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In this paper, we present theory and experimental data for a resonant-delay-line pulse-compression system. The system is fed by two high-power klystrons at X-band. The peak output power is four times the input power. The system produces flat-top output pulses. It uses evacuated room-temperature copper delay lines as a means of storing energy. These lines achieved a quality factor greater than 4.3/spl times/10/sup 5/, with total losses due to external components measured at 4%. We compare theory with experimental results. The system produced 150-ns pulses at power levels around 470 MW.

We present the design and a proof of principle experimental results of an optically controlled high-power RP pulse-compression system. In principle, the design should handle a few hundreds of megawatts of power at X-band. The system is based on the switched resonant delay-line theory [1]. It employs resonant delay lines as a means of storing RF energy. The coupling to the lines is optimized for maximum energy storage during the charging phase. To discharge the lines, a high-power microwave switch increases the coupling to the lines just before the start of the output pulse. The high-power microwave switch required for this system is realized using optical excitation of an electron-hole plasma layer on the surface of a pure silicon wafer. The switch is designed to operate in the TE/sub 01/ mode in a circular waveguide to avoid the edge effects present at the interface between the silicon wafer and the supporting waveguide; thus, enhancing its power handling capability.

The field emission was measured during the high- power testing of the LCLS photocathode RF gun. A careful study and analysis of the field emission electrons, or dark current is important in assessing the gun's internal surface quality in actual operation, especially those surfaces with high fields. The first indication of a good RF gun design and fabrication is short processing time to the required fields and low electron emission at high- fields. The charge per 2 microsecond long RF pulse (the dark charge) was measured as a function of the peak cathode field for the 1.6 cell, 2.856 GHz LCLS RF gun. Faraday cup data was taken for cathode peak RF fields up to 120 MV/m producing a maximum of 0.6 nC/RF pulse for a diamond-turned polycrystalline copper cathode installed in the gun. Digitized images of the dark charge were taken using a 100 micron thick YAG crystal for a range of solenoid fields to determine the location and angular distribution of the field emitters. The FN plots and emitter image analysis will be described in this paper.

A compact source of monoenergetic X-rays, generated via Compton backscattering, has been developed in a collaboration between U.C Davis and SLAC. The source consists of a 5.5 cell X-band photoinjector, a 1.05 m long high gradient accelerator structure and an interaction chamber where a high power (TW), short pulse (sub-ps) infrared laser beam is brought into a nearly head-on collision with a high quality focused electron beam. Successful completion of this project will result in the capability of generating a monoenergetic X-ray beam, continuously tunable from 20 - 85 keV. We have completed a series of measurements leading up to the generation of monoenergetic X-rays. Measurements of essential electron beam parameters and the techniques used in establishing electron/photon collisions will be presented. We discuss the design of an improved interaction chamber, future electro-optic experiments using this chamber and plans for expanding the overall program to the generation of Terahertz radiation.

In an effort to develop a monochromatic, tunable source of X-rays in the 20-85 KeV energy range, a 5.5 cell X-band RF gun has been designed and tested. Together with a 1.05 m long high gradient accelerating structure (an NLC Collider component), this system can generate and accelerate a beam of electrons to energies in excess of 60 MeV. Monochromatic X-rays are generated, via the Compton Effect, through a nearly head-on collision with a multi-terawatt TW laser beam. We describe the experimental setup and report on recent measurements of electron beam parameters as well as measurement techniques.

We present theory and experimental data for a resonant-delay-line pulse-compression system. The system is fed by two high power klystrons at X-band. The output power is four times bigger than the input power. The system produces flat-top output pulses. The system uses evacuated room-temperature copper delay lines as a means of storing energy. These lines achieved a quality factor greater than 4.3/spl times/10/sup 5/, with total losses due to external components measured at 4%. We compare theory with experimental results.

For more than ten years, we have been working on R&D for X-band accelerator structures for the JLC/NLC linear collider. Several types of Detuned (DS) and Damped Detuned Structures (DDS) have been successfully designed and fabricated. They have been experimentally tested at both low power and high power to characterize their mechanical and electrical properties. Recently we started developing a new type of damped detuned structure with optimized round-shaped cavities (RDDS). This paper discusses the special specifications, design methods, fabrication procedures, measurement technologies, and anticipated future improvements for all these structures.

