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Student
Abstracts at SLAC:
Building X-ray Diffraction Calibration Software. JOSHUA
LANDE (Marlboro College, Marlboro, VT, 05344) SAMUEL WEBB (Stanford Linear
Accelerator Center, Stanford, CA, 94025)
X-ray diffraction is a technique used
to analyze the structure of crystals. It records the interference pattern created
when x-rays travel through a crystal. Three dimensional structure can be inferred
from these two dimensional diffraction patterns. Before the patterns can be analyzed,
diffraction data must be precisely calibrated. Calibration is used to determine
the experimental parameters of the particular experiment. This is done by fitting
the experimental parameters to the diffraction pattern of a well understood crystal.
Fit2D is a software package commonly used to do this calibration but it leaves
much to be desired. In particular, it does not give very much control over the
calibration of the data, requires a significant amount of manual input, does
not allow for the calibration of highly tilted geometries, does not properly
explain the assumptions that it is making, and cannot be modified. We build code
to do this calibration while at the same time overcoming the limitations of Fit2D.
This paper describes the development of the calibration software and the assumptions
that are made in doing the calibration.
Bunch by Bunch Profiling with a Rotating X-Ray Mask. CHRISTOPHER
LEE (University of California, San Diego, La Jolla, CA, 92093) ALAN FISHER
(Stanford Linear Accelerator Center, Stanford, CA, 94025)
It is desirable to monitor the cross
sections of each positron bunch in the Low Energy Ring (LER) storage rings of
the Positron Electron Project II (PEP-II) located at the Stanford Linear Accelerator
Center. One method is to pass the x-rays given off by each bunch through a scintillator,
thereby studying a visible image. A rotating x-ray mask with three slots scans
the beam image in three different orientations, allowing us to mechanically collect
data to characterize and profile each image. Progress was made in designing the
x-ray mask, researching and procuring parts, as well as advancing project plans.
However, due to time constraints and difficulties in procuring special parts,
the full system was not completed. A simpler setup was built to test the hardware
as well as the feasibility of characterizing a circular image with a rotating
mask. A blinking green light emitting diode (LED) simulated a single positron
bunch stored in the LER ring. The selected hardware handled this simulation setup
well and produced data that led to a reasonable
estimation of the LED image diameter.
Calibration of the Camera of the LSST. ANDREW
SCACCO (University of Colorado, Boulder, CO, 80015) DAVID BURKE (Stanford
Linear Accelerator Center, Stanford, CA, 94025)
The camera of the Large Synoptic Survey
Telescope (LSST) is analyzed theoretically using the ZEMAX optical design software.
The purpose of this analysis is to have a theoretical model for the testing and
calibration of the optics before they are installed in the telescope. The most
effective way to perform this testing and calibration is also investigated. The
calibration of the lenses and sensors in the telescope will be performed using
either a highly focused laser beam or a filtered quartz lamp with a monochromator,
enabling very precise measurements to be made. The image the light source produces
on the focal plane of the camera will be compared to the image predicted by the
ZEMAX software and the optics and sensors for the camera will be adjusted until
the desired agreement is reached. The minimal size of the spot produced by the
light source is determined for a large sampling of angles and locations on the
focal plane. A spot size that matches the spot size of the point spread function
(PSF) of the telescope can be produced for light that strikes the focal plane
at its center or for light that strikes the focal plane parallel to the optical
axis of the camera, but not for light that strikes the focal plane off center
at a significant angle. This work is a starting point for the testing and calibration
of the LSST camera, which will be implemented and modified as necessary as the
camera is built, assembled and
tested.
