Design and development of a 6 MW peak, 24 kW average power S-band klystron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joshi, L.M.; Meena, Rakesh; Nangru, Subhash

2011-07-01

A 6 MW peak, 24 kW average power S-band Klystron is under development at CEERI, Pilani under an MoU between BARC and CEERI. The design of the klystron has been completed. The electron gun has been designed using TRAK and MAGIC codes. RF cavities have been designed using HFSS and CST Microwave Studio while the complete beam wave interaction simulation has been done using MAGIC code. The thermal design of collector and RF window has been done using ANSYS code. A Gun Collector Test Module (GCTM) was developed before making actual klystron to validate gun perveance and thermal design ofmore » collector. A high voltage solid state pulsed modulator has been installed for performance valuation of the tube. The paper will cover the design aspects of the tube and experimental test results of GCTM and klystron. (author)« less

A unique power supply for the PEP II klystron at SLAC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cassel, R.; Nguyen, M.N.

1997-07-01

Each of the eight 1.2 MW RF klystrons for the PEP-II storage rings require a 2.5 MVA DC power supply of 83 Kv at 23 amps. The design for the supply was base on three factors, low cost, small size to fit existing substation pads, and good protection against damage to the klystron including klystron gun arcs. The supply uses a 12 pulse 12.5 KV primary thyristor star point controller with primary filter inductor to provide rapid voltage control, good voltage regulation, and fast turn off during klystron tube faults. The supply also uses a unique secondary rectifier, filter capacitormore » configuration to minimize the energy available under a klystron fault. The voltage control is from 0--90 KV with a regulation of < 0.1% and voltage ripple of < 1% P-P, (< 0.2% RMS) above 60 KV. The supply utilizes a thyristor crowbar, which under a klystron tube arc limits the energy in the klystron arc to < 5 joules. If the thyristor crowbar is disabled the energy supplied is < 40 joules into the arc. The size of the supply was reduced small enough to fit the existing PEP transformer yard pads. The cost of the power supply was < $140 per KVA.« less

High-power klystrons

NASA Astrophysics Data System (ADS)

Siambis, John G.; True, Richard B.; Symons, R. S.

1994-05-01

Novel emerging applications in advanced linear collider accelerators, ionospheric and atmospheric sensing and modification and a wide spectrum of industrial processing applications, have resulted in microwave tube requirements that call for further development of high power klystrons in the range from S-band to X-band. In the present paper we review recent progress in high power klystron development and discuss some of the issues and scaling laws for successful design. We also discuss recent progress in electron guns with potential grading electrodes for high voltage with short and long pulse operation via computer simulations obtained from the code DEMEOS, as well as preliminary experimental results. We present designs for high power beam collectors.

SLAC pulsed X-ray facility

NASA Astrophysics Data System (ADS)

Ipe, N. E.; McCall, R. C.; Baker, E. D.

1986-05-01

The Stanford Linear Accelerator Center (SLAC) operates a high energy (up to 33 GeV) linear accelerator delivering pulses up to a few microseconds wide. The pulsed nature of the electron beam creates problems in the detection and measurement of radiation both from the accelerator beam and the klystrons that provide the RF power for the accelerator. Hence, a pulsed X-ray facility has been built at SLAC mainly for the purpose of testing the response of different radiation detection instruments to pulsed radiation fields. The X-ray tube consists of an electron gun with a control grid. This provides a stream of pulsed electrons that can be accelerated towards a confined target-window. The window is made up of aluminum 0.051 cm (20 mils) thick, plated on the vacuum side with a layer of gold 0.0006 cm (1/4 mil) thick. The frequency of electron pulses can be varied by an internal pulser from 60 to 360 pulses per second with pulse widths of 360 ns to 5 ms. The pulse amplitude can be varied over a wide range of currents. An external pulser can be used to obtain other frequencies or special pulse shapes. The voltage across the gun can be varied from 0 to 100 kV. The major part of the X-ray tube is enclosed in a large walk-in-cabinet made of 1.9 cm (3/4 in) plywood and lined with 0.32 cm (1/8 in) lead to make a very versatile facility.

Utilization of a Vircator to drive a High Power Relativistic Klystron Amplifier

NASA Astrophysics Data System (ADS)

Gardelle, J.; Bardy, J.; Cassany, B.; Desanlis, T.; Eyl, P.; Galtié, A.; Modin, P.; Voisin, L.; Balleyguier, P.; Gouard, P.; Donohue, J.

2002-11-01

At CESTA, we have been producing electron beams for some fifteen years by using induction accelerators and pulse diodes. First we had performed Frre-Electron Lasers experiments and we are currently studying the production of High-Power microwaves in the S-band. Among the possible sources we have chosen to perform Relativistic Klystron (RK) experiments with a pulse diode capable of generating a 700kV, 15 kA, 100 ns annular electron beam. In an amplifier configuration, we are testing the idea of using a Vircator as the driver for the first cavity of the klystron. This Vircator uses a simple electrical generator (Marx capacitor bank) which operates in the S-band in the GW class. By reducing the power level to about 100 MW, a 200 ns reliable and reproducible input driver pulse is obtained. First, we present the results of a preliminary experiment for which a coaxial cavity has been built in order to be fed by the Vircator emission at 2.45 GHz. Secondly, we give the experimental results in an oscillator configuration which corresponds to the fisrt step of our RK studies. Comparisons with the results of numerical simulations performed with MAGIC and MAFIA will be given for both experiments.

RF extraction issues in the relativistic klystron amplifiers

NASA Astrophysics Data System (ADS)

Serlin, Victor; Friedman, Moshe; Lampe, Martin; Hubbard, Richard F.

1994-05-01

Relativistic klystron amplifiers (RKAs) were successfully operated at NRL in several frequency regimes and power levels. In particular, an L-band RKA was optimized for high- power rf extraction into the atmosphere and an S-band RKA was operated, both in a two-beam and a single-beam configuration. At L-band the rf extraction at maximum power levels (>= 15 GW) was hindered by pulse shortening and poor repeatability. Preliminary investigation showed electron emission in the radiating horn, due to very high voltages associated with the multi-gigawatt rf power levels. This electron current constituted an electric load in parallel with the radiating antenna, and precipitated the rf pulse collapse. At S-band the peak extracted power reached 1.7 GW with power efficiency approximately 50%. However, pulse shortening limited the duration to approximately 50 nanoseconds. The new triaxial RKA promises to solve many of the existing problems.

Development and performance test of a new high power RF window in S-band PLS-II LINAC

NASA Astrophysics Data System (ADS)

Hwang, Woon-Ha; Joo, Young-Do; Kim, Seung-Hwan; Choi, Jae-Young; Noh, Sung-Ju; Ryu, Ji-Wan; Cho, Young-Ki

2017-12-01

A prototype of RF window was developed in collaboration with the Pohang Accelerator Laboratory (PAL) and domestic companies. High power performance tests of the single RF window were conducted at PAL to verify the operational characteristics for its application in the Pohang Light Source-II (PLS-II) linear accelerator (Linac). The tests were performed in the in-situ facility consisting of a modulator, klystron, waveguide network, vacuum system, cooling system, and RF analyzing equipment. The test results with Stanford linear accelerator energy doubler (SLED) have shown no breakdown up to 75 MW peak power with 4.5 μs RF pulse width at a repetition rate of 10 Hz. The test results with the current operation level of PLS-II Linac confirm that the RF window well satisfies the criteria for PLS-II Linac operation.

Modular compact solid-state modulators for particle accelerators

NASA Astrophysics Data System (ADS)

Zavadtsev, A. A.; Zavadtsev, D. A.; Churanov, D. V.

2017-12-01

The building of the radio frequency (RF) particle accelerator needs high-voltage pulsed modulator as a power supply for klystron or magnetron to feed the RF accelerating system. The development of a number of solid-state modulators for use in linear accelerators has allowed to develop a series of modular IGBT based compact solid-state modulators with different parameters. This series covers a wide range of needs in accelerator technology to feed a wide range of loads from the low power magnetrons to powerful klystrons. Each modulator of the series is built on base of a number of unified solid-state modules connected to the pulse transformer, and covers a wide range of modulators: voltage up to 250 kV, a peak current up to 250 A, average power up to 100 kW and the pulse duration up to 20 μsec. The parameters of the block with an overall dimensions 880×540×250 mm are: voltage 12 kV, peak current 1600 A, pulse duration 20 μsec, average power 10 kW with air-cooling and 40 kW with liquidcooling. These parameters do not represent a physical limit, and modulators to parameters outside these ranges can be created on request.

A high efficiency Ku-band radial line relativistic klystron amplifier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dang, Fangchao; Zhang, Xiaoping, E-mail: zhangxiaoping@nudt.edu.cn; Zhong, Huihuang

2016-07-15

To achieve the gigawatt-level microwave amplification output at Ku-band, a radial-line relativistic klystron amplifier is proposed and investigated in this paper. Different from the annular electron beam in conventional axial relativistic klystron amplifiers, a radial-radiated electron beam is employed in this proposed klystron. Owing to its radially spreading speciality, the electron density and space charge effect are markedly weakened during the propagation in the radial line drift tube. Additionally, the power capacity, especially in the output cavity, is enhanced significantly because of its large volume, which is profitable for the long pulse operation. Particle-in-cell simulation results demonstrate that a highmore » power microwave with the power of 3 GW and the frequency of 14.25 GHz is generated with a 500 kV, 12 kA electron beam excitation and the 30 kW radio-frequency signal injection. The power conversion efficiency is 50%, and the gain is about 50 dB. Meanwhile, there is insignificant electron beam self-excitation in the proposed structure by the adoption of two transverse electromagnetic reflectors. The relative phase difference between the injected signals and output microwaves keeps stable after the amplifier saturates.« less

Gigawatt peak power generation in a relativistic klystron amplifier driven by 1 kW seed-power

NASA Astrophysics Data System (ADS)

Wu, Y.; Xie, H. Q.; Li, Z. H.; Zhang, Y. J.; Ma, Q. S.

2013-11-01

An S-band high gain relativistic klystron amplifier driven by kW-level RF power is proposed and studied experimentally. In the device, the RF lossy material is introduced to suppress higher mode excitation. An output power of 1.95 GW with a gain of 62.8 dB is obtained in the simulation. Under conditions of an input RF power of 1.38 kW, a microwave pulse with power of 1.9 GW, frequency of 2.86 GHz, and duration of 105 ns is generated in the experiment, and the corresponding gain is 61.4 dB.

Control of energy sweep and transverse beam motion in induction linacs

NASA Astrophysics Data System (ADS)

Turner, W. C.

1991-05-01

Recent interest in the electron induction accelerator has focussed on its application as a driver for high power radiation sources; free electron laser (FEL), relativistic klystron (RK) and cyclotron autoresonance maser (CARM). In the microwave regime where many successful experiments have been carried out, typical beam parameters are: beam energy 1 to 10 MeV, current 1 to 3 kA and pulse width 50 nsec. Radiation source applications impose conditions on electron beam quality, as characterized by three parameters; energy sweep, transverse beam motion and brightness. These conditions must be maintained for the full pulse duration to assure high efficiency conversion of beam power to radiation. The microwave FEL that has been analyzed in the greatest detail requires energy sweep less than (+ or -) 1 pct., transverse beam motion less than (+ or -) 1 mm and brightness approx. 1 x 10(exp 8)A/sq m sq rad. In the visible region the requirements on these parameters become roughly an order of magnitude more strigent. With the ETAII accelerator at LLNL the requirements were achieved for energy sweep, transverse beam motion and brightness. The recent data and the advances that have made the improved beam quality possible are discussed. The most important advances are: understanding of focussing magnetic field errors and improvements in alignment of the magnetic axis, a redesign of the high voltage pulse distribution system between the magnetic compression modulators and the accelerator cells, and exploitation of a beam tuning algorithm for minimizing transverse beam motion. The prospects are briefly described for increasing the pulse repetition frequency to the range of 5 kHz and a delayed feedback method of regulating beam energy over very long pulse bursts, thus making average power megawatt level microwave sources at 140 GHz and above a possibility.

Electron cyclotron heating/current-drive system using high power tubes for QUEST spherical tokamak

NASA Astrophysics Data System (ADS)

Onchi, Takumi; Idei, H.; Hasegawa, M.; Nagata, T.; Kuroda, K.; Hanada, K.; Kariya, T.; Kubo, S.; Tsujimura, T. I.; Kobayashi, S.; Quest Team

2017-10-01

Electron cyclotron heating (ECH) is the primary method to ramp up plasma current non-inductively in QUEST spherical tokamak. A 28 GHz gyrotron is employed for short pulses, where the radio frequency (RF) power is about 300 kW. Current ramp-up efficiency of 0.5 A/W has been obtained with focused beam of the second harmonic X-mode. A quasi-optical polarizer unit has been newly installed to avoid arcing events. For steady-state tokamak operation, 8.56 GHz klystron with power of 200 kW is used as the CW-RF source. The high voltage power supply (54 kV/13 A) for the klystron has been built recently, and initial bench test of the CW-ECH system is starting. The array of insulated-gate bipolar transistor works to quickly cut off the input power for protecting the klystron. This work is supported by JSPS KAKENHI (15H04231), NIFS Collaboration Research program (NIFS13KUTR085, NIFS17KUTR128), and through MEXT funding for young scientists associated with active promotion of national university reforms.

Experimental demonstration of a Ku-band radial-line relativistic klystron oscillator based on transition radiation

NASA Astrophysics Data System (ADS)

Dang, Fangchao; Zhang, Xiaoping; Zhang, Jun; Ju, Jinchuan; Zhong, Huihuang

2017-03-01

We report on a radial-line relativistic klystron oscillator (RL-RKO), which is physically designed to generate gigawatt-level high power microwaves (HPMs) at Ku-band. The 3π/4 mode of a four-gap buncher is selected to highly modulate the radially propagating intense relativistic electron beam (IREB). A three-gap extractor operating at the π mode is employed to extract the radio-frequency energy efficiently. The Ku-band RL-RKO is investigated experimentally on an intense-current electron beam accelerator. The radially propagating IREB is well focused with an axial-width of 2 mm by a radial magnetic field of 0.4 T. Microwaves with a frequency of 14.86 GHz and a power of 1.5 GW are generated, corresponding to an efficiency of 24%, which indicates a significant advance for the research of radial-line HPM sources.

Analysis of High Power IGBT Short Circuit Failures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pappas, G.

2005-02-11

The Next Linear Collider (NLC) accelerator proposal at SLAC requires a highly efficient and reliable, low cost, pulsed-power modulator to drive the klystrons. A solid-state induction modulator has been developed at SLAC to power the klystrons; this modulator uses commercial high voltage and high current Insulated Gate Bipolar Transistor (IGBT) modules. Testing of these IGBT modules under pulsed conditions was very successful; however, the IGBTs failed when tests were performed into a low inductance short circuit. The internal electrical connections of a commercial IGBT module have been analyzed to extract self and mutual partial inductances for the main current pathsmore » as well as for the gate structure. The IGBT module, together with the partial inductances, has been modeled using PSpice. Predictions for electrical paths that carry the highest current correlate with the sites of failed die under short circuit tests. A similar analysis has been carried out for a SLAC proposal for an IGBT module layout. This paper discusses the mathematical model of the IGBT module geometry and presents simulation results.« less

Self-bunching electron guns

NASA Astrophysics Data System (ADS)

Mako, Frederick M.; Len, L. K.

1999-05-01

We report on three electron gun projects that are aimed at power tube and injector applications. The purpose of the work is to develop robust electron guns which produce self-bunched, high-current-density beams. We have demonstrated, in a microwave cavity, self-bunching, cold electron emission, long life, and tolerance to contamination. The cold process is based on secondary electron emission. FMT has studied using simulation codes the resonant bunching process which gives rise to high current densities (0.01-5 kA/cm2), high charge bunches (up to 500 nC/bunch), and short pulses (1-100 ps) for frequencies from 1 to 12 GHz. The beam pulse width is nominally ˜5% of the rf period. The first project is the L-Band Micro-Pulse Gun (MPG). Measurements show ˜40 ps long micro-bunches at ˜20 A/cm2 without contamination due to air exposure. Lifetime testing has been carried out for about 18 months operating at 1.25 GHz for almost 24 hours per day at a repetition rate of 300 Hz and 5 μs-long macro-pulses. Approximately 5.8×1013 micro-bunches or 62,000 coulombs have passed through this gun and it is still working fine. The second project, the S-Band MPG, is now operational. It is functioning at a frequency of 2.85 GHz, a repetition rate of 30 Hz, with a 2 μs-long macro-pulse. It produces about 45 A in the macro-pulse. The third project is a 34.2 GHz frequency-multiplied source driven by an X-Band MPG. A point design was performed at an rf output power of 150 MW at 34.2 GHz. The resulting system efficiency is 53% and the gain is 60 dB. The system efficiency includes the input cavity efficiency, input driver efficiency (a 50 MW klystron at 11.4 GHz), output cavity efficiency, and the post-acceleration efficiency.

Low Beam Voltage, 10 MW, L-Band Cluster Klystron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teryaev, V.; /Novosibirsk, IYF; Yakovlev, V.P.

2009-05-01

Conceptual design of a multi-beam klystron (MBK) for possible ILC and Project X applications is presented. The chief distinction between this MBK design and existing 10-MW MBK's is the low operating voltage of 60 kV. There are at least four compelling reasons that justify development at this time of a low-voltage MBK, namely (1) no pulse transformer; (2) no oil tank for high-voltage components and for the tube socket; (3) no high-voltage cables; and (4) modulator would be a compact 60-kV IGBT switching circuit. The proposed klystron consists of four clusters containing six beams each. The tube has common inputmore » and output cavities for all 24 beams, and individual gain cavities for each cluster. A closely related optional configuration, also for a 10 MW tube, would involve four totally independent cavity clusters with four independent input cavities and four 2.5 MW output ports, all within a common magnetic circuit. This option has appeal because the output waveguides would not require a controlled atmosphere, and because it would be easier to achieve phase and amplitude stability as required in individual SC accelerator cavities.« less

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

NASA Astrophysics Data System (ADS)

Zhang, Zehai

2015-03-01

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 TE11 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.

Experimental study on parasitic mode suppression using FeSiAl in Relativistic Klystron Amplifier.

PubMed

Zhang, Zehai

2015-03-01

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 TE11 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.

Towards coherent combining of X-band high power microwaves: phase-locked long pulse radiations by a relativistic triaxial klystron amplifier

PubMed Central

Ju, Jinchuan; Zhang, Jun; Qi, Zumin; Yang, Jianhua; Shu, Ting; Zhang, Jiande; Zhong, Huihuang

2016-01-01

The radio-frequency breakdown due to ultrahigh electric field strength essentially limits power handling capability of an individual high power microwave (HPM) generator, and this issue becomes more challenging for high frequency bands. Coherent power combining therefore provides an alternative approach to achieve an equivalent peak power of the order of ∼100 GW, which consequently provides opportunities to explore microwave related physics at extremes. The triaxial klystron amplifier (TKA) is a promising candidate for coherent power combing in high frequency bands owing to its intrinsic merit of high power capacity, nevertheless phase-locked long pulse radiation from TKA has not yet been obtained experimentally as the coaxial structure of TKA can easily lead to self-excitation of parasitic modes. In this paper, we present investigations into an X-band TKA capable of producing 1.1 GW HPMs with pulse duration of about 103 ns at the frequency of 9.375 GHz in experiment. Furthermore, the shot-to-shot fluctuation standard deviation of the phase shifts between the input and output microwaves is demonstrated to be less than 10°. The reported achievements open up prospects for accomplishing coherent power combining of X-band HPMs in the near future, and might also excite new development interests concerning high frequency TKAs. PMID:27481661

Towards coherent combining of X-band high power microwaves: phase-locked long pulse radiations by a relativistic triaxial klystron amplifier.

PubMed

Ju, Jinchuan; Zhang, Jun; Qi, Zumin; Yang, Jianhua; Shu, Ting; Zhang, Jiande; Zhong, Huihuang

2016-08-02

The radio-frequency breakdown due to ultrahigh electric field strength essentially limits power handling capability of an individual high power microwave (HPM) generator, and this issue becomes more challenging for high frequency bands. Coherent power combining therefore provides an alternative approach to achieve an equivalent peak power of the order of ∼100 GW, which consequently provides opportunities to explore microwave related physics at extremes. The triaxial klystron amplifier (TKA) is a promising candidate for coherent power combing in high frequency bands owing to its intrinsic merit of high power capacity, nevertheless phase-locked long pulse radiation from TKA has not yet been obtained experimentally as the coaxial structure of TKA can easily lead to self-excitation of parasitic modes. In this paper, we present investigations into an X-band TKA capable of producing 1.1 GW HPMs with pulse duration of about 103 ns at the frequency of 9.375 GHz in experiment. Furthermore, the shot-to-shot fluctuation standard deviation of the phase shifts between the input and output microwaves is demonstrated to be less than 10°. The reported achievements open up prospects for accomplishing coherent power combining of X-band HPMs in the near future, and might also excite new development interests concerning high frequency TKAs.

A Robust High Current Density Electron Gun

NASA Astrophysics Data System (ADS)

Mako, F.; Peter, W.; Shiloh, J.; Len, L. K.

1996-11-01

Proof-of-principle experiments are proposed to validate a new concept for a robust, high-current density Pierce electron gun (RPG) for use in klystrons and high brightness electron sources for accelerators. This rugged, long-life electron gun avoids the difficulties associated with plasma cathodes, thermionic emitters, and field emission cathodes. The RPG concept employs the emission of secondary electrons in a transmission mode as opposed to the conventional mode of reflection, i.e., electrons exit from the back face of a thin negative electron affinity (NEA) material, and in the same direction as the incident beam. Current amplification through one stage of a NEA material could be over 50 times. The amplification is accomplished in one or more stages consisting of one primary emitter and one or more secondary emitters. The primary emitter is a low current density robust emitter (e.g., thoriated tungsten). The secondary emitters are thin NEA electrodes which emit secondary electrons in the same direction as the incident beam. Specific application is targeted for a klystron gun to be used by SLAC with a cold cathode at 30-40 amps/cm^2 output from the secondary emission stage, a ~2 μs pulse length, and ~200 pulses/second.

Design of the klystron filament power supply control system for EAST LHCD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Zege; Wang, Mao; Hu, Huaichuan

A filament is a critical component of the klystron used to heat the cathode. There are totally 44 klystrons in experimental advanced superconducting tokamak (EAST) lower hybrid current drive (LHCD) systems. All klystron filaments are powered by AC power suppliers through isolated transformers. In order to achieve better klystron preheat, a klystron filament power supply control system is designed to obtain the automatic control of all filament power suppliers. Klystron filament current is measured by PLC and the interlock between filament current and klystron high voltage system is also implemented. This design has already been deployed in two LHCD systemsmore » and proves feasible completely.« less

Global synchronization of parallel processors using clock pulse width modulation

DOEpatents

Chen, Dong; Ellavsky, Matthew R.; Franke, Ross L.; Gara, Alan; Gooding, Thomas M.; Haring, Rudolf A.; Jeanson, Mark J.; Kopcsay, Gerard V.; Liebsch, Thomas A.; Littrell, Daniel; Ohmacht, Martin; Reed, Don D.; Schenck, Brandon E.; Swetz, Richard A.

2013-04-02

A circuit generates a global clock signal with a pulse width modification to synchronize processors in a parallel computing system. The circuit may include a hardware module and a clock splitter. The hardware module may generate a clock signal and performs a pulse width modification on the clock signal. The pulse width modification changes a pulse width within a clock period in the clock signal. The clock splitter may distribute the pulse width modified clock signal to a plurality of processors in the parallel computing system.

Reducing Energy Degradation Due to Back-bombardment Effect with Modulated RF Input in S-band Thermionic RF Gun

NASA Astrophysics Data System (ADS)

Kii, Toshiteru; Nakai, Yoko; Fukui, Toshio; Zen, Heishun; Kusukame, Kohichi; Okawachi, Norihito; Nakano, Masatsugu; Masuda, Kai; Ohgaki, Hideaki; Yoshikawa, Kiyoshi; Yamazaki, Tetsuo

2007-01-01

Energy degradation due to back-bombardment effect is quite serious to produce high-brightness electron beam with long macro-pulse with thermionic rf gun. To avoid the back-bombardment problem, a laser photo cathode is used at many FEL facilities, but usually it costs high and not easy to operate. Thus we have studied long pulse operation of the rf gun with thermionic cathode, which is inexpensive and easy to operate compared to the photocathode rf gun. In this work, to reduce the energy degradation, we controlled input rf power amplitude by controlling pulse forming network of the power modulator for klystron. We have successfully increased the pulse duration up to 4 μs by increasing the rf power from 7.8 MW to 8.5 MW during the macro pulse.

Different Solutions for the Generator-accelerator Module

NASA Astrophysics Data System (ADS)

Savin, E. A.; Matsievskiy, S. V.; Sobenin, N. P.; Zavadtsev, A. A.; Zavadtsev, D. A.

The most important part of the particle accelerators [1] - is the power generator together with the whole feeding system [2]. All types of generators, such as klystrons, magnetrons, solid state generators cover their own field of power and pulse length values. For the last couple of year the Inductive Output Tubes (IOT) becomes very popular because of their comparative construction simplicity: it represents the klystron output cavity with the grid modulated electron beam injected in it. Now such IOTs are used with the superconductive particle accelerators at 700 MHz operating frequency with around 1MW output power. Higher frequencies problem - is the inability to apply high frequency modulated voltage to the grid. Thus we need to figure out some kind of RF gun. But this article is about the first steps of the geometry and beam dynamics simulation in the six beam S-band IOT, which will be used with the compact biperiodic accelerating structure.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Zehai

2015-03-15

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,more » 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.« less

Magnetically Delayed Low-Pressure Gas Discharge Switching

DTIC Science & Technology

1993-06-01

the gap, minimizes this effect. It is this version of the low- pressure switch that we are presently studying. Our magnetically delayed low... pressure switch (MDLPS) test-stand was built primarily to support the long-pulse, relativistic klystron (RK) and free electron laser (FEL) work at... pressure switch and compared the performance with and without the saturable inductor. A comparison of typi- cal closure properties is shown in Fig

Multimode harmonic power measurement of 40 MW pulsed S-band klystrons

NASA Astrophysics Data System (ADS)

Fowkes, W. R.; Wu, E. S.

1984-08-01

An array of 12 calibrated RF electric field probes on the waveguide walls are used to sample the complex field profile at the second and third harmonics where the fundamental power is in the 40 MW range at 2856 MHz. The measured amplitude and phase signals from these are Fourier analyzed to determine with good accuracy the power in each of the many possible propagating modes.

Phase locking of an S-band wide-gap klystron amplifier with high power injection driven by a relativistic backward wave oscillator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai Xianchen; Zhang Jiande; Yang Jianhua

2012-12-15

Theoretical analyses and preliminary experiments on the phase-locking characteristics of an inductively loaded 2-cavity wide-gap klystron amplifier (WKA) with high power injection driven by a GW-class relativistic backward wave oscillator (RBWO) are presented. Electric power of the amplifier and oscillator is supplied by a single accelerator being capable of producing dual electron beams. The well phase-locking effect of the RBWO-WKA system requires the oscillator have good frequency reproducibility and stability from pulse to pulse. Thus, the main switch of the accelerator is externally triggered to stabilize the diode voltage and then the working frequency. In the experiment, frequency of themore » WKA is linearly locked by the RBWO. With a diode voltage of 530 kV and an input power of {approx}22 MW, an output power of {approx}230 MW with the power gain of {approx}10.2 dB is obtained from the WKA. As the main switch is triggered, the relative phase difference between the RBWO and the WKA is less than {+-}15 Degree-Sign in a single shot, and phase jitter of {+-}11 Degree-Sign is obtained within a series of shots with duration of about 40 ns.« less

Phase locking of an S-band wide-gap klystron amplifier with high power injection driven by a relativistic backward wave oscillator

NASA Astrophysics Data System (ADS)

Bai, Xianchen; Zhang, Jiande; Yang, Jianhua; Jin, Zhenxing

2012-12-01

Theoretical analyses and preliminary experiments on the phase-locking characteristics of an inductively loaded 2-cavity wide-gap klystron amplifier (WKA) with high power injection driven by a GW-class relativistic backward wave oscillator (RBWO) are presented. Electric power of the amplifier and oscillator is supplied by a single accelerator being capable of producing dual electron beams. The well phase-locking effect of the RBWO-WKA system requires the oscillator have good frequency reproducibility and stability from pulse to pulse. Thus, the main switch of the accelerator is externally triggered to stabilize the diode voltage and then the working frequency. In the experiment, frequency of the WKA is linearly locked by the RBWO. With a diode voltage of 530 kV and an input power of ˜22 MW, an output power of ˜230 MW with the power gain of ˜10.2 dB is obtained from the WKA. As the main switch is triggered, the relative phase difference between the RBWO and the WKA is less than ±15° in a single shot, and phase jitter of ±11° is obtained within a series of shots with duration of about 40 ns.

Enabling cost-effective high-current burst-mode operation in superconducting accelerators

DOE PAGES

Sheffield, Richard L.

2015-06-01

Superconducting (SC) accelerators are very efficient for CW or long-pulse operation, and normal conducting (NC) accelerators are cost effective for short-pulse operation. The addition of a short NC linac section to a SC linac can correct for the energy droop that occurs when pulsed high-current operation is required that exceeds the capability of the klystrons to replenish the cavity RF fields due to the long field fill-times of SC structures, or a requirement to support a broad range of beam currents results in variable beam loading. This paper describes the implementation of this technique to enable microseconds of high beam-current,more » 90 mA or more, in a 12 GeV SC long-pulse accelerator designed for the MaRIE 42-keV XFEL proposed for Los Alamos National Laboratory.« less

Using Large Signal Code TESLA for Wide Band Klystron Simulations

DTIC Science & Technology

2006-04-01

tuning procedure TESLA simulates of high power klystron [3]. accurately actual eigenmodes of the structure as a solution Wide band klystrons very often...on band klystrons with two-gap two-mode resonators. The decomposition of simulation region into an external results of TESLA simulations for NRL S ...UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP022454 TITLE: Using Large Signal Code TESLA for Wide Band Klystron

Pulse Width Affects Scalp Sensation of Transcranial Magnetic Stimulation.

PubMed

Peterchev, Angel V; Luber, Bruce; Westin, Gregory G; Lisanby, Sarah H

Scalp sensation and pain comprise the most common side effect of transcranial magnetic stimulation (TMS), which can reduce tolerability and complicate experimental blinding. We explored whether changing the width of single TMS pulses affects the quality and tolerability of the resultant somatic sensation. Using a controllable pulse parameter TMS device with a figure-8 coil, single monophasic magnetic pulses inducing electric field with initial phase width of 30, 60, and 120 µs were delivered in 23 healthy volunteers. Resting motor threshold of the right first dorsal interosseus was determined for each pulse width, as reported previously. Subsequently, pulses were delivered over the left dorsolateral prefrontal cortex at each of the three pulse widths at two amplitudes (100% and 120% of the pulse-width-specific motor threshold), with 20 repetitions per condition delivered in random order. After each pulse, subjects rated 0-to-10 visual analog scales for Discomfort, Sharpness, and Strength of the sensation. Briefer TMS pulses with amplitude normalized to the motor threshold were perceived as slightly more uncomfortable than longer pulses (with an average 0.89 point increase on the Discomfort scale for pulse width of 30 µs compared to 120 µs). The sensation of the briefer pulses was felt to be substantially sharper (2.95 points increase for 30 µs compared to 120 µs pulse width), but not stronger than longer pulses. As expected, higher amplitude pulses increased the perceived discomfort and strength, and, to a lesser degree the perceived sharpness. Our findings contradict a previously published hypothesis that briefer TMS pulses are more tolerable. We discovered that the opposite is true, which merits further study as a means of enhancing tolerability in the context of repetitive TMS. Copyright © 2016 Elsevier Inc. All rights reserved.

Pulse width affects scalp sensation of transcranial magnetic stimulation

PubMed Central

Peterchev, Angel V.; Luber, Bruce; Westin, Gregory G.; Lisanby, Sarah H.

2016-01-01

Background Scalp sensation and pain comprise the most common side effect of transcranial magnetic stimulation (TMS), which can reduce tolerability and complicate experimental blinding. Objective We explored whether changing the width of single TMS pulses affects the quality and tolerability of the resultant somatic sensation. Methods Using a controllable pulse parameter TMS device with a figure-8 coil, single monophasic magnetic pulses inducing electric field with initial phase width of 30, 60, and 120 µs were delivered in 23 healthy volunteers. Resting motor threshold of the right first dorsal interosseus was determined for each pulse width, as reported previously. Subsequently, pulses were delivered over the left dorsolateral prefrontal cortex at each of the three pulse widths at two amplitudes (100% and 120% of the pulse-width-specific motor threshold), with 20 repetitions per condition delivered in random order. After each pulse, subjects rated 0-to-10 visual analog scales for Discomfort, Sharpness, and Strength of the sensation. Results Briefer TMS pulses with amplitude normalized to the motor threshold were perceived as slightly more uncomfortable than longer pulses (with an average 0.89 points increase on the Discomfort scale for pulse width of 30 µs compared to 120 µs). The sensation of the briefer pulses was felt to be substantially sharper (2.95 point increase for 30 µs compared to 120 µs pulse width), but not stronger than longer pulses. As expected, higher amplitude pulses increased the perceived discomfort and strength, and, to a lesser degree the perceived sharpness. Conclusions Our findings contradict a previously published hypothesis that briefer TMS pulses are more tolerable. We discovered that the opposite is true, which merits further study as a means of enhancing tolerability in the context of repetitive TMS. PMID:28029593

Four Dimensional Analysis of Free Electron Lasers in the Amplifier Configuration

DTIC Science & Technology

2007-12-01

FEL. The power capability of this device was so much greater than that of conventional klystrons and magnetrons that records for peak power ...understand the four dimensional behavior of the high power FEL amplifier. The simulation program required dimensionless input parameters, which make...33 OPTICAL PARAMETERS inP Seed laser power inT Seed pulse duration S Distance to First Optic 0Z Rayleigh length 2 0 0 WZ π λ= λ

Project oriented klystron developments in Japan, China and India

NASA Astrophysics Data System (ADS)

Fukuda, Shigeki

2017-12-01

Modern accelerators are based on the rf technology and the klystron is the one of key components. Some special accelerator projects require their specified klystrons i.e., project-oriented klystrons. In this paper, project-oriented klystron developments for a decade in Japan are described. Related projects are ILC, cERL and SKEKB. Usually klystron is very expensive but has a finite life and needs to procure again. Trial to introduce the compatible tubes and have a competitive tender to reduce the cost is described. At the same time, since an efficiency improvement is one of the recent trend, such an attempt is also presented. International klystron collaboration among the Asian countries has been performed for a long time. In this paper, collaboration with China and India is introduced. Since topics are covered mainly author's experience, related counties described are limited.

Design and Operation of a 100 kW CW X-band Klystron for Spacecraft Communications

NASA Technical Reports Server (NTRS)

Balkcum, Adam; Mizuhara, Al; Stockwell, Brad; Begum, Rasheda; Cox, Lydia; Forrest, Scott; Perrin, Mark; Zitelli, Lou; Hoppe, Dan; Britcliffe, Mike;

Voyager Uranus encounter 0.2lbf T/VA short pulse test report

NASA Technical Reports Server (NTRS)

1986-01-01

The attitude control thrusters on the Voyager spacecraft were tested for operation at electrical pulse widths of less than the current 10-millisecond minimum to reduce impulse bit and, therefore, reduce image smear of pictures taken during the Uranus encounter. Thrusters with the identical configuration of the units on the spacecraft were fired in an altitude chamber to characterize impulse bit and impulse bit variations as a function of electrical pulse widths and to determine if the short pulses decreased thruster life. Pulse widths of 4.0 milliseconds provide approximately 45 percent of the impulse provided by a 10-ms pulse, and thruster-to-thruster and pulse-to-pulse variation is approximately plus or minus 10 percent. Pulse widths shorter than 4 ms showed wide variation, and no pulse was obtained at 3 ms. Three thrusters were each subjected to 75,000 short pulses of 4 ms or less without performance degradation. A fourth thruster exhibited partial flow blockage after 13,000 short pulses, but this was attributed to prevous test history and not short pulse exposure. The Voyager attitude control thrusters should be considered flight qualified for short pulse operation at pulse widths of 4.0 ms or more.

Ultra-narrow pulse generator with precision-adjustable pulse width

NASA Astrophysics Data System (ADS)

Fu, Zaiming; Liu, Hanglin

2018-05-01

In this paper, a novel ultra-narrow pulse generation approach is proposed. It is based on the decomposition and synthesis of pulse edges. Through controlling their relative delay, an ultra-narrow pulse could be generated. By employing field programmable gate array digital synthesis technology, the implemented pulse generator is with programmable ability. The amplitude of pulse signals is controlled by the radio frequency amplifiers and bias tees, and high precision can be achieved. More importantly, the proposed approach can break through the limitation of device's propagation delay and optimize the resolution and the accuracy of the pulse width significantly. The implemented pulse generator has two channels, whose minimum pulse width, frequency range, and amplitude range are 100 ps, 15 MHz-1.5 GHz, and 0.1 Vpp-1.8 Vpp, respectively. Both resolution of pulse width and channel delay are 1 ps, and amplitude resolution is 10 mVpp.

Control of laser pulse waveform in longitudinally excited CO2 laser by adjustment of excitation circuit

NASA Astrophysics Data System (ADS)

Uno, Kazuyuki; Jitsuno, Takahisa

2018-05-01

In a longitudinally excited CO2 laser that had a 45 cm-long discharge tube with a 1:1:2 mixture of CO2/N2/He gas at a pressure of 3.0 kPa, we realized the generation of a short laser pulse with a spike pulse width of about 200 ns and a pulse tail length of several tens of microseconds, control of the energy ratio of the spike pulse part to the pulse tail part in the short laser pulse, the generation of a long laser pulse with a pulse width of several tens of microseconds, and control of the pulse width in the long laser pulse, by using four types of excitation circuits in which the capacitance was adjusted. In the short laser pulse, the energy ratio was in the range 1:14-1:112. In the long laser pulse, the pulse width was in the range 25.7-82.7 μs.

A review of ultrabrief pulse width electroconvulsive therapy

PubMed Central

Katalinic, Natalie; Martin, Donel; Schweitzer, Isaac

2012-01-01

The effect of shortening the pulse width of the electrical stimulus when administering electroconvulsive therapy (ECT) has recently been systematically studied with promising results. This review examines reported outcomes from three randomized controlled trials which compared ultrabrief (≤0.3 ms) with brief (0.5–1.5 ms) pulse width ECT, and other recent clinical trials of ultrabrief pulse width ECT. The emerging evidence for ultrabrief pulse right unilateral (RUL) ECT suggests clinically meaningful efficacy and substantially reduced neuropsychological side effects compared with standard (brief) pulse ECT; this may represent a generational advance in the ECT technique. However, it is unclear if patients receiving ultrabrief pulse RUL ECT may have a slower speed of response and require additional treatments compared with brief pulse ECT. Therefore, until further data are available, clinicians may be well advised to use brief pulse ECT in situations requiring an urgent clinical response. The evidence base for ultrabrief bilateral ECT is limited, with findings that efficacy may be reduced compared with brief pulse width ECT. Thus ultrabrief bilateral ECT should not be used outside the research setting. PMID:23251770

Surface ablation of aluminum and silicon by ultrashort laser pulses of variable width

NASA Astrophysics Data System (ADS)

Zayarny, D. A.; Ionin, A. A.; Kudryashov, S. I.; Makarov, S. V.; Kuchmizhak, A. A.; Vitrik, O. B.; Kulchin, Yu. N.

2016-06-01

Single-shot thresholds of surface ablation of aluminum and silicon via spallative ablation by infrared (IR) and visible ultrashort laser pulses of variable width τlas (0.2-12 ps) have been measured by optical microscopy. For increasing laser pulse width τlas < 3 ps, a drastic (threefold) drop of the ablation threshold of aluminum has been observed for visible pulses compared to an almost negligible threshold variation for IR pulses. In contrast, the ablation threshold in silicon increases threefold with increasing τlas for IR pulses, while the corresponding thresholds for visible pulses remained almost constant. In aluminum, such a width-dependent decrease in ablation thresholds has been related to strongly diminished temperature gradients for pulse widths exceeding the characteristic electron-phonon thermalization time. In silicon, the observed increase in ablation thresholds has been ascribed to two-photon IR excitation, while in the visible range linear absorption of the material results in almost constant thresholds.

Secondary Electron Emission Measurements on Materials Under Stress

DTIC Science & Technology

2004-10-01

2) low rf reflection, and (3) a vacuum-tight seal. Pillbox rf windows are used for the output of S - band (2856MHz) pulsed klystrons (3.5 us, 30MW peak...of Multipactoring Electrons in an S - band Pillbox RF Window", IEEE Trans. on Nucl. Sci., Vol.39, pp.278-282, 1992. [101 Research on Microwave Window...Simulation of Multipactoring Electrons in S - Band Pillbox RF Window", IEEE Transaction on Nuclear Science, Vol. 39, No. 2, 1992. [41 R. V. Latham: "High

Development and Production of a 201 MHz, 5.0 MW Peak Power Klystron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aymar, Galen; Eisen, Edward; Stockwell, Brad

2016-01-01

Communications & Power Industries LLC has designed and manufactured the VKP-8201A, a high peak power, high gain, VHF band klystron. The klystron operates at 201.25 MHz, with 5.0 MW peak output power, 34 kW average output power, and a gain of 36 dB. The klystron is designed to operate between 1.0 MW and 4.5 MW in the linear range of the transfer curve. The klystron utilizes a unique magnetic field which enables the use of a proven electron gun design with a larger electron beam requirement. Experimental and predicted performance data are compared.

TEMPORAL EVOLUTION OF THE VELA PULSAR’S PULSE PROFILE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palfreyman, J. L.; Dickey, J. M.; Ellingsen, S. P.

The mechanisms of emission and changes in rotation frequency (“glitching”) of the Vela pulsar (J0835−4510) are not well understood. Further insight into these mechanisms can be achieved by long-term studies of integrated pulse width, timing residuals, and bright-pulse rates. We have undertaken an intensive observing campaign of Vela and collected over 6000 hr of single-pulse data. The data shows that the pulse width changes with time, including marked jumps in width after micro-glitches (frequency changes). The abundance of bright pulses also changes after some micro-glitches, but not all. The secular changes in pulse width have three possible cyclic periods thatmore » match with X-ray periodicities of a helical jet that are interpreted as free precession.« less

Broadband tunable integrated CMOS pulser with 80-ps minimum pulse width for gain-switched semiconductor lasers.

PubMed

Chen, Shaoqiang; Diao, Shengxi; Li, Pengtao; Nakamura, Takahiro; Yoshita, Masahiro; Weng, Guoen; Hu, Xiaobo; Shi, Yanling; Liu, Yiqing; Akiyama, Hidefumi

2017-07-31

High power pulsed lasers with tunable pulse widths are highly favored in many applications. When combined with power amplification, gain-switched semiconductor lasers driven by broadband tunable electric pulsers can meet such requirements. For this reason, we designed and produced a low-cost integrated CMOS pulse generator with a minimum pulse width of 80 ps and a wide tuning range of up to 270 ns using a 40-nm microelectronic process technique. We used this pulser to drive a 1.3-µm semiconductor laser diode directly, and thereafter investigated the gain-switching properties of the laser system. The optical pulses consist of a spike followed by a steady state region. Tuning the width of the electrical pulse down to approximately 1.5 ns produces optical pulses consisting only of the spike, which has a minimum pulse-width of 100 ps. Moreover, the duration of the steady state can be tuned continuously by tuning the electrical pulse width, with a peak power of approximately 5 mW. The output voltage of the electric pulser has a tuning range of 0.8-1.5 V that can be used to directly drive semiconductor laser diodes with wavelengths in the near-infrared spectrum, which are suitable for power amplification with rare-earth doped fiber amplifiers.

Well-behaved dynamics in a dissipative nonideal periodically kicked rotator.

PubMed

Chacón, R; Martínez García-Hoz, A

2003-12-01

Well-behaved dynamical properties are found in a dissipative kicked rotator subjected to a periodic string of asymmetric pulses of finite amplitude and width. The stability boundaries of the equilibrium are determined to arbitrary approximation for trigonometric pulses by means of circular harmonic balance, and to first approximation for general elliptic pulses by means of an elliptic harmonic balance method. The bifurcation behavior at the stability boundaries is determined numerically. We show how the extension of the instability region of the equilibrium in pulse parameter space reaches a maximum as the pulse width is varied. We also characterize the dependence of the mean duration of the transients to the equilibrium on the pulse width. The evolution of the basins of attraction of chaotic attractors when solely the pulse width is varied is characterized numerically. Finally, we show that the order-chaos route when solely the width of the pulses is altered appears to be especially rich, including different types of crises. The mechanism underlying these reshaping-induced crises is discussed with the aid of a two-dimensional map.

Transient high-field behavior of niobium superconducting cavities

NASA Astrophysics Data System (ADS)

Campisi, I. E.; Farkas, Z. D.; Deruyter, H.; Hogg, H. A.

1983-03-01

The breakdown behavior of a TM010 mode, S-band niobium cavity at low temperatures was examined. Unloaded Q's of 9 x 10(7) at 4.2 K and of 7 x 10(9) at 1.35 K were measured. The response of the cavity at 4.2 K to 1 MW, 2.5 (SIGMA)s pulses was tested in several cool downs. In these tests the cavity was heavily overcoupled to lower its time constant to a value of 0.80 times the RF pulse length of 2.5 (SIGMA)s. This condition maximizes the energy transfer from the klystron source to the cavity. It is indicated that fields of about 50 MV/m are reached in the cavity without breakdown.

Physics Goals for the Planned Next Linear Collider Engineering Test Facility

NASA Astrophysics Data System (ADS)

Raubenheimer, T. O.

2001-10-01

The Next Linear Collider (NLC) Collaboration is planning to construct an Engineering Test Facility (ETF) at Fermilab. As presently envisioned, the ETF would comprise a fundamental unit of the NLC main linac to include X-band klystrons and modulators, a delay-line power-distribution system (DLDS), and NLC accelerating structures that serve as loads. The principal purpose of the ETF is to validate stable operation of the power-distribution system, first without beam, then with a beam having the NLC pulse structure. This paper concerns the possibility of configuring and using the ETF to accelerate beam with an NLC pulse structure, as well as of doing experiments to measure beam-induced wakefields in the rf structures and their influence back on the beam.

Code TESLA for Modeling and Design of High-Power High-Efficiency Klystrons

DTIC Science & Technology

2011-03-01

CODE TESLA FOR MODELING AND DESIGN OF HIGH - POWER HIGH -EFFICIENCY KLYSTRONS * I.A. Chernyavskiy, SAIC, McLean, VA 22102, U.S.A. S.J. Cooke, B...and multiple-beam klystrons as high - power RF sources. These sources are widely used or proposed to be used in accelerators in the future. Comparison...of TESLA modelling results with experimental data for a few multiple-beam klystrons are shown. INTRODUCTION High - power and high -efficiency

Capacitor charging FET switcher with controller to adjust pulse width

DOEpatents

Mihalka, Alex M.

1986-01-01

A switching power supply includes an FET full bridge, a controller to drive the FETs, a programmable controller to dynamically control final output current by adjusting pulse width, and a variety of protective systems, including an overcurrent latch for current control. Power MOSFETS are switched at a variable frequency from 20-50 kHz to charge a capacitor load from 0 to 6 kV. A ferrite transformer steps up the DC input. The transformer primary is a full bridge configuration with the FET switches and the secondary is fed into a high voltage full wave rectifier whose output is connected directly to the energy storage capacitor. The peak current is held constant by varying the pulse width using predetermined timing resistors and counting pulses. The pulse width is increased as the capacitor charges to maintain peak current. A digital ripple counter counts pulses, and after the desired number is reached, an up-counter is clocked. The up-counter output is decoded to choose among different resistors used to discharge a timing capacitor, thereby determining the pulse width. A current latch shuts down the supply on overcurrent due to either excessive pulse width causing transformer saturation or a major bridge fault, i.e., FET or transformer failure, or failure of the drive circuitry.

Analysis on the mechanism of pulse-shortening in an X-band triaxial klystron amplifier due to the asymmetric mode competition

NASA Astrophysics Data System (ADS)

Qi, Zumin; Zhang, Jun; Xie, Yongjie; Zhang, Yi; Wang, Zehua; Zhou, Xiaofeng; Zhu, Jianhui; Zi, Yanyong; Zhong, Huihuang

2016-12-01

Asymmetric mode competitions are observed in the design of an X-band triaxial klystron amplifier with an asymmetric input cavity, and the generation mechanism of the asymmetric mode competition is analyzed in the paper. The results indicate that the asymmetric modes are excited in the buncher cavity. The asymmetric mode (coaxial TM612 mode) in the buncher cavity with the highest shunt impedance can start up first among the asymmetric modes with negative beam loading conductance. The coupling of the corresponding coaxial TE mode between the buncher and input cavity exacerbates the start oscillation of the asymmetric mode competition. The rationality of the analysis is demonstrated by cutting off the propagation of the corresponding coaxial TE modes between the buncher cavity and the input cavity, and the asymmetric mode competitions are thoroughly suppressed by specially designed reflectors and lossy material. In simulation, a microwave with a power of 1.28 GW and a frequency of 9.375 GHz is generated, and the extraction efficiency and the gain are 34.5% and 41.5 dB, respectively.

A concept of a wide aperture klystron with RF absorbing drift tubes for a linear collider

NASA Astrophysics Data System (ADS)

Dolbilov, G. V.; Azorsky, N. I.; Fateev, A. A.; Lebedev, N. I.; Petrov, V. A.; Shvetsov, V. S.; Yurkov, M. V.; Balakin, V. E.; Avrakhov, P. V.; Kazakov, S. Yu.; Solyak, N. A.; Teryaev, V. E.; Vogel, V. F.

1996-02-01

This paper is devoted to a problem of the optimal design of the electrodynamic structure of the X-band klystron for a linear collider. It is shown that the optimal design should provide a large aperture and a high power gain, about 80 dB. The most severe problem arising here is that of parasitic self-excitation of the klystron, which becomes more complicated at increasing aperture and power gain. Our investigations have shown that traditional methods for suppressing the self-excitation become ineffective at the desired technical parameters of the klystron. In this paper we present a novel concept of a wide aperture klystron with distributed suppression of parasitic oscillations. Results of an experimental study of the wide-aperture relativistic klystron for VLEPP are presented. Investigations have been performed using the driving beam of the JINR LIA-3000 induction accelerator ( E = 1 MeV, I = 250 A, τ = 250 ns). To suppress self-excitation parasitic modes we have used the technique of RF absorbing drift tubes. As a result, we have obtained design output parameters of the klystron and achieved a level of 100 MW output power.

Losses analysis of soft magnetic ring core under sinusoidal pulse width modulation (SPWM) and space vector pulse width modulation (SVPWM) excitations

NASA Astrophysics Data System (ADS)

Gao, Hezhe; Li, Yongjian; Wang, Shanming; Zhu, Jianguo; Yang, Qingxin; Zhang, Changgeng; Li, Jingsong

2018-05-01

Practical core losses in electrical machines differ significantly from those experimental results using the standardized measurement method, i.e. Epstein Frame method. In order to obtain a better approximation of the losses in an electrical machine, a simulation method considering sinusoidal pulse width modulation (SPWM) and space vector pulse width modulation (SVPWM) waveforms is proposed. The influence of the pulse width modulation (PWM) parameters on the harmonic components in SPWM and SVPWM is discussed by fast Fourier transform (FFT). Three-level SPWM and SVPWM are analyzed and compared both by simulation and experiment. The core losses of several ring samples magnetized by SPWM, SVPWM and sinusoidal alternating current (AC) are obtained. In addition, the temperature rise of the samples under SPWM, sinusoidal excitation are analyzed and compared.

Study program for design improvements of the X-3060 klystron. Phase 3: Electron gun fabrication and beam analyzer evaluation. Phase 4: Klystron prototype fabrication and testing

NASA Technical Reports Server (NTRS)

Goldfinger, A.

1981-01-01

A full scale model was produced to verify suggested design changes. Through beam analyzer study, the correct electron beam diameter and cross sectional profile were established in conjunction with the desired confining magnetic field. Comparative data on the performance of the X-3060 klystron, design predictions for the improved klystron, and performance data taken during acceptance testing of the prototype VKS-8274 JPL are presented.

Bandwidth Extension of an S-band, Fundamental-Mode Eight-Beam Klystron

DTIC Science & Technology

2006-04-01

Extension of an S - band , Fundamental-Mode Eight-Beam Klystron Khanh T. Nguyen Beam-Wave Research, Inc. Bethesda, MD 20814 Dean E. Pershing ATK Mission...of a five-cavity, approximately 18 cm downstream from the center of the broadband, high - power multiple-beam klystron (MBK) first gap - the logical...the circuit generates >550 kW across the band with a peak power of more than 600 kW at -3.27 Keywords: Multiple-beam klystron ; MBK; bandwidth GHz. The 1

High-Average Power Broadband 18-Beam Klystron Circuit and Collector Designs

DTIC Science & Technology

2008-04-01

high -average power S - band multiple-beam klystron are presented. The klystron will be powered by the recently completed 41.6 A, 42...al., “ High - power Four-cavity S - band multiple-beam klystron design,” IEEE Trans. Plasma Science, vol. 33, pp. 1119-1135, April 2005. [3] D.K Abe, et...APR 2008 2. REPORT TYPE 3. DATES COVERED 00-00-2008 to 00-00-2008 4. TITLE AND SUBTITLE High -average Power Broadband 18-beam

Development of a 670 GHz Extended Interaction Klystron Power Amplifier

DTIC Science & Technology

2011-03-01

Klystron Power Amplifier 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR( S ) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT...avelengths,” /40/EIK%20Tec W%20Wavelen oyski, R. Dobbs, act, High Power ction Klystron ,” Conf., Montere opments to the M or Modeling Cod 2005). ic...Research Projects Agency or the Department of Defense. Development of a 670 GHz Extended Interaction Klystron Power Amplifier David Chernin Science

Clinically insubstantial cognitive side effects of bitemporal electroconvulsive therapy at 0.5 msec pulse width.

PubMed

Warnell, Ronald L; Swartz, Conrad M; Thomson, Alice

2011-11-01

We measured cognitive side effects from bitemporal electroconvulsive therapy (ECT) using stimuli of 0.5 msec pulse width 900 milliamperes (mA). Mini-Mental State Exam (MMSE) and 21-item Hamilton Rating Scale for Depression (HRSD-21) were rated within 36 hours before and 36 hours after a series of 6 bitemporal ECT sessions on 15 patients age ≥45. MMSE remained high after ECT (pre-ECT mean 29, standard deviation [SD] 1.60, post-ECT mean 28.53, SD 1.36) with no significant change. The mean HRSD-21 fell from 27.5 to 16.3. Post-ECT MMSE was significantly and markedly higher than in previous studies of bitemporal ECT; all had used ECT stimuli of pulse width at least 1 msec. With stimuli of 0.5 msec pulse width and 900 mA, 6 bitemporal ECTs did not decrease MMSE score. This result leaves no opportunity for further decrease in basic cognitive side effects, and complements published reports of stronger physiological effects with stimuli of 0.5 msec pulse width and 900 mA. ECT stimuli of 0.5 msec pulse width and 900 mA are more desirable than wider pulse widths. Six bitemporal ECT sessions using these stimuli generally will not have more cognitive side effects than treatments with other placements, allowing maintenance of full efficacy with clinically insubstantial side effects.

LINEAR COUNT-RATE METER

DOEpatents

Henry, J.J.

1961-09-01

A linear count-rate meter is designed to provide a highly linear output while receiving counting rates from one cycle per second to 100,000 cycles per second. Input pulses enter a linear discriminator and then are fed to a trigger circuit which produces positive pulses of uniform width and amplitude. The trigger circuit is connected to a one-shot multivibrator. The multivibrator output pulses have a selected width. Feedback means are provided for preventing transistor saturation in the multivibrator which improves the rise and decay times of the output pulses. The multivibrator is connected to a diode-switched, constant current metering circuit. A selected constant current is switched to an averaging circuit for each pulse received, and for a time determined by the received pulse width. The average output meter current is proportional to the product of the counting rate, the constant current, and the multivibrator output pulse width.

Test results of 3.7 GHz 500kW CW klystron for SST1 LHCD system

NASA Astrophysics Data System (ADS)

Sharma, Promod Kumar; Ambulkar, Kiran K.; Dalakoti, Shefali; Rajan Babu, N.; Parmar, Pramod R.; Virani, Chetan G.; Thakur, Arvind L.

2012-10-01

A 3.7 GHz, LHCD system aims to driving non inductive plasma current for SST1 machine. Its capability has been enhanced up to 2 MW by adding two additional klystrons, each rated for 500kW, CW power. The additional klystrons are installed and commissioned at site, for rated power, for more than 1000 seconds, before connecting them to main LHCD system. The auxiliary systems, like supporting power supply system (magnet, filament, ion pump, etc.), active heat management system, slow and fast interlock system, transmission line pressurization system, low power rf drive system, etc. are inter-connected with klystron system through VME based data acquisition and control system for remote CW operation of klystron at rated power. The calorimetric measurements, employing Pt-100 sensors, suggests that the maximum rf power (˜500kW CW) extracted from klystron is dissipated on water cooled dummy loads. The unspent DC power (˜800 kW CW) is dissipated in collector which is heavily cooled with water flowing at ˜1300 litres/min (lpm). The power loss in the klystron body remained within 20 kW. The cavity temperature, measured using J-type thermocouple, remained below 150 ^oC. The output rf power, sampled through directional couplers and measured by rf detectors shows good agreement with calorimetric measurements. A detailed description of the klystron test set up and the test results obtained during its commissioning is presented in this paper.

Width-tunable pulse laser via optical injection induced gain modulation of semiconductor optical amplifiers

NASA Astrophysics Data System (ADS)

Pan, Honggang; Zhang, Ailing; Tong, Zhengrong; Zhang, Yue; Song, Hongyun; Yao, Yuan

2018-03-01

A width-tunable pulse laser via an optical injection induced gain modulation of a semiconductor optical amplifier (SOA) is demonstrated. When the pump current of the SOA is 330 mA or 400 mA and a continuous wave is injected into the laser cavity with different powers, bright or dark pulses with different pulse widths and frequency repetition rates are obtained. The bright and dark pulses are formed by the effect of gain dispersion and cross-gain modulation of the SOA.

High resolution, high rate X-ray spectrometer

DOEpatents

Goulding, Frederick S.; Landis, Donald A.

1987-01-01

A pulse processing system (10) for use in an X-ray spectrometer in which a ain channel pulse shaper (12) and a fast channel pulse shaper (13) each produce a substantially symmetrical triangular pulse (f, p) for each event detected by the spectrometer, with the pulse width of the pulses being substantially independent of the magnitude of the detected event and with the pulse width of the fast pulses (p) being substantially shorter than the pulse width of the main channel pulses (f). A pile-up rejector circuit (19) allows output pulses to be generated, with amplitudes linearly related to the magnitude of the detected events, whenever the peak of a main channel pulse (f) is not affected by a preceding or succeeding main channel pulse, while inhibiting output pulses wherein peak magnitudes of main channel pulses are affected by adjacent pulses. The substantially symmetrical triangular main channel pulses (f) are generated by the weighted addition (27-31) of successive RC integrations (24, 25, 26) of an RC differentiated step wave (23). The substantially symmetrical triangular fast channel pulses (p) are generated by the RC integration ( 43) of a bipolar pulse (o) in which the amplitude of the second half is 1/e that of the first half, with the RC time constant of integration being equal to one-half the width of the bipolar pulse.

Klystron-linac combination

DOEpatents

Stein, W.E.

1980-04-24

A combination klystron-linear accelerator which utilizes anti-bunch electrons generated in the klystron section as a source of electrons to be accelerated in the accelerator section. Electron beam current is controlled by second harmonic bunching, constrictor aperture size and magnetic focusing. Rf coupling is achieved by internal and external coupling.

Performance of large aperture tapered fiber phase conjugate mirror with high pulse energy and 1-kHz repetition rate.

PubMed

Zhao, Zhigang; Dong, Yantao; Pan, Sunqiang; Liu, Chong; Chen, Jun; Tong, Lixin; Gao, Qingsong; Tang, Chun

2012-01-16

A large aperture fused silica tapered fiber phase conjugate mirror is presented with a maximum 70% stimulated Brillouin scattering (SBS) reflectivity, which is obtained with 1 kHz repetition rate, 15 ns pulse width and 38 mJ input pulse energy. To the best of our knowledge, this is the highest SBS reflectivity ever reported by using optical fiber as a phase conjugate mirror for such high pulse repetition rate (1 kHz) and several tens of millijoule (mJ) input pulse energy. The influences of fiber end surface quality and pump pulse widths on SBS reflectivity are investigated experimentally. The results show that finer fiber end surface quality and longer input pulse widths are preferred for obtaining higher SBS reflectivity with higher input pulse energy. Double passing amplification experiments are also performed. 52 mJ pulse energy is achieved at 1 kHz repetition rate, with a reflected SBS pulse width of 1.5 ns and a M(2) factor of 2.3. The corresponding peak power reaches 34.6 MW. Obvious beam quality improvement is observed.

