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Summary report for the Microwave Source Working Group

Description: This report summarizes the discussions of the Microwave Source Working Group during the Advanced Accelerator Concepts Workshop held October 13-19, 1996 in the Granlibakken Conference Center at Lake Tahoe, California. Progress on rf sources being developed for linear colliders is reviewed. Possible choices for high-power rf sources at 34 GHz and 94 GHz for future colliders are examined. 27 refs.
Date: January 1, 1997
Creator: Westenskow, G. A.
Partner: UNT Libraries Government Documents Department

RF system for a 30 GHz, 5 TeV linear collider based on conventional technology

Description: In order that it may be built within a reasonable length and with reasonable ac power consumption, a 5 TeV linear collider must employ an accelerating gradient and rf frequency which are both higher than for present 1 TeV collider designs. The required rf power per meter, which will also be higher than for 1 TeV designs, can be provided either by relatively conventional rf technology or by a two-beam scheme such as that proposed for CLIC. In this paper the first alternative, a 30 GHz rf system employing microwave tube power sources together with rf pulse compression, is described which produces an accelerating gradient on the order of 200 MV per meter. Limitations on the peak power that can be obtained from conventional klystrons as a function of frequency are discussed; it is found that such klystrons are only marginally adequate as a power source at 30 GHz. Several alternative rf sources, such as multiple-beam klystrons, sheet-beam klystrons, gyroklystrons and annular-beam ubitrons are described which are capable of providing the required power, after pulse compression, of about 600 MW per meter.
Date: July 1, 1997
Creator: Wilson, P.B.; Raubenheimer, T. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Using Multispectral Imaging to Measure Temperature Profiles and Emissivity of Large Thermionic Dispenser, Cathodes

Description: Thermionic dispenser cathodes are widely used in modern high-power microwave tubes. Use of these cathodes has led to significant improvement in performance. In recent years these cathodes have been used in electron linear accelerators (LINACs), particularly in induction LINACs, such as the Experimental Test Accelerator at Lawrence Livermore National Laboratory and the Relativistic Test Accelerator at Lawrence Berkeley National Laboratory. For induction LINACs, the thermionic dispenser cathode provides greater reproducibility, longer pulse lengths, and lower emittance beams than does a field emission cathode. Los Alamos National Laboratory is fabricating a dual-axis X-ray radiography machine called dual-axis radiograph hydrodynamic test (DARHT). The second axis of DARHT consists of a 2-kA, 20-MeV induction LINAC that uses a 3.2-MeV electron gun with a tungsten thermionic-dispenser cathode. Typically the DARHT cathode current density is 10 A/cm{sup 2} at 1050 C. Under these conditions current density is space-charge limited, which is desirable since current density is independent of temperature. At lower temperature (the temperature-limited regime) there are variations in the local current density due to a nonuniform temperature profile. To obtain the desired uniform current density associated with space-charge limited operation, the coolest area on the cathode must be at a sufficiently high temperature so that the emission is space-charge limited. Consequently, the rest of the cathode is emitting at the same space-charge-limited current density but is at a higher temperature than necessary. Because cathode lifetime is such a strong function of cathode temperature, there is a severe penalty for nonuniformity in the cathode temperature. For example, a temperature increase of 50 C means cathode lifetime will decrease by a factor of at least four. Therefore, we are motivated to measure the temperature profiles of our large-area cathodes.
Date: September 2001
Creator: Simmons, D. F.; Fortgang, C. M. & Holtkamp, D. B.
Partner: UNT Libraries Government Documents Department

Design and cold testing of a high peak power x-band gyroklystron

Description: The main goal of the University of Maryland's gyroklystron project is to develop an efficient, high power, high gain, phase controllable amplifier at 10 GHz. While peak powers of several hundred megawatts are ultimately of interest, our initial experimental design values include 30 MW of output power in 1 ..mu..s pulses with a gain in excess of 50 dB. The 30 MW power level represents an enhancement of almost three orders of magnitude over the current state-of-the-art in gyroklystron amplifiers. This enhancement will be achieved by going to high beam energies (..gamma..approx. =2) and overmoded cavities (TE/sub 01//sup 0/). Outlined in this report are the steps being taken to realize our goal.
Date: January 1, 1985
Creator: Lawson, W.; Calame, J.; Granatstein, V.L.; Latham, P.E.; McAdoo, J.; Park, G.S. et al.
Partner: UNT Libraries Government Documents Department

