESIGN OF POST LINAC BEAM TRANSPORT FOR THE UK NEW LIGHT SOURCE PROJECT
The design of free electron laser (FEL) driver needs careful beam transport design to pass very short bunches through the switchyard/spreader to switch the beam to different FEL lines. The spreader design which allows flexibility in operation has been adapted following the LBNL design [1]. In order to measure the slice properties of the bunches two beam diagnostics lines are proposed, a straight one for beam commissioning purposes and a branch of the spreader similar to the FEL lines to measure the adverse effects that may arise due to passing the short bunches through the kicker and septum magnets. As a part of machine protection, post linac collimation system collimates the halo particles in transverse and energy planes. The design of the collimation, beam spreader and beam diagnostics lines is discussed.
119203536
A Modular Path Length Corrector for Recirculating Linacs
Abstract We present a novel modular magnetic system that can introduce a large and continuously variable path length difference without simultaneous variation of the longitudinal dispersion. This is achieved by using a combination of an electrically adjustable magnetic chicane and a mechanically adjustable focusing chicane. We describe how such a system may be made either isochronous or with a given longitudinal dispersion, and show that the nonlinear terms in such a system are relatively small.
112783302
Design of the MAX IV Ring Injector and SPF/FEL Driver
55801859
PULSE - A High-Repetition-Rate Linac Driver for X-ray FELs
We describe a staged concept for a linac-based freeelectron laser providing coherent tuneable VUV and soft X-ray output with pulse lengths down to 10 fs or less. Use of 1.3 GHz cryomodules operated with CW RF will allow flexible pulse patterns at potentially very high repetition rates up to 1 MHz. We consider the options for FELs that may be included in a facility of this type.
126189055
The status of the ALICE Accelerator R&D Facility at STFC Daresbury Laboratory
2857756
Comment regarding the functional form of the Schmidt law
Abstract Star formation rates on the galactic scale are described phenomenologically by two distinct relationships, as emphasized recently by Elmegreen [Elmegreen, B.G., 2002. ApJ, 577, 206. astro-ph/0207114 .]. The first of these is the Schmidt law, which is a power-law relation between the star formation rate SFR and the column density Σ. The other relationship is that there is a cutoff in the gas density below which star formation shuts off. The purpose of this paper is to argue that: (1) these two relationships can be accommodated by a single functional form of the Schmidt law, (2) this functional form is motivated by the hypothesis that star formation is a critical phenomenon, and that as a corollary, (3) the existence of a sharp cutoff may thus be an emergent property of galaxies, as was argued by Seiden [Seiden, P.E.,1983. ApJ, 266, 555.], as opposed to the classical view that this cutoff is due to an instability criterion.
118576869
Protostellar Jets Driven by a Disorganized Magnetic Field
We have proposed a viscoelastic model of the Maxwell stresses due to the disorganized magnetic field in MRI-driven MHD turbulence. Viscoelastic fluids in the laboratory are known to produce jet-like structures under the action of a rotating sphere. Here we argue that a similar mechanism may help explain jets in protostellar systems. Such jets would be driven not by large-scale organized magnetic fields, but by the mean-field stresses of small-scale tangled magnetic fields.
18007475
Turbulent Elasticity of the Solar Convective Zone and the Taylor Number Puzzle
Previous work on the angular momentum balance and meridional circulation of the solar convective zone (SCZ) generally consists either of semi-analytic approaches in which a simple turbulence model is adopted, or full direct numerical simulation (DNS) of the hydrodynamics or magnetohydrodynamics (MHD). In both instances the inclusion of magnetic fields has been troublesome. Also, both approaches have had difficulty reproducing the known angular velocity profile of the SCZ; this is the Taylor Number Puzzle. 
I discuss preliminary work in which I incorporate magnetic fields into a viscoelastic turbulence model for the SCZ and apply this to the problem of meridional circulation and angular momentum balance. I suggest that such an approach may help solve the Taylor Number Puzzle of the SCZ and bring theoretical predictions for the large-scale motion of the SCZ in line with observations.
16217538
Three routes to jet collimation by the Balbus–Hawley magnetorotational instability
Three completely different lines of work have recently led to the conclusion that the magnetorotational instability (MRI) may create a hoop stress that collimates jets. One argument is based upon consideration that magnetohydrodynamic (MHD) turbulence, in general, and turbulence driven by the MRI, in particular, is more nearly viscoelastic than it is viscous. Another argument is based upon the dispersion relation for the MRI in the context of 1 D simulations of core collapse. Yet a third argument rests in the results of direct numerical MHD simulations of collapsars and thick accretion flows. I elaborate on my previous work regarding the first argument above and I briefly discuss how these three sets of results are all related. I also discuss the different roles played by the magnetic tension and the magnetic pressure within the context of this work. I point out that this leads to consideration of the normal stress difference between the hoop stress and the radial stress, in preference to a focus on just the hoop stress itself. Additionally, I argue that simulations of thick accretion flows and collapsars are not self-consistent if they include a phenomenological model for an MRI-induced viscous stress but disregard these other MRI-induced stress components. I comment briefly on the RHESSI observation of polarization in the gamma-ray burst GRB0212206.1 argue that this polarization is consistent with a tangled field, and does not require a large-scale organized field. Finally, I suggest that the role of magnetic fields in creating jets, as described here, should be understood not to work within the confines of magnetocentrifugal models of jets, but rather as an alternative to them.
7486677
The Allen Telescope Array: The First Widefield, Panchromatic, Snapshot Radio Camera for Radio Astronomy and SETI
The first 42 elements of the Allen Telescope Array (ATA-42) are beginning to deliver data at the Hat Creek Radio Observatory in northern California. Scientists and engineers are actively exploiting all of the flexibility designed into this innovative instrument for simultaneously conducting surveys of the astrophysical sky and conducting searches for distant technological civilizations. This paper summarizes the design elements of the ATA, the cost savings made possible by the use of commercial off-the-shelf components, and the cost/performance tradeoffs that eventually enabled this first snapshot radio camera. The fundamental scientific program of this new telescope is varied and exciting; some of the first astronomical results will be discussed.