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Student
Abstracts at TJNAF:
Construction and Commissioning of a Micro-Mott Polarimeter for Photocathode
Research and Development. APRIL COOK (Monmouth College, Monmouth, IL, 61462) MARCY STUTZMAN (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
Thomas Jefferson National Accelerator
Facility uses polarized electrons to further the understanding of the atomic
nucleus. The polarized source produces electrons by directing laser light onto
a specially prepared gallium arsenide (GaAs) photocathode. During the course
of this project, an off-beamline micro-Mott polarimeter has been built and commissioned
within the Source Lab for photocathode research and development. A polarimeter
measures the polarization, or spin direction, of electrons. The micro-Mott runs
at 30 keV and can be used directly in the Source Lab, off of the main accelerator
beamline. Construction of the Mott system began with a polarized source, which
consists of a vacuum chamber complete with a cesiator and nitrogen triflouride
(NF3) to activate the photocathode, residual gas analyzer (RGA), ultra-high vacuum
pumps, an electrostatic deflector to bend the electron beam 90 degrees, and electrostatic
lenses. The polarimeter is housed in an adjacent vacuum chamber. The circularly
polarized laser light enters the polarized source, hits the GaAs photocathode,
and liberates polarized electrons. The original longitudinally-polarized electrons
are transformed into transversely-polarized electrons by the electrostatic bend.
They are then directed onto a gold target inside the Mott and scattered for data
analysis. The polarized source has been commissioned, achieving photoemission
from the activated GaAs crystal, and the electrostatic optics have been tuned
to direct the electrons onto the gold target. Nearly ten percent of the electrons
from the photocathode reach the target, giving adequate current for polarization
measurement. The micro-Mott polarimeter will aid in photocathode research and
pre-qualification of material for use in the injector.
Density Measurements of a 3He Target Cell. SARA MOHON
(College of William
and Mary, Williamsburg, VA, 23186) JIAN-PING CHEN (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
The discovery and study of elementary
particles in nature has always been attractive to scientists. The spin structure
of a neutron is one such popular study and typically involves collisions between
a high energy electron beam and a neutron target. At the Thomas Jefferson National
Accelerator Facility (TJNAF) in Virginia,
glass cells full of Helium-3 (3He) serve as effective polarized neutron targets in its particle
accelerator. A nucleus of 3He has two protons and one neutron. Typically, ninety percent
of a 3He
sample has two protons with opposite spins so that the overall spin of the nucleus
is determined by the spin of the neutron. Before experiments can begin, characteristics
of the cell must be measured and determined including its 3He
density. The purpose of this project was to describe how to measure the density
of 3He
target cells. A laser and optics setup was used to measure how much laser light
the 3He
would absorb within the target cell at certain frequencies and temperatures.
At each temperature, the data was curve-fitted using Root, and statistically
analyzed to give a density measurement. As expected, the wider the absorption,
the larger the density of 3He within the cell. Also, the density of the cell was
larger
at higher temperatures. These density measurements will be used to calculate
the cell’s maximum polarization, correct data measurements from the particle
accelerator experiment, and help further investigate the spin structure of the
neutron. In the future, improvements concerning cell alignment in the oven should
be made to provide more accurate results.
Design and Implementation of a Sulfur Hexafluoride Gas Transfer System for
the Free Electron Laser (FEL) Gun Test Stand. BRIAN
TUCKER (Virginia Tech, Blacksburg, VA, 23435)
KEVIN JORDAN (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
Jefferson Lab’s Free
Electron Laser (FEL) program is currently developing a photocathode test
gun to benchmark the performance of new gun technology for eventual use in
free electron lasers. The gun uses a 500 kV DC high voltage power supply
(HVPS) that connects to a high voltage stack held in a pressure vessel. When
the HVPS is being used, the vessel is filled with pressurized sulfur hexafluoride
(SF6),
a non-toxic, non-flammable gas that suppresses electrical discharges. Because
a full vessel of SF6 costs
approximately $4,000, the gas needs be recycled so that the vessel can be
opened without loss of gas. The goal of this project is to develop a system
to transfer gas between the pressure vessel and a storage bag without significant
loss of gas or contamination. A similar system has been used in the FEL vault
for the past eight years. Analyzing the old design revealed ways to improve
the gas transfer process. These improvements were used to select the new
system’s components. Finally, designs were made to fit the system into the
Gun Test Stand vault and to mount the components to the wall. The resulting
design improves the old system by implementing a more user friendly layout,
automating the entire process, and taking advantage of more advanced pumps
and valves. Improving the recycling of
SF6 saves
time and money, while helping to ensure smooth gun operation and make HVPS maintenance
routine. For now, the new system will serve as an important part of the testing
process for the photocathode test gun. Eventually, the changes will be used to
upgrade
the system in the FEL vault.