L-Band High Power Amplifiers for CEBAF Linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fugitt, Jock; Killion, Richard; Nelson, Richard

1990-09-01

The high power portion of the CEBAF RF system utilizes 340 5kW klystrons providing 339 separately controlled outputs. Modulating anodes have been included in the klystron design to provide for economically efficient operation. The design includes shunt regulator-type modulating anode power supplies running from the cathode power supply, and switching filament power supplies. Remotely programmable filament voltage allows maximum cathode life to be realized. Klystron operating setpoint and fast klystron protection logic are provided by individual external CEBAF RF control modules. A single cathode power supply powers a block of eight klystrons. The design includes circulators and custom extrusion andmore » hybrid waveguide components which have allowed reduced physical size and lower cost in the design of the WR-650 waveguide transmission system.« less

Revisiting NMR composite pulses for broadband 2H excitation

PubMed Central

Shen, Ming; Roopchand, Rabia; Mananga, Eugene S.; Amoureux, Jean-Paul; Chen, Qun; Boutis, Gregory S.; Hu, Bingwen

2014-01-01

Quadrupolar echo NMR spectroscopy of static solids often requires RF excitation that covers spectral widths exceeding 100 kHz, which is difficult to obtain due to instrumental limitations. In this work we revisit four well-known composite pulses (COM-I, II, III and IV) for broadband excitation in deuterium quadrupolar echo spectroscopy. These composite pulses are combined with several phase cycling schemes that were previously shown to decrease finite pulse width distortions in deuterium solid-echo experiments performed with two single pulses. The simulations and experiments show that COM-II and IV composite pulses combined with an 8-step phase cycling aid in achieving broadband excitation with limited pulse width distortions. PMID:25583576

SYSTEM FOR AND METHOD OF DETERMINING RANGE

DOEpatents

Horrell, M.W.; Sanders, E.R.

1963-11-01

A system and method for indicating a predetermined altitude of an object or aircraft is described. The device utilizes a pulse transmit-receive system wherein pulses of predetermined width are transmitted towards the ground and the reflected pulses received gating only pulses having a predetermined width. (AEC)

Experimental study of atmospheric-pressure micro-plasmas for the ambient sampling of conductive materials

NASA Astrophysics Data System (ADS)

Duan, Zhengchao; He, Feng; Si, Xinlu; Bradley, James W.; Ouyang, Jiting

2018-02-01

Conductive solid material sampling by micro-plasma under ambient atmosphere was studied experimentally. A high-voltage pulse generator was utilized to drive discharge between a tungsten needle and metal samples. The effects of pulse width on discharge, micro-plasma and sampling were investigated. The electrical results show that two discharge current pulses can be formed in one voltage pulse. The duration of the first current pulse is of the order of 100 ns. The duration of the second current pulse depends on the width of the voltage pulse. The electrical results also show that arc micro-plasma was generated during both current pulses. The results of the emission spectra of different sampled materials indicate that the relative emission intensity of elemental metal ions will increase with pulse width. The excitation temperature and electron density of the arc micro-plasmas increase with the voltage pulse width, which contributes to the increase of relative emission intensity of metal ions. The optical images and energy dispersive spectroscopy results of the sampling spots on metal surfaces indicate that discharge with a short voltage pulse can generate a small sputtering crater.

Hybrid Pulsed Nd:YAG Laser

NASA Astrophysics Data System (ADS)

Miller, Sawyer; Trujillo, Skyler; Fort Lewis College Laser Group Team

This work concerns the novel design of an inexpensive pulsed Nd:YAG laser, consisting of a hybrid Kerr Mode Lock (KLM) and Q-switch pulse. The two pulse generation systems work independently, non simultaneously of each other, thus generating the ability for the user to easily switch between ultra-short pulse widths or large energy density pulses. Traditionally, SF57 glass has been used as the Kerr medium. In this work, novel Kerr mode-locking mediums are being investigated including: tellurite compound glass (TeO2), carbon disulfide (CS2), and chalcogenide glass. These materials have a nonlinear index of refraction orders of magnitude,(n2), larger than SF57 glass. The Q-switched pulse will utilize a Pockels cell. As the two pulse generation systems cannot be operated simultaneously, the Pockels cell and Kerr medium are attached to kinematic mounts, allowing for quick interchange between systems. Pulse widths and repetition rates will vary between the two systems. A goal of 100 picosecond pulse widths are desired for the mode-locked system. A goal of 10 nanosecond pulse widths are desired for the Q-switch system, with a desired repetition rate of 50 Hz. As designed, the laser will be useful in imaging applications.

Performance benefits from pulsed laser heating in heat assisted magnetic recording

NASA Astrophysics Data System (ADS)

Xu, B. X.; Cen, Z. H.; Goh, J. H.; Li, J. M.; Toh, Y. T.; Zhang, J.; Ye, K. D.; Quan, C. G.

2014-05-01

Smaller cross track thermal spot size and larger down track thermal gradient are desired for increasing the density of heat assisted magnetic recording. Both parameters are affected significantly by the thermal energy accumulation and diffusion in the recording media. Pulsed laser heating is one of the ways to reduce the thermal diffusion. In this paper, we describe the benefits from the pulsed laser heating such as the dependences of the cross track thermal width, down track thermal gradient, the required laser pulse/average powers, and the transducer temperature rise on the laser pulse width at different media thermal properties. The results indicate that as the pulse width decreases, the thermal width decreases, the thermal gradient increases, the required pulse power increases and the average power decreases. For shorter pulse heating, the effects of the medium thermal properties on the thermal performances become weaker. This can greatly relax the required thermal properties of the media. The results also show that the pulsed laser heating can effectively reduce the transducer temperature rise and allow the transducer to reach its "dynamically" stable temperature more quickly.

Physics Goals for the Planned Next Linear Collider Engineering Test Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raubenheimer, Tor O

2001-10-02

The Next Linear Collider (NLC) Collaboration is planning to construct an Engineering Test Facility (ETF) at Fermilab. As presently envisioned, the ETF would comprise a fundamental unit of the NLC main linac to include X-band klystrons and modulators, a delay-line power-distribution system (DLDS), and NLC accelerating structures that serve as loads. The principal purpose of the ETF is to validate stable operation of the power-distribution system, first without beam, then with a beam having the NLC pulse structure. This paper concerns the possibility of configuring and using the ETF to accelerate beam with an NLC pulse structure, as well asmore » of doing experiments to measure beam-induced wakefields in the rf structures and their influence back on the beam.« less

Physics goals for the planned next linear collider engineering test facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Courtlandt L Bohn et al.

2001-06-26

The Next Linear Collider (NLC) Collaboration is planning to construct an Engineering Test Facility (ETF) at Fermilab. As presently envisioned, the ETF would comprise a fundamental unit of the NLC main linac to include X-band klystrons and modulators, a delay-line power-distribution system (DLDS), and NLC accelerating structures that serve as loads. The principal purpose of the ETF is to validate stable operation of the power-distribution system, first without beam, then with a beam having the NLC pulse structure. This paper concerns the possibility of configuring and using the ETF to accelerate beam with an NLC pulse structure, as well asmore » of doing experiments to measure beam-induced wakefields in the rf structures and their influence back on the beam.« less

Physics goals for the planned next linear collider engineering test facility.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bohn, C.; Michelotti, L.; Ostiguy, J.-F.

2001-07-17

The Next Linear Collider (NLC) Collaboration is planning to construct an Engineering Test Facility (ETF) at Fermilab. As presently envisioned, the ETF would comprise a fundamental unit of the NLC main linac to include X-band klystrons and modulators, a delay-line power-distribution system (DLDS), and NLC accelerating structures that serve as loads. The principal purpose of the ETF is to validate stable operation of the power-distribution system, first without beam, then with a beam having the NLC pulse structure. This paper concerns the possibility of configuring and using the ETF to accelerate beam with an NLC pulse structure, as well asmore » of doing experiments to measure beam-induced wakefields in the rf structures and their influence back on the beam.« less

Sub-nanosecond ranging possibilities of optical radar at various signal levels and transmitted pulse widths

NASA Technical Reports Server (NTRS)

Poultney, S. K.

1971-01-01

The behavior of the photomultiplier is considered, as well as the method of derivation of the photomultiplier output pulse and its relation to the reflected light pulse width and amplitude, and the calibration of range precision and accuracy. Pulsed laser radars with light pulse widths of 30, 3, and 0.1 nanosec a considered, with the 0.1 nanosec system capable of highest precision in several modes of operation, including a high repetition rate, single photoelectron reception mode. An alternate calibration scheme using a fast, triggerable light pulser is described in detail.

Dynamics of short-pulse generation via spectral filtering from intensely excited gain-switched 1.55-μm distributed-feedback laser diodes.

PubMed

Chen, Shaoqiang; Yoshita, Masahiro; Sato, Aya; Ito, Takashi; Akiyama, Hidefumi; Yokoyama, Hiroyuki

2013-05-06

Picosecond-pulse-generation dynamics and pulse-width limiting factors via spectral filtering from intensely pulse-excited gain-switched 1.55-μm distributed-feedback laser diodes were studied. The spectral and temporal characteristics of the spectrally filtered pulses indicated that the short-wavelength component stems from the initial part of the gain-switched main pulse and has a nearly linear down-chirp of 5.2 ps/nm, whereas long-wavelength components include chirped pulse-lasing components and steady-state-lasing components. Rate-equation calculations with a model of linear change in refractive index with carrier density explained the major features of the experimental results. The analysis of the expected pulse widths with optimum spectral widths was also consistent with the experimental data.

Emission Characteristics of Laser-Induced Plasma Using Collinear Long and Short Dual-Pulse Laser-Induced Breakdown Spectroscopy (LIBS).

PubMed

Wang, Zhenzhen; Deguchi, Yoshihiro; Liu, Renwei; Ikutomo, Akihiro; Zhang, Zhenzhen; Chong, Daotong; Yan, Junjie; Liu, Jiping; Shiou, Fang-Jung

2017-09-01

Collinear long and short dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) was employed to clarify the emission characteristics from laser-induced plasma. The plasma was sustained and became stable by the long pulse-width laser with the pulse width of 60 μs under free running (FR) conditions as an external energy source. Comparing the measurement results of stainless steel in air using single-pulse LIBS (SP-LIBS) and DP-LIBS, the emission intensity was markedly enhanced using DP-LIBS. The temperature of plasma induced by DP-LIBS was maintained at a higher temperature under different gate delay time and short pulse-width laser power conditions compared with those measured using short SP-LIBS. Moreover, the variation rates of plasma temperatures measured using DP-LIBS were also lower. The superior detection ability was verified by the measurement of aluminum sample in water. The spectra were clearly detected using DP-LIBS, whereas it cannot be identified using SP-LIBS of short and long pulse widths. The effects of gate delay time and short pulse-width laser power were also discussed. These results demonstrate the feasibility and enhanced detection ability of the proposed collinear long and short DP-LIBS method.

Receiver design, performance analysis, and evaluation for space-borne laser altimeters and space-to-space laser ranging systems

NASA Technical Reports Server (NTRS)

Davidson, Frederic M.; Sun, Xiaoli; Field, Christopher T.

1995-01-01

Laser altimeters measure the time of flight of the laser pulses to determine the range of the target. The simplest altimeter receiver consists of a photodetector followed by a leading edge detector. A time interval unit (TIU) measures the time from the transmitted laser pulse to the leading edge of the received pulse as it crosses a preset threshold. However, the ranging error of this simple detection scheme depends on the received, pulse amplitude, pulse shape, and the threshold. In practice, the pulse shape and the amplitude are determined by the target target characteristics which has to be assumed unknown prior to the measurement. The ranging error can be improved if one also measures the pulse width and use the average of the leading and trailing edges (half pulse width) as the pulse arrival time. The ranging error becomes independent of the received pulse amplitude and the pulse width as long as the pulse shape is symmetric. The pulse width also gives the slope of the target. The ultimate detection scheme is to digitize the received waveform and calculate the centroid as the pulse arrival time. The centroid detection always gives unbiased measurement even for asymmetric pulses. In this report, we analyze the laser altimeter ranging errors for these three detection schemes using the Mars Orbital Laser Altimeter (MOLA) as an example.

Precise delay measurement through combinatorial logic

NASA Technical Reports Server (NTRS)

Burke, Gary R. (Inventor); Chen, Yuan (Inventor); Sheldon, Douglas J. (Inventor)

2010-01-01

A high resolution circuit and method for facilitating precise measurement of on-chip delays for FPGAs for reliability studies. The circuit embeds a pulse generator on an FPGA chip having one or more groups of LUTS (the "LUT delay chain"), also on-chip. The circuit also embeds a pulse width measurement circuit on-chip, and measures the duration of the generated pulse through the delay chain. The pulse width of the output pulse represents the delay through the delay chain without any I/O delay. The pulse width measurement circuit uses an additional asynchronous clock autonomous from the main clock and the FPGA propagation delay can be displayed on a hex display continuously for testing purposes.

Design of 140 MW X-band Relativistic Klystron for Linear Collider

NASA Astrophysics Data System (ADS)

Dolbilov, G. V.; Azorsky, N. I.; Shvetsov, V. S.; Balakin, V. E.; Avrakhov, P. V.; Kazakov, S. Yu.; Teryaev, V. E.; Vogel, V. F.

1997-05-01

It has been reported at EPAC-96 on successful experimental results on achievement of 100 MW output rf power in a wide aperture (15 mm), high gain (80 dB) 14 GHz VLEPP klystron with distributed suppression of parasitic oscillations (G.V. Dolbilov et al., Proc. EPAC-96, Sitges (Barselona), 10-14 June, 1996, Vol. 3, p. 2143). This report presents design of an electrodynamic structure of the X-band klystron for linear collider with a higher efficiency up to 56 % which will be achieved at the same parameters of the electron beam (U = 1 MeV, I = 250 A, emittance 0.05 π cm\\cdotrad). Design rf output power of the klystron is 140 MW. Experimental investigations of electrodynamic structure of the klystron are planned to perform using the driving beam of the JINR LIA-3000 induction accelerator (E = 1 MeV, I = 250 A, τ = 250 ns).

Role of defects in laser-induced modifications of silica coatings and fused silica using picosecond pulses at 1053 nm: II Scaling laws and the density of precursors

DOE PAGES

Laurence, T. A.; Negres, R. A.; Ly, S.; ...

2017-06-22

Here, we investigate the role of defects in laser-induced damage of fused silica and of silica coatings produced by e-beam and PIAD processes which are used in damage resistant, multi-layer dielectric, reflective optics. We perform experiments using 1053 nm, 1–60 ps laser pulses with varying beam size, number of shots, and pulse widths in order to understand the characteristics of defects leading to laser-induced damage. This pulse width range spans a transition in mechanisms from intrinsic material ablation for short pulses to defect-dominated damage for longer pulses. We show that for pulse widths as short as 10 ps, laser-induced damagemore » properties of fused silica and silica films are dominated by isolated absorbers. The density of these precursors and their fluence dependence of damage initiation suggest a single photon process for initial energy absorption in these precursors. Higher density precursors that initiate close to the ablation threshold at shorter pulse widths are also observed in fused silica, whose fluence and pulse width scaling suggest a multiphoton initiation process. We also show that these initiated damage sites grow with subsequent laser pulses. We show that scaling laws obtained in more conventional ways depend on the beam size and on the definition of damage for ps pulses. For this reason, coupling scaling laws with the density of precursors are critical to understanding the damage limitations of optics in the ps regime.« less

Role of defects in laser-induced modifications of silica coatings and fused silica using picosecond pulses at 1053 nm: II Scaling laws and the density of precursors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laurence, T. A.; Negres, R. A.; Ly, S.

Here, we investigate the role of defects in laser-induced damage of fused silica and of silica coatings produced by e-beam and PIAD processes which are used in damage resistant, multi-layer dielectric, reflective optics. We perform experiments using 1053 nm, 1–60 ps laser pulses with varying beam size, number of shots, and pulse widths in order to understand the characteristics of defects leading to laser-induced damage. This pulse width range spans a transition in mechanisms from intrinsic material ablation for short pulses to defect-dominated damage for longer pulses. We show that for pulse widths as short as 10 ps, laser-induced damagemore » properties of fused silica and silica films are dominated by isolated absorbers. The density of these precursors and their fluence dependence of damage initiation suggest a single photon process for initial energy absorption in these precursors. Higher density precursors that initiate close to the ablation threshold at shorter pulse widths are also observed in fused silica, whose fluence and pulse width scaling suggest a multiphoton initiation process. We also show that these initiated damage sites grow with subsequent laser pulses. We show that scaling laws obtained in more conventional ways depend on the beam size and on the definition of damage for ps pulses. For this reason, coupling scaling laws with the density of precursors are critical to understanding the damage limitations of optics in the ps regime.« less

Progress Toward a Gigawatt-Class Annular Beam Klystron with a Thermionic Electron Gun

NASA Astrophysics Data System (ADS)

Fazio, M.; Carlsten, B.; Farnham, J.; Habiger, K.; Haynes, W.; Myers, J.; Nelson, E.; Smith, J.; Arfin, B.; Haase, A.

2002-08-01

In an effort to reach the gigawatt power level in the microsecond pulse length regime Los Alamos, in collaboration with SLAC, is developing an annular beam klystron (ABK) with a thermionic electron gun. We hope to address the causes of pulse shortening in very high peak power tubes by building a "hard-vacuum" tube in the 10-10 Torr range with a thermionic electron gun producing a constant impedance electron-beam. The ABK has been designed to operate at 5 Hz pulse repetition frequency to allow for RF conditioning. The electron gun has a magnetron injection gun configuration and uses a dispenser cathode running at 1100 degC to produce a 4 kA electron beam at 800 kV. The cathode is designed to run in the temperature-limited mode to help maintain beam stability in the gun. The beam-stick consisting of the electron gun, an input cavity, an idler cavity, and drift tube, and the collector has been designed collaboratively, fabricated at SLAC, then shipped to Los Alamos for testing. On the test stand at Los Alamos a low voltage emission test was performed, but unfortunately as we prepared for high voltage testing a problem with the cathode heater was encountered that prevented the cathode from reaching a high enough temperature for electron emission. A post-mortem examination will be done shortly to determine the exact cause of the heater failure. The RF design has been proceeding and is almost complete. The output cavity presents a challenging design problem in trying to efficiently extract energy from the low impedance beam while maintaining a gap voltage low enough to avoid breakdown and a Q high enough to maintain mode purity. In the next iteration, the ABK will have a new cathode assembly installed along with the remainder of the RF circuit. This paper will discuss the electron gun and the design of the RF circuit along with a report on the status of the work.

60-MW test using the 30-MW klystrons for the KEKB project

NASA Astrophysics Data System (ADS)

Fukuda, S.; Michizono, S.; Nakao, K.; Saito, Y.; Anami, S.

1995-07-01

The B-Factory is a future plan, requiring an energy upgrade of the KEK linac from 2.5 GeV to 8.0 GeV (KEKB Project). This paper describes the recent development of an S-band high-power pulse klystron to be used as the PF-linac rf-source of the B-Factory. This tube is a modified version of the existing 30-MW tube, which produces 51 MW at a 310 kV beam voltage by optimizing the focusing magnetic field. In order to increase the reliability, the cathode diameter, the gun housing, and the insulation ceramic-seal were enlarged. This tube was redesigned so as to have the same characteristics as the test results of 30-MW tubes at a higher applied voltage without changing the rf interaction region. Four prototype tubes have been manufactured; final test results showed that these new tubes produce an output power of more than 50 MW at 310 kV with an efficiency of 46%. Recently this tube has produced more than 60 MW at a 350 kV beam voltage for a demonstration test. A comparison between the FCI-code prediction and the test results is also given in this paper.

[Loudness optimized registration of compound action potential in cochlear implant recipients].

PubMed

Berger, Klaus; Hocke, Thomas; Hessel, Horst

2017-11-01

Background Postoperative measurements of compound action potentials are not always possible due to the insufficient acceptance of the CI-recipients. This study investigated the impact of different parameters on the acceptance of the measurements. Methods Compound action potentials of 16 CI recipients were measured with different pulse-widths. Recipients performed a loudness rating at the potential thresholds with the different sequences. Results Compound action potentials obtained with higher pulse-widths were rated softer than those obtained with smaller pulse-widths. Conclusions Compound action potentials measured with higher pulse-widths generate a gap between loudest acceptable presentation level and potential threshold. This gap contributes to a higher acceptance of postoperative measurements. Georg Thieme Verlag KG Stuttgart · New York.

Optimal time-domain technique for pulse width modulation in power electronics

NASA Astrophysics Data System (ADS)

Mayergoyz, I.; Tyagi, S.

2018-05-01

Optimal time-domain technique for pulse width modulation is presented. It is based on exact and explicit analytical solutions for inverter circuits, obtained for any sequence of input voltage rectangular pulses. Two optimal criteria are discussed and illustrated by numerical examples.

Pulse width and height modulation for multi-level resistance in bi-layer TaOx based RRAM

NASA Astrophysics Data System (ADS)

Alamgir, Zahiruddin; Beckmann, Karsten; Holt, Joshua; Cady, Nathaniel C.

2017-08-01

Mutli-level switching in resistive memory devices enables a wide range of computational paradigms, including neuromorphic and cognitive computing. To this end, we have developed a bi-layer tantalum oxide based resistive random access memory device using Hf as the oxygen exchange layer. Multiple, discrete resistance levels were achieved by modulating the RESET pulse width and height, ranging from 2 kΩ to several MΩ. For a fixed pulse height, OFF state resistance was found to increase gradually with the increase in the pulse width, whereas for a fixed pulse width, the increase in the pulse height resulted in drastic changes in resistance. Resistive switching in these devices transitioned from Schottky emission in the OFF state to tunneling based conduction in the ON state, based on I-V curve fitting and temperature dependent current measurements. These devices also demonstrated endurance of more than 108 cycles with a satisfactory Roff/Ron ratio and retention greater than 104 s.

Wedge-shaped slice-selective adiabatic inversion pulse for controlling temporal width of bolus in pulsed arterial spin labeling

PubMed Central

Guo, Jia; Buxton, Richard B.; Wong, Eric C.

2015-01-01

Purpose In pulsed arterial spin labeling (PASL) methods, arterial blood is labeled via inverting a slab with uniform thickness, resulting in different temporal widths of boluses in vessels with different flow velocities. This limits the temporal resolution and signal-to-noise ratio (SNR) efficiency gains in PASL-based methods intended for high temporal resolution and SNR efficiency, such as Turbo-ASL and Turbo-QUASAR. Theory and Methods A novel wedge-shaped (WS) adiabatic inversion pulse is developed by adding in-plane gradient pulses to a slice-selective (SS) adiabatic inversion pulse to linearly modulate the inversion thicknesses at different locations while maintaining the adiabatic properties of the original pulse. A hyperbolic secant (HS) based WS inversion pulse was implemented. Its performance was tested in simulations, phantom and human experiments, and compared to an SS HS inversion pulse. Results Compared to the SS inversion pulse, the WS inversion pulse is capable of inducing different inversion thicknesses at different locations. It can be adjusted to generate a uniform temporal width of boluses in arteries at locations with different flow velocities. Conclusion The WS inversion pulse can be used to control the temporal widths of labeled boluses in PASL experiments. This should benefit PASL experiments by maximizing labeling duty cycle, and improving temporal resolution and SNR efficiency. PMID:26451521

EVOLUTION OF FAST MAGNETOACOUSTIC PULSES IN RANDOMLY STRUCTURED CORONAL PLASMAS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, D.; Li, B.; Pascoe, D. J.

2015-02-01

We investigate the evolution of fast magnetoacoustic pulses in randomly structured plasmas, in the context of large-scale propagating waves in the solar atmosphere. We perform one-dimensional numerical simulations of fast wave pulses propagating perpendicular to a constant magnetic field in a low-β plasma with a random density profile across the field. Both linear and nonlinear regimes are considered. We study how the evolution of the pulse amplitude and width depends on their initial values and the parameters of the random structuring. Acting as a dispersive medium, a randomly structured plasma causes amplitude attenuation and width broadening of the fast wavemore » pulses. After the passage of the main pulse, secondary propagating and standing fast waves appear. Width evolution of both linear and nonlinear pulses can be well approximated by linear functions; however, narrow pulses may have zero or negative broadening. This arises because narrow pulses are prone to splitting, while broad pulses usually deviate less from their initial Gaussian shape and form ripple structures on top of the main pulse. Linear pulses decay at an almost constant rate, while nonlinear pulses decay exponentially. A pulse interacts most efficiently with a random medium with a correlation length of about half of the initial pulse width. This detailed model of fast wave pulses propagating in highly structured media substantiates the interpretation of EIT waves as fast magnetoacoustic waves. Evolution of a fast pulse provides us with a novel method to diagnose the sub-resolution filamentation of the solar atmosphere.« less

The 5K70SK automatically tuned, high power, S-band klystron

NASA Technical Reports Server (NTRS)

Goldfinger, A.

1977-01-01

Primary objectives include delivery of 44 5K70SK klystron amplifier tubes and 26 remote tuner assemblies with spare parts kits. Results of a reliability demonstration on a klystron test cavity are discussed, along with reliability tests performed on a remote tuning unit. Production problems and one design modification are reported and discussed. Results of PAT and DVT are included.

Multiple current peaks in room-temperature atmospheric pressure homogenous dielectric barrier discharge plasma excited by high-voltage tunable nanosecond pulse in air

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, De-Zheng; Wang, Wen-Chun; Zhang, Shuai

2013-05-13

Room temperature homogenous dielectric barrier discharge plasma with high instantaneous energy efficiency is acquired by using nanosecond pulse voltage with 20-200 ns tunable pulse width. Increasing the voltage pulse width can lead to the generation of regular and stable multiple current peaks in each discharge sequence. When the voltage pulse width is 200 ns, more than 5 organized current peaks can be observed under 26 kV peak voltage. Investigation also shows that the organized multiple current peaks only appear in homogenous discharge mode. When the discharge is filament mode, organized multiple current peaks are replaced by chaotic filament current peaks.

Design of a variable width pulse generator feasible for manual or automatic control

NASA Astrophysics Data System (ADS)

Vegas, I.; Antoranz, P.; Miranda, J. M.; Franco, F. J.

2017-01-01

A variable width pulse generator featuring more than 4-V peak amplitude and less than 10-ns FWHM is described. In this design the width of the pulses is controlled by means of the control signal slope. Thus, a variable transition time control circuit (TTCC) is also developed, based on the charge and discharge of a capacitor by means of two tunable current sources. Additionally, it is possible to activate/deactivate the pulses when required, therefore allowing the creation of any desired pulse pattern. Furthermore, the implementation presented here can be electronically controlled. In conclusion, due to its versatility, compactness and low cost it can be used in a wide variety of applications.

Operating Experience and Reliability Improvements on the 5 kW CW Klystron at Jefferson Lab

NASA Astrophysics Data System (ADS)

Nelson, R.; Holben, S.

1997-05-01

With substantial operating hours on the RF system, considerable information on reliability of the 5 kW CW klystrons has been obtained. High early failure rates led to examination of the operating conditions and failure modes. Internal ceramic contamination caused premature failure of gun potting material and ultimate tube demise through arcing or ceramic fracture. A planned course of repotting and reconditioning of approximately 300 klystrons, plus careful attention to operating conditions and periodic analysis of operational data, has substantially reduced the failure rate. It is anticipated that implementation of planned supplemental monitoring systems for the klystrons will allow most catastrophic failures to be avoided. By predicting end of life, tubes can be changed out before they fail, thus minimizing unplanned downtime. Initial tests have also been conducted on this same klystron operated at higher voltages with resultant higher output power. The outcome of these tests will provide information to be considered for future upgrades to the accelerator.

Large-Signal Klystron Simulations Using KLSC

NASA Astrophysics Data System (ADS)

Carlsten, B. E.; Ferguson, P.

1997-05-01

We describe a new, 2-1/2 dimensional, klystron-simulation code, KLSC. This code has a sophisticated input cavity model for calculating the klystron gain with arbitrary input cavity matching and tuning, and is capable of modeling coupled output cavities. We will discuss the input and output cavity models, and present simulation results from a high-power, S-band design. We will use these results to explore tuning issues with coupled output cavities.

Coherent Structures and Chaos Control in High-Power Microwave Devices

DTIC Science & Technology

2006-06-29

Theory of Multiresonator Cylindrical Magnetrons 2. High - Power Klystron Research 9 2.1. Determination of the Current Limit on the Confinement of Finite...Size Bunched Pencil Beams in High - Power Relativistic Klystrons 2.2. Exploration of the Possibility of Magnetic Cusp Formation in Highly Bunched...Annular Beams in High - Power Relativistic Klystrons 3. Development of Ellipse-Shaped Ribbon-Beam Theory for HPM Device Applications 12 3.1. Theory of

High Power Microwave Tubes: Basics and Trends, Volume 2

NASA Astrophysics Data System (ADS)

Kesari, Vishal; Basu, B. N.

2018-01-01

Volume 2 of the book begins with chapter 6, in which we have taken up conventional MWTs (such as TWTs, klystrons, including multi-cavity and multi-beam klystrons, klystron variants including reflex klystron, IOT, EIK, EIO and twystron, and crossed-field tubes, namely, magnetron, CFA and carcinotron). In chapter 7, we have taken up fast-wave tubes (such as gyrotron, gyro-BWO, gyro-klystron, gyro-TWT, CARM, SWCA, hybrid gyro-tubes and peniotron). In chapter 8, we discuss vacuum microelectronic tubes (such as klystrino module, THz gyrotron and clinotron BWO); plasma-assisted tubes (such as PWT, plasma-filled TWT, BWO, including PASOTRON, and gyrotron); and HPM (high power microwave) tubes (such as relativistic TWT, relativistic BWO, RELTRON (variant of relativistic klystron), relativistic magnetron, high power Cerenkov tubes including SWO, RDG or orotron, MWCG and MWDG, bremsstrahlung radiation type tube, namely, vircator, and M-type tube MILO). In Chapter 9, we provide handy information about the frequency and power ranges of common MWTs, although more such information is provided at relevant places in the rest of the book as and where necessary. Chapter 10 is an epilogue that sums up the authors' attempt to bring out the various aspects of the basics of and trends in high power MWTs.

Feasibility of producing a short, high energy s-band linear accelerator using a klystron power source.

PubMed

Baillie, Devin; St Aubin, J; Fallone, B G; Steciw, S

2013-04-01

To use a finite-element method (FEM) model to study the feasibility of producing a short s-band (2.9985 GHz) waveguide capable of producing x-rays energies up to 10 MV, for applications in a linac-MR, as well as conventional radiotherapy. An existing waveguide FEM model developed by the authors' group is used to simulate replacing the magnetron power source with a klystron. Peak fields within the waveguide are compared with a published experimental threshold for electric breakdown. The RF fields in the first accelerating cavity are scaled, approximating the effect of modifications to the first coupling cavity. Electron trajectories are calculated within the RF fields, and the energy spectrum, beam current, and focal spot of the electron beam are analyzed. One electron spectrum is selected for Monte Carlo simulations and the resulting PDD compared to measurement. When the first cavity fields are scaled by a factor of 0.475, the peak magnitude of the electric fields within the waveguide are calculated to be 223.1 MV∕m, 29% lower than the published threshold for breakdown at this operating frequency. Maximum electron energy increased from 6.2 to 10.4 MeV, and beam current increased from 134 to 170 mA. The focal spot FWHM is decreased slightly from 0.07 to 0.05 mm, and the width of the energy spectrum increased slightly from 0.44 to 0.70 MeV. Monte Carlo results show dmax is at 2.15 cm for a 10 × 10 cm(2) field, compared with 2.3 cm for a Varian 10 MV linac, while the penumbral widths are 4.8 and 5.6 mm, respectively. The authors' simulation results show that a short, high-energy, s-band accelerator is feasible and electric breakdown is not expected to interfere with operation at these field strengths. With minor modifications to the first coupling cavity, all electron beam parameters are improved.

Reactive nanolaminate pulsed-laser ignition mechanism: Modeling and experimental evidence of diffusion limited reactions

DOE PAGES

Yarrington, C. D.; Abere, M. J.; Adams, D. P.; ...

2017-04-03

We irradiated Al/Pt nanolaminates with a bilayer thickness (tb, width of an Al/Pt pair-layer) of 164 nm with single laser pulses with durations of 10 ms and 0.5 ms at 189 W/cm 2 and 1189 W/cm 2, respectively. The time to ignition was measured for each pulse, and shorter ignition times were observed for the higher power/shorter pulse width. While the shorter pulse shows uniform brightness, videographic images of the irradiated area shortly after ignition show a non-uniform radial brightness for the longer pulse. A diffusion-limited single step reaction mechanism was implemented in a finite element package to model themore » progress from reactants to products at both pulse widths. Finally, the model captures well both the observed ignition delay and qualitative observations regarding the non-uniform radial temperature.« less

Upgrade to a programmable timing system for the KOMAC proton linac and multi-purpose beam lines

NASA Astrophysics Data System (ADS)

Song, Young-Gi

2016-09-01

The KOMAC facility consists of low-energy components, including a 50-keV ion source, a lowenergy beam transport (LEBT), a 3-MeV radio-frequency quadrupole (RFQ), and a 20-MeV drift tube linac (DTL), as well as high-energy components, including seven DTL tanks for the 100-MeV proton beam. The KOMAC includes ten beam lines, five for 20-MeV beams and five for 100-MeV beams. The peak beam current and the maximum beam duty are 20 mA and 24% for the 20-MeV linac and 20 mA and 8% for the 100-MeV linac, respectively. Four high-voltage convertor modulators are used. Each modulator drives two or three klystrons. The peak output power is 5.8 MW, and the average power is 520 kW with a duty of 9%. The pulse width and repetition rate are 1.5 ms and 60 Hz, respectively. Each component of the pulsed operation mode has a timing trigger signal with precision synchronization. A timing system for beam extraction and for diagnostic components is required to provide precise pulse signals synchronized with a 300-MHz RF reference frequency. In addition, the timing parameters should be capable of real-time changes in accordance with the beam power. The KOMAC timing system has been upgraded to a programmable Micro Research Finland (MRF) event timing system that is synchronized with the RF, AC main frequency and with the global positioning system (GPS) 1-PPS signal. The event timing system consists of an event generator (EVG) and an event receiver (EVR). The event timing system is integrated with the KOMAC control system by using experimental physics and industrial control system (EPICS) software. For preliminary hardware and software testing, a long operation test with a synchronization of 300-MHz RF reference and 60-Hz AC has been completed successfully. In this paper, we will describe the software implementation, the testing, and the installation of the new timing system.

Ignition Characteristics of Single-Walled Carbon Nanotubes (SWCNTs) Utilizing a Camera Flash for Distributed Ignition of Liquid Sprays (Preprint)

DTIC Science & Technology

2008-10-01

acoustic phenomenon. Our results indicate that the shorter pulse width (with lower energy/pulse) required ~30-35 mJ/pulse to initiate ignition of... acoustic behavior and some other novel phenomena associated with radiation absorption by SWCNTs. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17...pressure level (SPL) from the photo acoustic phenomenon. Our results indicate that the shorter pulse width (with lower energy/pulse) required ~30-35

Tissue effects of Ho:YAG laser with varying fluences and pulse widths

NASA Astrophysics Data System (ADS)

Vari, Sandor G.; van der Veen, Maurits J.; Pergadia, Vani R.; Shi, Wei-Qiang; Duffy, J. T.; Weiss, Andrew B.; Fishbein, Michael C.; Grundfest, Warren S.

1994-02-01

We investigated the effect of varying fluence and pulse width on the ablation rate and consequent thermal damage of the Ho:YAG (2.130 micrometers ) laser. The rate of ablation on fresh bovine knee joint tissues, fibrous cartilage, hyaline cartilage, and bone in saline was determined after varying the fluence (160 - 640 J/cm2) and pulse width (150, 250, 450 microsecond(s) ec, FWHM) at a repetition rate of 2 Hz. A 400/440 micrometers fiber was used. The ablation rate increased linearly with the fluence. In fibrocartilage, different pulse durations generated significant changes in the ablation rates, but showed minor effects on hyaline cartilage and bone. The heat of ablation for all three tissue types decreased after lengthening the pulse.

Speed of response in ultrabrief and brief pulse width right unilateral ECT.

PubMed

Loo, Colleen K; Garfield, Joshua B B; Katalinic, Natalie; Schweitzer, Isaac; Hadzi-Pavlovic, Dusan

2013-05-01

Ultrabrief pulse width stimulation electroconvulsive therapy (ECT) results in less cognitive side-effects than brief pulse ECT, but recent work suggests that more treatment sessions may be required to achieve similar efficacy. In this retrospective analysis of subjects pooled from three research studies, time to improvement was analysed in 150 depressed subjects who received right unilateral ECT with a brief pulse width (at five times seizure threshold) or ultrabrief pulse width (at six times seizure threshold). Multivariate Cox regression analyses compared the number of treatments required for 50% reduction in depression scores (i.e. speed of response) in these two samples. The analyses controlled for clinical, demographic and treatment variables that differed between the samples or that were found to be significant predictors of speed of response in univariate analyses. In the multivariate analysis, older age predicted faster speed of response. There was a non-significant trend for faster time to 50% improvement with brief pulse ECT (p = 0.067). Remission rates were higher after brief pulse ECT than ultrabrief pulse ECT (p = 0.007) but response rates were similar. This study, the largest of its kind reported to date, suggests that fewer treatments may be needed to attain response with brief than ultrabrief pulse ECT and that remission rates are higher with brief pulse ECT. Further research with a larger randomized and blinded study is recommended.

Waveform synthesizer

DOEpatents

Franks, L.A.; Nelson, M.A.

1979-12-07

The invention is a method by which an optical pulse of an arbitrary but defined shape may be transformed into a virtual multitude of optical or electrical output pulse shapes. Since the method is not limited to any particular input pulse shape, the output pulse shapes that can be generated thereby are virtually unlimited. Moreover, output pulse widths as narrow as about 0.1 nsec can be readily obtained since optical pulses of less than a few picoseconds are available for use as driving pulses. The range of output pulse widths obtainable is very large, the limiting factors being the driving source energy and the particular shape of the desired output pulse.

Large-Signal Code TESLA: Current Status and Recent Development

DTIC Science & Technology

2008-04-01

K.Eppley, J.J.Petillo, “ High - power four cavity S - band multiple- beam klystron design”, IEEE Trans. Plasma Sci. , vol. 32, pp. 1119-1135, June 2004. 4...advances in the development of the large-signal code TESLA, mainly used for the modeling of high - power single- beam and multiple-beam klystron ...amplifiers. Keywords: large-signal code; multiple-beam klystrons ; serial and parallel versions. Introduction The optimization and design of new high power

Broadband supercontinuum generation with femtosecond pulse width in erbium-doped fiber laser (EDFL)

NASA Astrophysics Data System (ADS)

Rifin, S. N. M.; Zulkifli, M. Z.; Hassan, S. N. M.; Munajat, Y.; Ahmad, H.

2016-11-01

We demonstrate two flat plateaus and the low-noise spectrum of supercontinuum generation (SCG) in a highly nonlinear fiber (HNLF), injected by an amplified picosecond pulse seed of a carbon nanotube-based passively mode locked erbium-doped fiber laser. A broad spectrum of width approximately 1090 nm spanning the range 1130-2220 nm is obtained and the pulse width is compressed to the shorter duration of 70 fs. Variations of the injected peak power up to 33.78 kW into the HNLF are compared and the broad spectrum SCG profiles slightly expand for each of the injected peak powers. This straightforward configuration of SCG offers low output power and ultra-narrow femtosecond pulse width. The results facilitate the development of all fiber time-domain spectroscopy systems based on the photoconductive antenna technique.

State dependent model predictive control for orbital rendezvous using pulse-width pulse-frequency modulated thrusters

NASA Astrophysics Data System (ADS)

Li, Peng; Zhu, Zheng H.; Meguid, S. A.

2016-07-01

This paper studies the pulse-width pulse-frequency modulation based trajectory planning for orbital rendezvous and proximity maneuvering near a non-cooperative spacecraft in an elliptical orbit. The problem is formulated by converting the continuous control input, output from the state dependent model predictive control, into a sequence of pulses of constant magnitude by controlling firing frequency and duration of constant-magnitude thrusters. The state dependent model predictive control is derived by minimizing the control error of states and control roughness of control input for a safe, smooth and fuel efficient approaching trajectory. The resulting nonlinear programming problem is converted into a series of quadratic programming problem and solved by numerical iteration using the receding horizon strategy. The numerical results show that the proposed state dependent model predictive control with the pulse-width pulse-frequency modulation is able to effectively generate optimized trajectories using equivalent control pulses for the proximity maneuvering with less energy consumption.

Propagation and spatiotemporal coupling characteristics of ultra-short Gaussian vortex pulse

NASA Astrophysics Data System (ADS)

Nie, Jianye; Liu, Guodong; Zhang, Rongzhu

2018-05-01

Based on Collins diffraction integral formula, the propagation equation of ultra-short Gaussian vortex pulse beam has been derived. Using the equation, the intensity distribution variations of vortex pulse in the propagation process are calculated. Specially, the spatiotemporal coupling characteristics of ultra-short vortex beams are discussed in detail. The results show that some key parameters, such as transverse distance, transmission distance, pulse width and topological charge number will influence the spatiotemporal coupling characteristics significantly. With the increasing of transverse distance, the waveforms of the pulses distort obviously. And when transmission distance is far than 50 mm, the distribution curve of transverse intensity gradually changes into a Gaussian type. In addition, initial pulse width will affect the distribution of light field, however, when initial pulse width is larger than 3 fs, the spatiotemporal coupling effect will be insignificant. Topological charge number does not affect the time delay characteristics, since with the increasing of topological charge number, the waveform of the pulse distorts gradually but the time delay does not occur.

Pulsed helium ionization detection system

DOEpatents

Ramsey, R.S.; Todd, R.A.

1985-04-09

A helium ionization detection system is provided which produces stable operation of a conventional helium ionization detector while providing improved sensitivity and linearity. Stability is improved by applying pulsed dc supply voltage across the ionization detector, thereby modifying the sampling of the detectors output current. A unique pulse generator is used to supply pulsed dc to the detector which has variable width and interval adjust features that allows up to 500 V to be applied in pulse widths ranging from about 150 nsec to about dc conditions.

Pulsed helium ionization detection system

DOEpatents

Ramsey, Roswitha S.; Todd, Richard A.

1987-01-01

A helium ionization detection system is provided which produces stable operation of a conventional helium ionization detector while providing improved sensitivity and linearity. Stability is improved by applying pulsed dc supply voltage across the ionization detector, thereby modifying the sampling of the detectors output current. A unique pulse generator is used to supply pulsed dc to the detector which has variable width and interval adjust features that allows up to 500 V to be applied in pulse widths ranging from about 150 nsec to about dc conditions.

Effect of Pulse Width on Oxygen-fed Ozonizer

NASA Astrophysics Data System (ADS)

Okada, Sho; Wang, Douyan; Namihira, Takao; Katsuki, Sunao; Akiyama, Hidenori

Though general ozonizers based on silent discharge (barrier discharge) have been used to supply ozone at many industrial situations, there is still some problem, such as improvements of ozone yield. In this work, ozone was generated by pulsed discharge in order to improve the characteristics of ozone generation. It is known that a pulse width gives strong effect to the improvement of energy efficiency in exhaust gas processing. In this paper, the effect of pulse duration on ozone generation by pulsed discharge in oxygen would be reported.

Coherent Structures and Chaos Control in High-Power Microwave and Charged-Particle Beam Devices

DTIC Science & Technology

2009-01-31

34Equilibrium Theory of an Intense Elliptic Beam for High - Power Ribbon-Beam Klystron Applications," Proc. 2007 Part. Accel. Conf. p. 2316. Courant...34Equilibrium Theory of an Intense Elliptic Beam for High - Power Ribbon-Beam Klystron Applications," C. Chen and J. Zhou, Proc. 2007 Part. Accel. Conf. (2007...accelerator focusing systems. Over 600 high - power , high -efficiency klystrons , for example, may be needed to provide rf power for the acceleration

Inactivation of Viruses by Coherent Excitations with a Low Power Visible Femtosecond Laser

DTIC Science & Technology

2007-06-05

visible femtosecond laser having a wavelength of 425 nm and a pulse width of 100 fs, we show that M13 phages were inactivated when the laser power density...was greater than or equal to 50 MW/cm2. The inactivation of M13 phages was determined by plaque counts and had been found to depend on the pulse width...visible femtosecond laser having a wavelength of 425 nm and a pulse width of 100 fs, we show that M13 phages were inactivated when the laser power

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kant, Deepender, E-mail: dkc@ceeri.ernet.in; Joshi, L. M.; Janyani, Vijay

The klystron is a well-known microwave amplifier which uses kinetic energy of an electron beam for amplification of the RF signal. There are some limitations of conventional single beam klystron such as high operating voltage, low efficiency and bulky size at higher power levels, which are very effectively handled in Multi Beam Klystron (MBK) that uses multiple low purveyance electron beams for RF interaction. Each beam propagates along its individual transit path through a resonant cavity structure. Multi-Beam klystron cavity design is a critical task due to asymmetric cavity structure and can be simulated by 3D code only. The presentmore » paper shall discuss the design of multi beam RF cavities for klystrons operating at 2856 MHz (S-band) and 5 GHz (C-band) respectively. The design approach uses some scaling laws for finding the electron beam parameters of the multi beam device from their single beam counter parts. The scaled beam parameters are then used for finding the design parameters of the multi beam cavities. Design of the desired multi beam cavity can be optimized through iterative simulations in CST Microwave Studio.« less

The effect of laser pulse tailored welding of Inconel 718

NASA Technical Reports Server (NTRS)

Mccay, T. Dwayne; Mccay, Mary Helen; Sharp, C. Michael; Womack, Michael G.

1990-01-01

Pulse tailored laser welding has been applied to wrought, wrought grain grown, and cast Inconel 718 using a CO2 laser. Prior to welding, the material was characterized metallographically and the solid state transformation regions were identified using Differential Scanning Calorimetry and high temperature x-ray diffraction. Bead on plate welds (restrained and unrestrained) were then produced using a matrix of pulse duty cycles and pulsed average power. Subsequent characterization included heat affected zone width, penetration and underbead width, the presence of cracks, microfissures and porosity, fusion zone curvature, and precipitation and liquated region width. Pedigree welding on three selected processing conditions was shown by microstructural and dye penetrant analysis to produce no microfissures, a result which strongly indicates the viability of pulse tailored welding for microfissure free IN 718.

1645-nm single-frequency, injection-seeded Q-switched Er:YAG master oscillator and power amplifier

NASA Astrophysics Data System (ADS)

Wang, Shuo; Gao, Chunqing; Shi, Yang; Song, Rui; Na, Quanxin; Gao, Mingwei; Wang, Qing

2018-02-01

A 1645-nm injection-seeded Q-switched Er:YAG master oscillator and power amplifier system is reported. The master oscillator generates single-frequency pulse energy of 11.10 mJ with a pulse width of 188.8 ns at 200 Hz. An Er:YAG monolithic nonplanar ring oscillator is employed as a seed laser. The output pulse from the master oscillator is amplified to 14.33-mJ pulse energy through an Er:YAG amplifier, with a pulse width of 183.3 ns. The M2-factors behind the amplifier are 1.14 and 1.23 in x- and y-directions, respectively. The full width at half maximum of the fast Fourier transformation spectrum of the heterodyne beating signal is 2.84 MHz.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peratt, A.L.; Mostrom, M.A.

With the availability of 80--125 MHz microprocessors, the methodology developed for the simulation of problems in pulsed power and plasma physics on modern day supercomputers is now amenable to application on a wide range of platforms including laptops and workstations. While execution speeds with these processors do not match those of large scale computing machines, resources such as computer-aided-design (CAD) and graphical analysis codes are available to automate simulation setup and process data. This paper reports on the adaptation of IVORY, a three-dimensional, fully-electromagnetic, particle-in-cell simulation code, to this platform independent CAD environment. The primary purpose of this talk ismore » to demonstrate how rapidly a pulsed power/plasma problem can be scoped out by an experimenter on a dedicated workstation. Demonstrations include a magnetically insulated transmission line, power flow in a graded insulator stack, a relativistic klystron oscillator, and the dynamics of a coaxial thruster for space applications.« less

Theoretical analysis of low-power fast optogenetic control of firing of Chronos-expressing neurons.

PubMed

Saran, Sant; Gupta, Neha; Roy, Sukhdev

2018-04-01

A detailed theoretical analysis of low-power, fast optogenetic control of firing of Chronos-expressing neurons has been presented. A three-state model for the Chronos photocycle has been formulated and incorporated in a fast-spiking interneuron circuit model. The effect of excitation wavelength, pulse irradiance, pulse width, and pulse frequency has been studied in detail and compared with ChR2. Theoretical simulations are in excellent agreement with recently reported experimental results and bring out additional interesting features. At very low irradiances ([Formula: see text]), the plateau current in Chronos exhibits a maximum. At [Formula: see text], the plateau current is 2 orders of magnitude smaller and saturates at longer pulse widths ([Formula: see text]) compared to ChR2 ([Formula: see text]). [Formula: see text] in Chronos saturates at much shorter pulse widths (1775 pA at 1.5 ms and [Formula: see text]) than in ChR2. Spiking fidelity is also higher at lower irradiances and longer pulse widths compared to ChR2. Chronos exhibits an average maximal driven rate of over [Formula: see text] in response to [Formula: see text] stimuli, each of 1-ms pulse-width, in the intensity range 0 to [Formula: see text]. The analysis is important to not only understand the photodynamics of Chronos and Chronos-expressing neurons but also to design opsins with optimized properties and perform precision experiments with required spatiotemporal resolution.

FPGA-based Klystron linearization implementations in scope of ILC

DOE PAGES

Omet, M.; Michizono, S.; Matsumoto, T.; ...

2015-01-23

We report the development and implementation of four FPGA-based predistortion-type klystron linearization algorithms. Klystron linearization is essential for the realization of ILC, since it is required to operate the klystrons 7% in power below their saturation. The work presented was performed in international collaborations at the Fermi National Accelerator Laboratory (FNAL), USA and the Deutsches Elektronen Synchrotron (DESY), Germany. With the newly developed algorithms, the generation of correction factors on the FPGA was improved compared to past algorithms, avoiding quantization and decreasing memory requirements. At FNAL, three algorithms were tested at the Advanced Superconducting Test Accelerator (ASTA), demonstrating a successfulmore » implementation for one algorithm and a proof of principle for two algorithms. Furthermore, the functionality of the algorithm implemented at DESY was demonstrated successfully in a simulation.« less

Design, construction and evaluation of a 12.2 GHz, 4.0 kW-CW high efficiency klystron amplifier. [for satellite-borne TV broadcast transmitters

NASA Technical Reports Server (NTRS)

Vishida, J. M.; Brodersen, L. K.

1974-01-01

An analytical and experimental program is described, for studying design techniques for optimizing the conversion efficiency of klystron amplifiers, and to utilize these techniques in the development and fabrication of an X-band 4 kW cw klystron, for use in satellite-borne television broadcast transmitters. The design is based on a technique for increasing the RF beam current by using the second harmonic space charge forces in the bunched beam. Experimental analysis was also made of a method to enhance circuit efficiency in the klystron cavities. The design incorporates a collector which is demountable from the tube to facilitate multistage depressed collector experiments employing an axisymmetric, electrostatic collector for linear beam microwave tubes.

A compact high current pulsed electron gun with subnanosecond electron pulse widths

NASA Technical Reports Server (NTRS)

Khakoo, M. A.; Srivastava, S. K.

1984-01-01

A magnetically-collimated, double-pulsed electron gun capable of generating electron pulses with a peak instantaneous current of approximately 70 microamps and a temporal width of 0.35 ns (FWHM) has been developed. Calibration is accomplished by measuring the lifetime of the well known 2(1P)-to-1(1S) transition in helium (58.4nm) at a near-threshold electron-impact energy by use of the delayed-coincidence technique.

Effects of varying duty cycle and pulse width on high-intensity focused ultrasound (HIFU)-induced transcranial thrombolysis.

PubMed

Hölscher, Thilo; Raman, Rema; Fisher, David J; Ahadi, Golnaz; Zadicario, Eyal; Voie, Arne

2013-01-01

The goal was to test the effects of various combinations of pulse widths (PW) and duty cycles (DC) on high-intensity focused ultrasound (HIFU)-induced sonothrombolysis efficacy using an in vitro flow model. An ExAblate™ 4000 HIFU headsystem (InSightec, Inc., Israel) was used. Artificial blood clots were placed into test tubes inside a human calvarium and exposed to pulsatile flow. Four different duty cycles were tested against four different pulse widths. For all study groups, an increase in thrombolysis efficacy could be seen in association with increasing DC and/or PW (p < 0.0001). Using transcranial HIFU, significant thrombolysis can be achieved within seconds and without the use of lytic drugs in vitro. Longer duty cycles in combination with longer pulse widths seem to have the highest potential to optimize clot lysis efficacy.

Effects of varying duty cycle and pulse width on high-intensity focused ultrasound (HIFU)-induced transcranial thrombolysis

PubMed Central

2013-01-01

The goal was to test the effects of various combinations of pulse widths (PW) and duty cycles (DC) on high-intensity focused ultrasound (HIFU)-induced sonothrombolysis efficacy using an in vitro flow model. An ExAblate™ 4000 HIFU headsystem (InSightec, Inc., Israel) was used. Artificial blood clots were placed into test tubes inside a human calvarium and exposed to pulsatile flow. Four different duty cycles were tested against four different pulse widths. For all study groups, an increase in thrombolysis efficacy could be seen in association with increasing DC and/or PW (p < 0.0001). Using transcranial HIFU, significant thrombolysis can be achieved within seconds and without the use of lytic drugs in vitro. Longer duty cycles in combination with longer pulse widths seem to have the highest potential to optimize clot lysis efficacy. PMID:25512862

Design and performance of a pulse transformer based on Fe-based nanocrystalline core.

PubMed

Yi, Liu; Xibo, Feng; Lin, Fuchang

2011-08-01

A dry-type pulse transformer based on Fe-based nanocrystalline core with a load of 0.88 nF, output voltage of more than 65 kV, and winding ratio of 46 is designed and constructed. The dynamic characteristics of Fe-based nanocrystalline core under the impulse with the pulse width of several microseconds were studied. The pulse width and incremental flux density have an important effect on the pulse permeability, so the pulse permeability is measured under a certain pulse width and incremental flux density. The minimal volume of the toroidal pulse transformer core is determined by the coupling coefficient, the capacitors of the resonant charging circuit, incremental flux density, and pulse permeability. The factors of the charging time, ratio, and energy transmission efficiency in the resonant charging circuit based on magnetic core-type pulse transformer are analyzed. Experimental results of the pulse transformer are in good agreement with the theoretical calculation. When the primary capacitor is 3.17 μF and charge voltage is 1.8 kV, a voltage across the secondary capacitor of 0.88 nF with peak value of 68.5 kV, rise time (10%-90%) of 1.80 μs is obtained.

Recent advances in Reltron and Super-Reltron HPM source development

NASA Astrophysics Data System (ADS)

Miller, Robert B.; Muehlenweg, Carl A.; Habiger, Kerry W.; Smith, John R.; Shiffler, Donald A.

1994-05-01

Reltron and super-reltron microwave tubes use post acceleration of a well-modulated beam and multiple output cavity extraction sections to generate high power microwave pulses with excellent efficiency. We have continued our development of these tubes with emphasis being given to four specific topics: (1) Recent experiments with our 1-GHz super-reltron tube have demonstrated operation at a peak power level of 600 MW. With pulse durations of several hundred nanoseconds, the microwave energy per pulse is about 250 J. (2) We have extracted significant power (several tens of megawatts) at the third multiple (3 GHz) of our 1-GHz super-reltron tube using output cavities designed for operation in S-band. (3) We have fielded a small S-band super-reltron tube on our 260 kV modulator. We have obtained lifetime data for this tube under repetitive (20 Hz), long pulse (2 microsecond(s) ec) operating conditions. (4) We have initiated feasibility experiments of the reltron concept by post accelerating the bunched beam produced by a SLAC XK-5 klystron. In this paper we report our experimental results and discuss relevant theoretical considerations related to each of these four topics.

Relativistic klystron driven compact high gradient accelerator as an injector to an X-ray synchrotron radiation ring

DOEpatents

Yu, David U. L.

1990-01-01

A compact high gradient accelerator driven by a relativistic klystron is utilized to inject high energy electrons into an X-ray synchrotron radiation ring. The high gradients provided by the relativistic klystron enables accelerator structure to be much shorter (typically 3 meters) than conventional injectors. This in turn enables manufacturers which utilize high energy, high intensity X-rays to produce various devices, such as computer chips, to do so on a cost effective basis.

Multi-stage Depressed Collectors (MDC) for efficiency improvements of UHF broadcast klystrons

NASA Technical Reports Server (NTRS)

Kosmahl, H. G.

1982-01-01

The consumed primary power is reduced and the efficiency of traveling wave tubes is raised through the use of depressed collectors which passively convert potential energy into electric energy. Efficiency was kept with constant within a 3 dB range while the output power varied by 10 dB. Aspects to be considered in transferring this technology to UHF klystrons are the electron energy spectrum of the klystron and the magnitude of the injection angle required.

Probe-pulse optimization for nonresonant suppression in hybrid fs/ps coherent anti-Stokes Raman scattering at high temperature.

PubMed

Miller, Joseph D; Slipchenko, Mikhail N; Meyer, Terrence R

2011-07-04

Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) offers accurate thermometry at kHz rates for combustion diagnostics. In high-temperature flames, selection of probe-pulse characteristics is key to simultaneously optimizing signal-to-nonresonant-background ratio, signal strength, and spectral resolution. We demonstrate a simple method for enhancing signal-to-nonresonant-background ratio by using a narrowband Lorentzian filter to generate a time-asymmetric probe pulse with full-width-half-maximum (FWHM) pulse width of only 240 fs. This allows detection within just 310 fs after the Raman excitation for eliminating nonresonant background while retaining 45% of the resonant signal at 2000 K. The narrow linewidth is comparable to that of a time-symmetric sinc2 probe pulse with a pulse width of ~2.4 ps generated with a conventional 4-f pulse shaper. This allows nonresonant-background-free, frequency-domain vibrational spectroscopy at high temperature, as verified using comparisons to a time-dependent theoretical fs/ps CARS model.

Results of adaptive feedforward on GTA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ziomek, C.D.; Denney, P.M.; Regan, A.H.

1993-01-01

This paper presents the results of the adaptive feedforward system in use on the Ground Test Accelerator (GTA). The adaptive feedforward system was shown to correct repetitive, high-frequency errors in the amplitude and phase of the RF field of the pulsed accelerator. The adaptive feedforward system was designed as an augmentation to the RF field feedback control system and was able to extend the closed-loop bandwidth and disturbance rejection by a factor of ten. Within a second implementation, the adaptive feedforward hardware was implemented in place of the feedback control system and was shown to negate both beam transients andmore » phase droop in the klystron amplifier.« less

Results of adaptive feedforward on GTA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ziomek, C.D.; Denney, P.M.; Regan, A.H.

1993-06-01

This paper presents the results of the adaptive feedforward system in use on the Ground Test Accelerator (GTA). The adaptive feedforward system was shown to correct repetitive, high-frequency errors in the amplitude and phase of the RF field of the pulsed accelerator. The adaptive feedforward system was designed as an augmentation to the RF field feedback control system and was able to extend the closed-loop bandwidth and disturbance rejection by a factor of ten. Within a second implementation, the adaptive feedforward hardware was implemented in place of the feedback control system and was shown to negate both beam transients andmore » phase droop in the klystron amplifier.« less

flexTMS--a novel repetitive transcranial magnetic stimulation device with freely programmable stimulus currents.

PubMed

Gattinger, Norbert; Moessnang, Georg; Gleich, Bernhard

2012-07-01

Transcranial magnetic stimulation (TMS) is able to noninvasively excite neuronal populations due to brief magnetic field pulses. The efficiency and the characteristics of stimulation pulse shapes influence the physiological effect of TMS. However, commercial devices allow only a minimum of control of different pulse shapes. Basically, just sinusoidal and monophasic pulse shapes with fixed pulse widths are available. Only few research groups work on TMS devices with controllable pulse parameters such as pulse shape or pulse width. We describe a novel TMS device with a full-bridge circuit topology incorporating four insulated-gate bipolar transistor (IGBT) modules and one energy storage capacitor to generate arbitrary waveforms. This flexible TMS (flexTMS ) device can generate magnetic pulses which can be adjusted with respect to pulse width, polarity, and intensity. Furthermore, the equipment allows us to set paired pulses with a variable interstimulus interval (ISI) from 0 to 20 ms with a step size of 10  μs. All user-defined pulses can be applied continually with repetition rates up to 30 pulses per second (pps) or, respectively, up to 100 pps in theta burst mode. Offering this variety of flexibility, flexTMS will allow the enhancement of existing TMS paradigms and novel research applications.

Pulse-Width-Modulating Driver for Brushless dc Motor

NASA Technical Reports Server (NTRS)

Salomon, Phil M.