Studies of RF breakup and instability in the SLAC (Stanford Linear Accelerator Center) 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. 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 are outlined. >

A compact source of monoenergetic X‐rays generated via Compton backscattering is under development at SLAC. It consists of a Photoinjector operating at 11.424 GHz, a stage of post acceleration using a 1.05 m long high gradient accelerator structure and an interaction chamber where a high power (TW), short pulse (sub‐ps) infrared laser beam with a high quality focused electron beam are brought into collision. Successful completion of this project will result in the capability of generating a monoenergetic X‐ray beam, continuously tunable from 20 – 85 keV. All components have been installed and initial testing has commenced. We are currently generating and accelerating an electron beam up to the accelerator and measuring the essential beam parameters, i.e., quantum efficiency, emittance, energy and stability. The latest test results will be presented together with a description of the beamline components and laser system.

A number of experimental klystrons have been constructed and evaluated at SLAC, KEK and INP, aiming toward output power objectives of 100 and 120 MW at 11.4 GHz (SLAC and KEK respectively) or 150 MW at 14 GHz (INP), with pulse lengths of the order of 1 /spl mu/s. Since RF breakdown is considered to be the principal mechanism limiting power for such tubes, most of the effort has been concentrated on the design of output circuits that reduce RF gradients by distributing fields over a longer region of interaction. Another klystron component receiving emphasis has been the output window, where the approach for future tubes may be to use a circular TEO1-mode, half-wave window. Best results to date in this continuing international effort are: 50 MW with 1 /spl mu/s pulses, using a traveling-wave output circuit (SLAC and INP), and 85 MW with 200 ns. Pulses (SLAC), using two conventional reentrant, but uncoupled, output cavities. At KEK a klystron with a single, but not reentrant, cavity has produced 80 MW in 50 ns pulses. Finally, Haimson has demonstrated 100 MW at 50 ns with a traveling-wave output. This paper addresses primarily the work performed at SLAC during the last two years. >

The Binary Pulse Compression system installed at SLAC was tested using two klystrons, one with 10 MW and the other with 34 MW output. By compressing 560 ns klystron pulses into 70 ns, the measured BPC output was 175 MW, limited by the available power from the two klystrons. This output was used to provide 100-MW input to a 30-cell X-band structure in which a 100-MV/m gradient was obtained. This system, using the higher klystron outputs expected in the future has the potential to deliver the 350 MW needed to obtain 100 MV/m gradients in the 1.8-m NLC prototype structure. This note describes the timing, triggering, and phase coding used in the two-klystron experiment, and the expected and measured network response to three- or two-stage modulation. >

During the past several years, there has been tremendous progress on the development of the RF system and accelerating structures for a Next Linear Collider (NLC). Developments include high-power klystrons, RF pulse compression systems and damped/detuned accelerator structures to reduce wakefields. In order to integrate these separate development efforts into an actual X-band accelerator capable of accelerating the electron beams necessary for an NLC, we are building an NLC Test Accelerator (NLCTA). The goal of the NLCTA is to bring together all elements of the entire accelerating system by constructing and reliably operating an engineered model of a high-gradient linac suitable for the NLC. The NLCTA will serve as a testbed as the design of the NLC evolves. In addition to testing the RF acceleration system, the NLCTA is designed to address many questions related to the dynamics of the beam during acceleration. In this paper, we will report on the status of the design, component development, and construction of the NLC Test Accelerator. >

An experimental station for an X-band Next Linear Collider has been constructed at SLAC. This station consists of a klystron and modulator, a low-loss waveguide system for RF power distribution, a SLED II pulse-compression and peak-power multiplication system, acceleration sections and beam-line components (gun, pre-buncher, pre-accelerator, focussing elements and spectrometer). An extensive program of experiments to evaluate the performance of all components is underway. The station is described in detail in this paper, and results to date are presented. >

Increasing the peak RF power available from X-band microwave tubes by means of RF pulse compression is envisioned as a way of achieving the few-hundred-megawatt power levels needed to drive a next-generation linear collider with 50-100 MW klystrons. SLED-II is a method of pulse compression similar in principal to the SLED method currently in use on the SLC and the LEP injector linac. It utilizes low-loss resonant delay lines in place of the storage cavities of the latter. This produces the added benefit of a flat-topped output pulse. At SLAC, we have designed and constructed a prototype SLED-II pulse-compression system which operates in the circular TE/sub 01/ mode. It includes a circular guide 3-dB coupler and other novel components. Low-power and initial high-power tests have been made, yielding a peak power multiplication of 4.8 at an efficiency of 40%. The system will be used in providing power for structure tests in the ASTA (Accelerator Structures Test Area) bunker. An upgraded second prototype will have improved efficiency and will serve as a model for the pulse compression system of the NLCTA (Next Linear Collider Test Accelerator). >

