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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,711 records · Page 95
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

A Self-Biasing Pulsed Depressed Collector

Depressed collectors have been utilized successfully for many years to improve the electrical efficiency of vacuum electron devices. Increasingly, pulsed, high-peak power accelerator applications are placing a premium on electrical efficiency. As RF systems are responsible for a large percentage of the overall energy usage at accelerator laboratories, methods to improve upon the state-of-the-art in pulsed high-power sources are desired. This paper presents a technique for self-biasing the stages in a multistage depressed collector. With this technique, the energy lost during the rise and fall times of the pulse can be recovered, separate power supplies are not needed, and existing modulators can be retrofitted. Calculations show that significant cost savings can be realized with the implementation of this device in high-power systems. In this paper, the technique is described along with experimental demonstration. (auth)

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Generation and pointing stabilization of multi-GeV electron beams from a laser plasma accelerator driven in a pre-formed plasma waveguide

Laser pulses with peak power 0.3 PW were used to generate electron beams with energy >4 GeV within a 9 cm-long capillary discharge waveguide operated with a plasma density of ≈7×10{sup 17} cm{sup −3}. Simulations showed that the super-Gaussian near-field laser profile that is typical of high-power femtosecond laser systems reduces the efficacy of guiding in parabolic plasma channels compared with the Gaussian laser pulses that are typically simulated. In the experiments, this was mitigated by increasing the plasma density and hence the contribution of self-guiding. This allowed for the generation of multi-GeV electron beams, but these had angular fluctuation ≳2 mrad rms. Mitigation of capillary damage and more accurate alignment allowed for stable beams to be produced with energy 2.7±0.1 GeV. The pointing fluctuation was 0.6 mrad rms, which was less than the beam divergence of ≲1 mrad full-width-half-maximum.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1977

Short pulse radar used to measure sea surface wind speed and SWH

A joint airborne measurement program is being pursued by NRL and NASA Wallops Flight Center to determine the extent to which wind speed and sea surface significant wave height (SWH) can be measured quantitatively and remotely with a short pulse (2 ns), wide-beam (60 deg), nadir-looking 3-cm radar. The concept involves relative power measurements only and does not need a scanning antenna, Doppler filters, or absolute power calibration. The slopes of the leading and trailing edges of the averaged received power for the pulse limited altimeter are used to infer SWH and surface wind speed. The interpretation is based on theoretical models of the effects of SWH on the leading edge shape and rms sea-surface slope on the trailing-edge shape. The models include the radar system parameters of antenna beam width and pulsewidth.

Hammond, D. L.↗
DOE OSTI2015

Power enhancement of burst-mode UV pulses using a doubly-resonant optical cavity

We report a doubly-resonant enhancement cavity (DREC) that can realize a simultaneous enhancement of two incoming laser beams at different wavelengths and different temporal structures. The double-resonance condition is theoretically analyzed and different DREC locking methods are experimentally investigated. Simultaneous locking of a Fabry-Perot cavity to both an infrared (IR, 1064 nm) and its frequency tripled ultraviolet (UV, 355 nm) pulses has been demonstrated by controlling the frequency difference between the two beams with a fiber optic frequency shifter. The DREC technique opens a new paradigm in the applications of optical cavities to power enhancement of burst-mode lasers with arbitrary macropulse width and repetition rate.

