Kosmahl and Branch's derivation for the electric field in a round beam gap is closely followed to derive the electric field for a sheet beam klystron gap. The wider of the two transverse dimensions of the gap is taken to be infinite in extent and the field is derived based on an approximation of the gap field at the drift tube edge. The electric field equations are generalized using a Fourier series representation of the gap field at the drift tube edge. The analytical results are compared with the numerical computations.

The Sheet Beam Klystron (SBK) is characterized by a large drift tube, which allows the use of high beam current at a low voltage, resulting in low beam current density, high efficiency and the possibility of PPM focusing. CPI has designed, manufactured and is currently testing an X-Band SBK capable of 5 MW peak, 20 kW average output power This paper discusses the general design, manufacturing and performance to date of CPI's X-Band SBK.

In this study, the experimental results for tungsten and molybdenum are compared to copper under the same high field conditions (350 MV/m and 500 MV/m). The RF pulse length for all three experiments is 150 ns. Tungsten and molybdenum are both refractory metals with robust physical properties that are recognized for their high melting point, low thermal expandability, low vapour pressure, and high yield strength. The CLIC study group at CERN has conducted several accelerator experiments at 30 GHz with structures that have tungsten and molybdenum iris inserts.

The International Linear Collider (ILC) is a 200-500 GeV center-of-mass high-luminosity linear electron-positron collider, based on 1.3 GHz superconducting radio-frequency (SCRF) accelerating cavities. The ILC has a total footprint of about 31 km and is designed for a peak luminosity of 2x10^34 cm^-2 s^-1. The complex includes a polarized electron source, an undulator-based positron source, two 6.7 km circumference damping rings, two-stage bunch compressors, two 11 km long main linacs and a 4.5 km long beam delivery system. This report is Volume III (Accelerator) of the four volume Reference Design Report, which describes the design and cost of the ILC.

A sheet-beam klystron has been designed, built and tested in the klystron department at SLAC. The first prototype, WSBK-1A, is a 95 GHz W-band device with a 74 kV, 3.6 A electron gun. Electrostatic focusing in the gun produces a sheet beam of approximately elliptical cross section with a height to width ratio of 1 to 12. Beam transmission over 90% was measured

This paper reports on experimental results from the SLAC NLC accelerator structure closeout program, and discusses a study that was conducted to improve the smoothness of machined tungsten for use in high gradient structures. At the Next Linear Collider Test Accelerator (NLCTA), an X‐band (11.424 GHz) structure was operated at a lower temperature to determine whether this would decrease the low rate of breakdowns that still occur after initial processing. Also, various vacuum venting experiments were performed to determine the impact of air, airborne particulates, and oxidation on the performance of a processed accelerator structure. As part of a more long‐range high‐gradient structure development program, alternative materials to copper are being explored. The CLIC study group at CERN has conducted several accelerator experiments at 30 GHz with structures that have tungsten and molybdenum iris inserts. SLAC has also tested versions of the CLIC 30 GHz design scaled to 11.424 GHz. The results have prompted a tungsten material study directed at exploring new fabrication processes that would provide a cleaner and smoother tungsten surface topography suitable for high gradient applications. A significantly improved tungsten surface finish resulted from this material study, and a single cell X‐band cavity containing noses with such tungsten surfaces will be high power tested soon.

SLAC is developing sheet beam klystron technology for narrow bandwidth, high peak and average power applications from L-band to W-band. Sheet beam devices are advantageous for several reasons. The primary advantage is the increased surface area in the RF circuit which significantly increases the dissipated heat that can be transferred through the circuit. The reduced charge density in the beam decreases the magnetic field required for beam transport and increases the achievable efficiency compared to a pencil-beam tube with the same beam voltage and current. Finally, both the RF circuit and the magnetic focusing system are simpler and less expensive to fabricate. The combination of features provided by a sheet beam klystron make it an ideal source for linear accelerator and high average power applications

In radar and communication systems, a broad frequency band can be synthesized of several narrow ones. At millimeter and sub-millimeter waves, the multiplexer for combining narrow-banded channels can be composed of quasi-optical mirror cavities. However, mutual adjustment of the cavities for radar and communication should be quite different. In the radar with synthesized frequency band, an adaptive spectrum regularization algorithm provides automatic shrinkage of the range resolution scale with the target approaching.