It is important to minimize power loss in the waveguide system connecting klystron, pulse-compressor, and accelerator in an X-Band NLC. However, existing designs of klystron output cavity circuits and accelerator input couplers utilize rectangular waveguide which has relatively high transmission loss. It is therefore necessary to convert to and from the low-loss mode in circular waveguide at each end of the system. A description is given of development work on high-power, high-vacuum 'flower-petal' transducers, which convert the TE/sub 10/ mode in rectangular guide to the TE/sub 01/ mode in circular guide. A three-port modification of the flower petal device, which can be used as either a power combiner at the klystron or a power divider at the accelerator is also described. >

A klystron designed to operate at 11.4 GHz and 440 kV is presently Stanford Linear Accelerator Center's (SLAC's) strongest RF power source candidate for the Next Linear Collider. It is expected to provide 100 MW of RF power with a pulse width of 1 mu s. The authors describe progress in the development of this device including results from single- and double-gap output cavities and various styles of RF output windows. The design parameters for this klystron are shown. Three X-band klystrons have been designed to test various alternatives to RF windows, output cavities, and beam optics. At this time 72-MW RF power has been generated with a pulse width of 100 ns and 35 MW has been generated at 800 ns. >

A compact RF load has been designed using a cascaded array of lossy radial RF chokes to dissipate 100 MW peak and 8 kW average power uniformly along the length of the load. Operation in the circularly polarized TE/sub 11/ mode assures uniform dissipation azimuthally as well.

One of the major challenges in the next-generation electron-positron linear colliders is to produce and control multi-bunch beams with extremely small transverse emittance. The Accelerator Test Facility (ATF) at KEK is a test accelerator that has been built to study the feasibility of production, damping, control and diagnosis of such beams. The facility consists of a multi-bunch capable thermionic gun, bunchers, followed by a 1.54 GeV S-band injector, beam transport and a test damping ring. This paper reports the preliminary results from commissioning and accelerator studies of the test damping ring that has started in January, 1997.

In the Next Linear Collider (NLC) it is expected that the high power RF components be able to handle peak power levels in excess of 400 MW. We present recent results of high power tests designed to investigate the RF breakdown limits of the X-band pulse compression system used at SLAC. (SLED-II). Results of these tests show that both the TE/sub 01/-TE/sub 10/ mode converter and the 4-port hybrid have a maximum useful power limit of 220-250 MW. Based on these tests, modifications of these components have been undertaken to improve their peak field handling capability. Results of these modifications will be presented.

The overmoded RF transmission and pulsed power compression system for SLAC's Next Linear Collider (NLC) program requires a high degree of transmission efficiency and mode purity to be economically feasible. To this end, a number of new, high power components and systems have been developed at X-band, which transmit RF power in the low loss, circular TE01 mode with negligible mode conversion. In addition, a highly efficient SLED-II pulse compressor has been developed and successfully tested at high power. The system produced a 200 MW, 250 ns wide pulse with a near-perfect flat-top. In this paper we describe the design and test results of the high power pulse compression system using SLED-II.

High frequency linear collider schemes envisage the use of rather high accelerating gradients: 50 to 100 MV/m for X-band and 80 MV/m for CLIC. Because these gradients are well above those commonly used in accelerators, high gradient studies of high frequency structures have been initiated and test facilities have been constructed at KEK, SLAC and CERN. The studies seek to demonstrate that the above mentioned gradients are both achievable and practical. There is no well-defined criterion for the maximum acceptable level of dark current but it must be low enough not to generate unacceptable transverse wakefields, disturb beam position monitor readings or cause RF power losses. Because there are of the order of 10,000 accelerating sections in a high frequency linear collider, the conditioning process should not be too long or difficult. The test facilities have been instrumented to allow investigation of field emission and RF breakdown mechanisms. With an understanding of these effects, the high gradient performance of accelerating sections may be improved through modifications in geometry, fabrication methods and surface finish. These high gradient test facilities also allow the ultimate performance of high frequency/short pulse length accelerating structures to be probed. This report describes the high gradient test at SLAC of an X-band accelerating section built at CERN using technology developed for CLIC.