Characterization of the Structure of Cation-Doped Bacteriogenic Uranium Oxides
using X-Ray Diffraction. JONATHAN
STAHLMAN (Carnegie Mellon University, Pittsburgh, PA, 15289) JOHN
BARGAR (Stanford Linear Accelerator Center, Stanford, CA, 94025)
Remediation of uranium
contamination in subsurface groundwater has become imperative as previous research
and manufacturing involving radionuclides has led to contamination of groundwater
sources. A possible in situ solution for sequestration of uranium is a bacterial process
in which Shewanella
oneidensis MR-1 reduces the soluble (and thus mobile) U(VI) oxidation state
into the less mobile UO2 crystalline phase. However, the long term stability of the UO2 compound
must be studied as oxidative conditions could return it back into the U(VI)
state. Incorporation of other cations into the structure during manufacture
of the UO2 could
alter the dissolution behavior. A wide angle x-ray scattering (WAXS) experiment
was performed to determine whether or not calcium, manganese, and magnesium
are incorporated into this structure. If so, the substituted atoms would cause
a contraction or expansion in the lattice because of their differing size,
causing the lattice constant to be altered. After several stages of data reduction,
the WAXS diffraction peaks were fit using the Le Bail fit method in order to
determine the lattice constant. Initial results suggest that there may be incorporation
of manganese into the UO2 structure
due to a .03 Å decrease in lattice constant, but more data is needed to confirm
this. The calcium and magnesium doped samples showed little to no change in
the lattice constant, indicating no significant incorporation into the structure.
Most importantly, this experiment revealed an artifact of the cleaning process
used to remove the bacteria from the sample. It appears the NaOH used to clean
the samples is contracting the lattice also by ~ .03 Å, but no physical explanation
is offered as of yet.
Characterizing Surface Layers in Ntininol Using X-ray Photoelectron Spectroscopy. REBECCA CHRISTOPFEL (Western Washington University,
Bellingahm, WA, 98225) APURVA MEHTA (Stanford Linear Accelerator Center,
Stanford, CA, 94025)
Nitinol is a shape memory alloy whose
properties allow for large reversible deformations and a return to its original
geometry. This nickel-titanium alloy has become a material used widely in the
biomedical field as a stent to open up collapsed arteries. Both ambient and biological
conditions cause surface oxidation in these devices which in turn changes its
biocompatibility. Depending on the type and abundance of the chemical species
on or near the surface, highly toxic metal ions can leak into the body causing
cell damage or even cell death. Thus, biocompatibility of such devices is crucial.
By using highly surface sensitive x-ray photoelectron spectroscopy to probe the
surface of these structures, it is possible to decipher both layer composition
and layer thickness. Two different samples, both of which were mechanically polished
with one then exposed to a phosphate buffered saline solution to mimic the chemical
properties of blood, were investigated. It was found that the latter sample had
a slightly thicker oxide layer and more significantly a phosphate layer very
near the surface suggesting toxic metal components are well contained within
the sample. These are considerable indications of a biocompatible
device.
Characterizing the Noise Performance of the KPiX ASIC Readout Chip. JEROME CARMAN (Cabrillo College, Aptos, CA, 95003)
TIMOTHY KNIGHT NELSON (Stanford Linear Accelerator Center, Stanford,
CA, 94025)
KPiX is a prototype front-end readout chip designed for the Silicon
Detector Design Concept for the International Linear Collider (ILC). It is targeted
at readout of the outer tracker and the silicon-tungsten calorimeter and is under
consideration for the hadronic calorimeter and muon systems. This chip takes
advantage of the ILC timing structure by implementing pulsed-power operation
to reduce power and cooling requirements and buffered readout to minimize material.
Successful implementation of this chip requires optimal noise performance, of
which there are two measures. The first is the noise on the output signal, previously
measured at 1500e-,
which is much larger
than the anticipated 500e-. The other is the noise on the trigger logic branch, which determines
where thresholds must be set in order to eliminate noise hits, thus defining
the smallest signals to which the chip can be sensitive. A test procedure has
been developed to measure the noise in the trigger branch by scanning across
the pedestal in trigger threshold and taking self-triggered data to measure the
accept rate at each threshold. This technique measures the integral of the pedestal
shape. Shifts in the pedestal mean from injection of known calibration charges
are used to normalize the distribution in units of charge. The shape of the pedestal
is fit well by a Gaussian, the width of which is determined to be 2480e-, far in excess of the expected noise. The variation of the noise
as a function of several key parameters was studied, but no significant source
has been clearly isolated. However, several problems have been identified that
are being addressed or are under further investigation. Meanwhile, the techniques
developed here will be critical in ultimately verifying the performance goals
of the KPiX chip.
