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A monolithic 120 GHz free-space, continuous-wave source capable of providing 10 dBm of EIRP at 11.1 percent DC-to-EIRP conversion efficiency is presented.
A continuous wave Light Detection and Ranging (CW LiDAR) system utilizes two or more laser frequencies and time or range shifted pseudorandom noise (PN) codes to discriminate between the laser frequencies. The performance of these codes can be improved by subtracting out the bias before processing. The CW LiDAR system may be mounted to an artificial satellite orbiting the earth, and the relative strength of the return signal for each frequency can be utilized to determine the concentration of selected gases or other substances in the atmosphere.
The addition of spin-polarized, continuous-wave (c.w.) positron beams to the 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) would provide a significant capability to the experimental nuclear physics program at Jefferson Lab. Based on bremsstrahlung and pair-production in a high-Z target, the positron source requires a 120 MeV spin-polarized c.w. electron beam of several milliamperes. While the beam dynamics of the high-current electron beam are tenable, sustaining this current for weeks of user operations requires an unprecedented charge lifetime from a high-polarization GaAs-based photocathode. A promising approach to exceed the kilocoulomb charge lifetime barrier is reducing the ion back-bombardment fluence at the photocathode. By increasing the laser size and managing the emittance growth with an adequate cathode/anode design, significantly enhanced charge lifetime may be achieved. Based upon a new simulation model that qualitatively explains the lifetime data previously measured at different spot sizes, we describe the practical implications on the parameter space available for a kilocoulomb-lifetime polarized photogun design.
The addition of spin-polarized, continuous-wave (c.w.) positron beams to the 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) would provide a significant capability to the experimental nuclear physics program at Jefferson Lab. Based on bremsstrahlung and pair-production in a high-Z target, the positron source requires a 120 MeV spin-polarized c.w. electron beam of several milliamperes. While the beam dynamics of the high-current electron beam are tenable, sustaining this current for weeks of user operations requires an unprecedented charge lifetime from a high-polarization GaAs-based photocathode. A promising approach to exceed the kilocoulomb charge lifetime barrier is reducing the ion back-bombardment fluence at the photocathode. By increasing the laser size and managing the emittance growth with an adequate cathode/anode design, significantly enhanced charge lifetime may be achieved. Based upon a new simulation model that qualitatively explains the lifetime data previously measured at different spot sizes, we describe the practical implications on the parameter space available for a kilocoulomb-lifetime polarized photogun design.
We employ a 77–81 GHz frequency-modulated continuous-wave (FMCW) millimeter-wave radar to sense anomalous vibrations during vehicle transport at highway speeds for the first time. Secure metallic containers can be breached during transport by means of drilling into their sidewalls but detecting a drilling signature is difficult because the large vibrations of transport drown out the small vibrations of drilling. For the first time, we demonstrate that it is possible to use a non-contact millimeter-wave radar sensor to detect this micron-scale intrusive drilling while highway-speed vehicle movement shakes the container. With the millimeter-wave radar monitoring the microdoppler signature of the container’s vibrating walls, we create a novel signal-processing pipeline consisting of range–angle tracking, time–frequency analysis, horizontal stripe image convolution, and principal component analysis to create a robust and powerful detection statistic to alarm if drilling is present. To support this pipeline, we develop a statistical model combining the vibrating container and the random vibrations induced by vehicle movement to explore the robustness of the sensor’s detection capabilities. The presented results strongly support the inclusion of a millimeter-wave radar vibration sensor into a transport security system.
A baseline concept for a continuous wave (CW) polarized positron injector was developed for the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. This concept is based on the generation of CW longitudinally polarized positrons by a high-current, polarized electron beam (1 mA, 130‑370 MeV, and 90% longitudinal polarization) that passes through a rotating, water-cooled, tungsten target. The simulation results for the Ce+BAF injector at the Low Energy Recirculator Facility (LERF) are presented, including positron beam generation, capture, energy selection, and acceleration to 123 MeV. The positron yield (or positron current) and longitudinal polarization are calculated considering the longitudinal and transverse CEBAF acceptances (<1% energy spread, <1 mm bunch length and normalized emittance of <100 mm mrad). The impact of target thickness, drive electron beam energy, and transverse size on positron yield within the required emittance limit is evaluated.
A baseline concept for a continuous wave (CW) polarized positron injector was developed for the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. This concept is based on the generation of CW longitudinally polarized positrons by a high-current, polarized electron beam (1 mA, 130-370 MeV, and 90% longitudinal polarization) that passes through a rotating, water-cooled, tungsten target. The positron yield and longitudinal polarization are calculated for the 123 MeV Ce+BAF injector at the Low Energy Recirculator Facility (LERF). The longitudinal and transverse CEBAF acceptances, defined as an energy spread of less than 1% and a normalized emittance of less than 100 mm·mrad, have been used in these calculations. The impact of target thickness, transverse electron beam size, and electron beam energy on the yield and polarization of a positron injector is evaluated. The total energy deposited by the beams in the tungsten target and the peak energy density are calculated for different target thicknesses, electron beam sizes, and energies.
