A Catalog of Candidate High-Redshift Blazars for GLAST. TERSI
ARIAS (San Francisco State University, San Francisco, CA, 94132)
JENNIFER CARSON (Stanford Linear Accelerator Center, Stanford, CA, 94025)
High-redshift
blazars are promising candidates for detection by the Gamma-ray
Large Area Space Telescope (GLAST). GLAST, expected to be launched
in the Fall of 2007, is a high-energy gamma-ray observatory designed
for making observations of celestial gamma-ray sources in the energy
band extending from 10 MeV to more than 200 GeV. It is estimated
that GLAST will find several thousand blazars. The motivations
for measuring the gamma-ray emission from distant blazars include
the study of the high-energy emission processes occurring in these
sources and an indirect measurement of the extragalactic background
light. In anticipation of the launch of GLAST we have compiled
a catalog of candidate high-redshift blazars. The criteria for
sources chosen for the catalog were: high radio emission, high
redshift, and a flat radio spectrum. A preliminary list of 307
radio sources brighter than 70mJy with a redshift z = 2.5 was acquired
using data from the NASA Extragalactic Database. Flux measurements
of each source were obtained at two or more radio frequencies from
surveys and catalogs to calculate their radio spectral indices
. The sources with a flat-radio spectrum ( = 0.5) were selected
for the catalog, and the final catalog includes about 200 sources.
Afterglow Radiation from Gamma-Ray Bursts. HUGH DESMOND
(Katholieke Universiteit Leuven, Leuven, Belgium, 3000) WEIQUN
ZHANG (Stanford Linear Accelerator Center, Stanford, CA, 94025)
Gamma-ray bursts
(GRB) are huge fluxes of gamma rays that appear randomly in the
sky about once a day. It is now commonly accepted that GRBs are
caused by a stellar object shooting off a powerful plasma jet along
its rotation axis. After the initial outburst of gamma rays, a
lower intensity radiation remains, called the afterglow. Using
the data from a hydrodynamical numerical simulation that models
the dynamics of the jet, we calculated the expected light curve
of the afterglow radiation that would be observed on earth. We
calculated the light curve and spectrum and compared them to the
light curves and spectra predicted by two analytical models of
the expansion of the jet (which are based on the Blandford and
McKee solution of a relativistic isotropic expansion; see Sari's
model and Granot's model). We found that the light curve did not
decay as fast as predicted by Sari; the predictions by Granot were
largely corroborated. Some results, however, did not match Granot's
predictions, and more research is needed to explain these discrepancies.
Analysis of Off-Nuclear X-Ray Sources in Galaxy NGC 4945. SARAH
HARRISON (Massachusetts Institute of Technology, Cambridge, MA,
22901) GRZEGORZ MADEJSKI (Stanford Linear Accelerator Center, Stanford,
CA, 94025)
Recently, X-ray
astronomy has been used to investigate objects such as galaxies,
clusters of galaxies, Active Galactic Nuclei (AGN), quasars, starburst
superbubbles of hot gas, X-ray binary systems, stars, supernova
remnants, and interstellar and intergalactic material. By studying
the x-ray emission patterns of these objects, we can gain a greater
understanding of their structure and evolution. We analyze X-ray
emission from the galaxy NGC 4945 using data taken by the Chandra
X-ray Observatory. The Chandra Interactive Analysis of Observations
(CIAO) software package was used to extract and fit energy spectra
and to extract light curves for the brightest off-nuclear sources
in two different observations of NGC 4945 (January, 2000 and May,
2004). A majority of sources were closely fit by both absorbed
power law and absorbed bremsstrahlung models, with a significantly
poorer Χ2/dof for the absorbed blackbody model, and most sources had little
variability. This indicates that the sources are accreting binary
systems with either a neutron star or black hole as the compact
object. The calculated luminosities were about 1038 erg/s, which implies that the mass of the accreting object is
close to 10 solar masses and must be a black hole.