1991-01-01

High-current pulse-width-modulating driver for brushless dc motor features optical coupling of timing signals from low-current control circuitry to high-current motor-driving circuitry. Provides high electrical isolation of motor-power supply, helping to prevent fast, high-current motor-driving pulses from being coupled through power supplies into control circuitry, where they interfere with low-current control signals.

Steering population transfer of the Na2 molecule by an ultrashort pulse train

NASA Astrophysics Data System (ADS)

Niu, Dong-Hua; Wang, Shuo; Zhan, Wei-Shen; Tao, Hong-Cai; Wang, Si-Qi

2018-05-01

We theoretically investigate the complete population transfer among quantum states of the Na2 molecule using ultrashort pulse trains using the time-dependent wave packet method. The population accumulation of the target state can be steered by controlling the laser parameters, such as the variable pulse pairs, the different pulse widths, the time delays and the repetition period between two contiguous pulses; in particular, the pulse pairs and the pulse widths have a great effect on the population transfer. The calculations show that the ultrashort pulse train is a feasible solution, which can steer the population transfer from the initial state to the target state efficiently with lower peak intensities.

Device for detecting imminent failure of high-dielectric stress capacitors. [Patent application

DOEpatents

McDuff, G.G.

1980-11-05

A device is described for detecting imminent failure of a high-dielectric stress capacitor utilizing circuitry for detecting pulse width variations and pulse magnitude variations. Inexpensive microprocessor circuitry is utilized to make numerical calculations of digital data supplied by detection circuitry for comparison of pulse width data and magnitude data to determine if preselected ranges have been exceeded, thereby indicating imminent failure of a capacitor. Detection circuitry may be incorporated in transmission lines, pulse power circuitry, including laser pulse circuitry or any circuitry where capacitors or capacitor banks are utilized.

Device for detecting imminent failure of high-dielectric stress capacitors

DOEpatents

McDuff, George G.

1982-01-01

A device for detecting imminent failure of a high-dielectric stress capacitor utilizing circuitry for detecting pulse width variations and pulse magnitude variations. Inexpensive microprocessor circuitry is utilized to make numerical calculations of digital data supplied by detection circuitry for comparison of pulse width data and magnitude data to determine if preselected ranges have been exceeded, thereby indicating imminent failure of a capacitor. Detection circuitry may be incorporated in transmission lines, pulse power circuitry, including laser pulse circuitry or any circuitry where capacitors or capactior banks are utilized.

Note: A rectangular pulse generator for 50 kV voltage, 0.8 ns rise time, and 10 ns pulse width based on polymer-film switch.

PubMed

Wu, Hanyu; Zhang, Xinjun; Sun, Tieping; Zeng, Zhengzhong; Cong, Peitian; Zhang, Shaoguo

2015-10-01

In this article, we describe a rectangular pulse generator, consisting of a polymer-film switch, a tri-plate transmission line, and parallel post-shaped ceramic resistor load, for 50-kV voltage, 0.8-ns rise time, and 10-ns width. The switch and resistors are arranged in atmospheric air and the transmission line can work in atmospheric air or in transformer oil to change the pulse width from 6.7 ns to 10 ns. The fast switching and low-inductance characteristics of the polymer-film switch ensure the fast rising wavefront of <1 ns. This generator can be applied in the calibration of nanosecond voltage dividers and used for electromagnetic pulse tests as a fast-rising current injection source.

Cumulative detection probabilities and range accuracy of a pulsed Geiger-mode avalanche photodiode laser ranging system

NASA Astrophysics Data System (ADS)

Luo, Hanjun; Ouyang, Zhengbiao; Liu, Qiang; Chen, Zhiliang; Lu, Hualan

2017-10-01

Cumulative pulses detection with appropriate cumulative pulses number and threshold has the ability to improve the detection performance of the pulsed laser ranging system with GM-APD. In this paper, based on Poisson statistics and multi-pulses cumulative process, the cumulative detection probabilities and their influence factors are investigated. With the normalized probability distribution of each time bin, the theoretical model of the range accuracy and precision is established, and the factors limiting the range accuracy and precision are discussed. The results show that the cumulative pulses detection can produce higher target detection probability and lower false alarm probability. However, for a heavy noise level and extremely weak echo intensity, the false alarm suppression performance of the cumulative pulses detection deteriorates quickly. The range accuracy and precision is another important parameter evaluating the detection performance, the echo intensity and pulse width are main influence factors on the range accuracy and precision, and higher range accuracy and precision is acquired with stronger echo intensity and narrower echo pulse width, for 5-ns echo pulse width, when the echo intensity is larger than 10, the range accuracy and precision lower than 7.5 cm can be achieved.

A report on the introduction of ultrabrief pulse width ECT in a private psychiatric hospital.

PubMed

Galletly, Cherrie; Paterson, Tom; Burton, Cassandra

2012-03-01

We report on 6 months of data since the introduction of ultrabrief pulse width electroconvulsive therapy (UB ECT) at a private psychiatric hospital in Adelaide. Results suggest that psychiatrists welcomed the availability of UB ECT, with an increase in prescription of ECT. About a quarter of UB ECT patients changed to standard pulse width (SPW) ECT, but those who did respond to UB ECT had an equivalent response to those who had SPW ECT. Courses of treatment were longer with UB ECT, which was reflected in an increased length of stay.

Power supply circuit for an ion engine sequentially operated power inverters

NASA Technical Reports Server (NTRS)

Cardwell, Jr., Gilbert I. (Inventor)

2000-01-01

A power supply circuit for an ion engine suitable for a spacecraft has a voltage bus having input line and a return line. The power supply circuit includes a pulse width modulation circuit. A plurality of bridge inverter circuits is coupled to the bus and the pulse width modulation circuit. The pulse width modulation circuit generates operating signals having a variable duty cycle. Each bridge inverter has a primary winding and a secondary winding. Each secondary winding is coupled to a rectifier bridge. Each secondary winding is coupled in series with another of the plurality of rectifier bridges.

Effects of 532 nm pulsed-KTP laser parameters on vessel ablation in the avian chorioallantoic membrane: implications for vocal fold mucosa.

PubMed

Broadhurst, Matthew S; Akst, Lee M; Burns, James A; Kobler, James B; Heaton, James T; Anderson, R Rox; Zeitels, Steven M

2007-02-01

Selective vascular ablation (photoangiolysis) using pulsed lasers that target hemoglobin is an effective treatment strategy for many vocal fold lesions. However, vessel rupture with extravasation of blood reduces selectivity for vessels, which is frequently observed with the 0.45-ms, 585-nm pulsed dye laser. Previous studies have shown that vessel rupture is the result of vaporization of blood, an event that varies with laser pulse width and pulse fluence (energy per unit area). Clinical observations using a 532-nm wavelength pulsed potassium-titanyl-phosphate (KTP) laser revealed less laser-induced hemorrhage than the pulsed dye laser. This study investigated settings for the pulsed KTP laser to achieve selective vessel destruction without rupture using the avian chorioallantoic membrane under conditions similar to flexible laryngoscopic delivery of the laser in clinical practice. The chick chorioallantoic membrane offers convenient access to many small blood vessels similar in size to those targeted in human vocal fold. Using a 532-nm pulsed KTP laser, pulse width, pulse energy, and working distance from the optical delivery fiber were varied to assess influence on the ability to achieve vessel coagulation without vessel wall rupture. Third-order vessels (n = 135) were irradiated: Energy (471-550 mJ), pulse width (10, 15, 30 ms), and fiber-to-tissue distance (1 mm, 3 mm) were varied systematically. Selective vessel destruction without vessel wall rupture was more often achieved by increasing pulse width, increasing the fiber-to-tissue distance, and decreasing energy. Vessel destruction without rupture was consistently achieved using 15- or 30-ms pulses with a fiber-to-tissue distance of 3 mm (pulse fluence of 13-16 J/cm). This study substantiates our clinical observation that a 532-nm pulsed KTP laser was effective for ablating microcirculation while minimizing vessel wall rupture and hemorrhage.

A combined source of electron bunches and microwave power

NASA Astrophysics Data System (ADS)

Xie, J. L.; Wang, F. Y.; Yang, X. P.; Shen, B.; Gu, W.; Zhang, L. W.

2003-12-01

In this article, the possibility of using a high power klystron amplifier simultaneously as a microwave power source as usual and an electron bunches source by extracting the spent beam with a magnet and also as an oscillator by feedback is investigated. The purpose of this study is to demonstrate the feasibility of constructing a very compact electron linear accelerator or for other applications of electron bunches. The feasibility of the idea was first examined by computer simulation of the electron motion in a 5 MW klystron and the characteristics of the klystron spent beam. Experimental study was then carried out by installing a radio frequency cavity and a Faraday cage in sequence at the exit end of a bending magnet located at the top of the klystron collector. The energy and current of the chopped spent electron beam can then be measured. By properly choosing the feedback circuit elements, the frequency stability of the klystron in oscillator mode was proved to be good enough for linac operation. According to the results presented in this article, it is evident that an extremely compact linac for research and education with better affordability can be constructed to promote the applications of linacs.

Performance of high power S-band klystrons focused with permanent magnet

NASA Astrophysics Data System (ADS)

Fukuda, S.; Shidara, T.; Saito, Y.; Hanaki, H.; Nakao, K.; Homma, H.; Anami, S.; Tanaka, J.

1987-02-01

Performance of high power S-band klystrons focused with permanent magnet is presented. The axial magnetic field distribution and the transverse magnetic field play an important role in the tube performance. Effects of the reversal field in the collector and the cathode-anode region are discussed precisely. It is also shown that the tube efficiency is strongly affected with the residual transverse magnetic field. The allowable transverse field is less than 0.3 percent of the longitudinal field in the entire RF interaction region of the klystron.

Multi-frequency klystron designed for high efficiency

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jensen, Aaron

A multi-frequency klystron has an electron gun which generates a beam, a circuit of bunch-align-collect (BAC) tuned cavities that bunch the beam and amplify an RF signal, a collector where the beam is collected and dumped, and a standard output cavity and waveguide coupled to a window to output RF power at a fundamental mode to an external load. In addition, the klystron has additional bunch-align-collect (BAC) cavities tuned to a higher harmonic frequency, and a harmonic output cavity and waveguide coupled via a window to an additional external load.

Single-shot temporal characterization of kilojoule-level, picosecond pulses on OMEGA EP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waxer, Leon; Dorrer, Christophe; Kalb, Adam

To achieve a variety of experimental conditions, the OMEGA EP laser provides kilojoule-level pulses over a pulse-width range of 0.6 to 100 ps. Precise knowledge of the pulse width is important for laser system safety and the interpretation of experimental results. This paper describes the development and implementation of a single-shot, ultrashort-pulse measurement diagnostic, which provides an accurate characterization of the output pulse shape. We also present a brief overview of the measurement algorithm; discuss design considerations necessary for implementation in a complex, user-facility environment; and review the results of the diagnostic commissioning shots, which demonstrated excellent agreement with predictions.

Single-shot temporal characterization of kilojoule-level, picosecond pulses on OMEGA EP

DOE PAGES

Waxer, Leon; Dorrer, Christophe; Kalb, Adam; ...

2018-02-19

To achieve a variety of experimental conditions, the OMEGA EP laser provides kilojoule-level pulses over a pulse-width range of 0.6 to 100 ps. Precise knowledge of the pulse width is important for laser system safety and the interpretation of experimental results. This paper describes the development and implementation of a single-shot, ultrashort-pulse measurement diagnostic, which provides an accurate characterization of the output pulse shape. We also present a brief overview of the measurement algorithm; discuss design considerations necessary for implementation in a complex, user-facility environment; and review the results of the diagnostic commissioning shots, which demonstrated excellent agreement with predictions.

Purification of Nanoscale Electron-Beam-Induced Platinum Deposits via a Pulsed Laser-Induced Oxidation Reaction

DOE PAGES

Stanford, Michael G.; Lewis, Brett B.; Noh, Joo Hyon; ...

2014-11-05

Platinum–carbon deposits made via electron-beam-induced deposition were purified in this study via a pulsed laser-induced oxidation reaction and erosion of the amorphous carbon to form pure platinum. Purification proceeds from the top down and is likely catalytically facilitated via the evolving platinum layer. Thermal simulations suggest a temperature threshold of ~485 K, and the purification rate is a function of the PtC 5 thickness (80–360 nm) and laser pulse width (1–100 μs) in the ranges studied. The thickness dependence is attributed to the ~235 nm penetration depth of the PtC 5 composite at the laser wavelength, and the pulse-width dependencemore » is attributed to the increased temperatures achieved at longer pulse widths. Finally, remarkably fast purification is realized at cumulative laser exposure times of less than 1 s.« less

Purification of Nanoscale Electron-Beam-Induced Platinum Deposits via a Pulsed Laser-Induced Oxidation Reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stanford, Michael G.; Lewis, Brett B.; Noh, Joo Hyon

Platinum–carbon deposits made via electron-beam-induced deposition were purified in this study via a pulsed laser-induced oxidation reaction and erosion of the amorphous carbon to form pure platinum. Purification proceeds from the top down and is likely catalytically facilitated via the evolving platinum layer. Thermal simulations suggest a temperature threshold of ~485 K, and the purification rate is a function of the PtC 5 thickness (80–360 nm) and laser pulse width (1–100 μs) in the ranges studied. The thickness dependence is attributed to the ~235 nm penetration depth of the PtC 5 composite at the laser wavelength, and the pulse-width dependencemore » is attributed to the increased temperatures achieved at longer pulse widths. Finally, remarkably fast purification is realized at cumulative laser exposure times of less than 1 s.« less

Effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier

NASA Astrophysics Data System (ADS)

Song, Rui; Lei, Cheng-Min; Chen, Sheng-Ping; Wang, Ze-Feng; Hou, Jing

2015-08-01

The effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier is investigated theoretically and experimentally. The complex Ginzburg-Landau equation and adaptive split-step Fourier method are used to simulate the propagation of pulses with different pulse widths in the fiber amplifier, and the results show that a longer pulse is more profitable in near-infrared supercontinuum generation if the central wavelength of the input laser lies in the normal dispersion region of the gain fiber. A four-stage master oscillator power amplifier configuration is adopted and the output spectra under picosecond and nanosecond input pulses are compared with each other. The experimental results are in good accordance with the simulations which can provide some guidance for further optimization of the system. Project supported by the National Natural Science Foundation of China (Grant Nos. 11404404 and 11274385) and the Outstanding Youth Fund Project of Hunan Province and the Fund of Innovation of National University of Defense Technology, China (Grant No. B120701).

Total Ionizing Dose Test Report for the UC1823A Pulse Width Modulator

NASA Technical Reports Server (NTRS)

Chen, Dakai; Forney, James

2017-01-01

The purpose of this study is to examine the total ionizing dose susceptibility for the UC1823A pulse width modulator manufactured by Texas Instruments, Inc. The part is suspected to be vulnerable to enhanced low dose rate sensitivity (ELDRS).

Resolving the shape of a sonoluminescence pulse in sulfuric acid by the use of streak camera.

PubMed

Huang, Wei; Chen, Weizhong; Cui, Weicheng

2009-06-01

A streak camera is used to measure the shape of sonoluminescence pulses from a cavitation bubble levitated stably in a sulfuric acid solution. The shape and response to an acoustic pressure field of the sonoluminescence pulse in 85% by weight sulfuric acid are qualitatively similar to those in water. However, the pulse width in sulfuric acid is wider than that in water by over one order of magnitude. The width of the sonoluminescence pulse is strongly dependent on the concentration of the sulfuric acid solution, while the skewed distribution of the shape remains unchanged.

A compact plasma pre-ionized TEA-CO2 laser pulse clipper for material processing

NASA Astrophysics Data System (ADS)

Gasmi, Taieb

2017-08-01

An extra-laser cavity CO2-TEA laser pulse clipper using gas breakdown techniques for high spatial resolution material processing and shallow material engraving and drilling processes is presented. Complete extinction of the nitrogen tail, that extends the pulse width, is obtained at pressures from 375 up to 1500 torr for nitrogen and argon gases. Excellent energy stability and pulse repeatability were further enhanced using high voltage assisted preionized plasma gas technique. Experimental data illustrates the direct correlation between laser pulse width and depth of engraving in aluminum and alumina materials.

TU-FG-BRB-08: Challenges, Limitations and Future Outlook Towards Clinical Translation of Proton Acoustic Range Verification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yousefi, S; Ahmad, M; Xiang, L

Purpose: To report our investigations of proton acoustic imaging, including computer simulations and preliminary experimental studies at clinical facilities. The ultimate achievable accuracy, sensitivity and clinical translation challenges are discussed. Methods: The acoustic pulse due to pressure rise was estimated using finite element model. Since the ionoacoustic pulse is highly dependent on the proton pulse width and energy, multiple pulse widths were studied. Based on the received signal spectrum at piezoelectric ultrasound transducer with consideration of random thermal noise, maximum spatial resolution of the proton-acoustic imaging modality was calculated. The simulation studies defined the design specifications of the system tomore » detect proton acoustic signal from Hitachi and Mevion clinical machines. A 500 KHz hydrophone with 100 dB amplification was set up in a water tank placed in front of the proton nozzle A 40 MHz data acquisition was synchronized by a trigger signal provided by the machine. Results: Given 30–800 mGy dose per pulse at the Bragg peak, the minimum number of protons detectable by the proton acoustic technique was on the order of 10×10^6 per pulse. The broader pulse widths produce signal with lower acoustic frequencies, with 10 µs pulses producing signals with frequency less than 100 kHz. As the proton beam pulse width increases, a higher dose rate is required to measure the acoustic signal. Conclusion: We have established the minimal detection limit for protonacoustic range validation for a variety of pulse parameters. Our study indicated practical proton-acoustic range verification can be feasible with a pulse shorter than 10 µs, 5×10^6 protons/pulse, 50 nA beam current and a highly sensitive ultrasonic transducer. The translational challenges into current clinical machines include proper magnetic shielding of the measurement equipment, providing a clean trigger signal from the proton machine, providing a shorter proton beam pulse and higher dose per pulse.« less

Method for detecting and distinguishing between specific types of environmental radiation using a high pressure ionization chamber with pulse-mode readout

DOE Office of Scientific and Technical Information (OSTI.GOV)

Degtiarenko, Pavel V.

An environmental radiation detector for detecting and distinguishing between all types of environmental radiation, including photons, charged particles, and neutrons. A large volume high pressure ionization chamber (HPIC) includes BF.sub.3 gas at a specific concentration to render the radiation detector sensitive to the reactions of neutron capture in Boron-10 isotope. A pulse-mode readout is connected to the ionization chamber capable of measuring both the height and the width of the pulse. The heavy charged products of the neutron capture reaction deposit significant characteristic energy of the reaction in the immediate vicinity of the reaction in the gas, producing a signalmore » with a pulse height proportional to the reaction energy, and a narrow pulse width corresponding to the essentially pointlike energy deposition in the gas. Readout of the pulse height and the pulse width parameters of the signals enables distinguishing between the different types of environmental radiation, such as gamma (x-rays), cosmic muons, and neutrons.« less

Imaging Surfaces and Nanostructures

DTIC Science & Technology

2011-02-28

Principles and Perspectives," Phys. Chern. Chern. Phys. 10, 2879 (2008). 8) A. Gahlmann, S. T. Park, and A. H. Zewail , " Ultrashort Electron Pulses ...1~ copy with high spatiotemporal reso- 104 lutions. The time resolution becomes limited only by the laser pulse width and energy width of the...definition, transformations in which atoms move at speeds of the order of I krnls is in the femtosecond domain, and although laser light pulses can

Effects of finite pulse width on two-dimensional Fourier transform electron spin resonance.

PubMed

Liang, Zhichun; Crepeau, Richard H; Freed, Jack H

2005-12-01

Two-dimensional (2D) Fourier transform ESR techniques, such as 2D-ELDOR, have considerably improved the resolution of ESR in studies of molecular dynamics in complex fluids such as liquid crystals and membrane vesicles and in spin labeled polymers and peptides. A well-developed theory based on the stochastic Liouville equation (SLE) has been successfully employed to analyze these experiments. However, one fundamental assumption has been utilized to simplify the complex analysis, viz. the pulses have been treated as ideal non-selective ones, which therefore provide uniform irradiation of the whole spectrum. In actual experiments, the pulses are of finite width causing deviations from the theoretical predictions, a problem that is exacerbated by experiments performed at higher frequencies. In the present paper we provide a method to deal with the full SLE including the explicit role of the molecular dynamics, the spin Hamiltonian and the radiation field during the pulse. The computations are rendered more manageable by utilizing the Trotter formula, which is adapted to handle this SLE in what we call a "Split Super-Operator" method. Examples are given for different motional regimes, which show how 2D-ELDOR spectra are affected by the finite pulse widths. The theory shows good agreement with 2D-ELDOR experiments performed as a function of pulse width.

The Klystron Engineering Model Development (KEMD) Task - A New Design for the Goldstone Solar System Radar (GSR)

NASA Astrophysics Data System (ADS)

Teitelbaum, L.; Liou, R.; Vodonos, Y.; Velazco, J.; Andrews, K.; Kelley, D.

2017-08-01

The Goldstone Solar System Radar (GSSR) is one of the world's great planetary radar facilities. The heart of the GSSR is its high-power transmitter, which radiates 450 kW from DSS-14, the Deep Space Network's 70-m antenna at Goldstone, by combining the output from two 250-kW klystrons. Klystrons are vacuum tube electron beam devices that are the key amplifying elements of most radio frequency telecommunications and radar transmitter systems. NASA's Science Mission Directorate sponsored the development of a new design for a 250-kW power, 50-MHz bandwidth, reliable klystron, intended to replace the aging operational devices that were developed in the mid-1990s. The design, developed in partnership with Communications & Power Industries, was verified by implementing and testing a first article prototype, the engineering model. Key elements of the design are new beam optics and focusing magnet, a seven-cavity RF body, and a modern collector able to reliably dissipate the full power of the electron beam. The first klystron based on the new VKX-7864C design was delivered to the DSN High-Power Transmitter Test Facility on November 1, 2016, the culmination of a six-year effort initiated to explore higher-resolution imaging of potentially hazardous near-Earth asteroids. The new design met or exceeded all requirements, including supporting advanced GSSR ranging modulations. The first article prototype was placed into operational service on July 26, 2017, after failure of one of the older klystrons, restoring the GSSR to full-power operations.

Pulse-width-modulated servo valve for autopilot system

NASA Technical Reports Server (NTRS)

Garner, H. D.

1974-01-01

Valve was developed for autopilot wing-lever system and is to be used in light, single-engine aircraft. Valve is controlled by electronic circuit which feeds pulse-width-modulated correction signals to two solenoids. Valve housing is cast from plastic, making it very economical to fabricate.

Auditory-nerve single-neuron thresholds to electrical stimulation from scala tympani electrodes.

PubMed

Parkins, C W; Colombo, J

1987-12-31

Single auditory-nerve neuron thresholds were studied in sensory-deafened squirrel monkeys to determine the effects of electrical stimulus shape and frequency on single-neuron thresholds. Frequency was separated into its components, pulse width and pulse rate, which were analyzed separately. Square and sinusoidal pulse shapes were compared. There were no or questionably significant threshold differences in charge per phase between sinusoidal and square pulses of the same pulse width. There was a small (less than 0.5 dB) but significant threshold advantage for 200 microseconds/phase pulses delivered at low pulse rates (156 pps) compared to higher pulse rates (625 pps and 2500 pps). Pulse width was demonstrated to be the prime determinant of single-neuron threshold, resulting in strength-duration curves similar to other mammalian myelinated neurons, but with longer chronaxies. The most efficient electrical stimulus pulse width to use for cochlear implant stimulation was determined to be 100 microseconds/phase. This pulse width delivers the lowest charge/phase at threshold. The single-neuron strength-duration curves were compared to strength-duration curves of a computer model based on the specific anatomy of auditory-nerve neurons. The membrane capacitance and resulting chronaxie of the model can be varied by altering the length of the unmyelinated termination of the neuron, representing the unmyelinated portion of the neuron between the habenula perforata and the hair cell. This unmyelinated segment of the auditory-nerve neuron may be subject to aminoglycoside damage. Simulating a 10 micron unmyelinated termination for this model neuron produces a strength-duration curve that closely fits the single-neuron data obtained from aminoglycoside deafened animals. Both the model and the single-neuron strength-duration curves differ significantly from behavioral threshold data obtained from monkeys and humans with cochlear implants. This discrepancy can best be explained by the involvement of higher level neurologic processes in the behavioral responses. These findings suggest that the basic principles of neural membrane function must be considered in developing or analyzing electrical stimulation strategies for cochlear prostheses if the appropriate stimulation of frequency specific populations of auditory-nerve neurons is the objective.

An experimental and theoretical investigation into the ``worm-hole'' effect

NASA Astrophysics Data System (ADS)

Zhao, Liang; Su, Jiancang; Zhang, Xibo; Pan, Yafeng; Wang, Limin; Fang, Jinpeng; Sun, Xu; Li, Rui; Zeng, Bo; Cheng, Jie

2013-08-01

On a nanosecond time scale, solid insulators abnormally fail in bulk rather than on surface, which is termed as the "worm-hole" effect. By using a generator with adjustable output pulse width and dozens of organic glass (PMMA) and polystyrene (PS) samples, experiments to verify this effect are conducted. The results show that under short pulses of 10 ns, all the samples fail due to bulk breakdown, whereas when the pulse width is tuned to a long pulse of 7 μs, the samples fail as a result of surface flashover. The experimental results are interpreted by analyzing the conditions for the bulk breakdown and the surface flashover. It is found that under short pulses, the flashover threshold would be as high as the bulk breakdown strength (EBD) and the flashover time delay (td) would be longer than the pulse width (τ), both of which make the dielectrics' cumulative breakdown occur easily; whereas under long pulses, that Ef is much lower than EBD and td is smaller than τ is advantageous to the occurrence of the surface flashover. In addition, a general principle on solid insulation design under short pulse condition is proposed based on the experimental results and the theoretical analysis.

Complete chirp analysis of a gain-switched pulse using an interferometric two-photon absorption autocorrelation.

PubMed

Chin, Sang Hoon; Kim, Young Jae; Song, Ho Seong; Kim, Dug Young

2006-10-10

We propose a simple but powerful scheme for the complete analysis of the frequency chirp of a gain-switched optical pulse using a fringe-resolved interferometric two-photon absorption autocorrelator. A frequency chirp imposed on the gain-switched pulse from a laser diode was retrieved from both the intensity autocorrelation trace and the envelope of the second-harmonic interference fringe pattern. To verify the accuracy of the proposed phase retrieval method, we have performed an optical pulse compression experiment by using dispersion-compensating fibers with different lengths. We have obtained close agreement by less than a 1% error between the compressed pulse widths and numerically calculated pulse widths.

Extension of FRI for modeling of electrocardiogram signals.

PubMed

Quick, R Frank; Crochiere, Ronald E; Hong, John H; Hormati, Ali; Baechler, Gilles

2012-01-01

Recent work has developed a modeling method applicable to certain types of signals having a "finite rate of innovation" (FRI). Such signals contain a sparse collection of time- or frequency-limited pulses having a restricted set of allowable pulse shapes. A limitation of past work on FRI is that all of the pulses must have the same shape. Many real signals, including electrocardiograms, consist of pulses with varying widths and asymmetry, and therefore are not well fit by the past FRI methods. We present an extension of FRI allowing pulses having variable pulse width (VPW) and asymmetry. We show example results for electrocardiograms and discuss the possibility of application to signal compression and diagnostics.

Missing pulse detector for a variable frequency source

DOEpatents

Ingram, Charles B.; Lawhorn, John H.

1979-01-01

A missing pulse detector is provided which has the capability of monitoring a varying frequency pulse source to detect the loss of a single pulse or total loss of signal from the source. A frequency-to-current converter is used to program the output pulse width of a variable period retriggerable one-shot to maintain a pulse width slightly longer than one-half the present monitored pulse period. The retriggerable one-shot is triggered at twice the input pulse rate by employing a frequency doubler circuit connected between the one-shot input and the variable frequency source being monitored. The one-shot remains in the triggered or unstable state under normal conditions even though the source period is varying. A loss of an input pulse or single period of a fluctuating signal input will cause the one-shot to revert to its stable state, changing the output signal level to indicate a missing pulse or signal.

The two-beam accelerator and the relativistic klystron power source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sessler, A.M.

1988-04-01

This paper discusses the concept of a two-beam accelerator. Two versions are discussed; one employing a free electron laser, the second employing a branched beam sent through ''transfer cavities'' as in a klystron. 14 refs., 26 figs., 1 tab. (LSP)

Ultra high vacuum test setup for electron gun

NASA Astrophysics Data System (ADS)

Pandiyar, M. L.; Prasad, M.; Jain, S. K.; Kumar, R.; Hannurkar, P. R.

2008-05-01

Ultra High Vacuum (UHV) test setup for electron gun testing has been developed. The development of next generation light sources and accelerators require development of klystron as a radio frequency power source, and in turn electron gun. This UHV electron gun test setup can be used to test the electron guns ranging from high average current, quasi-continuous wave to high peak current, single pulse etc. An electron gun has been designed, fabricated, assembled and tested for insulation up to 80 kV under the programme to develop high power klystron for future accelerators. Further testing includes the electron emission parameters characterization of the cathode, as it determines the development of a reliable and efficient electron gun with high electron emission current and high life time as well. This needs a clean ultra high vacuum to study these parameters particularly at high emission current. The cathode emission current, work function and vapour pressure of cathode surface material at high temperature studies will further help in design and development of high power electron gun The UHV electron gun test setup consists of Turbo Molecular Pump (TMP), Sputter Ion Pump (SIP), pressure gauge, high voltage and cathode power supplies, current measurement device, solenoid magnet and its power supply, residual gas analyser etc. The ultimate vacuum less than 2×10-9 mbar was achieved. This paper describes the UHV test setup for electron gun testing.

Pulsatile Hormonal Signaling to Extracellular Signal-regulated Kinase

PubMed Central

Perrett, Rebecca M.; Voliotis, Margaritis; Armstrong, Stephen P.; Fowkes, Robert C.; Pope, George R.; Tsaneva-Atanasova, Krasimira; McArdle, Craig A.

2014-01-01

Gonadotropin-releasing hormone (GnRH) is secreted in brief pulses that stimulate synthesis and secretion of pituitary gonadotropin hormones and thereby mediate control of reproduction. It acts via G-protein-coupled receptors to stimulate effectors, including ERK. Information could be encoded in GnRH pulse frequency, width, amplitude, or other features of pulse shape, but the relative importance of these features is unknown. Here we examine this using automated fluorescence microscopy and mathematical modeling, focusing on ERK signaling. The simplest scenario is one in which the system is linear, and response dynamics are relatively fast (compared with the signal dynamics). In this case integrated system output (ERK activation or ERK-driven transcription) will be roughly proportional to integrated input, but we find that this is not the case. Notably, we find that relatively slow response kinetics lead to ERK activity beyond the GnRH pulse, and this reduces sensitivity to pulse width. More generally, we show that the slowing of response kinetics through the signaling cascade creates a system that is robust to pulse width. We, therefore, show how various levels of response kinetics synergize to dictate system sensitivity to different features of pulsatile hormone input. We reveal the mathematical and biochemical basis of a dynamic GnRH signaling system that is robust to changes in pulse amplitude and width but is sensitive to changes in receptor occupancy and frequency, precisely the features that are tightly regulated and exploited to exert physiological control in vivo. PMID:24482225

Enhancement and stabilization of plasma using collinear long-short double-pulse laser-induced breakdown spectroscopy

NASA Astrophysics Data System (ADS)

Cui, Minchao; Deguchi, Yoshihiro; Wang, Zhenzhen; Fujita, Yuki; Liu, Renwei; Shiou, Fang-Jung; Zhao, Shengdun

2018-04-01

A collinear long-short dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) method was employed to enhance and stabilize the laser-induced plasma from steel sample. The long-pulse-width laser beam with the pulse width of 60 μs was generated by a Nd: YAG laser which was operated at FR (free running) mode. The comparative experiments were carried out between single pulse LIBS (SP-LIBS) and long-short DP-LIBS. The recorded results showed that the emission intensities and the temperature of plasma were enhanced by long-short DP-LIBS. The plasma images showed that the plasma was bigger and had a longer lifetime in long-short DP-LIBS situation. Through the calculation of time-resolved plasma temperature and intensity ratio, it can be concluded that the plasma was stabilized by the long-pulse-width laser beam. The long-short DP-LIBS method also generated the stable plasma condition from the samples with different initial temperatures, which overcame the difficulties of LIBS in the online measurement for steel production line.

Noise-like pulse generation in an ytterbium-doped fiber laser using tungsten disulphide

NASA Astrophysics Data System (ADS)

Zhang, Wenping; Song, Yanrong; Guoyu, Heyang; Xu, Runqin; Dong, Zikai; Li, Kexuan; Tian, Jinrong; Gong, Shuang

2017-12-01

We demonstrated the noise-like pulse (NLP) generation in an ytterbium-doped fiber (YDF) laser with tungsten disulphide (WS2). Stable fundamental mode locking and second-order harmonic mode locking were observed. The saturable absorber (SA) was a WS2-polyvinyl alcohol film. The modulation depth of the WS2 film was 2.4%, and the saturable optical intensity was 155 MW cm-2. Based on this SA, the fundamental NLP with a pulse width of 20 ns and repetition rate of 7 MHz were observed. The autocorrelation trace of output pulses had a coherent spike, which came from NLP. The average pulse width of the spike was 550 fs on the top of a broad pedestal. The second-order harmonic NLP had a spectral bandwidth of 1.3 nm and pulse width of 10 ns. With the pump power of 400 mW, the maximum output power was 22.2 mW. To the best of our knowledge, this is the first time a noise-like mode locking in an YDF laser based on WS2-SA in an all normal dispersion regime was obtained.

Effects of single pulse energy on the properties of ceramic coating prepared by micro-arc oxidation on Ti alloy

NASA Astrophysics Data System (ADS)

Wang, Jun-Hua; Wang, Jin; Lu, Yan; Du, Mao-Hua; Han, Fu-Zhu

2015-01-01

The effects of single pulse energy on the properties of ceramic coating fabricated on a Ti-6Al-4V alloy via micro-arc oxidation (MAO) in aqueous solutions containing aluminate, phosphate, and some additives are investigated. The thickness, micro-hardness, surface and cross-sectional morphology, surface roughness, and compositions of the ceramic coating are studied using eddy current thickness meter, micro-hardness tester, JB-4C Precision Surface roughness meter, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Single pulse energy remarkably influences the ceramic coating properties. The accumulative time of impulse width is an important parameter in the scientific and rational measurement of the film forming law of ceramic coating. The ceramic coating thickness approximately linearly increases with the cumulative time of impulse width. Larger impulse width resulted in higher single pulse energy, film forming rates and thicker ceramic coating thickness. The sizes of oxide particles, micro-pores and micro-cracks slightly increase with impulse width and single pulse energy. The main surface conversion products generated during MAO process in aqueous solutions containing aluminate are rutile TiO2, anatase TiO2, and a large amount of Al2TiO5. The effects of single pulse energy on the micro-hardness and phase composition of ceramic coating are not as evident as those of frequency and duty cycle.

High Power Amplifier Harmonic Output Level Measurement

NASA Technical Reports Server (NTRS)

Perez, R. M.; Hoppe, D. J.; Khan, A. R.

1995-01-01

A method is presented for the measurement of the harmonic output power of high power klystron amplifiers, involving coherent hemispherical radiation pattern measurements of the radiated klystron output. Results are discussed for the operation in saturated and unsaturated conditions, and with a waveguide harmonic filter included.

Design of a 100 MW X-band klystron

NASA Astrophysics Data System (ADS)

Eppley, Kenneth

1989-02-01

Future linear colliders will require klystrons with higher peak power at higher frequency than are currently in use. SLAC is currently designing a 100 MW klystron at 11.4 GHz as a prototype for such a tube. The gun has been designed for 440 kV and 510 amps. Transporting this beam through a 5 mm radius X-band drift tube presents the major design problem. The area convergence ratio of 190 to one is over ten times higher than is found in conventional klystrons. Even with high magnetic fields of 6 to 7 kilogauss careful matching is required to prevent excessive scalloping. Extensive EGUN and CONDOR simulations have been made to optimize the transmission and RF efficiency. The EGUN simulations indicate that better matching is possible by using resonant magnetic focusing. CONDOR calculations indicate efficiencies of 45 percent are possible with a double output cavity. We will discuss the results of the simulations and the status of the experimental program.

Anomalous broadening and shift of emission lines in a femtosecond laser plasma filament in air

NASA Astrophysics Data System (ADS)

Ilyin, A. A.; Golik, S. S.; Shmirko, K. A.; Mayor, A. Yu.; Proschenko, D. Yu.

2017-12-01

The temporal evolution of the width and shift of N I 746.8 and O I 777.4 nm lines is investigated in a filament plasma produced by a tightly focused femtosecond laser pulse (0.9 mJ, 48 fs). The nitrogen line shift and width are determined by the joint action of electron impact shift and the far-off resonance AC Stark effect. The intensive (I = 1.2·1010 W/cm2) electric field of ASE (amplified spontaneous emission) and post-pulses result in a possible LS coupling break for the O I 3p 5P level and the generation of Rabi sidebands. The blueshifted main femtosecond pulse and Rabi sideband cause the stimulated emission of the N2 1+ system. The maximal widths of emission lines are approximately 6.7 times larger than the calculated Stark widths.

Multiwavelength self-pulsating fibre laser based on cascaded SPM spectral broadening and filtering

NASA Astrophysics Data System (ADS)

Rochette, Martin; Sun, Kai; Hernández-Cordero, Juan; Chen, Lawrence R.

2008-06-01

We experimentally demonstrate the operation of a laser based on self-phase modulation followed by offset spectral filtering. This laser has three operation modes: a continuous-wave mode, a self-pulsating mode where the laser self ignites and produces pulses, and a pulse-buffering mode where no new pulse is formed from spontaneous emission noise but only pulses already propagating or pulses injected in the laser cavity can be sustained. In the self-pulsating and pulse-buffering modes, the laser is multi-wavelength and continuously tunable over the entire gain band of the amplifiers. The output pulse width is quasi transform-limited with respect to the spectral-width of the filters used in the cavity. Overall, this device provides a simple alternative to pulsed laser source and also represents a promising approach for signal buffering.

Modeling and Numerical Simulation of Microwave Pulse Propagation in Air Breakdown Environment

NASA Technical Reports Server (NTRS)

Kuo, S. P.; Kim, J.

1991-01-01

Numerical simulation is used to investigate the extent of the electron density at a distant altitude location which can be generated by a high-power ground-transmitted microwave pulse. This is done by varying the power, width, shape, and carrier frequency of the pulse. The results show that once the breakdown threshold field is exceeded in the region below the desired altitude location, electron density starts to build up in that region through cascading breakdown. The generated plasma attenuates the pulse energy (tail erosion) and thus deteriorates the energy transmission to the destined altitude. The electron density saturates at a level limited by the pulse width and the tail erosion process. As the pulse continues to travel upward, though the breakdown threshold field of the background air decreases, the pulse energy (width) is reduced more severely by the tail erosion process. Thus, the electron density grows more quickly at the higher altitude, but saturates at a lower level. Consequently, the maximum electron density produced by a single pulse at 50 km altitude, for instance, is limited to a value below 10(exp 6) cm(exp -3). Three different approaches are examined to determine if the ionization at the destined location can be improved: a repetitive pulse approach, a focused pulse approach, and two intersecting beams. Only the intersecting beam approach is found to be practical for generating the desired density level.

Pulse width modulation inverter with battery charger

DOEpatents

Slicker, James M.

1985-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a microprocessor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .theta., where .theta. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands for electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a "flyback" DC-DC converter circuit for recharging the battery.

Pulse width modulation inverter with battery charger

NASA Technical Reports Server (NTRS)

Slicker, James M. (Inventor)

1985-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a microprocessor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .theta., where .theta. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands for electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a flyback DC-DC converter circuit for recharging the battery.

Adaptive beam-width control of echolocation sounds by CF-FM bats, Rhinolophus ferrumequinum nippon, during prey-capture flight.

PubMed

Matsuta, Naohiro; Hiryu, Shizuko; Fujioka, Emyo; Yamada, Yasufumi; Riquimaroux, Hiroshi; Watanabe, Yoshiaki

2013-04-01

The echolocation sounds of Japanese CF-FM bats (Rhinolophus ferrumequinum nippon) were measured while the bats pursued a moth (Goniocraspidum pryeri) in a flight chamber. Using a 31-channel microphone array system, we investigated how CF-FM bats adjust pulse direction and beam width according to prey position. During the search and approach phases, the horizontal and vertical beam widths were ±22±5 and ±13±5 deg, respectively. When bats entered the terminal phase approximately 1 m from a moth, distinctive evasive flight by G. pryeri was sometimes observed. Simultaneously, the bats broadened the beam widths of some emissions in both the horizontal (44% of emitted echolocation pulses) and vertical planes (71%). The expanded beam widths were ±36±7 deg (horizontal) and ±30±9 deg (vertical). When moths began evasive flight, the tracking accuracy decreased compared with that during the approach phase. However, in 97% of emissions during the terminal phase, the beam width was wider than the misalignment (the angular difference between the pulse and target directions). These findings indicate that bats actively adjust their beam width to retain the moving target within a spatial echolocation window during the final capture stages.

A simple sub-nanosecond ultraviolet light pulse generator with high repetition rate and peak power.

PubMed

Binh, P H; Trong, V D; Renucci, P; Marie, X

2013-08-01

We present a simple ultraviolet sub-nanosecond pulse generator using commercial ultraviolet light-emitting diodes with peak emission wavelengths of 290 nm, 318 nm, 338 nm, and 405 nm. The generator is based on step recovery diode, short-circuited transmission line, and current-shaping circuit. The narrowest pulses achieved have 630 ps full width at half maximum at repetition rate of 80 MHz. Optical pulse power in the range of several hundreds of microwatts depends on the applied bias voltage. The bias voltage dependences of the output optical pulse width and peak power are analysed and discussed. Compared to commercial UV sub-nanosecond generators, the proposed generator can produce much higher pulse repetition rate and peak power.

A frequency and pulse-width co-modulation strategy for transcutaneous neuromuscular electrical stimulation based on sEMG time-domain features

NASA Astrophysics Data System (ADS)

Zhou, Yu-Xuan; Wang, Hai-Peng; Bao, Xue-Liang; Lü, Xiao-Ying; Wang, Zhi-Gong

2016-02-01

Objective. Surface electromyography (sEMG) is often used as a control signal in neuromuscular electrical stimulation (NMES) systems to enhance the voluntary control and proprioceptive sensory feedback of paralyzed patients. Most sEMG-controlled NMES systems use the envelope of the sEMG signal to modulate the stimulation intensity (current amplitude or pulse width) with a constant frequency. The aims of this study were to develop a strategy that co-modulates frequency and pulse width based on features of the sEMG signal and to investigate the torque-reproduction performance and the level of fatigue resistance achieved with our strategy. Approach. We examined the relationships between wrist torque and two stimulation parameters (frequency and pulse width) and between wrist torque and two sEMG time-domain features (mean absolute value (MAV) and number of slope sign changes (NSS)) in eight healthy volunteers. By using wrist torque as an intermediate variable, customized and generalized transfer functions were constructed to convert the two features of the sEMG signal into the two stimulation parameters, thereby establishing a MAV/NSS dual-coding (MNDC) algorithm. Wrist torque reproduction performance was assessed by comparing the torque generated by the algorithms with that originally recorded during voluntary contractions. Muscle fatigue was assessed by measuring the decline percentage of the peak torque and by comparing the torque time integral of the response to test stimulation trains before and after fatigue sessions. Main Results. The MNDC approach could produce a wrist torque that closely matched the voluntary wrist torque. In addition, a smaller decay in the wrist torque was observed after the MNDC-coded fatigue stimulation was applied than after stimulation using pulse-width modulation alone. Significance. Compared with pulse-width modulation stimulation strategies that are based on sEMG detection, the MNDC strategy is more effective for both voluntary muscle force reproduction and muscle fatigue reduction.

Effects of pulse width and coding on radar returns from clear air

NASA Technical Reports Server (NTRS)

Cornish, C. R.

1983-01-01

In atmospheric radar studies it is desired to obtain maximum information about the atmosphere and to use efficiently the radar transmitter and processing hardware. Large pulse widths are used to increase the signal to noise ratio since clear air returns are generally weak and maximum height coverage is desired. Yet since good height resolution is equally important, pulse compression techniques such as phase coding are employed to optimize the average power of the transmitter. Considerations in implementing a coding scheme and subsequent effects of an impinging pulse on the atmosphere are investigated.

In Vitro Comparison of Holmium Lasers: Evidence for Shorter Fragmentation Time and Decreased Retropulsion Using a Modern Variable-pulse Laser.

PubMed

Bell, John Roger; Penniston, Kristina L; Nakada, Stephen Y

2017-09-01

To compare the performance of variable- and fixed-pulse lasers on stone phantoms in vitro. Seven-millimeter stone phantoms were made to simulate calcium oxalate monohydrate stones using BegoStone plus. The in vitro setting was created with a clear polyvinyl chloride tube. For each trial, a stone phantom was placed at the open end of the tubing. The Cook Rhapsody H-30 variable-pulse laser was tested on both long- and short-pulse settings and was compared to the Dornier H-20 fixed-pulse laser; 5 trials were conducted for each trial arm. Fragmentation was accomplished with the use of a flexible ureteroscope and a 273-micron holmium laser fiber using settings of 1 J × 12 Hz. The treatment time (in minute) for complete fragmentation was recorded as was the total retropulsion distance (in centimeter) during treatment. Laser fibers were standardized for all repetitions. The treatment time was significantly shorter with the H-30 vs the H-20 laser (14.3 ± 2.5 vs 33.1 ± 8.9 minutes, P = .008). There was no difference between the treatment times using the long vs short pulse widths of the H-30 laser (14.4 ± 3.4 vs 14.3 ± 1.7 minutes, P = .93). Retropulsion differed by laser type and pulse width, H-30 long pulse (15.8 ± 5.7 cm), H-30 short pulse (54.8 ± 7.1 cm), and H-20 (33.2 ± 12.5 cm) (P <.05). The H-30 laser fragmented stone phantoms in half the time of the H-20 laser regardless of the pulse width. Retropulsion effects differed between the lasers, with the H-30 causing the least retropulsion. Longer pulse widths result in less stone retropulsion. Copyright © 2017 Elsevier Inc. All rights reserved.

[Dependence of anti-inflammatory effects of high peak-power pulsed electromagnetic radiation of extremely high frequency on exposure parameters].

PubMed

Gapeev, A B; Mikhaĭlik, E N; Rubanik, A V; Cheremis, N K

2007-01-01

A pronounced anti-inflammatory effect of high peak-power pulsed electromagnetic radiation of extremely high frequency was shown for the first time in a model of zymosan-induced footpad edema in mice. Exposure to radiation of specific parameters (35, 27 GHz, peak power 20 kW, pulse widths 400-600 ns, pulse repetition frequency 5-500 Hz) decreased the exudative edema and local hyperthermia by 20% compared to the control. The kinetics and the magnitude of the anti-inflammatory effect were comparable with those induced by sodium diclofenac at a dose of 3 mg/kg. It was found that the anti-inflammatory effect linearly increased with increasing pulse width at a fixed pulse repetition frequency and had threshold dependence on the average incident power density of the radiation at a fixed pulse width. When animals were whole-body exposed in the far-field zone of radiator, the optimal exposure duration was 20 min. Increasing the average incident power density upon local exposure of the inflamed paw accelerated both the development of the anti-inflammatory effect and the reactivation time. The results obtained will undoubtedly be of great importance in the hygienic standardization of pulsed electromagnetic radiation and in further studies of the mechanisms of its biological action.

Development of new S-band RF window for stable high-power operation in linear accelerator RF system

NASA Astrophysics Data System (ADS)

Joo, Youngdo; Lee, Byung-Joon; Kim, Seung-Hwan; Kong, Hyung-Sup; Hwang, Woonha; Roh, Sungjoo; Ryu, Jiwan

2017-09-01

For stable high-power operation, a new RF window is developed in the S-band linear accelerator (Linac) RF systems of the Pohang Light Source-II (PLS-II) and the Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL). The new RF window is designed to mitigate the strength of the electric field at the ceramic disk and also at the waveguide-cavity coupling structure of the conventional RF window. By replacing the pill-box type cavity in the conventional RF window with an overmoded cavity, the electric field component perpendicular to the ceramic disk that caused most of the multipacting breakdowns in the ceramic disk was reduced by an order of magnitude. The reduced electric field at the ceramic disk eliminated the Ti-N coating process on the ceramic surface in the fabrication procedure of the new RF window, preventing the incomplete coating from spoiling the RF transmission and lowering the fabrication cost. The overmoded cavity was coupled with input and output waveguides through dual side-wall coupling irises to reduce the electric field strength at the waveguide-cavity coupling structure and the possibility of mode competitions in the overmoded cavity. A prototype of the new RF window was fabricated and fully tested with the Klystron peak input power, pulse duration and pulse repetition rate of 75 MW, 4.5 μs and 10 Hz, respectively, at the high-power test stand. The first mass-produced new RF window installed in the PLS-II Linac is running in normal operation mode. No fault is reported to date. Plans are being made to install the new RF window to all S-band accelerator RF modules of the PLS-II and PAL-XFEL Linacs. This new RF window may be applied to the output windows of S-band power sources like Klystron as wells as the waveguide windows of accelerator facilities which operate in S-band.

MO-F-16A-02: Simulation of a Medical Linear Accelerator for Teaching Purposes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlone, M; Lamey, M; Anderson, R

Purpose: Detailed functioning of linear accelerator physics is well known. Less well developed is the basic understanding of how the adjustment of the linear accelerator's electrical components affects the resulting radiation beam. Other than the text by Karzmark, there is very little literature devoted to the practical understanding of linear accelerator functionality targeted at the radiotherapy clinic level. The purpose of this work is to describe a simulation environment for medical linear accelerators with the purpose of teaching linear accelerator physics. Methods: Varian type lineacs were simulated. Klystron saturation and peak output were modelled analytically. The energy gain of anmore » electron beam was modelled using load line expressions. The bending magnet was assumed to be a perfect solenoid whose pass through energy varied linearly with solenoid current. The dose rate calculated at depth in water was assumed to be a simple function of the target's beam current. The flattening filter was modelled as an attenuator with conical shape, and the time-averaged dose rate at a depth in water was determined by calculating kerma. Results: Fifteen analytical models were combined into a single model called SIMAC. Performance was verified systematically by adjusting typical linac control parameters. Increasing klystron pulse voltage increased dose rate to a peak, which then decreased as the beam energy was further increased due to the fixed pass through energy of the bending magnet. Increasing accelerator beam current leads to a higher dose per pulse. However, the energy of the electron beam decreases due to beam loading and so the dose rate eventually maximizes and the decreases as beam current was further increased. Conclusion: SIMAC can realistically simulate the functionality of a linear accelerator. It is expected to have value as a teaching tool for both medical physicists and linear accelerator service personnel.« less

Effect of electric barrier on passage and physical condition of juvenile and adult rainbow trout

USGS Publications Warehouse

Layhee, Megan J.; Sepulveda, Adam; Shaw, Amy; Smuckall, Matthew; Kapperman, Kevin; Reyes, Alejandro

2016-01-01

Electric barriers can inhibit passage and injure fish. Few data exist on electric barrier parameters that minimize these impacts and on how body size affects susceptibility, especially to nontarget fish species. The goal of this study was to determine electric barrier voltage and pulse-width settings that inhibit passage of larger bodied rainbow trout Oncorhynchus mykiss (215–410 mm fork length) while allowing passage of smaller bodied juvenile rainbow trout (52–126 mm) in a static laboratory setting. We exposed rainbow trout to 30-Hz pulsed-direct current voltage gradients (0.00–0.45 V cm−1) and pulse widths (0.0–0.7 ms) and recorded their movement, injury incidence, and mortality. No settings tested allowed all juveniles to pass while impeding all adult passage. Juvenile and adult rainbow trout avoided the barrier at higher pulse widths, and fewer rainbow trout passed the barrier at 0.7-ms pulse width compared to 0.1 ms and when the barrier was turned off. We found no effect of voltage gradient on fish passage. No mortality occurred, and we observed external bruising in 5 (7%) juvenile rainbow trout and 15 (21%) adult rainbow trout. This study may aid managers in selecting barrier settings that allow for increased juvenile passage.

PCF based high power narrow line width pulsed fiber laser

NASA Astrophysics Data System (ADS)

Chen, H.; Yan, P.; Xiao, Q.; Wang, Y.; Gong, M.

2012-09-01

Based on semiconductor diode seeded multi-stage cascaded fiber amplifiers, we have obtained 88-W average power of a 1063-nm laser with high repetition rate of up to 1.5 MHz and a constant 2-ns pulse duration. No stimulated Brillouin scattering pulse or optical damage occurred although the maximum pulse peak power has exceeded 112 kW. The output laser exhibits excellent beam quality (M2x = 1.24 and M2y = 1.18), associated with a spectral line width as narrow as 0.065 nm (FWHM). Additionally, we demonstrate high polarization extinction ratio of 18.4 dB and good pulse stabilities superior to 1.6 % (RMS).

Real-time method and apparatus for measuring the temperature of a fluorescing phosphor

DOEpatents

Britton, Jr., Charles L.; Beshears, David L.; Simpson, Marc L.; Cates, Michael R.; Allison, Steve W.

1999-01-01

A method for determining the temperature of a fluorescing phosphor is provided, together with an apparatus for performing the method. The apparatus includes a photodetector for detecting light emitted by a phosphor irradiated with an excitation pulse and for converting the detected light into an electrical signal. The apparatus further includes a differentiator for differentiating the electrical signal and a zero-crossing discrimination circuit that outputs a pulse signal having a pulse width corresponding to the time period between the start of the excitation pulse and the time when the differentiated electrical signal reaches zero. The width of the output pulse signal is proportional to the decay-time constant of the phosphor.

Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

DOEpatents

Konrad, C.E.; Boothe, R.W.

1994-02-15

A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements. 6 figures.

Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

DOEpatents

Konrad, C.E.; Boothe, R.W.

1996-01-23

A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements. 6 figs.

Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

DOEpatents

Konrad, Charles E.; Boothe, Richard W.

1996-01-01

A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements.

Method and apparatus for improved efficiency in a pulse-width-modulated alternating current motor drive

DOEpatents

Konrad, Charles E.; Boothe, Richard W.

1994-01-01

A scheme for optimizing the efficiency of an AC motor drive operated in a pulse-width-modulated mode provides that the modulation frequency of the power furnished to the motor is a function of commanded motor torque and is higher at lower torque requirements than at higher torque requirements.

Efficient extreme ultraviolet plasma source generated by a CO2 laser and a liquid xenon microjet target

NASA Astrophysics Data System (ADS)

Ueno, Yoshifumi; Ariga, Tatsuya; Soumagne, George; Higashiguchi, Takeshi; Kubodera, Shoichi; Pogorelsky, Igor; Pavlishin, Igor; Stolyarov, Daniil; Babzien, Marcus; Kusche, Karl; Yakimenko, Vitaly

2007-05-01

We demonstrated efficacy of a CO2-laser-produced xenon plasma in the extreme ultraviolet (EUV) spectral region at 13.5nm at variable laser pulse widths between 200ps and 25ns. The plasma target was a 30μm liquid xenon microjet. To ensure the optimum coupling of CO2 laser energy with the plasma, they applied a prepulse yttrium aluminum garnet laser. The authors measured the conversion efficiency (CE) of the 13.5nm EUV emission for different pulse widths of the CO2 laser. A maximum CE of 0.6% was obtained for a CO2 laser pulse width of 25ns at an intensity of 5×1010W/cm2.

[Microsecond Pulsed Hollow Cathode Lamp as Enhanced Excitation Source of Hydride Generation Atomic Fluorescence Spectrometry].

PubMed

Zhang, Shuo

2015-09-01

The spectral, electrical and atomic fluorescence characteristics of As, Se, Sb and Pb hollow cathode lamps (HCLs) powered by a laboratory-built high current microsecond pulse (HCMP) power supply were studied, and the feasibility of using HCMP-HCLs as the excitation source of hydride generation atomic fluorescence spectrometry (HG-AFS) was evaluated. Under the HCMP power supply mode, the As, Se, Sb, Pb HCLs can maintain stable glow discharge at frequency of 100~1000 Hz, pulse width of 4.0~20 μs and pulse current up to 4.0 A. Relationship between the intensity of characteristic emission lines and HCMP power supply parameters, such as pulse current, power supply voltage, pulse width and frequency, was studied in detail. Compared with the conventional pulsed (CP) HCLs used in commercial AFS instruments, HCMP-HCLs have a narrower pulse width and much stronger pulse current. Under the optimized HCMP power supply parameters, the intensity of atomic emission lines of As, Se, Sb HCLs had sharp enhancement and that indicated their capacity of being a novel HG-AFS excitation source. However, the attenuation of atomic lines and enhancement of ionic lines negated such feasibility of HCMP-Pb HCL. Then the HG-AFS analytical capability of using the HCMP-As/Se/Sb HCLs excitation source was established and results showed that the HCMP-HCL is a promising excitation source for HG-AFS.

The influence of erbium:yttrium-aluminum-garnet laser ablation with variable pulse width on morphology and microleakage of composite restorations.

PubMed

Navarro, Ricardo Scarparo; Gouw-Soares, Sheila; Cassoni, Alessandra; Haypek, Patricia; Zezell, Denise Maria; de Paula Eduardo, Carlos

2010-11-01

The objective of this study was to evaluate the influence of various pulse widths with different energy parameters of erbium:yttrium-aluminum-garnet (Er:YAG) laser (2.94 mum) on the morphology and microleakage of cavities restored with composite resin. Identically sized class V cavities were prepared on the buccal surfaces of 54 bovine teeth by high-speed drill (n = 6, control, group 1) and prepared by Er:YAG laser (Fidelis 320A, Fotona, Slovenia) with irradiation parameters of 350 mJ/ 4 Hz or 400 mJ/2 Hz and pulse width: group 2, very short pulse (VSP); group 3, short pulse (SP); group 4, long pulse (LP); group 5, very long pulse (VLP). All cavities were filled with composite resin (Z-250-3 M), stored at 37 degrees C in distilled water, polished after 24 h, and thermally stressed (700 cycles/5-55 degrees C). The teeth were impermeabilized, immersed in 50% silver nitrate solution for 8 h, sectioned longitudinally, and exposed to Photoflood light for 10 min to reveal the stain. The leakage was evaluated under stereomicroscope by three different examiners, in a double-blind fashion, and scored (0-3). The results were analyzed by Kruskal-Wallis test (P > 0.05) and showed that there was no significant differences between the groups tested. Under scanning electron microscopy (SEM) the morphology of the cavities prepared by laser showed irregular enamel margins and dentin internal walls, and a more conservative pattern than that of conventional cavities. The different power settings and pulse widths of Er:YAG laser in cavity preparation had no influence on microleakage of composite resin restorations.

Simple ps microchip Nd:YVO4 laser with 3.3-ps pulses at 0.2 to 1.4 MHz and single-stage amplification to the microjoule level

NASA Astrophysics Data System (ADS)

Türkyilmaz, Erdal; Lohbreier, Jan; Günther, Christian; Mehner, Eva; Kopf, Daniel; Giessen, Harald; Braun, Bernd

2016-06-01

Commercial picosecond sources have found widespread applications. Typical system parameters are pulse widths below 20 ps, repetition rates between 0.1 and 2 MHz, and microjoule level pulse energies. Most systems are based on short pulse mode-locked oscillators, regenerative amplifiers, and pockel cells as active beam switches. In contrast, we present a completely passive system, consisting of a passively Q-switched microchip laser, a single-stage amplifier, and a pulse compressor. The Q-switched microchip laser has a 50-μm-long Nd:YVO4 gain material optically bonded to a 4.6-mm-thick undoped YVO4 crystal. It delivers pulse widths of 40 ps and repetition rates of 0.2 to 1.4 MHz at a wavelength of 1.064 μm. The pulse energy is a few nanojoule. These 40-ps pulses are spectrally broadened in a standard single-mode fiber and then compressed in a 24-mm-long chirped Bragg grating to as low as 3.3 ps. The repetition rate can be tuned from ˜0.2 to 1.4 MHz by changing the pump power, while the pulse width and the pulse energy from the microchip laser are unchanged. The spectral broadening in the fiber is observed throughout the pulse repetition rate, supporting sub-10-ps pulses. Finally, the pulses are amplified in a single-stage Nd:YVO4 amplifier up to the microjoule level (up to 4 μJ pulse energy). As a result, the system delivers sub-10-ps pulses at a microjoule level with about 1 MHz repetition rate, and thus fulfills the requirements for ps-micromachining. It does not contain any active switching elements and can be integrated in a very compact setup.

