Recirculating accelerator driver for a high-power free-electron laser: A design overview

Jefferson Lab is building a free-electron laser (FEL) to produce continuous-wave (cw), kW-level light at 3-6 {mu}m wavelength. A superconducting linac will drive the laser, generating a 5 mA average current, 42 MeV energy electron beam. A transport lattice will recirculate the beam back to the linac for deceleration and conversion of about 75% of its power into rf power. Bunch charge will range up to 135 pC, and bunch lengths will range down to 1 ps in parts of the transport lattice. Accordingly, space charge in the injector and coherent synchrotron radiation in magnetic bends come into play. The machine will thus enable studying these phenomena as a precursor to designing compact accelerators of high-brightness beams. The FEL is scheduled to be installed in its own facility by 1 October 1997. Given the short schedule, the machine design is conservative, based on modifications of the CEBAF cryomodule and MIT-Bates transport lattice. This paper surveys the machine design

Phase mixing of chaotic orbits as an irreversible ''relaxation'' mechanism

Orbits that are chaotic will tend to phase-mix exponentially through their accessible phase space. This phenomenon, commonly called ''chaotic mixing'', stands in marked contrast to phase mixing of regular orbits. It is inherently irreversible, and thus its associated e-folding time scale sets a condition on any process envisioned for emittance compensation. Accordingly, two questions arise. First, under what conditions does chaotic mixing manifest itself in beams? Second, when it is active, over what time scale does it operate? The work described here is part of an ongoing effort to answer these questions

G protein signaling-biased agonism at the k-opioid receptor is maintained in striatal neurons

Biased agonists of G protein-coupled receptors may present a means to refine receptor signaling in a way that separates side effects from therapeutic properties. Several studies have shown that agonists that activate the k-opioid receptor (KOR) in a manner that favors G protein coupling over b-Arrestin2 recruitment in cell culture may represent a means to treat pain and itch while avoiding sedation and dysphoria. Although it is attractive to speculate that the bias between G protein signaling and b-Arrestin2 recruitment is the reason for these divergent behaviors, little evidence has emerged to show that these signaling pathways diverge in the neuronal environment. We further explored the influence of cellular context on biased agonism at KOR ligand-directed signaling toward G protein pathways over b-Arrestin-dependent pathways and found that this bias persists in striatal neurons. These findings advance our understanding of how a G protein-biased agonist signal differs between cell lines and primary neurons, demonstrate that measuring [35S]GTPgS binding and the regulation of adenylyl cyclase activity are not necessarily orthogonal assays in cell lines, and emphasize the contributions of the environment to assessing biased agonism

Real-time transverse-emittance and phase-space monitor

A real-time multislit [1] transverse-emittance monitor has been developed for diagnosing the space-charge-dominated beam in the 10MeV injection line of the FEL at Thomas Jefferson National Accelerator Facility (formerly CEBAF). It gives emittance, Twiss parameters, and phase-space contours (without any symmetry assumptions) at the update rate of 1Hz. It reduces measurement noise in real-time, and incorporates a special algorithm for constructing the phase-space matrix, which yields more accurate results by sweeping the beam across the slits. In this paper we will discuss issues relevant to the software design and implementation. Experimental results obtained from a 250keV photocathode gun will also be presented and compared with other methods and with PARMELA simulations

Development of functionally selective, small molecule agonists at kappa opioid receptors

The kappa opioid receptor (KOR) is widely expressed in the CNS and can serve as a means to modulate pain perception, stress responses, and affective reward states. Therefore, the KOR has become a prominent drug discovery target toward treating pain, depression, and drug addiction. Agonists at KOR can promote G protein coupling and βarrestin2 recruitment as well as multiple downstream signaling pathways, including ERK1/2 MAPK activation. It has been suggested that the physiological effects ofKORactivation result from different signaling cascades, with analgesia being G protein-mediated and dysphoria being mediated through βarrestin2 recruitment. Dysphoria associated with KOR activation limits the therapeutic potential in the use of KOR agonists as analgesics; therefore, it may be beneficial to develop KOR agonists that are biased toward G protein coupling and away from βarrestin2 recruitment. Here, we describe two classes of biased KOR agonists that potently activateGprotein coupling but weakly recruitβarrestin2. These potent and functionally selective small molecule compounds may prove to be useful tools for refining the therapeutic potential of KOR-directed signaling in vivo

Características químicas de um latossolo adubado com uréia e cloreto de potássio em ambiente protegido

A produção de vegetais mais sadios e de boa qualidade e o fornecimento contínuo no mercado são fatores que têm determinado a adoção do sistema de cultivo protegido por um número maior de produtores. Porém, devido ao pouco conhecimento sobre o manejo do solo nessas condições, tem-se aplicado altas doses de fertilizantes, ocasionando problemas de salinidade e desequilíbrio nutricional. O objetivo desse trabalho foi avaliar os efeitos da aplicação da uréia e do cloreto de potássio nas características químicas de um LATOSSOLO VERMELHO Destrófico, principalmente nos índices de acidez e saturação em potássio. O N e o K foram aplicados em cobertura, nas doses equivalentes de 13,3 e 39,9 g m-2 de N e 5,5 e 16,6 g m-2 de K, em esquema fatorial (2x2+1), com tratamento adicional, sem a aplicação dos nutrientes. Cultivou-se pimentão, cultivar Mayata, em condições de ambiente protegido, durante 34 semanas. Após o pegamento das mudas, foi aplicado 1/6 dos nutrientes a cada dez dias. Ao final do ciclo, as formas de N nítrico e N amoniacal representaram melhor as doses do nutriente aplicados ao solo e não houve acidificação. As raízes tiveram significativo crescimento após a aplicação de N, enquanto que o aumento da dose de K, aplicado como KCl, prejudicou o crescimento radicular, provavelmente associado à alta concentração de K no solo e possíveis efeitos salinos, correspondendo a mais de 5,0 mmol c dm-3 e mais que 5,3% de saturação do K no complexo de troca, na camada superficial do solo

Conceptual foundation of the Fokker-Planck approach to space-charge effects

An rms-mismatched beam can evolve rapidly to a configuration of quasiequilibrium under the influence of space-charge forces. As sit evolves, its emittance grows and a diffuse halo forms. The beam's distribution function accounts for all the complicated dynamics. Unfortunately, the distribution function is difficult to calculate in as much as the physics lies at the interface between classical mechanics and thermodynamics. This paper presents the foundation for a statistical theory of the dynamics of nonequilibrium space-charge-dominated beams. Within certain approximations, the theory takes on a Fokker-Planck form. Key questions arise concerning the nature of the dynamical friction and diffusion in the beam's phase space and of the quasiequilibrium configuration that ensues

A program to research emittance growth in bends

A research program to explore the phenomenon of emittance growth in bends due to noninertial space-charge effects has been defined and initiated. The program combines theoretical, numerical, and experimental investigations. This paper summarizes the motivation of the work and highlights CEBAF`s need for immediate results. The program`s key elements, some of which qualitatively differ from the standard approach used to investigate the production and effects of coherent synchrotron radiation in synchrotrons and storage rings, are enumerated and discussed. 1 fig