Analysis Strategy of Powder Diffraction Data with 2-D Detector. ABHIK KUMAR (Austin College, Sherman, TX, 75090) APURVA
MEHTA (Stanford Linear Accelerator Center, Stanford, CA, 94025)
To gain a clearer
understanding of orientation and grain deformation of crystalline
materials, x-ray powder diffraction has played an integral role
in extracting three-dimensional structural information from one-dimensional
diffraction patterns. Powder diffraction models identical geometry
to the intersection of a normal right cone with a plane. The purpose
of this paper is to develop a general expression defining the conic
sections based on the geometry of a powder diffraction experiment.
Applying the derived formulation of a diffraction arc to experimental
data will give insight to the molecular and structural properties
of the sample in question. Instead of using complex three-dimensional
Euclidian geometry, we define the problem solving technique with
a simpler two-dimensional transformation approach to arrive at
a final equation describing the conic sections. Using the diffraction
geometry parameters, we can use this equation to calibrate the
diffractometer from the diffraction pattern of a known reference
material, or to determine the crystalline lattice structure of
the compound.
Characterization of an Electromagnetic Calorimeter for the Proposed International
Linear Collider. MERIDETH FREY (Wellesley College, Wellesley, MA, 2481)
NORMAN GRAF (Stanford Linear Accelerator Center, Stanford, CA, 94025)
The International
Linear Collider (ILC) is part of a new generation of accelerators
enabling physicists to gain a deeper understanding of the fundamental
components of the universe. The proposed ILC will accelerate positrons
and electrons towards each other with two facing linear colliders,
each twenty kilometers long. Designing and planning for the future
accelerator has been undertaken as a global collaboration, with
groups working on several possible detectors to be used at the
ILC. The following research at the Stanford Linear Accelerator
Center (SLAC) pertained to the design of an electromagnetic calorimeter.
The energy and spatial resolution of the calorimeter was tested
by using computer simulations for proposed detectors. In order
to optimize this accuracy, different designs of the electromagnetic
calorimeter were investigated along with various methods to analyze
the data from the simulated detector. A low-cost calorimeter design
was found to provide energy resolution comparable to more expensive
designs, and new clustering algorithms offered better spatial resolution.
Energy distribution and shape characteristics of electromagnetic
showers were also identified to differentiate various showers in
the calorimeter. With further research, a well-designed detector
will enable the ILC to observe new realms of physics.
Comparison of Non-Redundant Array and Double Pinhole CoherenceMeasurements with Soft X-rays. GABRIEL WEIL (Northwestern
University, Evanston, IL, 60201) JAN LUNING (Stanford Linear Accelerator Center, Stanford, CA, 94025)
Experiments on
the future Linac Coherent Light Source (LCLS) and other Free Electron
Lasers will need to be performed on a single-shot basis. The double
pinhole method of measuring spatial coherence requires a separate
measurement, with a different pinhole separation distance, for
each length scale sampled. This limits its utility for LCLS. A
potential alternative uses a Non-Redundant Array (NRA) of apertures
designed to probe the coherence over the range of length scales
defined by their physical extent, in a single measurement. This
approach was tested by comparing diffraction patterns from soft
x-rays incident on double pinhole and NRA absorption mask structures.
The double pinhole fringe visibility data serve as discrete reference
points that verify the continuous spectrum of the NRA coherence
data. The results present a quantitative analysis of the double
pinhole coherence measurements and a qualitative comparison to
the NRA images.
Determining Micromechanical Strain in Nitinol. MATTHEW
STRASBERG (Cornell University, Ithaca, NY, 14850) APURVA MEHTA
(Stanford Linear Accelerator Center, Stanford, CA, 94025)
Nitinol is a
superelastic alloy made of equal parts nickel and titanium. Due
to its unique shape memory properties, nitinol is used to make
medical stents, lifesaving devices used to allow blood flow in
occluded arteries. Micromechanical models and even nitinol-specific
finite element analysis (FEA) software are insufficient for unerringly
predicting fatigue and resultant failure. Due to the sensitive
nature of its application, a better understanding of nitinol on
a granular scale is being pursued through X-ray diffraction techniques
at the Stanford Synchrotron Radiation Laboratory (SSRL) at the
Stanford Linear Accelerator Center (SLAC). Through analysis of
powder diffraction patterns of nitinol under increasing tensile
loads, localized strain can be calculated. We compare these results
with micromechanical predictions in order to advance nitinol-relevant
FEA tools. From this we hope to gain a greater understanding of
how nitinol fatigues under multi-axial loads.