Crystallographic studies of two bacterial antibiotic resistance enzymes: Aminoglycoside
Phosphotransferase (2’’)-Ic and GES-1 ß-lactamase. LAURA BYRNES (Rensselaer Polytechnic Institute, Troy, NY, 12180)
CLYDE SMITH (Stanford Linear Accelerator Center, Stanford, CA, 94025)
Guiana Extended-Spectrum-1
(GES-1)
and Aminoglycoside phosphotransferase (2’’)-Ic (APH(2’’)-Ic) are two bacteria-produced
enzymes that essentially perform the same task: they provide resistance to an
array of antibiotics. Both enzymes are part of a growing resistance problem in
the medical world. In order to overcome the ever-growing arsenal of antibiotic-resistance
enzymes, it is necessary to understand the molecular basis of their action. Accurate
structures of these proteins have become an invaluable tool to do this. Using
protein crystallography techniques and X-ray diffraction, the protein structure
of GES-1 bound to imipenem
(an inhibitor) has been solved. Also, APH(2’’)-Ic has been successfully crystallized,
but its structure was unable to be solved using molecular replacement using APH(2’’)-Ib
as a search model. The structure of GES-1, with bound imipenem was solved to
a resolution of 1.89Å, and though the inhibitor is bound with only moderate occupancy,
the structure shows crucial interactions inside the active site that render the
enzyme unable to complete the hydrolysis of the ß-lactam ring. The APH(2’’)-Ic
dataset could not be matched to the model, APH(2’’)-Ib, with which it shares
25% sequence identity. The structural information gained from GES-1, and future
studies using isomorphous replacement to solve the APH(2’’)-Ic structure can
aid directly to the creation of novel drugs to combat both of these classes of
resistance enzymes.
Definition of a Twelve-Point Polygonal SAA Boundary for the GLAST Mission. SABRA DJOMEHRI (University of California, Santa Cruz,
Santa Cruz, CA, 94024) MARKUS ACKERMANN (Stanford Linear Accelerator
Center, Stanford, CA, 94025)
The Gamma-Ray Large Area
Space Telescope (GLAST), set to launch in early 2008, detects gamma rays within
a huge energy
range of 100 MeV - 300 GeV. Background cosmic radiation interferes with such
detection resulting in confusion over distinguishing cosmic from gamma rays encountered.
This quandary is resolved by encasing GLAST’s Large Area Telescope (LAT) with
an Anti-Coincidence Detector (ACD), a device which identifies and vetoes charged
particles. The ACD accomplishes this through plastic scintillator tiles; when
cosmic rays strike, photons produced induce currents in Photomulitplier Tubes
(PMTs) attached to these tiles. However, as GLAST orbits Earth at altitudes ~550km
and latitudes between -26° and 26°, it will confront the South Atlantic Anomaly
(SAA), a region of high particle flux caused by trapped radiation in the geomagnetic
field. Since the SAA flux would
degrade the sensitivity of the ACD’s PMTs over time, a determined boundary enclosing
this region need be attained, signaling when to lower the voltage on the PMTs
as a protective measure. The operational constraints on such a boundary require
a convex SAA polygon with twelve edges, whose area is minimal ensuring GLAST
has maximum observation time. The AP8 and PSB97 models describing the behavior
of trapped radiation were used in analyzing the SAA and defining a convex SAA
boundary of twelve sides. The smallest possible boundary was found to cover 14.58%
of GLAST’s observation time. Further analysis of defining a boundary safety margin
to account for inaccuracies in the models reveals if the total SAA hull area
is increased by ~20%, the loss of total observational area is < 5%. These
twelve coordinates defining the SAA flux region are ready for implementation
by the GLAST satellite.
Determining the Extent of Delocalization in Mixed-Valence Iron Dimers Using
x-ray Absorption Spectroscopy. ALISON
HOYT (Yale University, New Haven, CT, 06520) KELLY GAFFNEY (Stanford
Linear Accelerator Center, Stanford, CA, 94025)
This study examines the
extent of charge delocalization in mixed valence compounds. Understanding the
structure of charge delocalization is the first step in understanding the local
dynamics of charge transfer. This insight has diverse applications such as
the ability to mimic biological reactions and to enhance solar technology.
