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To provide a compact high-brightness heavy-ion beam source for Heavy Ion Fusion, we have performed experiments to study a proposed merging beamlet approach for the injector. We used an RF plasma source to produce the initial beamlets. An array of converging beamlets was used to produce a beam with the envelope radius, convergence, and ellipticity matched to an electrostatic quadrupole channel. Experimental results were in good quantitative agreement with simulation and have demonstrated the feasibility of this concept. The size of a driver-scale injector system using this approach will be several times smaller than one designed using traditional single large-aperture beams. The success of this experiment has possible significant economical and technical impacts on the architecture of HIF drivers.

For both HIF and ion driven HEDP experiments, the beams a driver produces must have both high brightness and high current. The US HIF program has had extensive experience and success working with single, monolithic ion sources for accelerator experiments with moderate injector current requirements. Such sources produce up to hundreds of milliAmps with normalized emittances less than 1 - π -mm mrad. However, with a need for higher current, and more compact, sources up to and over 1 A, monolithic sources begin to suffer from the poor scaling of source area to current. That is, by combining the limits of space-charge limited emission, voltage breakdown, and good optics, the source area is seen to scale as a high power of the current, A ∝ I 8 / 3 . A means of bypassing the scaling, leading to a much more compact injector, is the use of multiple beamlets, each of which can have a much higher current density than a larger monolithic beam. The beamlets are merged near the end of the injector. A major challenge is the inherent emittance growth that occurs as the beamlets merge. In this paper, the design of such an injector will be presented along with simulations used to study and validate the design. This design offers other advantages, and some disadvantages, that will be described. Finally, comparisons will be made to experimental results from the merging beamlet experimental campaign on STS-500.

Negative ions have attractive features as drivers for inertial confinement fusion, because they will avoid electron cloud effects, and could be efficiently photodetached to neutrals after the final focus, which could also be beneficial in heating warm dense matter targets. The halogens have large electron affinities, and thus should be able to produce high current densities of relatively robust negative ions. Recent experiments comparing chlorine beams to argon beams using the same source, extraction optics, and diagnostics have demonstrated that Cl− beams can be produced with similar emittance to Ar+ beams, and with about 34 the current density from the same configuration. The observed effective beam temperature of about 13eV, and the similarity of current densities show that negative halogen beams can meet the current density and emittance requirements of heavy ion fusion. The near equivalence of the Cl− and Cl++Cl2+ current densities reaching the Faraday cup after passage through a substantial line density of effluent gas demonstrates that beam losses in the higher vacuum of a heavy ion fusion accelerator should be acceptable. A number of lines of evidence show that negative ion–positive ion plasmas (hereafter ion–ion plasmas), composed primarily of negative and positive ions with a small population of electrons, were produced in the sources near the extractor plane. Since Cl, F, I, and Br should all show similar chemistry, any of these halogens should be suitable as fusion driver beams, and heating thin iodine or bromine foils may produce ion–ion plasmas in the warm dense matter regime.

Key scientific results from recent experiments, modeling tools, and heavy ion accelerator research are summarized that explore ways to investigate the properties of high energy density matter in heavy-ion-driven targets, in particular, strongly-coupled plasmas at 0.01 to 0.1 times solid density for studies of warm dense matter, which is a frontier area in high energy density physics. Pursuit of these near-term objectives has resulted in many innovations that will ultimately benefit heavy ion inertial fusion energy. These include: neutralized ion beam compression and focusing, which hold the promise of greatly improving the stage between the accelerator and the target chamber in a fusion power plant; and the Pulse Line Ion Accelerator (PLIA), which may lead to compact, low-cost modular linac drivers.