Simple ps microchip Nd:YVO4 laser with 3.3 ps pulses at 0.2 - 1.4 MHz and single-stage amplification to the microjoule level

NASA Astrophysics Data System (ADS)

Türkyilmaz, Erdal; Lohbreier, Jan; Günther, Christian; Mehner, Eva; Kopf, Daniel; Giessen, Harald; Braun, Bernd

2016-03-01

Commercial picosecond sources have found widespread applications. Typical system parameters are pulse widths below 20 ps, repetition rates between 0.1 to 2 MHz, and micro Joule level pulse energies. Most systems are based on short pulse modelocked oscillators, regenerative amplifiers, and pockel cells as active beam switches. In contrast we present a completely passive system, consisting of a passively Q-switched microchip laser, a single-stage amplifier, and a pulse compressor. The Q-switched microchip laser has a 50 μm long Nd:YVO4-gain material optically bonded to a 4.6 mm thick undoped YVO4-crystal. It delivers pulse widths of 40 ps and repetition rates of 0.2 - 1.4 MHz at a wavelength of 1.064 μm. The pulse energy is a few nJ. These 40-ps pulses are spectrally broadened in a standard single mode fibre and then compressed in a 24 mm long chirped Bragg grating to as low as 3.3 ps. The repetition rate can be tuned from app. 0.2 to 1.4 MHz by changing the pump power while the pulse width and the pulse energy from the microchip laser are unchanged. The spectral broadening in the fibre is observed throughout the pulse repetition rate, supporting sub-10- ps pulses. Finally, the pulses are amplified in a single-stage Nd:YVO4-amplifier up to the microjoule level (up to 4 μJ pulse energy). As a result the system delivers sub-10-ps pulses at a microjoule level with about 1 MHz repetition rate, and thus fulfills the requirements for ps-micromachining. It does not contain any active switching elements and can be integrated in a very compact setup.

The study of laser pulse width on efficiency of Ho:YAG laser lithotripsy

NASA Astrophysics Data System (ADS)

Zhang, Jian J.; Rutherford, Jonathan; Solomon, Metasebya; Cheng, Brian; Xuan, Jason R.; Gong, Jason; Yu, Honggang; Xia, Michael; Yang, Xirong; Hasenberg, Thomas; Curran, Sean

2017-02-01

When treating ureteral calculi, retropulsion can be reduced by using a longer pulse width without compromising fragmentation efficiency (from the studies by David S. Finley et al. and Hyun Wook Kang et al.). In this study, a lab build Ho:YAG laser was used as the laser pulse source, with pulse energy from 0.2J up to 3.0 J, and electrical pump pulse width from 150 us up to 1000 us. The fiber used in the investigation is a 365 μm core diameter fiber, SureFlexTM, Model S-LLF365. Plaster of Paris calculus phantoms were ablated at different energy levels (0.2, 0.5, 1, 2, 3J) and with different number of pulses (1, 3, 10) using different electrical pump pulse width (333, 667, 1000 μs). The dynamics of the recoil action of a calculus phantom was monitored using a high-speed camera with frame rate up to 1 million frame per second (Photron Fastcam SA5); and the laser-induced craters were evaluated with a 3-D digital microscope (Keyence VHX-900F). A design of experiment software (DesignExpert-10, Minneapolis, MN, USA) is used in this study for the best fit of surface response on volume of dusting and retropulsion amplitude. The numerical formulas for the response surfaces of dusting speed and retropulsion amplitude are generated. More detailed investigation on the optimal conditions for dusting of other kinds of stone samples and the fiber size effect will be conducted as a future study.

Effect of tendon vibration during wide-pulse neuromuscular electrical stimulation (NMES) on the decline and recovery of muscle force.

PubMed

Bochkezanian, Vanesa; Newton, Robert U; Trajano, Gabriel S; Vieira, Amilton; Pulverenti, Timothy S; Blazevich, Anthony J

2017-05-02

Neuromuscular electrical stimulation (NMES) is commonly used to activate skeletal muscles and reverse muscle atrophy in clinical populations. Clinical recommendations for NMES suggest the use of short pulse widths (100-200 μs) and low-to-moderate pulse frequencies (30-50 Hz). However, this type of NMES causes rapid muscle fatigue due to the (non-physiological) high stimulation intensities and non-orderly recruitment of motor units. The use of both wide pulse widths (1000 μs) and tendon vibration might optimize motor unit activation through spinal reflex pathways and thus delay the onset of muscle fatigue, increasing muscle force and mass. Thus, the objective of this study was to examine the acute effects of patellar tendon vibration superimposed onto wide-pulse width (1000 μs) knee extensor electrical stimulation (NMES, 30 Hz) on peak muscle force, total impulse before "muscle fatigue", and the post-exercise recovery of muscle function. Tendon vibration (Vib), NMES (STIM) or NMES superimposed onto vibration (STIM + Vib) were applied in separate sessions to 16 healthy adults. Total torque-time integral (TTI), maximal voluntary contraction torque (MVIC) and indirect measures of muscle damage were tested before, immediately after, 1 h and 48 h after each stimulus. TTI increased (145.0 ± 127.7%) in STIM only for "positive responders" to the tendon vibration (8/16 subjects), but decreased in "negative responders" (-43.5 ± 25.7%). MVIC (-8.7%) and rectus femoris electromyography (RF EMG) (-16.7%) decreased after STIM (group effect) for at least 1 h, but not after STIM + Vib. No changes were detected in indirect markers of muscle damage in any condition. Tendon vibration superimposed onto wide-pulse width NMES increased TTI only in 8 of 16 subjects, but reduced voluntary force loss (fatigue) ubiquitously. Negative responders to tendon vibration may derive greater benefit from wide-pulse width NMES alone.

Experimental demonstration of wavelength conversion between ps-pulses based on cascaded sum- and difference frequency generation (SFG+DFG) in LiNbO3 waveguides

NASA Astrophysics Data System (ADS)

Wang, Jian; Sun, Junqiang; Lou, Chuanhong; Sun, Qizhen

2005-09-01

All-optical wavelength conversion between ps-pulses based on cascaded sum- and difference frequency generation (SFG+DFG) is proposed and experimentally demonstrated in periodically poled LiNbO3 (PPLN) waveguides. The signal pulse with 40-GHz repetition rate and 1.57- ps pulse width is adopted. The converted idler wavelength can be tuned from 1527.4 to 1540.5nm as the signal wavelength is varied from 1561.9 to 1548.4nm. No obvious changes of the pulse shape and width, also no chirp are observed in the converted idler pulse. The results imply that single-to-multiple channel wavelength conversions can be achieved by appropriately tuning the two pump wavelengths.

Experimental demonstration of wavelength conversion between ps-pulses based on cascaded sum- and difference frequency generation (SFG+DFG) in LiNbO3 waveguides.

PubMed

Wang, Jian; Sun, Junqiang; Lou, Chuanhong; Sun, Qizhen

2005-09-19

All-optical wavelength conversion between ps-pulses based on cascaded sum- and difference frequency generation (SFG+DFG) is proposed and experimentally demonstrated in periodically poled LiNbO3 (PPLN) waveguides. The signal pulse with 40-GHz repetition rate and 1.57- ps pulse width is adopted. The converted idler wavelength can be tuned from 1527.4 to 1540.5nm as the signal wavelength is varied from 1561.9 to 1548.4nm. No obvious changes of the pulse shape and width, also no chirp are observed in the converted idler pulse. The results imply that single-to-multiple channel wavelength conversions can be achieved by appropriately tuning the two pump wavelengths.

Klystron having electrostatic quadrupole focusing arrangement

DOEpatents

Maschke, Alfred W.

1983-08-30

A klystron includes a source for emitting at least one electron beam, and an accelerator for accelarating the beam in a given direction through a number of drift tube sections successively aligned relative to one another in the direction of the beam. A number of electrostatic quadrupole arrays are successively aligned relative to one another along at least one of the drift tube sections in the beam direction for focusing the electron beam. Each of the electrostatic quadrupole arrays forms a different quadrupole for each electron beam. Two or more electron beams can be maintained in parallel relationship by the quadrupole arrays, thereby enabling space charge limitations encountered with conventional single beam klystrons to be overcome.

Klystron having electrostatic quadrupole focusing arrangement

DOEpatents

Maschke, A.W.

1983-08-30

A klystron includes a source for emitting at least one electron beam, and an accelerator for accelerating the beam in a given direction through a number of drift tube sections successively aligned relative to one another in the direction of the beam. A number of electrostatic quadrupole arrays are successively aligned relative to one another along at least one of the drift tube sections in the beam direction for focusing the electron beam. Each of the electrostatic quadrupole arrays forms a different quadrupole for each electron beam. Two or more electron beams can be maintained in parallel relationship by the quadrupole arrays, thereby enabling space charge limitations encountered with conventional single beam klystrons to be overcome. 4 figs.

Solar power satellite 50 kW VKS-7773 cw klystron evaluation

NASA Technical Reports Server (NTRS)

Larue, A. D.

1977-01-01

A test program for evaluating the electrical characteristics of a cw, 50 kW power output klystron at 2.45 GHz is described. The tube tested was an 8-cavity klystron, the VKS-7773 which had been in storage for seven years. Tests included preliminary testing of the tube, cold tests of microwave components, tests of the electromagnet, and first and second hot tests of the tube. During the second hot test, the tuner in the fifth cavity went down to air, preventing any further testing. Cause of failure is not known, and recommendations are to repair and modify the tube, then proceed with testing as before to meet program objectives.

A novel compact low impedance Marx generator with quasi-rectangular pulse output

NASA Astrophysics Data System (ADS)

Liu, Hongwei; Jiang, Ping; Yuan, Jianqiang; Wang, Lingyun; Ma, Xun; Xie, Weiping

2018-04-01

In this paper, a novel low impedance compact Marx generator with near-square pulse output based on the Fourier theory is developed. Compared with the traditional Marx generator, capacitors with different capacity have been used. It can generate a high-voltage quasi-rectangular pulse with a width of 100 ns at low impedance load, and it also has high energy density and power density. The generator consists of 16 modules. Each module comprises an integrative single-ended plastic case capacitor with a nominal value of 54 nF, four ceramic capacitors with a nominal value of 1.5 nF, a gas switch, a charging inductor, a grounding inductor, and insulators which provide mechanical support for all elements. In the module, different discharge periods from different capacitors add to the main circuit to form a quasi-rectangular pulse. The design process of the generator is analyzed, and the test results are provided here. The generator achieved pulse output with a rise time of 32 ns, pulse width of 120 ns, flat-topped width (95%-95%) of 50 ns, voltage of 550 kV, and power of 20 GW.

Method and apparatus for pulse width modulation control of an AC induction motor

DOEpatents

Geppert, Steven; Slicker, James M.

1984-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a micro-processor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .THETA., where .THETA. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands of electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a "flyback" DC-DC converter circuit for recharging the battery.

Method and apparatus for pulse width modulation control of an AC induction motor

NASA Technical Reports Server (NTRS)

Geppert, Steven (Inventor); Slicker, James M. (Inventor)

1984-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a micro-processor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .THETA., where .THETA. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands of electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a flyback DC-DC converter circuit for recharging the battery.

Selected topics in particle accelerators: Proceedings of the CAP meetings. Volume 5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parsa, Z.

1995-10-01

This Report includes copies of transparencies and notes from the presentations made at the Center for Accelerator Physics at Brookhaven National Laboratory Editing and changes to the authors` contributions in this Report were made only to fulfill the publication requirements. This volume includes notes and transparencies on nine presentations: ``The Energy Exchange and Efficiency Consideration in Klystrons``, ``Some Properties of Microwave RF Sources for Future Colliders + Overview of Microwave Generation Activity at the University of Maryland``, ``Field Quality Improvements in Superconducting Magnets for RHIC``, ``Hadronic B-Physics``, ``Spiking Pulses from Free Electron Lasers: Observations and Computational Models``, ``Crystalline Beams inmore » Circular Accelerators``, ``Accumulator Ring for AGS & Recent AGS Performance``, ``RHIC Project Machine Status``, and ``Gamma-Gamma Colliders.``« less

A high power, pulsed, microwave amplifier for a synthetique aperture radar electrical model. Phase 1: Design

NASA Astrophysics Data System (ADS)

Atkinson, J. E.; Barker, G. G.; Feltham, S. J.; Gabrielson, S.; Lane, P. C.; Matthews, V. J.; Perring, D.; Randall, J. P.; Saunders, J. W.; Tuck, R. A.

1982-05-01

An electrical model klystron amplifier was designed. Its features include a gridded gun, a single stage depressed collector, a rare earth permanent magnet focusing system, an input loop, six rugged tuners and a coaxial line output section incorporating a coaxial-to-waveguide transducer and a pillbox window. At each stage of the design, the thermal and mechanical aspects were investigated and optimized within the framework of the RF specification. Extensive use was made of data from the preliminary design study and from RF measurements on the breadboard model. In an additional study, a comprehensive draft tube specification has been produced. Great emphasis has been laid on a second additional study on space-qualified materials and processes.

Reliability of High-Power Pulsed IMPATT Diodes.

DTIC Science & Technology

1981-11-01

FOLLOWING 168 HOUR STORAGE AT 3100 C D- 20816 5-14 FIGURE 5.11 READ DOUBLE DRIFT DEVICE FROM WAFER 21693-1 WITH GOLD GERMANIUM SOLDER FOLLOWING...vs. DUTY CYCLE FOR VARIOUS WIDTHS FOR SINGLE DRIFT SCHOTTKY LHL X-BAND GaAs DEVICES D- 20816 6-2 10 _PULSE WIDTH z,- 4 CL 0.11I 0.1 1.0 10 100 DUTY

High voltage breakdown phenomena in RF window, electron gun and RF cavities in 250 kW CW C band Klystron and their preventive measures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lamba, O.S.; Badola, Richa; Baloda, Suman

The paper describes voltage break down phenomenon and preventive measures in components of 250 KW CW, C band Klystron under development at CEERI Pilani. The Klystron operates at a beam voltage of 50 kV and delivers 250 kW RF power at 5 GHz frequency. The Klystron consists of several key components and regions, which are subject to high electrical stress. The most important regions of electrical breakdown are electron gun, the RF ceramic window and output cavity gap area. In the critical components voltage breakdown considered at design stage by proper gap and other techniques. All these problems discussed, asmore » well as solution to alleviate this problem. The electron gun consists basically of cathode, BFE and anode. The cathode is operated at a voltage of 50 kV. In order to maintain the voltage standoff between cathode and anode a high voltage alumina seal and RF window have been designed developed and successfully used in the tube. (author)« less

Study on the amplifier experiment of end-pumped long pulse slab laser

NASA Astrophysics Data System (ADS)

Jin, Quanwei; Chen, Xiaoming; Jiang, JianFeng; Pang, Yu; Tong, Lixin; Li, Mi; Hu, Hao; Lv, Wenqiang; Gao, Qingsong; Tang, Chun

2018-03-01

The amplifier experiment research of end-pumped long pulse slab laser is developed, the results of out-put energy, optical-optical efficiency and pulse waveform are obtained at different experiment conditions, such as peak pumped power, amplifier power and pumped pulse width. The seed laser is CW fundamental transverse-mode operation fiber laser, the laser medium is composited Nd:YAG slab. Under end-pumped and the 2 passes, the laser obtain 7.65J out-put energy and 43.1% optical-optical efficiency with 45kW peak-pumped power and 386μs pump pulse width. The experimental results provide the basic for the optimization design to high frequency, high energy and high beam-quality slab lasers.

Three-Level 48-Pulse STATCOM with Pulse Width Modulation

NASA Astrophysics Data System (ADS)

Singh, Bhim; Srinivas, Kadagala Venkata

2016-03-01

In this paper, a new control strategy of a three-level 48-pulse static synchronous compensator (STATCOM) is proposed with a constant dc link voltage and pulse width modulation at fundamental frequency switching. The proposed STATCOM is realized using eight units of three-level voltage source converters (VSCs) to form a three-level 48-pulse STATCOM. The conduction angle of each three-level VSC is modulated to control the ac converter output voltage, which controls the reactive power of the STATCOM. A fuzzy logic controller is used to control the STATCOM. The dynamic performance of the STATCOM is studied for the control of the reference reactive power, the reference terminal voltage and under the switching of inductive and capacitive loads.

Real-time method and apparatus for measuring the decay-time constant of a fluorescing phosphor

DOEpatents

Britton, Jr., Charles L.; Beshears, David L.; Simpson, Marc L.; Cates, Michael R.; Allison, Steve W.

1999-01-01

A method for determining the decay-time constant of a fluorescing phosphor is provided, together with an apparatus for performing the method. The apparatus includes a photodetector for detecting light emitted by a phosphor irradiated with an excitation pulse and for converting the detected light into an electrical signal. The apparatus further includes a differentiator for differentiating the electrical signal and a zero-crossing discrimination circuit that outputs a pulse signal having a pulse width corresponding to the time period between the start of the excitation pulse and the time when the differentiated electrical signal reaches zero. The width of the output pulse signal is proportional to the decay-time constant of the phosphor.

OH Production Enhancement in Bubbling Pulsed Discharges

NASA Astrophysics Data System (ADS)

Lungu, Cristian P.; Porosnicu, Corneliu; Jepu, Ionut; Chiru, Petrica; Zaroschi, Valentin; Lungu, Ana M.; Saito, Nagahiro; Bratescu, Maria; Takai, Osamu; Velea, Theodor; Predica, Vasile

2010-10-01

The generation of active species, such as H2O2, O*, OH*, HO2*, O3, N2*, etc, produced in aqueous solutions by HV pulsed discharges was studied in order to find the most efficient way in waste water treatment taking into account that these species are almost stronger oxidizers than ozone. Plasma was generated inside gas bubbles formed by the argon, air and oxygen gas flow between the special designed electrodes. The pulse width and pulse frequency influence was studied in order to increase the efficiency of the OH active species formation. The produced active species were investigated by optical emission spectroscopy and correlated with electrical parameters of the discharges (frequency, pulse width, amplitude, and rise and decay time).

A Model-Based Fast Protection System for High-Power RF Tube Amplifiers Used at the European XFEL Accelerator

NASA Astrophysics Data System (ADS)

Butkowski, Łukasz; Vogel, Vladimir; Schlarb, Holger; Szabatin, Jerzy

2017-06-01

The driving engine of the superconducting accelerator of the European X-ray free electron laser (XFEL) is a set of 27 radio frequency (RF) stations. Each of the underground RF stations consists of a multibeam horizontal klystron that can provide up to 10 MW of power at 1.3 GHz. Klystrons are sensitive devices with a limited lifetime and a high mean time between failures. In real operation, the lifetime of the tube can be significantly reduced because of failures. The special fast protection klystron lifetime management (KLM) system has been developed to minimize the influence of service conditions on the lifetime of klystrons. The main task of this system is to detect all events which can destroy the tube as quickly as possible, and switch off the driving RF signal or the high voltage. Detection of events is based on a comparison of the value of the real signal obtained at the system output with the value estimated on the basis of a high-power RF amplifier model and input signals. The KLM system has been realized in field-programmable gate array (FPGA) and implemented in XFEL. Implementation is based on the standard low-level RF micro telecommunications computing architecture (MTCA.4 or xTCA). The main part of the paper focuses on an estimation of the klystron model and the implementation of KLM in FPGA. The results of the performance of the KLM system will also be presented.

Using the ultra-long pulse width pulsed dye laser and elliptical spot to treat resistant nasal telangiectasia.

PubMed

Madan, Vishal; Ferguson, Janice

2010-01-01

Thick linear telangiectasia on the ala nasi and nasolabial crease can be resistant to treatment with the potassium-titanyl-phosphate (KTP) laser and the traditional round spot on a pulsed dye laser (PDL). We evaluated the efficacy of a 3 mm x 10 mm elliptical spot using the ultra-long pulse width on a Candela Vbeam(R) PDL for treatment of PDL- and KTP laser-resistant nasal telangiectasia. Nasal telangiectasia resistant to PDL (12 patients) and KTP laser (12 patients) in 18 patients were treated with a 3 mm x 10 mm elliptical spot on the ultra-long pulse pulsed dye laser (ULPDL) utilising long pulse width [595 nm, 40 ms, double pulse, 30:20 dynamic cooling device (DCD)]. Six patients had previously received treatment with both PDL and KTP laser prior to ULPDL (40 treatments, range1-4, mean 2.2). Complete clearance was seen in ten patients, and eight patients displayed more than 80% improvement after ULPDL treatment. Self-limiting purpura occurred with round spot PDL and erythema with KTP laser and ULPDL. Subtle linear furrows along the treatment sites were seen in three patients treated with the KTP laser. ULPDL treatment delivered using a 3 mm x 10 mm elliptical spot was non-purpuric and highly effective in the treatment of nasal telangiectasia resistant to KTP laser and PDL.

Passive, active, and hybrid mode-locking in a self-optimized ultrafast diode laser

NASA Astrophysics Data System (ADS)

Alloush, M. Ali; Pilny, Rouven H.; Brenner, Carsten; Klehr, Andreas; Knigge, Andrea; Tränkle, Günther; Hofmann, Martin R.

2018-02-01

Semiconductor lasers are promising sources for generating ultrashort pulses. They are directly electrically pumped, allow for a compact design, and therefore they are cost-effective alternatives to established solid-state systems. Additionally, their emission wavelength depends on the bandgap which can be tuned by changing the semiconductor materials. Theoretically, the obtained pulse width can be few tens of femtoseconds. However, the generated pulses are typically in the range of several hundred femtoseconds only. Recently, it was shown that by implementing a spatial light modulator (SLM) for phase and amplitude control inside the resonator the optical bandwidth can be optimized. Consequently, by using an external pulse compressor shorter pulses can be obtained. We present a Fourier-Transform-External-Cavity setup which utilizes an ultrafast edge-emitting diode laser. The used InGaAsP diode is 1 mm long and emits at a center wavelength of 850 nm. We investigate the best conditions for passive, active and hybrid mode-locking operation using the method of self-adaptive pulse shaping. For passive mode-locking, the bandwidth is increased from 2.34 nm to 7.2 nm and ultrashort pulses with a pulse width of 216 fs are achieved after external pulse compression. For active and hybrid mode-locking, we also increased the bandwidth. It is increased from 0.26 nm to 5.06 nm for active mode-locking and from 3.21 nm to 8.7 nm for hybrid mode-locking. As the pulse width is strongly correlated with the bandwidth of the laser, we expect further reduction in the pulse duration by increasing the bandwidth.

Coherent THz Repetitive Pulse Generation in a GaSe Crystal by Dual-wavelength Nd:YLF Laser

NASA Astrophysics Data System (ADS)

Bezotosnyi, V. V.; Cheshev, E. A.; Gorbunkov, M. V.; Koromyslov, A. L.; Krokhin, O. N.; Mityagin, Yu. A.; Popov, Yu. M.; Savinov, S. A.; Tunkin, V. G.

We present modification of difference frequency generator of coherent THz radiation in a nonlinear GaSe crystal using dual-wavelength diode-pumped solid-state Nd:YLF laser. Generation at the two wavelengths (1.047 and 1.053 μm) was carried out by equalization of the gains at these wavelengths near the frequency degeneracy of the transverse modes in resonator cavity, Q-switched by acousto-optical modulator. The main parameters of the device were measured: angular synchronism (width 0.6 degrees), polarization ratio (1:100), conversion efficiency (10-7), pulse power (0.8 mW), frequency and width (53,8 сm-1, 0,6 сm-1), pulse width and repetition rate (10 ns,7 kHz). The method is promising for practical purposes.

The use of short and wide x-ray pulses for time-of-flight x-ray Compton Scatter Imaging in cargo security

NASA Astrophysics Data System (ADS)

Calvert, Nick; Betcke, Marta M.; Cresswell, John R.; Deacon, Alick N.; Gleeson, Anthony J.; Judson, Daniel S.; Mason, Peter; McIntosh, Peter A.; Morton, Edward J.; Nolan, Paul J.; Ollier, James; Procter, Mark G.; Speller, Robert D.

2015-05-01

Using a short pulse width x-ray source and measuring the time-of-flight of photons that scatter from an object under inspection allows for the point of interaction to be determined, and a profile of the object to be sampled along the path of the beam. A three dimensional image can be formed by interrogating the entire object. Using high energy x rays enables the inspection of cargo containers with steel walls, in the search for concealed items. A longer pulse width x-ray source can also be used with deconvolution techniques to determine the points of interaction. We present time-of-flight results from both short (picosecond) width and long (hundreds of nanoseconds) width x-ray sources, and show that the position of scatter can be localised with a resolution of 2 ns, equivalent to 30 cm, for a 3 cm thick plastic test object.

All-fiber high-power monolithic femtosecond laser at 1.59 µm with 63-fs pulse width

NASA Astrophysics Data System (ADS)

Hekmat, M. J.; Omoomi, M.; Gholami, A.; Yazdabadi, A. Bagheri; Abdollahi, M.; Hamidnejad, E.; Ebrahimi, A.; Normohamadi, H.

2018-01-01

In this research, by adopting an alternative novel approach to ultra-short giant pulse generation which basically originated from difficulties with traditional employed methods, an optimized Er/Yb co-doped double-clad fiber amplifier is applied to boost output average power of single-mode output pulses to a high level of 2-W at 1.59-µm central wavelength. Output pulses of approximately 63-fs pulse width at 52-MHz repetition rate are obtained in an all-fiber monolithic laser configuration. The idea of employing parabolic pulse amplification for stretching output pulses together with high-power pulse amplification using Er/Yb co-doped active fibers for compressing and boosting output average power plays crucial role in obtaining desired results. The proposed configuration enjoys massive advantages over previously reported literature which make it well-suited for high-power precision applications such as medical surgery. Detailed dynamics of pulse stretching and compressing in active fibers with different GVD parameters are numerically and experimentally investigated.

Generation of switchable domain wall and Cubic-Quintic nonlinear Schrödinger equation dark pulse

NASA Astrophysics Data System (ADS)

Tiu, Z. C.; Suthaskumar, M.; Zarei, A.; Tan, S. J.; Ahmad, H.; Harun, S. W.

2015-10-01

A switchable domain-wall (DW) and Cubic-Quintic nonlinear Schrödinger equation (CQNLSE) dark soliton pulse generation are demonstrated in Erbium-doped fiber laser (EDFL) for the first time. The DW pulse train operates at 1575 nm with a fundamental repetition rate of 1.52 MHz and pulse width of 203 ns as the pump power is increased above the threshold pump power of 80 mW. The highest pulse energy of 2.24 nJ is obtained at the maximum pump power of 140 mW. CQNLSE pulse can also be realized from the same cavity by adjusting the polarization state but at a higher threshold pump power of 104 mW. The repetition rate and pulse width of the CQNLSE dark pulses are obtained at 1.52 MHz and 219 ns, respectively. The highest energy of 0.58 nJ is obtained for the CQNLSE pulse at pump power of 140 mW.

Intense Nanosecond-Pulsed Cavity-Dumped Laser Radiation at 1.04 THz

NASA Astrophysics Data System (ADS)

Wilson, Thomas

2013-03-01

We report first results of intense far-infrared (FIR) nanosecond-pulsed laser radiation at 1.04 THz from a previously described[2] cavity-dumped, optically-pumped molecular gas laser. The gain medium, methyl fluoride, is pumped by the 9R20 line of a TEA CO2 laser[3] with a pulse energy of 200 mJ. The THz laser pulses contain of 30 kW peak power in 5 nanosecond pulse widths at a pulse repetition rate of 10 Hz. The line width, measured by a scanning metal-mesh FIR Fabry-Perot interferometer, is 100 MHz. The novel THz laser is being used in experiments to resonantly excite coherent ns-pulsed 1.04 THz longitudinal acoustic phonons in silicon doping-superlattices. The research is supported by NASA EPSCoR NNX11AM04A and AFOSR FA9550-12-1-0100 awards.

A Novel Transcranial Magnetic Stimulator Inducing Near Rectangular Pulses with Controllable Pulse Width (cTMS)

PubMed Central

Jalinous, Reza; Lisanby, Sarah H.

2013-01-01

A novel transcranial magnetic stimulation (TMS) device with controllable pulse width (PW) and near rectangular pulse shape (cTMS) is described. The cTMS device uses an insulated gate bipolar transistor (IGBT) with appropriate snubbers to switch coil currents up to 7 kA, enabling PW control from 5 μs to over 100 μs. The near-rectangular induced electric field pulses use 22–34% less energy and generate 67–72% less coil heating compared to matched conventional cosine pulses. CTMS is used to stimulate rhesus monkey motor cortex in vivo with PWs of 20 to 100 μs, demonstrating the expected decrease of threshold pulse amplitude with increasing PW. The technological solutions used in the cTMS prototype can expand functionality, and reduce power consumption and coil heating in TMS, enhancing its research and therapeutic applications. PMID:18232369

Optimization,Modeling, and Control: Applications to Klystron Designing and Hepatitis C Virus Dynamics

NASA Astrophysics Data System (ADS)

Lankford, George Bernard

In this dissertation, we address applying mathematical and numerical techniques in the fields of high energy physics and biomedical sciences. The first portion of this thesis presents a method for optimizing the design of klystron circuits. A klystron is an electron beam tube lined with cavities that emit resonant frequencies to velocity modulate electrons that pass through the tube. Radio frequencies (RF) inserted in the klystron are amplified due to the velocity modulation of the electrons. The routine described in this work automates the selection of cavity positions, resonant frequencies, quality factors, and other circuit parameters to maximize the efficiency with required gain. The method is based on deterministic sampling methods. We will describe the procedure and give several examples for both narrow and wide band klystrons, using the klystron codes AJDISK (Java) and TESLA (Python). The rest of the dissertation is dedicated to developing, calibrating and using a mathematical model for hepatitis C dynamics with triple drug combination therapy. Groundbreaking new drugs, called direct acting antivirals, have been introduced recently to fight off chronic hepatitis C virus infection. The model we introduce is for hepatitis C dynamics treated with the direct acting antiviral drug, telaprevir, along with traditional interferon and ribavirin treatments to understand how this therapy affects the viral load of patients exhibiting different types of response. We use sensitivity and identifiability techniques to determine which parameters can be best estimated from viral load data. We use these estimations to give patient-specific fits of the model to partial viral response, end-of-treatment response, and breakthrough patients. We will then revise the model to incorporate an immune response dynamic to more accurately describe the dynamics. Finally, we will implement a suboptimal control to acquire a drug treatment regimen that will alleviate the systemic cost associated with constant drug treatment.

Mechanism and influencing factors on critical pulse width of oil-immersed polymer insulators under short pulses

NASA Astrophysics Data System (ADS)

Zhao, Liang; Su, Jian Cang; Li, Rui; Zeng, Bo; Cheng, Jie; Zheng, Lei; Yu, Bin Xiong; Wu, Xiao Long; Zhang, Xi Bo; Pan, Ya Feng

2015-04-01

The critical pulse width (τc) is a pulse width at which the surface flashover threshold (Ef) is equal to the bulk breakdown threshold (EBD) for liquid-polymer composite insulation systems, which is discovered by Zhao et al. [Annual Report Conference on Electrical Insulation and Dielectric Phenomena (IEEE Dielectrics and Electrical Insulation Society, Shenzhen, China, 2013), Vol. 2, pp. 854-857]. In this paper, the mechanism of τc is interpreted in perspective of the threshold and the time delay (td) of surface flashover and bulk breakdown, respectively. It is found that two changes appear as the pulse width decreases which are responsible for the existence of τc: (1) EBD is lower than Ef; (2) td of bulk breakdown is shorter than td of surface flashover. In addition, factors which have influences on τc are investigated, such as the dielectric type, the insulation length, the dielectric thickness, the dielectrics configuration, the pulse number, and the liquid purity. These influences of factors are generalized as three types if τc is expected to increase: (1) factors causing EBD to decrease, such as increasing the pulse number or employing a dielectric of lower EBD; (2) factors causing Ef to increase, such as complicating the insulator's configuration or increasing the liquid purity; (3) factors causing EBD and Ef to increase together, but Ef increases faster than EBD, such as decreasing the dielectric thickness or the insulation length. With the data in references, all the three cases are verified experimentally. In the end, a general method based on τc for solid insulation design is presented and the significance of τc on solid insulation design and on solid demolition are discussed.

Characterization of Pilot Technique

NASA Technical Reports Server (NTRS)

Bachelder, Edward; Aponso, Bimal; Godfroy, Martine

2017-01-01

Skilled pilots often use pulse control when controlling higher order (i.e. acceleration-command) vehicle dynamics. Pulsing does not produce a stick response that resembles what the human Crossover Model predicts. The Crossover Model (CM) assumes the pilot provides compensation necessary (lead or lag) such that the suite of display-human-vehicle approximates an integrator in the region of crossover frequency. However, it is shown that the CM does appear to drive the pilots pulsing behavior in a very predictable manner. Roughly speaking, the pilot generates pulses such that the area under the pulse (pulse amplitude multiplied by pulse width) is approximately equal to area under the hypothetical CM output. This can allow a pilot to employ constant amplitude pulsing so that only the pulse duration (width) is modulated a drastic simplification over the demands of continuous tracking. A pilot pulse model is developed, with which the parameters of the pilots internally-generated CM can be computed in real time for pilot monitoring and display compensation. It is also demonstrated that pursuit tracking may be activated when pulse control is employed.

Compact rf polarizer and its application to pulse compression systems

DOE PAGES

Franzi, Matthew; Wang, Juwen; Dolgashev, Valery; ...

2016-06-01

We present a novel method of reducing the footprint and increasing the efficiency of the modern multi-MW rf pulse compressor. This system utilizes a high power rf polarizer to couple two circular waveguide modes in quadrature to a single resonant cavity in order to replicate the response of a traditional two cavity configuration using a 4-port hybrid. The 11.424 GHz, high-Q, spherical cavity has a 5.875 cm radius and is fed by the circularly polarized signal to simultaneously excite the degenerate TE 114 modes. The overcoupled spherical cavity has a Q 0 of 9.4×10 4 and coupling factor (β) ofmore » 7.69 thus providing a loaded quality factor Q L of 1.06×10 4 with a fill time of 150 ns. Cold tests of the polarizer demonstrated good agreement with the numerical design, showing transmission of -0.05 dB and reflection back to the input rectangular WR 90 waveguide less than -40 dB over a 100 MHz bandwidth. This novel rf pulse compressor was tested at SLAC using XL-4 Klystron that provided rf power up to 32 MW and generated peak output power of 205 MW and an average of 135 MW over the discharged signal. A general network analysis of the polarizer is discussed as well as the design and high power test of the rf pulse compressor.« less

Instrumental development of a quasi-relativistic ultrashort electron beam source for electron diffractions and spectroscopies

NASA Astrophysics Data System (ADS)

Shin, Young-Min; Figora, Michael

2017-10-01

A stable femtosecond electron beam system has been configured for time-resolved pump-probe experiments. The ultrafast electron diffraction (UED) system is designed with a sub-MeV photoelectron beam source pulsed by a femtosecond UV laser and nondispersive beamline components, including a bunch compressor—a pulsed S-band klystron is installed and fully commissioned with 5.5 MW peak power in a 2.5 μs pulse length. A single-cell RF photo-gun is designed to produce 1.6-16 pC electron bunches in a photoemission mode with 150 fs pulse duration at 0.5-1 MeV. The measured RF system jitters are within 1% in magnitude and 0.2° in phase, which would induce 3.4 keV and 0.25 keV of ΔE, corresponding to 80 fs and 5 fs of Δt, respectively. Our particle-in-cell simulations indicate that the designed bunch compressor reduces the time-of-arrival jitter by about an order of magnitude. The transport and focusing optics of the designed beamline with the bunch compressor enables an energy spread within 10-4 and a bunch length (electron probe) within <500 fs. In this paper, the design analysis and instrumental test results are presented along with the development of the quasi-relativistic UED system.

Instrumental development of a quasi-relativistic ultrashort electron beam source for electron diffractions and spectroscopies.

PubMed

Shin, Young-Min; Figora, Michael

2017-10-01

A stable femtosecond electron beam system has been configured for time-resolved pump-probe experiments. The ultrafast electron diffraction (UED) system is designed with a sub-MeV photoelectron beam source pulsed by a femtosecond UV laser and nondispersive beamline components, including a bunch compressor-a pulsed S-band klystron is installed and fully commissioned with 5.5 MW peak power in a 2.5 μs pulse length. A single-cell RF photo-gun is designed to produce 1.6-16 pC electron bunches in a photoemission mode with 150 fs pulse duration at 0.5-1 MeV. The measured RF system jitters are within 1% in magnitude and 0.2° in phase, which would induce 3.4 keV and 0.25 keV of ΔE, corresponding to 80 fs and 5 fs of Δt, respectively. Our particle-in-cell simulations indicate that the designed bunch compressor reduces the time-of-arrival jitter by about an order of magnitude. The transport and focusing optics of the designed beamline with the bunch compressor enables an energy spread within 10 -4 and a bunch length (electron probe) within <500 fs. In this paper, the design analysis and instrumental test results are presented along with the development of the quasi-relativistic UED system.

Exploiting solitons in all-optical networks

NASA Astrophysics Data System (ADS)

Atieh, Ahmad K.

Two key components, the pulse generator and optical signal demultiplexer, needed for the implementation of all-optical soliton-based local area and wide area networks are investigated. The technology of generating a bright soliton pulse train from a sinusoidal pulse train produced as the beat signal of two distributed feedback laser diodes passed through a so-called comblike fiber structure is developed. A design methodology for this structure is discussed, and using this approach a soliton pulse source is constructed generating 1553 nm pulses at a repetition rate of 50 GHz, with pulses of full width at half maximum of 2.0 ps. The fiber structure used to generate the bright soliton pulse train employs the lowest average power for the beat signal ever reported in the literature, and the shortest length of fiber. The same structure (with a different design) is also used to produce a 47.6 GHz dark soliton pulse train with a full width at half maximum of 3.8 ps. This is the first reported use of this structure to generate dark solitons. It is shown that the comblike dispersion profile fiber structures may also be exploited for soliton pulse compression producing widths as short as 200 fs. Two approaches to implementation of optical signal demultiplexing are discussed. These are the nonlinear optical loop mirror (NOLM) and the separation of multilevel time division multiplexed signal pulses in the frequency domain by exploiting the relationship between the pulse's energy (i.e. pulse amplitude and width) and the Raman self-frequency shift. A modification of the NOLM scheme is investigated where feedback that adjusts the power of the control signal (by controlling the gain of an erbium-doped fiber amplifier introduced into the control signal input path) is employed to make the structure insensitive to the state of polarization of the signal and control pulses. In order to better understand the physical phenomena exploited in optical fiber soliton transmission and the above schemes, two experiments are conducted to measure the fiber nonlinear ratio (n2/Aeff) and the Raman time constant (TR) in single-mode fibers at 1550 nm. The fiber nonlinear ratio was measured for standard telecommunication fiber, dispersion shifted fiber, and dispersion compensating fiber. A value of 3.0 fs for the Raman time constant was measured and is recommended for soliton pulse propagation modeling in single-mode optical fibers.

Single event effects in pulse width modulation controllers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Penzin, S.H.; Crain, W.R.; Crawford, K.B.

1996-12-01

SEE testing was performed on pulse width modulation (PWM) controllers which are commonly used in switching mode power supply systems. The devices are designed using both Set-Reset (SR) flip-flops and Toggle (T) flip-flops which are vulnerable to single event upset (SEU) in a radiation environment. Depending on the implementation of the different devices the effect can be significant in spaceflight hardware.

High efficiency klystron for the SPS application

NASA Technical Reports Server (NTRS)

Larue, A. D.

1980-01-01

The enhancement of klystron efficiency through the use of collector depression, that is by recovering energy from the spent electron beam after microwave amplification, was investigated. Design considerations included noise, harmonics, cooling, and service life. The mod anode, to be employed for beam control, and the depressed collector, used in spent electron beam energy recovery, are described.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Omet, M.; Michizono, S.; Matsumoto, T.

We report the development and implementation of four FPGA-based predistortion-type klystron linearization algorithms. Klystron linearization is essential for the realization of ILC, since it is required to operate the klystrons 7% in power below their saturation. The work presented was performed in international collaborations at the Fermi National Accelerator Laboratory (FNAL), USA and the Deutsches Elektronen Synchrotron (DESY), Germany. With the newly developed algorithms, the generation of correction factors on the FPGA was improved compared to past algorithms, avoiding quantization and decreasing memory requirements. At FNAL, three algorithms were tested at the Advanced Superconducting Test Accelerator (ASTA), demonstrating a successfulmore » implementation for one algorithm and a proof of principle for two algorithms. Furthermore, the functionality of the algorithm implemented at DESY was demonstrated successfully in a simulation.« less

Mode control in a high gain relativistic klystron amplifier with 3 GW output power

NASA Astrophysics Data System (ADS)

Wu, Yang; Xie, Hong-Quan; Xu, Zhou

2014-01-01

Higher mode excitation is very serious in the relativistic klystron amplifier, especially for the high gain relativistic amplifier working at tens of kilo-amperes. The mechanism of higher mode excitation is explored in the PIC simulation and it is shown that insufficient separation of adjacent cavities is the main cause of higher mode excitation. So RF lossy material mounted on the drift tube wall is adopted to suppress higher mode excitation. A high gain S-band relativistic klystron amplifier is designed for the beam current of 13 kA and the voltage of 1 MV. PIC simulation shows that the output power is 3.2 GW when the input power is only 2.8 kW.

Very broad bandwidth klystron amplifiers

NASA Astrophysics Data System (ADS)

Faillon, G.; Egloff, G.; Farvet, C.

Large surveillance radars use transmitters at peak power levels of around one MW and average levels of a few kW, and possibly several tens of kW, in S band, or even C band. In general, the amplification stage of these transmitters is a microwave power tube, frequently a klystron. Although designers often turn to klystrons because of their good peak and average power capabilities, they still see them as narrow band amplifiers, undoubtedly because of their resonant cavities which, at first sight, would seem highly selective. But, with the progress of recent years, it has now become quite feasible to use these tubes in installations requiring bandwidths in excess of 10 - 12 percent, and even 15 percent, at 1 MW peak for example, in S-band.

PAL-XFEL soft X-ray scientific instruments and X-ray optics: First commissioning results

NASA Astrophysics Data System (ADS)

Park, Sang Han; Kim, Minseok; Min, Changi-Ki; Eom, Intae; Nam, Inhyuk; Lee, Heung-Soo; Kang, Heung-Sik; Kim, Hyeong-Do; Jang, Ho Young; Kim, Seonghan; Hwang, Sun-min; Park, Gi-Soo; Park, Jaehun; Koo, Tae-Yeong; Kwon, Soonnam

2018-05-01

We report an overview of soft X-ray scientific instruments and X-ray optics at the free electron laser (FEL) of the Pohang Accelerator Laboratory, with selected first-commissioning results. The FEL exhibited a pulse energy of 200 μJ/pulse, a pulse width of <50 fs full width at half maximum, and an energy bandwidth of 0.44% at a photon energy of 850 eV. Monochromator resolving power of 10 500 was achieved. The estimated total time resolution between optical laser and X-ray pulses was <270 fs. A resonant inelastic X-ray scattering spectrometer was set up; its commissioning results are also reported.

OH Production Enhancement in Bubbling Pulsed Discharges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lungu, Cristian P.; Porosnicu, Corneliu; Jepu, Ionut

2010-10-13

The generation of active species, such as H{sub 2}O{sub 2}, O{sup *}, OH*, HO{sub 2}*, O{sub 3}, N{sub 2}{sup *}, etc, produced in aqueous solutions by HV pulsed discharges was studied in order to find the most efficient way in waste water treatment taking into account that these species are almost stronger oxidizers than ozone. Plasma was generated inside gas bubbles formed by the argon, air and oxygen gas flow between the special designed electrodes. The pulse width and pulse frequency influence was studied in order to increase the efficiency of the OH active species formation. The produced active speciesmore » were investigated by optical emission spectroscopy and correlated with electrical parameters of the discharges (frequency, pulse width, amplitude, and rise and decay time).« less

Repetitive transcranial magnetic stimulator with controllable pulse parameters

NASA Astrophysics Data System (ADS)

Peterchev, Angel V.; Murphy, David L.; Lisanby, Sarah H.

2011-06-01

The characteristics of transcranial magnetic stimulation (TMS) pulses influence the physiological effect of TMS. However, available TMS devices allow very limited adjustment of the pulse parameters. We describe a novel TMS device that uses a circuit topology incorporating two energy storage capacitors and two insulated-gate bipolar transistor (IGBT) modules to generate near-rectangular electric field pulses with adjustable number, polarity, duration, and amplitude of the pulse phases. This controllable pulse parameter TMS (cTMS) device can induce electric field pulses with phase widths of 10-310 µs and positive/negative phase amplitude ratio of 1-56. Compared to conventional monophasic and biphasic TMS, cTMS reduces energy dissipation up to 82% and 57% and decreases coil heating up to 33% and 41%, respectively. We demonstrate repetitive TMS trains of 3000 pulses at frequencies up to 50 Hz with electric field pulse amplitude and width variability less than the measurement resolution (1.7% and 1%, respectively). Offering flexible pulse parameter adjustment and reduced power consumption and coil heating, cTMS enhances existing TMS paradigms, enables novel research applications and could lead to clinical applications with potentially enhanced potency.

Repetitive transcranial magnetic stimulator with controllable pulse parameters.

PubMed

Peterchev, Angel V; Murphy, David L; Lisanby, Sarah H

2011-06-01

The characteristics of transcranial magnetic stimulation (TMS) pulses influence the physiological effect of TMS. However, available TMS devices allow very limited adjustment of the pulse parameters. We describe a novel TMS device that uses a circuit topology incorporating two energy storage capacitors and two insulated-gate bipolar transistor (IGBT) modules to generate near-rectangular electric field pulses with adjustable number, polarity, duration, and amplitude of the pulse phases. This controllable pulse parameter TMS (cTMS) device can induce electric field pulses with phase widths of 10-310 µs and positive/negative phase amplitude ratio of 1-56. Compared to conventional monophasic and biphasic TMS, cTMS reduces energy dissipation up to 82% and 57% and decreases coil heating up to 33% and 41%, respectively. We demonstrate repetitive TMS trains of 3000 pulses at frequencies up to 50 Hz with electric field pulse amplitude and width variability less than the measurement resolution (1.7% and 1%, respectively). Offering flexible pulse parameter adjustment and reduced power consumption and coil heating, cTMS enhances existing TMS paradigms, enables novel research applications and could lead to clinical applications with potentially enhanced potency.

Design and Analysis of Nano-Pulse Generator for Industrial Wastewater Application

NASA Astrophysics Data System (ADS)

Jang, Sung-Duck; Son, Yoon-Kyoo; Cho, Moo-Hyun; Norov, Enkhbat

2018-05-01

Recently, the application of a pulsed power system is being extended to environmental and industrial fields. The non-dissolution wastewater pollutants from industrial plants can be processed by applying high-voltage pulses with a fast rising time (a few nanoseconds) and short duration (nano to microseconds) in a pulsed corona discharge reactor. The high-voltage nano-pulse generator with a magnetic switch has been developed. It can be used for a spray type water treatment facility. Its corona current in load can be adjusted by pulse width and repetition rate. We investigated the performance of the nano-pulse generator by using the dummy load that is composed of resistor and capacitor equivalent to the actual reactor. In this paper, the results of design, construction and characterization of a high-voltage nano-pulse generator for an industrial wastewater treatment are reported. Consequently, a pulse width of 1.1 μs at the repetition rate of 200 pps, a peak voltage of 41 kV for the nano-pulse generator were achieved across a 640 Ω load. The simulation results on magnetic switch show reasonable agreement with experimental ones.

Thermal Considerations of Space Solar Power Concepts with 3.5 GW RF Output

NASA Technical Reports Server (NTRS)

Choi, Michael K.

2000-01-01

This paper presents the thermal challenge of the Space Solar Power (SSP) design concepts with a 3.5 GW radio-frequency (RF) output. High efficiency klystrons are thermally more favored than solid state (butterstick) to convert direct current (DC) electricity to radio-frequency (RF) energy at the transmitters in these concepts. Using klystrons, the heat dissipation is 0.72 GW. Using solid state, the heat dissipation is 2.33 GW. The heat dissipation of the klystrons is 85% at 500C, 10% at 300C, and 5% at 125C. All the heat dissipation of the solid state is at 100C. Using klystrons, the radiator area is 74,500 square m Using solid state, the radiator area is 2,362,200 square m Space constructable heat pipe radiators are assumed in the thermal analysis. Also, to make the SSP concepts feasible, the mass of the heat transport system must be minimized. The heat transport distance from the transmitters to the radiators must be minimized. It can be accomplished by dividing the radiator into a cluster of small radiators, so that the heat transport distances between the klystrons and radiators can be minimized. The area of each small radiator is on the order of 1 square m. Two concepts for accommodating a cluster of small radiators are presented. If the distance between the transmitters and radiators is 1.5 m or less, constant conductance heat pipes (CCHPs) are acceptable for heat transport. If the distance exceeds 1.5 m, loop heat pipes (LHPs) are needed.

Pulsed characterization of a UV LED for pulsed power applications on a silicon carbide photoconductive semiconductor switch

NASA Astrophysics Data System (ADS)

Wilson, Nicholas; Mauch, Daniel; Meyers, Vincent; Feathers, Shannon; Dickens, James; Neuber, Andreas

2017-08-01

The electrical and optical characteristics of a high-power UV light emitting diode (LED) (365 nm wavelength) were evaluated under pulsed operating conditions at current amplitudes several orders of magnitude beyond the LED's manufacturer specifications. Geared towards triggering of photoconductive semiconductor switches (PCSSs) for pulsed power applications, measurements were made over varying pulse widths (25 ns-100 μs), current (0 A-250 A), and repetition rates (single shot-5 MHz). The LED forward voltage was observed to increase linearly with increasing current (˜3.5 V-53 V) and decrease with increasing pulse widths. The peak optical power observed was >30 W, and a maximum system efficiency of 23% was achieved. The evaluated LED and auxiliary hardware were successfully used as the optical trigger source for a 4H-SiC PCSS. The lowest measured on-resistance of SiC was approximately 67 kΩ.

Pulsed characterization of a UV LED for pulsed power applications on a silicon carbide photoconductive semiconductor switch.

PubMed

Wilson, Nicholas; Mauch, Daniel; Meyers, Vincent; Feathers, Shannon; Dickens, James; Neuber, Andreas

2017-08-01

The electrical and optical characteristics of a high-power UV light emitting diode (LED) (365 nm wavelength) were evaluated under pulsed operating conditions at current amplitudes several orders of magnitude beyond the LED's manufacturer specifications. Geared towards triggering of photoconductive semiconductor switches (PCSSs) for pulsed power applications, measurements were made over varying pulse widths (25 ns-100 μs), current (0 A-250 A), and repetition rates (single shot-5 MHz). The LED forward voltage was observed to increase linearly with increasing current (∼3.5 V-53 V) and decrease with increasing pulse widths. The peak optical power observed was >30 W, and a maximum system efficiency of 23% was achieved. The evaluated LED and auxiliary hardware were successfully used as the optical trigger source for a 4H-SiC PCSS. The lowest measured on-resistance of SiC was approximately 67 kΩ.

METHOD FOR STABILIZING KLYSTRONS

DOEpatents

Magnuson, D.W.; Smith, D.F.

1959-04-14

High-frequency oscillators for the generation of microwaves, particularly a system for stabilizing frequency-modulated klystron oscillators of the reflex type, are described. The system takos advantage of the fact that a change in oscillator frequency will alter the normal phase displacement between the cavity and its modulator, creating an error voltage which is utilized to regulate the frequency of the oscillator and stabilize it.

Feasibility of using acoustic method in monitoring the penetration status during the Pulse Mode Laser Welding process

NASA Astrophysics Data System (ADS)

Yusof, M. F. M.; Ishak, M.; Ghazali, M. F.

2017-09-01

In this paper, the feasibility of using acoustic method to monitor the depth of penetration was investigated by determine the characteristic of the acquired sound throughout the pulse mode laser welding process. To achieve the aim, the sound signal was acquired during the pulsed laser welding process on the 2 mm structural carbon steel plate. During the experiment, the laser peak power and pulse width was set to be varied while welding speed was constantly at 2 mm/s. Result from the experiment revealed that the sound pressure level of the acquired sound was linearly related to the pulse energy as well as the depth of penetration for welding process using 2ms pulse width. However, as the pulse width increase, the sound pressure level show insignificant change with respect to the change in the depth of penetration when the pulse energy reaches certain values. The reported result shows that this was happen due to the occurrence of spatter which suppressed the information associated with the generation of plasma plume as the product of high pulse energy. In this work, it was demonstrated that in some condition, the acoustic method was found to be potentially suitable to be used as a medium to monitor the depth of weld on online basis. To increase the robustness of this method to be used in wider range of parameter, it was believed that some other post processing method is needed in order to extract the specific information associated with the depth of penetration from the acquired sound.

High power klystrons for efficient reliable high power amplifiers

NASA Astrophysics Data System (ADS)

Levin, M.

1980-11-01

This report covers the design of reliable high efficiency, high power klystrons which may be used in both existing and proposed troposcatter radio systems. High Power (10 kW) klystron designs were generated in C-band (4.4 GHz to 5.0 GHz), S-band (2.5 GHz to 2.7 GHz), and L-band or UHF frequencies (755 MHz to 985 MHz). The tubes were designed for power supply compatibility and use with a vapor/liquid phase heat exchanger. Four (4) S-band tubes were developed in the course of this program along with two (2) matching focusing solenoids and two (2) heat exchangers. These tubes use five (5) tuners with counters which are attached to the focusing solenoids. A reliability mathematical model of the tube and heat exchanger system was also generated.

An 8-GW long-pulse generator based on Tesla transformer and pulse forming network

DOE Office of Scientific and Technical Information (OSTI.GOV)

Su, Jiancang; Zhang, Xibo; Li, Rui

A long-pulse generator TPG700L based on a Tesla transformer and a series pulse forming network (PFN) is constructed to generate intense electron beams for the purpose of high power microwave (HPM) generation. The TPG700L mainly consists of a 12-stage PFN, a built-in Tesla transformer in a pulse forming line, a three-electrode gas switch, a transmission line with a trigger, and a load. The Tesla transformer and the compact PFN are the key technologies for the development of the TPG700L. This generator can output electrical pulses with a width as long as 200 ns at a level of 8 GW andmore » a repetition rate of 50 Hz. When used to drive a relative backward wave oscillator for HPM generation, the electrical pulse width is about 100 ns on a voltage level of 520 kV. Factors affecting the pulse waveform of the TPG700L are also discussed. At present, the TPG700L performs well for long-pulse HPM generation in our laboratory.« less

An 8-GW long-pulse generator based on Tesla transformer and pulse forming network.

PubMed

Su, Jiancang; Zhang, Xibo; Li, Rui; Zhao, Liang; Sun, Xu; Wang, Limin; Zeng, Bo; Cheng, Jie; Wang, Ying; Peng, Jianchang; Song, Xiaoxin

2014-06-01

A long-pulse generator TPG700L based on a Tesla transformer and a series pulse forming network (PFN) is constructed to generate intense electron beams for the purpose of high power microwave (HPM) generation. The TPG700L mainly consists of a 12-stage PFN, a built-in Tesla transformer in a pulse forming line, a three-electrode gas switch, a transmission line with a trigger, and a load. The Tesla transformer and the compact PFN are the key technologies for the development of the TPG700L. This generator can output electrical pulses with a width as long as 200 ns at a level of 8 GW and a repetition rate of 50 Hz. When used to drive a relative backward wave oscillator for HPM generation, the electrical pulse width is about 100 ns on a voltage level of 520 kV. Factors affecting the pulse waveform of the TPG700L are also discussed. At present, the TPG700L performs well for long-pulse HPM generation in our laboratory.

Impact of Raman scattering on pulse dynamics in a fiber laser with narrow gain bandwidth

NASA Astrophysics Data System (ADS)

Uthayakumar, T.; Alsaleh, M.; Igbonacho, J.; Tchomgo Felenou, E.; Tchofo Dinda, P.; Grelu, Ph; Porsezian, K.

2018-06-01

We examine theoretically the multi-pulse dynamics in a dispersion-managed fiber laser, in which the pulse’s spectral width is controlled by a pass-band filter. We show that in the domain of stable states with very narrow spectral width, i.e. which is one order of magnitude smaller than the bandwidth of the Raman gain of the intra-cavity fiber system, the Raman scattering (RS) significantly alters the multi-pulse dynamics. RS is found to have a greater impact in the immediate vicinity of some critical values of the pump power of the intra-cavity gain medium, where processes of pulse fragmentation occur. As a result, all the borders between the zones of stability of the multi-pulse states are altered, i.e. either shifted or suppressed.

15 mJ single-frequency Ho:YAG laser resonantly pumped by a 1.9 µm laser diode

NASA Astrophysics Data System (ADS)

Na, Q. X.; Gao, C. Q.; Wang, Q.; Zhang, Y. X.; Gao, M. W.; Ye, Q.; Li, Y.

2016-09-01

A 2.09 µm injection-seeded single-frequency Ho:YAG laser resonantly pumped by a 1.91 µm laser diode is demonstrated for the first time. The seed laser is a continuous wave (CW) Ho:YAG non-planar ring oscillator. 15.15 mJ single-frequency output energy is obtained from the injection-seeded Q-switched Ho:YAG laser, with a pulse repetition rate of 200 Hz and a pulse width of 109 ns. The half-width of the pulse spectrum is measured to be 4.19 MHz by using the heterodyne technique. The fluctuation of the center frequency of the single-frequency pulses is 1.52 MHz (root mean square (RMS)) in 1 h.

Multiphoton correlations in parametric down-conversion and their measurement in the pulsed regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ivanova, O A; Iskhakov, T Sh; Penin, A N

2006-10-31

We consider normalised intensity correlation functions (CFs) of different orders for light emitted via parametric down-conversion (PDC) and their dependence on the number of photons per mode. The main problem in measuring such correlation functions is their extremely small width, which considerably reduces their contrast. It is shown that if the radiation under study is modulated by a periodic sequence of pulses that are short compared to the CF width, no decrease in the contrast occurs. A procedure is proposed for measuring normalised CFs of various orders in the pulsed regime. For nanosecond-pulsed PDC radiation, normalised second-order CF is measuredmore » experimentally as a function of the mean photon number. (nonlinear optical phenomena)« less

Pulse Width Dependence Of Pigment Cell Damage At 694 nm In Guinea Pig Skin

NASA Astrophysics Data System (ADS)

Dover, Jeffrey S.; Polla, Luigi L.; Margolis, Randall J.; Whitaker, Diana; Watanabe, Schinichi; Murphy, George F.; Parrish, John A.; Anderson, R. R.

1987-03-01

351 nm, 20-nsec XeF excimer laser irradiation has previously been shown to selectively target and damage melanosomes in human skin. In the following studies selective targeting with melanosomal photodisruption has been demonstrated in pigmented guinea pig skin with a Q-switched 40-nsec ruby laser, and a 750-nsec pulsed dye laser but not with a 400-usec pulsed dye laser. The pulse width dependence of melanosomal disruption, occurring only at pulsewidths shorter than the thermal relaxation time of the melanosome (0.5 - 1.0 usec), is in accordance with the theory of selective photothermolysis. Possible mechanisms of melanosomal photodisruption include development of sudden thermal gradients leading to cavitation or shock wave production.

ADJUSTABLE DOUBLE PULSE GENERATOR

DOEpatents

Gratian, J.W.; Gratian, A.C.

1961-08-01

>A modulator pulse source having adjustable pulse width and adjustable pulse spacing is described. The generator consists of a cross coupled multivibrator having adjustable time constant circuitry in each leg, an adjustable differentiating circuit in the output of each leg, a mixing and rectifying circuit for combining the differentiated pulses and generating in its output a resultant sequence of negative pulses, and a final amplifying circuit for inverting and square-topping the pulses. (AEC)

Micro-fractional ablative skin resurfacing with two novel erbium laser systems.

PubMed

Dierickx, Christine C; Khatri, Khalil A; Tannous, Zeina S; Childs, James J; Cohen, Richard H; Erofeev, Andrei; Tabatadze, David; Yaroslavsky, Ilya V; Altshuler, Gregory B

2008-02-01

Fractional ablation offers the potential benefits of full-surface ablative skin resurfacing while minimizing adverse effects. The purpose of this study was to evaluate the safety, damage profile, and efficacy of erbium fractional lasers. Histology from animal and human skin as well as clinical evaluations were conducted with erbium YAG (2,940 nm) and erbium YSGG (2,790 nm) fractional lasers varying pulse width, microbeam (microb) energy, number of passes, and stacking of pulses. Single-pulse treatment parameters from 1 to 12 mJ per 50-70 microm diameter microbeam and 0.25-5 milliseconds pulse widths produced microcolumns of ablation with border coagulation of up to 100 microm width and 450 microm depth. Stacking of pulses generated deeper microcolumns. Clinical observations and in vivo histology demonstrate rapid re-epithelization and limited adverse side effects. Facial treatments were performed in the periorbital and perioral areas using 1-8 passes of single and stacked pulses. Treatments were well-tolerated and subjects could resume their normal routine in 4 days. A statistically significant reduction in wrinkle scores at 3 months was observed for both periorbital and perioral wrinkles using blinded grading. For periorbital treatments of four passes or more, over 90% had > or =1 score wrinkle reduction (0-9 scale) and 42% had > or =2. For perioral wrinkles, over 50% had substantial improvements (> or =2). The clinical observations and histology findings demonstrate that micro-fractional ablative treatment with 2,790 and 2,940 nm erbium lasers resulted in safe and effective wrinkle reduction with minimal patient downtime. The depth and width of the ablated microcolumns and varying extent of surrounding coagulation can be controlled and used to design new treatment procedures targeted for specific indications and areas such as moderate to severe rhytides and photodamaged skin.