We present design methodology for high power microwave switches. Among all possible applications for such a switch we emphasize the design parameters for application to the pulse compression system associated with the Next Linear Collider (NLC). The switch is based on the excitation of a plasma layer within a silicon wafer by either a laser or an electron beam. We investigate problems associated with high power operation of such a switch. Mainly, we explore solutions to the problems of thermal runaway, avalanche breakdown, photo-emission, and secondary emission. Different design methodologies are presented.

We present design and experimental results of a high power X-band load. The load is formed as a disk-loaded waveguide structure using lossy, type 430, stainless steel. The design parameters have been optimized using the recently developed mode-matching code MLEGO. The load has been designed for compactness while maintaining a band width greater than 300 MHz.

This paper presents a study and design methodology for enhancing the efficiency of the SLED II rf pulse-compression system [P.B. Wilson, Z.D. Farkas and R.D. Ruth, Linear Accel. Conf., Albuquerque, NM, 1990]. This system employs resonant delay lines as a means of storing rf energy. By making the external quality factor of these lines vary as a function of time, the intrinsic efficiency of the system can reach 100%. However, we demonstrate a considerable increase in efficiency even if the change of the quality factor is limited to a single event in time. During this event, the quality factor of the lines changes from one value to another. The difference between these two values is minimized to simplify the realization of the quality factor switch. We present the system optimum parameters for this case. We also show the extension of this system to two events in time, during which the quality factor of the line changes between three predetermined states. The effects of the losses due to the delay lines and the switch used to change the quality factor are also studied.

The successful design of high power windows play an essential role in RF power source development in accelerator programs such as the Next Linear Collider (NLC). Different window design approaches have been developed at several institutions to develop a successful high power window design. Some of the design considerations include the utilization of low loss RF modes, multiple RF modes and different window materials. In the past year some of these designs have been tested at SLAC using a pair of 50+ MW X-band klystrons as power sources. This permitted testing to power levels exceeding 100 MW at pulse widths ranging from 0.15 to 1.5 microseconds. We will present results of these tests including their RF performance and their optical and X-ray emission characteristics as a function of pulse width and power levels.

As part of a National Cancer Institute contract to develop a compact source of monoenergetic X-rays via Compton backscattering, we have completed the design and construction of a 5.5 cell Photoinjector operating at 11.424 GHz. Successful completion of this project will result in the capability of generating a monoenergetic Xray beam, continuously tunable from 20 - 85 KeV. The immediate goal is the development of a Photoinjector producing 7 MeV, 0.5nC, sub-picosecond electron bunches with normalized RMS emittances of 1 pi-mmmR at repetition rates up to 60 Hz.. This beam will then be further accelerated to 60 MeV using a 1.05 m accelerating structure. This Photoinjector is somewhat different than the traditional 1.5 cell design both because of the number of cells and the symmetrically fed input coupler cell. Its operating frequency is also unique. Since the cathode is non-removable, cold-test tuning was somewhat more difficult than in other designs. We will present results of “bead-drop” measurements used in tuning this structure. Initial beam measurements are currently in progress and results will be presented as well as results of RF conditioning to high gradients at X-band. Details of the RF system, emittance-compensating solenoid, and cathode laser system as well as PARMELA simulations will also be presented.

X-band klystrons capable of 75 MW and utilizing either solenoidal or Periodic Permanent Magnet (PPM) focusing are undergoing design, fabrication and testing at the Stanford Linear Accelerator Center (SLAC). The klystron development is part of an effort to realize components necessary for the construction of the Next Linear Collider (NLC). SLAC has completed a solenoidal-focused X-band klystron development effort to study the design and operation of tubes with beam microperveances of 1.2. As of early 2000, nine 1.2 (mu) K klystrons have been tested to 50 MW at 1.5 microsecond(s) . The first 50 MW PPM klystron, constructed in 1996, was designed with a 0.6 (mu) K beam at 465 kV and uses a 5-cell traveling-wave output structure. Recent testing of this tube at wider pulsewidths has reached 50 MW at 55% efficiency, 2.4 microsecond(s) and 60 Hz. A 75 MW PPM klystron prototype was constructed in 1998 and has reached the NLC design target of 75 MW at 1.5 microsecond(s) . A new 75 MW PPM klystron design, which is aimed at reducing the cost and increasing the reliability of multi- megawatt PPM klystrons, is under investigation. The tube is scheduled for testing during early 2001.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

