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The lasertron rf generator for FEL (free-electron laser) applications

Description: The lasertron rf generator uses an rf-modulated laser beam to generate a tightly bunched electron beam that is accelerated by a dc power supply to the fractional megawatt region. The tightly bunched beam then crosses an output cavity where most of the kinetic energy may be extracted. The bunching is so good that efficient microwave generation at 3 GHz and above is feasible, and three projects worldwide are under way for these frequencies. All three existing projects focus on the linear collider application of high peak power with good efficiency, short output pulses, and low average power. A short review of these projects is presented. The main thrust of this paper is to discuss the lasertron as the rf generator for free-electron laser (FEL) rf systems. The author has developed a ring model of the lasertron device that shows excellent dc-to-rf conversion efficiency at high output power over the 400- to 1700-MHz frequency range. The issue of the lasertron advantages at higher average output power is also explored. First-order estimates of the weight versus frequency and power are also made. An outline of an experiment that uses the Los Alamos photoinjector to make a lasertron is also presented. 7 refs., 3 figs.
Date: September 1, 1987
Creator: Tallerico, P.J.
Partner: UNT Libraries Government Documents Department

150-kW, 450-MHz gyrocon rf generator

Description: The output-power and conversion efficiency of the Los Alamos gyrocon were increased by a factor of 150 in the past year. Major improvements in the phase- and amplitude-control system and in understanding the electron multipactor and surface-conditioning processes increased the output power. The highest measured efficiency on this gyrocon is 23%, which was obtained with several combinations of parameters. Both the output power and the efficiency are a factor of 3 below the design values, and several possibilities are being examined to remove the discrepancy between theory and experiment.
Date: January 1, 1983
Creator: Tallerico, P.J.
Partner: UNT Libraries Government Documents Department

Gyrocon: a deflection-modulated, high-power microwave amplifier

Description: A large-signal, relativistic theory of the electron-field interaction in a new class of microwave amplifiers is presented and applied to the analysis of a high-power, 450-MHz amplifier for accelerator applications. The analysis indicates that electronic efficiencies in excess of 90 percent are obtainable and that overall efficiencies of 90 percent are possible. The amplifier is unique in several respects; the electron velocity is perpendicular to the circuit energy flow, the device uses a fast-wave circuit, and the electron beam is deflection modulated.
Date: October 1, 1977
Creator: Tallerico, P.J.
Partner: UNT Libraries Government Documents Department

Class of deflection-modulated, high-power microwave amplifiers

Description: An unusual deflection-modulated, fast-wave electron device is analyzed. It has several unique properties; the electron beam is unbunched and is perpendicular to the direction of power flow in the circuit, and the circuit could be a simple fundamental-mode rectangular waveguide. The amplifier consists of an electron gun, a deflection cavity, an optional beam-bending system, and an output interaction region. An idealized theory showing that 100 percent electronic efficiency may be achieved, and several large-signal calculations with over 90 percent electronic and circuit efficiencies, are presented. The power, gain, and frequency limits to this type of amplifier or frequency multiplier are discussed. The beam power must be greater than 100 kW for efficient operation because the output circuit losses and deflection power depend on beam voltage, not on beam power. The devices operate best at frequencies below a few gigahertz because of limitations on the ratio of beam size to circuit size. The power gains vary between 10 and 25 dB.
Date: January 1, 1977
Creator: Tallerico, P.J.
Partner: UNT Libraries Government Documents Department

Recent advances in RF power generation

Description: This paper is a review of the progress and methods used in RF generation for particle accelerators. The frequencies of interest are from a few megahertz to 100 GHz, and the powers are for super linear collider applications, but in this case the pulses are short, generally below 1 {mu}s. The very high-power, short-pulse generators are only lightly reviewed here, and for more details the reader should follow the specialized references. Different RF generators excel over various parts of the frequency spectrum. Below 100 MHz solid-state devices and gridded tubes prevail, while the region between 400 MHz and 3 GHz, the cyclotron-resonant devices predominate, and above 250 GHz, Free-Electron Lasers and ubitrons are the most powerful generators. The emphasis for this review is on microwave generation at frequencies below 20 GHz, so the cyclotron-resonant devices are only partially reviewed, while the progress on free-electron laser and ubitrons is not reviewed in this paper. 39 refs., 4 figs.
Date: January 1, 1990
Creator: Tallerico, P.J.
Partner: UNT Libraries Government Documents Department