42 ENGINEERING↗
DOE OSTI2017

Novel Low-Temperature Plasma Reactor for Industrial Applications

UV water disinfection for municipalities around the world is expected to grow over 15% annually, leading to a $2.8 billion dollar market by 2020. This growth is driving the need for higher power and more efficient UV sources. By far the greatest potential market for UV disinfection is drinking water. UV is now accepted as an available technology to deactivate Cryptosporidium and Giardia in surface water and other vulnerable sources. The output power of typical mercury-vapor UV lamps is limited to 30 W/m, requiring large arrays to treat relevant volumes of water. Higher power sources can be built with low-temperature plasmas, but require large, lossy, light-blocking magnetic cores. These cores require extensive cooling, and place a hard ceiling on power transfer to the plasma, optical efficiency, and ultimately on radiant light flux. In Phase I of this SBIR, DTI developed a novel, magnetically-coupled, toroidal pulsed plasma reactor that could run without ferrite cores, though the cores increased the coupling. DTI’s proposed geometry and exciter circuit topology enables the use of comparatively inexpensive electronic modules to operate in a pulsed-RF mode. The pulsed high-power discharge (1.5 MW peak, 500 kHz, < 5% duty cycle) creates high plasma temperatures for short durations, while maintaining a much lower steady-state temperature. This proposed reactor will be designed primarily to disinfect and denature wastewater or drinking water products, exploiting large-scale UV disinfection techniques. The UVC efficiency with the highest output power was 6.2%; for comparison, the efficiency of present high-power UV sources is 13%. It may be possible to increase the efficiency by operating pulses in a burst mode.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Numerical simulation of narrow bipolar electromagnetic pulses generated by thunderstorm discharges

Using the concept of avalanche relativistic runaway electrons (REs), we perform numerical simulations of compact intracloud discharge (CID) as a generator of powerful natural electromagnetic pulses (EMPs) in the HF-VHF range, called narrow bipolar pulses (NBPs). For several values of the field overvoltage and altitude at which the discharge develops, the numbers of seed electrons initiating the avalanche are evaluated, with which the calculated EMP characteristics are consistent with the measured NBP parameters. We note shortcomings in the hypothesis assuming participation of cosmic ray air showers in avalanche initiation. The discharge capable of generating NBPs produces REs in numbers close to those in the source of terrestrial {gamma}-ray flashes (TGFs), which can be an argument in favor of a unified NBP and TGF source.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Measuring the energy flux at the substrate position during magnetron sputter deposition processes

In this work, the energetic conditions at the substrate were investigated in dc magnetron sputtering (DCMS), pulsed dc magnetron sputtering (pDCMS), and high power impulse magnetron sputtering (HiPIMS) discharges by means of an energy flux diagnostic based on a thermopile sensor, the probe being set at the substrate position. Measurements were performed in front of a titanium target for a highly unbalanced magnetic field configuration. The average power was always kept to 400 W and the probe was at the floating potential. Variation of the energy flux against the pulse peak power in HiPIMS was first investigated. It was demonstrated that the energy per deposited titanium atom is the highest for short pulses (5 {mu}s) high pulse peak power (39 kW), as in this case, the ion production is efficient and the deposition rate is reduced by self-sputtering. As the argon pressure is increased, the energy deposition is reduced as the probability of scattering in the gas phase is increased. In the case of the HiPIMS discharge run at moderate peak power density (10 kW), the energy per deposited atom was found to be lower than the one measured for DCMS and pDCMS discharges. In these conditions, the HiPIMS discharge could be characterized as soft and close to a pulsed DCMS discharge run at very low duty cycle. For the sake of comparison, measurements were also carried out in DCMS mode with a balanced magnetron cathode, in the same working conditions of pressure and power. The energy flux at the substrate is significantly increased as the discharge is generated in an unbalanced field.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

A pulse-front-tilt–compensated streaked optical spectrometer with high throughput and picosecond time resolution

A high-throughput, broadband optical spectrometer coupled to the Rochester optical streak system equipped with a Photonis P820 streak tube was designed to record time-resolved spectra with 1-ps time resolution. Spectral resolution of 0.8 nm is achieved over a wavelength coverage range of 480 to 580 nm, using a 300-groove/mm diffraction grating in conjunction with a pair of 225-mm-focal-length doublets operating at an f/2.9 aperture. Overall pulse-front tilt across the beam diameter generated by the diffraction grating is reduced by preferentially delaying discrete segments of the collimated input beam using a 34-element reflective echelon optic. The introduced delay temporally aligns the beam segments and the net pulse-front tilt is limited to the accumulation across an individual sub-element. The resulting spectrometer design balances resolving power and pulse-front tilt while maintaining high throughput.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2018

Hall Current Plasma Source Having a Center-Mounted or a Surface-Mounted Cathode

A miniature Hall current plasma source apparatus having magnetic shielding of the walls from ionized plasma, an integrated discharge channel and gas distributor, an instant-start hollow cathode mounted to the plasma source, and an externally mounted keeper, is described. The apparatus offers advantages over other Hall current plasma sources having similar power levels, including: lower mass, longer lifetime, lower part count including fewer power supplies, and the ability to be continuously adjustable to lower average power levels using pulsed operation and adjustment of the pulse duty cycle. The Hall current plasma source can provide propulsion for small spacecraft that either do not have sufficient power to accommodate a propulsion system or do not have available volume to incorporate the larger propulsion systems currently available. The present low-power Hall current plasma source can be used to provide energetic ions to assist the deposition of thin films in plasma processing applications.