Many studies have demonstrated that improving the surface smoothness and cleanliness of high voltage electrodes increases the voltage standoff capability, but none have specifically investigated the role of nano-scale and atomic level surface roughness. Using AFM imaging, we have studied the effect of gas cluster ion beams (GOB) on oxygen-free Cu electrode material that is used in high gradient RF cavities. Using Ar clusters accelerated by 30 kV, with a dose of 6 x 10(14) cm(-2), we have effectively removed an asperity that was 3500 (A) over circle wide and 350 (A) over circle high. Subsequent processing with 5 kV acceleration reduced the surface roughness from an Ra value of 13.2 (A) over circle to 4.8 (A) over circle. This demonstrates the effectiveness of GCIB for reducing sub-micron roughness to atom level smoothness. (c) 2005 Elsevier B.V. All rights reserved.

Sheet beam devices provide important advantages for very high power, narrow bandwidth RF sources like accelerator klystrons. Reduced current density and increased surface area result in increased power capability, reduced magnetic fields for focusing and reduced cathode loading. These advantages are offset by increased complexity, beam formation and transport issues and potential for mode competition in the overmoded cavities and drift tube. This paper describes the design issues encountered in developing a 100 kW peak and 2 kW average power sheet beam klystron at W-band including beam formation, beam transport, circuit design, circuit fabrication and mode competition.

We are currently addressing the lengthy simulation issue by operating parallel processor versions of MAGIC 3D. The Klystron department cluster at SLAC is a typical Beowulf Linux cluster running 24 processors in dual CPU boxes. Thanks to the cooperation of MRC, SLAC has been able to finish the parallel operation feature that MRC had operational and adjust it for accuracy against the single CPU version. We were also able to port Magic to Linux where parallel operation runs on our cluster. During parallel software development, it became obvious to us that the Magic user interface did not lend itself to the automation of numerical comparisons between runs.

The next generation of powerful electronic devices requires new approaches to overcome the known limitations of existing tube technology. Multibeam and sheet beam approaches are novel concepts for the high power microwave devices. Direct and indirect modeling methods are being developed at SLAC to meet the new requirements in the 3D modeling. The direct method of solving of Poisson's equations for the multtbeam and sheet beam guns is employed in the TOPAZ 3D tool. The combination of TOPAZ 2D and EGUN (in the beginning) with MAFIA 3D and MAGIC 3D (at the end) is used in an indirect method to model the high power electron guns. Both methods complement each other to get reliable representation of the beam trajectories. Several gun ideas are under consideration at the present time. The collected results of these simulations are discussed.

An improved version of the TOPAZ 3D gun code is presented as a powerful tool for beam optics simulation. In contrast to the previous version of TOPAZ 3D, the geometry of the device under test is introduced into TOPAZ 3D directly from a CAD program, such as Solid Edge or AutoCAD. In order to have this new feature, an interface was developed, using the GiD software package as a meshing code. The article describes this method with two models to illustrate the results.

Summary form only given, as follows. The X-band klystrons being developed at the Stanford Linear Accelerator Center (SLAC) for the Next Linear Collider(NLC) use periodic permanent magnets (PPM) to focus the electron beam.. In an effort to cut magnet and manufacturing costs, a two-piece clamshell magnet and polepiece assembly was used. Measurements of 3-D magnetic fields in this assembly gave transverse fields on the order of 20 G for a PPM field with an RMS axial field of 2600 G. A series of 3-D beam transport simulations were performed to determine the effect of transverse fields on the interception on the walls of the beam tunnel. The simulations were done using the electromagnetic particle-in-cell (PIC) code, MACIC3D.

Summary of the background presentation and synopsis of the subsequent discussion on microfabrication and THz sources.