Advances in high-power rf amplifiers

Description: Several powerful accelerators and storage rings are being considered that will require tens or even hundreds of megawatts of continuous rf power. The economics of such large machines can be dictated by the cost and efficiency of the rf amplifiers. The overall design and performance of such narrow-band amplifiers, operating in the 50- to 1500-MHz region, are being theoretically studied as a function of frequency to determine the optimum rf amplifier output power, gain, efficiency, and dc power requirements. The state of the art for three types of amplifiers (gridded tubes, klystrons, and gyrocons) is considered and the development work necessary to improve each is discussed. The gyrocon is a new device, hence its various embodiments are discussed in detail. The Soviet designs are reviewed and the gyrocon's strengths and weaknesses are compared to other types of microwave amplifiers. The primary advantages of the gyrocon are the very large amount of power available from a single device and the excellent efficiency and stable operation. The klystron however, has much greater gain and is simpler mechanically. At very low frequencies, the small size of the gridded tube makes it the optimum choice for all but the most powerful systems.
Date: January 1, 1979
Creator: Tallerico, P.J.
Partner: UNT Libraries Government Documents Department

Gyrocon radio-frequency generator for FY-80 and FY-81

Description: The gyrocon is a high-power, high-efficiency amplifier that operates by deflection modulation of an electron beam. The spatial bunching can be better than the temporal bunching in a klystron, especially for high output powers and uhf frequencies. Soviet gyrocons have produced over 40 MW of pulsed power at 430 MHz and 250-kW cw at 181 MHz. The progress on the construction and testing of a 450-MHz prototype gyrocon is discussed. The maximum pulsed output power that has been achieved in the reporting period is 1 kW. Although these powers are significantly below the design goal of 650 kW, there is a good chance that the experimental program in FY-82 will result in increased output power.
Date: September 1, 1982
Creator: Tallerico, P.J.
Partner: UNT Libraries Government Documents Department

Status of the Los Alamos gyrocon

Description: The gyrocon is a deflection-modulated RF amplifier that can achieve very high peak- and average-output power, as well as excellent direct-current-to- radio-frequency conversion efficiency. The electron dynamics of the gyrocon are analyzed with a large-signal computer code that is used to design a prototype gyrocon. This gyrocon is now built and it has been operated at low duty cycle. The design goals, construction details, and initial operating results of the prototype gyrocon are discussed.
Date: January 1, 1981
Creator: Tallerico, P.J.
Partner: UNT Libraries Government Documents Department

Progress on the gyrocon deflection-modulated amplifier

Description: The gyrocon is a high-power deflection-modulated amplifier that can have excellent spatial bunching and, hence, high dc-to-rf conversion efficiency. A program to design and build a prototype amplifier at 450 MHz is discussed. Peak powers of 150 kW and conversion efficiencies of 23% have been measured; the testing program is being pursued to improve this performance. Some possible mechanisms for the difference between the experimental and calculated performance are discussed.
Date: January 1, 1982
Creator: Tallerico, P.J.
Partner: UNT Libraries Government Documents Department

Racetrack microtron radio-frequency system

Description: The design and construction progress of a prototype rf system to drive the Los Alamos-NBS racetrack microtron (RTM) electron accelerator is described. The rf system requires 450-kW cw at 2380 MHz from a single klystron. The output from the klystron is split three ways to drive a capture section, a preaccelerator section, and the main accelerator section. The fields in each section are phase- and amplitude-controlled to tight tolerances. Temperature control of the accelerator sections also is linked to the amplitude-control system, because the system's average power is so high.
Date: January 1, 1981
Creator: Tallerico, P.J. & Mitra, A.K.
Partner: UNT Libraries Government Documents Department