Because of its fast time scale, synchrotron radiation was used to probe the
iron K-edge for three organometallic systems. In these complexes, two bridged
metal atoms share an effective charge of 5+. In a Robin-Day Class II compound,
charge is localized and the two iron atoms have effective oxidation states
of 2+ and 3+ respectively. For Class III delocalized compounds each metal center
has an effective charge of 2.5+. Class II/III compounds exhibit characteristics
of both localized and delocalized systems according to various optical spectroscopies.
Synchrotron radiation was used to study charge distribution in these poorly-understood
Class II/III intermediate systems. In the limit of absolute localization, spectra
of the mixed valence species were expected to be a linear combination of the
reduced and oxidized species. For the delocalized case, a linear combination
was not expected. These two cases were used as calibration limits to determine
the extent of delocalization in the unknown Class II/III compound. Results
showed that synchrotron radiation classifies the Class II/III compound as localized.
However, data also demonstrated that the linear combination model did not hold
as expected and a revised model is necessary to better understand this phenomenon.
Determining the Local Structure of Platinum Streptidine using X-Ray Absorption
Spectroscopy. MICHAELLE MAYALU (Massachusetts Institute of Technology,
Cambridge, MA, 02139) SERENA DEBEER GEORGE (Stanford Linear
Accelerator Center, Stanford, CA, 94025)
X-Ray absorption
spectroscopy (XAS) is a technique that utilizes high energy X-rays
commonly obtained from synchrotron radiation to determine the structure
of known and unknown substances and materials. By examining the absorption
vs. energy pattern, one can determine the local structure surrounding
the absorbing atom. Analysis of a region of the absorption vs. energy
graph called extended x-ray absorption fine structure (EXAFS) leads
to information about the identity of the atoms surrounding the absorber,
the number of atoms surrounding the absorber, and the distances between
the absorber and neighboring atoms. Using XAS, structural descriptions
of platinum streptidine, a newly synthesized platinum anti-cancer agent,
have been obtained. The results show that the platinum is in fact coordinated
to the streptidine, which was the main question that needed to be answered
about
the drug.
Electromagnetic Interference from the ILC Beams. LAVONDA
BROWN (Norfolk State University, Norfolk, VA, 23504) GARY BOWER (Stanford
Linear Accelerator Center, Stanford, CA, 94025)
Electromagnetic interference
is an emerging problem of the future. This investigation analyzed the data collected
from airborne radiation waves that caused electronic devices to fail. This investigation
was set up at SLAC in End Station A and the data collected from the electromagnetic
waves were received from antennas. In order to calibrate the antennas it required
a signal generator to transmit the signals to the antenna and a digital oscilloscope
to receive the radiation waves from the other antenna. The signal generator that
was used was only able to generate signals between 1 and 1.45 GHz; therefore,
the calibrations were not able to be completed. Instead, excel was used to create
a curve fitting for the attenuation factors that were already factory calibrated.
The function from the curve fitting was then used to extend the calibrations
on the biconical and yagi antennas. A fast Fourier Transform was then ran in
Matlab on the radiation waves received by the oscilloscope; in addition, the
attenuation factors were calculated into the program to show the actual amplitudes
of these radiation waves. For future research, the antennas will be manually
calibrated and the results will be reanalyzed.
