1,721,017 research outputs found
Testbed for X-band multipactor investigation
No full textThe multipactor effect is studied in X-band waveguide-like geometries. A
plug and play testbed was designed to allow for quick changing of different ge-
ometries and materials. To detect multipactor events global detection methods
are used. These methods include phase detection via a double-balanced mixer
and power measurements. Phase detection allows for detection of multipactor by
comparing the phase of incident and through waves in the testbed. Once multi-
pactor events occur, the through waves will experience phase shift, and this will
be visible on the mixer output. Power measurements allow for detection of mul-
tipactor formation via observation of the through power and reflected power in
reference to the testbed.
Multipactor thresholds for a stepped impedance transformer, operated at
9.6 GHz, were measured with powers in the kW to tens of kW range. The effects of
surface conditioning via electron impact were also studied with an interest on the
mitigation of multipactor. This is achieved through changes to the SEY of the test
material by scrubbing from multipacting electrons. To achieve this the system was
rep rating, causing multipactor events to happen frequently. This method showed
good improvements in thresholds with a 50% increase in threshold values from
the start to end of testing.Embargo status: Restricted until 09/2023. To request the author grant access, click on the PDF link to the left
High Power Microwave Breakdown of C4F7N (Novec 4710) Gas Mixtures
No full textThe quest for sustainable and environmentally friendly alternatives to sulfur hexafluoride (SF) as an insulating gas in high voltage applications has prompted extensive research efforts in recent years. Among the promising alternatives, CFN has emerged as a potential candidate due to its superior insulation and dielectric properties. While previous research concerning breakdown characteristics of CFN has been mainly focused on long-timescale DC and 60 Hz AC conditions, this thesis aims to investigate the breakdown behavior of CFN under high power microwave (HPM) conditions and establish a correlation with SF. The breakdown strength of gas mixtures comprised of 5\%, 10\%, and 20\% CFN in a N or CO background were examined under pulsed, microsecond HPM conditions at room temperature, spanning a pressure range of 16 psia to 32 psia (110.3 kPa to 220.6 kPa). This thesis provides comprehensive background information on HPM breakdown, outlines the development of the Texas Tech traveling-wave ring resonator, and presents an analysis of the dielectric strength of CFN based admixtures within the experimental system.Embargo status: Restricted until 09/2173. To request the author grant access, click
on the PDF link to the left
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Multipactor mitigation in S-band waveguide
No full textTo investigate multipactor, a rectangular waveguide testbed was designed
for S-band frequencies with the broad wall dimension matching the standard
WR-284 waveguide geometry. Setting the waveguide height to 5.5 mm yielded
a frequency-gap product susceptible to multipactor. One of the test sources, a
coaxial magnetron, provides test input power at a frequency of 2.85 GHz with a
peak power output of 4 MW and 3.5 μs pulse width. The other, an RF solid-state
source using GaN HEMTs, delivers a pulse width of 100 μs with a test input power
of 3 kW to compare threshold power. The two sources were used to access an input
power range of 3 kW to 4 MW. Two diagnostic methods were implemented,
the first being local detection via an electron multiplier tube and the second a
global detection via power couplers. At power levels tested (MW) and a 5.5 mm
gap, low multipactor orders (N = 1) are observed, whereas an order of N = 9
is observed at the lower power level. To suppress multipactor, previous numerical
simulations of the geometry have shown that adding a grooved structure to
one of the broadsides aids in mitigating multipactor. In this case, grooves are
machined into the broadside wall in the direction of propagation, which avoids
a series of impedance mismatching and large E-field perturbations. The efficacy
of this mitigation technique was experimentally evaluated. Experimentally, there
were distinct differences between the standard case (smooth broadside wall) and
the case with grooves in multipactor delay and magnitude. The improvement in
power transmitted before multipactor onset occurred was about 13%.Embargo status: Restricted until 09/2023. To request the author grant access, click on the PDF link to the left
The sensitivity of PBX 9501 and PBX 9502 to milling and sawing
No full textExplosive driven pulsed power research benefits from modern polymer-bonded high explosives (HE). In practical application, high precision in the dimensional shape is required, and high machining speeds are desired. The limits of machining speed, driven mainly by the thermal response of the energetic material, are investigated. Specifically, the thermal response of PBX 9501 (95% HMX, 2.5% Estane, 2.5% BDNPA-F) and PBX 9502 (95% TATB, 5% Kel F-800) under conventional milling and sawing methods is examined.
The presented work focuses on face milling performed with dry machining on a CNC, remote-controlled milling machine. The primary parameters of interest are the spindle speed (RPM), feed rate (IPM), step size (% dia.), depth of cut (inches), and endmill diameter (inches). The temperature of the system is monitored via high-speed infrared (IR) videography and near the cutting interface with a K-type thermocouple inserted into the endmill’s through-coolant channel. Operational forces and torques are recorded by a 6-axis force sensor mounted beneath the HE samples.
An experimental setup for sawing into PBX is also presented. A dual-column horizontal band saw has been modified for remote control operations. Similar to the milling setup, the temperature of the system is measured using a high-speed IR camera and K-type thermocouples. Forces and torques are measured using a 6-axis force sensor mounted beneath the HE samples, with a fixed rail mounted in between the HE and the force sensor to allow the cutting “slice” thickness to be adjusted with each test.