The U.S. Heavy Ion Fusion program has recently commissioned several new experiments. In the High Current Experiment [P. A. Seidl et al., Laser Part. Beams 20, 435 (2003)], a single low-energy beam with driver-scale charge-per-unit-length and space-charge potential is being used to study the limits to transportable current posed by nonlinear fields and secondary atoms, ions, and electrons. The Neutralized Transport Experiment similarly employs a low-energy beam with driver-scale perveance to study final focus of high perveance beams and neutralization for transport in the target chamber. Other scaled experiments—the University of Maryland Electron Ring [P. G. O’Shea et al., accepted for publication in Laser Part. Beams] and the Paul Trap Simulator Experiment [R. C. Davidson, H. Qin, and G. Shvets, Phys. Plasmas 7, 1020 (2000)]—will provide fundamental physics results on processes with longer scale lengths. An experiment to test a new injector concept is also in the design stage. This paper will describe th...

A test facility is established at Lawrence Berkeley National Laboratory (LBNL) to study RF power sources for linear colliders based on the relativistic klystron two-beam accelerator (RK-TBA) concept. A 24-m long prototype source, the RTA, will be constructed in this facility to study physics, engineering, and cost issues related to RK-TBAs. The RTA will generate 200-ns 180-MW RF (11.4-GHz) pulses from each of eight output ports. The major components of the RTA include a 2.8-MeV 1.2-kA induction injector, transverse beam modulator, adiabatic compressor, and RF extraction section. The beam energy is increased to 4 MeV and the RF bunch length is shortened from 240/spl deg/ to 110/spl deg/ in the adiabatic compressor. The 8-m long extraction section includes 40 induction accelerator cells to maintain beam energy at an average 4 MeV, eight equally spaced RF output structures, and a ppm quadrupole focusing system. In this paper, we describe the RTA and present results of component testing and computer simulations.

An overview of the design parameters of a compact high-gradient high-luminosity X-band (8.568 GHz) photoinjector is followed by a more detailed description of each of its major subsystems: X-band RF gun, GHz repetition rate synchronously modelocked AlGaAs quantum well laser oscillator, and eight-pass Ti:Al/sub 2/O/sub 3/ chirped pulse laser amplifier. The photoinjector uses a high quantum efficiency (/spl sim/5%) Cs/sub 2/Te photocathode, and is capable of producing high-charge (>1 nC) relativistic (5 MeV) ultrashort (

We have recently initiated an investigation of electron emission from ferroelectric cathodes. Our experimental apparatus consisted of an electron diode and a 250 kV, 12 Ω, 70 ns pulsed high voltage power source. A planar triode modulator driven by a synthesized waveform generator initiates the polarization inversion and allows inversion pulse tailoring. The pulsed high voltage power source is capable of delivering two high voltage pulses within 50 μs of each other and is capable of operating at a sustained repetition rate of 5 Hz. Our initial measurements indicate that emission current densities above the Child-Langmuir space charge limit, JCL, are possible. We explain this effect to be based on a non-zero initial energy of the emitted electrons. We also determined that this effect is strongly coupled to relative timing between the inversion pulse and application of the main anode-cathode pulse. We also have initiated brightness measurements of the emitted beam and estimate a preliminary lower bound to be on the order of 109 A/m2rad2. As in our previous measurements at this Laboratory, we performed the measurement using a pepper pot technique. Beamlet profiles are recorded with a fast phosphor and gated cameras. We describe our apparatus and preliminary measurements.

Relativistic klystrons (RK's) are being developed as an RF power source for high gradient accelerator applications which include large linear electron-positron colliders, compact accelerators, and FEL sources. In a relativistic klystron two-beam accelerator (RK-TBA), the drive beam passes through a large number of RF output structures. High conversion efficiency of electron beam energy to RF energy is achieved in this concept by reacceleration of the modulated drive beam between output structures. We have conducted experiments studying the RF power extracted from various RK structures driven by modulated induction accelerator current pulses; our studies include work on improving the transport dynamics of the drive beam. We have started a demonstration in which the modulated induction beam current is reaccelerated by passage through subsequent induction accelerator cells. >

We have performed experiments and modeling to evaluate a proposed merging beamlet approach for use in a compact high-brightness Heavy Ion Fusion injector. We used an rf plasma source to produce the initial beamlets. An extraction current density of 100 mA/cm2 was achieved, and the thermal temperature of the ions was below 1 eV. An array of converging beamlets was used to produce a beam with the envelope radius, convergence, and ellipticity matched to an electrostatic quadrupole channel. Experimental results were in good quantitative agreement with computer simulations and have demonstrated the feasibility of this concept. The size of a driver-scale injector system using this approach will be several times smaller than one designed using traditional single large-aperture beams. The success of this experiment has possible significant economical and technical impacts on the architecture of HIF drivers.

