An amplitude and phase compensation system has been developed and tested at the University of Hawai'i for the optimization of the RF drive system to the Mark V free-electron laser. Temporal uniformity of the RF drive is essential to the generation of an electron beam suitable for optimal free-electron laser performance and the operation of an inverse Compton scattering x-ray source. The design of the RF measurement and compensation system is described in detail and the results of RF phase compensation are presented. Performance of the free-electron laser was evaluated by comparing the measured effects of phase compensation with the results of a computer simulation. Finally, preliminary results are presented for the effects of amplitude compensation on the performance of the complete system.
Abstract High speed wireless communication has proven elusive in subsea environments due to the inherent bandwidth limitations of acoustics and range limitations of other transmission modalities. A truly connected subsea system necessitates a high-speed, resilient architecture that can enable the integration of new sensor technologies and edge analytics and allow closed-loop monitoring and control of subsea operations for integrity monitoring and optimization. Like terrestrial Internet of Things applications, the realization of this "digital subsea" vision requires the application of high speed, point-to-point wireless technologies to complement rather than replace "hard-wired" communications such as optical fiber or acoustic systems. This work addresses the development of ULTRA (Underwater LASER Telemetry and Remote Access), an ultra-long range underwater laser communications system for use in critical points of the subsea communications architecture to increase reliability, operational flexibility, and reduce communication system maintenance associated with physical subsea connections. To demonstrate the data capacity and range of ULTRA, a subscale laboratory point-to-point wireless laser communication system was constructed with the flexibility to transmit through either air or water. The test system used power and modulation frequencies for air, fresh water, and different qualities of seawater. Optical and RF encoding methodologies were implemented to facilitate and characterize data transmission through the various media. The laboratory experiment used a subscale, filtered, and attenuated 5 mW blue-green laser in a 22-meter folded path configuration to demonstrate real-time data transmission at 312 Megabit per Second (Mbps) data rate using single channel Quadrature Phase Shift Keying (QPSK) modulation. A field prototype ULTRA system will use an unattenuated 5 mW laser that can reach approximately 280-meter range at 312 Mbps in clear conditions, which are typical of deepwater subsea. The selection of laser power and data rate are considered operational tradeoffs in environments where underwater vehicles operate. The extended range of ULTRA can enable various use cases to greatly augment subsea data communications capacity to enable the "Digital Subsea".
The Free-Electron Laser Laboratory at the University of Hawai`i has constructed and tested a scanning wire beam position monitor to aid the alignment and optimization of a high spectral brightness inverse-Compton scattering x-ray source. X-rays are produced by colliding the 40 MeV electron beam from a pulsed S-band linac with infrared laser pulses from a mode-locked free-electron laser driven by the same electron beam. The electron and laser beams are focused to 60 μm diameters at the interaction point to achieve high scattering efficiency. This wire-scanner allows for high resolution measurements of the size and position of both the laser and electron beams at the interaction point to verify spatial coincidence. Time resolved measurements of secondary emission current allow us to monitor the transverse spatial evolution of the e-beam throughout the duration of a 4 μs macro-pulse while the laser is simultaneously profiled by pyrometer measurement of the occulted infrared beam. Using this apparatus we have demonstrated that the electron and laser beams can be co-aligned with a precision better than 10 μm as required to maximize x-ray yield.
We describe a simple method to measure the back-bombardment heating temperature rise as a function of time in pulsed microwave thermionic guns using a fast rise-time InGaAs detector and optical pyrometer. Gaining knowledge of the nature of that temperature rise and the corresponding current out of the gun are the first steps in devising a scheme to counteract the back-bombardment heating which lengthens the micropulses, limits the macropulse length, and increases the energy spread of the emitted electron beam. We measured a temperature rise of 59 K in our LaB6 cathode which delivered a peak of 600 mA over a 5 μs RF pulse in our 0.33 MV/cm peak field, 2.856 GHz thermionic electron gun.
Nanite™ is a cementitious material that contains a proprietary formulation of functionalized nanomaterial additive to transform conventional cement into a smart material responsive to pressure (or stress), temperature, and any intrinsic changes in composition. This project has identified optimal sensing modalities of smart well cement and demonstrated how real-time sensing of Nanite™ can improve long-term wellbore integrity and zonal isolation in shale gas and applicable oil and gas operations. Oceanit has explored Nanite’s electrical sensing properties in depth and has advanced the technology from laboratory proof-of-concept to sub-scale testing in preparation for field trials.
Free-electron lasers (FEL) and synchrotron sources of high brilliance x-rays have proven to be of tremendous value in basic and applied research. Inverse-Compton sources (ICS) can achieve brilliance matching the requirements of many applications pioneered at those FEL and synchrotron facilities---including phase contrast imaging, macromolecular x-ray crystallography, and x-ray microscopy---but with size, cost, and complexity compatible with a small laboratory. The free-electron laser inverse-Compton interaction compact x-ray source at the University of Hawaii at Manoa is a unique approach to an ICS which employs an FEL as the laser source. We have measured a total average flux of $3.0\ifmmode\times\else\texttimes\fi{}{10}^{5}\text{ }\text{ }\mathrm{photons}/\mathrm{second}$ with an average brilliance of $2.0\ifmmode\times\else\texttimes\fi{}{10}^{7}\text{ }\text{ }\mathrm{photons}/\mathrm{s}\text{ }{\mathrm{mm}}^{2}\text{ }{\mathrm{mrad}}^{2}$ 0.1% of bandwidth (BW) with a peak energy of 10.9 keV from the source. While these results are modest in comparison to the standards set by other IC sources, upgrades to the system have the potential to increase the total average flux to $9.2\ifmmode\times\else\texttimes\fi{}{10}^{11}\text{ }\text{ }\mathrm{photons}/\mathrm{second}$ with an average brilliance of $1.9\ifmmode\times\else\texttimes\fi{}{10}^{12}\text{ }\text{ }\mathrm{photons}/\mathrm{s}\text{ }{\mathrm{mm}}^{2}\text{ }{\mathrm{mrad}}^{2}$ 0.1% BW: comparing more favorably to other sources. We discuss the scientific program, the progress made in design and development, and the achievements of the source to date. We also outline future upgrades and integration needed to yield an enabling source for emerging high brilliance x-ray applications.
Experiments with a Hamamatsu C5680 dual-sweep streak camera have been performed on the Mark V Free- electron Laser (FEL) oscillator linac beams at the University of Hawaii. The bunch length and phase of the e-beam were evaluated throughout the macropulse duration via both optical transition radiation and coherent spontaneous harmonic radiation sources. Bunch lengths of 3-5 ps FWHM and phase slews of 7 ps over 2 μs are reported under lasing conditions.
Real time macropulse waveform measurements of electron beam will provide valuable data, such as phase, amplitude and energy spread, without disturbing the beam which will allow online bunch diagnostics on electron beam in linear accelerators. Therefore a low cost and space effective prototype system with an oscilloscope on a chip for real time measurement of the macropulse waveform is being developed for the Linear Accelerator at University of Hawai‘i. We utilize a custom application specific integrated circuit (ASIC) for the purpose of sampling, storing and digitizing signals. The ASIC is controlled by a field-programmable gate array (FPGA). Initial assembly and testing of the system are complete. Full assembly and installation of the system is in progress. The technology and preliminary results of this project are presented here.