A baseline concept for a continuous wave (CW) polarized positron injector was developed for the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab [1]. This concept is based on positron beam generation by a high current polarized electron beam (1 mA, 120 MeV, >85% polarization) irradiating a 4 mm thick rotating water-cooled tungsten target or liquid metal target. The update on the development of the Ce+BAF injector concept including the polarized electron source, the development of high power targets, simulations of positron capture, the design of the transport line from the positron injector to the CEBAF North Linac and the planned experiment to measure the upper limits of transverse and longitudinal emittances accepted by the 12 GeV CEBAF optics are presented. [1] J. Grames et al., "Positron beams at Ce+BAF", in Proc. 14th Int. Particle Accelerator Conf. (IPAC’23), Venice, Italy, MOPL152, pp. 896–899 (2023). doi:10.18429/JACoW-IPAC2023-MOPL152
In the recent years, continuous-wave (CW) near-field and lens-focused millimeter wave imaging systems have been effectively. used to demonstrate their utility for producing high-resolution images of metallic structures covered with spray on foam insulation (SOFI) such as the space shuttle external tank. These systems have produced images with a spatial resolution of approximately 2 mm at a frequency of 150 GHz, and can easily interrogate thin as well as thick SOFI (> 9") enabling detection and evaluation of flaws such as voids, disbands, delaminations and corrosion. These systems are relatively simple, inexpensive, easy-to-use, require little to no signal processing of the raw data, on-site friendly, real-time and small. However, for some specific structures a certain interference pattern may be superimposed on the produced images. Generally, this occurs when the SOFI surface is at a relatively significant angle with respect to the surface of the substrate (or other sub-structures) on which it is sprayed. Consequently, the reflection from the surface of the SOFI and that from the substrate (or sub-structure) coherently combine into an interference pattern as the SOFI surface is scanned. There are methods by which the influence of this unwanted interference can be reduced, such as the incorporation of an incidence angle and the proper use of signal polarization. This paper presents the basics of this problem and describes the use of the methods for reducing this unwanted influence through several specific examples. A discussion on how the use of a swept-frequency or pulsed method may also alleviate this problem is also presented.
A first principles theory is developed to study the nonlinear spatial evolution of a near-resonance triad of instability waves in boundary layer transition. This triad consists of a plane wave at fundamental frequency and a pair of symmetrical, oblique waves at the subharmonic frequency. A low frequency, high Reynolds number asymptotic scaling leads to a distinct critical layer where nonlinearity first becomes important; the development of the triad's waves is determined by the critical layer's nonlinear, viscous dynamics. The resulting theory is fully nonlinear in that all nonlinearly generated oscillatory and nonoscillatory components are accounted for. The presence of the plane wave initially causes exponential of exponential growth of the oblique waves. However, the plane wave continues to follow the linear theory, even when the oblique waves' amplitude attains the same order of magnitude as that of the plane wave. A fully interactive stage then comes into effect when the oblique waves exceed a certain level compared to that of the plane wave. The oblique waves react back on the fundamental, slowing its growth rate. The oblique waves' saturation results from their self-interaction - a mechanism that does not require the presence of the plane wave. The oblique waves' saturation level is independent of their initial level, but decreases as the obliqueness angle increases.
Electromagnetic ion cyclotron (EMIC) waves are understood to be one of the dominant drivers of relativistic electron loss from Earth's radiation belts. Theory predicts that the associated gyroresonant wave‐particle interaction results in a distinct energy‐dependent “bite‐out” signature in the normalized flux distribution of electrons as they are scattered into the loss cone. We identify such signatures along with the responsible EMIC waves captured in situ by the Van Allen Probes on 15–16 February 2017. Using the cold plasma approximation, we predict the pitch‐angle cutoffs for the scattering signature for the captured EMIC wave and find it in good agreement with the observed electron bite‐out scattering signature. Employing the close conjunction between the Van Allen Probes and THEMIS during this time, we explore the temporal and spatial evolution of the scattering signature, as well as the surrounding wave activity, and find that the scattering signature formed during continued wave activity over a period less than a day. These results are consistent with wave‐particle interaction theory and support the hypothesis that EMIC waves are an important mechanism for rapid relativistic electron loss from the radiation belts.
In the recent years, continuous-wave near-field and lens-focused millimeter wave imaging systems have been effectively used to demonstrate their utility for producing high-resolution images of metallic structures covered with spay on foam insulation (SOFI) such as the Space Shuttle external fuel tank. However, for some specific structures a certain interference -pattern may be superimposed on the produced images. There are methods by which the influence of this unwanted interference can be reduced, such as the incorporation of an incidence .angle and the proper use of signal polarization. This paper presents the basics of this problem and describes the use of the methods for reducing this unwanted influence through specific examples.