Racetrack microtron radio-frequency system

Description: The design and construction progress of a prototype rf system to drive the Los Alamos-NBS racetrack microtron (RTM) electron accelerator is described. The rf system requires 450-kW cw at 2380 MHz from a single klystron. The output from the klystron is split three ways to drive a capture section, a preaccelerator section, and the main accelerator section. The fields in each section are phase- and amplitude-controlled to tight tolerances. Temperature control of the accelerator sections also is linked to the amplitude-control system, because the system's average power is so high.
Date: January 1, 1981
Creator: Tallerico, P.J. & Mitra, A.K.
Partner: UNT Libraries Government Documents Department

Racetrack microtron rf system

Description: The rf system for the National Bureau of Standards (NBS)/Los Alamos cw racetrack microtron is described. The low-power portion consists of five 75-W amplifers that drive two input ports in each of two chopper deflection cavities and one port in the prebuncher cavity. A single 500-kW klystron drives four separate 2380-MHz cavity sections: the two main accelerator sections, a capture section, and a preaccelerator section. The phases and amplitudes in all cavities are controlled by electronic or electromechanical controls. The 1-MW klystron power supply and crowbar system were purchased as a unit; several modifications are described that improve power-supply performance. The entire rf system has been tested and shipped to the NBS, and the chopper-buncher system has been operated with beam at the NBS. 5 refs., 2 figs.
Date: January 1, 1985
Creator: Tallerico, P.J. & Keffeler, D.R.
Partner: UNT Libraries Government Documents Department

Computer modeling of the gyrocon

Description: A gyrocon computer model is discussed in which the electron beam is followed from the gun output to the collector region. The initial beam may be selected either as a uniform circular beam or may be taken from the output of an electron gun simulated by the program of William Herrmannsfeldt. The fully relativistic equations of motion are then integrated numerically to follow the beam successively through a drift tunnel, a cylindrical rf beam deflection cavity, a combination drift space and magnetic bender region, and an output rf cavity. The parameters for each region are variable input data from a control file. The program calculates power losses in the cavity wall, power required by beam loading, power transferred from the beam to the output cavity fields, and electronic and overall efficiency. Space-charge effects are approximated if selected. Graphical displays of beam motions are produced. We discuss the Los Alamos Scientific Laboratory (LASL) prototype design as an example of code usage. The design shows a gyrocon of about two-thirds megawatt output at 450 MHz with up to 86% overall efficiency.
Date: January 1, 1979
Creator: Tallerico, P.J. & Rankin, J.E.
Partner: UNT Libraries Government Documents Department

Self-consistent klystron simulations

Description: A numerical analysis of large-signal klystron behavior based on general wave-particle interaction theory is presented. The computer code presented is tailored for the minimum amount of complexity needed in klystron simulation. The code includes self-consistent electron motion, space-charge fields, and intermediate and output fields. It also includes use of time periodicity to simplify the problem, accurate representation of the space-charge fields, accurate representation of the cavity standing-wave fields, and a sophisticated particle-pushing routine. In the paper, examples are given that show the effects of cavity detunings, of varying the magnetic field profile, of electron beam asymmetries from the gun, and of variations in external load impedance. 4 refs., 7 figs.
Date: January 1, 1985
Creator: Carlsten, B.E. & Tallerico, P.J.
Partner: UNT Libraries Government Documents Department