Microwave process control through a traveling wave tube source

Description: A rapid feedback control system was designed to operate with a traveling wave tube for regulating the sintering temperature of tows and tubes in a single mode microwave cavity. The control system regulated the microwave frequency and power absorbed by the sample in order to maintain the sample temperature. Testing with NICALON tows and mullite tubes demonstrated that the control scheme worked well for stationary and slowly moving ({lt}10mm/min) samples, but failed for fast moving samples. Difficulty with measuring sample temperatures was resolved by using a light sensor to measure the emitted light intensity and to relative degree of heating.
Date: April 1, 1996
Creator: Vogt, G.J.; Regan, A.; Rohlev, A. & Curtin, M.
Partner: UNT Libraries Government Documents Department

Accelerator research studies. Final report, June 1, 1991--May 31, 1994

Description: The Accelerator Research Studies program at the University of Maryland, sponsored by the Department of Energy is currently in the third year of its three-year funding cycle. The program consists of the following three tasks: Task A -- Study of the transport and longitudinal compression of intense, high-brightness beams; Task B -- Study of high-brightness beam generation in pseudospark devices; Task C -- Study of a gyroklystron high-power microwave source for linear colliders. The research for each task is detailed in this report.
Date: December 31, 1994
Partner: UNT Libraries Government Documents Department

Accelerator research studies. Final report, June 1, 1994--May 31, 1995

Description: The Accelerator Research Studies program at the University of Maryland, sponsored by the Department of Energy has completed the third year of its three-year funding cycle and an additional one-year, no-cost extension. The program consisted of the following three tasks: Task A -- Study of the transport and longitudinal compression of intense, high-brightness beams; Task B -- Study of high-brightness beam generation in pseudospark devices; Task C -- Study of a gyroklystron high-power microwave source for linear colliders. The research carried out for each task and progress made is reported.
Date: August 1, 1995
Partner: UNT Libraries Government Documents Department

Stability of klystron operation as a function of input parameters

Description: Instabilities in the operation of a high-power multicavity klystron have been studied as a function of various input parameters. Among these, the focusing magnetic field, rf input power and tuning of the second harmonic cavity were observed to have a striking effect in deciding the regions of unstable operation. One region of instability could be identified with a value of magnetic field corresponding to cyclotron resonance, at the operating frequency. The magnetic field value in the region of the input end, and the second harmonic cavity, was found to have a more decisive influence on stability, than the magnetic field at the output end. A hysteresis effect has been associated with the instabilities. This could be explained in terms of multipactor phenomena. These observations indicate, among other things, that in designing new tubes, it might be desirable that the operating magnetic field stay well away from cyclotron resonance conditions, especially in the gun region, and the cavities at the input end. The experimental techniques can be used for optimizing the operating conditions of existing tubes.
Date: March 1, 1984
Creator: Singh, A.; Konrad, G.T. & Griffin, C.
Partner: UNT Libraries Government Documents Department

Megawatt-klystron amplifiers in L-band

Description: The purpose of this note is to serve as a short guide for the SSC-Linac Injector Workshop. It contains a general overview of historical development and of modern design of L-band klystron amplifiers in the range of about 1 to 30 Megawatt output (CW or pulse). Absolute power limits, efficiency, modulation characteristics, protection devices and typical application examples are briefly considered. It should be mentioned that this overview is not restricted to specific needs of the SSC-Injector Linac. 14 refs., 12 figs., 2 tabs.
Date: January 1, 1989
Creator: Schaffer, G.
Partner: UNT Libraries Government Documents Department