Development of Nanofluidic Cells for Ultrafast X-ray Studies of Water. MELVIN IRIZARRY (University of Puerto Rico, Mayaguez,
PR, 667) AARON LINDENBEREG (Stanford Linear Accelerator Center,
Stanford, CA, 94025)
In order to study
the molecular structure and dynamics of liquid water with soft
x-ray probes, samples with nanoscale dimensions are needed. This
paper describes a simple method for preparing nanofluidic water
cells. The idea is to confine a thin layer of water between two
silicon nitride windows. The windows are 1 mm × 1 mm and 0.5 mm × 0.5
mm in size and have a thickness of 150 nm. The thickness of the
water layer was measured experimentally by probing the infrared
spectrum of water in the cells with a Fourier Transform InfraRed
(FTIR) apparatus and from soft x-ray static measurements at the
Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory.
Water layers ranging from 10 nm to more than 2 µm were observed.
Evidence for changes in the water structure compared to bulk water
is observed in the ultrathin cells.
Development of Powder Diffraction Analysis Tools for a Nanocrystalline Specimen:
An Emphasis upon NiTi (Nitinol). ERICH
OWENS (Albion College, Albion, MI, 49224)
APURVA MEHTA (Stanford Linear Accelerator Center, Stanford, CA, 94025)
Powder diffraction
is a specialized technique whose investigatory limits are constrained
by the scale of the crystallized substance being scanned versus
the probe beam used. When disparate in scale, with the photon spot
size larger than the crystal being probed, many are employed, the
resulting diffraction image being cast from all possible incident
angles, constructing -arcs containing information about the crystalline
structure of the material under examination. Of particular interest
to our collaboration is the structure of Nitinol, a superelastic
Nickel-Titanium alloy, whose phase transformations and load bearing
deformations can be studied by usage of diffraction, with wide
sweeping biomedical uses. Analysis of this data is complicated
by phase transformation and material fluorescence, which make difficult
the computational modeling of the peaks within concentric -arcs.
We endeavored to construct a series of computational tools (the
amalgamation of them known as 2DPeakFinder) for refining and extracting
this relevant data, toward the end of employing previously developed
algorithms in the material’s structural analysis. We succeeded
to a large degree with the use of an iterative algorithm to navigate
radial complexity of the signal and manage to retain a distinction
between useful signal and superfluous background noise. The tools
developed in this project are a small step in readily streamlining
the analysis and physical modeling of a Nanocrystalline material’s
structural properties.
Host Galaxies of X-Shaped Radio Sources. ALESSONDRA
SPRINGMANN (Wellesley College, Wellesley, MA,
2481) TEDDY CHEUNG (Stanford Linear Accelerator Center, Stanford, CA, 94025)
The majority
of radiation from galaxies containing active galactic nuclei (AGNs)
is emitted not by the stars composing the galaxy, but from an active
source at the galactic center, most likely a supermassive black
hole. Of particular interest are radio galaxies, the active galaxies
emitting much of their radiation at radio wavelengths. Within each
radio galaxy, an AGN powers a pair of collimated jets of relativistic
particles, forming a pair of giant lobes at the end of the jets
and thus giving a characterisitic double-lobed appearance. A particular
class of radio galaxies have an “X”-shaped morphology: in these,
two pairs of lobes appear to originate from the galactic center,
producing a distinctive X-shape. Two main mechanisms have been
proposed to explain the X-shape morphology: one being through the
merger of a binary supermassive black hole system and the second
being that the radio jets are expanding into an asymmetric medium.