Developing a Tree Search Algorithm for Track Reconstruction in the Hall A BigBite
Spectrometer. BRANDON BELEW (Rensselaer Polytechnic Institute, Troy, NY, 12180)
OLE HANSEN (Thomas Jefferson National Accelerator Facility, Newport
News, VA, 23606)
In many experiments that
involves particle collisions, the ability to track the paths of the particles
is essential. In the Hall A BigBite Spectrometer at the Thomas Jefferson National
Accelerator Facility (JLab), wire drift chambers are used to detect these paths.
For each individual measurement, there is an associated hit pattern that shows
which detector bins were activated by the particles traveling through the drift
chamber. The track information can be reconstructed from the hit pattern with
the help of software. The current algorithm uses a brute-force method to analyze
all possible ways of connecting lines through the hits. This has been sufficient
thus far, but future experiments will need faster performance because the expected
rates and particle multiplicities will be higher and a larger number of wire
planes will be used. The HERMES Spectrometer at the Deutsches Elektronen-Synchrotron
uses a much more efficient tree search algorithm. The goal of this project
was to implement such an algorithm for use at JLab. The code developed for
this project was written based on a general description of the HERMES algorithm.
It compares the associated hit pattern to a pre-generated database of all possible
patterns that could be produced by particles moving in a straight line, arranged
in a branching structure of increasing resolution. This tree structure allows
for logarithmic rather than linear comparison time. It has been demonstrated
to work with a high level of accuracy using Monte Carlo simulations. For a
sufficiently high detector resolution and reasonably low levels of simulated
background noise, the algorithm was shown to very quickly match all the simulated
tracks and to produce very few “ghost tracks,” or false positives. In the future,
this algorithm will be moved out of the testing phase and integrated with JLab's
existing software to be used on a regular basis. The increased speed of this
new matching algorithm will make many future experiments possible.
Implementing and Testing a Data Acquisition System for use with the BigBite
Spectrometer. BRENT TERRES (Old Dominion University, Norfolk, VA, 23508) DR. ROBERT MICHAELS (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
Nuclear physics
experimentation relies on particle detectors whose analog signals must
be digitized and archived by a data acquisition (DAQ) system. A DAQ
system must digitize, format, and store all required data from an experiment
so that it can be retrieved later for in depth analysis. At the Jefferson
National Accelerator Facility, DAQ systems are implemented using the
CEBAF Online Data Acquisition (CODA) system, a set of hardware and
software devices developed specifically for nuclear physics experimentation.
This project involved the implementation and testing of a new multi-crate
DAQ for the BigBite Spectrometer, in Hall A at Jefferson Lab, to be
used for a series of experiments to run in 2008. A trigger supervisor,
a custom device that coordinates and synchronizes the data, was implemented.
Next, deadtime, the time during which the hardware is busy and cannot
record data, was minimized for application with the BigBite spectrometer
and was found to be consistent with expectation. Finally, an analysis
program was created that quickly checked the data for missing or extra
hits, verified the synchronization of the data, and measure the deadtime.
It was determined that a functioning DAQ system could be built for
use with the BigBite spectrometer that would both meet the specification
and make use of two design standards for redundancy. Also, it was determined
that the DAQ system would be suitable for use with the BigBite Spectrometer.
The DAQ system developed meets and exceeds the specifications required
by the experiment. A properly functioning DAQ system will provide researchers
with a high quantity of precise data when
using the BigBite detector.
Measurement of Density of Polarized 3He Target Cell Using Laser Interferometer. ANDREW LEISTER (The College of William and Mary, Williamsburg, VA, 23187) JIAN-PING CHEN (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
As scientists continue to learn more
about fundamental matter, they are trying to fully understand the structure of
nucleons (protons and neutrons). One of the difficulties in studying the neutron
structure is that the isolated neutron decays after approximately ten minutes
and is therefore not ideal for experimentation. Fortunately, it has been found
that the structure of polarized Helium-3 (3He)
allows it to serve as an effective polarized neutron target for studying neutron
spin-structure.