Increasing output power of an 850 MHz tetrode with a floating-deck modulator

Description: Designers of high-power amplifiers generally regard the region above 300 MHz as a domain dominated by velocity-modulated (klystron/TWT) devices. However, as the power requirements diminish, there are attractive alternatives. The high-power 850-MHz requirements of the ground test accelerator (GTA) program can be filled by 1-MW klystrons, but it would be more efficient to use a lower-power device for a 50-kW requirement. To meet the 850-MHz medium-power requirements, Los Alamos National Laboratory is developing an 850-MHz tetrode amplifier. These amplifiers will provide rf power to the momentum compactor and bunch rotator cavities of the GTA. Available tubes provide only a limited safety margin for a low-risk design at the power levels and duty factor required for GTA cavities. At 850 MHz, the output power capability of available tubes is reduced because of transit time effects and limited anode voltage holdoff. Pulsing the anode of the output tetrode amplifier will allow higher output power with minimum design risk. A floating-deck modulator acts as a high-voltage/high-current switch, so voltage is applied to the anode of the gridded tube only during the rf pulse. The anode voltage holdoff capability of the tube is substantially enhanced by operating in this mode. This paper will describe the design of the floating deck modulator and its impact on the design risk of the 850-MHz tetrode amplifier.
Date: January 1, 1990
Creator: Rees, D. & Friedrichs, C.
Partner: UNT Libraries Government Documents Department

Improving the efficiency of microwave devices with a double output cavity

Description: Double output cavities have been used experimentally to increase the efficiency of high-power klystrons. We have used particle-in-cell simulations with the 2 + 1/2 dimensional code MASK to optimize the design of double output cavities for the lasertron and the 50 MW klystron under development at SLAC. We discuss design considerations for double output cavities (e.g., optimum choice of voltages and phases, efficiency, wall interception, breakdown). We describe how one calculates the cavity impedance matrix from the gap voltages and phases. Simulation results are compared to experience with the 150 MW klystron.
Date: May 1, 1986
Creator: Eppley, K.R.; Herrmannsfeldt, W.B. & Lee, T.G.
Partner: UNT Libraries Government Documents Department

Anomalous electron loading in SLAC 5045 klystron and relativistic klystron input cavities

Description: Recent studies of RF breakup and instability in the SLAC 5045 klystrons have revealed that many production klystrons show loading of the input cavity by low energy electrons even under cold cathode no beam conditions. Sometime after the onset of the RF drive pulse, the input cavity absorbs a portion of the incident RF drive that would otherwise be reflected from the not-beam-loaded cavity. This power absorption is a function of drive level, and of axial magnetic field surrounding the cavity. No power absorption is present when the axial magnetic field is zero. This same phenomenon has been observed in the input cavity of relativistic klystron experiments being conducted as part of the SLAC-LBL-LLNL development program. The phenomenon may be associated with RF breakup and RF instability in SLAC 5045 klystrons, and with unstable pulse shortening in the relativistic klystron experiments. This paper outlines some old and new observations of microwave beam device malfunctions that probably are associated with low energy electron fluxes in the vacuum environments of microwave power devices. 2 refs., 5 figs.
Date: March 1, 1989
Creator: Koontz, R.F.; Fowkes, R.W.; Lavine, T.L.; Miller, R.H. & Vlieks, A.E.
Partner: UNT Libraries Government Documents Department

Breakdown phenomena in high power klystrons

Description: In the course of developing new high peak power klystrons at SLAC, high electric fields in several regions of these devices have become an important source of vacuum breakdown phenomena. In addition, a renewed interest in breakdown phenomena for nanosecond pulse, multi-megavolt per centimeter fields has been sparked by recent R and D work in the area of gigawatt RF sources. The most important regions of electrical breakdown are in the output cavity gap area, the RF ceramic windows, and the gun ceramic insulator. The details of the observed breakdown in these regions, experiments performed to understand the phenomena and solutions found to alleviate the problems will be discussed. Recently experiments have been performed on a new prototype R and D klystron. Peak electric fields across the output cavity gaps of this klystron exceed 2 MV/cm. The effect of peak field duration (i.e. pulse width) on the onset of breakdown have been measured. The pulse widths varied from tens of nanoseconds to microseconds. Results from these experiments will be presented. The failure of ceramic RF windows due to multipactor and puncturing was an important problem to overcome in order that our high power klystrons would have a useful life expectancy. Consequently many studies and tests were made to understand and alleviate window breakdown phenomena. Some of the results in this area, especially the effects of surface coatings, window materials and processing techniques and their effects on breakdown will be discussed. Another important source of klystron failure in the recent past at SLAC has been the puncturing of the high voltage ceramic insulator in the gun region. A way of alleviating this problem has been found although the actual cause of the puncturing is not yet clear. The ''practical'' solution to this breakdown process will be described and a possible mechanism ...
Date: March 1, 1988
Creator: Vlieks, A.E.; Allen, M.A.; Callin, R.S.; Fowkes, W.R.; Hoyt, E.W.; Lebacqz, J.V. et al.
Partner: UNT Libraries Government Documents Department