RF breakdown is a critical issue in the conditioning of klystrons, accelerator sections, and rf components for the next linear collider (NLC), as well as other high gradient accelerators and high power microwave sources. SLAC is conducting a series of experiments using an X-band traveling wave ring to characterize the processes and trigger mechanisms associated with rf breakdown. The goal of the research is to identify materials, processes, and manufacturing methods that will increase the breakdown threshold and minimize the time required for conditioning.

The Delay Line Distribution System (DLDS) is an alternative to conventional pulse compression, which enhances the peak power of rf sources while matching the long pulse of those sources to the shorter filling time of accelerator structures. We present an implementation of this scheme that combines pairs of parallel delay lines of the system into single lines. The power of several sources is combined into a single waveguide delay line using a multi-mode launcher. The output mode of the launcher is determined by the phase coding of the input signals. The combined power is extracted from the delay line using mode-selective extractors, each of which extracts a single mode. Hence, the phase coding of the sources controls the output port of the combined power. The power is then fed to the local accelerator structures. We present a detailed design of such a system, including several implementation methods for the launchers, extractors, and ancillary high power rf components. The system is designed so that it can handle the 600 MW peak power required by the NLC design while maintaining high efficiency.

This paper describes an X-band RF system for the Next Linear Collider Test Accelerator. The RF system consists of a 90 MeV injector and a 540 MeV linac. The main components of the injector are two low-Q single-cavity prebunchers and two 0.9-m-long detuned accelerator sections. The linac system consists of six 1.8-m-long detuned and damped detuned accelerator sections powered in pairs. The RF power generation, compression, delivery, distribution and measurement systems consist of klystrons, SLED-II energy compression systems, rectangular waveguides, magic-T's, and directional couplers. The phase and amplitude for each prebuncher is adjusted via a magic-T type phase shifter/attenuator. Correct phasing between the two 0.9 m accelerator sections is obtained by properly aligning the sections and adjusting two squeeze type phase shifters. Bunch phase and bunch length can be monitored with special microwave cavities and measurement systems. The design, fabrication, microwave measurement, calibration, and operation of the sub-systems and their components are briefly presented.

Conventional CW millimeter amplifiers (coupled-cavity TWTs or gyro-klystrons) are limited in power by the maximum current hat can be accommodated in a single beam. Cathode current density, beam optics, and the magnetic field necessary to confine the beam, combine to limit beam current and add cost and bulk to the device. If the microwave source is designed as a pulsed klystron operating at a high voltage, larger lateral as well as axial dimensions can be employed. Beam optics become easier and permanent magnet periodic focusing is possible. A higher efficiency also results, because of the low perveance. A number of klystrons can then be fabricated on single substrate, using a deep- etch lithography technique. They can be water-cooled individually, and operated in parallel. Several such modules can be stacked to form a klystron `brick,' requiring a relatively low voltage for the peak and average power produced. The `brick' can be provided with a single output, or with individual, spatially-combined radiators. The design of a 4 X 10 X 1.5-inch module producing 500 kW peak, 500 W average at 91 GHz, and operating at 120 kV, 10 A, will be described.

The overmoded rf transmission and pulsed power compression system for SLAC’s Next Linear Collider (NLC) program requires a high degree of transmission efficiency and mode purity to be economically feasible. To this end, a number of new, high power components and systems have been developed at X-band, which transmit rf power in the low loss, circular TE01 mode with negligible mode conversion. In addition, a highly efficient SLED-II [1] pulse compressor has been developed and successfully tested at high power at two accelerator test facilities at SLAC. The systems produced a 200 MW pulse with a near-perfect flat-top with pulse widths ranging from 150–245 ns. In this paper we describe the design and test results of a rectangular-to-circular mode converter and the components/transmission systems based on them, as well as the design and measurements of the high power pulse compression systems using SLED-II. We will also describe how these components are being used to efficiently provide high power rf in the NL...