By analyzing radio host galaxy shapes, we probe the distribution
of the stellar mass to compare the differing model expectations
regarding the distribution of the surrounding gas and stellar material
about the AGN.
Improvement of PEP-II Linear Optics with a MIA-Derived Virtual Accelerator. BEN CERIO (Colgate University, Hamilton, NY, 13346)
YITON YAN (Stanford Linear Accelerator Center, Stanford, CA, 94025)
In several past
studies, model independent analysis, in conjunction with a virtual
accelerator model, has been successful in improving PEP-II linear
geometric optics. In many cases, optics improvement yielded an
increase in machine luminosity. In this study, an updated characterization
of linear optics is presented. With the PEP-II beam position monitor
(BPM) system, four independent beam centroid orbits were extracted
and used to determine phase advances and linear Green’s functions
among BPM locations. A magnetic lattice model was then constructed
with a singular value decomposition-enhanced least-square fitting
of phase advances and Green’s functions, which are functions of
quadrupole strengths, sextupole feed-downs, as well as BPM errors,
to the corresponding measured quantities. The fitting process yielded
a machine model that matched the measured linear optics of the
real machine and was therefore deemed the virtual accelerator.
High beta beat, as well as linear coupling, was observed in both
LER and HER of the virtual accelerator. Since there was higher
beta beating in LER, focus was shifted to the improvement of this
ring. By adjusting select quadrupoles of the virtual LER and fitting
the resulting beta functions and phase advances to those of the
desired lattice, the average beta beat of the virtual machine was
effectively reduced. The new magnet configuration was dialed into
LER on August 10, 2006, and beta beat was reduced by a factor of
three. After fine tuning HER to match the improved LER for optimal
collision, a record peak luminosity of 12.069x1033 cm-2s-1 was
attained on August 16, 2006.
Limited Streamer Tube System for Detecting Contamination in the Gas Used in
the BaBar Instrumented Flux Return. LAURA
HUNTLEY (Franklin & Marshall College, Lancaster, PA, 17603)
MARK CONVERY (Stanford Linear Accelerator Center, Stanford, CA, 94025)
The Resistive
Plate Chambers (RPCs) initially installed in the Instrumented Flux
Return (IFR) of the BaBar particle detector have proven unreliable
and inefficient for detecting muons and neutral hadrons. In the
summer of 2004, the BaBar Collaboration began replacing the RPCs
with Limited Streamer Tubes (LSTs). LST operation requires a mixture
of very pure gases and an operating voltage of 5500 V to achieve
maximum efficiency. In the past, the gas supplies obtained by the
BaBar Collaboration have contained contaminants that caused the
efficiency of the IFR LSTs to drop from approximately 90% to approximately
60%. Therefore, it was necessary to develop a method for testing
this gas for contaminants. An LST test system was designed and
built using two existing LSTs, one placed 1 cm above the other.
These LSTs detect cosmic muons in place of particles created during
the BaBar experiment. The effect of gas contamination was mimicked
by reducing the operating voltage of the test system in order to
lower the detection efficiency. When contaminated gas was simulated,
the coincidence rate and the percent coincidence between the LSTs
in the test system dropped off significantly, demonstrating that
test system can be used as an indicator of gas purity. In the fall
of 2006, the LST test system will be installed in the gas storage
area near the BaBar facility for the purpose of testing the gas
being sent to the IFR.
Monitoring Displays for GLAST: Building ISOC Status Displays for the Large
Area Telescope Aboard the Gamma Ray Large Area Space Telescope
(GLAST) Observatory. CHRISTINA KETCHUM (Lewis and Clark College, Portland, OR, 97219)
ROB CAMERON (Stanford Linear Accelerator Center, Stanford, CA, 94025)
In September
2007 the Gamma Ray Large Area Space Telescope (GLAST) is scheduled
to launch aboard a Delta II rocket in order to put two high-energy
gamma-ray detectors, the Large Area Telescope (LAT) and the GLAST
Burst Monitor (GBM) into low earth orbit. The Instrument Science
Operations Center (ISOC) at SLAC is responsible for the LAT operations
for the duration of the mission, and will therefore build an operations
center including a monitoring station at SLAC to inform operations
staff and visitors of the status of the LAT instrument and GLAST.