Fast Track Finding in the ILC's Proposed SiD Detector. DAVID
BAKER (Carnegie Mellon University, Pittsburgh, PA, 15289) DR. NORMAN
GRAF (Stanford Linear Accelerator Center, Stanford, CA, 94025)
A fast track finder is presented
which,
unlike its more efficient, more computationally costly O(n3) time counterparts,
tracks particles in O(n) time (for n being the number of hits). Developed as
a tool for processing data from the ILC’s proposed SiD detector, development
of this fast track finder began with that proposed by Pablo Yepes in 1996 [1]
and adjusted to accommodate the changes in geometry of the SiD detector. First,
space within the detector is voxellated, with hits assigned to voxels according
to their r, f, and coordinates. A hit on the outermost layer is selected, and
a "sample space" is built from the hits in the
selected hit’s surrounding voxels. The hit in the sample space with the smallest
distance to the first is then selected, and the sample space recalculated for
this hit. This process continues until the list of hits becomes large enough,
at which point the helical circle in the x, y plane is conformally mapped to
a line in the x’, y’ plane, and hits are chosen from the sample spaces of the
previous fit by selecting the hits which fit a line to the previously selected
points with the smallest 2. Track finding terminates when the innermost layer
has been reached or no hit in the sample space fits those previously selected
to an acceptable 2. Again, a hit on the outermost layer is selected and the
process repeats until no assignable hits remain. The algorithm proved to be very
efficient on artificial diagnostic events, such as one hundred muons scattered
at momenta of 1 GeV/c to 10 GeV/c. Unfortunately, when tracking simulated events
corresponding to actual physics, the track finder’s efficiency decreased drastically
(mostly due to signal noise), though future data cleaning programs could noticeably
increase its efficiency on these events.
ILC Electron Source Injector Simulations. MANU LAKSHMANAN
(Cornell University, Ithaca, NY, 14853) AXEL BRACHMANN (Stanford Linear
Accelerator Center, Stanford, CA, 94025)
As part of the global project
aimed
at proposing an efficient design for the ILC (International Linear Collider),
we simulated possible setups for the electron source injector, which will provide
insight into how the electron injector for the ILC should be designed in order
to efficiently accelerate the electron beams through the bunching system. This
study uses three types of software: E-Gun to simulate electron beam emission,
Superfish to calculate solenoidal magnetic fields, and GPT (General Particle
Tracer) to trace charged particles after emission through magnetic fields and
subharmonic bunchers. We performed simulations of the electron source injector
using various electron gun bias voltages (140kV – 200kV), emitted beam lengths
(500ps – 1ns) and radii (7mm – 10mm), and electromagnetic field strengths of
the first subharmonic buncher (5 – 20 MV/m). The results of the simulations show
that for the current setup of the ILC, a modest electron gun bias voltage (~140kV)
is sufficient to achieve the required bunching of the beam in the injector. Extensive
simulations of parameters also involving the second subharmonic buncher should
be performed in order to gain more insight into possible efficient designs for
the ILC electron source injector.
Improving LER Coupling and Increasing PEP-II Luminosity with Model-Independent
Analysis. LACEY KITCH (Massachusetts Institute of Technology,
Cambridge, MA, 02139) YITON YAN (Stanford Linear Accelerator Center,
Stanford, CA, 94025)
The PEP-II storage ring at SLAC houses
electrons (in the High-Energy Ring, or HER) and positrons (in the Low-Energy
Ring, or LER) for collision. The goal of this project was to improve the linear
optics of the LER in order to decrease coupling, thereby decreasing emittance
and increasing luminosity. To do this, we first took turn by turn BPM (Beam Position
Monitor) data of a single positron bunch at two betatron resonance excitations,
extracted orbits from this data using Model-Independent Analysis, and from these
orbits formed a virtual model of the accelerator. We then took this virtual model
and found an accelerator configuration which we predicted would, by creating
vertical symmetric sextupole bumps and adjusting the strengths of several key
quadrupole magnets, improve the coupling and decrease the emittance in the LER.
We dialed this configuration into the LER and observed the coupling, emittance,
and luminosity. Coupling immediately improved, as predicted, and the y emittance
dropped by a dramatic 40%. After the HER was adjusted to match the LER at the
Interaction Point (IP), we saw a
10% increase in luminosity, from 10.2 x 1033 cm-2sec-1 to
11.2 x 1033 cm-2sec-1,
and achieved a record
peak specific luminosity.