Fundamentals of klystron testing

Description: Fundamentals of klystron testing is a text primarily intended for the indoctrination of new klystron group test stand operators. It should significantly reduce the familiarization time of a new operator, making him an asset to the group sooner than has been experienced in the past. The new employee must appreciate the mission of SLAC before he can rightfully be expected to make a meaningful contribution to the group's effort. Thus, the introductory section acquaints the reader with basic concepts of accelerators in general, then briefly describes major physical aspects of the Stanford Linear Accelerator. Only then is his attention directed to the klystron, with its auxiliary systems, and the rudiments of klystron tube performance checks. It is presumed that the reader is acquainted with basic principles of electronics and scientific notation. However, to preserve the integrity of an indoctrination guide, tedious technical discussions and mathematical analysis have been studiously avoided. It is hoped that the new operator will continue to use the text for reference long after his indoctrination period is completed. Even the more experienced operator should find that particular sections will refresh his understanding of basic principles of klystron testing.
Date: August 1, 1978
Creator: Caldwell, J.W. Jr.
Partner: UNT Libraries Government Documents Department

Experimental progress on virtual-cathode very high power microwave source development

Description: The evolution of rf accelerator technology toward high-power, high-current, low-emittance beams produces an ever-increasing demand for efficient, very high power microwave sources. The present klystron technology has performed very well but is not expected to produce reliable gigawatt peak-power units in the 1- to 10-GHz regime. Further major advancements must involve other types of sources. The reflexing electron sources can produce microwave powers at the gigawatt level and have demonstrated operation from 800 MHz to 40 GHz. Pulse length appears to be limited by electron-beam diode closure, and reflexing electron devices have been operated in a repetitively pulsed mode. An experiment is under way to investigate concepts to stabilize the frequency of the virtual cathode source. If one can successfully frequency and phase lock this source to an external signal, then this source can operate as a very high power microwave amplifier making it practical for accelerator applications. The progress on an experiment to test these concepts will be discussed.
Date: January 1, 1987
Creator: Fazio, M.V. & Hoeberling, R.F.
Partner: UNT Libraries Government Documents Department

Design of a 100 MW X-band klystron

Description: 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. 3 refs., 6 figs., 2 tabs.
Date: February 1, 1989
Creator: Eppley, K.
Partner: UNT Libraries Government Documents Department

Advanced technology on the megawatt modulator for the ground test accelerator

Description: This paper presents the new concept of accelerator technology developed by Los Alamos National Laboratory, AT-Division. The modulator is driven on-off by rf switching power supply to achieve 1-MW rf accelerator energy from the klystron and klystrode at 850 MHz. The advantages are listed below: system cost saving up to 70%, operating cost saving up to 60%, weight reduced from 24,000 lbs. to 700 lbs., size reduced from 512 to 12 cu. ft., and efficiency improved from 75 to 97%. 2 figs.
Date: January 1, 1989
Creator: Yasotornrat, Hemtong
Partner: UNT Libraries Government Documents Department

Mean life of klystrons

Description: It would be useful to have the best possible estimate of this mean life-time of our new klystrons based on the most recent, available operating experience. A simple formula is given for this best estimate, based on the maximum likelihood method. This method also provides an indication of the reliability of the estimated lifetime. The results given here apply uniquely to a uniform klystron population for which we can assume that deaths occur randomly, and independently of the previous history (operating time) of any one klystron.
Date: October 30, 1985
Creator: Sands, M.
Partner: UNT Libraries Government Documents Department