A ring model of the lasertron

Description: A large-signal, 2-1/2 dimensional relativistic particle dynamics code has been written to simulate the electrical behavior of the lasertron. The theory and the approximations involved in this code are discussed in detail. Numerical results are presented to show the comparison with previous work and to show the general variation in lasertron performance with frequency, beam voltage, and beam current. The code has also been used to design a prototype 6-GHz lasertron for construction at the Laboratoire de l'Accelerateur Lineaire in Orsay, France. The calculations show that this prototype can produce 4.7-MW peak-power output with a conversion efficiency of 65%. At 3 GHz, the power would be increased by a factor approaching 10, and the conversion efficiency would be over 70%.
Date: January 1, 1988
Creator: Tallerico, P.J. & Coulon, J.P.
Partner: UNT Libraries Government Documents Department

rf modulator design and phase amplitude control for a high-power free-electron-laser linac

Description: The continued interest for building tunable lasers using an electron accelerator as the source of primary energy has resulted in the design of a new accelerator. Earlier work by other members of the Los Alamos team has demonstrated that this design does work in an amplifier mode. The accelerator is to be upgraded for use in an oscillator experiment and the new rf power amplifier system must meet some of the very stringent demands for power and stability placed on the electron beam for the free-electron laser (FEL) interaction to be observed. These demands are particularly stringent because the electron beam energy ultimately will be circulated back through the accelerator so that the electron beam energy not used in the FEL interaction is not wasted. These considerations have to some measure been incorporated into the design of the second FEL system at Los Alamos and are discussed.
Date: January 1, 1981
Creator: Hoeberling, R.F. & Tallerico, P.J.
Partner: UNT Libraries Government Documents Department

Gyrocon Radio-Frequency-Generator project for FY-78 and -79

Description: The gyrocon is a high-power, high-efficiency amplifier that operates by deflection modulation of an electron beam. The bunching is better than that in a klystron, especially for very high powers and UHF frequencies, so the overall efficiency and the maximum output power can be higher than in a klystron. The present theory includes the effects of large signals, space charge, and finite beam size. The equations of motion are relativistically correct, and the space-charge fields are correct to first order in v/c. The theory is derived and a computer code to solve these equations is discussed. The code is then used to obtain several specific examples of gyrocon designs that have significant advantages over klystrons or gridded tubes in the 0.2- to 1.0-GHz frequency range. Several embodiments of the gyrocon are possible: the radial style and the spherical style are discussed in this report. The radial style has a bender magnet to increase the deflection of the beam, whereas the spherical gyrocon does not employ the bender magnet. The optimum frequency range for the spherical gyrocon is from 1.0 to 2.5 GHz.
Date: September 1, 1980
Creator: Tallerico, P.J. & Rankin, J.E.
Partner: UNT Libraries Government Documents Department

Computer simulation of the lasertron with a ring model

Description: The lasertron is more efficient, lighter, and smaller than a klystron, especially at outputs below 2 GHz. Higher peak output powers are possible with the lasertron, and a separate modulator is not required. These advantages are useful for rf accelerators and linear colliders. The electron dynamics are simulated to estimate the device performance limits and to design an experimental lasertron. The relativistic electron dynamics are followed from the photocathode through the acceleration region and through the output region. The total fields are the sum of the space-charge, external magnetic, and acceleration or output-cavity fields. Wake fields are ignored, and the steady-state output fields are found. Lasertron performance as a function of acceleration field, charge per pulse nd frequency is calculated, showing its avantages and limitations. A preliminary design for the first Orsay lasertron experiment is presented.
Date: March 16, 1987
Creator: Tallerico, P.J. & Coulon, J.P.
Partner: UNT Libraries Government Documents Department

Computer modeling of the klystron

Description: Although the klystron was invented over 40 years ago, it still is quite a scientific challenge to analyze this seemingly simple device. Accurate calculation of space-charge density and particle motions are required, but there are dozens of parameters that must be optimized. Thus the analysis must be inexpensive to run, because over 100 runs typically are required to optimize a particular design. A self-consistent ring model of the klystron interaction is being developed for use as a design tool, with the initial goal of improving the LAMPF klystrons to conserve electrical energy. A mathematical model that includes large-signal effects, relativity, harmonic and fundamental cavities, extended cavity fields, and self-consistent calculations of the induced currents is being developed. The model is self-consistent because the gap fields are calculated interactively, because the currents that drive the cavities are not known until after the beam transverses the cavities. Several test cases have been run, and the basic theory and results to date are discussed.
Date: January 1, 1983
Creator: Tallerico, P.J. & Carlsten, B.E.
Partner: UNT Libraries Government Documents Department

