Design and Performance of the Advanced-Light-Source Double-crystal Monochromator

A new “Cowan type” double-crystal monochromator, based on the boomerang design used at National Synchrotron Light Source (NSLS) beamline X-24A, has been developed for beamline 9.3.1 at the Advanced Light Source (ALS), a windowless ultrahigh vacuum beamline covering the 1-6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design of the monochromator has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x-rays at NSLS beamline X-23Ʌ2, maximum deviations in the intensity of monochromatic light were just 7% during scans of several hundred eV in the vicinity of the Cr K edge (6 keV) with the monochromator operating without intensity feedback. Such precision is essential because of the high brightness of the ALS radiation and the overall length of beamline 9.3.1 (26 m)

Characterization of an alpha tubulin gene sequence from Neospora caninum and Hammondia heydorni, and their comparison to homologous genes from Apicomplexa

The gene coding for α tubulin has been isolated by the polymerase chain reaction and sequenced from 2 isolates of Neospora caninum (Nc-Liverpool and Nc-SweB1). The data show that the gene, as in Toxoplasma gondii, is single copy and contains 3 exons and 2 introns and is identical in sequence in the 2 isolates studied. Comparison of the predicted protein sequence shows it to be identical to the α tubulin protein encoded by the T. gondii gene. The majority of the nucleotide substitutions that have occurred during the evolution of the T. gondii and N. caninum genes from their common ancestor have occurred in the third codon position. A partial coding sequence for α tubulin was also obtained from Hammondia heydorni and compared to other α tubulin sequences from Apicomplexa. The results show the sequences of the T. gondii, N. caninum and H. heydorni α tubulin genes to be similar but not identical in sequence, thereby providing new evidence that N. caninum and H. heydorni are genetically distinct species

Isolation of Neospora caninum genes detected during a chronic murine infection

In order to isolate genes coding for antigens of Neospora caninum which are recognised by the host immune system during a chronic murine infection, a cDNA library was immunoscreened with pooled sera from mice which survived three independent infections by N. caninum. Two new genes from N. caninum were isolated and expressed in Escherichia coli. The genes identified include one homologous to GRA1 of Toxoplasma gondii, plus another (NCP20) previously unknown in any taxon. Both genes encode small polypeptides which induced an IgG response in the mouse and were also recognised by IgG from a cow chronically infected with N. caninum. These results are consistent with the hypothesis that the polypeptides encoded by these genes are a target for the host immune system during chronic infections of N. caninum. © 2001 Published by Elsevier Science Ltd

Design and performance of the ALS double-crystal monochromator

A new ``Cowan type`` double-crystal monochromator, based on the boomerang design used at NSLS beamline X-24A, has been developed for beamline 9.3.1 at the ALS, a windowless UHV beamline covering the 1-6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x-rays at NSLS beamline X-A, maximum deviations in the intensity of monochromatic light were just 7% during scans of several hundred eV in the vicinity of the Cr K edge (6 keV) with the monochromator operating without intensity feedback. Such precision is essential because of the high brightness of the ALS radiation and the overall length of beamline 9.3.1 (26 m)

Ion Source and Injector Improvements at the SuperHILAC

Major improvements have been made on the Adam injector at the SuperHILAC heavy ion accelerator. Adam is a pressurized Cockcroft-Walton injector, typically run at voltages in excess of 2 MeV. The PIG ion source was redesigned to increase the length of the discharge column and the extraction slit, while remaining within the magnet poles of the source magnet. To maintain cooling, part of the thinner soft-iron end cap was replaced with a copper section, modifying the magnetic circuit. These modifications resulted in more than doubling the ion beam intensity. A large liquid nitrogen cryotrap within the pressure vessel was replaced by an RF shielded, commercial cryopump head with a custom pumping array. This reduced the pressure at the ground end of the injector by an order of magnitude and reduced that at the source by a factor of two, even with the additional gas load due to the longer slit. The pressure reduction was essential to minimize charge exchange loss of the highly charged ions, such as Fe{sup 4+}. Plans are underway to replace a 3 watt cryopump in the terminal end with a 10 watt pump which is expected to result in a 50% faster cooldown time, and greater than a 50% increase in running time before regeneration of the cryopump is necessary. 3 refs., 4 figs

Design and Performance of the ALS Double-Crystal Monochromator

A new ``Cowan type`` double-crystal monochromator, based on the boomerang design used at NSLS beamline X-24A, has been developed for beamline 9.3.1 at the ALS, a windowless UHV beamline covering the 1-6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x-rays at NSLS beamline X-A, maximum deviations in the intensity of monochromatic light were just 7% during scans of several hundred eV in the vicinity of the Cr K edge (6 keV) with the monochromator operating without intensity feedback. Such precision is essential because of the high brightness of the ALS radiation and the overall length of beamline 9.3.1 (26 m)