A 2 kA cathode was successfully developed for the DARHT-II injector [1]. Since the DARHT injector cannot be baked and there may be virtual leaks, the local pressure near the cathode was not ideal even though the system pressure was in the 10-8 Torr range. In a series of experiments using quarter-inch size button cathodes, we showed that gas poisoning was a significant factor in this pressure range. Furthermore we found that the 311-XM (doped with scandium and has an M coating) cathode was less affected by gas poisoning than the 612-M, corresponding to a lower effective work function. Water vapor was found to be the worst contaminant among the various gases that we have tested. With a 6.5rdquo diameter 311-XM cathode, the DARHT-II injector produced > 2 kA corresponding to a current density of 10 A/cm2.

During heavy-ion operation in several particle accelerators worldwide, dynamic pressure rises of orders of magnitude were triggered by lost beam ions that bombarded the vacuum chamber walls. This ion-induced molecular desorption, observed at CERN, GSI, and BNL, can seriously limit the ion beam lifetime and intensity of the accelerator. From dedicated test stand experiments we have discovered that heavy-ion-induced gas desorption scales with the electronic energy loss (dE{sub e}/dx) of the ions slowing down in matter; but it varies only little with the ion impact angle, unlike electronic sputtering.

The cost of accelerators for heavy-ion inertial fusion energy (HIF) can be reduced by using the smallest possible clearance between the beam and the wall from the beamline. This increases beam loss to the walls, generating ion-induced electrons that could be trapped by beam space charge potential into an "electron cloud", which can cause degradation or loss of the ion beam. In order to test the physical mechanism model of ion induced electrons production we have measured the impact of K+ ions with energies up to 400 KeV on stainless steel surfaces near grazing incidence, using the ion source test stand (STS-500) at LLNL. The electron yield will be discussed and compared with experimental measurements from 1 MeV K+ ions in the High-Current Experiment at LBNL.

To provide a compact high-brightness heavy-ion beam source for Heavy Ion Fusion (HIF) accelerators, we have been experimenting with merging multi-beamlets in an injector which uses an RF plasma source. In an 80-kV 20-microsecond experiment, the RF plasma source has produced up to 5 mA of Ar+in a single beamlet. An extraction current density of 100 mA/cm2was achieved, and the thermal temperature of the ions was below 1 eV. We have tested at full voltage gradient the first 4 gaps of an injector design. Einzel lens were used to focus the beamlets while reducing the beamlet to beamlet space charge interaction. We were able to reach greater than 100 kV/cm in the first four gaps. We also performed experiments on a converging 119 multi-beamlet source. Although the source has the same optics as a full 1.6 MV injector system, these test were carried out at 400 kV due to the test stand HV limit. We have measured the beam’s emittance after the beamlets are merged and passed through an electrostatic quadrupole (ESQ). Our goal is to confirm the emittance growth and to demonstrate the technical feasibility of building a driver-scale HIF injector.

We describe the proposed developement of a 17.1 GHz microwave source based on an induction-linac-driven free-electron laser that is expected to produce peak power levels at the several-GW level. This system is being designed to serve as the power source for a TeV linear collider or for other high-gradient accelerators. We will discuss the power-source requirements for TeV colliders and present the initial design of an FEL that will produce the desired power. In addition, we shall discuss efficiency enhancement schemes such as a relativistic klystron “afterburner”, the requirements for beam reacceleration, and concepts for extraction of the microwave power while preserving key properties of the beam such as emittance and phase.