Long-pulse applications of pulse-forming lines for high-power linac application

Description: The ever present demands for high efficiency in the RF power stations for particle accelerators have caused increased interest in longer RF pulses (ten's of microseconds) for linacs such as the Pion Generator for Medical Irradiation (PIGMI) and Free Electron Laser (FEL). For either RF power station, a fundamental decision is whether to use a modulating anode/hard-tube driver or pulsed cathode/line-type pulser configuration. The choices in the extremes of low power for very long pulses or for very-high-power, short pulses are, respectively, a modulated anode/hard tube modulator and pulsed cathode/pulse forming line. However, the demarcation between these two extremes is not clearcut. The criteria (cost, flexibility performance, reliability, efficiency) that resulted in the RF station definition of these two specific systems will be described.
Date: January 1, 1981
Creator: Hoeberling, R.F. & Tallerico, P.J.
Partner: UNT Libraries Government Documents Department

Development of a RAMI model for LANSCE and high power APT accelerators

Description: Assessment of the reliability, availability, maintainability and inspectability (RAMI) of all high power, high cost systems is important to justify and improve the cost effectiveness of these systems. For the very large (over 100 MW) accelerator systems associated with APT, a RAMI model is very valuable in guiding the design and allocation of resources. A RAMI model of an existing machine is also valuable, since machine improvement funds must be allocated to increase the availability by the largest amount. The authors have developed a RAMI model using the critical subsystems of the LANSCE accelerator and beam delivery complex as an example and to evaluate the effectiveness for estimating reliability and beam availability. LAMPF and LANSCE together provide most of the features required for the accelerator and beam delivery part of a high-power APT machine, but LANSCE is pulsed, rather than CW. This complex is capable of a 1-MW average power H{sup {minus}} beam, and it is the most powerful proton accelerator in the US built to date.
Date: December 1, 1994
Creator: Tallerico, P. J.
Partner: UNT Libraries Government Documents Department

Design and performance of the LAMPF 1-1/4 MW klystron modulator

Description: From 11th modulator symposium; New York, New York, USA (18 Sep 1973). A design for a very reliable single-triode modulator for a 11/4 MW modulating-anode klystron is presented. The operating voltage is 86 kV and the variable pulse length ranges from 200 4mmsec to 1.2 msec. The basic modulator circuit, which uses a novel Zener diode bias circuit, and several of the individual components are described in detail. Over 140,000 high-voltage hours have been accumulated on these modulators. The principal failure mechanism is grid emission from the triode. These failures can be anticipated and repaired during a normal maintenance period. The triode is then reprocessed and reused. Tube life data and a summary of the failures modes are presented. (auth)
Date: April 30, 1974
Creator: Tallerico, P.J.; Cady, R.L. & Doss, J.D.
Partner: UNT Libraries Government Documents Department

Phase and amplitude feedback control system for the Los Alamos free-electron laser

Description: Phase and amplitude feedback control systems for the Los Alamos free-electron laser (FEL) are described. Beam-driven voltages are very high in the buncher cavity because the electron gun is pulsed at the fifth subharmonic of the buncher resonant frequency. The high beam loading necessitated a novel feedback and drive configuration for the buncher. A compensation cirucit has been added to the gun/driver system to reduce observed drift. Extremely small variations in the accelerator gradients had dramatic effects on the laser output power. These problems and how they were solved are described and plans for improvements in the feedback control system are discussed. 5 refs., 7 figs.
Date: January 1, 1985
Creator: Lynch, M.T.; Tallerico, P.J. & Higgins, E.F.
Partner: UNT Libraries Government Documents Department