This is because the spins of the two protons in 3He are anti-aligned about 90% of the time. Therefore the remaining
spin is derived entirely from the neutron. There are several factors that determine
the maximum polarization of a target 3He
cell, one of the key factors being the density of the cell. The focus of this
study is to determine
an accurate value for the density of a target 3He
cell, "Aaron". To calculate the density, a laser with a specified frequency
range was projected
through the 3He target cell while the intensity was read by a photo-diode.
This data was then read by the LabView and Root programs which generated a Lorentzian
curve to fit the data. One of the parameters of this Lorentzian curve is directly
proportional to the density of the cell. It was found that the density of the
target cell was 8.547 ± .333 amagats (amg) at sufficiently high temperatures.
Since the density of the cell is now known, the maximum polarization of the cell
can be determined. With this value known, there is greater knowledge of the characteristics
of "Aaron" and the results of further experiments with the cell can
be understood more fully. This will ultimately lead to a deeper understanding
of the spin-structure of nucleons.
Monitoring Patient motion During Head Single Photon Emission Computed Tomography
Imaging. GEVORG STEPANYAN (Hampden-Sydney College,
Hampden Sydney, va, 23606) STAN MAJEWSKI (Thomas Jefferson National
Accelerator Facility, Newport News, VA, 23606)
Patient motion during head
single photon emission computed tomography (SPECT) could adversely affect the
resolution in diagnostic imaging. The sudden movements compromise the high
spatial resolution capabilities of the SPECT imager. To eliminate the image
degradation through shifts in the six degrees of freedom, a motion compensation
technique is required. The goal of this project is to provide real time tracking
with sub-millimeter accuracy of patient motion. The Vicra system uses two infrared
(IR) position sensors that track passive IR reflections. The Vicra system was
placed to track the retro reflective markers positioned on the head of the
patient. This stereo-infrared system provided excellent results from the tracking,
of the six degrees of freedom, with errors well within the proposed limits.
The 3D root mean square error was .101mm. The full width at half max error
was lower then that of the SPECT gamma camera. Analysis of other methods of
patient motion tracking suggests that regular stereo-optical tracking systems
do not provide the accuracy and repeatability that the Vicra system does. The
data obtained using the Vicra system can be utilized for patient motion compensation
during SPECT image reconstruction. Image reconstruction allows for an accurate
diagnostic of the administered radiopharmaceutical source. The specific goal
of this project is to assist in monitoring 131Iodine treatment of glioblastoma multiform using a high resolution
SPECT gamma camera.
Ohmic Heating of Gallium Arsenide Photocathodes. MATT WOOD
(Fort Hays State University, Hays, KS, 67601) MARCY L.
STUTZMAN (Thomas Jefferson National Accelerator Facility, Newport
News, VA, 23606)
The polarized electron beam
at Thomas Jefferson National Accelerator Facility (Jefferson Lab) is produced
using photoemission
from a gallium arsenide (GaAs) cathode. To turn a GaAs crystal into a photocathode,
it must be heated to above
500°C to clean the surface, then “activated” using chemicals applied to the surface.
At Jefferson Lab, the crystal is heated by conduction using commercial heaters;
however, because of a lack of resources, universities and smaller government
labs must heat crystals through ohmic heating by passing current through the
crystal. These labs have not been successful in using special strained GaAs crystals
that can provide high polarization. The goal of this project was to determine
if ohmically heating high polarization GaAs crystals can produce a quantum efficiency
that is comparable to crystals heated conductively. The two heating methods were
compared in the same vacuum conditions, and the effectiveness of each was assessed
by monitoring the photoemission from each cathode. The resistive heating method
was found to be comparable to the conductive heating method for high polarization
crystals. As expected, the vacuum quality and thermal conductivity are the likely
reasons that other labs have not had success with high polarization crystals.
This suggests that in order to produce high polarization electron beams, other
labs need to focus on improving the quality of their vacuum.