We are developing high-current ion sources for Heavy Ion Fusion (HIF) applications. Our proposed RF plasma source starts with an array of high current density mini-beamlets (of a few milliampere each at ∼100 mA/cm 2 ) that are kept separated from each other within a set of acceleration grids. After they have gained sufficient kinetic energy (>1.2 MeV), the mini-beamlets are allowed to merge together to form a high current beam (about 0.5 A) with low emittance. Simulations have been done to maximize the beam brightness within the physical constraints of the source. We have performed a series of experiments on an RF plasma source. A 80-kV 20-μs source has produced up to 5 mA of Ar + in a single beamlet and we measured the emittance of a beamlet, its energy spread, and the fraction of ions in higher charge states. We have also tested a 50-kV 61-hole multi-beamlet array. Two upcoming experiments are being prepared: the first experiment will test full-gradient extraction and transport of 61 beamlets through the first four electrodes, and the second experiment will converge 119 beamlets into an ESQ channel at one-quarter scaled voltage of a 1.6 MV HIF injector.

Typically a large diameter surface ionization source is used to produce > 0.5 A K{sup +} current with emittance < 1 {pi}-mm-mrad for heavy ion fusion experiments. So far we have observed aberrations that are slightly different from those predicted by computer simulations. We have now set up an experiment to study in detail the beam optics of such a large diameter ion diode and to benchmark the simulation code.

A energy analyzer system is being built for the DARHT-II accelerator similar to the energy analyzer used on the Astron accelerator. This system consists of a scattering wire, magnetic bend, and null signal detector. The wire thickness of 40 mil carbon and the scattering angle of 11 degrees is chosen for good signal to noise ratio. The dipole bend angle is 60 degrees, with a 30 cm radius of curvature. The image-plane focal distance is chosen for the required energy resolution. The energy resolution and acceptance are 0.1% and /spl plusmn/5% with a time response of 10 nsec. The wire must survive the 2 usec 2 kA, 18.4 MeV DARHT-II beam. The MCNP code was used to study the wire scattered properties. The scattered beam fills the available 1/spl times/2 cm dipole aperture. The dispersion normal to the beam direction is 0.43 cm/%. The detector is a PIN diode array which determines the beam position on the chip. This array consists of 40 2.5/spl times/0.1/spl times/0.25 mm bins with a gain in excess of 10000. The system will be installed in the space between the debris blocker and the cruncher solenoid up-stream from the shuttle dump.

Modern diagnostic techniques provide detailed information on beam conditions in injector, transport, and final focus experiments in the HIF-VNL. Parameters of interest include beam current, beam energy, transverse and longitudinal distributions, emittance, and space charge neutralization. Imaging techniques, based on kapton films and optical scintillators, complement and, in some cases, may replace conventional techniques based on slit scans. Time-resolved optical diagnostics that provide 4-D transverse information on the experimental beams are in operation on the existing experiments. Current work includes a compact optical diagnostic suitable for insertion in transport lines, improved algorithms for optical data analysis and interpretation, a high-resolution electrostatic energy analyzer, and an electron beam probe. A longitudinal diagnostic kicker generates longitudinal space-charge waves that travel on the beam. Time of flight of the space-charge waves and an electrostatic energy analyzer provide an absolute measure of the beam energy. Special diagnostics to detect secondary electrons and gases desorbed from the wall have been developed.

An experiment was set up on a 500-kV test stand to study the beam optics of an extraction diode using a 10-cm diameter alumino-silicate source. The beam was also sent through an aperture to reduce aberrations, thus enhancing its brightness. In comparing the experimental results with WARP-3D computer simulations, we found excellent agreement in the emittance diagrams and in the beam current rise-time. By benchmarking the computer code, we now have the capability to perform detail optical designs and to create the proper voltage waveform for producing a current pulse with a fast rise-time. A fast rise-time pulse is desirable because many potential near-term HIF experiments will require short beam pulses which have a fast rise-time.

The heavy-ion fusion program is conducting several ion source and injector experiments to support ongoing HIF beam transport experiments and to develop new injector concepts for future fusion drivers. In the area of large diameter surface source, we studied the beam optics, experimented with aperturing, and benchmarked the computer simulation code. Steady progress was made in the merging beamlet experiment. The RF plasma source was optimized to produce high current density beamlets. Computer simulation of merging beamlets had produced a design and the hardware is being fabricated. We are examining a new concept based on accel–decel injection to produce super-high line charge density for application in driving targets for high energy density physics studies. Since trapping of secondary electrons in high current positive ion beams is still a concern for HIF, we consider a backup option using negative ion beams.