Long-term X-ray Variability of NGC 4945. AMARA
MILLER (University of California, Davis, Davis, CA, 95616) GRZEGORZ MADEJSKI
(Stanford Linear Accelerator Center, Stanford, CA, 94025)
Though short-term X-ray variability
has been studied for the active galaxy NGC 4945, long-term studies promise to
contribute to our understanding of the processes involved in accretion onto supermassive
black holes. In order to understand the relationship between black hole mass
and breaks in the power spectral density (PSD), the long-term X-ray variability
of NGC 4945 was studied over the energy range 8-30 keV. Observations occurred
over the year 2006 using the Rossi X-ray Timing Explorer.
The data was reduced using the package FTOOLS, most notably the scripts Rex and
faxbary. Light curves were produced and a PSD was obtained using a Fast Fourier
Transform algorithm. Preliminary studies of the light curve show greater X-ray
variability at higher frequencies. This result complements previous studies of
NGC 4945 by Martin Mueller. However, the PSD produced must go through further
study before accurate results can be obtained. A way to account for the window
function of the PSD must be found before the behavior at lower frequencies can
be studied with accuracy and the relationship between black hole mass and the
break in NGC 4945's PSD can be better understood. Further work includes exploration
into ways to subtract the window function from the PSD, as well as a closer analysis
of the PSD produced by averaging the data into logarithmic bins. The possibility
of a better way to bin the data should be considered so that the window function
would be minimized.
Measurements of High-Field THz Induced Photocurrents in Semiconductors. MICHAEL WICZER (University of Illinois, Urbana, IL,
61801) AARON LINDENBERG (Stanford Linear Accelerator Center, Stanford,
CA, 94025)
THz pulses have provided
a useful tool for probing, with time resolution, the free carriers in a system.
The development
of methods to produce intense THz radiation has been slow since spectroscopists
and condensed matter physicists first began probing materials with THz pulses.
We have developed a method for producing intense ultra-short THz pulses, which
have full width half maximum
of 300 fs – approximately a half cycle of THz radiation. These intense half cycle
pulses (HCPs) allow us to use THz radiation not only as a probe of the free carriers
in a system but also as a source of excitation to alter a system in some way.
In particular, HPCs perturb free carriers considerably in short time scales but
show minimal effect to individual free carriers over long time. By exposing the
semiconductor indium antimonide (InSb) to our intense THz HCP radiation, we have
observed non-linear optical effects which suggest the generation of new free
carriers by below band-gap THz photons. This generation of free carriers appears
to be caused by an avalanche multiplication process, which should amplify the
number of free carriers already in the system and then induce a current in the
timescale of our THz pulse. This amplification on such a short timescale suggests
the possibility of an ultra-fast detector of weak above band-gap radiation. We
constructed a device which detects these currents by painting an electrode structure
on the surface of the semiconductor. The currents induced across the electrodes
by this avalanche multiplication process were measured and compared with other
measurements of this non-linear optical process. We successfully measured THz
induced currents in InSb, which indicate promise towards the development of an
ultra-fast detector, and we gain insight into a possible physical explanation
of the THz induced free carriers we observe in InSb.
Measuring Strain Using X-Ray Diffraction. JAMES
BELASCO (Villanova University, Villanova, PA, 19085) APURVA MEHTA (Stanford
Linear Accelerator Center, Stanford, CA, 94025)
Determining the strain
in a material has often been a crucial component in determining the mechanical
behavior and integrity of a structural component. While continuum mechanics
provides a foundation for dealing with strain on the bulk scale, how a material
responds to strain at the very local level-the understanding of which is fundamental
to the development of a cohesive framework for the behavior of strained material-is
still not well understood. One of the critical components in determination
of the behavior of materials under strain at a local scale is an understanding
how global average deformation, as a response to an externally applied load,
gets distributed locally. This is critical and very poorly understood for a
polycrystalline materials-the material of choice for a large variety of structural
components. We studied this problem for BCC iron using x-ray diffraction. By
using a nanocrystalline iron sample and taking x-ray diffraction patterns at
different load levels and at different rotation angles, a complete 2nd rank
strain tensor was determined for the three sets of crystallites with three
distinct crystallographic orientations. The determination of the strain tensors
subsequently allowed the calculation of the elastic modulus along each crystallographic
plane. When compared to measured values from single crystal for the corresponding
crystal orientations, the data from our polycrystalline sample demonstrated
a higher degree of correlation to the single crystal data than expected. The
crystallographic planes demonstrated a high degree of anisotropy, and therefore,
to maintain displacement continuity, there must be a secondary mode of strain
accommodation in a regime that is conventionally
thought to be purely elastic.