Two-Photon Excited Fluorescence from Biological Aerosol Particles

DTIC Science & Technology

2010-09-29

in material damage. We overcame these limitations by building a band-limited Yb-doped fiber laser with no dispersion compensation [9], as the master...master oscillator was an all-normal- dispersion Yb-doped fiber laser [9], followed by high- dispersion fiber for stretching the pulses, a single-mode...of ~670 fs in duration, and its expected transform-limited pulse width for a normal- dispersion laser with this spectral width would be ~454 fs [10

NRL (Naval Research Laboratory) Review

DTIC Science & Technology

1989-07-01

newmatrial. Vriou difracion The division has recently developed the 475-ftto invent new materials. Various diffraction e-hdel(S- 5 noa dacdfr...study sample between 4 and 400 K without breaking the fabrication methods by using new and/or unusual vacuum. The facility is currently used for...combine the output of multiaperture HF laser amplifiers. 24 . 4 Relativistic Klystron Amplifier New , high-power RF klystron-like amplifiers have been

A possible pole problem in the formula for klystron gap fields

NASA Technical Reports Server (NTRS)

Kosmahl, H. G.

1977-01-01

In isolated cases a pole may be encountered in a previously published solution for the fields in a klystron gap. Formulas, permitting the critical combinations of parameters to be defined, are presented. It is noted that the region of inaccuracy surrounding the pole is sufficiently small and that a 0.1% change in the field changing parameter is enough to avoid it.

Dose rate effect on micronuclei induction in human blood lymphocytes exposed to single pulse and multiple pulses of electrons.

PubMed

Acharya, Santhosh; Bhat, N N; Joseph, Praveen; Sanjeev, Ganesh; Sreedevi, B; Narayana, Y

2011-05-01

The effects of single pulses and multiple pulses of 7 MV electrons on micronuclei (MN) induction in cytokinesis-blocked human peripheral blood lymphocytes (PBLs) were investigated over a wide range of dose rates per pulse (instantaneous dose rate). PBLs were exposed to graded doses of 2, 3, 4, 6, and 8 Gy of single electron pulses of varying pulse widths at different dose rates per pulse, ranging from 1 × 10(6) Gy s(-1) to 3.2 × 10(8) Gy s(-1). Different dose rates per pulse were achieved by changing the dose per electron pulse by adjusting the beam current and pulse width. MN yields per unit absorbed dose after irradiation with single electron pulses were compared with those of multiple pulses of electrons. A significant decrease in the MN yield with increasing dose rates per pulse was observed, when dose was delivered by a single electron pulse. However, no reduction in the MN yield was observed when dose was delivered by multiple pulses of electrons. The decrease in the yield at high dose rates per pulse suggests possible radical recombination, which leads to decreased biological damage. Cellular response to the presence of very large numbers of chromosomal breaks may also alter the damage.

Endurance Enhancement and High Speed Set/Reset of 50 nm Generation HfO2 Based Resistive Random Access Memory Cell by Intelligent Set/Reset Pulse Shape Optimization and Verify Scheme

NASA Astrophysics Data System (ADS)

Higuchi, Kazuhide; Miyaji, Kousuke; Johguchi, Koh; Takeuchi, Ken

2012-02-01

This paper proposes a verify-programming method for the resistive random access memory (ReRAM) cell which achieves a 50-times higher endurance and a fast set and reset compared with the conventional method. The proposed verify-programming method uses the incremental pulse width with turnback (IPWWT) for the reset and the incremental voltage with turnback (IVWT) for the set. With the combination of IPWWT reset and IVWT set, the endurance-cycle increases from 48 ×103 to 2444 ×103 cycles. Furthermore, the measured data retention-time after 20 ×103 set/reset cycles is estimated to be 10 years. Additionally, the filamentary based physical model is proposed to explain the set/reset failure mechanism with various set/reset pulse shapes. The reset pulse width and set voltage correspond to the width and length of the conductive-filament, respectively. Consequently, since the proposed IPWWT and IVWT recover set and reset failures of ReRAM cells, the endurance-cycles are improved.

Hitomi X-ray studies of giant radio pulses from the Crab pulsar

NASA Astrophysics Data System (ADS)

Hitomi Collaboration; Aharonian, Felix; Akamatsu, Hiroki; Akimoto, Fumie; Allen, Steven W.; Angelini, Lorella; Audard, Marc; Awaki, Hisamitsu; Axelsson, Magnus; Bamba, Aya; Bautz, Marshall W.; Blandford, Roger; Brenneman, Laura W.; Brown, Gregory V.; Bulbul, Esra; Cackett, Edward M.; Chernyakova, Maria; Chiao, Meng P.; Coppi, Paolo S.; Costantini, Elisa; de Plaa, Jelle; de Vries, Cor P.; den Herder, Jan-Willem; Done, Chris; Dotani, Tadayasu; Ebisawa, Ken; Eckart, Megan E.; Enoto, Teruaki; Ezoe, Yuichiro; Fabian, Andrew C.; Ferrigno, Carlo; Foster, Adam R.; Fujimoto, Ryuichi; Fukazawa, Yasushi; Furuzawa, Akihiro; Galeazzi, Massimiliano; Gallo, Luigi C.; Gandhi, Poshak; Giustini, Margherita; Goldwurm, Andrea; Gu, Liyi; Guainazzi, Matteo; Haba, Yoshito; Hagino, Kouichi; Hamaguchi, Kenji; Harrus, Ilana M.; Hatsukade, Isamu; Hayashi, Katsuhiro; Hayashi, Takayuki; Hayashida, Kiyoshi; Hiraga, Junko S.; Hornschemeier, Ann; Hoshino, Akio; Hughes, John P.; Ichinohe, Yuto; Iizuka, Ryo; Inoue, Hajime; Inoue, Yoshiyuki; Ishida, Manabu; Ishikawa, Kumi; Ishisaki, Yoshitaka; Iwai, Masachika; Kaastra, Jelle; Kallman, Tim; Kamae, Tsuneyoshi; Kataoka, Jun; Katsuda, Satoru; Kawai, Nobuyuki; Kelley, Richard L.; Kilbourne, Caroline A.; Kitaguchi, Takao; Kitamoto, Shunji; Kitayama, Tetsu; Kohmura, Takayoshi; Kokubun, Motohide; Koyama, Katsuji; Koyama, Shu; Kretschmar, Peter; Krimm, Hans A.; Kubota, Aya; Kunieda, Hideyo; Laurent, Philippe; Lee, Shiu-Hang; Leutenegger, Maurice A.; Limousin, Olivier O.; Loewenstein, Michael; Long, Knox S.; Lumb, David; Madejski, Greg; Maeda, Yoshitomo; Maier, Daniel; Makishima, Kazuo; Markevitch, Maxim; Matsumoto, Hironori; Matsushita, Kyoko; McCammon, Dan; McNamara, Brian R.; Mehdipour, Missagh; Miller, Eric D.; Miller, Jon M.; Mineshige, Shin; Mitsuda, Kazuhisa; Mitsuishi, Ikuyuki; Miyazawa, Takuya; Mizuno, Tsunefumi; Mori, Hideyuki; Mori, Koji; Mukai, Koji; Murakami, Hiroshi; Mushotzky, Richard F.; Nakagawa, Takao; Nakajima, Hiroshi; Nakamori, Takeshi; Nakashima, Shinya; Nakazawa, Kazuhiro; Nobukawa, Kumiko K.; Nobukawa, Masayoshi; Noda, Hirofumi; Odaka, Hirokazu; Ohashi, Takaya; Ohno, Masanori; Okajima, Takashi; Oshimizu, Kenya; Ota, Naomi; Ozaki, Masanobu; Paerels, Frits; Paltani, Stéphane; Petre, Robert; Pinto, Ciro; Porter, Frederick S.; Pottschmidt, Katja; Reynolds, Christopher S.; Safi-Harb, Samar; Saito, Shinya; Sakai, Kazuhiro; Sasaki, Toru; Sato, Goro; Sato, Kosuke; Sato, Rie; Sawada, Makoto; Schartel, Norbert; Serlemtsos, Peter J.; Seta, Hiromi; Shidatsu, Megumi; Simionescu, Aurora; Smith, Randall K.; Soong, Yang; Stawarz, Łukasz; Sugawara, Yasuharu; Sugita, Satoshi; Szymkowiak, Andrew; Tajima, Hiroyasu; Takahashi, Hiromitsu; Takahashi, Tadayuki; Takeda, Shiníchiro; Takei, Yoh; Tamagawa, Toru; Tamura, Takayuki; Tanaka, Takaaki; Tanaka, Yasuo; Tanaka, Yasuyuki T.; Tashiro, Makoto S.; Tawara, Yuzuru; Terada, Yukikatsu; Terashima, Yuichi; Tombesi, Francesco; Tomida, Hiroshi; Tsuboi, Yohko; Tsujimoto, Masahiro; Tsunemi, Hiroshi; Tsuru, Takeshi Go; Uchida, Hiroyuki; Uchiyama, Hideki; Uchiyama, Yasunobu; Ueda, Shutaro; Ueda, Yoshihiro; Uno, Shiníchiro; Urry, C. Megan; Ursino, Eugenio; Watanabe, Shin; Werner, Norbert; Wilkins, Dan R.; Williams, Brian J.; Yamada, Shinya; Yamaguchi, Hiroya; Yamaoka, Kazutaka; Yamasaki, Noriko Y.; Yamauchi, Makoto; Yamauchi, Shigeo; Yaqoob, Tahir; Yatsu, Yoichi; Yonetoku, Daisuke; Zhuravleva, Irina; Zoghbi, Abderahmen; Terasawa, Toshio; Sekido, Mamoru; Takefuji, Kazuhiro; Kawai, Eiji; Misawa, Hiroaki; Tsuchiya, Fuminori; Yamazaki, Ryo; Kobayashi, Eiji; Kisaka, Shota; Aoki, Takahiro

2018-03-01

To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2-300 keV band and the Kashima NICT radio telescope in the 1.4-1.7 GHz band with a net exposure of about 2 ks on 2016 March 25, just before the loss of the Hitomi mission. The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1000 and 100 GRPs were simultaneously observed at the main pulse and inter-pulse phases, respectively, and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main pulse or inter-pulse phase. All variations are within the 2 σ fluctuations of the X-ray fluxes at the pulse peaks, and the 3 σ upper limits of variations of main pulse or inter-pulse GRPs are 22% or 80% of the peak flux in a 0.20 phase width, respectively, in the 2-300 keV band. The values for main pulse or inter-pulse GRPs become 25% or 110%, respectively, when the phase width is restricted to the 0.03 phase. Among the upper limits from the Hitomi satellite, those in the 4.5-10 keV and 70-300 keV bands are obtained for the first time, and those in other bands are consistent with previous reports. Numerically, the upper limits of the main pulse and inter-pulse GRPs in the 0.20 phase width are about (2.4 and 9.3) × 10-11 erg cm-2, respectively. No significant variability in pulse profiles implies that the GRPs originated from a local place within the magnetosphere. Although the number of photon-emitting particles should temporarily increase to account for the brightening of the radio emission, the results do not statistically rule out variations correlated with the GRPs, because the possible X-ray enhancement may appear due to a >0.02% brightening of the pulse-peak flux under such conditions.

Full Spectrum Conversion Using Traveling Pulse Wave Quantization

DTIC Science & Technology

2017-03-01

Full Spectrum Conversion Using Traveling Pulse Wave Quantization Michael S. Kappes Mikko E. Waltari IQ-Analog Corporation San Diego, California...temporal-domain quantization technique called Traveling Pulse Wave Quantization (TPWQ). Full spectrum conversion is defined as the complete...pulse width measurements that are continuously generated hence the name “traveling” pulse wave quantization. Our TPWQ-based ADC is composed of a

Effects of pulsed electrical field processing on microbial survival, quality change and nutritional characteristics of blueberries

USDA-ARS?s Scientific Manuscript database

Whole fresh blueberries were treated using a parallel pulsed electric field (PEF) treatment chamber and a sanitizer solution (60 ppm peracetic acid [PAA]) as PEF treatment medium with square wave bipolar pulses at 2 kV/cm electric field strength, 1us pulse width, and 100 pulses per second for 2, 4, ...

Advanced Orion Optimized Laser System Analysis

NASA Technical Reports Server (NTRS)

1996-01-01

Contractor shall perform a complete analysis of the potential of the solid state laser in the very long pulse mode (100 ns pulse width, 10-30 hz rep-rate) and in the very short pulse mode (100 ps pulse width 10-30 hz rep rate) concentrating on the operation of the device in the 'hot-rod' mode, where no active cooling the laser operation is attempted. Contractor's calculations shall be made of the phase aberrations which develop during the repped-pulse train, and the results shall feed into the adaptive optics analyses. The contractor shall devise solutions to work around ORION track issues. A final report shall be furnished to the MSFC COTR including all calculations and analysis of estimates of bulk phase and intensity aberration distribution in the laser output beam as a function of time during the repped-pulse train for both wave forms (high-energy/long-pulse, as well as low-energy/short-pulse). Recommendations shall be made for mitigating the aberrations by laser re-design and/or changes in operating parameters of optical pump sources and/or designs.

Repetitive Transcranial Magnetic Stimulator with Controllable Pulse Parameters

PubMed Central

Peterchev, Angel V; Murphy, David L; Lisanby, Sarah H

2013-01-01

The characteristics of transcranial magnetic stimulation (TMS) pulses influence the physiological effect of TMS. However, available TMS devices allow very limited adjustment of the pulse parameters. We describe a novel TMS device that uses a circuit topology incorporating two energy storage capacitors and two insulated-gate bipolar transistor (IGBT) modules to generate near-rectangular electric field pulses with adjustable number, polarity, duration, and amplitude of the pulse phases. This controllable pulse parameter TMS (cTMS) device can induce electric field pulses with phase widths of 10–310 μs and positive/negative phase amplitude ratio of 1–56. Compared to conventional monophasic and biphasic TMS, cTMS reduces energy dissipation by up to 82% and 57%, and decreases coil heating by up to 33% and 41%, respectively. We demonstrate repetitive TMS trains of 3,000 pulses at frequencies up to 50 Hz with electric field pulse amplitude and width variability less than the measurement resolution (1.7% and 1%, respectively). Offering flexible pulse parameter adjustment and reduced power consumption and coil heating, cTMS enhances existing TMS paradigms, enables novel research applications, and could lead to clinical applications with potentially enhanced potency. PMID:21540487

High resolution time interval counter

DOEpatents

Condreva, Kenneth J.

1994-01-01

A high resolution counter circuit measures the time interval between the occurrence of an initial and a subsequent electrical pulse to two nanoseconds resolution using an eight megahertz clock. The circuit includes a main counter for receiving electrical pulses and generating a binary word--a measure of the number of eight megahertz clock pulses occurring between the signals. A pair of first and second pulse stretchers receive the signal and generate a pair of output signals whose widths are approximately sixty-four times the time between the receipt of the signals by the respective pulse stretchers and the receipt by the respective pulse stretchers of a second subsequent clock pulse. Output signals are thereafter supplied to a pair of start and stop counters operable to generate a pair of binary output words representative of the measure of the width of the pulses to a resolution of two nanoseconds. Errors associated with the pulse stretchers are corrected by providing calibration data to both stretcher circuits, and recording start and stop counter values. Stretched initial and subsequent signals are combined with autocalibration data and supplied to an arithmetic logic unit to determine the time interval in nanoseconds between the pair of electrical pulses being measured.

High resolution time interval counter

DOEpatents

Condreva, K.J.

1994-07-26

A high resolution counter circuit measures the time interval between the occurrence of an initial and a subsequent electrical pulse to two nanoseconds resolution using an eight megahertz clock. The circuit includes a main counter for receiving electrical pulses and generating a binary word--a measure of the number of eight megahertz clock pulses occurring between the signals. A pair of first and second pulse stretchers receive the signal and generate a pair of output signals whose widths are approximately sixty-four times the time between the receipt of the signals by the respective pulse stretchers and the receipt by the respective pulse stretchers of a second subsequent clock pulse. Output signals are thereafter supplied to a pair of start and stop counters operable to generate a pair of binary output words representative of the measure of the width of the pulses to a resolution of two nanoseconds. Errors associated with the pulse stretchers are corrected by providing calibration data to both stretcher circuits, and recording start and stop counter values. Stretched initial and subsequent signals are combined with autocalibration data and supplied to an arithmetic logic unit to determine the time interval in nanoseconds between the pair of electrical pulses being measured. 3 figs.

Numerical simulation of passively mode-locked fiber laser based on semiconductor optical amplifier

NASA Astrophysics Data System (ADS)

Yang, Jingwen; Jia, Dongfang; Zhang, Zhongyuan; Chen, Jiong; Liu, Tonghui; Wang, Zhaoying; Yang, Tianxin

2013-03-01

Passively mode-locked fiber laser (MLFL) has been widely used in many applications, such as optical communication system, industrial production, information processing, laser weapons and medical equipment. And many efforts have been done for obtaining lasers with small size, simple structure and shorter pulses. In recent years, nonlinear polarization rotation (NPR) in semiconductor optical amplifier (SOA) has been studied and applied as a mode-locking mechanism. This kind of passively MLFL has faster operating speed and makes it easier to realize all-optical integration. In this paper, we had a thorough analysis of NPR effect in SOA. And we explained the principle of mode-locking by SOA and set up a numerical model for this mode-locking process. Besides we conducted a Matlab simulation of the mode-locking mechanism. We also analyzed results under different working conditions and several features of this mode-locking process are presented. Our simulation shows that: Firstly, initial pulse with the peak power exceeding certain threshold may be amplified and compressed, and stable mode-locking may be established. After about 25 round-trips, stable mode-locked pulse can be obtained which has peak power of 850mW and pulse-width of 780fs.Secondly, when the initial pulse-width is greater, narrowing process of pulse is sharper and it needs more round-trips to be stable. Lastly, the bias currents of SOA affect obviously the shape of mode-locked pulse and the mode-locked pulse with high peak power and narrow width can be obtained through adjusting reasonably the bias currents of SOA.

High voltage systems (tube-type microwave)/low voltage system (solid-state microwave) power distribution

NASA Technical Reports Server (NTRS)

Nussberger, A. A.; Woodcock, G. R.

1980-01-01

SPS satellite power distribution systems are described. The reference Satellite Power System (SPS) concept utilizes high-voltage klystrons to convert the onboard satellite power from dc to RF for transmission to the ground receiving station. The solar array generates this required high voltage and the power is delivered to the klystrons through a power distribution subsystem. An array switching of solar cell submodules is used to maintain bus voltage regulation. Individual klystron dc voltage conversion is performed by centralized converters. The on-board data processing system performs the necessary switching of submodules to maintain voltage regulation. Electrical power output from the solar panels is fed via switch gears into feeder buses and then into main distribution buses to the antenna. Power also is distributed to batteries so that critical functions can be provided through solar eclipses.

Study of the emission performance of high-power klystrons: SLAC XK-5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Y.

1981-07-01

There are hundreds of high power klystrons operated in the Linac gallery and about fifty to sixty tubes fail every year. The lifetime ranges from a few thousand up to seventy thousand hours except those which fail during an early period. The overall percentage of failures due to emission problems is approximately 25%. It is also noted that a 10% increase in mean lifetime of klystrons will reduce the overall cost per hour as much as a 10% increase in efficiency. Therefore, it is useful to find some method to predict the expected life of an individual tube. The finalmore » goal has not been attained yet, but some useful information was obtained. It is thought that this information might be helpful for those people who will study this subject further.« less

Delay-tunable gap-soliton-based slow-light system

NASA Astrophysics Data System (ADS)

Mok, Joe T.; de Sterke, C. Martijn; Eggleton, Benjamin J.

2006-12-01

We numerically and analytically evaluate the delay of solitons propagating slowly, and without broadening, in an apodized Bragg grating. Simulations indicate that a 100 mm Bragg grating with Δn = 10-3 can delay sub-nanosecond pulses by nearly 20 pulse widths without any change in the output pulse width. Delay tunability is achieved by simultaneously adjusting the launch power and detuning. A simple analytic model is developed to describe the monotonic dependence of delay on Δn and compared with simulations. As the intensity may be greatly enhanced due to a reduced velocity, a procedure for improving the delay while avoiding material damage is outlined.

1030-nm diode-laser-based light source delivering pulses with nanojoule energies and picosecond duration adjustable by mode locking or pulse gating operation

NASA Astrophysics Data System (ADS)

Klehr, A.; Liero, A.; Wenzel, H.; Bugge, F.; Brox, O.; Fricke, J.; Ressel, P.; Knigge, A.; Heinrich, W.; Tränkle, G.

2017-02-01

A new compact 1030 nm picosecond light source which can be switched between pulse gating and mode locking operation is presented. It consists of a multi-section distributed Bragg reflector (DBR) laser, an ultrafast multisection optical gate and a flared power amplifier (PA), mounted together with high frequency electronics and optical elements on a 5×4 cm micro bench. The master oscillator (MO) is a 10 mm long ridge wave-guide (RW) laser consisting of 200 μm long saturable absorber, 1500 μm long gain, 8000 μm long cavity, 200 μm long DBR and 100 μm long monitor sections. The 2 mm long optical gate consisting of several RW sections is monolithically integrated with the 4 mm long gain-guided tapered amplifier on a single chip. The light source can be switched between pulse gating and passive mode locking operation. For pulse gating all sections of the MO (except of the DBR and monitor sections) are forward biased and driven by a constant current. By injecting electrical pulses into one section of the optical gate the CW beam emitted by the MO is converted into a train of optical pulses with adjustable widths between 250 ps and 1000 ps. Peak powers of 20 W and spectral linewidths in the MHz range are achieved. Shorter pulses with widths between 4 ps and 15 ps and peak powers up to 50 W but larger spectral widths of about 300 pm are generated by mode locking where the saturable absorber section of the MO is reversed biased. The repetition rate of 4.2 GHz of the pulse train emitted by the MO can be reduced to values between 1 kHz and 100 MHz by utilizing the optical gate as pulse picker. The pulse-to-pulse distance can be controlled by an external trigger source.

A laser-Compton scattering prototype experiment at 100 MeV linac of Shanghai Institute of Applied Physics.

PubMed

Luo, W; Xu, W; Pan, Q Y; Cai, X Z; Chen, J G; Chen, Y Z; Fan, G T; Fan, G W; Guo, W; Li, Y J; Liu, W H; Lin, G Q; Ma, Y G; Shen, W Q; Shi, X C; Xu, B J; Xu, J Q; Xu, Y; Zhang, H O; Yan, Z; Yang, L F; Zhao, M H

2010-01-01

As a prototype of the Shanghai Laser Electron Gamma Source in the Shanghai Synchrotron Radiation Facility, an x-ray source based on laser-Compton scattering (LCS) has been installed at the terminal of the 100 MeV linac of the Shanghai Institute of Applied Physics. LCS x-rays are generated by interactions between Q-switched Nd:yttrium aluminum garnet laser pulses [with wavelength of 1064 nm and pulse width of 21 ns (full width at half maximum)] and electron bunches [with energy of 108 MeV and pulse width of 0.95 ns (rms)] at an angle of 42 degrees between laser and electron beam. In order to measure the energy spectrum of LCS x-rays, a Si(Li) detector along the electron beam line axis is positioned at 9.8 m away from a LCS chamber. After background subtraction, the LCS x-ray spectrum with the peak energy of 29.1+/-4.4|(stat)+/-2.1|(syst) keV and the peak width (rms) of 7.8+/-2.8|(stat)+/-0.4|(syst) keV is observed. Normally the 100 MeV linac operates with the electron macropulse charge of 1.0 nC/pulse, and the electron and laser collision repetition rate of 20 Hz. Therefore, the total LCS x-ray flux of (5.2+/-2.0) x 10(2) Hz can be achieved.

Broadband optical frequency comb generator based on driving N-cascaded modulators by Gaussian-shaped waveform

NASA Astrophysics Data System (ADS)

Hmood, Jassim K.; Harun, Sulaiman W.

2018-05-01

A new approach for realizing a wideband optical frequency comb (OFC) generator based on driving cascaded modulators by a Gaussian-shaped waveform, is proposed and numerically demonstrated. The setup includes N-cascaded MZMs, a single Gaussian-shaped waveform generator, and N-1 electrical time delayer. The first MZM is driven directly by a Gaussian-shaped waveform, while delayed replicas of the Gaussian-shaped waveform drive the other MZMs. An analytical model that describes the proposed OFC generator is provided to study the effect of number and chirp factor of cascaded MZM as well as pulse width on output spectrum. Optical frequency combs at frequency spacing of 1 GHz are generated by applying Gaussian-shaped waveform at pulse widths ranging from 200 to 400 ps. Our results reveal that, the number of comb lines is inversely proportional to the pulse width and directly proportional to both number and chirp factor of cascaded MZMs. At pulse width of 200 ps and chirp factor of 4, 67 frequency lines can be measured at output spectrum of two-cascaded MZMs setup. Whereas, increasing the number of cascaded stages to 3, 4, and 5, the optical spectra counts 89, 109 and 123 frequency lines; respectively. When the delay time is optimized, 61 comb lines can be achieved with power fluctuations of less than 1 dB for five-cascaded MZMs setup.

Effects of the pulse width on the reactive species production and DNA damage in cancer cells exposed to atmospheric pressure microsecond-pulsed helium plasma jets

NASA Astrophysics Data System (ADS)

Joh, Hea Min; Choi, Ji Ye; Kim, Sun Ja; Kang, Tae Hong; Chung, T. H.

2017-08-01

Plasma-liquid and plasma-cell interactions were investigated using an atmospheric pressure dc microsecond-pulsed helium plasma jet. We investigated the effects of the electrical parameters such as applied voltage and pulse width (determined by the pulse frequency and duty ratio) on the production of reactive species in the gas/liquid phases and on the DNA damage responses in the cancer cells. The densities of reactive species including OH radicals were estimated inside the plasma-treated liquids using a chemical probe method, and the nitrite concentration was detected by Griess assay. Importantly, the more concentration of OH resulted in the more DNA base oxidation and breaks in human lung cancer A549 cells. The data are very suggestive that there is strong correlation between the production of OH in the plasmas/liquids and the DNA damage.

Effect of second harmonic in pulse-width-modulation-based DAC for feedback of digital fluxgate magnetometer

NASA Astrophysics Data System (ADS)

Belyayev, Serhiy; Ivchenko, Nickolay

2018-04-01

Digital fluxgate magnetometers employ processing of the measured pickup signal to produce the value of the compensation current. Using pulse-width modulation with filtering for digital to analog conversion is a convenient approach, but it can introduce an intrinsic source of nonlinearity, which we discuss in this design note. A code shift of one least significant bit changes the second harmonic content of the pulse train, which feeds into the pick-up signal chain despite the heavy filtering. This effect produces a code-dependent nonlinearity. This nonlinearity can be overcome by the specific design of the timing of the pulse train signal. The second harmonic is suppressed if the first and third quarters of the excitation period pulse train are repeated in the second and fourth quarters. We demonstrate this principle on a digital magnetometer, achieving a magnetometer noise level corresponding to that of the sensor itself.

Passively mode-locked soliton femtosecond pulses employing graphene saturable absorber

NASA Astrophysics Data System (ADS)

Lau, K. Y.; Muhammad, F. D.; Latif, A. A.; Abu Bakar, M. H.; Yusoff, Z.; Mahdi, M. A.

2017-09-01

We demonstrate a passively mode-locked fiber laser incorporating graphene thin film (GTF) as saturable absorber (SA). The SA is fabricated by sandwiching the GTF between two single mode fiber ferrules through a fiber adaptor. The transmission loss at 1560 nm and non-linear saturation absorption modulation depth for GTF-SA are 0.8 dB and 2.90%, respectively. An erbium-doped fiber laser cavity is constructed to verify the functionality of GTF-SA and is designed to have net anomalous dispersion. It generates large spectral width of 4.99 nm with pulse repetition rate of 9.655 MHz and pulse width of 670 fs. Net anomalous dispersion and time bandwidth product higher than the sech2 transform-limited pulse validate the experimental result. In short, we demonstrate high performance GTF-SA that is able to generate ultrafast pulse duration in femtosecond range effortlessly with simple and green SA fabrication procedures.

Klystron Manufacturing Technology Program.

DTIC Science & Technology

1983-09-01

processes, and methodology used on the current production tube, VKU-7735E, and the new methods and techniques used to improve and reduce the cost of...the bellows. This alignment is c~tclto the smoothi operation of the internal tuniing mezhanism. IT METR𔃼D - VKCU-7795F The new assembly method changes...Varian, the MT contractor that the new methodology , technologies and process changes introduced into the MT power klystron and autotuner assembly - VKU

Microwave Tubes.

DTIC Science & Technology

1980-06-02

better possibilities). It should be stated, also, that there exists for both TWT and the klystron, quite straight forward theoretical approaches which can...methods of large signal calculations for coupled cavity TWTs . Copies of this internal memo can be made available to any recipient of this report. M716S GP"I...electrodes and magnetic fields. The magnetic fields, in some cases (klystrons and TWTs ), serve merely to focus the beam, that is, confine the electron

Generation of programmable temporal pulse shape and applications in micromachining

NASA Astrophysics Data System (ADS)

Peng, X.; Jordens, B.; Hooper, A.; Baird, B. W.; Ren, W.; Xu, L.; Sun, L.

2009-02-01

In this paper we presented a pulse shaping technique on regular solid-state lasers and the application in semiconductor micromachining. With a conventional Q-switched laser, all of the parameters can be adjusted over only limited ranges, especially the pulse width and pulse shape. However, some laser link processes using traditional laser pulses with pulse widths of a few nanoseconds to a few tens of nanoseconds tend to over-crater in thicker overlying passivation layers and thereby cause IC reliability problems. Use of a laser pulse with a special shape and a fast leading edge, such as tailored pulse, is one technique for controlling link processing. The pulse shaping technique is based on light-loop controlled optical modulation to shape conventional Q-switched solid-state lasers. One advantage of the pulse shaping technique is to provide a tailored pulse shape that can be programmed to have more than one amplitude value. Moreover, it has the capability of providing programmable tailored pulse shapes with discrete amplitude and time duration components. In addition, it provides fast rising and fall time of each pulse at fairly high repetition rate at 355nm with good beam quality. The regular-to-shaped efficiency is up to 50%. We conclude with a discussion of current results for laser processing of semiconductor memory link structures using programmable temporal pulse shapes. The processing experiments showed promising results with shaped pulse.

Study of nonlinear interaction between bunched beam and intermediate cavities in a relativistic klystron amplifier

NASA Astrophysics Data System (ADS)

Wu, Y.; Xu, Z.; Li, Z. H.; Tang, C. X.

2012-07-01

In intermediate cavities of a relativistic klystron amplifier (RKA) driven by intense relativistic electron beam, the equivalent circuit model, which is widely adopted to investigate the interaction between bunched beam and the intermediate cavity in a conventional klystron design, is invalid due to the high gap voltage and the nonlinear beam loading in a RKA. According to Maxwell equations and Lorentz equation, the self-consistent equations for beam-wave interaction in the intermediate cavity are introduced to study the nonlinear interaction between bunched beam and the intermediate cavity in a RKA. Based on the equations, the effects of modulation depth and modulation frequency of the beam on the gap voltage amplitude and its phase are obtained. It is shown that the gap voltage is significantly lower than that estimated by the equivalent circuit model when the beam modulation is high. And the bandwidth becomes wider as the beam modulation depth increases. An S-band high gain relativistic klystron amplifier is designed based on the result. And the corresponding experiment is carried out on the linear transformer driver accelerator. The peak output power has achieved 1.2 GW with an efficiency of 28.6% and a gain of 46 dB in the corresponding experiment.

Generation of 70 fs broadband pulses in a hybrid nonlinear amplification system with mode-locked Yb:YAG ceramic oscillator

NASA Astrophysics Data System (ADS)

Liu, Yang; Wang, Chao; Luo, Daping; Yang, Chao; Li, Jiang; Ge, Lin; Pan, Yubai; Li, Wenxue

2017-12-01

We demonstrate the passively mode-locked laser performances of bulk Yb:YAG ceramic prepared by non-aqueous tape casting, which generates initial pulses in temporal width of 3 ps and spectrum width of 3 nm without intra-cavity dispersion management. The ceramic laser is further used as seeding oscillator in a fiber nonlinear amplification system, where ultrashort pulses in maximum output power of ˜100 W and pulse duration of 70 fs are achieved. Moreover, the laser spectrum is broadened to be ˜41 nm due to self-phase modulation effects in the gain fiber, overcoming the narrow spectrum limitations of ceramic materials. Our approach opens a new avenue for power-scaling and spectrum-expanding of femtosecond ceramic lasers.

Type-I frequency-doubling characteristics of high-power, ultrafast fiber laser in thick BIBO crystal.

PubMed

Chaitanya N, Apurv; Aadhi, A; Singh, R P; Samanta, G K

2014-09-15

We report on experimental realization of optimum focusing condition for type-I second-harmonic generation (SHG) of high-power, ultrafast laser in "thick" nonlinear crystal. Using single-pass, frequency doubling of a 5 W Yb-fiber laser of pulse width ~260 fs at repetition rate of 78 MHz in a 5-mm-long bismuth triborate (BIBO) crystal we observed that the optimum focusing condition is more dependent on the birefringence of the crystal than its group-velocity mismatch (GVM). A theoretical fit to our experimental results reveals that even in the presence of GVM, the optimum focusing condition matches the theoretical model of Boyd and Kleinman, predicted for continuous-wave and long-pulse SHG. Using a focusing factor of ξ=1.16 close to the estimated optimum value of ξ=1.72 for our experimental conditions, we generated 2.25 W of green radiation of pulse width 176 fs with single-pass conversion efficiency as high as 46.5%. Our study also verifies the effect of pulse narrowing and broadening of angular phase-matching bandwidth of SHG at tighter focusing. This study signifies the advantage of SHG in "thick" crystal in controlling SH-pulse width by changing the focusing lens while accessing high conversion efficiency and broad angular phase-matching bandwidth.

Development of new S-band SLED for PAL-XFEL Linac

NASA Astrophysics Data System (ADS)

Joo, Youngdo; Park, Yongjung; Heo, Hoon; Heo, Jinyul; Park, Sung-Soo; Kim, Sang-Hee; Kim, Kwang-Hoon; Kang, Heung-Sik; Lee, Heung-Soo; Noh, Sungju; Oh, Kyoungmin

2017-01-01

In order to achieve beam acceleration to the beam energy of 10 GeV at the end of its 716 m-long linear accelerator (Linac), the Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL) is going to operate the Stanford Linear Accelerator Energy Doubler (SLED) at the maximum klystron output peak power of 80 MW, with a pulse length of 4 μs, and at a repetition rate of 60 Hz. The original SLED that had been used in Pohang Light Source-II (PLS-II) can no longer sustain such a high-power operation because excessive radiation caused by RF breakdown has been frequently detected even at the lower klystron peak power during the PLS-II operation. Therefore, a new SLED is designed by modifying both the 3-dB power hybrid and the waveguide-cavity coupling structure of the original SLED where the excessive radiation has been mainly detected. The finite-difference time-domain (FDTD) simulation in the CST Microwave Studio shows that the new SLED has a peak electric field and a surface current lower than those of the original SLED at the same level of the RF input peak power, which would secure stable high-power operation. All of the 42 SLEDs in the PAL-XFEL Linac are newly fabricated and installed. During the RF conditioning of the PAL-XFEL Linac, no significant vacuum and radiation issue was found in the new SLEDs. Finally, the accelerated electron beam energy of 10 GeV obtained at the end of the PAL-XFEL Linac verified that the RF performance of the new SLED is stable.

Energy-conserving programming of VVI pacemakers: a telemetry-supported, long-term, follow-up study.

PubMed

Klein, H H; Knake, W

1990-06-01

Thirty patients with VVI pacemakers (Quantum 253-09, 253-19, Intermedics Inc., Freeport, TX) were observed for a mean of 65 months. Within 12 months after implantation, optimized output programming was performed in 29 patients. This included a decrease in pulse amplitude (22 patients), pulse width (4 patients), and/or pacing rate (11 patients). After 65 months postimplantation, telemetered battery voltage and battery impedance were compared with the predicted values expected when the pulse generator constantly stimulates at nominal program conditions (heart rate 72.3 beats/min, pulse amplitude 5.4 V, pulse width 0.61 ms). Instead of an expected cell voltage of 2.6 V and a cell impedance of 10 k omega mean telemetered values amounted to 2.78 V and 1.4 k omega, respectively. These data correspond to a battery age of 12-15 months at nominal program conditions. This long-term follow-up study suggests that adequate programming will extend battery longevity and thus pulse generator survival in many patients.

Selective two-photon excitation of a vibronic state by correlated photons.

PubMed

Oka, Hisaki

2011-03-28

We theoretically investigate the two-photon excitation of a molecular vibronic state by correlated photons with energy anticorrelation. A Morse oscillator having three sets of vibronic states is used, as an example, to evaluate the selectivity and efficiency of two-photon excitation. We show that a vibrational mode can be selectively excited with high efficiency by the correlated photons, without phase manipulation or pulse-shaping techniques. This can be achieved by controlling the quantum correlation so that the photon pair concurrently has two pulse widths, namely, a temporally narrow width and a spectrally narrow width. Though this concurrence is seemingly contradictory, we can create such a photon pair by tailoring the quantum correlation between two photons.

A hybrid pulse combining topology utilizing the combination of modularized avalanche transistor Marx circuits, direct pulse adding, and transmission line transformer.

PubMed

Li, Jiangtao; Zhao, Zheng; Sun, Yi; Liu, Yuhao; Ren, Ziyuan; He, Jiaxin; Cao, Hui; Zheng, Minjun

2017-03-01

Numerous applications driven by pulsed voltage require pulses to be with high amplitude, high repetitive frequency, and narrow width, which could be satisfied by utilizing avalanche transistors. The output improvement is severely limited by power capacities of transistors. Pulse combining is an effective approach to increase the output amplitude while still adopting conventional pulse generating modules. However, there are drawbacks in traditional topologies including the saturation tendency of combining efficiency and waveform oscillation. In this paper, a hybrid pulse combining topology was adopted utilizing the combination of modularized avalanche transistor Marx circuits, direct pulse adding, and transmission line transformer. The factors affecting the combining efficiency were determined including the output time synchronization of Marx circuits, and the quantity and position of magnetic cores. The numbers of the parallel modules and the stages were determined by the output characteristics of each combining method. Experimental results illustrated the ability of generating pulses with 2-14 kV amplitude, 7-11 ns width, and a maximum 10 kHz repetitive rate on a matched 50-300 Ω resistive load. The hybrid topology would be a convinced pulse combining method for similar nanosecond pulse generators based on the solid-state switches.

A hybrid pulse combining topology utilizing the combination of modularized avalanche transistor Marx circuits, direct pulse adding, and transmission line transformer

NASA Astrophysics Data System (ADS)

Li, Jiangtao; Zhao, Zheng; Sun, Yi; Liu, Yuhao; Ren, Ziyuan; He, Jiaxin; Cao, Hui; Zheng, Minjun

2017-03-01

Numerous applications driven by pulsed voltage require pulses to be with high amplitude, high repetitive frequency, and narrow width, which could be satisfied by utilizing avalanche transistors. The output improvement is severely limited by power capacities of transistors. Pulse combining is an effective approach to increase the output amplitude while still adopting conventional pulse generating modules. However, there are drawbacks in traditional topologies including the saturation tendency of combining efficiency and waveform oscillation. In this paper, a hybrid pulse combining topology was adopted utilizing the combination of modularized avalanche transistor Marx circuits, direct pulse adding, and transmission line transformer. The factors affecting the combining efficiency were determined including the output time synchronization of Marx circuits, and the quantity and position of magnetic cores. The numbers of the parallel modules and the stages were determined by the output characteristics of each combining method. Experimental results illustrated the ability of generating pulses with 2-14 kV amplitude, 7-11 ns width, and a maximum 10 kHz repetitive rate on a matched 50-300 Ω resistive load. The hybrid topology would be a convinced pulse combining method for similar nanosecond pulse generators based on the solid-state switches.

A Hybrid Fiber/Solid-State Regenerative Amplifier with Tunable Pulse Widths for Satellite Laser Ranging

NASA Technical Reports Server (NTRS)

Coyle, Barry; Poulios, Demetrios

2013-01-01

A fiber/solid-state hybrid seeded regenerative amplifier, capable of achieving high output energy with tunable pulse widths, has been developed for satellite laser ranging applications. The regenerative amplifier cavity uses a pair of Nd:YAG zigzag slabs oriented orthogonally to one another in order to make thermal lensing effects symmetrical and simplify optical correction schemes. The seed laser used is a fiber-coupled 1,064-nm narrowband (<0.02 nm) diode laser that is discretely driven in a new short-pulsed mode, enabling continuously tunable seed pulse widths in the 0.2-to-0.4-ns range. The amplifier gain unit consists of a pair of Brewster-cut 6-bounce zigzag Nd:YAG laser slabs, oriented 90deg relative to each other in the amplifier head. This arrangement creates a net-symmetrical thermal lens effect (an opposing singleaxis effect in each slab), and makes thermo-optical corrections simple by optimizing the curvature of the nearest cavity mirror. Each slab is pumped by a single 120-W, pulsed 808-nm laser diode array. In this configuration, the average pump beam distribution in the slabs had a 1-D Gaussian shape, which matches the estimated cavity mode size. A half-wave plate between the slabs reduces losses from Fresnel reflections due to the orthogonal slabs Brewster-cut end faces. Successful "temporal" seeding of the regenerative amplifier cavity results in a cavity Q-switch pulse envelope segmenting into shorter pulses, each having the width of the input seed, and having a uniform temporal separation corresponding to the cavity round-trip time of approx. =10 ns. The pulse energy is allowed to build on successive passes in the regenerative amplifier cavity until a maximum is reached, (when cavity gains and losses are equal), after which the pulse is electro- optically switched out on the next round trip The overall gain of the amplifier is approx. =82 dB (or a factor of 1.26 million). After directing the amplified output through a LBO frequency doubling crystal, approx. = 2.1 W of 532-nm output (>1 mJ) was measured. This corresponds to a nonlinear conversion efficiency of >60%. Furthermore, by pulse pumping this system, a single pulse per laser shot can be created for the SLR (satellite laser ranging) measurement, and this can be ejected into the instrument. This is operated at the precise frequency needed by the measurement, as opposed to commercial short-pulsed, mode-locked systems that need to operate in a continuous fashion, or CW (continuous wave), and create pulses at many MHz. Therefore, this design does not need to throw away or dump 99% of the laser energy to produce what is required; this system can be far smaller, more efficient, cheaper, and readily deployed in the field when packaged efficiently. Finally, by producing custom diode seed pulses electronically, two major advantages over commercial systems are realized: First, this pulse shape is customizable and not affected by the cavity length or gain of the amplifier cavity, and second, it can produce adjustable (selectable) pulse widths by simply adding multiple seed diodes and coupling each into commercial, low-cost fiber-optic combiners.

All-optical controlled switching of solitons

NASA Astrophysics Data System (ADS)

Man, Wai Sing

1999-11-01

In this dissertation, we have numerically investigated various method of switching solitons using two different nonlinear optical switching devices, namely the twin core nonlinear directional coupler (TCNLDC) and the nonlinear optical loop mirror (NOLM). In the case of TCNLDC, four different schemes were explored where the polarization of the controlling pulse is either parallel or orthogonal to that of the signal soliton, or the controlling pulse may be launched into either of the input ports or it may have a wavelength different from that of the signal. It has been shown that high switching efficiency and distortionless propagation of the signal pulse through the coupler can only be achieved for the case in which the control pulse is launched into the adjacent port of the directional coupler and that its dispersion has equal magnitude but opposite sign as that of the signal. The effect of varying pulse width, walk-off and timing jitter were also investigated for this particular scheme for signal pulse width of 1 ps wide. In the case of NOLM, a control pulse having central wavelength located at the normal dispersion region is used to switch the soliton. The control pulse width and the NOLM's loop length were varied to obtain the switched soliton with minimum distortion and high switching efficiency. In this analysis, Raman effect is included because the control pulse transfers part of its energy to the co-propagating signal pulse in the optical loop. A compact soliton laser has also been developed for this project and its performance was analyzed experimentally and numerically. In our analysis of this soliton laser, we found that the wavelength of the mode-locked pulse can be tuned by varying the polarization elements in the laser and this is entirely due to the birefringence in the laser cavity. In summary, our works have shown that optical solitons can be switched effectively by TCNLDC and NOLM in the high bit-rate and low switching energy regime. (Abstract shortened by UMI.)

High peak power actively Q-switched mid-infrared fiber lasers at 3 μm

NASA Astrophysics Data System (ADS)

Shen, Yanlong; Wang, Yishan; Luan, Kunpeng; Chen, Hongwei; Tao, Mengmeng; Si, Jinhai

2017-04-01

Diode-pumped pulsed Er3+-doped ZBLAN fiber lasers at 2.8 μm actively Q-switched by using an mechanical Q-switch with feedbacks of a protected gold mirror and a blazing grating were investigated, respectively. A pulse energy of 0.13 mJ and repetition rate of 10 kHz with a pulse width of 127.3 ns at 2.78 μm was obtained when using a protected gold mirror as the feedback. By replacing the mirror with a blazing grating in Littrow configuration, the wavelength of the Q-switched pulse train was tunable with over 100 nm tuning range from 2.71 to 2.82 μm and a linewidth of 1.5 nm. A maxinmum pulse energy of up to 0.15 mJ and repetition rate of 10 kHz with a pulse width of 92.6 ns was achieved, yielding the maximum peak power of exceeding 1.6 kW. The pulse energy and peak power, to our knowledge, are the highest ever reported in the mid-infrared Q-switched fiber lasers.

Reinjection laser oscillator and method

DOEpatents

McLellan, Edward J.

1984-01-01

A uv preionized CO.sub.2 oscillator with integral four-pass amplifier capable of providing 1 to 5 GW laser pulses with pulse widths from 0.1 to 0.5 ns full width at half-maximum (FWHM) is described. The apparatus is operated at any pressure from 1 atm to 10 atm without the necessity of complex high voltage electronics. The reinjection technique employed gives rise to a compact, efficient system that is particularly immune to alignment instabilities with a minimal amount of hardware and complexity.

CORE SATURATION BLOCKING OSCILLATOR

DOEpatents

Spinrad, R.J.

1961-10-17

A blocking oscillator which relies on core saturation regulation to control the output pulse width is described. In this arrangement an external magnetic loop is provided in which a saturable portion forms the core of a feedback transformer used with the thermionic or semi-conductor active element. A first stationary magnetic loop establishes a level of flux through the saturation portion of the loop. A second adjustable magnet moves the flux level to select a saturation point giving the desired output pulse width. (AEC)

Design of a Ku band miniature multiple beam klystron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bandyopadhyay, Ayan Kumar, E-mail: ayan.bandyopadhyay@gmail.com; Pal, Debasish; Kant, Deepender

2016-03-09

The design of a miniature multiple beam klystron (MBK) working in the Ku-band frequency range is presented in this article. Starting from the main design parameters, design of the electron gun, the input and output couplers and radio frequency section (RF-section) are presented. The design methodology using state of the art commercial electromagnetic design tools, analytical formulae as well as noncommercial design tools are briefly presented in this article.

Solar power satellite system definition study. Volume 4: Solid State SPS Analysis, Phase 3

NASA Technical Reports Server (NTRS)

1980-01-01

A 2500 megawatt solid ground output Solar Power Satellite (SPS) of conventional configuration was designed and analyzed. Because the power per receiving antenna is halved, as compared with the klystron reference, twice the number of receiving antennas are needed to deliver the same total power. The solid state approach appears feasible with a slightly greater specific mass and slightly higher cost than the klystron SPS design.

Mode control in a high-gain relativistic klystron amplifier

NASA Astrophysics Data System (ADS)

Li, Zheng-Hong; Zhang, Hong; Ju, Bing-Quan; Su, Chang; Wu, Yang

2010-05-01

Middle cavities between the input and output cavity can be used to decrease the required input RF power for the relativistic klystron amplifier. Meanwhile higher modes, which affect the working mode, are also easy to excite in a device with more middle cavities. In order for the positive feedback process for higher modes to be excited, a special measure is taken to increase the threshold current for such modes. Higher modes' excitation will be avoided when the threshold current is significantly larger than the beam current. So a high-gain S-band relativistic klystron amplifier is designed for the beam of current 5 kA and beam voltage 600 kV. Particle in cell simulations show that the gain is 1.6 × 105 with the input RF power of 6.8 kW, and that the output RF power reaches 1.1 GW.

Measured pulse width of sonoluminescence flashes in the form of resonance radiation

NASA Astrophysics Data System (ADS)

Giri, Asis; Arakeri, Vijay H.

1998-09-01

Recent studies have shown that the measured flash widths from single and multibubble sonoluminescence are in subnanosecond or even picosecond regime. Here, we provide conclusive evidence for the existence of nanosecond multibubble sonoluminescence. This has become possible by our ability to find a medium from which exclusive sodium D line resonance radiation as a form of sonoluminescence is possible. The measured flash width of this emission is found to be in the range of tens of nanoseconds and is sensitively dependent on experimental parameters. Our finding is important since all the earlier pulse width measurements have been limited to emission with the physical source or species responsible for observed optical radiation not being clearly identified. We propose that the presently observed resonance radiation is from ``soft'' bubble collapse as analyzed by V. Kamath et al. [J. Acoust. Soc. Am. 94, 248 (1993)].

Inference and analysis of xenon outflow curves under multi-pulse injection in two-dimensional chromatography.

PubMed

Shu-Jiang, Liu; Zhan-Ying, Chen; Yin-Zhong, Chang; Shi-Lian, Wang; Qi, Li; Yuan-Qing, Fan

2013-10-11

Multidimensional gas chromatography is widely applied to atmospheric xenon monitoring for the Comprehensive Nuclear-Test-Ban Treaty (CTBT). To improve the capability for xenon sampling from the atmosphere, sampling techniques have been investigated in detail. The sampling techniques are designed by xenon outflow curves which are influenced by many factors, and the injecting condition is one of the key factors that could influence the xenon outflow curves. In this paper, the xenon outflow curves of single-pulse injection in two-dimensional gas chromatography has been tested and fitted as a function of exponential modified Gaussian distribution. An inference formula of the xenon outflow curve for six-pulse injection is derived, and the inference formula is also tested to compare with its fitting formula of the xenon outflow curve. As a result, the curves of both the one-pulse and six-pulse injections obey the exponential modified Gaussian distribution when the temperature of the activated carbon column's temperature is 26°C and the flow rate of the carrier gas is 35.6mLmin(-1). The retention time of the xenon peak for one-pulse injection is 215min, and the peak width is 138min. For the six-pulse injection, however, the retention time is delayed to 255min, and the peak width broadens to 222min. According to the inferred formula of the xenon outflow curve for the six-pulse injection, the inferred retention time is 243min, the relative deviation of the retention time is 4.7%, and the inferred peak width is 225min, with a relative deviation of 1.3%. Copyright © 2013 Elsevier B.V. All rights reserved.

The influence of laser pulse duration and energy on ICP-MS signal intensity, elemental fractionation, and particle size distribution in NIR fs-LA-ICP-MS

PubMed Central

Diwakar, Prasoon K.; Harilal, Sivanandan S.; LaHaye, Nicole L.; Hassanein, Ahmed; Kulkarni, Pramod

2015-01-01

Laser parameters, typically wavelength, pulse width, irradiance, repetition rate, and pulse energy, are critical parameters which influence the laser ablation process and thereby influence the LA-ICP-MS signal. In recent times, femtosecond laser ablation has gained popularity owing to the reduction in fractionation related issues and improved analytical performance which can provide matrix-independent sampling. The advantage offered by fs-LA is due to shorter pulse duration of the laser as compared to the phonon relaxation time and heat diffusion time. Hence the thermal effects are minimized in fs-LA. Recently, fs-LA-ICP-MS demonstrated improved analytical performance as compared to ns-LA-ICP-MS, but detailed mechanisms and processes are still not clearly understood. Improvement of fs-LA-ICP-MS over ns-LA-ICP-MS elucidates the importance of laser pulse duration and related effects on the ablation process. In this study, we have investigated the influence of laser pulse width (40 fs to 0.3 ns) and energy on LA-ICP-MS signal intensity and repeatability using a brass sample. Experiments were performed in single spot ablation mode as well as rastering ablation mode to monitor the Cu/Zn ratio. The recorded ICP-MS signal was correlated with total particle counts generated during laser ablation as well as particle size distribution. Our results show the importance of pulse width effects in the fs regime that becomes more pronounced when moving from femtosecond to picosecond and nanosecond regimes. PMID:26664120

Graphene Oxide: A Perfect Material for Spatial Light Modulation Based on Plasma Channels

PubMed Central

Tan, Chao; Wu, Xinghua; Wang, Qinkai; Tang, Pinghua; Shi, Xiaohui; Zhan, Shiping; Xi, Zaifang; Fu, Xiquan

2017-01-01

The graphene oxide (GO) is successfully prepared from a purified natural graphite through a pressurized oxidation method. We experimentally demonstrate that GO as an optical media can be used for spatial light modulation based on plasma channels induced by femtosecond pulses. The modulated beam exhibits good propagation properties in free space. It is easy to realize the spatial modulation on the probe beam at a high concentration of GO dispersion solutions, high power and smaller pulse width of the pump beam. We also find that the spatial modulation on the probe beam can be conveniently adjusted through the power and pulse width of pump lasers, dispersion solution concentration. PMID:28772712

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen Weicheng; Chen Guojie; Han Dingan

A fibre laser with a SESAM as a passive mode-locker is constructed for obtaining a vector soliton with the Kelly sidebands. The analysis of the peculiarities of the sidebands shows that the polarisation states are nonuniform across the entire pulse spectral profile from the leading edge to the trailing edge. Polarisation filtering effect is proposed to obtain a vector soliton with a uniform polarisation state. It is shown that during the polarisation filtering by a polariser incorporated into the laser cavity, the spectral width of the vector solitons gradually broadens and the pulse power decreases. It is found that atmore » a maximum spectral width and a minimum pulse power, vector solitons with a uniform polarisation state are generated. (nonlinear optical phenomena)« less

Radar RFI at Goldstone DSS 12 and DSS 16

NASA Astrophysics Data System (ADS)

Slobin, S. D.; Peng, T. K.

1990-02-01

Radio frequency interference (RFI) from the DSS 14 Goldstone Solar System Radar (GSSR) was investigated at DSS 12 and DSS 16 with the goal of assisting in the choice of the location of future DSN antennas. Total power measurements at both locations were made at the S-band carrier frequency of 2320 MHz. X-band measurements at the carrier frequency of 8495 MHz could not be made. Exciter-chain output spectrum and klystron output spectrum measurements were made at S- and X-bands using a probable worst-case modulation of the radar signal (short pseudorandom number (PN) code length and short pulse length). Based on these measurements, it is estimated that RFI levels in the DSN receiving bands at both sites (above 10-deg elevation) would be below -192 dBm for a 1-Hz bandwidth

Radar RFI at Goldstone DSS 12 and DSS 16

NASA Technical Reports Server (NTRS)

Slobin, S. D.; Peng, T. K.

1990-01-01

Radio frequency interference (RFI) from the DSS 14 Goldstone Solar System Radar (GSSR) was investigated at DSS 12 and DSS 16 with the goal of assisting in the choice of the location of future DSN antennas. Total power measurements at both locations were made at the S-band carrier frequency of 2320 MHz. X-band measurements at the carrier frequency of 8495 MHz could not be made. Exciter-chain output spectrum and klystron output spectrum measurements were made at S- and X-bands using a probable worst-case modulation of the radar signal (short pseudorandom number (PN) code length and short pulse length). Based on these measurements, it is estimated that RFI levels in the DSN receiving bands at both sites (above 10-deg elevation) would be below -192 dBm for a 1-Hz bandwidth

Laser micro-machining strategies for transparent brittle materials using ultrashort pulsed lasers

NASA Astrophysics Data System (ADS)

Bernard, Benjamin; Matylitsky, Victor

2017-02-01

Cutting and drilling of transparent materials using short pulsed laser systems are important industrial production processes. Applications ranging from sapphire cutting, hardened glass processing, and flat panel display cutting, to diamond processing are possible. The ablation process using a Gaussian laser beam incident on the topside of a sample with several parallel overlapping lines leads to a V-shaped structured groove. This limits the structuring depth for a given kerf width. The unique possibility for transparent materials to start the ablation process from the backside of the sample is a well-known strategy to improve the aspect ratio of the ablated features. This work compares the achievable groove depth depending on the kerf width for front-side and back-side ablation and presents the best relation between the kerf width and number of overscans. Additionally, the influence of the number of pulses in one burst train on the ablation efficiency is investigated. The experiments were carried out using Spirit HE laser from Spectra-Physics, with the features of adjustable pulse duration from <400 fs to 10 ps, three different repetition rates (100 kHz, 200 kHz and 400 kHz) and average output powers of >16 W ( at 1040 nm wavelength).

Laser Pulse Width Dependence and Ionization Mechanism of Matrix-Assisted Laser Desorption/Ionization

NASA Astrophysics Data System (ADS)

Liang, Sheng-Ping; Lu, I.-Chung; Tsai, Shang-Ting; Chen, Jien-Lian; Lee, Yuan Tseh; Ni, Chi-Kung

2017-10-01

Ultraviolet laser pulses at 355 nm with variable pulse widths in the region from 170 ps to 1.5 ns were used to investigate the ionization mechanism of matrix-assisted laser desorption/ionization (MALDI) for matrices 2,5-dihydroxybenzoic acid (DHB), α-cyano-4-hydroxycinnamic acid (CHCA), and sinapinic acid (SA). The mass spectra of desorbed ions and the intensity and velocity distribution of desorbed neutrals were measured simultaneously for each laser shot. These quantities were found to be independent of the laser pulse width. A comparison of the experimental measurements and numerical simulations according to the multiphoton ionization, coupled photophysical and chemical dynamics (CPCD), and thermally induced proton transfer models showed that the predictions of thermally induced proton transfer model were in agreement with the experimental data, but those of the multiphoton ionization model were not. Moreover, the predictions of the CPCD model based on singlet-singlet energy pooling were inconsistent with the experimental data of CHCA and SA, but were consistent with the experimental data of DHB only when some parameters used in the model were adjusted to extreme values. [Figure not available: see fulltext.

New hybrid reverse differential pulse position width modulation scheme for wireless optical communication

NASA Astrophysics Data System (ADS)

Liao, Renbo; Liu, Hongzhan; Qiao, Yaojun

2014-05-01

In order to improve the power efficiency and reduce the packet error rate of reverse differential pulse position modulation (RDPPM) for wireless optical communication (WOC), a hybrid reverse differential pulse position width modulation (RDPPWM) scheme is proposed, based on RDPPM and reverse pulse width modulation. Subsequently, the symbol structure of RDPPWM is briefly analyzed, and its performance is compared with that of other modulation schemes in terms of average transmitted power, bandwidth requirement, and packet error rate over ideal additive white Gaussian noise (AWGN) channels. Based on the given model, the simulation results show that the proposed modulation scheme has the advantages of improving the power efficiency and reducing the bandwidth requirement. Moreover, in terms of error probability performance, RDPPWM can achieve a much lower packet error rate than that of RDPPM. For example, at the same received signal power of -28 dBm, the packet error rate of RDPPWM can decrease to 2.6×10-12, while that of RDPPM is 2.2×10. Furthermore, RDPPWM does not need symbol synchronization at the receiving end. These considerations make RDPPWM a favorable candidate to select as the modulation scheme in the WOC systems.

Control Systems with Pulse Width Modulation in Matrix Converters

NASA Astrophysics Data System (ADS)

Bondarev, A. V.; Fedorov, S. V.; Muravyova, E. A.

2018-03-01

In this article, the matrix frequency converter for the system of the frequency control of the electric drive is considered. Algorithms of formation of an output signal on the basis of pulse width modulation were developed for the quantitative analysis of quality of an output signal on the basis of mathematical models. On the basis of simulation models of an output signal, assessment of quality of this signal was carried out. The analysis of harmonic composition of the voltage output received on the basis of pulse width modulation was made for the purpose of determination of opportunities of the control system for improving harmonic composition. The result of such analysis led to the fact that the device formation of switching functions of the control system on the basis of PWM does not lead to a distortion reduction of a harmonic of the control signal, and leads to offset of harmonic in the field of frequencies, the multiple relatively carrier frequency.