Summary form only given. A novel source of transform-limited pulses of coherent electromagnetic radiation relying on the synchrotron radiation process in a fast wave guiding structure is investigated. An ultrashort electron bunch transversally accelerated by a periodic external field is considered. At grazing, where the bunch and group velocities are matched, the duration of the resulting ultrawideband chirped pulse is governed by group velocity dispersion instead of slippage. Because of the intimate connection between the rate of chirping and the bandwidth, the corresponding pulse duration is shown to be very close to the Fourier transform limit. In addition, the propagation of such chirped pulses through a guiding structure with negative group velocity dispersion is investigated both theoretically and computationally. The spectral and temporal characteristics of the chirped and compressed pulses are derived analytically. Detailed computer calculations complement this theoretical analysis. In addition, a detailed description of our X-band photoinjector facility (currently under construction), capable of producing trains of 100, 1 nC, subpicosecond photoelectron bunches at a micropulse repetition rate of 2.142 GHz and with a normalized emittance of 0.75 /spl pi/ mm-mrad (at 0.1 nC) will be given.

The authors address the problem of phase and amplitude stability of the RF pulse and present a technique for improving it in high-power, short-pulsed free-electron lasers and relativistic klystrons to a level that is acceptable for accelerator applications. They summarize the results of bench tests and computer simulations, and discuss a proposed high-power klystron experiment aimed at establishing the feasibility of the overall concept and the workability of the stabilization circuits. >

A high-power 11.4-GHz RF generator which consists of a 5.7-GHz chopping system and two 11.4-GHz traveling-wave output structures has been tested. The device was designed to generate about 500 MW of pulsed RF power at 11.4 GHz when driven by a 1-kA, 3-MeV induction beam. Problems with beam breakup in the output structures have limited the width of the RF output pulse for currents above 600 A. Short RF pulses up to 420 MW have been produced. Modifications are being made to decrease the growth of the beam-breakup fields in the output structures, and the chopping section will be used to study various extraction structures and the reacceleration of a bunched beam by induction cells. >

The authors have completed the initial phase of a 250 GHz cyclotron autoresonant maser (CARM) ARC facility. A non-Brillouin, solid, electron beam is generated from a flux-threaded, thermionic cathode. As the beam traverses a 10 kG plateau produced by a superconducting magnet, ten percent of the beam energy is converted into rotational energy in a bifilar helix wiggler that produces a spiraling, 50 G, transverse magnetic field. The beam is then compressed to a 5 mm diameter as it drifts into a 30 kG plateau. For the experiment, the CARM interaction region consisted of a single Bragg section resonator, followed by a smooth-bore amplifier section. Using high-pass filters, the authors observed broadband output signals estimated to be at the several megawatt level in the range 140 to over 230 GHz. This is consistent with operation as a superradiant amplifier. Simultaneously, K/sub a/ band power levels near 3 MW have also been observed. >

LLNL has proposed a multi-pulsed, multi-line of sight radiographic machine based on induction linac technology to be the core of the advanced hydrotest facility (AHF) being considered by the Department of Energy. In order to test the new technologies being developed for AHF we have recommissioned the Experimental Test Accelerator (ETA II). We will conduct our initial experiments using kickers and large angle bending optics at the ETA II facility. Our current status and our proposed experimental schedule are presented.

A Relativistic Klystron Two-Beam Accelerator (RK-TBA) is envisioned as a RF power source upgrade of the Next Linear Collider. Construction of a prototype, called the RTA, based on the RK-TBA concept has commenced at the Lawrence Berkeley National Laboratory. This prototype will be used to study physics, engineering, and costing issues involved in the application of the RK-TBA concept to linear colliders. The first half of the injector, a 1 MeV, 1.2 kA, 300 ns induction electron gun, has been built and is presently being tested. The design of the injector cells and the pulsed power drive units are presented in this paper.

