Reliability History and Improvements to the ANL 50 MEV H- Accelerator

The H- Accelerator consists of a 750 keV Cockcroft Walton preaccelerator and an Alvarez type 50 MeV linac. The accelerator has been in operation since 1961. Since 1981, it has been used as the injector for the Intense Pulsed Neutron Source (IPNS), a national user facility for neutron scattering. The linac delivers about 3.5x1012 H- ions per pulse, 30 times per second (30 Hz), for multi-turn injection to a 450 MeV Rapid Cycling Synchrotron (RCS). IPNS presently operates about 4,000 hours per year, and operating when scheduled is critical to meeting the needs of the user community. For many years the IPNS injector/RCS has achieved an average reliability of 95%, helped in large part by the preaccelerator/linac which has averaged nearly 99%. To maintain and improve system reliability, records need to show what each subsystem contributes to the total down time. The history of source and linac subsystem reliability, and improvements that have been made to improve reliability, will be described. Plans to maintain or enhance this reliability for at least another ten years of operation, will also be discussed.Comment: 3 pages, 1 figur

A Real-Time Energy Monitor System for the Ipns Linac

Injected beam energy and energy spread are critical parameters affecting the performance of our rapid cycling synchrotron (RCS). A real-time energy monitoring system is being installed to examine the H- beam out of the Intense Pulsed Neutron Source (IPNS) 50 MeV linac. The 200 MHz Alvarez linac serves as the injector for the 450 MeV IPNS RCS. The linac provides an 80 ms macropulse of approximately 3x1012 H- ions 30 times per second for coasting-beam injection into the RCS. The RCS delivers protons to a heavy-metal spallation neutron target for material science studies. Using a number of strip-line beam position monitors (BPMs) distributed along the 50 MeV transport line from the linac to the RCS, fast signals from the strip lines are digitized and transferred to a computer which performs an FFT. Corrections for cable attenuation and oscilloscope bandwidth are made in the frequency domain. Rectangular pulse train phasing (RPTP) is imposed on the spectra prior to obtaining the inverse transform (IFFT). After the IFFT, the reconstructed time-domain signal is analyzed for pulse width as it progresses along the transport line. Time-of-flight measurements of the BPM signals provide beam energy. Finally, using the 3-size measurement technique, the longitudinal emittance and energy spread of the beam are determined

Bunch stabilization using rf phase modulation in the intense pulse neutron source (IPNS) rapid cycling synchrotron (RCS)

Phase modulation (PM) is used to increase the current limit in the IPNS RCS. A device referred to as a scrambler introduces a small oscillating phase between the two RCS rf cavities at approximately twice the synchrotrons frequency, f{sub s}. The modulation introduced by the scrambler generates longitudinal oscillations in the bunch at 2f{sub s}. Modulations in the bunch are also observed transversely indicating a coupling between longitudinal and transverse motion. Comparing PM with amplitude modulation (AM), coupling to the beam is roughly equivalent at 2f{sub s}

Hormonal signaling in cnidarians : do we understand the pathways well enough to know whether they are being disrupted?

Author Posting. © The Author, 2006. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Ecotoxicology 16 (2007): 5-13, doi:10.1007/s10646-006-0121-1.Cnidarians occupy a key evolutionary position as basal metazoans and are ecologically important as predators, prey and structure-builders. Bioregulatory molecules (e.g., amines, peptides and steroids) have been identified in cnidarians, but cnidarian signaling pathways remain poorly characterized. Cnidarians, especially hydras, are regularly used in toxicity testing, but few studies have used cnidarians in explicit testing for signal disruption. Sublethal endpoints developed in cnidarians include budding, regeneration, gametogenesis, mucus production and larval metamorphosis. Cnidarian genomic databases, microarrays and other molecular tools are increasingly facilitating mechanistic investigation of signaling pathways and signal disruption. Elucidation of cnidarian signaling processes in a comparative context can provide insight into the evolution and diversification of metazoan bioregulation. Characterizing signaling and signal disruption in cnidarians may also provide unique opportunities for evaluating risk to valuable marine resources, such as coral reefs

Myelin Proteomics: Molecular Anatomy of an Insulating Sheath

Fast-transmitting vertebrate axons are electrically insulated with multiple layers of nonconductive plasma membrane of glial cell origin, termed myelin. The myelin membrane is dominated by lipids, and its protein composition has historically been viewed to be of very low complexity. In this review, we discuss an updated reference compendium of 342 proteins associated with central nervous system myelin that represents a valuable resource for analyzing myelin biogenesis and white matter homeostasis. Cataloging the myelin proteome has been made possible by technical advances in the separation and mass spectrometric detection of proteins, also referred to as proteomics. This led to the identification of a large number of novel myelin-associated proteins, many of which represent low abundant components involved in catalytic activities, the cytoskeleton, vesicular trafficking, or cell adhesion. By mass spectrometry-based quantification, proteolipid protein and myelin basic protein constitute 17% and 8% of total myelin protein, respectively, suggesting that their abundance was previously overestimated. As the biochemical profile of myelin-associated proteins is highly reproducible, differential proteome analyses can be applied to material isolated from patients or animal models of myelin-related diseases such as multiple sclerosis and leukodystrophies