Frequency-resolved optical gating system with a tellurium crystal for characterizing free-electron lasers in the wavelength range of 10-30 {mu}m

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iijima, Hokuto; Nagai, Ryoji; Nishimori, Nobuyuki

2009-12-15

A second-harmonic generation frequency-resolved optical gating (SHG-FROG) system has been developed for the complete characterization of laser pulses in the wavelength range of 10-30 {mu}m. A tellurium crystal is used so that spectrally resolved autocorrelation signals with a good signal-to-noise ratio are obtained. Pulses (wavelength {approx}22 {mu}m) generated from a free-electron laser are measured by the SHG-FROG system. The SHG intensity profile and the spectrum obtained by FROG measurements are well consistent with those of independent measurements of the pulse length and spectrum. The pulse duration and spectral width determined from the FROG trace are 0.6 ps and 5.2 THzmore » at full width half maximum, respectively.« less

Optically powered oil tank multichannel detection system with optical fiber link

NASA Astrophysics Data System (ADS)

Yu, Zhijing

1998-08-01

A novel oil tanks integrative parameters measuring system with optically powered are presented. To realize optical powered and micro-power consumption multiple channels and parameters detection, the system has taken the PWM/PPM modulation, ratio measurement, time division multiplexing and pulse width division multiplexing techniques. Moreover, the system also used special pulse width discriminator and single-chip microcomputer to accomplish signal pulse separation, PPM/PWM signal demodulation, the error correction of overlapping pulse and data processing. This new transducer has provided with high characteristics: experimental transmitting distance is 500m; total consumption of the probes is less than 150 (mu) W; measurement error: +/- 0.5 degrees C and +/- 0.2 percent FS. The measurement accuracy of the liquid level and reserves is mainly determined by the pressure accuracy. Finally, some points of the experiment are given.

Numerical analysis of breakdown dynamics dependence on pulse width in laser-induced damage in fused silica: Role of optical system

NASA Astrophysics Data System (ADS)

Hamam, Kholoud A.; Gamal, Yosr E. E.-D.

2018-06-01

We report a numerical investigation of the breakdown and damage in fused silica caused by ultra-short laser pulses. The study based on a modified model (Gaabour et al., 2012) that solves the rate equation numerically for the electron density evolution during the laser pulse, under the combined effect of both multiphoton and electron impact ionization processes. Besides, electron loss processes due to diffusion out of the focal volume and recombination are also considered in this analysis. The model is applied to investigate the threshold intensity dependence on laser pulse width in the experimental measurements that are given by Liu et al. (2005). In this experiment, a Ti-sapphire laser source operating at 800 nm with pulse duration varies between 240 fs and 2.5 ps is used to irradiate a bulk of fused silica with dimensions 10 × 5 × 3 mm. The laser beam was focused into the bulk using two optical systems with effective numerical apertures (NA) 0.126 and 0.255 to give beam spot radius at the focus of the order 2.0 μm and 0.95 μm respectively. Reasonable agreement between the calculated thresholds and the measured ones is attained. Moreover, a study is performed to examine the respective role of the physical processes of the breakdown of fused silica in relation to the pulse width and focusing optical system. The analysis revealed a real picture of the location and size of the generated plasma.

Sub-Fourier characteristics of a δ-kicked-rotor resonance.

PubMed

Talukdar, I; Shrestha, R; Summy, G S

2010-07-30

We experimentally investigate the sub-Fourier behavior of a δ-kicked-rotor resonance by performing a measurement of the fidelity or overlap of a Bose-Einstein condensate exposed to a periodically pulsed standing wave. The temporal width of the fidelity resonance peak centered at the Talbot time and zero initial momentum exhibits an inverse cube pulse number (1/N3)-dependent scaling compared to a 1/N2 dependence for the mean energy width at the same resonance. A theoretical analysis shows that for an accelerating potential the width of the resonance in acceleration space depends on 1/N3, a property which we also verify experimentally. Such a sub-Fourier effect could be useful for high precision gravity measurements.

Nonlinear harmonic generation in distributed optical klystrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

H.P. Freund; George R. Neil

2001-12-01

A distributed optical klystron has the potential for dramatically shortening the total interaction length in high-gain free-electron lasers (INP 77-59, Novosibirsk, 1977; Nucl. Instr. and Meth A 304 (1991) 463) in comparison to a single-wiggler-segment configuration. This shortening can be even more dramatic if a nonlinear harmonic generation mechanism is used to reach the desired wavelength. An example operating at a 4.5{angstrom} fundamental and a 1.5{angstrom} harmonic is discussed.

A New Measurement of the Spectral Lag of Gamma-Ray Bursts and its Implications for Spectral Evolution Behaviors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Lang; Wang, Fu-Ri; Cheng, Ye-Hao

We carry out a systematical study of the spectral lag properties of 50 single-pulsed gamma-ray bursts (GRBs) detected by the Fermi Gamma-Ray Burst Monitor. By dividing the light curves into multiple consecutive energy channels, we provide a new measurement of the spectral lag that is independent of energy channel selections. We perform a detailed statistical study of our new measurements. We find two similar power-law energy dependencies of both the pulse arrival time and pulse width. Our new results on the power-law indices would favor the relativistic geometric effects for the origin of spectral lag. However, a complete theoretical frameworkmore » that can fully account for the diverse energy dependencies of both arrival time and pulse width revealed in this work is still lacking. We also study the spectral evolution behaviors of the GRB pulses. We find that a GRB pulse with negligible spectral lag would usually have a shorter pulse duration and would appear to have a “hardness-intensity tracking” behavior, and a GRB pulse with a significant spectral lag would usually have a longer pulse duration and would appear to have a “hard-to-soft” behavior.« less

Development of the dense plasma focus for short-pulse applications

NASA Astrophysics Data System (ADS)

Bennett, N.; Blasco, M.; Breeding, K.; Constantino, D.; DeYoung, A.; DiPuccio, V.; Friedman, J.; Gall, B.; Gardner, S.; Gatling, J.; Hagen, E. C.; Luttman, A.; Meehan, B. T.; Misch, M.; Molnar, S.; Morgan, G.; O'Brien, R.; Robbins, L.; Rundberg, R.; Sipe, N.; Welch, D. R.; Yuan, V.

2017-01-01

The dense plasma focus (DPF) has long been considered a compact source for pulsed neutrons and has traditionally been optimized for the total neutron yield. In this paper, we describe the efforts to optimize the DPF for short-pulse applications by introducing a reentrant cathode at the end of the coaxial plasma gun. The resulting neutron pulse widths are reduced by an average of 21 ±9 % from the traditional long-drift DPF design. Pulse widths and yields achieved from deuterium-tritium fusion at 2 MA are 61.8 ±30.7 ns FWHM and 1.84 ±0.49 ×1012 neutrons per shot. Simulations were conducted concurrently to elucidate the DPF operation and confirm the role of the reentrant cathode. A hybrid fluid-kinetic particle-in-cell modeling capability demonstrates correct sheath velocities, plasma instabilities, and fusion yield rates. Consistent with previous findings that the DPF is dominated by beam-target fusion from superthermal ions, we estimate that the thermonuclear contribution is at the 1% level.

Experimental investigation on a diode-pumped cesium-vapor laser stably operated at continuous-wave and pulse regime.

PubMed

Chen, Fei; Xu, Dongdong; Gao, Fei; Zheng, Changbin; Zhang, Kuo; He, Yang; Wang, Chunrui; Guo, Jin

2015-05-04

Employing a fiber-coupled diode-laser with a center wavelength of 852.25 nm and a line width of 0.17 nm, experimental investigation on diode-end-pumped cesium (Cs) vapor laser stably operated at continuous-wave (CW) and pulse regime is carried out. A 5 mm long cesium vapor cell filled with 60 kPa helium and 20 kPa ethane is used as laser medium. Using an output coupler with reflectivity of 48.79%, 1.26 W 894.57 nm CW laser is obtained at an incident pump power of 4.76 W, corresponding an optical-optical efficiency of 26.8% and a slope-efficiency of 28.8%, respectively. The threshold temperature is 67.5 °C. Stable pulsed cesium laser with a maximum average output power of 2.6 W is obtained at a repetition rate of 76 Hz, and the pulse repetition rate can be extend to 1 kHz with a pulse width of 18 μs.

Effects of copper vapor laser (CVL) on mice skin: histologic evaluation of damage and tissue stimulation

NASA Astrophysics Data System (ADS)

Nunes, Syllene; Moreno, E.; Oliveira, H.; Osaka, J.; Salvador, G.; Michalany, N.; Tolosa, E.

2002-10-01

This study was to evaluate the effects of the CVL with low energy and short pulse widths. 18 female mice, C57BL/6 (9-11 weeks old) were distributed into four groups. The control group (CG) wasn't exposed to laser beam . Group L1 had 2 laser expositions with 24 hours gap between them (0.5W). Group L2 had 3 expositions (0.5W and 0.25W) and group L3 had 4 expositions (0.25 W). It was used a CVL prototype (5lOnm, 13 Khz, pulse width of 20 ms and spot size of 0.8cm). 7 days after last laser pulse no groups presented actinic keratosis, tumors or collagen changes. CVL had effective action on pilosebaceous units. High energy with few short pulses induced hair follicles proliferation while low energy with many repetitive short pulses showed increased and specific tissue damage besides hair plugging.

Design and test of a simple fast electromagnetic inductive gas valve for planar pulsed inductive plasma thruster

NASA Astrophysics Data System (ADS)

Guo, Dawei; Cheng, Mousen; Li, Xiaokang

2017-10-01

In support of our planar pulsed inductive plasma thruster research, a fast electromagnetic inductive valve for a gas propellant injection system has been built and tested. A new and important design feature is the use of a conical diaphragm as the action part, which greatly contributes to the virtue of simplicity for adopting the resultant force of the diaphragm deformation as the closing force. An optical transmission technique is adopted to measure the opening and closing characters of the valve while the gas throughput is determined by measuring the pressure change per pulse in a test chamber with a capacitance manometer. The experimental results revealed that the delay time before the valve reaction is less than 40 μs, and the valve pulse width is no longer than 160 μs full width at half maximum. The valve delivers 0-2.5 mg of argon gas per pulse varied by adjusting the drive voltage and gas pressure.

Design and test of a simple fast electromagnetic inductive gas valve for planar pulsed inductive plasma thruster.

PubMed

Guo, Dawei; Cheng, Mousen; Li, Xiaokang

2017-10-01

In support of our planar pulsed inductive plasma thruster research, a fast electromagnetic inductive valve for a gas propellant injection system has been built and tested. A new and important design feature is the use of a conical diaphragm as the action part, which greatly contributes to the virtue of simplicity for adopting the resultant force of the diaphragm deformation as the closing force. An optical transmission technique is adopted to measure the opening and closing characters of the valve while the gas throughput is determined by measuring the pressure change per pulse in a test chamber with a capacitance manometer. The experimental results revealed that the delay time before the valve reaction is less than 40 μs, and the valve pulse width is no longer than 160 μs full width at half maximum. The valve delivers 0-2.5 mg of argon gas per pulse varied by adjusting the drive voltage and gas pressure.

Up gradation of LHCD system for rf power level up to 2MW for SST1

NASA Astrophysics Data System (ADS)

Sharma, P. K.; Ambulkar, K. K.; Parmar, P. R.; Virani, C. G.; Thakur, A. L.; Kulkarni, S. V.; Lhcd Group

2010-02-01

To operate superconducting steadystate tokamak (SST1) for 1000 seconds, lower hybrid current drive (LHCD) system has been designed at a frequency of 3.7 GHz., which would couple 1.0 MW CW of microwave power to the shaped plasma. The system consists of various rf passive components and transmission line, employing which the rf power from the source is transported to the antenna. During calibration of transmission line, it was observed that the losses in the transmission line is substantial and eventually would lead to less coupled power to the plasma. Further it is anticipated that more LH power would be required for advanced operation of SST1 machine. Thus it is decided to upgrade the existing LHCD system to 2 MW CW power level. The proposed up gradation would demand several infra structural changes and needs to be addressed. Due to lack of space, we have proposed a scheme in which additional two klystrons, along with existing two klystrons would be accommodated in the existing space. The low rf power requirements have also been increased to cater the new needs. Accordingly additional cooling requirements have been proposed to accommodate the two new klystrons. The DAC and auxiliary power supplies have been also designed. The new up graded LHCD system would address several key technological issues. Firstly it would establish the operation of four klystrons at rated power in parallel employing single RHVPS (80kV, 70A). Secondly it would establish the operation of two high power klystrons operation at rated power when their collectors are cooled in series. In this paper we would present the various requirements for up-gradation of LHCD system to 2MW. The main requirements like high power rf source, along with modified support structure, low power rf systems to drive the high power rf source, auxiliary power supplies required for high power rf source, DAC system improvement, cooling improvements, etc. would be discussed.

Investigations in x-radiation stimulation

NASA Astrophysics Data System (ADS)

Gupta, K. D.

1982-03-01

The objective is to invent a crystal x-ray laser. Investigations in the Radiation Research Lab. at Texas Tech University have established in a very straightforward way the line narrowing associated with a threshold pumping and a nonlinear rise in intensity. Recent work on x-ray Borrmann channeling via monocrystals has demonstrated the existence of a monochromatic x-ray beam without any vertical divergence. This would allow the transport of x-ray energy in space for thousands of miles without any loss of power. Preliminary experiments with a monocrystal excited by pulsed x-rays at Air Force Weapons Laboratory, KAFB, Albuquerque, seem to indicate a gain in intensity of the nondivergent hot spot with a concomitant fading of the regular Laue pattern. Current investigations in this line indicates that with proper doping of the monocrystal the nondivergent beam could be increased in intensity using a flash x-ray tube to pump the doped monocrystal. A concial target double beam flash x-ray line source instrument has been constructed to obtain a beam of nondivergent, stimulated, coherent, and monochromatic x-rays from doped monocrystals. A generation of stimulated x-rays using bunched electrons from pulsed high power klystron striking a monocrystal has been conceived.

Self-focusing and group-velocity dispersion of pulsed laser beams in the inhomogeneous atmosphere.

PubMed

Zhang, Yuqiu; Ji, Xiaoling; Zhang, Hao; Li, Xiaoqing; Wang, Tao; Wang, Huan; Deng, Yu

2018-05-28

We study self-focusing and group-velocity dispersion (GVD) effects in the inhomogeneous atmosphere on pulsed-laser space debris removal facilitated by a ground-based laser. It is found that changes of the pulse duration and the beam spot size with the propagation distance are noticeable due to the interplay of the GVD effect and the self-focusing effect, which is quite different from the behavior in the linear case. It is shown that the temporal pulse splitting may appear on the space debris, and the spatial side lobe usually appears together with the temporal pulse splitting. As compared with the linear case, the beam width and the pulse width on the debris target increase. On the other hand, crucial formulae of the modified focal length and the M 2 -factor for laser debris removal are also derived. It is found that the beam quality on the debris target becomes better if our modified focal length is adopted, and the beam quality on the debris target will be good if the value of M 2 -factor is less than 1.6.

Phase-matching of attosecond XUV supercontinuum

NASA Astrophysics Data System (ADS)

Gilbertson, Steve; Mashiko, Hiroki; Li, Chengquan; Khan, Sabih; Shakya, Mahendra; Moon, Eric; Chang, Zenghu

2008-05-01

Adding a weak second harmonic field to an ellipticity dependent polarization gating field allowed for the production of XUV supercontinua from longer (˜10 fs) input pulses in argon. The spectra support 200 as single isolated pulses. This technique, dubbed double optical gating (DOG), demonstrated a large enhancement of the harmonic yield as compared with polarization gating. These results can be attributed to the reduced depletion of the ground state of the target from the leading edge of the pulse and the increased intensity inside the polarization gate width. Through optimization of the harmonic generation process under the phase matching conditions, we were able to further increase the harmonic flux. The parameters included the target gas pressure, laser focus position, input pulse duration, and polarization gate width. By varying the CE phase of the pulse, we were able to verify that the results were indeed from DOG due to its unique 2 pi dependence on the harmonic spectrum. We were able to extend our results to neon. Its higher ionization potential allowed an extension of the harmonic cutoff for the production of even shorter pulses.

Laser one-dimensional range profile and the laser two-dimensional range profile of cylinders

NASA Astrophysics Data System (ADS)

Gong, Yanjun; Wang, Mingjun; Gong, Lei

2015-10-01

Laser one-dimensional range profile, that is scattering power from pulse laser scattering of target, is a radar imaging technology. The laser two-dimensional range profile is two-dimensional scattering imaging of pulse laser of target. Laser one-dimensional range profile and laser two-dimensional range profile are called laser range profile(LRP). The laser range profile can reflect the characteristics of the target shape and surface material. These techniques were motivated by applications of laser radar to target discrimination in ballistic missile defense. The radar equation of pulse laser is given in this paper. This paper demonstrates the analytical model of laser range profile of cylinder based on the radar equation of the pulse laser. Simulations results of laser one-dimensional range profiles of some cylinders are given. Laser range profiles of cylinder, whose surface material with diffuse lambertian reflectance, is given in this paper. Laser range profiles of different pulse width of cylinder are given in this paper. The influences of geometric parameters, pulse width, attitude on the range profiles are analyzed.

A simple fast pulse gas valve using a dynamic pressure differential as the primary closing mechanism

NASA Astrophysics Data System (ADS)

Thomas, J. C.; Hwang, D. Q.; Horton, R. D.; Rogers, J. H.; Raman, R.

1993-06-01

In this article we describe a simple fast pulse gas valve developed for use in a plasma discharge experiment. The valve delivers 1017-1019 molecules per pulse varied by changing the voltage on the electromagnetic driver power supply. Valve pulse widths are observed to be less than 300 μs full width at half maximum with a rise time of less than 100 μs resulting in a maximum gas flow rate of ˜1022 molecules per second. An optical transmission technique was used to determine the mechanical opening and closing characteristics of the valve piston. A fast ionization gauge (FIG) was used for diagnosis of the temporal character of the gas pulse while the total gas throughput was determined by measuring the change in pressure per pulse in a small test chamber with a convectron tube gauge. Calibration of the FIG was accomplished by comparing the net change in pressure in a large chamber as measured by the FIG to the net change in pressure in a small test chamber as measured by the convectron tube gauge.

Performance and applications of the 14 MEV electron radiation linac at CIAE

NASA Astrophysics Data System (ADS)

Zhai, X. L.; Chen, G. C.; Qi, B. M.; Xu, F. J.; Pan, L. H.; Zhang, Z. M.; Shi, X. Z.; Chen, J. K.; Wang, F. Y.

1993-07-01

A 14 MeV electron linear accelerator which was designed and manufactured by the China Institute of Atomic Energy (CIAE) has been modified into an radiation processing accelerator in 1987. It consists of an electron gun, two prebunchers, one buncher, a three meter long accelerating section, and a 90 degree bending magnet. The linac is S-band (2856 MHz), travelling wave accelerator driven by a Chinese-made klystron. The energy of electrons can be adjusted from 8 MeV to 18 MeV and the average beam power is about 2 kW. The beam width is 600 mm and the uniformity of scanning beam is better than 10%. The linac is used to irradiate power semiconductor devices for controlling the minority carrier lifetime (MCL). More than twenty factories and scientific institutions use this linac to irradiate silicon controlled rectifiers (SCR) and the fast recovery diodes (FRD), and more than 0.2 million pieces of SCR have been irradiated. Tests have also been carried out for colour-change of topaz.

Compact biomedical pulsed signal generator for bone tissue stimulation

DOEpatents

Kronberg, J.W.

1993-06-08

An apparatus for stimulating bone tissue for stimulating bone growth or treating osteoporosis by applying directly to the skin of the patient an alternating current electrical signal comprising wave forms known to simulate the piezoelectric constituents in bone. The apparatus may, by moving a switch, stimulate bone growth or treat osteoporosis, as desired. Based on low-power CMOS technology and enclosed in a moisture-resistant case shaped to fit comfortably, two astable multivibrators produce the desired waveforms. The amplitude, pulse width and pulse frequency, and the subpulse width and subpulse frequency of the waveforms are adjustable. The apparatus, preferably powered by a standard 9-volt battery, includes signal amplitude sensors and warning signals indicate an output is being produced and the battery needs to be replaced.

Fabrication of narrow pulse passively Q-switched self-stimulated Raman laser with c-cut Nd:GdVO4

NASA Astrophysics Data System (ADS)

Shen, Gao; Li, Zuo-han; Han, Ming

2016-11-01

Combining the self-stimulated Raman scattering technology and saturable absorber of Cr4+:YAG, a 1.17 μm c-cut Nd:GdVO4 picosecond Q-switched laser is demonstrated in this paper. With an incident pump power of 10 W, the Q-switched laser with average power of 430 mW for 1.17 μm, pulse width of 270 ps, repetition rate of 13 kHz and the first order Stokes conversion efficiency of 4.3% is obtained. The Q-switched pulse width can be the narrowest in our research. In addition, the yellow laser at 0.58 μm is also achieved by using the LiB3O5 frequency doubling crystal.

Compact biomedical pulsed signal generator for bone tissue stimulation

DOEpatents

Kronberg, James W.

1993-01-01

An apparatus for stimulating bone tissue for stimulating bone growth or treating osteoporosis by applying directly to the skin of the patient an alternating current electrical signal comprising wave forms known to simulate the piezoelectric constituents in bone. The apparatus may, by moving a switch, stimulate bone growth or treat osteoporosis, as desired. Based on low-power CMOS technology and enclosed in a moisture-resistant case shaped to fit comfortably, two astable multivibrators produce the desired waveforms. The amplitude, pulse width and pulse frequency, and the subpulse width and subpulse frequency of the waveforms are adjustable. The apparatus, preferably powered by a standard 9-volt battery, includes signal amplitude sensors and warning signals indicate an output is being produced and the battery needs to be replaced.

JPRS Report, Science & Technology, Japan, SOR Technology Update

DTIC Science & Technology

1990-12-18

GUN Electron gun c3 GV Gate valve R- ± HL Helmholtz coil IG Ion vacuum gauge IP Ion pump KFC Klystron focusing coil KLY Klystron PB Pre-buncher Q...Therefore, we started studying the manufacture of this kind of film. Recently, such films have been placed on the market as test samples by some foreign... Mixing of sputtered particles from the two targets can also be prevented by making the structure of the bulkhead in the sputtering chamber most

Computer-aided design of the RF-cavity for a high-power S-band klystron

NASA Astrophysics Data System (ADS)

Kant, D.; Bandyopadhyay, A. K.; Pal, D.; Meena, R.; Nangru, S. C.; Joshi, L. M.

2012-08-01

This article describes the computer-aided design of the RF-cavity for a S-band klystron operating at 2856 MHz. State-of-the-art electromagnetic simulation tools SUPERFISH, CST Microwave studio, HFSS and MAGIC have been used for cavity design. After finalising the geometrical details of the cavity through simulation, it has been fabricated and characterised through cold testing. Detailed results of the computer-aided simulation and cold measurements are presented in this article.

Periodic permanent magnet focused klystron

DOEpatents

Ferguson, Patrick; Read, Michael; Ives, R Lawrence

2015-04-21

A periodic permanent magnet (PPM) klystron has beam transport structures and RF cavity structures, each of which has permanent magnets placed substantially equidistant from a beam tunnel formed about the central axis, and which are also outside the extent of a cooling chamber. The RF cavity sections also have permanent magnets which are placed substantially equidistant from the beam tunnel, but which include an RF cavity coupling to the beam tunnel for enhancement of RF carried by an electron beam in the beam tunnel.

Pulse compression in an electro-optic Q-switched diode-pumped YVO4/Nd:YVO4 laser with a Cr4+:YAG saturable absorber.

PubMed

Li, Tao; Zhao, Shengzhi; Zhuo, Zhuang; Yang, Kejian; Li, Guiqiu; Li, Dechun

2009-04-20

A diode end-pumped doubly Q-switched YVO4/Nd:YVO4 laser has been realized for the first time to our knowledge by using both an electro-optic (EO) modulator and a Cr4):YAG saturable absorber. A 3.8 ns pulse width is generated by this laser under a pump power of 15 W at 2 kHz, which is obviously compressed in comparison with that of 8.8 ns from a single actively EO Q-switched laser. Under the same conditions, peak power values of 174.7 and 93 kW are also obtained. A coupled equation is given to theoretically analyze the experimental data. The experimental and theoretical results show that the doubly Q-switched laser has the advantages of a shorter pulse width and higher pulse peak power in contrast with a singly Q-switched laser.

Compact pulse generators with soft ferromagnetic cores driven by gunpowder and explosive.

PubMed

Ben, Chi; He, Yong; Pan, Xuchao; Chen, Hong; He, Yuan

2015-12-01

Compact pulse generators which utilized soft ferromagnets as an initial energy carrier inside multi-turn coil and hard ferromagnets to provide the initial magnetic field outside the coil have been studied. Two methods of reducing the magnetic flux in the generators have been studied: (1) by igniting gunpowder to launch the core out of the generator, and (2) by detonating explosives that demagnetize the core. Several types of compact generators were explored to verify the feasibility. The generators with an 80-turn coil that utilize gunpowder were capable of producing pulses with amplitude 78.6 V and the full width at half maximum was 0.41 ms. The generators with a 37-turn coil that utilize explosive were capable of producing pulses with amplitude 1.41 kV and the full width at half maximum was 11.68 μs. These two methods were both successful, but produce voltage waveforms with significantly different characteristics.

Conceptual design of sub-exa-watt system by using optical parametric chirped pulse amplification

NASA Astrophysics Data System (ADS)

Kawanaka, J.; Tsubakimoto, K.; Yoshida, H.; Fujioka, K.; Fujimoto, Y.; Tokita, S.; Jitsuno, T.; Miyanaga, N.; Gekko-EXA Design Team

2016-03-01

A 50 PW ultrahigh-peak-power laser has been conceptually designed, which is based on optical parametric chirped pulse amplification (OPCPA). A 250 J DPSSL and a flash- lamp-pumped kJ laser are adopted as new repeatable pump source. The existed LFEX-laser with more than ten kilo joules are used in the final amplifier stage and the OPCPA with the 2x2 tiled pump beams in random phase has been proposed with several ten centimeter aperture. A pulse duration of amplified pulses is set at less than 10 fs. A broadband OPCPA with ∼500 nm of the gain spectral width near 1 μm is required. A partially deuterated KDP (p-DKDP) crystal is one of the most promising nonlinear crystals and our numerical calculation ensured such ultra-broad gain width. p-DKDP crystals with several deuteration ratio have been successfully grown.

SAS-2 gamma-ray observations of PSR 1747-46. [radio pulsar

NASA Technical Reports Server (NTRS)

Thompson, D. J.; Fichtel, C. E.; Kniffen, D. A.; Ogelman, H. B.; Lamb, R. C.

1976-01-01

Evidence is reported for the observation of gamma-ray emission from the radio pulsar PSR 1747-46 by the gamma-ray telescope aboard SAS 2. The evidence is based on the presence of both an approximately 3-sigma enhancement of gamma rays at the pulsar's location and an approximately 4-sigma peak in the phase plot of 79 gamma-ray events whose phase was calculated from the pulsar's known period. The gamma-ray pulsation is found to appear at a phase lag of about 0.16 from that predicted by the radio observations. The pulsed gamma-ray fluxes above 35 MeV and 100 MeV are estimated, and it is shown that the gamma-ray pulse width is similar to the radio pulse width. It is concluded that PSR 1747-46 is a most likely candidate for pulsed gamma-ray emission.

Study of monopropellants for electrothermal thrusters

NASA Technical Reports Server (NTRS)

Kuenzly, J. D.

1974-01-01

A 333 mN electrothermal thruster designed to use MIL-grade hydrazine was demonstrated to be suitable for operation with low freezing point monopropellants containing hydrazine azide, monomethylhydrazine, unsymmetrical-dimethylhydrazine and ammonia. The steady-state specific impulse was greater than 200 sec for all propellants. The pulsed-mode specific impulse for an azide blend exceeded 175 sec for pulse widths greater than 50 msec; propellants containing carbonaceous species delivered 175 sec pulsed-mode specific impulses for pulse widths greater than 100 msec. Longer thrust chamber residence times were required for the carbonaceous propellants; the original thruster design was modified by increasing the characteristic chamber length and screen packing density. Specific recommendations were made for the work required to design and develop flight worthy thrusters, including methods to increase propellant dispersal at injection, thruster geometry changes to reduce holding power levels and methods to initiate the rapid decomposition of the carbonaceous propellants.

Comparison of symmetric and asymmetric double quantum well extended-cavity diode lasers for broadband passive mode-locking at 780  nm.

PubMed

Christopher, Heike; Kovalchuk, Evgeny V; Wenzel, Hans; Bugge, Frank; Weyers, Markus; Wicht, Andreas; Peters, Achim; Tränkle, Günther

2017-07-01

We present a compact, mode-locked diode laser system designed to emit a frequency comb in the wavelength range around 780 nm. We compare the mode-locking performance of symmetric and asymmetric double quantum well ridge-waveguide diode laser chips in an extended-cavity diode laser configuration. By reverse biasing a short section of the diode laser chip, passive mode-locking at 3.4 GHz is achieved. Employing an asymmetric double quantum well allows for generation of a mode-locked optical spectrum spanning more than 15 nm (full width at -20  dB) while the symmetric double quantum well device only provides a bandwidth of ∼2.7  nm (full width at -20  dB). Analysis of the RF noise characteristics of the pulse repetition rate shows an RF linewidth of about 7 kHz (full width at half-maximum) and of at most 530 Hz (full width at half-maximum) for the asymmetric and symmetric double quantum well devices, respectively. Investigation of the frequency noise power spectral density at the pulse repetition rate shows a white noise floor of approximately 2100  Hz 2 /Hz and of at most 170  Hz 2 /Hz for the diode laser employing the asymmetric and symmetric double quantum well structures, respectively. The pulse width is less than 10 ps for both devices.

Characterization of an optimized light source and comparison to pulsed dye laser for superficial and deep vessel clearance.

PubMed

Weiss, Robert A; Ross, E Victor; Tanghetti, Emil A; Vasily, David B; Childs, James J; Smirnov, Mikhail Z; Altshuler, Gregory B

2011-02-01

An arc lamp-based device providing optimized spectrum and pulse shape was characterized and compared with two pulsed dye laser (PDL) systems using a vascular phantom. Safety and effectiveness for facial telangiectasia are presented in clinical case studies. An optimized pulsed light source's (OPL) spectral and power output were characterized and compared with two 595 nm PDL devices. Purpuric threshold fluences were determined for the OPL and PDLs on Fitzpatrick type II normal skin. A vascular phantom comprising blood-filled quartz capillaries beneath porcine skin was treated by the devices at their respective purpuric threshold fluences for 3 ms pulse widths, while vessel temperatures were monitored with an infrared (IR) camera. Patients with Fitzpatrick skin types II-III received a split-face treatment with the OPL and a 595 nm PDL. The OPL provided a dual-band output spectrum from 500 to 670 nm and 850-1,200 nm, pulse widths from 3 to 100 ms, and fluences to 80 J/cm(2). The smooth output power measured during all pulse widths provides unambiguous vessel size selectivity. Percent energy in the near infra-red increased with decreasing output power from 45% to 60% and contributed 15-26% to heating of deep vessels, respectively. At purpuric threshold fluences the ratio of OPL to PDL vessel temperature rise was 1.7-2.8. OPL treatments of facial telangiectasia were well-tolerated by patients demonstrating significant improvements comparable to PDL with no downtime. Intense pulsed light (IPL) and PDL output pulse and spectral profiles are important for selective treatment of vessels in vascular lesions. The OPL's margin between purpuric threshold fluence and treatment fluence for deeper, larger vessels was greater than the corresponding margin with PDLs. The results warrant further comparison studies with IPLs and other PDLs. Copyright © 2011 Wiley-Liss, Inc.

The role of defects in laser-induced modifications of silica coatings and fused silica using picosecond pulses at 1053 nm: I Damage morphology

DOE PAGES

Laurence, T. A.; Ly, S.; Shen, N.; ...

2017-06-22

Laser-induced damage with ps pulse widths straddles the transition from intrinsic, multi-photon ionization and avalanche ionization-based ablation with fs pulses to defect-dominated, thermal-based damage with ns pulses. We investigated the morphology of damage for fused silica and silica coatings between 1 ps and 60 ps at 1053 nm. Using calibrated laser-induced damage experiments, in situ imaging, and high-resolution optical microscopy, atomic force microscopy, and scanning electron microscopy, we show that defects play an important role in laser-induced damage down to 1 ps. Three types of damage are observed: ablation craters, ultra-high density pits, and smooth, circular depressions with central pits.more » For 10 ps and longer, the smooth, circular depressions limit the damage performance of fused silica and silica coatings. The observed high-density pits and material removal down to 3 ps indicate that variations in surface properties limit the laser-induced damage onset to a greater extent than expected below 60 ps. Below 3 ps, damage craters are smoother although there is still evidence as seen by AFM of inhomogeneous laser-induced damage response very near the damage onset. These results show that modeling the damage onset only as a function of pulse width does not capture the convoluted processes leading to laser induced damage with ps pulses. It is necessary to account for the effects of defects on the processes leading to laser-induced damage. In conclusion, the effects of isolated defects or inhomogeneities are most pronounced above 3 ps but are still discernible and possibly important down to the shortest pulse width investigated here.« less

The role of defects in laser-induced modifications of silica coatings and fused silica using picosecond pulses at 1053 nm: I Damage morphology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laurence, T. A.; Ly, S.; Shen, N.

Laser-induced damage with ps pulse widths straddles the transition from intrinsic, multi-photon ionization and avalanche ionization-based ablation with fs pulses to defect-dominated, thermal-based damage with ns pulses. We investigated the morphology of damage for fused silica and silica coatings between 1 ps and 60 ps at 1053 nm. Using calibrated laser-induced damage experiments, in situ imaging, and high-resolution optical microscopy, atomic force microscopy, and scanning electron microscopy, we show that defects play an important role in laser-induced damage down to 1 ps. Three types of damage are observed: ablation craters, ultra-high density pits, and smooth, circular depressions with central pits.more » For 10 ps and longer, the smooth, circular depressions limit the damage performance of fused silica and silica coatings. The observed high-density pits and material removal down to 3 ps indicate that variations in surface properties limit the laser-induced damage onset to a greater extent than expected below 60 ps. Below 3 ps, damage craters are smoother although there is still evidence as seen by AFM of inhomogeneous laser-induced damage response very near the damage onset. These results show that modeling the damage onset only as a function of pulse width does not capture the convoluted processes leading to laser induced damage with ps pulses. It is necessary to account for the effects of defects on the processes leading to laser-induced damage. In conclusion, the effects of isolated defects or inhomogeneities are most pronounced above 3 ps but are still discernible and possibly important down to the shortest pulse width investigated here.« less

Generation of spectrally stable continuous-wave emission and ns pulses with a peak power of 4 W using a distributed Bragg reflector laser and a ridge-waveguide power amplifier.

PubMed

Klehr, A; Wenzel, H; Fricke, J; Bugge, F; Erbert, G

2014-10-06

We have developed a diode-laser based master oscillator power amplifier (MOPA) light source which emits high-power spectrally stabilized and nearly-diffraction limited optical pulses in the nanoseconds range as required by many applications. The MOPA consists of a distributed Bragg reflector (DBR) laser as master oscillator driven by a constant current and a ridge waveguide power amplifier (PA) which can be driven by a constant current (DC) or by rectangular current pulses with a width of 5 ns at a repetition frequency of 200 kHz. Under pulsed operation the amplifier acts as an optical gate, converting the CW input beam emitted by the DBR laser into a train of short amplified optical pulses. With this experimental MOPA arrangement no relaxation oscillations occur. A continuous wave power of 1 W under DC injection and a pulse power of 4 W under pulsed operation are reached. For both operational modes the optical spectrum of the emission of the amplifier exhibits a peak at a constant wavelength of 973.5 nm with a spectral width < 10 pm.

A model Ni-Al-Mo superalloy studied by ultraviolet pulsed-laser-assisted local-electrode atom-probe tomography.

PubMed

Tu, Yiyou; Plotnikov, Elizaveta Y; Seidman, David N

2015-04-01

This study investigates the effects of the charge-state ratio of evaporated ions on the accuracy of local-electrode atom-probe (LEAP) tomographic compositional and structural analyses, which employs a picosecond ultraviolet pulsed laser. Experimental results demonstrate that the charge-state ratio is a better indicator of the best atom-probe tomography (APT) experimental conditions compared with laser pulse energy. The thermal tails in the mass spectra decrease significantly, and the mass resolving power (m/Δm) increases by 87.5 and 185.7% at full-width half-maximum and full-width tenth-maximum, respectively, as the laser pulse energy is increased from 5 to 30 pJ/pulse. The measured composition of this alloy depends on the charge-state ratio of the evaporated ions, and the most accurate composition is obtained when Ni2+/Ni+ is in the range of 0.3-20. The γ(f.c.c.)/γ'(L12) interface is quantitatively more diffuse when determined from the measured concentration profiles for higher laser pulse energies. Conclusions of the APT compositional and structural analyses utilizing the same suitable charge-state ratio are more comparable than those collected with the same laser pulse energy.

978-nm square-wave in an all-fiber single-mode ytterbium-doped fiber laser

NASA Astrophysics Data System (ADS)

Li, Shujie; Xu, Lixin; Gu, Chun

2018-01-01

A 978 nm single mode passively mode-locked all-fiber laser delivering square-wave pulses was demonstrated using a figure-8 cavity and a 75 cm commercial double-clad ytterbium-doped fiber. We found the three-level system near 978 nm was able to operate efficiently under clad pumping, simultaneously oscillation around 1030 nm well inhibited. The optimized nonlinear amplifying loop mirror made the mode locking stable and performed the square-pulses shaping. To the best of our knowledge, it is the first time to report the square-wave pulse fiber laser operating at 980 nm. The spectral width of the 978 mode-locked square pulses was about 4 nm, far greater than that of the mode-locked square pulses around 1060 nm reported before, which would be helpful to deeply understand the various square-wave pulses' natures and forming mechanisms. Compared with modulated single-mode or multimode 980 nm LDs, this kind of 980 nm square-wave sources having higher brightness, more steeper rising and falling edge and shorter pulse width, might have potential applications in pumping nanosecond ytterbium or erbium fiber lasers and amplifiers.

Controllable pulse parameter transcranial magnetic stimulator with enhanced circuit topology and pulse shaping

NASA Astrophysics Data System (ADS)

Peterchev, Angel V.; DʼOstilio, Kevin; Rothwell, John C.; Murphy, David L.

2014-10-01

Objective. This work aims at flexible and practical pulse parameter control in transcranial magnetic stimulation (TMS), which is currently very limited in commercial devices. Approach. We present a third generation controllable pulse parameter device (cTMS3) that uses a novel circuit topology with two energy-storage capacitors. It incorporates several implementation and functionality advantages over conventional TMS devices and other devices with advanced pulse shape control. cTMS3 generates lower internal voltage differences and is implemented with transistors with a lower voltage rating than prior cTMS devices. Main results. cTMS3 provides more flexible pulse shaping since the circuit topology allows four coil-voltage levels during a pulse, including approximately zero voltage. The near-zero coil voltage enables snubbing of the ringing at the end of the pulse without the need for a separate active snubber circuit. cTMS3 can generate powerful rapid pulse sequences (\\lt 10 ms inter pulse interval) by increasing the width of each subsequent pulse and utilizing the large capacitor energy storage, allowing the implementation of paradigms such as paired-pulse and quadripulse TMS with a single pulse generation circuit. cTMS3 can also generate theta (50 Hz) burst stimulation with predominantly unidirectional electric field pulses. The cTMS3 device functionality and output strength are illustrated with electrical output measurements as well as a study of the effect of pulse width and polarity on the active motor threshold in ten healthy volunteers. Significance. The cTMS3 features could extend the utility of TMS as a research, diagnostic, and therapeutic tool.

Controllable pulse parameter transcranial magnetic stimulator with enhanced circuit topology and pulse shaping

PubMed Central

D’Ostilio, Kevin; Rothwell, John C; Murphy, David L

2014-01-01

Objective This work aims at flexible and practical pulse parameter control in transcranial magnetic stimulation (TMS), which is currently very limited in commercial devices. Approach We present a third generation controllable pulse parameter device (cTMS3) that uses a novel circuit topology with two energy-storage capacitors. It incorporates several implementation and functionality advantages over conventional TMS devices and other devices with advanced pulse shape control. cTMS3 generates lower internal voltage differences and is implemented with transistors with lower voltage rating than prior cTMS devices. Main results cTMS3 provides more flexible pulse shaping since the circuit topology allows four coil-voltage levels during a pulse, including approximately zero voltage. The near-zero coil voltage enables snubbing of the ringing at the end of the pulse without the need for a separate active snubber circuit. cTMS3 can generate powerful rapid pulse sequences (<10 ms inter pulse interval) by increasing the width of each subsequent pulse and utilizing the large capacitor energy storage, allowing the implementation of paradigms such as paired-pulse and quadripulse TMS with a single pulse generation circuit. cTMS3 can also generate theta (50 Hz) burst stimulation with predominantly unidirectional electric field pulses. The cTMS3 device functionality and output strength are illustrated with electrical output measurements as well as a study of the effect of pulse width and polarity on the active motor threshold in 10 healthy volunteers. Significance The cTMS3 features could extend the utility of TMS as a research, diagnostic, and therapeutic tool. PMID:25242286

Multiplexer and time duration measuring circuit

DOEpatents

Gray, Jr., James

1980-01-01

A multiplexer device is provided for multiplexing data in the form of randomly developed, variable width pulses from a plurality of pulse sources to a master storage. The device includes a first multiplexer unit which includes a plurality of input circuits each coupled to one of the pulse sources, with all input circuits being disabled when one input circuit receives an input pulse so that only one input pulse is multiplexed by the multiplexer unit at any one time.

Numerical Response Surfaces of Volume of Ablation and Retropulsion Amplitude by Settings of Ho:YAG Laser Lithotripter

PubMed Central

Rutherford, Jonathan; Solomon, Metasebya; Cheng, Brian; Xuan, Jason R.; Gong, Jason; Yu, Honggang; Xia, Michael L. D.; Yang, Xirong; Hasenberg, Thomas; Curran, Sean

2018-01-01

Objectives Although laser lithotripsy is now the preferred treatment option for urolithiasis due to shorter operation time and a better stone-free rate, the optimal laser settings for URS (ureteroscopic lithotripsy) for less operation time remain unclear. The aim of this study was to look for quantitative responses of calculus ablation and retropulsion by performing operator-independent experiments to determine the best fit versus the pulse energy, pulse width, and the number of pulses. Methods A lab-built Ho:YAG laser was used as the laser pulse source, with a pulse energy from 0.2 J up to 3.0 J and a pulse width of 150 μs up to 1000 μs. The retropulsion was monitored using a high-speed camera, and the laser-induced craters were evaluated with a 3-D digital microscope. The best fit to the experimental data is done by a design of experiment software. Results The numerical formulas for the response surfaces of ablation speed and retropulsion amplitude are generated. Conclusions The longer the pulse, the less the ablation or retropulsion, while the longer pulse makes the ablation decrease faster than the retropulsion. The best quadratic fit of the response surface for the volume of ablation varied nonlinearly with pulse duration and pulse number. PMID:29707187

Lightning Optical Pulse Statistics from Storm Overflights During the Altus Cumulus Electrification Study

NASA Technical Reports Server (NTRS)

Mach, D. M.; Blakeslee, R. J.; Bailey, J. C.; Farrell, W. M.; Goldberg, R. A.; Desch, M. D.; Houser, J. G.

2004-01-01

The Altus Cumulus Electrification Study (ACES) was conducted during the month of August, 2002 in an area near Key West, Florida. One of the goals of this uninhabited aerial vehicle (UAV) study was to collect time resolved optical pulse data from thunderstorms. During the month long campaign, we acquired 5294 lightning generated optical pulses. Most of these observations were made while close to the top of the storms. We divided our data into two amplitude groups based on prior NASA U2 aircraft optical data and our pulse characteristics. The group of large pulses with radiance greater than 2.1 mW /sq m sr had mean and median 10 - 10% optical pulse widths of 765 and 735 microns respectively, the 50-50% pulse widths of 396 and 355 microns respectively, and 10-90% rise times of 290 and 260 microns. These values are very similar to the previous U2 based optical results The other group of pulses consisting of slightly more than a quarter of the total pulses observed had radiances less than the minimum values detected in the U2 study. The small pulses were narrower than the large pulses with 5040% mean and median values of 198 and 160 ps respectively. Only 12 % of the flashes contained only small pulses, minimizing the impact of this data on the estimates of detection efficiencies of the orbital instruments, the Lightning Imaging Sensor and Optical Transient Detector.

Isolated Attosecond Pulse Generation without the Need to Stabilize the Carrier-Envelope Phase of Driving Lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilbertson, Steve; Khan, Sabih D.; Wu Yi

2010-08-27

Single isolated attosecond pulses can be extracted from a pulse train with an ultrafast gate in the generation target. By setting the gate width sufficiently narrow with the generalized double optical gating, we demonstrate that single isolated attosecond pulses can be generated with any arbitrary carrier-envelope phase value of the driving laser. The carrier-envelope phase only affects the photon flux, not the pulse duration or contrast. Our results show that isolated attosecond pulses can be generated using carrier-envelope phase unstabilized 23 fs pulses directly from chirped pulse amplifiers.

A study on the high-order mode oscillation in a four-cavity intense relativistic klystron amplifier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Ying-Hui; Niu, Xin-Jian; Wang, Hui

The high-order mode oscillation is studied in designing a four-cavity intense relativistic klystron amplifier. The reason for the oscillation caused by high-order modes and a method to suppress these kinds of spurious modes are found through theoretical analyses and the study on the influence of major parameters of a high frequency structure (such as the oscillation frequency of cavities, the cavity Q value, the length of drift tube section, and the characteristic impedance). Based on much simulation, a four-cavity intense relativistic klystron amplifier with a superior performance has been designed, built, and tested. An output power of 2.22 GW corresponding tomore » 27.4% efficiency and 61 dB gain has been obtained. Moreover, the high-order mode oscillation is suppressed effectively, and an output power of 1.95 GW corresponding to 26% efficiency and 62 dB gain has been obtained in our laboratory.« less

Migration of cell surface concanavalin A receptors in pulsed electric fields.

PubMed Central

Lin-Liu, S; Adey, W R; Poo, M M

1984-01-01

Concanavalin A (con A) receptors on the surface of cultured Xenopus myoblasts redistributed in response to monopolar, pulsed electric fields. The prefield uniform distribution of the receptors became asymmetrical, and was polarized toward the cathodal pole, in the same way as in DC fields. The extent of asymmetry depended on the duration of field exposure, pulse width (or alternatively, interpulse interval), frequency, and intensity. This relationship was most conveniently expressed by using duty cycle, a quantity determined by both pulse width and frequency. Pulses of average intensity 1.5 V/cm induced detectable asymmetry within 5 min. At the lowest average field intensity used, 0.8 V/cm, significant asymmetry was detected at 150 min. For pulses of high duty cycle (greater than 25%), steady state was reached after 30 min exposure and the steady state asymmetry was dependent on average field intensity. For low duty cycle fields, the time required to reach steady state was prolonged (greater than 50 min). Before reaching a steady state, effectiveness of the pulses, as compared with DC fields of equivalent intensity, was a function of duty cycle. A low duty cycle field (fixed number of pulses at low frequency or long interpulse interval) was less effective than high duty cycle fields or DC. PMID:6743751

Picosecond pulsed micro-module emitting near 560 nm using a frequency doubled gain-switched DBR ridge waveguide semiconductor laser

NASA Astrophysics Data System (ADS)

Kaltenbach, André; Hofmann, Julian; Seidel, Dirk; Lauritsen, Kristian; Bugge, Frank; Fricke, Jörg; Paschke, Katrin; Erdmann, Rainer; Tränkle, Günther

2017-02-01

A miniaturized picosecond pulsed semiconductor laser source in the spectral range around 560nm is realized by integrating a frequency doubled distributed Bragg reflector ridge waveguide laser (DBR-RWL) into a micromodule. Such compact laser sources are suitable for mobile application, e.g. in microscopes. The picosecond optical pulses are generated by gain-switching which allows for arbitrary pulse repetition frequencies. For frequency conversion a periodically poled magnesium doped lithium niobate ridge waveguide crystal (PPLN) is used to provide high conversion efficiency with single-pass second harmonic generation (SHG). The coupling of the pulsed radiation into the PPLN crystal is realized by a GRIN-lens. Such types of lenses collect the divergent laser radiation and focus it into the crystal waveguide providing high coupling efficiency at a minimum of space compared to the usage of fast axis collimator(FAC)/slow axis collimator (SAC) lens combinations. The frequency doubled output pulses show a pulse width of about 60 ps FWHM and a spectral width around 0.06nm FWHM at a central wavelength of 557nm at 15Å. The pulse peak power could be determined to be more than 300mW at a repetition frequency of 40 MHz.

Calibration approach for fluorescence lifetime determination for applications using time-gated detection and finite pulse width excitation.

PubMed

Keller, Scott B; Dudley, Jonathan A; Binzel, Katherine; Jasensky, Joshua; de Pedro, Hector Michael; Frey, Eric W; Urayama, Paul

2008-10-15

Time-gated techniques are useful for the rapid sampling of excited-state (fluorescence) emission decays in the time domain. Gated detectors coupled with bright, economical, nanosecond-pulsed light sources like flashlamps and nitrogen lasers are an attractive combination for bioanalytical and biomedical applications. Here we present a calibration approach for lifetime determination that is noniterative and that does not assume a negligible instrument response function (i.e., a negligible excitation pulse width) as does most current rapid lifetime determination approaches. Analogous to a transducer-based sensor, signals from fluorophores of known lifetime (0.5-12 ns) serve as calibration references. A fast avalanche photodiode and a GHz-bandwidth digital oscilloscope is used to detect transient emission from reference samples excited using a nitrogen laser. We find that the normalized time-integrated emission signal is proportional to the lifetime, which can be determined with good reproducibility (typically <100 ps) even for data with poor signal-to-noise ratios ( approximately 20). Results are in good agreement with simulations. Additionally, a new time-gating scheme for fluorescence lifetime imaging applications is proposed. In conclusion, a calibration-based approach is a valuable analysis tool for the rapid determination of lifetime in applications using time-gated detection and finite pulse width excitation.

N-butanol and isobutanol as alternatives to gasoline: Comparison of port fuel injector characteristics

NASA Astrophysics Data System (ADS)

Fenkl, Michael; Pechout, Martin; Vojtisek, Michal

2016-03-01

The paper reports on an experimental investigation of the relationship between the pulse width of a gasoline engine port fuel injector and the quantity of the fuel injected when butanol is used as a fuel. Two isomers of butanol, n-butanol and isobutanol, are considered as potential candidates for renewable, locally produced fuels capable of serving as a drop-in replacement fuel for gasoline, as an alternative to ethanol which poses material compatibility and other drawbacks. While the injected quantity of fuel is typically a linear function of the time the injector coil is energized, the flow through the port fuel injector is complex, non ideal, and not necessarily laminar, and considering that butanol has much higher viscosity than gasoline, an experimental investigation was conducted. A production injector, coupled to a production fueling system, and driven by a pulse width generator was operated at various pulse lengths and frequencies, covering the range of engine rpm and loads on a car engine. The results suggest that at least at room temperature, the fueling rate remains to be a linear function of the pulse width for both n-butanol and isobutanol, and the volumes of fuel injected are comparable for gasoline and both butanol isomers.

Pulse oximeter plethysmographic waveform changes in awake, spontaneously breathing, hypovolemic volunteers.

PubMed

McGrath, Susan P; Ryan, Kathy L; Wendelken, Suzanne M; Rickards, Caroline A; Convertino, Victor A

2011-02-01

The primary objective of this study was to determine whether alterations in the pulse oximeter waveform characteristics would track progressive reductions in central blood volume. We also assessed whether changes in the pulse oximeter waveform provide an indication of blood loss in the hemorrhaging patient before changes in standard vital signs. Pulse oximeter data from finger, forehead, and ear pulse oximeter sensors were collected from 18 healthy subjects undergoing progressive reduction in central blood volume induced by lower body negative pressure (LBNP). Stroke volume measurements were simultaneously recorded using impedance cardiography. The study was conducted in a research laboratory setting where no interventions were performed. Pulse amplitude, width, and area under the curve (AUC) features were calculated from each pulse wave recording. Amalgamated correlation coefficients were calculated to determine the relationship between the changes in pulse oximeter waveform features and changes in stroke volume with LBNP. For pulse oximeter sensors on the ear and forehead, reductions in pulse amplitude, width, and area were strongly correlated with progressive reductions in stroke volume during LBNP (R(2) ≥ 0.59 for all features). Changes in pulse oximeter waveform features were observed before profound decreases in arterial blood pressure. The best correlations between pulse features and stroke volume were obtained from the forehead sensor area (R(2) = 0.97). Pulse oximeter waveform features returned to baseline levels when central blood volume was restored. These results support the use of pulse oximeter waveform analysis as a potential diagnostic tool to detect clinically significant hypovolemia before the onset of cardiovascular decompensation in spontaneously breathing patients.

Project Echo: 960-Megacycle, 10-Kilowatt Transmitter

NASA Technical Reports Server (NTRS)

Schafer, J. P.; Brandt, R. H.

1961-01-01

A 10-kw transmitter operating at 960 to 961 Mc was used at the eastern terminus of the Project Echo communications experiment. This transmitter is located on Crawford's Hill near Holmdel, New Jersey. The 10-kw output feeds into a waveguide line leading to a 60-foot dish antenna. Exciter-driver units are available to drive the power amplifier with various modulations, such as wide-deviation FM, low-index phase modulation, single-sideband or double-sideband modulation with or without carrier, 960.05 or 961.05 Mc constant-frequency CW, and radar on-off pulses at 961.05 Mc. The main output amplifier consists primarily of a four-stage, externally-tuned-cavity, water-cooled klystron, operating at a beam voltage of 16 to 18 kv. The transmitter has been operated during many Moonbounce, tropospheric scatter, and Echo I tests with very satisfactory results. This paper describes its use before March 1, 1961.

200 MW S-band traveling wave resonant ring development at IHEP

NASA Astrophysics Data System (ADS)

Zhou, Zu-Sheng; Chi, Yun-Long; Git, Meng-Ping; Pei, Guo-Xi

2010-03-01

The resonant-ring is a traveling wave circuit, which is used to produce high peak power with comparatively smaller stored energy. The application to be considered is its use as a high power simulator mainly for testing the klystron ceramic output window, as well as for high power microwave transmission devices. This paper describes the principle of a resonant ring and introduces the structure and property of the newly constructed traveling wave resonant ring at IHEP. Our goal is to produce a 200 MW class resonant ring at 2.856 GHz with a pulse length of 2 μs and repetition rate of 25 Hz. The installation, commissioning and testing of the ring have been completed and a peak power of 200 MW at 3 μs has been achieved. The conditioning results show that all the parameters of the resonant ring reach the design goals.

Development of a 402.5 MHz 140 kW Inductive Output Tube

DOE Office of Scientific and Technical Information (OSTI.GOV)

R. Lawrence Ives; Michael Read, Robert Jackson

2012-05-09

This report contains the results of Phase I of an SBIR to develop a Pulsed Inductive Output Tube (IOT) with 140 kW at 400 MHz for powering H-proton beams. A number of sources, including single beam and multiple beam klystrons, can provide this power, but the IOT provides higher efficiency. Efficiencies exceeding 70% are routinely achieved. The gain is typically limited to approximately 24 dB; however, the availability of highly efficient, solid state drivers reduces the significance of this limitation, particularly at lower frequencies. This program initially focused on developing a 402 MHz IOT; however, the DOE requirement for thismore » device was terminated during the program. The SBIR effort was refocused on improving the IOT design codes to more accurately simulate the time dependent behavior of the input cavity, electron gun, output cavity, and collector. Significant improvement was achieved in modeling capability and simulation accuracy.« less

Ring-shaped active mode-locked tunable laser using quantum-dot semiconductor optical amplifier

NASA Astrophysics Data System (ADS)

Zhang, Mingxiao; Wang, Yongjun; Liu, Xinyu

2018-03-01

In this paper, a lot of simulations has been done for ring-shaped active mode-locked lasers with quantum-dot semiconductor optical amplifier (QD-SOA). Based on the simulation model of QD-SOA, we discussed about the influence towards mode-locked waveform frequency and pulse caused by QD-SOA maximum mode peak gain, active layer loss coefficient, bias current, incident light pulse, fiber nonlinear coefficient. In the meantime, we also take the tunable performance of the laser into consideration. Results showed QD-SOA a better performance than original semiconductor optical amplifier (SOA) in recovery time, line width, and nonlinear coefficients, which makes it possible to output a locked-mode impulse that has a higher impulse power, narrower impulse width as well as the phase is more easily controlled. After a lot of simulations, this laser can realize a 20GHz better locked-mode output pulse after 200 loops, where the power is above 17.5mW, impulse width is less than 2.7ps, moreover, the tunable wavelength range is between 1540nm-1580nm.

A comparison of battery testing protocols: Those used by the U.S. advanced battery consortium and those used in China

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robertson, David C.; Christophersen, Jon P.; Bennett, Taylor

Two testing protocols, QC/T 743 and those used by the U.S. Advanced Battery Consortium (USABC), were compared using cells based on LiFePO4/graphite chemistry. Differences in the protocols directly affected the data and the performance decline mechanisms deduced from the data. In all cases, the rate of capacity fade was linear with time. Overall, the testing protocols produced very similar data when the testing conditions and metrics used to define performance were similar. The choice of depth of discharge and pulse width had a direct effect on the apparent rate of resistance increased and estimated cell life. At greater percent depthmore » of discharge (%DOD) and pulse width, the estimated life was shorter that at lower %DOD and shorter pulse width. This indicates that cells which were at the end of life based on the USABC protocol were not at end of life based on the QC/T 743 protocol by a large margin. (C) 2016 ELSEVIER B.V. All rights reserved.« less

Design and Simulation of Control Technique for Permanent Magnet Synchronous Motor Using Space Vector Pulse Width Modulation

NASA Astrophysics Data System (ADS)

Khan, Mansoor; Yong, Wang; Mustafa, Ehtasham

2017-07-01

After the rapid advancement in the field of power electronics devices and drives for last few decades, there are different kinds of Pulse Width Modulation techniques which have been brought to the market. The applications ranging from industrial appliances to military equipment including the home appliances. The vey common application for the PWM is three phase voltage source inverter, which is used to convert DC to AC in the homes to supply the power to the house in case electricity failure, usually named as Un-interrupted Power Supply. In this paper Space Vector Pulse Width Modulation techniques is discussed and analysed under the control technique named as Field Oriented Control. The working and implementation of this technique has been studied by implementing on the three phase bridge inverter. The technique is used to control the Permanente Magnet Synchronous Motor. The drive system is successfully implemented in MATLAB/Simulink using the mathematical equation and algorithm to achieve the satisfactory results. PI type of controller is used to tuned ers of the motothe parametr i.e. torque and current.

Development of New Photorefractive Polymer Materials

DTIC Science & Technology

2015-05-19

which gives an indirect measurement of the field strength. The setup used is presented on Figure 8. A femtosecond pulsed fiber laser emits light at...measure the diffraction efficiency. The pulsed fiber laser characteristics are:  Energy per pulse: up to 100 µJ/pulse  Pulse temporal width: from 250 ns...to 250 µs  Repetition rate: up to 10kHz  Coherence length: 1cm Figure 26: Four wave mixing setup fed by the fiber laser . Three primary time

Synthesis of Nanosecond Ultrawideband Radiation Pulses

NASA Astrophysics Data System (ADS)

Koshelev, V. I.; Plisko, V. V.; Sevostyanov, E. A.

2017-12-01

The synthesis of electromagnetic pulses with an extended spectrum by summing pulses of different duration in free space has been studied. The radiation spectrum has been estimated analytically for a 4-element array of combined antennas excited by bipolar voltage pulses of duration 0.5, 1, 2, and 3 ns. It has been shown experimentally that radiation with a spectral width of more than three octaves can be produced using a 2×2 array of combined antennas excited by bipolar pulses of duration 2 and 3 ns.

An analysis of superluminal propagation becoming subluminal in highly dispersive media

NASA Astrophysics Data System (ADS)

Nanda, L.

2018-05-01

In this article the time-moments of the Poynting vector associated with an electromagnetic pulse are used to characterize the traversal time and the pulse width as the pulse propagates through highly dispersive media. The behaviour of these quantities with propagation distance is analyzed in two physical cases: Lorentz absorptive medium, and Raman gain doublet amplifying medium. It is found that the superluminal pulse propagation in these two cases with anomalous dispersion is always accompanied by pulse compression and eventually the pulse becomes subluminal with increasing distance of propagation.

Molecular dynamics study of lubricant depletion by pulsed laser heating

NASA Astrophysics Data System (ADS)

Seo, Young Woo; Rosenkranz, Andreas; Talke, Frank E.

2018-05-01

In this study, molecular dynamics simulations were performed to numerically investigate the effect of pulsed laser heating on lubricant depletion. The maximum temperature, the lubricant depletion width, the number of evaporated lubricant beads and the number of fragmented lubricant chains were studied as a function of laser peak power, pulse duration and repetition rate. A continuous-wave laser and a square pulse laser were simulated and compared to a Gaussian pulse laser. With increasing repetition rate, pulsed laser heating was found to approach continuous-wave laser heating.

Molecular isomerization induced by ultrashort infrared pulses. I. Few-cycle to sub-one-cycle Gaussian pulses and the role of the carrier-envelope phase.