This monitoring station is to include sky maps showing the location
of GLAST in its orbit as well as the LAT’s projected field of view
on the sky containing known gamma-ray sources. The display also
requires a world map showing the locations of GLAST and three Tracking
and Data Relay Satellites (TDRS) relative to the ground, their
trail lines, and "footprint" circles indicating the range
of communications for each satellite. The final display will also
include a space view showing the orbiting and pointing information
of GLAST and the TDRS satellites. In order to build the displays
the astronomy programs Xephem, DS9, SatTrack, and STK were employed
to model the position of GLAST and pointing information of the
LAT instrument, and the programming utilities Python and Cron were
used in Unix to obtain updated information from database and load
them into the programs at regular intervals. Through these methods
the indicated displays were created and combined to produce a monitoring
display for the LAT and GLAST.
Monitoring Temperature and Fan Speed Using Ganglia and Winbond Chips. CAITIE MCCAFFREY (Cornell University, Ithaca, NY,
14850) YEMI ADESANYA (Stanford Linear Accelerator Center, Stanford,
CA, 94025)
Effective monitoring
is essential to keep a large group of machines, like the ones at
Stanford Linear Accelerator Center (SLAC), up and running. SLAC
currently uses Ganglia Monitoring System to observe about 2000
machines, analyzing metrics like CPU usage and I/O rate. However,
metrics essential to machine hardware health, such as temperature
and fan speed, are not being monitored. Many machines have a Winbond
w83782d chip which monitors three temperatures, two of which come
from dual CPUs, and returns the information when the sensor command
is invoked. Ganglia also provides a feature, gmetric, that allows
the users to monitor their own metrics and incorporate them into
the monitoring system. The programming language Perl is chosen
to implement a script that invokes the sensors command, extracts
the temperature and fan speed information, and calls gmetric with
the appropriate arguments. Two machines were used to test the script;
the two CPUs on each machine run at about 65º Celsius, which is
well within the operating temperature range (The maximum safe temperature
range is 77º -82º Celsius for the Pentium III processors being
used). Installing the script on all machines with a Winbond w83782d
chip allows the SLAC Scientific Computing and Computing Services
group to better evaluate current cooling methods.
Search for Mechanically-Induced Grain Morphology Changes in Oxygen Free Electrolytic
(OFE) Copper. JENNIFER SANDERS (Westminster College, Fulton, MO, 65251)
ROBERT KIRBY (Stanford Linear Accelerator Center, Stanford, CA, 94025)
The deformation
of the microscopic, pure metal grains (0.1 to > 1 millimeter)
in the copper cells of accelerator structures decreases the power
handling capabilities of the structures. The extent of deformation
caused by mechanical fabrication damage is the focus of this study.
Scanning electron microscope (SEM) imaging of a bonded test stack
of six accelerating cells at magnifications of 30, 100, 1000 were
taken before simulated mechanical damage was done. After a 2º -
3º twist was manually applied to the test stack, the cells were
cut apart and SEM imaged separately at the same set magnifications
(30, 100, and 1000), to examine any effects of the mechanical stress.
Images of the cells after the twist were compared to the images
of the stack end (cell 60) before the twist. Despite immense radial
damage to the end cell from the process of twisting, SEM imaging
showed no change in grain morphology from images taken before the
damage: copper grains retained shape and the voids at the grain
boundaries stay put. Likewise, the inner cells of the test stack
showed similar grain consistency to that of the end cell before
the twist was applied. Hence, there is no mechanical deformation
observed on grains in the aperture disk, either for radial stress
or for rotational stress. Furthermore, the high malleability of
copper apparently absorbed stress and strain very well without
deforming the grain structure in the surface.