Induction accelerating gap designs are being studied for Relativistic Klystron Two-Beam Accelerator (RK-TBA) applications. The accelerating gap has to satisfy the following major requirements: hold-off of the applied accelerating voltage pulse, low transverse impedance to limit beam breakup, low longitudinal impedance at the beam-modulation frequency to minimize power loss. Various gap geometries, materials and novel insulating techniques were explored to optimize the gap design. We report on the experimental effort to evaluate the RF properties of the accelerating gaps in a simple pillbox cavity structure. The experimental cavity setup was designed using the AMOS, MAFIA and URMEL numerical codes. Longitudinal impedance measurements above beam-tube cut-off frequency using a single-wire measuring system are presented.

Stacked insulators, with alternating layers of insulating material and conducting film, have been shown to support high surface electrical field stresses. We have investigated the application of the stacked insulator technology to the design of induction accelerator modules for the Relativistic-Klystron Two-Beam Accelerator program. The RF properties of the accelerating gaps using stacked insulators, particularly the impedance at frequencies above the beam pipe cutoff frequency, are investigated. Low impedance is critical for Relativistic-Klystron Two-Beam Accelerator applications where a high current, bunched beam is transported through many accelerating gaps. An induction accelerator module designs using a stacked insulator is presented.

We have measured a current emission density of 36 A-cm/sup -2/ over an 11.4-cm/sup 2/-area lead-titanate-zirconate (PZT) ferroelectric cathode with a pulsed anode-cathode (A-K) potential of 50 kV. We have also observed currents above those predicted by classical Child-Langmuir formula for a wide variety of cases. Since a plasma within the A-K gap could also lead to increase current emission we are attempting to measure the properties of the plasma near the cathode surface at emission time. In other measurements, we have observed strong gap currents in the absence of an A-K potential. Further, we continue to make brightness measurements of the emitted beam and observe spatially non-uniform emission and large shot-to-shot variation. Measurements show individual beamlets with a brightness as high 10/sup 11/ A m/sup -2/ rad/sup -2/.

Double pulse transport experiments were conducted on the front end of the ATA accelerator to obtain data on the capability of a velvet cloth cathode to produce two successive pulses. Pulses of approximately 3 kA were extracted from the cathode with interpulse spacings varying from 150 ns to 2.8 /spl mu/s using an anode-cathode voltage of about 1 MV. Analysis of the current and voltage waveform data from the injector indicate that the effects of cathode plasma on the second pulse of a two-pulse burst is minimal.

We are designing an experiment to study physics, engineering, and costing issues of an extended Relativistic Klystron Two-Beam Accelerator (RK-TBA). The experiment is a prototype for an RK-TBA based microwave power source suitable for driving a 1 TeV linear collider. Major components of the experiment include a 2.5-MV, 1.5-kA electron source, a 11.4-GHz modulator, a bunch compressor, and a 8-m extraction section. The extraction section will be comprised of 4 traveling-wave output structures, each generating about 360 MW of RF power. Induction cells will be used in the extraction section to maintain the average beam energy at 5 MeV. Status of the design is presented.

The proposal to perform a series of plasma lens experiments at the Final Focus Test Beam at SLAC has been described earlier. We report on our progress towards validation of concepts involved in the experiments, including the laser ionized plasma production test, development of the supersonic gas jet as the plasma source, and study on focused beam size measurement techniques. Most importantly, the effects of background events due to plasma lenses in future linear collider detectors, such as that in the NLC, are studied in details and are shown to be within detector tolerances.