New space traveling-wave tube (TWT) provides coherent source of 75 watts of continuous-wave power output over bandwidth of 5 GHz at frequency of 65 GHz. Coupled-cavity TWT provides 50 dB of saturated gain. Includes thermionic emitter, M-type dispenser cathode providing high-power electron beam. Beam focused by permanent magnets through center of radio-frequency cavity structure. Designed for reliable operation for 10 years, and overall efficiency of 35 percent minimizes prime power input and dissipation of heat.
Here, the 3D-printed titanium alloy Ti5553 solid and octet truss lattice specimens are studied via resonant ultrasound spectroscopy, free decay of vibration and quasi-static methods to determine viscoelastic damping. Damping in solid alloy and a lattice is between 10 -4 and 10 -3 . Much of the damping at high sonic frequency is attributed to stress-induced heat flow between heterogeneities due to 3D printing. Pulsed wave ultrasound experiments disclose reverberation in the cell structure of the lattice. Continuous wave ultrasound experiments show that the transmissibility in the lattice rolls off beginning at about 50 kHz and becomes negligible above 110 kHz. By contrast, the polymer polymethyl methacrylate (PMMA), though it is viscoelastic, readily transmits waves up to 1 MHz. The cutoff frequency in the lattice is associated with the structure size, not intrinsic damping in the alloy. The octet truss lattice, in addition to providing good mechanical performance, is also an ultrasonic metamaterial.
Positron beams would provide a new and meaningful probe for the experimental program at the Thomas Jefferson National Accelerator Facility (JLab). The JLab Positron Working Group, formed in 2018 and now with over 250 members from 75 institutions, continues to develop an experimental program with high duty-cycle positron beams including but not limited to future hadronic physics and dark matter experiments. Critical requirements involve generating positron beams with a high degree of spin polarization, sufficient intensity and a continuous-wave (CW) bunch train compatible with acceleration to 12 GeV at the Continuous Electron Beam Accelerator Facility (CEBAF). In this presentation we describe a start-to-end layout for positron beams at 12 GeV CEBAF utilizing the Low Energy Research Facility (LERF) at Jefferson Lab to build two new injectors. A GaAs dc high voltage photo-gun first generates >1 mA of polarized electrons which are then accelerated to 80-150 MeV and directed to a high-power spinning W target for polarized bremsstrahlung and positron pair creation. A second injector then collects, bunches and accelerates the positrons to 123 MeV. The positron beams are transported by a new beam line and injected into the CEBAF acceptance for acceleration to the end stations with energies up to 12 GeV. The layout is optimized to provide Users with positron spin polarization >60% and intensity greater than >100 nA, and with higher intensities when polarization is not required.
Laser powder bed fusion (LPBF) is an additive manufacturing technology with the capability of printing complex metal parts directly from digital models. Between two available emission modes employed in LPBF printing systems, pulsed wave (PW) emission provides more control over the heat input compared to continuous wave (CW) emission, which is highly beneficial for printing parts with intricate features. However, parts printed with pulsed wave LPBF (PW-LPBF) commonly contain pores, which degrade their mechanical properties. In this study, we reveal pore formation mechanisms during PW-LPBF in real time by using an in-situ high-speed synchrotron x-ray imaging technique. We found that vapor depression collapse proceeds when the laser irradiation stops within one pulse, resulting in occasional pore formation during PW-LPBF. We also revealed that the melt ejection and rapid melt pool solidification during pulsed-wave laser melting resulted in cavity formation and subsequent formation of a pore pattern in the melted track. The pore formation dynamics revealed here may provide guidance on developing pore elimination approaches.
Coherent mixing of optical radiation from a tunable continuous-wave dye laser and a stabilized He-Ne laser was used to generate millimeter-wave signals in GaAs FETs attached to printed-circuit millimeter-wave antennas. The generated signal was further down-converted to a 2-GHz IF by an antenna-coupled millimeter-wave local oscillator at 62 GHz. Detailed characterizations of power and S/N under different bias conditions have been performed. This technique is expected to allow signal generation and frequency-response evaluation of millimeter-wave devices at frequencies as high as 100 GHz.
Gravitational waves with frequencies below 1 nHz are notoriously difficult to detect. With periods exceeding current experimental lifetimes, they induce slow drifts in observables rather than periodic correlations. Observables with well-known intrinsic contributions provide a means to probe this regime. In this Letter, we demonstrate the viability of using observed pulsar timing parameters to discover such “ultralow” frequency gravitational waves, presenting two complementary observables for which the systematic shift induced by ultralow-frequency gravitational waves can be extracted. Using existing data for these parameters, we search the ultralow-frequency regime for continuous-wave signals, finding a sensitivity near the expected prediction from inspirals of supermassive black holes. We do not see an excess in the data, setting a limit on the strain of 1.3 × 10 –12 at 450 pHz with a sensitivity dropping approximately quadratically with frequency until 10 pHz. Finally, our search method opens a new frequency range for gravitational wave detection and has profound implications for astrophysics, cosmology, and particle physics.