Optical and Mechanical Design Features of the Qweak Main Detector. ELLIOTT JOHNSON (North Dakota State University, Fargo,
ND, 58105) JAMES SPENCER (Stanford Linear Accelerator Center, Stanford,
CA, 94025)
Photonic Band-Gap (PBG) fibers are
a periodic array of optical materials arranged in a lattice called a photonic
crystal. The use of PBG fibers for particle acceleration is being studied by
the Advanced Accelerator Research Department (AARD) at Stanford Linear Accelerator
Center. By introducing defects in such fibers, e.g. removing one or more capillaries
from a hexagonal lattice, spatially confined modes suitable for particle acceleration
may be created. The AARD has acquired several test samples of PBG fiber arrays
with varying refractive index, capillary size, and length from an external vendor
for testing. The PBGs were inspected with a microscope and characteristics of
the capillaries including radii, spacing, and errors in construction were determined.
Transmission tests were performed on these samples using a broad-range spectrophotometer.
In addition, detailed E-field simulations of different PBG configurations were
done using the CUDOS and RSOFT codes. Several accelerating modes for different
configurations were found and studied in detail.
Simulation of Neutron Backgrounds from the ILC Extraction Line Beam Dump. SIVA DARBHA (University of Toronto, Toronto, ON, M5S
1A1) TAKASHI MARUYAMA (Stanford Linear Accelerator Center, Stanford,
CA, 94025)
The operation of the International
Linear Collider (ILC) as a precision measurement machine is dependent upon the
quality of the charge-coupled device (CCD) silicon vertex detector. A neutron
flux of 1010 neutrons/cm2 incident upon the vertex detector will degrade its
performance by causing displacement damage in the silicon. One source of a neutron
background arises from the dumping of the spent electron and positron beams into
the extraction line beam dumps. The Monte Carlo program FLUKA was used to simulate
the collision of the electron beam with the dump and to determine the resulting
neutron fluence at the interaction point (IP). A collimator and tunnel were added
and their effect on the fluence was analyzed. A neutron source was then generated
and directed along the extraction line towards a model of the BeamCal, vertex
detector, and beampipe to determine the neutron fluence in the silicon layers
of the detector. Scattering in the BeamCal and beampipe was studied by manipulating
the composition of the BeamCal. The fluence in the first silicon layer for the
current tungsten BeamCal geometry was corrected according to a 1 MeV equivalent
silicon displacement damage to obtain a comparable value for the damage done
to the CCD vertex detector. The IP fluence was determined to be 3.65*1010 +/-
2.34*1010 neutrons/cm2/year when the tunnel and collimator were in place, with
no appreciable increase in statistics when the tunnel was removed. The BeamCal
was discovered to act as a collimator by significantly impeding the flow of neutrons
towards the detector. The majority of damage done to the first layer of the detector
was found to come from neutrons with a direct line of sight from the quadrupole,
with only a small fraction scattering off of the beampipe and into the detector.
The 1 MeV equivalent neutron fluence was determined to be 1.85*109 neutrons/cm2/year
when the positron beam was considered, or 9.27*108 neutrons/cm2/year by one beam
alone, which contributes 18.5% of the threshold value in one year. Future work
will improve the detector model by adding the endcap sections of the silicon
detector, and will study in detail the neutron scattering off of the tunnel walls.
Other sources of neutron backgrounds will also be analyzed, including electron-positron
pairs, Beamstrahlung photons, and radiative Bhabha scattering, in order to obtain
a complete picture of the overall
neutron damage done to the vertex detector.
Structure of ZnO Nanorods using X-Ray Diffraction. MARCI
HOWDYSHELL (Albion College, Albion, MI, 49224) MICHAEL TONEY (Stanford
Linear Accelerator Center, Stanford, CA, 94025)
Many properties of zinc oxide, including
wide bandgap semiconductivity, photoconductivity, and chemical sensing, make
it a very promising material for areas such as optoelectronics and sensors. This
research involves analysis of the formation, or nucleation, of zinc oxide by
electrochemical deposition in order to gain a better understanding of the effect
of different controlled parameters on the subsequently formed nanostructures.