PubMed

Uiberacker, Christoph; Jakubetz, Werner

2004-06-22

Using 550 previously calculated vibrational energy levels and dipole moments we performed simulations of the HCN-->HNC isomerization dynamics induced by sub-one-cycle and few-cycle IR pulses, which we represent as Gaussian pulses with 0.25-2 optical cycles in the pulse width. Starting from vibrationally pre-excited states, isomerization probabilities of up to 50% are obtained for optimized pulses. With decreasing number of optical cycles a strong dependence on the carrier-envelope phase (CEP) emerges. Although the optimized pulse parameters change significantly with the number of optical cycles, the distortion by the Gaussian envelope produces nearly equal fields, with a positive lobe followed by a negative one. The positions and areas of the lobes are also almost unchanged, irrespective of the number of cycles in the half-width. Isomerization proceeds via a pump-dumplike mechanism induced by the sequential lobes. The first lobe prepares a wave packet incorporating many delocalized states above the barrier. It is the motion of this wave packet across the barrier, which determines the timing of the pump and dump lobes. The role of the pulse parameters, and in particular of the CEP, is to produce the correct lobe sequence, size and timing within a continuous pulse. (c) 2004 American Institute of Physics.

Generation and amplification of sub-THz radiation in a rare gases plasma formed by a two-color femtosecond laser pulse

NASA Astrophysics Data System (ADS)

Bogatskaya, A. V.; Volkova, E. A.; Popov, A. M.

2018-06-01

A new approach to constructing the source of radiation in the sub-THz frequency range is discussed. It is based on the strong-field ionization of heavy rare gases with Ramsauer minimum in the transport cross-section by a two-color () femtosecond laser pulse. Then a four-photon nonlinear process ( are the frequencies from the spectral width of the pulse with frequency ω, and is the frequency from the spectral width of the second harmonic 2ω) with a transition to the initial state results in a low-frequency spontaneous emission that can be amplified in the strongly nonequilibrium laser plasma if the position of the photoelectron peaks is located in the region of growing energy transport cross-section.

Closed-loop pulsed helium ionization detector

DOEpatents

Ramsey, Roswitha S.; Todd, Richard A.

1987-01-01

A helium ionization detector for gas chromatography is operated in a constant current, pulse-modulated mode by configuring the detector, electrometer and a high voltage pulser in a closed-loop control system. The detector current is maintained at a fixed level by varying the frequency of fixed-width, high-voltage bias pulses applied to the detector. An output signal proportional to the pulse frequency is produced which is indicative of the charge collected for a detected species.

Controller for a High-Power, Brushless dc Motor

NASA Technical Reports Server (NTRS)

Fleming, David J.; Makdad, Terence A.

1987-01-01

Driving and braking torques controllable. Control circuit operates 7-kW, 45-lb-ft (61-N-m), three-phase, brushless dc motor in both motor and generator modes. In motor modes, energy from power source is pulse-width modulated to motor through modified "H-bridge" circuit, in generator mode, energy from motor is pulse-width modulated into bank of load resistors to provide variable braking torques. Circuit provides high-resolution torque control in both directions over wide range of speeds and torques. Tested successfully at bus voltages up to 200 Vdc and currents up to 45 A.

High efficiency SPS klystron design

NASA Technical Reports Server (NTRS)

Nalos, E. J.

1980-01-01

The most likely compact configuration to realize both high efficiency and high gain (approx. 40 dB) is a 5-6 cavity design focused by an electromagnet. The basic klystron efficiency cannot be expected to exceed 70-75% without collector depression. It was estimated that the net benefit of a 5 stage collector over a 2 stage collector is between 1.5 and 3.5 kW per tube. A modulating anode is incorporated in the design to enable rapid shutoff of the beam current in case the r.f. drive should be removed.

Experimental Performance of the NRL 8-Beam, 4-Cavity Multiple-Beam Klystron

NASA Astrophysics Data System (ADS)

Abe, D. K.; Pershing, D. E.; Nguyen, K. T.; Wood, F. N.; Myers, R. E.; Eisen, E. L.; Cusick, M.; Levush, B.

2006-01-01

Multiple-beam amplifiers (MBAs) represent a device technology with the potential to produce high-power, efficient amplifiers with relatively wide bandwidths that are compact, low-weight, low-noise, and operate at reduced voltages relative to comparable single-beam devices. To better understand the device physics and technical issues involved in the design, fabrication, and operation of these devices, the U.S. Naval Research Laboratory (NRL) has an on-going program to develop high peak power (> 600 kW) multiple-beam klystrons (MBKs) operating in S-band (˜3.3 GHz).

Hyperbolic chaos in the klystron-type microwave vacuum tube oscillator

NASA Astrophysics Data System (ADS)

Emel'yanov, V. V.; Kuznetsov, S. P.; Ryskin, N. M.

2010-12-01

The ring-loop oscillator consisting of two coupled klystrons which is capable of generating hyperbolic chaotic signal in the microwave band is considered. The system of delayed-differential equations describing the dynamics of the oscillator is derived. This system is further reduced to the two-dimensional return map under the assumption of the instantaneous build-up of oscillations in the cavities. The results of detailed numerical simulation for both models are presented showing that there exists large enough range of control parameters where the sustained regime corresponds to the structurally stable hyperbolic chaos.

High speed micromachining with high power UV laser

NASA Astrophysics Data System (ADS)

Patel, Rajesh S.; Bovatsek, James M.

2013-03-01

Increasing demand for creating fine features with high accuracy in manufacturing of electronic mobile devices has fueled growth for lasers in manufacturing. High power, high repetition rate ultraviolet (UV) lasers provide an opportunity to implement a cost effective high quality, high throughput micromachining process in a 24/7 manufacturing environment. The energy available per pulse and the pulse repetition frequency (PRF) of diode pumped solid state (DPSS) nanosecond UV lasers have increased steadily over the years. Efficient use of the available energy from a laser is important to generate accurate fine features at a high speed with high quality. To achieve maximum material removal and minimal thermal damage for any laser micromachining application, use of the optimal process parameters including energy density or fluence (J/cm2), pulse width, and repetition rate is important. In this study we present a new high power, high PRF QuasarR 355-40 laser from Spectra-Physics with TimeShiftTM technology for unique software adjustable pulse width, pulse splitting, and pulse shaping capabilities. The benefits of these features for micromachining include improved throughput and quality. Specific example and results of silicon scribing are described to demonstrate the processing benefits of the Quasar's available power, PRF, and TimeShift technology.

Development of the dense plasma focus for short-pulse applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bennett, N.; Blasco, M.; Breeding, K.

The dense plasma focus (DPF) has long been considered a compact source for pulsed neutrons and has traditionally been optimized for the total neutron yield. Here, we describe the efforts to optimize the DPF for short-pulse applications by introducing a reentrant cathode at the end of the coaxial plasma gun. We reduced the resulting neutron pulse widths by an average of 21±921±9% from the traditional long-drift DPF design. Pulse widths and yields achieved from deuterium-tritium fusion at 2 MA are 61.8±30.761.8±30.7 ns FWHM and 1.84±0.49×10121.84±0.49×10 12 neutrons per shot. Simulations were conducted concurrently to elucidate the DPF operation and confirmmore » the role of the reentrant cathode. Furthermore, a hybrid fluid-kinetic particle-in-cell modeling capability demonstrates correct sheath velocities, plasma instabilities, and fusion yield rates. Consistent with previous findings that the DPF is dominated by beam-target fusion from superthermal ions, we estimate that the thermonuclear contribution is at the 1% level.« less

Supermode-noise-free eighth-order femtosecond soliton from a backward dark-optical-comb-injection mode-locked semiconductor optical amplifier fiber laser.

PubMed

Lin, Gong-Ru; Pan, Ci-Ling; Chiu, I-Hsiang

2006-03-15

A backward dark-optical-comb-injection mode-locked semiconductor optical amplifier fiber laser (SOAFL) with a femtosecond pulse width and an ultrahigh supermode-noise suppressing ratio (SMSR) is primarily demonstrated. The mode-locked SOAFL pulse with a spectral linewidth of 0.45 nm is shortened from 15 to 8.6 ps under chirp compensation in a 420 m long dispersion-compensated fiber, corresponding to a time-bandwidth product of 0.48. The eighth-order soliton is obtained by the nonlinearly soliton's compression of the chirp-compensated SOAFL pulse in a 112 m long single-mode fiber at an input peak power of 51 W, providing the pulse width, the linewidth, and the nearly transform-limited time-bandwidth product are <200 fs, 13.8 nm, and 0.34, respectively. The phase noise and integrated timing jitter at an offset frequency below 1 MHz are -105 dBc/Hz and 0.8 ps, respectively. An ultrahigh pulse-compression ratio of 43 and a SMSR of 87 dB for the eighth-order SOAFL soliton are reported.

Terahertz Streaking of Few-Femtosecond Relativistic Electron Beams

NASA Astrophysics Data System (ADS)

Zhao, Lingrong; Wang, Zhe; Lu, Chao; Wang, Rui; Hu, Cheng; Wang, Peng; Qi, Jia; Jiang, Tao; Liu, Shengguang; Ma, Zhuoran; Qi, Fengfeng; Zhu, Pengfei; Cheng, Ya; Shi, Zhiwen; Shi, Yanchao; Song, Wei; Zhu, Xiaoxin; Shi, Jiaru; Wang, Yingxin; Yan, Lixin; Zhu, Liguo; Xiang, Dao; Zhang, Jie

2018-04-01

Streaking of photoelectrons with optical lasers has been widely used for temporal characterization of attosecond extreme ultraviolet pulses. Recently, this technique has been adapted to characterize femtosecond x-ray pulses in free-electron lasers with the streaking imprinted by far-infrared and terahertz (THz) pulses. Here, we report successful implementation of THz streaking for time stamping of an ultrashort relativistic electron beam, whose energy is several orders of magnitude higher than photoelectrons. Such an ability is especially important for MeV ultrafast electron diffraction (UED) applications, where electron beams with a few femtosecond pulse width may be obtained with longitudinal compression, while the arrival time may fluctuate at a much larger timescale. Using this laser-driven THz streaking technique, the arrival time of an ultrashort electron beam with a 6-fs (rms) pulse width has been determined with 1.5-fs (rms) accuracy. Furthermore, we have proposed and demonstrated a noninvasive method for correction of the timing jitter with femtosecond accuracy through measurement of the compressed beam energy, which may allow one to advance UED towards a sub-10-fs frontier, far beyond the approximate 100-fs (rms) jitter.

Development of channel organization and roughness following sediment pulses in single‐thread, gravel bed rivers

USGS Publications Warehouse

Madej, Mary Ann

2001-01-01

Large, episodic inputs of coarse sediment (sediment pulses) in forested, mountain streams may result in changes in the size and arrangement of bed forms and in channel roughness. A conceptual model of channel organization delineates trajectories of response to sediment pulses for many types of gravel bed channels. Channels exhibited self‐organizing behavior to various degrees based on channel gradient, presence of large in‐channel wood or other forcing elements, the size of the sediment pulse, and the number of bed‐mobilizing flows since disturbance. Typical channel changes following a sediment pulse were initial decreases in water depth, in variability of bed elevations, and in the regularity of bed form spacing. Trajectories of change subsequently showed increased average water depth, more variable and complex bed topography, and increased uniformity of bed form spacing. Bed form spacing in streams with abundant forcing elements developed at a shorter spatial scale (two to five channel widths) than in streams without such forcing mechanisms (five to 10 channel widths). Channel roughness increased as bed forms developed.

A chopper system for shortening the duration of pulsed supersonic beams seeded with NO or Br2 down to 13 μs.

PubMed

Lam, Jessica; Rennick, Christopher J; Softley, Timothy P

2015-05-01

A chopper wheel construct is used to shorten the duration of a molecular beam to 13 μs. Molecular beams seeded with NO or with Br2 and an initial pulse width of ≥200 μs were passed through a spinning chopper wheel, which was driven by a brushless DC in vacuo motor at a range of speeds, from 3000 rpm to 80,000 rpm. The resulting duration of the molecular-beam pulses measured at the laser detection volume ranged from 80 μs to 13 μs and was the same for both NO and Br2. The duration is consistent with a simple analytical model, and the minimum pulse width measured is limited by the spreading of the beam between the chopper and the detection point as a consequence of the longitudinal velocity distribution of the beam. The setup adopted here effectively eliminates buildup of background gas without the use of a differential pumping stage, and a clean narrow pulse is obtained with low rotational temperature.

Laser processing of sapphire with picosecond and sub-picosecond pulses

NASA Astrophysics Data System (ADS)

Ashkenasi, D.; Rosenfeld, A.; Varel, H.; Wähmer, M.; Campbell, E. E. B.

1997-11-01

Laser processing of sapphire using a Ti:sapphire laser at 790 and 395 nm and pulse widths varying between 0.2 and 5 ps is reported. A clear improvement in quality is demonstrated for multi-shot processing with sub-ps laser pulses. For fluences between 3 and 12 J/cm 2 two ablation phases were observed, in agreement with previous work from Tam et al. using 30 ps, 266 nm laser pulses [A.C. Tam, J.L. Brand, D.C. Cheng, W. Zapka, Appl. Phys. Lett. 55 (20) (1994) 2045]. During the `gentle ablation' phase periodic wavelike structures, i.e. ripples, were observed on the Al 2O 3 surface, perpendicular to the laser polarisation and with a spacing almost equalling the laser wavelength, indicating metallic-like behaviour. The ripple modulation depth was in the order of a few tens of nm. For fluences between 1 and 2.5 J/cm 2, below the single-shot surface damage threshold and at a pulse width above 200 fs, microstructures could be produced at the rear side of a 1 mm thick sapphire substrate without affecting the front surface.

Development of the dense plasma focus for short-pulse applications

DOE PAGES

Bennett, N.; Blasco, M.; Breeding, K.; ...

2017-01-05

The dense plasma focus (DPF) has long been considered a compact source for pulsed neutrons and has traditionally been optimized for the total neutron yield. Here, we describe the efforts to optimize the DPF for short-pulse applications by introducing a reentrant cathode at the end of the coaxial plasma gun. We reduced the resulting neutron pulse widths by an average of 21±921±9% from the traditional long-drift DPF design. Pulse widths and yields achieved from deuterium-tritium fusion at 2 MA are 61.8±30.761.8±30.7 ns FWHM and 1.84±0.49×10121.84±0.49×10 12 neutrons per shot. Simulations were conducted concurrently to elucidate the DPF operation and confirmmore » the role of the reentrant cathode. Furthermore, a hybrid fluid-kinetic particle-in-cell modeling capability demonstrates correct sheath velocities, plasma instabilities, and fusion yield rates. Consistent with previous findings that the DPF is dominated by beam-target fusion from superthermal ions, we estimate that the thermonuclear contribution is at the 1% level.« less

Sub-200 femtosecond dispersion-managed soliton ytterbium-doped fiber laser based on carbon nanotubes saturable absorber.

PubMed

Hou, Lei; Guo, Hongyu; Wang, Yonggang; Sun, Jiang; Lin, Qimeng; Bai, Yang; Bai, Jintao

2018-04-02

Ultrafast fiber laser light sources attract enormous interest due to the booming applications they are enabling, including long-distance communication, optical metrology, detecting technology of infra-biophotons, and novel material processing. In this paper, we demonstrate 175 fs dispersion-managed soliton (DMS) mode-locked ytterbium-doped fiber (YDF) laser based on single-walled carbon nanotubes (SWCNTs) saturable absorber (SA). The output DMSs have been achieved with repetition rate of 21.2 MHz, center wavelength of 1025.5 nm, and a spectral width of 32.7 nm. The operation directly pulse duration of 300 fs for generated pulse is the reported shortest pulse width for broadband SA based YDF lasers. By using an external grating-based compressor, the pulse duration could be compressed down to 175 fs. To the best of our knowledge, it is the shortest pulse duration obtained directly from YDF laser based on broadband SAs. In this paper, SWCNTs-SA has been utilized as the key optical component (mode locker) and the grating pair providing negative dispersion acts as the dispersion controller.

Pulse stuttering as a remedy for aliased ground backscatter

NASA Astrophysics Data System (ADS)

Bowhill, S. A.

1983-12-01

An algorithm that aides in the removal of ground scatter from low frequency Mesosphere, Stratosphere, Troposphere (MST) radar signals is examined. The unwanted ground scatter is shown as a sequence of velocity plots which are almost typical at the various altitudes. The interpulse period is changed in a cyclic way, thereby destroying the coherence of the unwanted signal. The interpulse period must be changed by an amount at least equal to the transmitted pulse width, and optimum performance is obtained when the number of different interpulse period occupies a time span greater than the coherence time of the unwanted signal. Since a 20-msec pulse width is used, it was found convenient to cycle through 50 pulses, the interpulse period changing from 2 msec to 3 msec during the 1/8-second time. This particular pattern of interpulse periods was provided by a software radar controller. With application of this algorithm, the unwanted scatter signal becomes incoherent from one pulse to the next, and therefore is perceived as noise by the coherent integrator and correlator.

Pulse stuttering as a remedy for aliased ground backscatter

NASA Technical Reports Server (NTRS)

Bowhill, S. A.

1983-01-01

An algorithm that aides in the removal of ground scatter from low frequency Mesosphere, Stratosphere, Troposphere (MST) radar signals is examined. The unwanted ground scatter is shown as a sequence of velocity plots which are almost typical at the various altitudes. The interpulse period is changed in a cyclic way, thereby destroying the coherence of the unwanted signal. The interpulse period must be changed by an amount at least equal to the transmitted pulse width, and optimum performance is obtained when the number of different interpulse period occupies a time span greater than the coherence time of the unwanted signal. Since a 20-msec pulse width is used, it was found convenient to cycle through 50 pulses, the interpulse period changing from 2 msec to 3 msec during the 1/8-second time. This particular pattern of interpulse periods was provided by a software radar controller. With application of this algorithm, the unwanted scatter signal becomes incoherent from one pulse to the next, and therefore is perceived as noise by the coherent integrator and correlator.

3D two-photon lithographic microfabrication system

DOEpatents

Kim, Daekeun [Cambridge, MA; So, Peter T. C. [Boston, MA

2011-03-08

An imaging system is provided that includes a optical pulse generator for providing an optical pulse having a spectral bandwidth and includes monochromatic waves having different wavelengths. A dispersive element receives a second optical pulse associated with the optical pulse and disperses the second optical pulse at different angles on the surface of the dispersive element depending on wavelength. One or more focal elements receives the dispersed second optical pulse produced on the dispersive element. The one or more focal element recombine the dispersed second optical pulse at a focal plane on a specimen where the width of the optical pulse is restored at the focal plane.

DIRECT COUPLED PROGRESSIVE STAGE PULSE COUNTER APPARATUS

DOEpatents

Kaufman, W.M.

1962-08-14

A progressive electrical pulse counter circuit was designed for the counting of a chain of input pulses of random width and/or frequency. The circuit employs an odd and even pulse input line alternately connected to a series of directly connected bistable counting stages. Each bistable stage has two d-c operative states which stage, when in its rnrtial state, prevents the next succeeding stage from changing its condition when the latter stage is pulsed. Since only altennate stages are pulsed for each incoming pulse, only one stage will change its state for each input pulse thereby providing prog essive stage by stage counting. (AEC)

A graphite based STT-RAM cell with reduction in switching current

NASA Astrophysics Data System (ADS)

Varghani, Ali; Peiravi, Ali

2015-10-01

Spin Transfer Torque Random Access Memory (STT-RAM) is a serious candidate for "universal memory" because of its non-volatility, fast access time, high density, good scalability, high endurance and relatively low power dissipation. However, problems with low write speed and large write current are important existing challenges in STT-RAM design and there is a tradeoff between them and data retention time. In this study, a novel STT-RAM cell structure which uses perfect graphite based Magnetic Tunnel Junction (MTJ) is proposed. First, the cross-section of the structure is selected to be an ellipse of 45 nm and 180 nm dimensions and a six-layer graphite is used as tunnel barrier. By passing a lateral current with a short pulse width (before applying STT current and independent of it) through four middle graphene layers of the tunnel barrier, a 27% reduction in the amplitude of the switching current (for fast switching time of 2 ns) or a 58% reduction in its pulse width is achieved without any reduction in data retention time. Finally, the effect of downscaling of technology on the proposed structure is evaluated. A reduction of 31.6% and 9% in switching current is achieved for 90 and 22 nm cell width respectively by passing sufficient current (100 μA with 0.1 ns pulse width) through the tunnel barrier. Simulations are done using Object Oriented Micro Magnetic Framework (OOMMF).

An in silico analysis of oxygen uptake of a mild COPD patient during rest and exercise using a portable oxygen concentrator

PubMed Central

Katz, Ira; Pichelin, Marine; Montesantos, Spyridon; Kang, Min-Yeong; Sapoval, Bernard; Zhu, Kaixian; Thevenin, Charles-Philippe; McCoy, Robert; Martin, Andrew R; Caillibotte, Georges

2016-01-01

Oxygen treatment based on intermittent-flow devices with pulse delivery modes available from portable oxygen concentrators (POCs) depends on the characteristics of the delivered pulse such as volume, pulse width (the time of the pulse to be delivered), and pulse delay (the time for the pulse to be initiated from the start of inhalation) as well as a patient’s breathing characteristics, disease state, and respiratory morphology. This article presents a physiological-based analysis of the performance, in terms of blood oxygenation, of a commercial POC at different settings using an in silico model of a COPD patient at rest and during exercise. The analysis encompasses experimental measurements of pulse volume, width, and time delay of the POC at three different settings and two breathing rates related to rest and exercise. These experimental data of device performance are inputs to a physiological-based model of oxygen uptake that takes into account the real dynamic nature of gas exchange to illustrate how device- and patient-specific factors can affect patient oxygenation. This type of physiological analysis that considers the true effectiveness of oxygen transfer to the blood, as opposed to delivery to the nose (or mouth), can be instructive in applying therapies and designing new devices. PMID:27729783

Spectral Flattening at Low Frequencies in Crab Giant Pulses

NASA Astrophysics Data System (ADS)

Meyers, B. W.; Tremblay, S. E.; Bhat, N. D. R.; Shannon, R. M.; Kirsten, F.; Sokolowski, M.; Tingay, S. J.; Oronsaye, S. I.; Ord, S. M.

2017-12-01

We report on simultaneous wideband observations of Crab giant pulses with the Parkes radio telescope and the Murchison Widefield Array (MWA). The observations were conducted simultaneously at 732 and 3100 MHz with Parkes and at 120.96, 165.76, and 210.56 MHz with the MWA. Flux density calibration of the MWA data was accomplished using a novel technique based on tied-array beam simulations. We detected between 90 and 648 giant pulses in the 120.96-210.56 MHz MWA subbands above a 5.5σ threshold, while in the Parkes subbands we detected 6344 and 231 giant pulses above a threshold of 6σ at 732 and 3100 MHz, respectively. We show, for the first time over a wide frequency range, that the average spectrum of Crab giant pulses exhibits a significant flattening at low frequencies. The spectral index, α, for giant pulses evolves from a steep, narrow distribution with a mean α =-2.6 and width {σ }α =0.5 between 732 and 3100 MHz to a wide, flat distribution of spectral indices with a mean α =-0.7 and width {σ }α =1.4 between 120.96 and 165.76 MHz. We also comment on the plausibility of giant pulse models for fast radio bursts based on this spectral information.

High-rate dead-time corrections in a general purpose digital pulse processing system

PubMed Central

Abbene, Leonardo; Gerardi, Gaetano

2015-01-01

Dead-time losses are well recognized and studied drawbacks in counting and spectroscopic systems. In this work the abilities on dead-time correction of a real-time digital pulse processing (DPP) system for high-rate high-resolution radiation measurements are presented. The DPP system, through a fast and slow analysis of the output waveform from radiation detectors, is able to perform multi-parameter analysis (arrival time, pulse width, pulse height, pulse shape, etc.) at high input counting rates (ICRs), allowing accurate counting loss corrections even for variable or transient radiations. The fast analysis is used to obtain both the ICR and energy spectra with high throughput, while the slow analysis is used to obtain high-resolution energy spectra. A complete characterization of the counting capabilities, through both theoretical and experimental approaches, was performed. The dead-time modeling, the throughput curves, the experimental time-interval distributions (TIDs) and the counting uncertainty of the recorded events of both the fast and the slow channels, measured with a planar CdTe (cadmium telluride) detector, will be presented. The throughput formula of a series of two types of dead-times is also derived. The results of dead-time corrections, performed through different methods, will be reported and discussed, pointing out the error on ICR estimation and the simplicity of the procedure. Accurate ICR estimations (nonlinearity < 0.5%) were performed by using the time widths and the TIDs (using 10 ns time bin width) of the detected pulses up to 2.2 Mcps. The digital system allows, after a simple parameter setting, different and sophisticated procedures for dead-time correction, traditionally implemented in complex/dedicated systems and time-consuming set-ups. PMID:26289270

Efficacy of right unilateral ultrabrief pulse width ECT: a preliminary report.

PubMed

Magid, Michelle; Truong, Liz; Trevino, Kenneth; Husain, Mustafa

2013-12-01

Ultrabrief (right unilateral) electroconvulsive therapy (UB-RU ECT) is a newer form of ECT, which uses a shorter pulse width than the standard ECT (0.3 vs 1.0 millisecond, respectively). As a result, the use of UB ECT may provide a means of further decreasing ECT-related cognitive adverse effects. In 2011, the University of Texas Southwestern Department of ECT in Austin adopted a UB ECT protocol. The purpose of this study was to perform a preliminary evaluation of the effectiveness and efficiency of UB-RU ECT. This study also examined whether sex, age, or diagnosis affected response rates. This retrospective chart review identified 62 patients treated with the UB ECT protocol. An analysis of ECT response rates and demographic characteristics was conducted based on the data from clinical evaluations and Patient Health Questionnaire 9. Sixty-eight percent of patients in the study responded to ECT; 55% responded to UB pulse width RU ECT with another 13% responding when switched to standard pulse width bilateral ECT. The mean number of treatments in an index ECT series was 12.5. There was no statistically significant difference in response rates between bipolar and unipolar depressed patients. Men required progression to bilateral treatment more than women. This UB ECT protocol demonstrated a similar response rate when compared to standard ECT protocols; however, an increase in the number of treatments was required. Ultrabrief protocols are a viable option for both bipolar and unipolar depression. In men, UB ECT protocols may be less advantageous due to a need to overcome a potentially higher seizure threshold in men; however, additional research is needed to confirm this finding.

Method and apparatus for improved high power impulse magnetron sputtering

DOEpatents

Anders, Andre

2013-11-05

A high power impulse magnetron sputtering apparatus and method using a vacuum chamber with a magnetron target and a substrate positioned in the vacuum chamber. A field coil being positioned between the magnetron target and substrate, and a pulsed power supply and/or a coil bias power supply connected to the field coil. The pulsed power supply connected to the field coil, and the pulsed power supply outputting power pulse widths of greater that 100 .mu.s.

Q-switched and mode-locked Er{sup 3+}-doped fibre laser using a single-multi-single fibre filter and piezoelectric

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ji Wang; Yunjun Zhang; Aotuo Dong

2014-04-28

The active Q-switched and passive mode-locked Er{sup 3+}-doped all-fibre laser is presented. The fibre laser centre wavelength is located at 1563 nm and determined by the homemade singlemulti- single (SMS) in-line fibre filter. The laser spectrum width is nearly 0.1 nm. The active Q-switched mechanism relies on the polarisation state control using a piezoelectric to press a segment of passive fibre on the circular cavity. The nonlinear polarisation rotation technology is used to realise the passive self-started modelocked operation. In the passive mode-locked regimes, the output average power is 2.1 mW, repetition frequency is 11.96 MHz, and single pulse energymore » is 0.18 nJ. With the 100-Hz Q-switched regimes running, the output average power is 1.5 mW. The total Q-switched pulse width is 15 μs, and every Q-switched pulse is made up by several tens of mode-locked peak pulses. The calculated output pulse energy of the Q-switched fibre laser is about 15 μJ, and the energy of every mode-locked pulse is about 64–68 nJ during a Q-switched pulse taking into account the power fraction propagating between pulses. (lasers)« less

Low Probability of Intercept Laser Range Finder

DTIC Science & Technology

2017-07-19

time of arrival, and it may also include wavelength, pulse width, and pulse repetition frequency (PRF). Second photodetector 38 in conjunction with... conjunction with lens 32 and telescope 36 that can correct for turbulence along the free space path. [0024] In all embodiments, the time interval

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lam, Jessica; Rennick, Christopher J.; Softley, Timothy P.

A chopper wheel construct is used to shorten the duration of a molecular beam to 13 μs. Molecular beams seeded with NO or with Br{sub 2} and an initial pulse width of ≥200 μs were passed through a spinning chopper wheel, which was driven by a brushless DC in vacuo motor at a range of speeds, from 3000 rpm to 80 000 rpm. The resulting duration of the molecular-beam pulses measured at the laser detection volume ranged from 80 μs to 13 μs and was the same for both NO and Br{sub 2}. The duration is consistent with a simple analyticalmore » model, and the minimum pulse width measured is limited by the spreading of the beam between the chopper and the detection point as a consequence of the longitudinal velocity distribution of the beam. The setup adopted here effectively eliminates buildup of background gas without the use of a differential pumping stage, and a clean narrow pulse is obtained with low rotational temperature.« less

Analysis of the damage threshold of the GaAs pseudomorphic high electron mobility transistor induced by the electromagnetic pulse

NASA Astrophysics Data System (ADS)

Xi, Xiao-Wen; Chai, Chang-Chun; Liu, Yang; Yang, Yin-Tang; Fan, Qing-Yang; Shi, Chun-Lei

2016-08-01

An electromagnetic pulse (EMP)-induced damage model based on the internal damage mechanism of the GaAs pseudomorphic high electron mobility transistor (PHEMT) is established in this paper. With this model, the relationships among the damage power, damage energy, pulse width and signal amplitude are investigated. Simulation results show that the pulse width index from the damage power formula obtained here is higher than that from the empirical formula due to the hotspot transferring in the damage process of the device. It is observed that the damage energy is not a constant, which decreases with the signal amplitude increasing, and then changes little when the signal amplitude reaches up to a certain level. Project supported by the National Basic Research Program of China (Grant No. 2014CB339900) and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (CAEP) (Grant No. 2015-0214.XY.K).

Effect of tendon vibration during wide-pulse neuromuscular electrical stimulation (NMES) on muscle force production in people with spinal cord injury (SCI).

PubMed

Bochkezanian, Vanesa; Newton, Robert U; Trajano, Gabriel S; Vieira, Amilton; Pulverenti, Timothy S; Blazevich, Anthony J

2018-02-13

Neuromuscular electrical stimulation (NMES) is commonly used in skeletal muscles in people with spinal cord injury (SCI) with the aim of increasing muscle recruitment and thus muscle force production. NMES has been conventionally used in clinical practice as functional electrical stimulation (FES), using low levels of evoked force that cannot optimally stimulate muscular strength and mass improvements, and thus trigger musculoskeletal changes in paralysed muscles. The use of high intensity intermittent NMES training using wide-pulse width and moderate-intensity as a strength training tool could be a promising method to increase muscle force production in people with SCI. However, this type of protocol has not been clinically adopted because it may generate rapid muscle fatigue and thus prevent the performance of repeated high-intensity muscular contractions in paralysed muscles. Moreover, superimposing patellar tendon vibration onto the wide-pulse width NMES has been shown to elicit further increases in impulse or, at least, reduce the rate of fatigue in repeated contractions in able-bodied populations, but there is a lack of evidence to support this argument in people with SCI. Nine people with SCI received two NMES protocols with and without superimposing patellar tendon vibration on different days (i.e. STIM and STIM+vib), which consisted of repeated 30 Hz trains of 58 wide-pulse width (1000 μs) symmetric biphasic pulses (0.033-s inter-pulse interval; 2 s stimulation train; 2-s inter-train interval) being delivered to the dominant quadriceps femoris. Starting torque was 20% of maximal doublet-twitch torque and stimulations continued until torque declined to 50% of the starting torque. Total knee extensor impulse was calculated as the primary outcome variable. Total knee extensor impulse increased in four subjects when patellar tendon vibration was imposed (59.2 ± 15.8%) but decreased in five subjects (- 31.3 ± 25.7%). However, there were no statistically significant differences between these sub-groups or between conditions when the data were pooled. Based on the present results there is insufficient evidence to conclude that patellar tendon vibration provides a clear benefit to muscle force production or delays muscle fatigue during wide-pulse width, moderate-intensity NMES in people with SCI. ACTRN12618000022268 . Date: 11/01/2018. Retrospectively registered.

Development of an X-Band 50 MW Multiple Beam Klystron

NASA Astrophysics Data System (ADS)

Song, Liqun; Ferguson, Patrick; Ives, R. Lawrence; Miram, George; Marsden, David; Mizuhara, Max

2003-12-01

Calabazas Creek Research, Inc. is developing an X-band 50 MW multiple beam klystron (MBK) on a DOE SBIR Phase II grant. The electrical design and preliminary mechanical design were completed on the Phase I. This MBK consists of eight discrete klystron circuits driven by eight electron beams located symmetrically on a circle with a radius of 6.3 cm. Each beam operates at 190 kV and 66 A. The eight beam electron gun is in development on a DOE SBIR Phase II grant. Each circuit consists of an input cavity, two gain cavities, three penultimate cavities, and a three cavity output circuit operating in the PI/2 mode. Ring resonators were initially proposed for the complete circuit; however, low beam — wave interaction resulted in the necessity to use discrete cavities for all eight circuits. The input cavities are coupled via hybrid waveguides to ensure constant drive power amplitude and phase. The output circuits can either be combined using compact waveguide twists driving a TE01 high power window or combined into a TM04 mode converter driving the same TE01 window. The gain and efficiency for a single circuit has been optimized using KLSC, a 2 1/2D large signal klystron code. Simulations for a single circuit predict an efficiency of 53% for a single output cavity and 55% for the three cavity output resonator. The total RF output power for this MBK is 55 MW. During the Phase II emphasis will be given to cost reduction techniques resulting in a robust — high efficient — long life high power amplifier.

Nanosecond pulsed laser welding of high carbon steels

NASA Astrophysics Data System (ADS)

Ascari, Alessandro; Fortunato, Alessandro

2014-03-01

The present paper deals with the possibility to exploit low-cost, near infra-red, nanosecond pulsed laser sources in welding of high carbon content thin sheets. The exploitation of these very common sources allows to achieve sound weld beads with a good depth-to-width ratio and very small heat affected zones when the proper process parameters are involved. In particular the role of pulse frequency, pulse duration, peak power and welding speed on the characteristics of the weld beads is studied and the advantage of the application of short-pulse laser sources over traditional long-pulse or continuous wave one is assessed.

Chirped pulse digital holography for measuring the sequence of ultrafast optical wavefronts

NASA Astrophysics Data System (ADS)

Karasawa, Naoki

2018-04-01

Optical setups for measuring the sequence of ultrafast optical wavefronts using a chirped pulse as a reference wave in digital holography are proposed and analyzed. In this method, multiple ultrafast object pulses are used to probe the temporal evolution of ultrafast phenomena and they are interfered with a chirped reference wave to record a digital hologram. Wavefronts at different times can be reconstructed separately from the recorded hologram when the reference pulse can be treated as a quasi-monochromatic wave during the pulse width of each object pulse. The feasibility of this method is demonstrated by numerical simulation.

Multifunctional optical correlator for picosecond ultraviolet laser pulse measurement

DOE PAGES

Rakhman, Abdurahim; Wang, Yang; Garcia, Frances; ...

2014-01-01

A compact optical correlator system that measures both the autocorrelation between two infrared (IR) lights and the cross-correlation between an IR and an ultraviolet (UV) light using a single nonlinear optical crystal has been designed and experimentally demonstrated. The rapid scanning of optical delay line, switching between auto and cross-correlations, crystal angle tuning, and data acquisition and processing are all computer controlled. Pulse widths of an IR light from a mode-locked laser are measured by the correlator and the results are compared with a direct measurement using a high-speed photodetector system. The correlator has been used to study the parametermore » dependence of the pulse width of a macropulse UV laser designed for laser-assisted hydrogen ion (H-) beam stripping for the Spallation Neutron Source at Oak Ridge National Laboratory.« less

Neuroperformance Imaging

DTIC Science & Technology

2012-10-01

EMBC10.1722. 10. Mitra, P.P., Halperin, B.I.: Effects of finite gradient-pulse widths in pulsed- field - gradient diffusion measurements . Journal of Magnetic ...December 2011 ABSTRACT: The addition of a pair of magnetic field gradient pulses had initially enabled the measurement of spin motion to nuclear mag- netic...introduced a pair of (homogenous) magnetic field gradients into the spin echo experi- ment with the purpose of accurately measuring the scalar diffusion

Control System for the LLNL Kicker Pulse Generator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watson, J A; Anaya, R M; Cook, E G

2002-06-18

A solid-state high voltage pulse generator with multi-pulse burst capability, very fast rise and fall times, pulse width agility, and amplitude modulation capability for use with high speed electron beam kickers has been designed and tested at LLNL. A control system calculates a desired waveform to be applied to the kicker based on measured electron beam displacement then adjusts the pulse generators to provide the desired waveform. This paper presents the design of the control system and measure performance data from operation on the ETA-11 accelerator at LLNL.

Ultrashort pulse chirp measurement via transverse second-harmonic generation in strontium barium niobate crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trull, J.; Wang, B.; Parra, A.

2015-06-01

Pulse compression in dispersive strontium barium niobate crystal with a random size and distribution of the anti-parallel orientated nonlinear domains is observed via transverse second harmonic generation. The dependence of the transverse width of the second harmonic trace along the propagation direction allows for the determination of the initial chirp and duration of pulses in the femtosecond regime. This technique permits a real-time analysis of the pulse evolution and facilitates fast in-situ correction of pulse chirp acquired in the propagation through an optical system.

Generation of sub-100-fs pulses from a CW mode-locked chromium-doped forsterite laser

NASA Technical Reports Server (NTRS)

Seas, A.; Petricevic, V.; Alfano, R. R.

1992-01-01

Generation of femtosecond pulses from a continuous-wave mode-locked chromium-doped forsterite laser is reported. The forsterite laser was actively mode locked by using an acoustooptic modulator operating at 78 MHz with two Brewster high-dispersion glass prisms for intracavity chirp compensation. Transform-limited sub-100-fs pulses were routinely generated in the TEM(00) mode with 85 mW of continuous power (with 1 percent output coupler), tunable over 1230-1280 nm. The shortest pulses measured had a 60-fs pulse width.

UWB dual burst transmit driver

DOEpatents

Dallum, Gregory E [Livermore, CA; Pratt, Garth C [Discovery Bay, CA; Haugen, Peter C [Livermore, CA; Zumstein, James M [Livermore, CA; Vigars, Mark L [Livermore, CA; Romero, Carlos E [Livermore, CA

2012-04-17

A dual burst transmitter for ultra-wideband (UWB) communication systems generates a pair of precisely spaced RF bursts from a single trigger event. An input trigger pulse produces two oscillator trigger pulses, an initial pulse and a delayed pulse, in a dual trigger generator. The two oscillator trigger pulses drive a gated RF burst (power output) oscillator. A bias driver circuit gates the RF output oscillator on and off and sets the RF burst packet width. The bias driver also level shifts the drive signal to the level that is required for the RF output device.

Nanosecond pulsed electric fields (nsPEFs) low cost generator design using power MOSFET and Cockcroft-Walton multiplier circuit as high voltage DC source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sulaeman, M. Y.; Widita, R.

2014-09-30

Purpose: Non-ionizing radiation therapy for cancer using pulsed electric field with high intensity field has become an interesting field new research topic. A new method using nanosecond pulsed electric fields (nsPEFs) offers a novel means to treat cancer. Not like the conventional electroporation, nsPEFs able to create nanopores in all membranes of the cell, including membrane in cell organelles, like mitochondria and nucleus. NsPEFs will promote cell death in several cell types, including cancer cell by apoptosis mechanism. NsPEFs will use pulse with intensity of electric field higher than conventional electroporation, between 20–100 kV/cm and with shorter duration of pulsemore » than conventional electroporation. NsPEFs requires a generator to produce high voltage pulse and to achieve high intensity electric field with proper pulse width. However, manufacturing cost for creating generator that generates a high voltage with short duration for nsPEFs purposes is highly expensive. Hence, the aim of this research is to obtain the low cost generator design that is able to produce a high voltage pulse with nanosecond width and will be used for nsPEFs purposes. Method: Cockcroft-Walton multiplier circuit will boost the input of 220 volt AC into high voltage DC around 1500 volt and it will be combined by a series of power MOSFET as a fast switch to obtain a high voltage with nanosecond pulse width. The motivation using Cockcroft-Walton multiplier is to acquire a low-cost high voltage DC generator; it will use capacitors and diodes arranged like a step. Power MOSFET connected in series is used as voltage divider to share the high voltage in order not to damage them. Results: This design is expected to acquire a low-cost generator that can achieve the high voltage pulse in amount of −1.5 kV with falltime 3 ns and risetime 15 ns into a 50Ω load that will be used for nsPEFs purposes. Further detailed on the circuit design will be explained at presentation.« less

Cladding-pumped passively mode-locked fiber laser generating femtosecond and picosecond pulses

NASA Astrophysics Data System (ADS)

Fermann, M. E.; Harter, D.; Minelly, J. D.; Vienne, G. G.

1996-07-01

Passively mode-locked fiber lasers cladding pumped by broad-area diode-laser arrays are described. With a dispersion-compenstated erbium-ytterbium fiber oscillator, 200-fs pulses with pulse energies up to 100 pJ are generated at a wavelength of 1560 nm. In a highly dispersive cavity, pulse widths of 3 ps with pulse energies up to 1 nJ are obtained. A saturable absorber is used for pulse startup, whereas nonlinear polarization evolution is exploited for steady-state pulse shaping. An environmentally stable design is ensured by use of a compensation scheme for linear polarization drifts in the cavity.

Cladding-pumped passively mode-locked fiber laser generating femtosecond and picosecond pulses.

PubMed

Fermann, M E; Harter, D; Minelly, J D; Vienne, G G

1996-07-01

Passively mode-locked fiber lasers cladding pumped by broad-area diode-laser arrays are described. With a dispersion-compenstated erbium-ytterbium fiber oscillator, 200-fs pulses with pulse energies up to 100 pJ are generated at a wavelength of 1560 nm. In a highly dispersive cavity, pulse widths of 3 ps with pulse energies up to 1 nJ are obtained. A saturable absorber is used for pulse startup, whereas nonlinear polarization evolution is exploited for steady-state pulse shaping. An environmentally stable design is ensured by use of a compensation scheme for linear polarization drifts in the cavity.

Proposal of a defense application for a chemical oxygen laser

NASA Astrophysics Data System (ADS)

Takehisa, K.

2015-05-01

Defense application for a chemical oxygen laser (COL) is explained. Although a COL has not yet been successful in lasing, the oscillator was estimated to produce a giant pulse with the full width at half maximum (FWHM) of ~0.05ms which makes the damage threshold for the mirrors several-order higher than that for a typical solid-state laser with a ~10ns pulse width. Therefore it has a potential to produce MJ class output considering the simple scalability of being a chemical laser. Since within 0.05ms a supersonic aircraft can move only a few centimeters which is roughly equal to the spot size of the focused beam at ~10km away using a large-diameter focusing mirror, a COL has a potential to make a damage to an enemy aircraft by a single shot without beam tracking. But since the extracted beam can propagate up to a few kilometers due to the absorption in the air, it may be suitable to use in space. While a chemical oxygen-iodine laser (COIL) can give a pulsed output with a width of ~2 ms using a high-pressure singlet oxygen generator (SOG). Therefore a pulsed COIL may also not require beam tracking if a target aircraft is approaching. Another advantage for these pulsed high-energy lasers (HELs) is that, in case of propagating in cloud or fog, much less energy is required for a laser for aerosol vaporization (LAV) than that of a LAV for a CW HEL. Considerations to use a COL as a directed energy weapon (DEW) in a point defense system are shown.

Characterization of an electrochemical mercury sensor using alternating current, cyclic, square wave and differential pulse voltammetry.

PubMed

Guerreiro, Gabriela V; Zaitouna, Anita J; Lai, Rebecca Y

2014-01-31

Here we report the characterization of an electrochemical mercury (Hg(2+)) sensor constructed with a methylene blue (MB)-modified and thymine-containing linear DNA probe. Similar to the linear probe electrochemical DNA sensor, the resultant sensor behaved as a "signal-off" sensor in alternating current voltammetry and cyclic voltammetry. However, depending on the applied frequency or pulse width, the sensor can behave as either a "signal-off" or "signal-on" sensor in square wave voltammetry (SWV) and differential pulse voltammetry (DPV). In SWV, the sensor showed "signal-on" behavior at low frequencies and "signal-off" behavior at high frequencies. In DPV, the sensor showed "signal-off" behavior at short pulse widths and "signal-on" behavior at long pulse widths. Independent of the sensor interrogation technique, the limit of detection was found to be 10nM, with a linear dynamic range between 10nM and 500nM. In addition, the sensor responded to Hg(2+) rather rapidly; majority of the signal change occurred in <20min. Overall, the sensor retains all the characteristics of this class of sensors; it is reagentless, reusable, sensitive, specific and selective. This study also highlights the feasibility of using a MB-modified probe for real-time sensing of Hg(2+), which has not been previously reported. More importantly, the observed "switching" behavior in SWV and DPV is potentially generalizable and should be applicable to most sensors in this class of dynamics-based electrochemical biosensors. Copyright © 2013 Elsevier B.V. All rights reserved.

Numerical study on the maximum small-signal gain coefficient in passively mode-locked fiber lasers

NASA Astrophysics Data System (ADS)

Tang, Xin; Wang, Jian; Chen, Zhaoyang; Lin, Chengyou; Ding, Yingchun

2017-06-01

Ultrashort pulses have been found to have important applications in many fields, such as ultrafast diagnosis, biomedical engineering, and optical imaging. Passively mode-locked fiber lasers have become a tool for generating picosecond and femtosecond pulses. In this paper, the evolution of a picosecond laser pulse in different stable passively mode-locked fiber laser is analyzed using nonlinear Schrödinger equation. Firstly, different mode-locked regimes are calculated with different net cavity dispersion (from -0.3 ps2 to +0.3 ps2 ). Then we calculate the maximum small-signal gain on the different net cavity dispersion conditions, and estimate the pulse width, 3 dB bandwidth and time bandwidth product (TBP) when the small-signal gain coefficient is selected as the maximum value. The results show that the small signal gain coefficient is approximately proportional to the net cavity. Moreover, when the small signal gain coefficient reaches the maximum value, the pulse width of the output pulse and their corresponding TBP show a trend of increase gradually, and 3dB bandwidth shows a trend of increase firstly and then decrease. In addition, in the case that the net dispersion is positive, because of the pulse with quite large frequency chirp, the revolution to dechirp the pulse is researched and the output of the pulse is compressed and its compression ratio reached more than 10 times. The results provide a reference for the optimization of passively mode-locked fiber lasers.

Fiber Bragg grating Fabry-Perot cavity sensor based on pulse laser demodulation technique

NASA Astrophysics Data System (ADS)

Gao, Fangfang; Chen, Jianfeng; Liu, Yunqi; Wang, Tingyun

2011-12-01

We demonstrate a fiber laser sensing technique based on fiber Bragg grating Fabry-Perot (FBG-FP) cavity interrogated by pulsed laser, where short pulses generated from active mode-locked erbium-doped fiber ring laser and current modulated DFB laser are adopted. The modulated laser pulses launched into the FBG-FP cavity produce a group of reflected pulses. The optical loss in the cavity can be determined from the power ratio of the first two pulses reflected from the cavity. This technique does not require high reflectivity FBGs and is immune to the power fluctuation of the light source. Two short pulse laser sources were compared experimentally with each other on pulse width, pulse stability, pulse chirp and sensing efficiency.

Mechanism and influencing factors on critical pulse width of oil-immersed polymer insulators under short pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Liang, E-mail: zhaoliang@ninit.ac.cn; Li, Rui; Zheng, Lei

2015-04-15

The critical pulse width (τ{sub c}) is a pulse width at which the surface flashover threshold (E{sub f}) is equal to the bulk breakdown threshold (E{sub BD}) for liquid-polymer composite insulation systems, which is discovered by Zhao et al. [Annual Report Conference on Electrical Insulation and Dielectric Phenomena (IEEE Dielectrics and Electrical Insulation Society, Shenzhen, China, 2013), Vol. 2, pp. 854–857]. In this paper, the mechanism of τ{sub c} is interpreted in perspective of the threshold and the time delay (t{sub d}) of surface flashover and bulk breakdown, respectively. It is found that two changes appear as the pulse widthmore » decreases which are responsible for the existence of τ{sub c}: (1) E{sub BD} is lower than E{sub f}; (2) t{sub d} of bulk breakdown is shorter than t{sub d} of surface flashover. In addition, factors which have influences on τ{sub c} are investigated, such as the dielectric type, the insulation length, the dielectric thickness, the dielectrics configuration, the pulse number, and the liquid purity. These influences of factors are generalized as three types if τ{sub c} is expected to increase: (1) factors causing E{sub BD} to decrease, such as increasing the pulse number or employing a dielectric of lower E{sub BD}; (2) factors causing E{sub f} to increase, such as complicating the insulator's configuration or increasing the liquid purity; (3) factors causing E{sub BD} and E{sub f} to increase together, but E{sub f} increases faster than E{sub BD}, such as decreasing the dielectric thickness or the insulation length. With the data in references, all the three cases are verified experimentally. In the end, a general method based on τ{sub c} for solid insulation design is presented and the significance of τ{sub c} on solid insulation design and on solid demolition are discussed.« less

Spatial vector soliton and its collisions in isotropic self-defocusing Kerr media.

PubMed

Radhakrishnan, R; Aravinthan, K

2007-06-01

A fairly general form of the two-component (dark-dark) vector one-soliton solution of the integrable coupled nonlinear Schrödinger equation (Manakov model) with self-defocusing nonlinearity is obtained by using the Hirota method. It couples two dark components with the same envelope width, envelope speed, and envelope trough location using two complex arbitrary parameters not only in the envelope amplitude but also in the complex modulation. Although it has the freedom to change its pulse width without affecting its speed, it can also tune its grayness (depth of the pulse relative to background) without disturbing the envelope width and speed. The variations in peak power against the depth of localization of two dark components are investigated with and without a parametric restriction. The collision between many dark-dark vector solitons has also been studied by constructing a multisoliton solution with more free parameters.

Subadditive responses to extremely short blue and green pulsed light on visual evoked potentials, pupillary constriction and electroretinograms.

PubMed

Lee, Soomin; Uchiyama, Yuria; Shimomura, Yoshihiro; Katsuura, Tetsuo

2017-11-17

The simultaneous exposure to blue and green light was reported to result in less melatonin suppression than monochromatic exposure to blue or green light. Here, we conducted an experiment using extremely short blue- and green-pulsed light to examine their visual and nonvisual effects on visual evoked potentials (VEPs), pupillary constriction, electroretinograms (ERGs), and subjective evaluations. Twelve adult male subjects were exposed to three light conditions: blue-pulsed light (2.5-ms pulse width), green-pulsed light (2.5-ms pulse width), and simultaneous blue- and green-pulsed light with white background light. We measured the subject's pupil diameter three times in each condition. Then, after 10 min of rest, the subject was exposed to the same three light conditions. We measured the averaged ERG and VEP during 210 pulsed-light exposures in each condition. We also determined subjective evaluations using a visual analog scale (VAS) method. The pupillary constriction during the simultaneous exposure to blue- and green-pulsed light was significantly lower than that during the blue-pulsed light exposure despite the double irradiance intensity of the combination. We also found that the b/|a| wave of the ERGs during the simultaneous exposure to blue- and green-pulsed light was lower than that during the blue-pulsed light exposure. We confirmed the subadditive response to pulsed light on pupillary constriction and ERG. However, the P100 of the VEPs during the blue-pulsed light were smaller than those during the simultaneous blue- and green-pulsed light and green-pulsed light, indicating that the P100 amplitude might depend on the luminance of light. Our findings demonstrated the effect of the subadditive response to extremely short pulsed light on pupillary constriction and ERG responses. The effects on ipRGCs by the blue-pulsed light exposure are apparently reduced by the simultaneous irradiation of green light. The blue versus yellow (b/y) bipolar cells in the retina might be responsible for this phenomenon.

Temporal complexity in emission from Anderson localized lasers

NASA Astrophysics Data System (ADS)

Kumar, Randhir; Balasubrahmaniyam, M.; Alee, K. Shadak; Mujumdar, Sushil

2017-12-01

Anderson localization lasers exploit resonant cavities formed due to structural disorder. The inherent randomness in the structure of these cavities realizes a probability distribution in all cavity parameters such as quality factors, mode volumes, mode structures, and so on, implying resultant statistical fluctuations in the temporal behavior. Here we provide direct experimental measurements of temporal width distributions of Anderson localization lasing pulses in intrinsically and extrinsically disordered coupled-microresonator arrays. We first illustrate signature exponential decays in the spatial intensity distributions of the lasing modes that quantify their localized character, and then measure the temporal width distributions of the pulsed emission over several configurations. We observe a dependence of temporal widths on the disorder strength, wherein the widths show a single-peaked, left-skewed distribution in extrinsic disorder and a dual-peaked distribution in intrinsic disorder. We propose a model based on coupled rate equations for an emitter and an Anderson cavity with a random mode structure, which gives excellent quantitative and qualitative agreement with the experimental observations. The experimental and theoretical analyses bring to the fore the temporal complexity in Anderson-localization-based lasing systems.

Parallel PWMs Based Fully Digital Transmitter with Wide Carrier Frequency Range

PubMed Central

Zhou, Bo; Zhang, Kun; Zhou, Wenbiao; Zhang, Yanjun; Liu, Dake

2013-01-01

The carrier-frequency (CF) and intermediate-frequency (IF) pulse-width modulators (PWMs) based on delay lines are proposed, where baseband signals are conveyed by both positions and pulse widths or densities of the carrier clock. By combining IF-PWM and precorrected CF-PWM, a fully digital transmitter with unit-delay autocalibration is implemented in 180 nm CMOS for high reconfiguration. The proposed architecture achieves wide CF range of 2 M–1 GHz, high power efficiency of 70%, and low error vector magnitude (EVM) of 3%, with spectrum purity of 20 dB optimized in comparison to the existing designs. PMID:24223503

Sensorless Modeling of Varying Pulse Width Modulator Resolutions in Three-Phase Induction Motors

PubMed Central

Marko, Matthew David; Shevach, Glenn

2017-01-01

A sensorless algorithm was developed to predict rotor speeds in an electric three-phase induction motor. This sensorless model requires a measurement of the stator currents and voltages, and the rotor speed is predicted accurately without any mechanical measurement of the rotor speed. A model of an electric vehicle undergoing acceleration was built, and the sensorless prediction of the simulation rotor speed was determined to be robust even in the presence of fluctuating motor parameters and significant sensor errors. Studies were conducted for varying pulse width modulator resolutions, and the sensorless model was accurate for all resolutions of sinusoidal voltage functions. PMID:28076418

Sensorless Modeling of Varying Pulse Width Modulator Resolutions in Three-Phase Induction Motors.

PubMed

Marko, Matthew David; Shevach, Glenn

2017-01-01

A sensorless algorithm was developed to predict rotor speeds in an electric three-phase induction motor. This sensorless model requires a measurement of the stator currents and voltages, and the rotor speed is predicted accurately without any mechanical measurement of the rotor speed. A model of an electric vehicle undergoing acceleration was built, and the sensorless prediction of the simulation rotor speed was determined to be robust even in the presence of fluctuating motor parameters and significant sensor errors. Studies were conducted for varying pulse width modulator resolutions, and the sensorless model was accurate for all resolutions of sinusoidal voltage functions.

The theory and implementation of a high quality pulse width modulated waveform synthesiser applicable to voltage FED inverters

NASA Astrophysics Data System (ADS)

Lower, Kim Nigel

1985-03-01

Modulation processes associated with the digital implementation of pulse width modulation (PWM) switching strategies were examined. A software package based on a portable turnkey structure is presented. Waveform synthesizer implementation techniques are reviewed. A three phase PWM waveform synthesizer for voltage fed inverters was realized. It is based on a constant carrier frequency of 18 kHz and a regular sample, single edge, asynchronous PWM switching scheme. With high carrier frequencies, it is possible to utilize simple switching strategies and as a consequence, many advantages are highlighted, emphasizing the importance to industrial and office markets.

A comparison of battery testing protocols: Those used by the U.S. advanced battery consortium and those used in China

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robertson, David C.; Christophersen, Jon P.; Bennett, Taylor

Two testing protocols, QC/T 743 and those used by the U.S. Advanced Battery Consortium (USABC), were compared using cells based on LiFePO4/graphite chemistry. Differences in the protocols directly affected the data and the performance decline mechanisms deduced from the data. A change in capacity fade mechanism from linear-with-time to t1/2 was observed when the power density measurement was included in the QC/T 743 testing. The rate of resistance increase was linear with time using both protocols. Overall, the testing protocols produced very similar data when the testing conditions and metrics used to define performance were similar. The choice of depthmore » of discharge and pulse width had a direct effect on estimated cell life. At greater percent depth of discharge (%DOD) and pulse width, the estimated life was shorter that at lower %DOD and shorter pulse width. This indicates that cells which were at the end of life based on the USABC protocol were not at end of life based on the QC/T 743 protocol by a large margin.« less

High power vertical stacked diode laser development using macro-channel water cooling and hard solder bonding technology

NASA Astrophysics Data System (ADS)

Yu, Dongshan; Liang, Xuejie; Wang, Jingwei; Li, Xiaoning; Nie, Zhiqiang; Liu, Xingsheng

2017-02-01

A novel marco channel cooler (MaCC) has been developed for packaging high power diode vertical stacked (HPDL) lasers, which eliminates many of the issues in commercially-available copper micro-channel coolers (MCC). The MaCC coolers, which do not require deionized water as coolant, were carefully designed for compact size and superior thermal dissipation capability. Indium-free packaging technology was adopted throughout product design and fabrication process to minimize the risk of solder electromigration and thermal fatigue at high current density and long pulse width under QCW operation. Single MaCC unit with peak output power of up to 700W/bar at pulse width in microsecond range and 200W/bar at pulse width in millisecond range has been recorded. Characteristic comparison on thermal resistivity, spectrum, near filed and lifetime have been conducted between a MaCC product and its counterpart MCC product. QCW lifetime test (30ms 10Hz, 30% duty cycle) has also been conducted with distilled water as coolant. A vertical 40-MaCC stack product has been fabricated, total output power of 9 kilowatts has been recorded under QCW mode (3ms, 30Hz, 9% duty cycle).

Effect of input signal and filter parameters on patterning effect in a semiconductor optical amplifier

NASA Astrophysics Data System (ADS)

Hussain, Kamal; Pratap Singh, Satya; Kumar Datta, Prasanta

2013-11-01

A numerical investigation is presented to show the dependence of patterning effect (PE) of an amplified signal in a bulk semiconductor optical amplifier (SOA) and an optical bandpass filter based amplifier on various input signal and filter parameters considering both the cases of including and excluding intraband effects in the SOA model. The simulation shows that the variation of PE with input energy has a characteristic nature which is similar for both the cases. However the variation of PE with pulse width is quite different for the two cases, PE being independent of the pulse width when intraband effects are neglected in the model. We find a simple relationship between the PE and the signal pulse width. Using a simple treatment we study the effect of the amplified spontaneous emission (ASE) on PE and find that the ASE has almost no effect on the PE in the range of energy considered here. The optimum filter parameters are determined to obtain an acceptable extinction ratio greater than 10 dB and a PE less than 1 dB for the amplified signal over a wide range of input signal energy and bit-rate.

Laser direct writing (LDW) of magnetic structures

NASA Astrophysics Data System (ADS)

Alasadi, Alaa; Claeyssens, F.; Allwood, D. A.

2018-05-01

Laser direct writing (LDW) has been used to pattern 90nm thick permalloy (Ni81Fe19) into 1-D and 2-D microstructures with strong shape anisotropy. Sub-nanosecond laser pulses were focused with a 0.75 NA lens to a 1.85μm diameter spot, to achieve a fluence of approximately 350 mJ.cm-2 and ablate the permalloy film. Computer-controlled sample scanning then allowed structures to be defined. Scan speeds were controlled to give 30% overlap between successive laser pulses and reduce the extent of width modulation in the final structures. Continuous magnetic wires that adjoined the rest of the film were fabricated with widths from 650 nm - 6.75μm and magneto-optical measurements showed coercivity reducing across this width range from 47 Oe to 11 Oe. Attempts to fabricate wires narrower than 650nm resulted in discontinuities in the wires and a marked decrease in coercivity. This approach is extremely rapid and was carried out in air, at room temperature and with no chemical processing. The 6-kHz laser pulse repetition rate allowed wire arrays across an area of 4 mm x 0.18 mm to be patterned in 85 s.

Pulsed ion beam investigation of the kinetics of surface reactions

NASA Technical Reports Server (NTRS)

Horton, C. C.; Eck, T. G.; Hoffman, R. W.

1989-01-01

Pulsed ion beam measurements of the kinetics of surface reactions are discussed for the case where the width of the ion pulse is comparable to the measured reaction time, but short compared to the time between successive pulses. Theoretical expressions are derived for the time dependence of the ion-induced signals for linear surface reactions. Results are presented for CO emission from surface carbon and CF emission from Teflon induced by oxygen ion bombardment. The strengths and limitations of this technique are described.