Martinez, Rafael A.↗
NASA NTRS2001

Magnetic Flux Compression Reactor Concepts for Spacecraft Propulsion and Power (MSFC Center Director's Discretionary Fund; Project No. 99-24)

This technical publication (TP) examines performance and design issues associated with magnetic flux compression reactor concepts for nuclear/chemical pulse propulsion and power. Assuming that low-yield microfusion detonations or chemical detonations using high-energy density matter can eventually be realized in practice, various magnetic flux compression concepts are conceivable. In particular, reactors in which a magnetic field would be compressed between an expanding detonation-driven plasma cloud and a stationary structure formed from a high-temperature superconductor are envisioned. Primary interest is accomplishing two important functions: (1) Collimation and reflection of a hot diamagnetic plasma for direct thrust production, and (2) electric power generation for fusion standoff drivers and/or dense plasma formation. In this TP, performance potential is examined, major technical uncertainties related to this concept accessed, and a simple performance model for a radial-mode reactor developed. Flux trapping effectiveness is analyzed using a skin layer methodology, which accounts for magnetic diffusion losses into the plasma armature and the stationary stator. The results of laboratory-scale experiments on magnetic diffusion in bulk-processed type II superconductors are also presented.

Litchford, R. J.↗
DOE OSTI2014

Molecular dynamics simulation of Coulomb explosion, melting and shock wave creation in silicon after an ionization pulse

Strong electronic stopping power of swift ions in a semiconducting or insulating substrate can lead to localized electron stripping. The subsequent repulsive interactions among charged target atoms can cause Coulomb explosion. Using molecular dynamics simulation, we simulate Coulomb explosion in silicon by introducing an ionization pulse lasting for different periods, and at different substrate temperatures. We find that the longer the pulse period, the larger the melting radius. The observation can be explained by a critical energy density model assuming that melting required thermal energy density is a constant value and the total thermal energy gained from Coulomb explosion is linearly proportional to the ionization period. Our studies also show that melting radius is larger at higher substrate temperatures. The temperature effect is explained due to a longer structural relaxation above the melting temperature at original ionization boundary due to lower heat dissipation rates. Furthermore, simulations show the formation of shock waves, created due to the compression from the melting core.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Control of the shape of laser pulses amplified in the strong saturation regime

A new criterion for estimating the distortions of quasirectangular pulses in high-power amplifiers is proposed together with a method that allows generation of quasi-rectangular pulses at the output of a high-efficiency amplifier, i. e., in the regime of strong saturation. The efficiency of the method is demonstrated by the example of calculating the neodymium glass amplifier, used for pumping the petawatt parametric amplifier. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Experimental study on parasitic mode suppression using FeSiAl in relativistic klystron amplifier

Experimental study of parasitic mode suppression using electromagnetic attenuate material FeSiAl in an S-band Relativistic Klystron Amplifier (RKA) is presented in this paper. The FeSiAl powder is coated and sintered onto the inner surface of a drift tube which locates between the input and the middle cavity of the RKA. Cold tests show that the attenuate rate of the tube against parasitic mode TE{sub 11} is about 50%. Experiments carried out on the Torch-01 accelerator present that the tube is effective in suppressing the parasitic mode. Two typical outputs are obtained. When the diode voltage is on a moderate level, the RKA operates well and the parasitic mode is totally suppressed. The pulse length of the High Power Microwave (HPM) almost equals the electron beam pulse length and the HPM average output power is about 300 MW, with a power efficiency of 10%. When the diode voltage is on a higher level, the output power and efficiency rise but the parasitic mode oscillation occurred and the pulse length is shortened. By contrast, the parasitic mode oscillation is too strong for the RKA to operate normally with un-sintered drift tube. The experimental study implies that FeSiAl is effective in suppressing the parasitic mode oscillation in a certain extent. However, total suppression needs a deeper attenuate rate and further investigation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