Electrochemical deposition involves the application of a potential to an electrolytic
solution containing the species of interest, which causes the ions within to
precipitate on one of the electrodes. While there are other ways of forming zinc
oxide, this particular process is done at relatively low temperatures, and with
the high amount of x-ray flux available at SSRL it is possible to observe such
nucleation in situ. Additionally, several parameters can be controlled using
the x-ray synchrotron; the concentration of Zn2+ and the potential applied were
controlled during this project. The research involved both gathering the X-ray
diffraction data on SSRL beamline 11-3, and analyzing it using fit2d, Origin
6.0 and Microsoft Excel. A time series showed that both the in-plane and out-of-plane
components of the ZnO nanorods grew steadily at approximately the same rate throughout
deposition. Additionally, analysis of post-scans showed that as potential goes
from less negative to more negative, the resulting nanostructures become more
oriented.
Study of KS Production With The BaBar Experiment. THOMAS
COLVIN (The Ohio State University, Columbus, OH, 43201) JOCHEN DINGFELDER
(Stanford Linear Accelerator Center, Stanford, CA, 94025)
We study the inclusive production of
short-lived neutral kaons KS with the BaBar experiment at the Stanford Linear Accelerator
Center. The study is based on a sample of 383 million B-Bbar pairs produced in
e+e- collisions
at the Y(4S) resonance, in which one B meson has been fully reconstructed. We
select a clean
sample of KS mesons and compare kinematic spectra for data and simulation.
We find that the simulation overestimates the total production rate of KSand
we see differences
in the shape of the KS momentum spectra. We derive correction factors for different
momentum intervals to bring the simulation into better agreement with the observed
data.
Surveying and Mapping for a Localized GIS. INDIA
CALHOUN (Savannah State University, Savannah, GA, 31414) BRIAN FUSS
(Stanford Linear Accelerator Center, Stanford, CA, 94025)
The Alignment Engineering
Group (AEG) is responsible for an extensive array of alignment and positioning
activities at the Stanford Linear Accelerator Center (SLAC). In particular,
the location of accelerator components using specialized tools and data adjustment
procedures are the center mission(s) of the group. My established goals for
this project are to accurately measure a set of buildings known as Forte Apache
to produce a 3-dimensional CAD drawing that will be used to create a 2-dimensional
Geographic Information Systems (GIS). Computer Aided Design (CAD) is the use
of a wide range of computer-based tools that assist engineers, architects and
other design professionals in their design activities [5]. Overall, in the
project, I will construct a 2-dimensional GIS that can be used to analyze relationships
between features.
What the Formation of the First Stars Left in its Wake. CHRISTENE
LYNCH (Gettysburg College, Gettysburg, PA, 17325) MARCELO ALVAREZ (Stanford
Linear Accelerator Center, Stanford, CA, 94025)
The formation of the first stars marked
a crucial transition in the formation of structure in the universe. Through their
feedback effects, which include ionization by their radiation and the supernovae
or black holes formed at the end of their lives, they were able to influence
the evolution of their surroundings. In this paper we present a new visualization
and use analytical calculations in order to study the influence of these first
stars. The visualization was created using both Enzo, a simulation program that
uses adaptive mesh refinement, and Amira, a 3D volume rending program. The visualization
allows for a better understanding of the impact these stars had on their surroundings
and conveys the importance of these stars to a broader audience. The analytical
calculations used investigate the possibility that black holes left by the first
stars could be seeds for the
109 solar mass black holes seen as quasars at redshift z~6. We found
that if a remnant black hole was to begin Eddington accretion at z~20 they will
be able to form the 109 solar mass quasars by z~6 but that there is likely to be a delay
in the onset of accretion onto the seed black hole because of the radiative feedback
of its progenitor. Future, more detailed, numerical calculations will be necessary
to understand whether the black holes left by the first stars could possibly
be seeds for quasar formation.
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