An empirical relationship between temperature and the milling parameters is presented. Overall, milling regimes exist outside of DOE-STD-1212-2019 for which milling temperatures remain well below the HE critical temperatures.Embargo status: Restricted until 06/2172. To request the author grant access, click on the PDF link to the left
A Study of Charge Decay on Dielectrics in Varying Atmospheric Conditions
No full textElectrostatic surface charge decay on dielectrics and metals was investigated to determine loss mechanisms, the effect of humidity, as well as enclosure size and material. This work focuses on charging dielectric surfaces close to the electrical breakdown threshold in atmospheric air for humid and dry conditions. After initial charging of the spheres to up to 30 kV, the associated surface charge is allowed to decay due to recombining with ions from the natural background, resulting in decay waveforms ranging from minutes to hours to days. Spheres of 100 mm diameter of varying materials (PTFE and metal as reference) were charged and tested, with minimal measurement interference, at relative humidities of 10%, 35%, and 64%. Investigating the dependence of charge decay behavior on enclosure size revealed a pronounced slowdown of the charge recombination for enclosure sizes below one cubic meter. For the smallest investigated enclosure, 0.1 cubic meters, the charge recombination time increased from less than one hour to 16 hours. Additional experiments focused on the ion-ion pair production rate and charge carrier density compared to ambient air and enclosures. The impact of air convection on charge decay in the open air (no enclosure) is discussed. The humidity noticeably affected the charge decay on both groups of spheres; metal and dielectric. The charge on the PTFE sphere decay took approximately 25 minutes to decay to 50% of its charging voltage in 35% R.H., while the charge decayed to merely 66% in 10% R.H. during the same time period. The experimental results are discussed, acknowledging that humidity also influences the supporting rod that holds the spheres in place. Finally, the number of available charge carriers in the air is assessed in detail, and background pair production rates are shown to be humidity dependent, ranging from 10 cm−3s−1 to 24 cm−3s−1.Embargo status: Restricted until 09/2173. To request the author grant access, click
on the PDF link to the left
Two-color pyrometer measurement of stainless steels due to relativistic electron beam heating in VHV/UHV environments
No full textTemperature measurement of SS anodes is of particular importance for Sandia
National Laboratories. This is because the theory of SS anode outgassing is thought to
be a function of temperature increase. To investigate the temperature of the stainless
steel anode without the need for an absolute calibration a two-color pyrometer has
been implemented. Using the ratio between two IR passbands along with two separate
photodetectors a temperature vs. time graph can be plotted based upon Planck’s
blackbody radiation law. Overall, an improved understanding of the temperature
increase of stainless steel anodes will allow future scientists and engineers to make
cost-effective and intelligent designs in vacuum environments when performing high
energy discharge experiments.Embargo status: Restricted until 06/2172. To request the author grant access, click on the PDF link to the left
Thermal analysis of skidding energetic materials
No full textDetailed is the investigation of the thermal behavior of high explosives (HE). Temperature is determined by measuring the thermal infrared radiation emitted PBX 9501 and PBX 9502 during skidding over a sapphire surface. Skidding is referred to as the act of impacting a surface with forces oblique to the surface. This skidding is performed on an apparatus that allows individual control over normal force, surface velocity, and presence of grit particles. The HE is attached to an I-beam where mechanical strain is measured and converted to force. Experiments are verified with a Phantom VEO710s high-speed visible camera, capable of recording up to 680,000 fps with a 7 GHz pixel clock. A FLIR X6901sc high-speed mid-wave infrared (MWIR) camera is used to measure the temperature of the skidding HE. PBX 9501 and PBX 9502 are semi-transparent in the MWIR regime, posing a difficult task in determining their temperatures from measured thermal radiation. Accurate temperature readings require knowledge of the absorption coefficients of the HE, and the temperature gradients produced from skidding. Experiments with the FLIR camera and a thermal radiator were performed to estimate the absorption coefficient of the HE. COMSOL simulations were implemented to estimate temperature gradients beneath the surface.Embargo status: This title is currently under embargo. Request a copy through the form linked to the left, or by emailing [email protected]. You can also contact the author directly
Design and Characterization of an Explosive Opening Switch for Flux Compression Generator Applications
No full textThe study of an explosive opening switch (EOS), including the design and build of a test bed, is discussed in this thesis. An explosive opening switch (EOS) operates on the principle of a conductor’s mechanical destruction from the detonation of a high explosive (HE). Specifically, an explosive opening switch acting as a circuit disconnect capable of a 200 kA pulse just before opening and a voltage hold off of 50 kV for 100 us after opening is studied with application in a multipulse FCG. The EOS under discussion differs from the traditional use of EOSs, including but not limited to current pulse sharpening and power conditioning, with typical applications in MCGs and FCGs, or other explosive-type generators. This research considers two configurations of EOSs: a cylindrical EOS with detonating cord as the HE core and copper/aluminum tubing as the outer conductor and a flat configuration with copper/aluminum foil laying flat over detonating cord. Varying lengths and thicknesses of the conductors are studied. The switches’ effectiveness is studied using voltage and current measurements and high-speed imaging. This thesis discusses in detail a testbed comprised of a 36 uF capacitor, EOS housing structure, 50 kV pulse supply, high-speed cameras, and other equipment and tools for diagnostics and explosive detonation. This thesis contributes to the overall better understanding of explosive opening switches. Further, it reveals a sense of EOS parameters for applications where a circuit disconnect or circuit isolation is needed.Embargo status: Restricted until 01/2174. To request the author grant access, click on the PDF link to the left
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