Parameterization of Polarized 3He Quasi-Elastic Scattering Cross Sections. OCTAVIAN GEAGLA (University
of Virginia, Charlottesville, VA, 22905) XIAOCHAO ZHENG (Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
The substructure of the atom can be
revealed in electron scattering experiments through the analysis of the scattering
cross-section. The scattering can be determined as elastic, quasi-elastic, and
inelastic from the relative size of the energy loss of the electron and the four-momentum
transfer squared of the virtual photon. In quasi-elastic scattering, each proton
and neutron reacts to the electron beam independently. In order to apply radiative
corrections to the 3He
nucleus, an accurate parameterization of these cross-sectional data are needed.
Current world parameterizations do not have access to polarized quasi-elastic
scattering cross-sections for the 3He nucleus, but instead use data from other nuclei and combine
them with theoretical predictions for the polarized 3He nucleus. However, 3He nuclear effects are neglected. This leads to great discrepancies
and uncertainties in the results. In order to perform the parameterization, various
computational methods were used to create a physical model of the scattering
using magnetic and electric form factors which would not neglect the 3He nuclear effects. The Jefferson Lab National Accelerator Facility
data were fit to various nonlinear distribution models and the best fits were
found for each beam energy. A global fit was created by fitting the parameters
of these distributions. These results can be used to predict polarized quasi-elastic
cross sections for unmeasured kinematics and for applying radiative corrections
where such parameterizations are needed.
PDF Contributions and Parity Violation at High Bjorken x. TIMOTHY
HOBBS (The University of Chicago, Chicago, IL, 60637) WALLY MELNITCHOUK
(Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
In recent decades, leptonic
deep inelastic scattering (DIS) has been widely used to probe nucleon structure.
Despite continued
success, a number of surprising results have complicated the original picture
of a quark-dominated nucleon. Among the most significant recent studies of parton
distributions, the European Muon Collaboration (EMC) and NuTeV at Fermilab have
challenged these old assumptions in nuclear structure. Problematically, precision
data characterizing the d-quark parton distribution function (PDF) and the PDF
ratio d/u at high values (i.e. > 0.7) of the momentum fraction (Bjorken x)
are fairly incomplete. Calculations of the d/u PDF ratio contribution to parity-violating
asymmetries in unpolarized DIS are performed for a range of values of the square
momentum transfer Q2; for completeness, calculations involve several PDF models and
target/polarization schemes for the neutral/electromagnetic interference current.
So far, models demonstrate a significant dependence of beam asymmetries upon
the d/u PDF ratio -- a confirmation of theoretical expectation. This evaluation
of PDF effects through d/u concurs with and expands earlier findings in nucleon
structure, thereby driving further interest and tests of the Quark-Parton Model
(QPM). Moreover, these calculations complement a discussion of parity and charge
symmetry violation with implications for ongoing study in sub-nuclear theory.
Reviving and Upgrading of the eP Device. IDAYKIS
RODRIGUEZ (Florida International University, Miami, FL, 33199)
DR. DOUGLAS W. HIGINBOTHAM (Thomas Jefferson National Accelerator Facility, Newport
News, VA, 23606)
At Thomas Jefferson National
Accelerator Facility, an electron beam is used to probe the fundamental properties
of the nucleus. In these experiments, it is essential to know the precise energy
of the beam. An important instrument along the beamline to measure the beam
energy is the eP device. The device measures the scattered electron angle and
the recoil proton angle of an elastic collision. From these angle measurements,
the beam energy can be calculated. The eP device components such as computer
software, controls, and mechanical parts needed to be upgraded and/or replaced
in order for the eP device to be operational again. A research study was conducted
of the current hydrogen target and its properties as well as alternate targets
for better performance. An analysis was also done on potential changes to the
position of the electron and proton detectors for the 12 GeV upgrade because
eP can only measure energies up to 5.5 GeV. Calculations show that for the
new energy upgrade,
electron detectors need to be positioned
at 50 above and below the beamline to measure the energy of 11 GeV.
Another two proton detectors need to be placed at an angle of 49.20 above
and below the beamline to measure energies of 6.6 GeV and 8.8 GeV. With these
changes the eP device will measure the range of new energies from 2.2 GeV to
11GeV. From the target research studies it was found that a carbon nanotube mixture
with polypropylene could be the ideal target for the eP device because of its
high thermal conductivity
and it’s high hydrogen content. The changes made to the eP device demonstrate
the importance of continued research and new technologies.