Simulation of the BaBar Drift Chamber. RACHEL
ANDERSON (University of Wisconsin - Eau Claire, Eau Claire, WI,
54701) JOCHEN DINGFELDER (Stanford Linear Accelerator Center, Stanford,
CA, 94025)
The BaBar drift
chamber (DCH) is used to measure the properties of charged particles
created from e+ e- collisions
in the PEP-II asymmetric-energy storage rings by making precise
measurements of position, momentum and ionization energy loss (dE/dx). In October of 2005, the PEP-II storage rings operated with
a luminosity of 10x1033 cm-2 s-1; the goal for 2007 is a luminosity of 20x1033 cm-2s-1,
which will increase the readout dead time, causing uncertainty
in drift chamber measurements to become more significant in physics
results. The research described in this paper aims to reduce position
and dE/dx uncertainties by improving our understanding of the BaBar drift
chamber performance. A simulation program --- called GARFIELD---
is used to model the behavior of the drift chamber with adjustable
parameters such as gas mixture, wire diameter, voltage, and magnetic
field. By exploring the simulation options offered in GARFIELD,
we successfully produced a simulation model of the BaBar drift
chamber. We compared the time-to-distance calibration from BaBar
to that calculated by GARFIELD to validate our model as well as
check for discrepancies between the simulated and calibrated time-to-distance
functions, and found that for a 0° entrance angle there is a very
good match between calibrations, but at an entrance angle of 90° the
calibration breaks down. Using this model, we also systematically
varied the gas mixture to find one that would optimize chamber
operation, which showed that the gas mixture of 80:20 Helium:isobutane
is a good operating point, though more calculations need to be
done to confirm that it is the optimal mixture.
Simulations of the ILC Electron Gun and Electron Bunching System. CHRISTIAN HAAKONSEN (McGill University, Montreal,
QC, 0) AXEL BRACHMANN (Stanford Linear Accelerator Center, Stanford,
CA, 94025)
The International
Linear Collider (ILC) is a proposed electron-positron collider,
expected to provide insight into important questions in particle
physics. A part of the global R&D effort for the ILC is the
design of its electron gun and electron bunching system. The present
design of the bunching system has two sub-harmonic bunchers, one
operating at 108 MHz and one at 433MHz, and two 5-cell 1.3 GHz
(L-band) bunchers. This bunching system has previously been simulated
using the Phase and Radial Motion in Electron Linear Accelerators
(PARMELA) software, and those simulations indicated that the design
provides sufficient bunching and acceleration. Due to the complicated
dynamics governing the electrons in the bunching system we decided
to verify and expand the PARMELA results using the more recent
and independent simulation software General Particle Tracer (GPT).
GPT tracks the motion and interactions of a set of macro particles,
each of which represent a number of electrons, and provides a variety
of analysis capabilities. To provide initial conditions for the
macro particles, a method was developed for deriving the initial
conditions from detailed simulations of particle trajectories in
the electron gun. These simulations were performed using the Egun
software. For realistic simulation of the L-band bunching cavities,
their electric and magnetic fields were calculated using the Superfish
software and imported into GPT. The GPT simulations arrived at
similar results to the PARMELA simulations for sub-harmonic bunching.
However, using GPT it was impossible to achieve an efficient bunching
performance of the first L-band bunching cavity. To correct this,
the first L-band buncher cell was decoupled from the remaining
4 cells and driven as an independent cavity. Using this modification
we attained results similar to the PARMELA simulations. Although
the modified bunching system design performed as required, the
modifications are technically challenging to implement. Further
work is needed to optimize the L-Band buncher design.