High power experimental studies of hybrid photonic band gap accelerator structures

This paper reports the first high power tests of hybrid Photonic Band Gap (PBG) accelerator structures. Three hybrid PBG (HPBG) structures were designed, built and tested at 17.14 GHz. Each structure had a triangular lattice array with 60 inner sapphire rods and 24 outer copper rods sandwiched between copper disks. The dielectric PBG band gap map allows the unique feature of overmoded operation in a TM02 mode, with suppression of both lower order modes, such as the TM11 mode, as well as higher order modes. The use of sapphire rods, which have negligible dielectric loss, required inclusion of the dielectric birefringence in the design. The three structures were designed to sequentially reduce the peak surface electric field. Simulations showed relatively high surface fields at the triple point as well as in any gaps between components in the clamped assembly. The third structure used sapphire rods with small pin extensions at each end and obtained the highest gradient of 19 MV/m, corresponding to a surface electric field of 78 MV/m, with a breakdown probability of 0.5 per pulse per meter for a 100-ns input power pulse. Operation at a gradient above 20 MV/m led to runaway breakdowns with extensive light emission and eventual damage. For all three structures, multipactor light emission was observed at gradients well below the breakdown threshold. This research indicated that multipactor triggered at the triple point limited the operational gradient of the hybrid structure.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

An ultrafast laser pulse picker technique for high-average-current high-brightness photoinjectors

Beam diagnostics in high brightness photoinjectors requires that optical pulses from a high-power drive laser be picked up with an ultrahigh pulse contrast ratio and without temporal profile distortion. In high-average-current high-brightness photoinjectors, high-power drive lasers are routinely operated at GHz-level pulse repetition rate and it is challenging to achieve pulse picking without any pulse distortion. Here, we report on a new ultrafast pulse picker technique for beam diagnostics in high-average-current high-brightness photoinjectors. By efficiently combining an ultrafast low-power electro-optic modulator, high-power fiber laser amplifiers, a high-power Pockels Cell, and a frequency doubling module, we have successfully demonstrated optical bunch (30 pulses per bunch) pickup from a 704 MHz high-power drive laser and achieved a 10 6 :1 pulse contrast ratio and nearly zero pulse distortion. The performance of this pulse picking technique has been verified through beam characterization and electron cooling in the low energy RHIC electron cooling accelerator at Brookhaven National Laboratory.

43 PARTICLE ACCELERATORS↗
NASA NTRS1987

Multiplex electric discharge gas laser system

A multiple pulse electric discharge gas laser system is described in which a plurality of pulsed electric discharge gas lasers are supported in a common housing. Each laser is supplied with excitation pulses from a separate power supply. A controller, which may be a microprocessor, is connected to each power supply for controlling the application of excitation pulses to each laser so that the lasers can be fired simultaneously or in any desired sequence. The output light beams from the individual lasers may be combined or utilized independently, depending on the desired application. The individual lasers may include multiple pairs of discharge electrodes with a separate power supply connected across each electrode pair so that multiple light output beams can be generated from a single laser tube and combined or utilized separately.

Laudenslager, James B.↗
NASA NTRS1992

Adaptive optics for laser power beaming

It has been proposed to use a high energy pulsed laser to beam power into space for satellites or a lunar base. The effects of atmospheric transmission are critical to such a system. Thermal blooming in the atmosphere can cause the beam to spread rapidly. Atmospheric turbulence can cause beam bending or beam spreading, resulting in the loss of transmitted energy that fails to hit the target receiver.

Leland, Robert P.↗
DOE OSTI2018

Subpicosecond pulse generation above 2 μm in longitudinally inhomogeneous single-mode fibres

We consider the evolution of the spectrum of a medium-power input telecom laser pulse during propagation in a longitudinally inhomogeneous flattened dispersion silica fibre. Using modelling results, we find an optimal longitudinal fibre diameter profile ensuring transfer of more than 60 % of the input pulse energy to a subpicosecond pulse in the range 2.2 – 2.3 μm. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