The Dual-Axis Radiographic Hydrodynamics Test (DARHT) facility will employ two perpendicular electron Linear Induction Accelerators to produce intense, bremsstrahlung x-ray pulses for flash radiography. We intend to produce measurements containing three-dimensional information with sub-millimeter spatial resolution of the interior features of very dense, explosively-driven objects. The facility will be completed in two phases with the first phase having become operational in July 1999 utilizing a single-pulse, 20-MeV, 2-kA, 60-ns accelerator, a high-resolution electro-optical x-ray imaging system, and other hydrodynamics testing systems. We will briefly describe this machine. The first electron beams will be generated in the second phase of DARHT this year. The second DARHT accelerator consists of a 18.4-MeV, 2-kA, 2-microsecond pulse-width accelerator. Four short electron micropulses of variable pulse-width and spacing will be chopped out of the original, long accelerator pulse for producing time-resolved x-ray images. The second phase also features an extended, high-resolution electro-optical x-ray system with a framing speed of about 2-MHz. We will discuss this accelerator by summarizing the overall design of the long-pulse injector and accelerator. We will also discuss the fast kicker used to separate the long-pulse beam into short bursts suitable for radiography.

During normal DARHT II operation, the beam exiting the accelerator will be well characterized by its nominal design parameters of 20-MeV, 2000-Amperes, 2-/spl mu/sec-pulse length, and 3 cm-mr unnormalized emittance. Normal operation will have the beam delivered to a beam dump via several DC magnets. A 2-way kicker magnet is used to deflect portions of the beam into the straight ahead beamline leading to either a diagnostic beamline or to the converter target beamline. During start up and or beam development periods, the beam exiting the accelerator may have parameters outside the acceptable range of values for normal operation. The Enge beamline must accommodate this range of unacceptable beam parameters, delivering the entire 80 KiloJoule of beam to the dump even though the energy, emittance, and/or match is outside the nominal design range.

The technical challenge for making two-beam accelerators into realizable power sources for high-energy colliders lies in the creation of the drive beam and in its propagation over long distances through multiple extraction sections. This year we have been constructing a 1.2-kA, 1-MeV, induction gun for a prototype relativistic klystron two-beam accelerator (RK-TBA). The electron source will be a 8.9 cm diameter, thermionic, flat-surface cathode with a maximum shroud field stress of approximately 165 kV/cm. Additional design parameters for the injector include a pulse length of over 150-ns flat top (1% energy variation), and a normalized edge emittance of less than 300 pi-mm-mr. The prototype accelerator will be used to study, physics, engineering, and costing issues involved in the application of the RK-TBA concept to linear colliders. We have also been studying optimization parameters, such as frequency, for the application of the RK-TBA concept to multi-TeV linear colliders. As an rf power source the RK-TBA scales favorably up to frequencies around 35 GHz. An overview of this work with details of the design and performance of the prototype injector, beam line, and diagnostics will be presented.

For multi-pulse radiography facilities, we are investigating the possible adverse effects of (1) backstreaming ion emission from the bremsstrahlung converter target and (2) the interaction of the resultant plasma with the electron beam during subsequent pulses. These effects would primarily manifest themselves in a static focusing system as a rapidly varying X-ray spot. To study these effects, we are conducting beam-target interaction experiments on the ETA-II accelerator (a 6.0 MeV, 2.5 kA, 70 ns FWHM pulsed, electron accelerator) by measuring spot dynamics and characterizing the resultant plasma for various configurations.

The technical challenge for making two-beam accelerators into realizable power sources lies in the creation of the drive beam and in its propagation over long distances through multiple extraction sections. This year we have been constructing a 1.2-kA, 1-MeV, electron induction prototype injector as a collaborative effort between LBL and LLNL. The electron source will be a 3.5″-diameter, thermionic, flat-surface cathode with a maximum shroud field stress of approximately 165 kV/cm. Additional design parameters for the injector include a pulse length of over 120-ns flat top (1% energy variation), and a normalized edge emittance of less than 200 π-mm-mr. Planned diagnostics include an isolated cathode with resistive divider for direct measurement of current emission, resistive-wall and magnetic probe current monitors for measuring beam current and centroid position, capacitive probes for measuring A-K gap voltage, an energy spectrometer, and a pepper-pot emittance diagnostic. Details of the injector, beam line, and diagnostics are presented.