Speeding up the Raster Scanning Methods used in the X-Ray Fluorescence Imaging
of the. MANISHA TURNER (Norfolk State University, Norfolk, VA, 23504)
UWE BERGMANN (Stanford Linear Accelerator Center, Stanford, CA, 94025)
Progress has
been made at the Stanford Linear Accelerator Center (SLAC) toward
deciphering the remaining 10-20% of ancient Greek text contained
in the Archimedes palimpsest. The text is known to contain valuable
works by the mathematician, including the Method of Mechanical
Theorems, the Equilibrium of Planes, On Floating Bodies, and several
diagrams as well. The only surviving copy of the text was recycled
into a prayer book in the Middle Ages. The ink used to write on
the goat skin parchment is partly composed of iron, which is visible
by x-ray radiation. To image the palimpsest pages, the parchment
is framed and placed in a stage that moves according to the raster
method. When an x-ray beam strikes the parchment, the iron in the
ink is detected by a germanium detector. The resulting signal is
converted to a gray-scale image on the imaging program, Rasplot.
It is extremely important that each line of data is perfectly aligned
with the line that came before it because the image is scanned
in two directions. The objectives of this experiment were to determine
the best parameters for producing well-aligned images and to reduce
the scanning time. Imaging half a page of parchment during previous
beam time for this project was achieved in thirty hours. Equations
were produced to evaluate count time, shutter time, and the number
of pixels in this experiment. On Beamline 6-2 at the Stanford Synchrotron
Radiation Laboratory (SSRL), actual scanning time was reduced by
one fourth. The remaining pages were successfully imaged and sent
to ancient Greek experts for translation.
The Effect of the Earth's Atmosphere on LSST Photometry. ALEXANDRA
RAHLIN (Massachusetts Institute of Technology, Cambridge, MA, 2139)
DAVID L. BURKE (Stanford Linear Accelerator Center, Stanford, CA,
94025)
The Large Synoptic
Survey Telescope (LSST), a ground-based telescope currently under
development, will allow a thorough study of dark energy by measuring,
more completely and accurately than previously, the rate of expansion
of the universe and the large-scale structure of the matter in
it. The telescope utilizes a broadband photometric system of six
wavelength bands to measure the redshifts of distant objects. The
earth's atmosphere makes it difficult to acquire accurate data,
since some of the light passing through the atmosphere is scattered
or absorbed due to Rayleigh scattering, molecular absorption, and
aerosol scattering. Changes in the atmospheric extinction distribution
due to each of these three processes were simulated by altering
the parameters of a sample atmospheric distribution. Spectral energy
distributions of standard stars were used to simulate data acquired
by the telescope. The effects of changes in the atmospheric parameters
on the photon flux measurements through each wavelength band were
observed in order to determine which atmospheric conditions must
be monitored most closely to achieve the desired 1% uncertainty
on flux values. It was found that changes in the Rayleigh scattering
parameter produced the most significant variations in the data;
therefore, the molecular volume density (pressure) must be measured
with at most 8% uncertainty. The molecular absorption parameters
produced less significant variations and could be measured with
at most 62% uncertainty. The aerosol scattering parameters produced
almost negligible variations in the data and could be measured
with >100% uncertainty. These atmospheric effects were found
to be almost independent of the redshift of the light source. The
results of this study will aid the design of the atmospheric monitoring
systems for the LSST.
Thermal Analysis of the ILC Superconducting Magnets. IAN ROSS
(Rose-Hulman Institute of Technology, Terre
Haute, IN, 47803)
JOHN WEISEND (Stanford Linear Accelerator Center, Stanford, CA, 94025)
Critical to a
particle accelerator’s functioning, superconducting magnets serve
to focus and aim the particle beam. The Stanford Linear Accelerator
Center (SLAC) has received a prototype superconducting quadrupole
designed and built by the Centro de Investigaciones Energticas,
Medioambientales y Tecnolgicas (CIEMAT) to be evaluated for the
International Linear Collider (ILC) project. To ensure proper functioning
of the magnet, the device must be maintained at cryogenic temperatures
by use of a cooling system containing liquid nitrogen and liquid
helium. The cool down period of a low temperature cryostat is critical
to the success of an experiment, especially a prototype setup such
as this one. The magnet and the dewar each contain unique heat
leaks and material properties. These differences can lead to tremendous
thermal stresses. The system was analyzed mathematically, leading
to ideal liquid helium and liquid nitrogen flow rates during the
magnet’s cool-down to 4.2 K, along with a reasonable estimate of
how long this cool-down will take. With a flow rate of ten gaseous
liters of liquid nitrogen per minute, the nitrogen shield will
take approximately five hours to cool down to 77 K. With a gaseous
helium flow rate of sixty liters per minute, the magnet will take
at least nineteen hours to cool down to a temperature of 4.2 K.