Intense pulsed neutron source accelerator status

The Intense Pulsed Neutron Source (IPNS) facility has been in operation since November 1, 1981. From that date through August 1, 1983, the accelerator system was scheduled for 7191 hours of operation. During this period, 627 million pulses totaling about 1.1 x 10/sup 21/ protons were delivered to the spallation target. The accelerator has exceeded goals set in 1981 by averaging 8.65 ..mu..A over this two year period. This average beam current, while modest by the standards of proposed machines, makes the IPNS synchrotron (Rapid Cycling Synchrotron (RCS)) the highest intensity proton synchrotron in the world today. Detailed data on accelerator operation are presented. Weekly average currents of 12 ..mu..A have been achieved along with peaks of 13.9 ..mu..A. A great deal has been learned about the required operating constraints during high beam current operation. It should be possible to increase the average beam current during this next year to 12 ..mu..A while observing these restraints. Improvement plans have been formulated to increase the beam current to 16 ..mu..A over the next three years

Impedance considerations for the Intense Pulse Neutron Source (IPNS) Rapid Cycling Synchrotron (RCS).

The use of Second Harmonic (SH) rf is being investigated to increase the Rapid Cycling Synchrotron (RCS) current limit. Hofmann-Pedersen distributions are employed to provide analytical guidance. The SH phase {theta}, is optimized using a numerical analysis to maximize transmission and minimize instabilities. The effect of the RCS stainless steel liner on the impedance of the machine is also discussed

The IPNS accelerator 50 MeV and 500 MeV transport lines

The Intense Pulsed Neutron Source (IPNS) accelerator delivers up to 500 MeV protons to a depleted uranium target producing spallation neutrons for material science and other research. A 70-80 ns bunch strikes the target at a rate of 30 Hz with an average beam current of 15 {mu}A. The 50 MeV and 500 MeV beam lines transport protons from the Drift Tube Linac (DTL) to the Rapid Cycling Synchrotron (RCS) and from the RCS to the Neutron Generating Source (NGS) target, respectively. Through over 15 years of operation, the accelerator has been highly reliable with the 5 billionth pulse on target recorded March 12, 1997. During this time, IPNS operators have discovered tunes for various parts of the DTL/RCS accelerator allowing for continual improvement in average current delivered to the target; however, in numerous cases this has been achieved by moving significantly away from the original design parameters. A new attempt is being made to analyze the lines and develop computer models that can be used to alleviate some of the undesirable features of the present {open_quotes}best tune.{close_quotes} In the 500 MeV line, higher order elements will be included in the modeling with the goal of providing a uniform power density profile at the NGS target. This paper describes features of the present lines, and progress-to-date in analyzing and improving them

Plasma considerations in the IPNS RCS.

Significant ionization appears to occur in the Rapid Cycling Synchrotron (RCS) during its 14 ms acceleration period leading to plasma formation and neutralization. The beam may in fact be over-neutralized, causing the tune to increase during the acceleration cycle. The overall tune shift in the RCS appears to be close to +0.5. The presence of plasma may help explain why longitudinal phase modulation can so quickly couple to transverse motion. In addition, plasmas tend to be inductive and the RCS appears to exhibit a relatively high inductance. Measurements of the electron cloud and plasma densities adjacent to the beam should be made. In addition to the RFA and Swept Analyzer diagnostics mentioned at the Workshop, other techniques might be attempted. If plasma is present, then a small, biased-probe might be useful (e.g., a Langmuir probe), or with the proper choice of geometry, an optics-based measurement for line density (e.g., an interferometer) might be employed, perhaps using microwaves for increased sensitivity

Diagnostic investigation of tune and tune shift in the IPNS RCS.

The Intense Pulse Neutron Source (IPNS) Rapid Cycling Synchrotron (RCS) accelerates 50 MeV protons to 450 MeV 30 times per second for spallation neutron production. Average current from the RCS has recently exceeded 16 {micro}A with peak instantaneous current approaching 15 A. The RCS makes efficient use of 21 kV of RF accelerating voltage and uses phase-modulation between the two rf cavities to damp vertical instabilities. Split-ring electrodes in the ring suggest an anomalous tune shift that increases with time in the acceleration cycle. Based on a background gas pressure of 1 {micro}Torr, the neutralization time for the beam is approximately 0.5 ms at injection suggesting the beam becomes fully neutralized relatively quickly in the cycle. Over-neutralization of the beam can lead to a positive tune shift that is presumably incoherent. Studies are underway to characterize the ionization within the RCS using the existing Profile and Position System (PAPS) and a newly installed Retarding Field Analyzer (RFA). Also a newly installed fast, deep-memory digitizing oscilloscope allows the entire history of a single acceleration cycle to be recorded from all four components of the split ring electrodes simultaneously at a rate of 250 MS/s