Merging magnetic droplets by a magnetic field pulse

NASA Astrophysics Data System (ADS)

Wang, Chengjie; Xiao, Dun; Liu, Yaowen

2018-05-01

Reliable manipulation of magnetic droplets is of immense importance for their applications in spin torque oscillators. Using micromagnetic simulations, we find that the antiphase precession state, which originates in the dynamic dipolar interaction effect, is a favorable stable state for two magnetic droplets nucleated at two identical nano-contacts. A magnetic field pulse can be used to destroy their stability and merge them into a big droplet. The merging process strongly depends on the pulse width as well as the pulse strength.

Effect of idler absorption in pulsed optical parametric oscillators.

PubMed

Rustad, Gunnar; Arisholm, Gunnar; Farsund, Øystein

2011-01-31

Absorption at the idler wavelength in an optical parametric oscillator (OPO) is often considered detrimental. We show through simulations that pulsed OPOs with significant idler absorption can perform better than OPOs with low idler absorption both in terms of conversion efficiency and beam quality. The main reason for this is reduced back conversion. We also show how the beam quality depends on the beam width and pump pulse length, and present scaling relations to use the example simulations for other pulsed nanosecond OPOs.

Design and development of line type modulators for high impedance electron gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dixit, Kavita P.; Tillu, Abhijit; Chavan, Ramchandra

Conventional line type modulators are routinely used for powering pulsed power microwave devices such as magnetrons and klystrons used for radar, medical and scientific applications. The load impedance (operating point) is fairly well defined in these cases, and makes the design of the discharging circuit of the modulator straight forward. This paper describes the Line type modulators that have been developed and being routinely used for powering the Triode Electron Gun of industrial electron linacs. The beam parameters of such guns are user defined and the pulse current varies from few mA to 800mA (typ). The beam energies requirement variesmore » from 40 keV to 80 keV. Hence the impedance offered by the electron gun to the power source (modulator) is not well defined. The load capacitance which is inclusive of the various stray capacitances along with the intrinsic gun capacitance is ∼ 200-400 pF. This capacitance, which depends on the configuration, shunts the load and makes the effective load highly capacitive with the resistive part varying over a wide range. The paper describes the design and development of conventional line type modulators for powering Electron gun load of the type described above. (author)« less

Design of an RF System for Electron Bernstein Wave Studies in MST

NASA Astrophysics Data System (ADS)

Kauffold, J. X.; Seltzman, A. H.; Anderson, J. K.; Nonn, P. D.; Forest, C. B.

2010-11-01

Motivated by the possibility of current profile control a 5.5GHz RF system for EBW is being developed. The central component is a standard radar Klystron with 1.2MW peak power and 4μs typical pulse length. Meaningful experiments require RF pulse lengths similar to the characteristic electron confinement times in MST necessitating the creation of a power supply providing 80kV at 40A for 10ms. A low inductance IGBT network switches power at 20kHz from an electrolytic capacitor bank into the primary of a three-phase resonant transformer system that is then rectified and filtered. The system uses three magnetically separate transformers with microcrystalline iron cores to provide suitable volt-seconds and low hysteresis losses. Each phase has a secondary with a large leakage inductance and a parallel capacitor providing a boost ratio greater than 60:1 with a physical turns ratio of 13.5:1. A microprocessor feedback control system varies the drive frequency around resonance to regulate the boost ratio and provide a stable output as the storage bank discharges. The completed system will deliver RF to the plasma boundary where coupling to the Bernstein mode and subsequent heating and current drive can occur.

Computer simulation of electron flow in linear-beam microwave tubes

NASA Astrophysics Data System (ADS)

Kumar, Lalit

1990-12-01

The computer simulation of electron flow in linear-beam microwave tubes, such as a travelling-wave tube (TWT) and klystron, is used for designing and optimising the electron gun and collector and for analysing the large-signal beam-wave interaction phenomenon. Major aspects of simulation of electron flow in static and rf fields present in such tubes are discussed. Some advancements made in this respect and results obtained from computer programs developed by the research group at CEERI for a gridded electron gun, depressed collector, and large-signal analysis of TWT and klystron are presented.

Design of a New Water Load for S-band 750 kW Continuous Wave High Power Klystron Used in EAST Tokamak

NASA Astrophysics Data System (ADS)

Liu, Liang; Liu, Fukun; Shan, Jiafang; Kuang, Guangli

2007-04-01

In order to test the klystrons operated at a frequency of 3.7 GHz in a continuous wave (CW) mode, a type of water load to absorb its power up to 750 kW is presented. The distilled water sealed with an RF ceramic window is used as the absorbent. At a frequency range of 70 MHz, the VSWR (Voltage Standing Wave Ratio) is below 1.2, and the rise in temperature of water is about 30 oC at the highest power level.

A novel technique for tuning of co-axial cavity of multi-beam klystron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saha, Sukalyan, E-mail: sstechno18@gmail.com; Bandyopadhyay, Ayan Kumar; Pal, Debashis

2016-03-09

Multi-beam Klystrons (MBKs) have gained wide acceptances in the research sector for its inherent advantages. But developing a robust tuning technique for an MBK cavity of coaxial type has still remained a challenge as these designs are very prone to suffer from asymmetric field distribution with inductive tuning of the cavity. Such asymmetry leads to inhomogeneous beam-wave interaction, an undesirable phenomenon. Described herein is a new type of coaxial cavity that has the ability to suppress the asymmetry, thereby allowing tuning of the cavity with a single tuning post.

Giant Pulses from PSR B1937+21 with Widths <=15 Nanoseconds and Tb>=5×1039 K, the Highest Brightness Temperature Observed in the Universe

NASA Astrophysics Data System (ADS)

Soglasnov, V. A.; Popov, M. V.; Bartel, N.; Cannon, W.; Novikov, A. Yu.; Kondratiev, V. I.; Altunin, V. I.

2004-11-01

Giant radio pulses of the millisecond pulsar B1937+21 were recorded with the S2 VLBI system at 1.65 GHz with NASA/JPL's 70 m radio telescope at Tidbinbilla, Australia. These pulses have been observed as strong as 65,000 Jy with widths <=15 ns, corresponding to a brightness temperature of Tb>=5×1039 K, the highest observed in the universe. The vast majority of these pulses occur in 5.8 and 8.2 μs windows at the very trailing edges of the regular main pulse and interpulse profiles, respectively. Giant pulses occur, in general, with a single spike. Only in one case of 309 was the structure clearly more complex. The cumulative distribution is fitted by a power law with index -1.40+/-0.01 with a low-energy but no high-energy cutoff. We estimate that giant pulses occur frequently but are only rarely detected. When corrected for the directivity factor, 25 giant pulses are estimated to be generated in one neutron star revolution alone. The intensities of the giant pulses of the main pulses and interpulses are not correlated with each other nor with the intensities or energies of the main pulses and interpulses themselves. Their radiation energy density can exceed 300 times the plasma energy density at the surface of the neutron star and can even exceed the magnetic field energy density at that surface. We therefore do not think that the generation of giant pulses is linked to the plasma mechanisms in the magnetosphere. Instead we suggest that it is directly related to discharges in the polar cap region of the pulsar.

Adaptive Phase Delay Generator

NASA Technical Reports Server (NTRS)

Greer, Lawrence

2013-01-01

There are several experimental setups involving rotating machinery that require some form of synchronization. The adaptive phase delay generator (APDG) the Bencic-1000 is a flexible instrument that allows the user to generate pulses synchronized to the rising edge of a tachometer signal from any piece of rotating machinery. These synchronized pulses can vary by the delay angle, pulse width, number of pulses per period, number of skipped pulses, and total number of pulses. Due to the design of the pulse generator, any and all of these parameters can be changed independently, yielding an unparalleled level of versatility. There are two user interfaces to the APDG. The first is a LabVIEW program that has the advantage of displaying all of the pulse parameters and input signal data within one neatly organized window on the PC monitor. Furthermore, the LabVIEW interface plots the rpm of the two input signal channels in real time. The second user interface is a handheld portable device that goes anywhere a computer is not accessible. It consists of a liquid-crystal display and keypad, which enable the user to control the unit by scrolling through a host of command menus and parameter listings. The APDG combines all of the desired synchronization control into one unit. The experimenter can adjust the delay, pulse width, pulse count, number of skipped pulses, and produce a specified number of pulses per revolution. Each of these parameters can be changed independently, providing an unparalleled level of versatility when synchronizing hardware to a host of rotating machinery. The APDG allows experimenters to set up quickly and generate a host of synchronizing configurations using a simple user interface, which hopefully leads to faster results.

Phase coded, micro-power impulse radar motion sensor

DOEpatents

McEwan, Thomas E.

1996-01-01

A motion sensing, micro-power impulse radar MIR impresses on the transmitted signal, or the received pulse timing signal, one or more frequencies lower than the pulse repetition frequency, that become intermediate frequencies in a "IF homodyne" receiver. Thus, many advantages of classical RF receivers can be thereby be realized with ultra-wide band radar. The sensor includes a transmitter which transmits a sequence of electromagnetic pulses in response to a transmit timing signal at a nominal pulse repetition frequency. A receiver samples echoes of the sequence of electromagnetic pulses from objects within the field with controlled timing, in response to a receive timing signal, and generates a sample signal in response to the samples. A timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver. The relative timing of the transmit timing signal and the receive timing signal is modulated between a first relative delay and a second relative delay at an intermediate frequency, causing the receiver to sample the echoes such that the time between transmissions of pulses in the sequence and samples by the receiver is modulated at the intermediate frequency. Modulation may be executed by modulating the pulse repetition frequency which drives the transmitter, by modulating the delay circuitry which controls the relative timing of the sample strobe, or by modulating amplitude of the transmitted pulses. The electromagnetic pulses will have a nominal center frequency related to pulse width, and the first relative delay and the second relative delay between which the timing signals are modulated, differ by less than the nominal pulse width, and preferably by about one-quarter wavelength at the nominal center frequency of the transmitted pulses.

Phase coded, micro-power impulse radar motion sensor

DOEpatents

McEwan, T.E.

1996-05-21

A motion sensing, micro-power impulse radar MIR impresses on the transmitted signal, or the received pulse timing signal, one or more frequencies lower than the pulse repetition frequency, that become intermediate frequencies in a ``IF homodyne`` receiver. Thus, many advantages of classical RF receivers can be thereby be realized with ultra-wide band radar. The sensor includes a transmitter which transmits a sequence of electromagnetic pulses in response to a transmit timing signal at a nominal pulse repetition frequency. A receiver samples echoes of the sequence of electromagnetic pulses from objects within the field with controlled timing, in response to a receive timing signal, and generates a sample signal in response to the samples. A timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver. The relative timing of the transmit timing signal and the receive timing signal is modulated between a first relative delay and a second relative delay at an intermediate frequency, causing the receiver to sample the echoes such that the time between transmissions of pulses in the sequence and samples by the receiver is modulated at the intermediate frequency. Modulation may be executed by modulating the pulse repetition frequency which drives the transmitter, by modulating the delay circuitry which controls the relative timing of the sample strobe, or by modulating amplitude of the transmitted pulses. The electromagnetic pulses will have a nominal center frequency related to pulse width, and the first relative delay and the second relative delay between which the timing signals are modulated, differ by less than the nominal pulse width, and preferably by about one-quarter wavelength at the nominal center frequency of the transmitted pulses. 5 figs.

Long-Lag, Wide-pulse Gamma-Ray Bursts

NASA Technical Reports Server (NTRS)

Norris, J. P.; Bonnell, J. T.; Kazanas, D.; Scargle, . D.; Hakkila, J.; Giblin, T. W.

2004-01-01

Currently, the best available probe of the early phase of gamma-ray burst (GRB) jet attributes is the prompt gamma-ray emission, in which several intrinsic and extrinsic variables determine GRB pulse evolution. Bright, usually complex bursts have many narrow pulses that are difficult to model due to overlap. However, the relatively simple, long spectral lag, wide-pulse bursts may have simpler physics and are easier to model. In this work we analyze the temporal and spectral behavior of wide pulses in 24 long-lag bursts, using a pulse model with two shape parameters - width and asymmetry - and the Band spectral model with three shape parameters. We find that pulses in long-lag bursts are distinguished both temporally and spectrally from those in bright bursts: the pulses in long spectral lag bursts are few in number, and approximately 100 times wider (10s of seconds), have systematically lower peaks in vF(v), harder low-energy spectra and softer high-energy spectra. We find that these five pulse descriptors are essentially uncorrelated for our long-lag sample, suggesting that at least approximately 5 parameters are needed to model burst temporal and spectral behavior. However, pulse width is strongly correlated with spectral lag; hence these two parameters may be viewed as mutual surrogates. We infer that accurate formulations for estimating GRB luminosity and total energy will depend on several gamma-ray attributes, at least for long-lag bursts. The prevalence of long-lag bursts near the BATSE trigger threshold, their predominantly low vF(v) spectral peaks, and relatively steep upper power-law spectral indices indicate that Swift will detect many such bursts.

Comparison of Single-Event Transients Induced in an Operational Amplifier (LM124) by Pulsed Laser Light and a Broad Beam of Heavy Ions

NASA Technical Reports Server (NTRS)

Buchner, Steve; McMorrow, Dale; Poivey, Christian; Howard, James, Jr.; Pease, Rom; Savage, Mark; Boulghassoul, Younis; Massengill, Lloyd

2003-01-01

A comparison of transients from heavy-ion and pulsed-laser testing shows good agreement for many different voltage configurations. The agreement is illustrated by comparing directly individual transients and plots of transient amplitude versus width.

Modeling transient gain dynamics in a cladding-pumped Yb-doped fiber ampliefier pulsed at low repetition rates

NASA Technical Reports Server (NTRS)

Valley, G. C.; Wright, M.

2001-01-01

Simulations of 1-50 kHz repetition rate, pulsed Yb-fiber amplifiers show peak powers to 10 kW with half-widths < 30 ns, consistent with commercial amplifier performance. This device is a potential source for deep space-communication.

Quickbird Satellite in-orbit Modulation Transfer Function (MTF) Measurement Using Edge, Pulse and Impulse Methods for Summer 2003

NASA Technical Reports Server (NTRS)

Helder, Dennis; Choi, Taeyoung; Rangaswamy, Manjunath

2005-01-01

The spatial characteristics of an imaging system cannot be expressed by a single number or simple statement. However, the Modulation Transfer Function (MTF) is one approach to measure the spatial quality of an imaging system. Basically, MTF is the normalized spatial frequency response of an imaging system. The frequency response of the system can be evaluated by applying an impulse input. The resulting impulse response is termed the Point Spread function (PSF). This function is a measure of the amount of blurring present in the imaging system and is itself a useful measure of spatial quality. An underlying assumption is that the imaging system is linear and shift-independent. The Fourier transform of the PSF is called the Optical Transfer Function (OTF) and the normalized magnitude of the OTF is the MTF. In addition to using an impulse input, a knife-edge in technique has also been used in this project. The sharp edge exercises an imaging system at all spatial frequencies. The profile of an edge response from an imaging system is called an Edge Spread Function (ESF). Differentiation of the ESF results in a one-dimensional version of the Point Spread Function (PSF). Finally, MTF can be calculated through use of Fourier transform of the PSF as stated previously. Every image includes noise in some degree which makes MTF of PSF estimation more difficult. To avoid the noise effects, many MTF estimation approaches use smooth numerical models. Historically, Gaussian models and Fermi functions were applied to reduce the random noise in the output profiles. The pulse-input method was used to measure the MTF of the Landsat Thematic Mapper (TM) using 8th order even functions over the San Mateo Bridge in San Francisco, California. Because the bridge width was smaller than the 30-meter ground sample distance (GSD) of the TM, the Nyquist frequency was located before the first zero-crossing point of the sinc function from the Fourier transformation of the bridge pulse. To avoid the zero-crossing points in the frequency domain from a pulse, the pulse width should be less than the width of two pixels (or 2 GSD's), but the short extent of the pulse results in a poor signal-to-noise ratio. Similarly, for a high-resolution satellite imaging system such as Quickbird, the input pulse width was critical because of the zero crossing points and noise present in the background area. It is important, therefore, that the width of the input pulse be appropriately sized. Finally, the MTF was calculated by taking ratio between Fourier transform of output and Fourier transform of input. Regardless of whether the edge, pulse and impulse target method is used, the orientation of the targets is critical in order to obtain uniformly spaced sub-pixel data points. When the orientation is incorrect, sample data points tend to be located in clusters that result in poor reconstruction of the edge or pulse profiles. Thus, a compromise orientation must be selected so that all spectral bands can be accommodated. This report continues by outlining the objectives in Section 2, procedures followed in Section 3, descriptions of the field campaigns in Section 4, results in Section 5, and a brief summary in Section 6.

All solid-state high power microwave source with high repetition frequency.

PubMed

Bragg, J-W B; Sullivan, W W; Mauch, D; Neuber, A A; Dickens, J C

2013-05-01

An all solid-state, megawatt-class high power microwave system featuring a silicon carbide (SiC) photoconductive semiconductor switch (PCSS) and a ferrimagnetic-based, coaxial nonlinear transmission line (NLTL) is presented. A 1.62 cm(2), 50 kV 4H-SiC PCSS is hard-switched to produce electrical pulses with 7 ns full width-half max (FWHM) pulse widths at 2 ns risetimes in single shot and burst-mode operation. The PCSS resistance drops to sub-ohm when illuminated with approximately 3 mJ of laser energy at 355 nm (tripled Nd:YAG) in a single pulse. Utilizing a fiber optic based optical delivery system, a laser pulse train of four 7 ns (FWHM) signals was generated at 65 MHz repetition frequency. The resulting electrical pulse train from the PCSS closely follows the optical input and is utilized to feed the NLTL generating microwave pulses with a base microwave-frequency of about 2.1 GHz at 65 MHz pulse repetition frequency (prf). Under typical experimental conditions, the NLTL produces sharpened output risetimes of 120 ps and microwave oscillations at 2-4 GHz that are generated due to damped gyromagnetic precession of the ferrimagnetic material's axially pre-biased magnetic moments. The complete system is discussed in detail with its output matched into 50 Ω, and results covering MHz-prf in burst-mode operation as well as frequency agility in single shot operation are discussed.

1164.4  nm and 1174.7  nm dual-wavelength Nd : GdVO4/Cr4+ : YAG/YVO4 passively Q-switched Raman microchip laser.

PubMed

Wang, Xiaojie; Wang, Xiaolei; Zheng, Zhifen; Qiao, Xihao; Dong, Jun

2018-04-20

A synchronous pulsed, dual-wavelength Raman laser at 1164.4 nm and 1174.7 nm has been demonstrated in a Nd:GdVO 4 /Cr 4+ :YAG/YVO 4 passively Q-switched Raman microchip laser (PQSRML). The 1164.4 nm and 1174.7 nm dual-wavelength first-order Stokes laser oscillation is attributed to the conversion of the 1063.2 nm and 1063.43 nm two-longitudinal-mode fundamental lasers with Raman frequency shifts of 816  cm -1 and 890  cm -1 , respectively. Stable dual-wavelength Raman laser pulses with nearly equal spectral intensities have been achieved independent of the pump power. A pulse repetition rate as high as 139.4 kHz has been achieved with T 0 =85%, and the pulse width has been shortened to 825 ps with T 0 =70%. A dual-wavelength Raman laser with sub-nanosecond pulse width and peak power of over 1 kW has been achieved in the Nd:GdVO 4 /Cr 4+ :YAG/YVO 4 PQSRML.

Slow positron applications at slow positron facility of institute of materials structure science, KEK

NASA Astrophysics Data System (ADS)

Hyodo, Toshio; Mochizuki, Izumi; Wada, Ken; Toge, Nobukazu; Shidara, Tetsuo

2018-05-01

Slow Positron Facility at High Energy Accelerator Research Organization (KEK) is a user dedicated facility with an energy-tunable (0.1 - 35 keV) slow positron beam created by a dedicated ˜ 50 MeV linac. It operates in a short pulse (width 1-12 ns, variable, 5×106 e+/s) and a long pulse (width 1.2 µs, 5×107 e+/s) modes of 50 Hz. High energy positrons from pair creation are moderated by reemission after thermalization in W foils. The reemitted positrons are then electrostatically accelerated to a desired energy up to 35 keV and magnetically transported. A pulse-stretching section (pulse stretcher) is installed in the middle of the beamline. It stretches the slow positron pulse for the experiments where too many positrons annihilating in the sample at the same time has to be avoided. Four experiment stations for TRHEPD (total-reflection high-energy positron diffraction), LEPD (low-energy positron diffraction), Ps- (positronium negative ion), and Ps-TOF (positronium time-of-flight) experiments are connected to the beamline branches, SPF-A3, SPF-A4, SPF-B1 and SPF-B2, respectively. Recent results of these stations are briefly described.

Influence of Time-Pickoff Circuit Parameters on LiDAR Range Precision

PubMed Central

Wang, Hongming; Yang, Bingwei; Huyan, Jiayue; Xu, Lijun

2017-01-01

A pulsed time-of-flight (TOF) measurement-based Light Detection and Ranging (LiDAR) system is more effective for medium-long range distances. As a key ranging unit, a time-pickoff circuit based on automatic gain control (AGC) and constant fraction discriminator (CFD) is designed to reduce the walk error and the timing jitter for obtaining the accurate time interval. Compared with Cramer–Rao lower bound (CRLB) and the estimation of the timing jitter, four parameters-based Monte Carlo simulations are established to show how the range precision is influenced by the parameters, including pulse amplitude, pulse width, attenuation fraction and delay time of the CFD. Experiments were carried out to verify the relationship between the range precision and three of the parameters, exclusing pulse width. It can be concluded that two parameters of the ranging circuit (attenuation fraction and delay time) were selected according to the ranging performance of the minimum pulse amplitude. The attenuation fraction should be selected in the range from 0.2 to 0.6 to achieve high range precision. The selection criterion of the time-pickoff circuit parameters is helpful for the ranging circuit design of TOF LiDAR system. PMID:29039772

Frequency-doubled DBR-tapered diode laser for direct pumping of Ti:sapphire lasers generating sub-20 fs pulses.

PubMed

Müller, André; Jensen, Ole Bjarlin; Unterhuber, Angelika; Le, Tuan; Stingl, Andreas; Hasler, Karl-Heinz; Sumpf, Bernd; Erbert, Götz; Andersen, Peter E; Petersen, Paul Michael

2011-06-20

For the first time a single-pass frequency doubled DBR-tapered diode laser suitable for pumping Ti:sapphire lasers generating ultrashort pulses is demonstrated. The maximum output powers achieved when pumping the Ti:sapphire laser are 110 mW (CW) and 82 mW (mode-locked) respectively at 1.2 W of pump power. This corresponds to a reduction in optical conversion efficiencies to 75% of the values achieved with a commercial diode pumped solid-state laser. However, the superior electro-optical efficiency of the diode laser improves the overall efficiency of the Ti:sapphire laser by a factor > 2. The optical spectrum emitted by the Ti:sapphire laser when pumped with our diode laser shows a spectral width of 112 nm (FWHM). Based on autocorrelation measurements, pulse widths of less than 20 fs can therefore be expected.

Picosecond laser system with 30-W average power via cavity dumping and amplifying

NASA Astrophysics Data System (ADS)

Fu, J.; Pang, Q. S.; Chang, L.; Bai, Z. A.; Ai, Q. K.; Chen, L. Y.; Chen, M.; Li, G.; Ma, Y. F.; Fan, Z. W.; Niu, G.; Yu, J.; Liu, Y.; Zhang, X.; Kang, W. Y.; He, K.

2011-06-01

We present a picosecond laser system with high energy by technologies of cavity dumping and amplifying. Firstly, pulses with 10 ps and ˜520 nJ were obtained by cavity-dumped mode-locked laser at 10 kHz repetition rate. Secondly those pulses were seeded into a side-pumped regenerative amplifier (RA). Then pulses output from the regenerative amplifier were amplified by two four-pass post amplifiers. From the laser system pulses with an average power of 30 W corresponding to 3 mJ pulse energy were achieved with the pulse-width of 25.4 ps at repetition rate of 10 kHz.

Ultrafocused Electromagnetic Field Pulses with a Hollow Cylindrical Waveguide

NASA Astrophysics Data System (ADS)

Maurer, P.; Prat-Camps, J.; Cirac, J. I.; Hänsch, T. W.; Romero-Isart, O.

2017-07-01

We theoretically show that a dipole externally driven by a pulse with a lower-bounded temporal width, and placed inside a cylindrical hollow waveguide, can generate a train of arbitrarily short and focused electromagnetic pulses. The waveguide encloses vacuum with perfect electric conducting walls. A dipole driven by a single short pulse, which is properly engineered to exploit the linear spectral filtering of the cylindrical hollow waveguide, excites longitudinal waveguide modes that are coherently refocused at some particular instances of time, thereby producing arbitrarily short and focused electromagnetic pulses. We numerically show that such ultrafocused pulses persist outside the cylindrical waveguide at distances comparable to its radius.

Compressed 6 ps pulse in nonlinear amplification of a Q-switched microchip laser

NASA Astrophysics Data System (ADS)

Diao, Ruxin; Liu, Zuosheng; Niu, Fuzeng; Wang, Aimin; Taira, Takunori; Zhang, Zhigang

2017-02-01

We present a passively Q-switched Nd:YVO4 crystal microchip laser with a 6 ps pulse width, which is based on SPM-induced spectral broadening and pulse compression. The passive Q-switching is obtained by a semiconductor saturable absorber mirror. The laser’s seed source centered at 1064 nm pulses with a duration of 80 ps, at a repetition rate of 600 kHz corresponding to an average output power of 10 mW. After amplification and compression, the pulses were compressed to 6 ps with a maximum pulse energy of 0.5 µJ.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulmer, W

Purpose: During the past decade the quantization of coupled/forced electromagnetic circuits with or without Ohm’s resistance has gained the subject of some fundamental studies, since even problems of quantum electrodynamics can be solved in an elegant manner, e.g. the creation of quantized electromagnetic fields. In this communication, we shall use these principles to describe optimization procedures in the design of klystrons, synchrotron irradiation and high energy bremsstrahlung. Methods: The base is the Hamiltonian of an electromagnetic circuit and the extension to coupled circuits, which allow the study of symmetries and perturbed symmetries in a very apparent way (SU2, SU3, SU4).more » The introduction resistance and forced oscillators for the emission and absorption in such coupled systems provides characteristic resonance conditions, and atomic orbitals can be described by that. The extension to virtual orbitals leads to creation of bremsstrahlung, if the incident electron (velocity v nearly c) is described by a current, which is associated with its inductivitance and the virtual orbital to the charge distribution (capacitance). Coupled systems with forced oscillators can be used to amplify drastically the resonance frequencies to describe klystrons and synchrotron radiation. Results: The cross-section formula for bremsstrahlung given by the propagator method of Feynman can readily be derived. The design of klystrons and synchrotrons inclusive the radiation outcome can be described and optimized by the determination of the mutual magnetic couplings between the oscillators induced by the currents. Conclusions: The presented methods of quantization of circuits inclusive resistance provide rather a straightforward way to understand complex technical processes such as creation of bremsstrahlung or creation of radiation by klystrons and synchrotrons. They can either be used for optimization procedures and, last but not least, for pedagogical purposes with regard to a qualified understanding of radiation physics for students.« less

Development of a Flow Visualization Technique for Transient Fluid Flow

DTIC Science & Technology

1992-12-31

high repetition rates, 2 to 10 kHz. The CW laser with a chopper wheel is limited to 4 kHz with a relatively large pulse width of 125 microseconds. The... four data points are in one CRAY word *I I* print«" bufloop %d width %d bufbytes %d image offset %ld xoffset %d \

Synthesis of ultrawideband radiation of combined antenna arrays excited by nanosecond bipolar voltage pulses

NASA Astrophysics Data System (ADS)

Koshelev, V. I.; Plisko, V. V.; Sevostyanov, E. A.

2017-05-01

To broaden the spectrum of high-power ultrawideband radiation, it is suggested to synthesize an electromagnetic pulse summing the pulses of different length in free space. On the example of model pulses corresponding to radiation of combined antennas excited by bipolar voltage pulses of the length of 2 and 3 ns, the possibility of twofold broadening of the radiation spectrum was demonstrated. Radiation pulses with the spectrum width exceeding three octaves were obtained. Pattern formation by the arrays of different geometry excited by the pulses having different time shifts was considered. Optimum array structure with the pattern maximum in the main direction was demonstrated on the example of a 2×2 array.

Random pulse generator

NASA Technical Reports Server (NTRS)

Lindsey, R. S., Jr. (Inventor)

1975-01-01

An exemplary embodiment of the present invention provides a source of random width and random spaced rectangular voltage pulses whose mean or average frequency of operation is controllable within prescribed limits of about 10 hertz to 1 megahertz. A pair of thin-film metal resistors are used to provide a differential white noise voltage pulse source. Pulse shaping and amplification circuitry provide relatively short duration pulses of constant amplitude which are applied to anti-bounce logic circuitry to prevent ringing effects. The pulse outputs from the anti-bounce circuits are then used to control two one-shot multivibrators whose output comprises the random length and random spaced rectangular pulses. Means are provided for monitoring, calibrating and evaluating the relative randomness of the generator.

CO2-Tea pulse clipping using pulsed high voltage preionization for high spatial resolution I.R. Lidar systems

NASA Astrophysics Data System (ADS)

Gasmi, Taieb

2018-04-01

An extra-cavity CO2-TEA laser pulse clipper for high spatial resolution atmospheric monitoring is presented. The clipper uses pulsed high voltageto facilitate the breakdown of the gas within the clipper cell. Complete extinction of the nitrogen tail, that degrades the range resolution of LIDARS, is obtained at pressures from 375 up to 1500 Torr for nitrogen and argon gases whereas an attenuation coefficient of almost 102 is achieved for helium. Excellent energy stability and pulse width repeatability were achieved using high voltage pre-ionized gas technique.

Femtosecond laser pulse distortion in Ti:sapphire multipass amplifier by atomic phase shifts

NASA Astrophysics Data System (ADS)

Hwang, Seungjin; Jeong, Jihoon; Cho, Seryeyohan; Lee, Jongmin; Yu, Tae Jun

2017-11-01

We have derived modified Frantz-Nodvik equations that simultaneously account for atomic phase shift (APS) and gain depletion as the chirped laser pulse passes through a gain medium, and have analyzed the effect of temporal pulse distortion in a Ti:sapphire multipass amplifier chain. The combination of APS and gain depletion distorted a temporal pulse and decreased the peak power. The pulse width increased from 21.3 fs to 22.8 fs and the peak power reduced to 89% for the PW class Ti:sapphire CPA laser system in the particular conditions.

Study of Storage Ring Free-Electron Laser Using Experimental and Simulation Approaches

NASA Astrophysics Data System (ADS)

Jia, Botao

2011-12-01

The Duke electron storage ring, first commissioned in November of 1994, has been developed as a dedicated driver for storage ring free-electron lasers (SRFELs) operating in a wide wavelength range from infrared, to visible, to ultraviolet (UV) and vacuum ultraviolet (VUV). The storage ring has a long straight section for various insertion devices and can be operated in a wide energy range (0.25 GeV to 1.15 GeV). Commissioned in 1995, the first free-electron laser (FEL) on the Duke storage ring was the OK-4 FEL, an optical klystron with two planar undulators sandwiching a buncher magnet. In 2005, the OK-5 FEL with two helical undulators was commissioned. Operating four undulators---two OK-4 and two OK-5 undulators, the world's first distributed optical klystron FEL was brought to operation in 2005. Via Compton scattering of FEL photons and electrons in the storage ring, the Duke FEL drives the world's most powerful, nearly monochromatic, and polarized Compton gamma-ray source, the High Intensity Gamma-ray Source (HIgammaS). Today, a variety of configurations of the storage ring FELs at Duke have been used in a wide range of research areas from nuclear physics to biophysics, from chemical and medical research to industrial applications. The capability of accurately measuring the storage ring electron beam energy spread is crucial for understanding the longitudinal beam dynamics and the dynamics of the storage ring FEL. In this dissertation, we have successfully developed a noninvasive, versatile, and accurate method to measure the energy spread using optical klystron radiation. Novel numerical methods based upon the Gauss-Hermite expansion have been developed to treat both spectral broadening and modulation on an equal footing. Through properly configuring the optical klystron, this energy spread measurement method has a large dynamic range. In addition, a model-based scheme has been developed for correcting the electron beam emittance related inhomogeneous spectral broadening effect, to further enhance the accuracy of measuring the electron beam energy spread. Taking advantage of the direct measurement method of the electron beam energy spread, we have developed another novel technique to simultaneously measure the FEL power, electron beam energy spread, and other beam parameters. This allowed us to study the FEL power in a systematic manner for the first time. Based on the experimental findings and results of the theoretical predictions, we have proposed a compact formula to predict the FEL power using only the knowledge of electron beam current, beam energy, and bunch length. As part of the dissertation work, we have developed a self-consistent numerical model to study the storage ring FEL. The simulation program models the electron beam propagation along the storage ring, multi-turn FEL interaction in the undulators, gradual intra-cavity optical power buildup, etc. This simulation code captures the main features of a storage ring FEL at different time and space scales. The simulated FEL gain has been benchmarked against measured gain and calculated gain with good agreement. The simulation package can provide comprehensive information about the FEL gain, optical pulse growth, electron beam properties, etc. In the near future, we plan to further improve the simulation model, by including additional physics effects such as microwave instability, to make it a more useful tool for FEL research.

Optimal pulse design for communication-oriented slow-light pulse detection.

PubMed

Stenner, Michael D; Neifeld, Mark A

2008-01-21

We present techniques for designing pulses for linear slow-light delay systems which are optimal in the sense that they maximize the signal-to-noise ratio (SNR) and signal-to-noise-plus-interference ratio (SNIR) of the detected pulse energy. Given a communication model in which input pulses are created in a finite temporal window and output pulse energy in measured in a temporally-offset output window, the SNIR-optimal pulses achieve typical improvements of 10 dB compared to traditional pulse shapes for a given output window offset. Alternatively, for fixed SNR or SNIR, window offset (detection delay) can be increased by 0.3 times the window width. This approach also invites a communication-based model for delay and signal fidelity.

Secure distance ranging by electronic means

DOEpatents

Gritton, Dale G.

1992-01-01

A system for secure distance ranging between a reader 11 and a tag 12 wherein the distance between the two is determined by the time it takes to propagate a signal from the reader to the tag and for a responsive signal to return, and in which such time is random and unpredictable, except to the reader, even though the distance between the reader and tag remains the same. A random number (19) is sent from the reader and encrypted (26) by the tag into a number having 16 segments of 4 bits each (28). A first tag signal (31) is sent after such encryption. In response, a random width start pulse (13) is generated by the reader. When received in the tag, the width of the start pulse is measured (41) in the tag and a segment of the encrypted number is selected (42) in accordance with such width. A second tag pulse is generated at a time T after the start pulse arrives at the tag, the time T being dependent on the length of a variable time delay t.sub.v which is determined by the value of the bits in the selected segment of the encrypted number. At the reader, the total time from the beginning of the start pulse to the receipt of the second tag signal is measured (36, 37). The value of t.sub.v (21, 22, 23, 34) is known at the reader and the time T is subtracted (46) from the total time to find the actual propagation t.sub.p for signals to travel between the reader 11 and tag 12. The propagation time is then converted into distance (46).

Film Implementation of a Neutron Detector (FIND): Critical Materials Properties

DTIC Science & Technology

2007-09-01

In the implementation of the TRR method used initially,2 a pulsed titanium -sapphire laser with a repetition rate of 82 MHz and a pulse width of...for this fluorescence to appear. The carriers are excited by a very short (20 fs) laser pulse generated by a titanium -sapphire laser oscillator...were made using the following methods: • Lifetime: time-resolved (pump-probe) reflectivity method with dual fiber laser system • Mobility: free

Generating nonlinear FM chirp radar signals by multiple integrations

DOEpatents

Doerry, Armin W [Albuquerque, NM

2011-02-01

A phase component of a nonlinear frequency modulated (NLFM) chirp radar pulse can be produced by performing digital integration operations over a time interval defined by the pulse width. Each digital integration operation includes applying to a respectively corresponding input parameter value a respectively corresponding number of instances of digital integration.

Applications of Pulsed Power in Advanced Oxidation and Reduction Processes for Pollution Control

DTIC Science & Technology

1993-06-01

electrical driver pulse width and rise time, electrical drive circuit coupling to plasma cells, and the role of UV light in the plasma chemistry and...will permit industrial service. Basic understanding of the plasma chemistry has evolved to the point where trends and equipment scaling can be

Passively Q-switched of EDFL employing multi-walled carbon nanotubes with diameter less than 8 nm as saturable absorber

NASA Astrophysics Data System (ADS)

Nur Fatin Zuikafly, Siti; Ahmad, Fauzan; Haniff Ibrahim, Mohd; Wadi Harun, Sulaiman

2017-11-01

The paper demonstrates passively Q-switched erbium-doped fiber laser implementing multiwalled carbon nanotubes (MWCNTs) based saturable absorber. The paper is the first to report the use of the MWCNTs with diameter less than 8 nm as typically, the diameter used is 10 to 20 nm. The MWCNTs is incorporated with water soluble host polymer, polyvinyl alcohol (PVA) to produce a MWCNTs polymer composite thin film which is then sandwiched between two fiber connectors. The fabricated SA is employed in the laser experimental setup in ring cavity. The Q-switching regime started at threshold pump power of 103 mW and increasable to 215 mW. The stable pulse train from 41.6 kHz to 76.92 kHz with maximum average output power and pulse energy of 0.17 mW and 3.39 nJ are produced. The shortest pulse width of 1.9 μs is obtained in the proposed experimental work, making it the lowest pulse width ever reported using MWCNTs-based saturable absorber.

Highly-nonlinear polarization-maintaining As2Se3-based photonic quasi-crystal fiber for supercontinuum generation

NASA Astrophysics Data System (ADS)

Zhao, Tongtong; Lian, Zhenggang; Benson, Trevor; Wang, Xin; Zhang, Wan; Lou, Shuqin

2017-11-01

We propose an As2Se3-based photonic quasi-crystal fiber (PQF) with high nonlinearity and birefringence. By optimizing the structure parameters, a nonlinear coefficient up to 2079 W-1km-1 can be achieved at the wavelength of 2 μm; the birefringence reaches up to the order of 10-2 due to the introduction of large circular air holes in the cladding. Using an optical pulse with a peak power of 6 kW, a pulse width of 150 fs, and a central wavelength of 2.94 μm as the pump pulse, a mid-infrared polarized supercontinuum is obtained by using a 15 mm long PQF. The spectral width for x- and y-polarizations covers 1 μm-10.2 μm and 1 μm-12.5 μm, respectively. The polarization state can be well maintained when the incident angle of the input pulse changes within ±2°. The proposed PQF, with high nonlinear coefficient and birefringence, has potential applications in mid-infrared polarization-maintaining supercontinuum generation.

Evaluation of the shock-wave pattern for endoscopic electrohydraulic lithotripsy.

PubMed

Vorreuther, R; Engelmann, Y

1995-01-01

We evaluated the electrical events and the resulting shock waves of the spark discharge for electrohydraulic lithotripsy at the tip of a 3.3F probe. Spark generation was achieved by variable combinations of voltage and capacity. The effective electrical output was determined by means of a high-voltage probe, a current coil, and a digital oscilloscope. Peak pressures, rise times, and pulse width of the pressure profiles were recorded using a polyvinylidene difluoride needle hydrophone in 0.9% NaCl solution at a distance of 10 mm. The peak pressure and the slope of the shock front depend solely on the voltage, while the pulse width was correlated with the capacity. Pulses of less than 1-microsecond duration can be obtained when low capacity is applied and the inductivity of the cables and plugs is kept at a low level. Using chalk as a stone model it was proven that short pulses of high peak pressure provided by a low capacity and a high voltage have a greater impact on fragmentation than the corresponding broader shock waves of lower peak pressure carrying the same energy.

Pulse duration settings in subthalamic stimulation for Parkinson's disease

PubMed Central

Steigerwald, Frank; Timmermann, Lars; Kühn, Andrea; Schnitzler, Alfons; Reich, Martin M.; Kirsch, Anna Dalal; Barbe, Michael Thomas; Visser‐Vandewalle, Veerle; Hübl, Julius; van Riesen, Christoph; Groiss, Stefan Jun; Moldovan, Alexia‐Sabine; Lin, Sherry; Carcieri, Stephen; Manola, Ljubomir

2017-01-01

ABSTRACT Background Stimulation parameters in deep brain stimulation (DBS) of the subthalamic nucleus for Parkinson's disease (PD) are rarely tested in double‐blind conditions. Evidence‐based recommendations on optimal stimulator settings are needed. Results from the CUSTOM‐DBS study are reported, comparing 2 pulse durations. Methods A total of 15 patients were programmed using a pulse width of 30 µs (test) or 60 µs (control). Efficacy and side‐effect thresholds and unified PD rating scale (UPDRS) III were measured in meds‐off (primary outcome). The therapeutic window was the difference between patients’ efficacy and side effect thresholds. Results The therapeutic window was significantly larger at 30 µs than 60 µs (P = ·0009) and the efficacy (UPDRS III score) was noninferior (P = .00008). Interpretation Subthalamic neurostimulation at 30 µs versus 60 µs pulse width is equally effective on PD motor signs, is more energy efficient, and has less likelihood of stimulation‐related side effects. © 2017 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society. PMID:29165837

980 nm all-fiber NPR mode-locking Yb-doped phosphate fiber oscillator and its amplifier

NASA Astrophysics Data System (ADS)

Li, Pingxue; Yao, Yifei; Chi, Junjie; Hu, Haowei; Yang, Chun; Zhao, Ziqiang; Zhang, Guangju

2014-12-01

We report on a 980 nm all-fiber passively mode-locking Yb-doped phosphate fiber oscillator with the nonlinear polarization rotation (NPR) technique and its amplifier. In order to obtaining the stable self-starting mode-locking oscillator at 980 nm, a bandpass filter with 30 nm transmission bandwidth around 980 nm is inserted into the cavity. The oscillator generates the average output power of 26.1 mW with the repetition rate of 20.38 MHz, corresponding to the single pulse energy of 1.28 nJ. The pulse width is 159.48 ps. The output spectrum of the pulses is centered at 977 nm with a full width half maximum (FWHM) of 10 nm and has the characteristic steep spectral edges of dissipative soliton. No undesired ASE and harmful oscillation around 1030 nm is observed. Moreover, through two stage all-fiber-integrated amplifier by using the 980 nm oscillator as seed source, an amplified output power of 205 mW at 980 nm and pulse duration of 178.10 ps is achieved.

GRB Diversity vs. Utility as Cosmological Probes

NASA Technical Reports Server (NTRS)

Norris, J. P.; Scargle, J. D.; Bonnell, J. T.; Nemiroff, R. J.; Young, Richard E. (Technical Monitor)

1997-01-01

Recent detections of apparent gamma-ray burst (GRB) counterparts in optical and radio wavebands strongly favor the cosmological distance scale, at least for some GRBs, opening the possibility of GRBs serving as cosmological probes. But GRBs exhibit great diversity: in total duration; in number, width and pulse configuration; and in pulse and overall spectral evolution. However, it is possible that a portion of this behavior reflects a luminosity distribution, and possible that evolution of with cosmic time introduces dispersion into the average GRB characteristics -- issues analogous to those encountered with quasars. The temporal domain offers a rich avenue to investigate this problem. When corrected for assumed spectral redshift, time dilation of event durations, pulse widths, and intervals between pulses must yield the same time-dilation factor as a function of peak flux, or else a luminosity distribution may be the cause of observed time dilation effects. We describe results of burst analysis using an automated, Bayesian-based algorithm to determine burst temporal characteristics for different peak flux groups, and derived constraints on any physical process that would introduce a luminosity distribution.

Transmission and correlation of a two-photon pulse in a one-dimensional waveguide coupled with quantum emitters

NASA Astrophysics Data System (ADS)

Hu, Qingmei; Zou, Bingsuo; Zhang, Yongyou

2018-03-01

Transmission and correlation properties of a two-photon pulse are studied in a one-dimensional waveguide (1DW) in the presence of three types of quantum emitters: two-level atom (TLA), side optical cavity (SOC), and Jaynes-Cummings model (JCM). Since there are many plane-wave components for a two-photon pulse, a nonlinear waveguide dispersion is used instead of the linearized one. The two-photon transmission spectra become flatter with decreasing the pulse width. With respect to the δ coupling between the 1DW and quantum emitter the transmission dips show a blueshift for the non-δ one and the blueshift first increases and then decreases with increasing the width of the coupling. The TLA and JCM can induce an effective photon-photon interaction that depends on the distance between the two photons, while the SOC cannot. We show that the 1DW coupled with the TLA or JCM is able to evaluate the overlap of the two photons and that the non-δ coupling has potential for controlling the two-photon correlation.

A Temperature-Hardened Sensor Interface with a 12-Bit Digital Output Using a Novel Pulse Width Modulation Technique

PubMed Central

Badets, Franck; Nouet, Pascal; Masmoudi, Mohamed

2018-01-01

A fully integrated sensor interface for a wide operational temperature range is presented. It translates the sensor signal into a pulse width modulated (PWM) signal that is then converted into a 12-bit digital output. The sensor interface is based on a pair of injection locked oscillators used to implement a differential time-domain architecture with low sensitivity to temperature variations. A prototype has been fabricated using a 180 nm partially depleted silicon-on-insulator (SOI) technology. Experimental results demonstrate a thermal stability as low as 65 ppm/°C over a large temperature range from −20 °C up to 220 °C. PMID:29621171

Single-frequency operation of diode-pumped 2 microm Q-switched Tm:YAG laser injection seeded by monolithic nonplanar ring laser.

PubMed

Gao, Chunqing; Lin, Zhifeng; Gao, Mingwei; Zhang, Yunshan; Zhu, Lingni; Wang, Ran; Zheng, Yan

2010-05-20

We present a diode-pumped, 2mum single-frequency Q-switched Tm:YAG laser. The Q-switched laser is injection seeded by a monolithic Tm:YAG nonplanar ring oscillator with the ramp-hold-fire technique. The output energy of the 2mum single-frequency Q-switched pulse is 2.23mJ, with a pulse width of 290ns and a repetition rate of 200Hz. From the heterodyne beating measurement, the frequency difference between the seed laser and the Q-switched laser is determined to be 37.66MHz, with a half-width of the symmetric spectrum of about 2 MHz.

Picosecond 1064-nm fiber laser with tunable pulse width and low timing jitter

NASA Astrophysics Data System (ADS)

Tian, Wenyan; Zhang, Shukui

2018-02-01

We report an all-fiber, linearly polarized, 1.1-W, 1064-nm fiber laser based on a two-stage Ytterbium-doped fiber amplifier seeded by a gain-switched diode laser with tunable pulse width from 21 to 200 ps at repetition rates of 0.5-1.5 GHz. Timing jitter of our 1064-nm fiber laser was measured to be 0.60 ps over 10 Hz-40 MHz when the gain-switched diode laser was operated at a repetition rate of 0.5, 1, and 1.5 GHz. The fiber laser offers an excellent long term power stability of +/- 0.3% and wavelength stability of +/- 0.01 nm over 8 hours

Dual-Pulse Pulse Position Modulation (DPPM) for Deep-Space Optical Communications: Performance and Practicality Analysis

NASA Technical Reports Server (NTRS)

Li, Jing; Hylton, Alan; Budinger, James; Nappier, Jennifer; Downey, Joseph; Raible, Daniel

2012-01-01

Due to its simplicity and robustness against wavefront distortion, pulse position modulation (PPM) with photon counting detector has been seriously considered for long-haul optical wireless systems. This paper evaluates the dual-pulse case and compares it with the conventional single-pulse case. Analytical expressions for symbol error rate and bit error rate are first derived and numerically evaluated, for the strong, negative-exponential turbulent atmosphere; and bandwidth efficiency and throughput are subsequently assessed. It is shown that, under a set of practical constraints including pulse width and pulse repetition frequency (PRF), dual-pulse PPM enables a better channel utilization and hence a higher throughput than it single-pulse counterpart. This result is new and different from the previous idealistic studies that showed multi-pulse PPM provided no essential information-theoretic gains than single-pulse PPM.

Gaussian temporal modulation for the behavior of multi-sinc Schell-model pulses in dispersive media

NASA Astrophysics Data System (ADS)

Liu, Xiayin; Zhao, Daomu; Tian, Kehan; Pan, Weiqing; Zhang, Kouwen

2018-06-01

A new class of pulse source with correlation being modeled by the convolution operation of two legitimate temporal correlation function is proposed. Particularly, analytical formulas for the Gaussian temporally modulated multi-sinc Schell-model (MSSM) pulses generated by such pulse source propagating in dispersive media are derived. It is demonstrated that the average intensity of MSSM pulses on propagation are reshaped from flat profile or a train to a distribution with a Gaussian temporal envelope by adjusting the initial correlation width of the Gaussian pulse. The effects of the Gaussian temporal modulation on the temporal degree of coherence of the MSSM pulse are also analyzed. The results presented here show the potential of coherence modulation for pulse shaping and pulsed laser material processing.

Peak holding circuit for extremely narrow pulses

NASA Technical Reports Server (NTRS)

Oneill, R. W. (Inventor)

1975-01-01

An improved pulse stretching circuit comprising: a high speed wide-band amplifier connected in a fast charge integrator configuration; a holding circuit including a capacitor connected in parallel with a discharging network which employs a resistor and an FET; and an output buffer amplifier. Input pulses of very short duration are applied to the integrator charging the capacitor to a value proportional to the input pulse amplitude. After a predetermined period of time, conventional circuitry generates a dump pulse which is applied to the gate of the FET making a low resistance path to ground which discharges the capacitor. When the dump pulse terminates, the circuit is ready to accept another pulse to be stretched. The very short input pulses are thus stretched in width so that they may be analyzed by conventional pulse height analyzers.

Ultrafast Nyquist OTDM demultiplexing using optical Nyquist pulse sampling in an all-optical nonlinear switch.

PubMed

Hirooka, Toshihiko; Seya, Daiki; Harako, Koudai; Suzuki, Daiki; Nakazawa, Masataka

2015-08-10

We propose the ultrahigh-speed demultiplexing of Nyquist OTDM signals using an optical Nyquist pulse as both a signal and a sampling pulse in an all-optical nonlinear switch. The narrow spectral width of the Nyquist pulses means that the spectral overlap between data and control pulses is greatly reduced, and the control pulse itself can be made more tolerant to dispersion and nonlinear distortions inside the nonlinear switch. We apply the Nyquist control pulse to the 640 to 40 Gbaud demultiplexing of DPSK and DQPSK signals using a nonlinear optical loop mirror (NOLM), and demonstrate a large performance improvement compared with conventional Gaussian control pulses. We also show that the optimum spectral profile of the Nyquist control pulse depends on the walk-off property of the NOLM.

Characterization of a Laser-Generated Perturbation in High-Speed Flow for Receptivity Studies

DTIC Science & Technology

2014-01-01

to trip the boundary layer. Figure 1. Schematic of the Boeing/AFOSR Mach-6 Quiet Tunnel (BAM6QT) The BAM6QT is a Ludwieg tube with a double- burst ...reduced to a 4-mm beam diameter by an aperture. Although the PIV-400 is a double- pulse laser, only the first pulse is used to generate perturbations in the...also both seeded, and pulse at 10 Hz, with a pulse width of about 7 ns. 2. Forming Optics The laser-generated perturbation is created by focusing a

Active frequency matching in stimulated Brillouin amplification for production of a 2.4  J, 200  ps laser pulse.

PubMed

Yuan, Hang; Wang, Yulei; Lu, Zhiwei; Zheng, Zhenxing

2018-02-01

A frequency matching Brillouin amplification in high-power solid-state laser systems is proposed. The energy extraction efficiency could be maintained at a high level in a non-collinear Brillouin amplification structure using an exact Stokes frequency shift. Laser pulses having a width of 200 ps and energy of 2.4 J were produced. This method can be used to transfer energy from a long pulse to a short pulse through a high-power solid-state laser system.

KAHVE Laboratory RF circulator and transmission line project

NASA Astrophysics Data System (ADS)

Cetinkaya, Hakan; ćaǧlar, Aslıhan; ćiçek, Cihan; Özbey, Aydın; Sunar, Ezgi; Türemen, Görkem; Yıldız, Hüseyin; Yüncü, Alperen; Özcan, Erkcan; Ünel, Gökhan; Yaman, Fatih

2018-02-01

An 800 MHz RF circulator and transmission line project has recently started at the newly commissioned Kandilli Detector, Accelerator and Instrumentation (KAHVE) Laboratory at the Boğaziçi University. The aims are to design, build and construct an RF circulator and transmission line in Turkey for high power and high frequency applications. The project consists of 8 transmission line elements: 800 MHz RF generator with 60 kW power (klystron), klystron to waveguide converter, waveguides, E and H bends, 3-port circulator and waveguide to coaxial converter to transmit RF power to a pillbox RF cavity. Design studies and details of the ongoing project will be presented.

Long-Lag, Wide-pulse Gamma-Ray Bursts

NASA Technical Reports Server (NTRS)

Norris, J. P.; Bonnell, J. T.; Kazanas, D.; Scargie, J. D.; Hakkila, J.; Giblin, T. W.

2005-01-01

The best available probe of the early phase of gamma-ray burst (GRB) jet attributes is the prompt gamma-ray emission, in which several intrinsic and extrinsic variables determine observed GRB pulse evolution, including at least: jet opening angle, profiles of Lorentz factor and matter/field density, distance of emission region from central source, and viewing angle. Bright, usually complex bursts have many narrow pulses that are difficult to model due to overlap. However, the relatively simple, long spectral lag, wide-pulse bursts may have simpler physics and are easier to model. We have analyzed the temporal and spectral behavior of wide pulses in 24 long-lag bursts from the BATSE sample, using a pulse model with two shape parameters - width and asymmetry - and the Band spectral model with three shape parameters. We find that pulses in long-lag bursts are distinguished both temporally and spectrally from those in bright bursts: the pulses in long spectral lag bursts are few in number, and approximately 100 times wider (10s of seconds), have systemtically lower peaks in nu*F(nu), harder low-energy spectra and softer high-energy spectra. These five pulse descriptors are essentially uncorrelated for our long-lag sample, suggesting that at least approximately 5 parameters are needed to model burst temporal and spectral behavior, roughly commensurate with the theoretical phase space. However, we do find that pulse width is strongly correlated with spectral lag; hence these two parameters may be viewed as mutual surrogates. The prevalence of long-lag bursts near the BATSE trigger threshold, their predominantly low nu*F(nu) spectral peaks, and relatively steep upper power-law spectral indices indicate that Swiift will detect many such bursts.

Laser range profile of cones

NASA Astrophysics Data System (ADS)

Zhou, Wenzhen; Gong, Yanjun; Wang, Mingjun; Gong, Lei

2016-10-01

technology. Laser one-dimensional range profile can reflect the characteristics of the target shape and surface material. These techniques were motivated by applications of laser radar to target discrimination in ballistic missile defense. The radar equation of pulse laser about cone is given in this paper. This paper demonstrates the analytical model of laser one-dimensional range profile of cone based on the radar equation of the pulse laser. Simulations results of laser one-dimensional range profiles of some cones are given. Laser one-dimensional range profiles of cone, whose surface material with diffuse lambertian reflectance, is given in this paper. Laser one-dimensional range profiles of cone, whose surface mater with diffuse materials whose retroreflectance can be modeled closely with an exponential term that decays with increasing incidence angles, is given in this paper. Laser one-dimensional range profiles of different pulse width of cone is given in this paper. The influences of surface material, pulse width, attitude on the one-dimensional range are analyzed. The laser two-dimensional range profile is two-dimensional scattering imaging of pulse laser of target. The two-dimensional range profile of roughness target can provide range resolved information. An analytical model of two-dimensional laser range profile of cone is proposed. The simulations of two-dimensional laser range profiles of some cones are given. Laser two-dimensional range profiles of cone, whose surface mater with diffuse lambertian reflectance, is given in this paper. Laser two-dimensional range profiles of cone, whose surface mater with diffuse materials whose retroreflectance can be modeled closely with an exponential term that decays with increasing incidence angles, is given in this paper. The influence of pulse width, surface material on laser two-dimensional range profile is analyzed. Laser one-dimensional range profile and laser two-dimensional range profile are called as laser range profile (LRP).

Experimental high gradient testing of a 17.1 GHz photonic band-gap accelerator structure

DOE PAGES

Munroe, Brian J.; Zhang, JieXi; Xu, Haoran; ...

2016-03-29

In this paper, we report the design, fabrication, and high gradient testing of a 17.1 GHz photonic band-gap (PBG) accelerator structure. Photonic band-gap (PBG) structures are promising candidates for electron accelerators capable of high-gradient operation because they have the inherent damping of high order modes required to avoid beam breakup instabilities. The 17.1 GHz PBG structure tested was a single cell structure composed of a triangular array of round copper rods of radius 1.45 mm spaced by 8.05 mm. The test assembly consisted of the test PBG cell located between conventional (pillbox) input and output cells, with input power ofmore » up to 4 MW from a klystron supplied via a TM 01 mode launcher. Breakdown at high gradient was observed by diagnostics including reflected power, downstream and upstream current monitors and visible light emission. The testing procedure was first benchmarked with a conventional disc-loaded waveguide structure, which reached a gradient of 87 MV=m at a breakdown probability of 1.19 × 10 –1 per pulse per meter. The PBG structure was tested with 100 ns pulses at gradient levels of less than 90 MV=m in order to limit the surface temperature rise to 120 K. The PBG structure reached up to 89 MV=m at a breakdown probability of 1.09 × 10 –1 per pulse per meter. These test results show that a PBG structure can simultaneously operate at high gradients and low breakdown probability, while also providing wakefield damping.« less

Conducted noise analysis and protection of 45 kJ/s, ±50 kV capacitor charging power supply when interfaced with repetitive Marx based pulse power system.

PubMed

Naresh, P; Patel, Ankur; Sharma, Archana

2015-09-01

Pulse power systems with highly dynamic loads like klystron, backward wave oscillator (BWO), and magnetron generate highly dynamic noise. This noise leads to frequent failure of controlled switches in the inverter stage of charging power supply. Designing a reliable and compatible power supply for pulse power applications is always a tricky job when charging rate is in multiples of 10 kJ/s. A ±50 kV and 45 kJ/s capacitor charging power supply based on 4th order LCLC resonant topology has been developed for a 10 Hz repetitive Marx based system. Conditions for load independent constant current and zero current switching (ZCS) are derived mathematically. Noise generated at load end due to dynamic load is tackled effectively and reduction in magnitude noise voltage is achieved by providing shielding between primary and secondary of high voltage high frequency transformer and with LCLC low pass filter. Shielding scales down the ratio between coupling capacitance (Cc) and the collector-emitter capacitance of insulated gate bi-polar transistor switch, which in turn reduces the common mode noise voltage magnitude. The proposed 4th order LCLC resonant network acts as a low pass filter for differential mode noise in the reverse direction (from load to source). Power supply has been tested repeatedly with 5 Hz repetition rate with repetitive Marx based system connected with BWO load working fine without failure of single switch in the inverter stage.

Conducted noise analysis and protection of 45 kJ/s, ±50 kV capacitor charging power supply when interfaced with repetitive Marx based pulse power system

NASA Astrophysics Data System (ADS)

Naresh, P.; Patel, Ankur; Sharma, Archana

2015-09-01

Pulse power systems with highly dynamic loads like klystron, backward wave oscillator (BWO), and magnetron generate highly dynamic noise. This noise leads to frequent failure of controlled switches in the inverter stage of charging power supply. Designing a reliable and compatible power supply for pulse power applications is always a tricky job when charging rate is in multiples of 10 kJ/s. A ±50 kV and 45 kJ/s capacitor charging power supply based on 4th order LCLC resonant topology has been developed for a 10 Hz repetitive Marx based system. Conditions for load independent constant current and zero current switching (ZCS) are derived mathematically. Noise generated at load end due to dynamic load is tackled effectively and reduction in magnitude noise voltage is achieved by providing shielding between primary and secondary of high voltage high frequency transformer and with LCLC low pass filter. Shielding scales down the ratio between coupling capacitance (Cc) and the collector-emitter capacitance of insulated gate bi-polar transistor switch, which in turn reduces the common mode noise voltage magnitude. The proposed 4th order LCLC resonant network acts as a low pass filter for differential mode noise in the reverse direction (from load to source). Power supply has been tested repeatedly with 5 Hz repetition rate with repetitive Marx based system connected with BWO load working fine without failure of single switch in the inverter stage.

1.5-GW S-band relativistic klystron amplifier

NASA Astrophysics Data System (ADS)

Ferguson, Patrick E.

1992-04-01

There is a strong symbiotic relationship between a developing technology and its applications. New technologies can generate applications previously either unrealizable or impractical. Conversely, applications can demand the development of new technological capability. Examples of both types of development can be found in the evolution of HPM. The high power and energy output made possible by HPM have created a technology driven interest in directed energy weapons and short pulse radar. On the other hand, the requirements for heating of fusion plasmas have resulted in an application driven program to develop high average power microwave devices. In this paper we address these and other applications such as RF electron linacs, laser pumping, and beaming of power. Emerging applications, such as ionispheric modification and environmental cleanup, are also touched upon. The approach of this paper will be to review each application separately and then compare the requirements of the applications in terms of the power, frequency and other key requirements necessary for HPM to usefully address the application.