Dynamical Collapse of Nonrotating Magnetic Molecular Cloud Cores: Evolution Through Point-Mass Formation

We present a numerical simulation of the dynamical collapse of a nonrotating magnetic molecular cloud core and follow the core's evolution through the formation of a central point mass and its subsequent growth to a 1 solar-mass protostar. The epoch of point-mass formation (PMF) is investigated by a self- consistent extension of previously presented models of core formation and contraction in axisymmetric, self-gravitating, isothermal, magnetically supported interstellar molecular clouds. Prior to PMF, the core is dynamically contracting and is not well approximated by a quasistatic equilibrium model. Ambipolar diffusion, which plays a key role in the early evolution of the core, is unimportant during the dynamical pre-PMF collapse phase. However, the appearance of a central mass, through its effect on the gravitational field in the inner core regions, leads to a "revitalization" of ambipolar diffusion in the weakly ionized gas surrounding the central protostar. This process is so efficient that it leads to a decoupling of the field from the matter and results in an outward propagating hydromagnetic C-type shock. The existence of an ambipolar diffusion-mediated shock was predicted by Li & McKee (1996), and we find that the basic shock structure given by their analytical model is well reproduced by our more accurate numerical results. Our calculation also demonstrates that ambipolar diffusion, rather than Ohmic diffusivity operating in the innermost core region, is the main field decoupling mechanism responsible for driving the shock after PMF.Comment: 59 pages, 10 figures, AASTeX4.0 accepted for publication in The Astrophysical Journa

Prompt bunch by bunch synchrotron oscillation detection via a fast phase measurement

An electronic system is presented which detects synchrotron oscillations of individual bunches with 4 ns separation. The system design and performance are motivated by the requirements of the proposed B factory facility at SLAC. Laboratory results are presented which show that the prototype is capable of measuring individual bunch phases with better than 0.5 degree resolution at the 476 MHz RF frequency. 13 refs., 6 figs., 1 tab

Electronic technology and the SLD detector

The SLD detector consists of five major subsystems, each with associated front-end electronics and an integrated FASTBUS control and data acquisition system. This paper highlights the choices among electronic technologies that have been developed for the SLD detector electronics. The common control, calibration, and data acquisition architectures are described. The functions of selected SLD integrated circuits, standard cells, gate arrays, and hybrids are summarized, and the integration of these functions into the common data acquisition path is described. Particular attention is directed to four areas of electronic technology developed for the SLD detector: the preamplifier hybrid designs are compared to their performance and implementation examined; the application of full custom CMOS digital circuits in SLD is compared to gate array and EPLD (electrically programmable logic device) implementations; the fiberoptic signal transmission techniques in SLD are examined and the data rates and link topology are presented; and finally, the packaging, power consumption, and cooling requirements for system functions resident inside the detector structure are explored. The rationale for the implementation choices in the SLD electronics is presented so that others might benefit from our experience