We are constructing a 1.2-kA, 1-MeV, electron induction injector as part of the RTA program, a collaborative effort between LLNL and LBNL to develop relativistic klystrons for Two-Beam Accelerator applications. The RTA injector will also be used in the development of a high-gradient, low-emittance, electron source and beam diagnostics for the second axis of the Dual Axis Radiographic Hydrodynamic Test (DARHT) Facility. The electron source will be a 3.5``-diameter, thermionic, flat-surface, m-type cathode with a maximum shroud field stress of approximately 165 kV/cm. Additional design parameters for the injector include a pulse length of over 150-ns flat top (1% energy variation), and a normalized edge emittance of less than 200 {pi}-mm-mr. Precise measurement of the beam parameters is required so that performance of the RTA injector can be confidently scaled to the 4-kA, 3-MeV, and 2-microsecond pulse parameters of the DARHT injector. Planned diagnostics include an isolated cathode with resistive divider for direct measurement of current emission, resistive wall and magnetic probe current monitors for measuring beam current and centroid position, capacitive probes for measuring A-K gap voltage, an energy spectrometer, and a pepper-pot emittance diagnostic. Details of the injector, beam line, and diagnostics are presented.

Summary form only given, as follows. A compact, high repetition rate (2.142 GHz in burst mode), relativistic (5 MeV) photoinjector facility is currently under construction at the UC Davis Department of Applied Science, on the LLNL site. Photoelectron bunches are produced by irradiating a high quantum efficiency Cs/sub 2/Te (Cesium Telluride) photocathode with a train of 100 UV (210 nm), ultrashort (250 fs) laser pulses. These bunches are accelerated in a 1-1/2 cell /spl pi/-mode X-band RF structure energized by a 20 MW, 8.568 GHz SLAC klystron. The peak current is 0.25 kA (0.25 nC, 1 ps bunches), with a normalized beam emittance /spl epsi/

We intend to carry out a series of plasma lens experiments at the Final Focus Test Beam facility at SLAC. These experiments will be the first to study the focusing of particle beams by plasma focusing devices in the parameter regime of interest for high energy colliders, and is expected to lead to plasma lens designs capable of unprecedented spot sizes. Plasma focusing of positron beams will be attempted for the first time. We will study the effects of lens aberrations due to various lens imperfections. Several approaches will be applied to create the plasma required including laser ionization and beam induced tunneling ionization of a working gas—the latter which has never been observed before. The compactness of our device should prove to be of interest for applications at the SLC and the next generation linear colliders.

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

A neutron-detection system was built for the purpose of measuring the neutron flux from an Inertial-Electrostatic Confinement Device located at Brigham Young University. A BF$sub 3$ proportional counter was used for absolute flux measurements and a pair of scintillation detectors was used to compare neutron output under different operating conditions. The detectors were designed to be compatible with the operating conditions of the device and to be able to measure small changes in neutron output. The detectors were calibrated using a Pu-Be source with corrections made for laboratory conditions. Performance of the counting system was checked and data were collected on the neutron flux from the device. (auth)

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 creation of the drive beam remains one of the most challenging technical endeavours in constructing two-beam accelerators. We have begun testing the 1.2-kA, 1.0-MeV electron induction injector for the RTA experiment. The electron source is a 3.5-inch diameter, thermionic, flat-surface cathode with a maximum shroud field stress of approximately 165 kV/cm. The pulse length of the injector is approximately 250 ns, with a 120-ns flattop region. We report here measurements of the pulsed power system performance, beam voltage and current. Plans to measure the emittance and current density profile are discussed.

The Two-Beam Accelerator (TBA) concept is currently being investigated both at Lawrence Berkeley National Laboratory (LBNL) and at CERN. As part of this program, a 7 MeV, 1-kA electron beam produced by the PIVAIR accelerator at CESTA has been used to power a free electron laser (FEL) amplifier at 35 GHz. At the FEL exit, the bunched electron beam is transported and focused into a resonant cavity built by the CLIC group at CERN. The power and frequency of the microwave output generated when the bunched beam traverses two different cavities are measured.

The confinement of electrons and the partial thermalization of their energies has been observed in a prototype cryogenic source in which the energy of charged particles can be thermalized to 4° K.