Roughness Analysis of Variously Polished Niobium Surfaces. GUILHEM
RIBEILL (North Carolina State University, Raleigh, NC, 27606) CHARLES
REECE (Thomas Jefferson National Accelerator Facility, Newport News,
VA, 23606)
Niobium superconducting radio
frequency (SRF) cavities have gained widespread use in accelerator systems. It
has been
shown that surface roughness is a determining
factor in the cavities’ efficiency and maximum accelerating potential achievable
through this technology. Irregularities in the surface can lead to spot heating,
undesirable local electrical field enhancement and electron multipacting. Surface
quality is typically ensured through the use of acid etching in a Buffered Chemical
Polish (BCP) bath and electropolishing (EP). In this study, the effects of these
techniques on surface morphology have been investigated in depth. The surface
of niobium samples polished using different combinations of these techniques
has been characterized through atomic force microscopy (AFM) and stylus profilometry
across a range of length scales. The surface morphology was analyzed using spectral
techniques to determine roughness and characteristic dimensions. Furthermore,
electrical impedance spectroscopy (EIS) was used to investigate the electrical
properties of the niobium-acid interaction during electropolishing. Experimentation
has shown that the spectral method is a valuable tool that provides quantitative
information about surface roughness at different length scales, and has explored
the use of EIS in electropolishing. It has demonstrated that light BCP pretreatment
and lower electrolyte temperature favors a smoother electropolish. These results
will allow for the design of a superior polishing process for niobium SRF cavities
and therefore increased accelerator operating efficiency and power.
Silicon Photo Multiplier for Scintillation Hodoscope. ERIK SKAU
(North Carolina State University, Raleigh, NC, 27695) STEPAN STEPANYAN
(Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
Photon counting is a key component
in many high energy physics experiments. With the silicon photo multiplier (SiPM),
a type of multi-pixel photon counter (MPPC), previous obstacles such as magnetic
fields are being surmounted. Though operating at a relatively low voltage (~70V),
high gain (~106) should be expected of a SiPM. The focus of this study was to
determine if the efficiency of a SiPM with 1mm active area is suitable for charged
particle detection in a scintillator layer, read out via green wavelength shifting
fiber. A test setup was designed to study the efficiency of a Hamamatsu SiPM
system. By situating a SiPM on the end of the green wavelength shifting fiber
attached to a scintillator, the MPPC was able to detect the light generated by
charged particles passing through the scintillators. Experiments demonstrated
that the efficiency of the SiPM setup was an acceptable value. The one millimeter
active area is sufficient for detecting photons from a scintillator to wavelength
shifting fiber system. With the advantage of being unaffected by magnetic fields,
unlike photomultiplier tubes, MPPCs may quickly become an alternative. With the
diversity of newly developed MPPC available, scientists are now able to extend
previous experimental boundaries.
Simulating Multipacting in Tapered Waveguides using Xing RK4. DAN ZOU
(University Of Wisconsin - Madison, Madison, WI, 53706) HAIPENG WANG
(Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606)
Radio frequency (RF) waveguides
propagate and couple high RF power that is used to accelerate charged particles
over short
distances. Under certain resonant conditions in the waveguide, this high power
can lead to undesirable discharging, or multipacting, consuming the RF power
and possibly damaging the waveguide. One method of preventing multipaction is
by avoiding these specific resonant conditions, which are most efficiently found
by using appropriate computer simulation software. Xing RK4, written in FORTRAN,
is one such software, though originally limited to rectangular waveguide analysis.
The purpose of this study was to port Xing RK4 to C++, then to expand it to analyze
multipaction in tapered waveguides. Expansion of Xing focused primarily on deriving
appropriate empirical and analytic formulae for the electromagnetic (EM) fields
within tapered structures. The majority of other necessary functions were inherited
from the original code, slightly modified to accommodate the new geometry. EM
field implementation was not completed due to time constraints and complexity
of the analysis. Once completed, however,
Xing RK4’s new capabilities will allow scientists to determine the resonant conditions
to avoid when using tapered RF waveguides and to benchmark other simulation codes.
Additional accuracy may be achieved through further fine-tuning of the analytic
formulae.
Testing a Novel Laser Polarimeter Design. JOAN DREILING
(Fort Hays State University, Hays, KS, 67601) MARCY STUTZMAN (Thomas
Jefferson National Accelerator Facility, Newport News, VA, 23606)
Polarized electron beams are used at
Thomas Jefferson National Accelerator Facility to study the properties of nuclei.