RF pulse compression and alternative RF sources for linear colliders

Description: Future linear colliders will require a very high peak power per meter of accelerating structure at a relatively high frequency/endash/greater than 10 GHz/endash/but at a relatively short pulse length/endash/less than 100 ns. One technique for generating the required peak power is to use a more or less conventional microwave power source, which produces power at a pulse length typically on the order of 1 s, together with RF pulse compression. Some parameters are given for a Binary Power Multiplier (BPM) pulse compression system operating at 17.1 GHz with an output pulse length of 60 ns. The peak power gain for a three stage system is estimated to be 6.6 (82% compression efficiency). Some possible long-pulse microwave sources which/endash/when coupled with such a pulse compression system/endash/would be suitable for driving a linear collider are briefly discussed. 13 refs., 1 fig., 1 tab.
Date: December 1, 1988
Creator: Wilson, P.B.
Partner: UNT Libraries Government Documents Department

An rf-driven lasertron

Description: An rf-driven lasertron has been built and is being tested. It is designed to produce over 1 MW of power at 1.3 GHz, with over 60% conversion efficiency between the beam's kinetic energy and microwaves. The design and experiment are discussed, and calculations are presented that show lasertrons can operate at frequencies up to 20 GHz. 3 refs., 5 figs.
Date: January 1, 1988
Creator: Tallerico, P.J.; Sheffield, R.L.; Cornelius, W.D.; Gray, E.R.; Wilson, M.T.; Nguyen, D.C. et al.
Partner: UNT Libraries Government Documents Department

Relativistic klystron wakefields

Description: Monopole, dipole and quadrupole wake potentials are calculated for two cavities in a standing-wave relativistic klystron, using two independent programs, TBCI and AMOS. Reflections from model terminations which may distort long-range wakes can be mitigated either by using a very long pipe or by using absorptive materials at the pipe boundaries. 7 refs., 10 figs.
Date: April 14, 1989
Creator: Yu, D.U.L. (Duly Consultants, Rancho Palos Verdes, CA (USA)); Craig, G.D. & DeFord, J.F. (Lawrence Livermore National Lab., CA (USA))
Partner: UNT Libraries Government Documents Department

Modulator considerations for beam chopping in the low energy beam transport at the SSC Laboratory

Description: Beam chopping in the low energy transport line at the Superconducting Super Collider Laboratory is accomplished using an electrostatic deflection system. LINAC requirements dictate the design of two modulators operating at 10 Hz with rise and fall times (as measured from approximately 10--99%) of {approximately}100 ns. Design of the first pulser, normally at 10 kV and pulsed to ground potential, utilizes a transformer-coupled diode-clamped solid state circuit to achieve the 2--35 {mu}s pulse width range required. The second pulser, which pulses from ground to approximately 7 kV, relies on a series vacuum tube circuit. The current designs, as well as recent test results and other circuit topologies considered, will be presented. 6 refs.
Date: June 1, 1991
Creator: Anderson, D. & Pappas, G.
Partner: UNT Libraries Government Documents Department

Generation of oxygen, carbon and metallic ion beams by a compact microwave source

Description: A small microwave ion source fabricated from a quartz tube and enclosed externally by a cavity has been operated with different geometries and for various gases in a cw mode. This source has been used to generate oxygen ion beams with energy as low as 5.5 eV. Beam energy spread has been measured to be less than 1 eV. By installing different metal plates on the front extraction electrode, metallic ion beams such as (Be, Cu, Al, etc.) can be produced.
Date: July 1, 1986
Creator: Walther, S.R.; Leung, K.N.; Ehlers, K.W. & Kunkel, W.B.
Partner: UNT Libraries Government Documents Department

Metallic coating of microspheres

Description: Extremely smooth, uniform metal coatings of micrometer thicknesses on microscopic glass spheres (microspheres) are often needed as targets for inertial confinement fusion (ICF) experiments. The first part of this paper reviews those methods used successfully to provide metal coated microspheres for ICF targets, including magnetron sputtering, electro- and electroless plating, and chemical vapor pyrolysis. The second part of this paper discusses some of the critical aspects of magnetron sputter coating of microspheres, including substrate requirements, the sticking of microspheres during coating (preventing a uniform coating), and the difficulties in growing the desired dense, smooth, uniform microstructure on continuously moving spherical substrates.
Date: August 15, 1980
Creator: Meyer, S.F.
Partner: UNT Libraries Government Documents Department