Upgrading the digital electronics of the bunch current monitors at the Stanford
linear accelerator center. JOSH KLINE
(Sacramento State, Sacramento, CA, 95813) ALAN FISHER (Stanford Linear Accelerator Center, Stanford, CA, 94025)
The testing of
the upgrade prototype for the bunch current monitors (BCMs) in
the PEP-II storage rings at the Stanford Linear Accelerator Center
(SLAC) is the topic of this paper. Bunch current monitors are used
to measure the charge in the electron/positron bunches traveling
in particle storage rings. The BCMs in the PEP-II storage rings
need to be upgraded because components of the current system have
failed and are known to be failure prone with age, and several
of the integrated chips are no longer produced making repairs difficult
if not impossible. The main upgrade is replacing twelve old (1995)
field programmable gate arrays (FPGAs) with a single Virtex II
FPGA. The prototype was tested using computer synthesis tools,
a commercial signal generator, and a fast pulse generator.
Using Boosted Decision Trees to Separate Signal and Background in B→Xsγ Decays. JAMES BARBER (University of Massachusetts, Amherst, Amherst, MA,
1003) PHILIP BECHTLE (Stanford Linear Accelerator Center, Stanford, CA, 94025)
The measurement
of the branching fraction of the flavor changing neutral current B→Xsγ transition can be used to expose physics outside the Standard
Model. In order to make a precise measurement of this inclusive
branching fraction, it is necessary to be able to effectively separate
signal and background in the data. In order to achieve better separation,
an algorithm based on Boosted Decision Trees (BDTs) is implemented.
Using Monte Carlo simulated events, `forests' of trees were trained
and tested with different sets of parameters. This parameter space
was studied with the goal of maximizing the figure of merit, Q,
the measure of separation quality used in this analysis. It is
found that the use of 1000 trees, with 100 values tested for each
variable at each node, and 50 events required for a node to continue
separating give the highest figure of merit, Q = 18.37.
X-ray photoelectron spectroscopy of GaP(1-x)N(x) photocorroded as a result
of hydrogen production through water electrolysis. MARIE
MAYER (University of Illinois
at Urbana Champaign, Urbana-Champaign, IL, 61801) ANDERS NILSSON (Stanford Linear Accelerator Center, Stanford, CA, 94025)
Photoelectrochemical
(PEC) cells produce hydrogen gas through the sunlight driven electrolysis
of water. By extracting hydrogen and oxygen from water and storing
solar energy in the H-H bond, they offer a promising renewable
energy technology. Addition of dilute amounts of nitrogen to III-V
semiconductors has been shown to dramatically increase the stability
of these materials for hydrogen production. In an effort to learn
more about the origin of semiconductor photocorrosion in PEC cells,
three samples of p-type GaP1-xNx (x = 0, 0.002, 0.02) were photocorroded and examined by X-ray
Photoelectron Spectroscopy (XPS). GaPN samples were observed to
be more efficient during the hydrogen production process than the
pure GaP samples. Sample surfaces contained gallium oxides in the
form of Ga2O3 and
Ga(OH)3 and
phosphorus oxide (P2O5),
as well as surface oxides from exposure to air. A significant shift
in intensity from bulk to surface peaks dramatic nitrogen segregation
to the surface during photoelectrochemical hydrogen production.
Further investigations, including using a scanning electron microscope
to investigate sample topography and inductively coupled plasma
mass spectroscopy (ICP-MS) analysis for solution analyses, are
under way to determine the mechanism for these changes.