When circularly polarized light of the appropriate wavelength illuminates a gallium
arsenide cathode, polarized electrons are emitted. Right-hand circularly polarized
light excites electrons of one spin polarization state, and left-hand circularly
polarized light excites the opposite spin polarization state. The polarization
of the electrons is typically measured with complex polarimeters, either in the
lab or in the accelerator and experimental halls. A novel polarimetry technique
was explored to determine if a simple optical setup could be used to measure
polarization of the electron beam from a gallium arsenide cathode. A pump and
probe system similar to those in atomic absorption spectroscopy was employed.
A circularly polarized pump laser was used in an attempt to deplete one polarization
state of the crystal, while the probe laser was varied between the same and opposite
circular polarizations. If the pump laser depleted one polarization state, the
probe laser would cause additional photocurrent only when the two lasers had
opposite polarizations. It was found that the photocurrent did not vary when
the polarization of the probe laser was changed. The absence of a statistically
significant difference in photocurrent suggests that depletion of electron states
was not achieved. Therefore, this proposed easy and low cost method of polarimetry
is not feasible, and the more complex polarimeters are still required when knowledge
of electron beam polarization is needed.
The Assembly and Testing of the BigBite Hadron Detector System. GORDON LOTT (Virginia Tech, Blacksburg, VA, 24061)
DOUGLAS HIGINBOTHAM (Thomas Jefferson National Accelerator Facility,
Newport News, VA, 23606)
Scintillator detectors
are a basic part of nuclear and high energy physics research. When a charged
particle passes through a scintillator, it creates photons. The photons travel
to the ends of the scintillator and into photomultiplier tubes (PMTs) which
turn the photons into an electric pulse. The BigBite Hadron particle detector
package has a scintillator plane made of two layers of 24 scintillator bars.
This project focuses on this detector package which will be used in a Thomas
Jefferson National Accelerator Facility Hall A experiment next year and its
scintillator plane and electronics needed to be assembled. All the PMTs were
connected to labeled high voltage (HV) cables and signal cables. The signal
cables were connected to a series of nuclear instrument modules (NIM) which
amplify the signal and convert the analog signal to a digital signal. The
different NIM modules needed for logic and triggering were arranged and cabled
in an organized fashion for easy troubleshooting and repair. The HV cables
were connected to LeCroy high voltage supplies. The whole system was tested
with cosmic rays to find problems. This assembly and testing put the detector
in complete working order and verified the quality of the set up. The prepared
package can now be moved into Hall A for the experiment.
Use of RF and Digital Signal Processing for Beam Position Monitoring. SARA CARR (Rochester Institute of Technology, Rochester,
NY, 14623) JOHN MUSSON (Thomas Jefferson National Accelerator Facility,
Newport News, VA, 23606)
A Beam Position Monitor (BPM)
is a useful device because it accurately detects the location of an electron
beam at very low current. A BPM coupled with a Beam Current Monitor (BCM), located
in Hall A of the Continuous Electron Beam Accelerator Facility (CEBAF), originates
the analog signal on three channels: an X-position, a Y-position, and a current
channel. The BPM detects the output voltage proportional to the product of current
and position, while the BCM detects the voltage proportional to current. It was
believed that the quotient of the two signals would result in the position of
the beam. The purpose of this project was to attain a good resolution by optimizing
signal-to-noise ratio; this was accomplished by limiting the bandwidth of the
noise. With the use of RF signaling and digital filtering, the bandwidth was
configured using a Field Programmable Gate Array (FPGA), a small integrated microprocessor.
Using Altera Analog Hardware Description Language (AHDL) a coded block diagram
of digital logic was programmed onto the chip. Once the bandwidth was limited
to the desired frequency, the current channel was divided into the X-position
channel resulting in the beam’s position on that plane. It was shown that a low
current run of 50nA could be detected with 100µm of resolution by limiting the
bandwidth to 5kHz. This was accomplished with a series of digital filters that
were able to cut the frequency with a method called decimation. In order to detect
different magnitudes of current, there was a second filtering path with a bandwidth
of 100kHz, that measured current runs up to 40µA. The design of the system can
easily be tailored to the needs of Users by implementing different firmware to
the FPGA, which is both time and cost effective.
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