We present the design and a proof of principle experimental results of an optically controlled high power rf pulse compression system. The design should, in principle, handle few hundreds of Megawatts of power at X-band. The system is based on the switched resonant delay line theory (1). It employs resonant delay lines as a means of storing rf energy. The coupling to the lines is optimized for maximum energy storage during the charging phase. To discharge the lines, a high power microwave switch increases the coupling to the lines just before the start of the output pulse. The high power microwave switch, required for this system, is realized using optical excitation of an electron-hole plasma layer on the surface of a pure silicon wafer. The switch is designed to operate in the TE01 mode in a circular waveguide to avoid the edge effects present at the interface between the silicon wafer and the supporting waveguide; thus, enhancing its power handling capability.

A system for characterizing the phase shift per cell of a long X-band accelerator structure is described. The fields within the structure are perturbed by a small cylindrical metal bead pulled along the axis. A computer controls the bead position and processes the data from a network analyzer connected to the accelerator section. Measurements made on prototype accelerator sections are described, and they are shown to be in good agreement with theory.

This paper describes the design and performance of the XL-1 klystron; a 50 MW klystron operating at a frequency of 11.424 GHz for use on the SLAC Next Linear Collider Test Accelerator (NLCTA). Problems associated with the development of high-power rf sources for NLC, and the solutions implemented on XL-1 are discussed.

Summary form only given, as follows. We present design methodology and initial experimental results for a high power microwave switch. The switch is designed for application to the pulse compression system associated with the Next Linear Collider Test Accelerator (NLCTA). The switch is based on the excitation of a plasma layer within a silicon wafer by either a laser or an electron beam. We investigate problems associated with high power operation of such a switch. We explore solutions to the problems of thermal runaway, avalanche breakdown, photo-emission, and secondary emission.

Summary form only given, as follows. The next generation of linear colliders will require high accelerating gradients to achieve teraelectronvolt energies in an accelerator of reasonable length. To achieve these gradients while avoiding breakdown will require microwave sources in the range of 11-17 GHz with RF pulses of lengths approximately equal to the fill time of the accelerating structure. To increase luminosity, it will be necessary to accelerate many bunches in one filling of the RF structure while maintaining extremely restrictive bunch-to-bunch energy variation. The dispersion characteristics of the accelerating structure can cause significant distortion of the short RF pulses, both in magnitude and phase, which will cause undesirable energy variation between bunches. An analysis of this dispersion effect using a filter theory approach was compared to experimental observations performed on a SLAC (Stanford Linear Accelerator Center) type high-gradient accelerator, operating at 11.42 GHz with an average accelerating gradient of 100 MV/m and a fill time of 28 ns. A numerical study of multibunch operation in this accelerator was performed. Beam loading due to wakefield effects was calculated using the AMOS computer code

In the course of developing new high-peak-power klystrons, high electric fields in several regions of these devices have become an important source of vacuum breakdown. In addition, a renewed interest in breakdown phenomena for nanosecond-pulse, megavolt-per-centimeter fields has been sparked by recent 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 experiments and results on the breakdown in these regions are discussed, as well as the solutions to alleviate this breakdown problem. >

We have used relativistic klystron technology to extract 290 MW of peak power at 11.4 GHz from an induction linac beam, and to power a short 11.4-GHz high-gradient accelerator. We have measured rf phase stability, field emission, and the momentum spectrum of an accelerated electron beam. An average accelerating gradient of 84 MV/m has been achieved with 80 MW of relativistic klystron power.

The Next Linear Collider (NLC) injector system is designed to produce low emittance, 10 GeV electron and positron beams at 120 hertz for injection into the NLC main linacs. Each beam consists of a train of 95 bunches spaced by 2.8 ns; each bunch has a population of 1.15/spl times/10/sup 10/ particles. At injection into the main linacs, the horizontal and vertical emittances are specified to be /spl gamma//spl isin//sub x/=3/spl times/10/sup 16/ m-rad and /spl gamma//spl isin//sub y/=3/spl times/10/sup -8/ m-rad and the bunch length is 100 /spl mu/m. Electron polarization of greater than 80% is required. Electron and positron beams are generated in separate accelerator complexes each of which contain the source, damping ring systems, L-band, S-band, and X-band linacs, bunch length compressors, and collimation regions. The need for low technical risk, reliable injector subsystems is a major consideration in the design effort. This paper presents an overview of the NLC injector systems.