The current baseline design for the 500-GeV SLAC/KEK future collider requires approximately 5000 75-MW, 1.6 mus, PPM pencil-beam klystrons. A prototype is currently on test. Although the estimated cost of the klystrons is a small part of the total collider cost, this number of klystrons is at least an order of magnitude higher than the klystron population in any scientific or military system ever fielded.A back-up sheet-beam klystron design has been under study at SLAC for the last six years. It offers several advantages: If two sheet beams were employed in parallel, the current density at the two cathodes would be low, and the power density at the output cavity a fraction of that in the pencil-beam klystron. Furthermore, because of significantly fewer vacuum parts, the 150-MW SBK should have a substantially lower cost than the baseline 75-MW pencil-beam klystron. Finally, it is considered that because of the lower power density, a longer rf pulse (3.2 mus) could be employed. All this means is that, with more pulse compression, the total number of klystrons in the collider could be reduced by a factor of 4, to approximately 1250. The total cost of the klystrons would be cut by an even larger factor.Since a practical SBK has never been designed before, two major problems had to be solved before a meaningful computer simulation of the entire tube could be performed. First, a sheet-beam gun had to be designed, along with a periodically-focused beam transport system outside the vacuum. Secondly, since extended interaction cavities are used throughout, new techniques had to be developed to provide useful designs with adequate stability and mode separation. This work is essentially complete. The work to parallel 24 CPUs, and modify the MAGIC 3D code so simulations of the complete SBK can be performed in a reasonable time, has progressed sufficiently for an interim report on the project to be presented.

The 95 GHz klystrino under development at SLAC is designed to operate at 110 kV, 2.4 A and produce 100 kW peak output power and 1 kW average power at 1% duty. The final machining of the LIGA assemblies for the round beam klystrino and initial RF testing are underway The presentation will include the initial RF performance of the klystrino, the thermal modeling of the round and sheet beam designs, as well as beam transport issues and cavity field shaping for W-band sheet beams.

Summary form only given. The klystrino program was initiated to develop a high power RF source at W-band for tabletop accelerator, radar and communications applications. The goal of the program was to produce a 95 GHz, PPM focused, 100 kW peak power, 1% duty klystron. At W-band, both the small cavity dimensions and the required surface finish present fabrication challenges. In order to overcome these difficulties, the RF circuit for the klystrino is fabricated using an X-ray lithographic process called LIGA. The LIGA process can produce deep features (/spl les/ 3 mm) with submicron accuracy and excellent surface finish(< 50 nm). The RF design of the klystrino is straightforward with five regular cavities plus a five-gap extended interaction output cavity. The planar cross-section of the LIGA fabricated cavities requires 3-D simulation codes to model the non-axisymmetric fields. The rectangular magnets and butterfly-shaped polepieces also require a 3-D magnetostatic code to model the magnetic fields. Development of accurate 3-D simulations has been an ongoing issue in the klystrino program. The 110 kV beam voltage was chosen to make PPM focusing easier by reducing the plasma frequency. The length of the output cavity is proportional to beam velocity, so the high voltage also results in additional surface area to dissipate heat. Post-LIGA machining operations have presented the most difficult challenges to the klystrino development. Normal machining processes are pushed to the limit to achieve the one to two micron tolerances required for alignment and machining of the beam tunnel and coupling irises. Initial klystrino testing will start in February and RF performance data will be presented.

Summary form only given, as follows. The current design for the X-band Next Linear Collider (NLC) requires electric field gradients significantly higher than SLAC's operating S-band Linear Collider (SLC). Finding methods to achieve these higher gradients and minimize processing time is the focal point of the study. The test platform for the RF breakdown study is a "windowtron" which consists of a transmission cavity with demountable nose tips situated between two windows. The nose tips can be made from various materials, and different cleaning and machining techniques can be applied. The RF power is supplied to the cavity by a 50 MW X-band (11.4 GHz) klystron. Automation is currently being developed for this study in order to provide a consistent comparison between experiments. The breakdown criterion, previously based on gas or visible light, has been changed and is now based on the percentage of missing transmitted energy within each RF pulse. A fast interlock system is utilized that prevents damage by successive pulses, and enables a higher degree of control during experiments. Current experiments include comparing breakdown damage inside a high Q and low Q cavity, where the low Q cavity has eight times the energy available inside the cavity. This information is relevant to constant gradient accelerator structures where the group velocity and impedance vary inside the structure. Other experiments include high temperature (450/spl deg/C) vacuum bakeout compared to heat tape baking, the effect of multiple hydrogen braze cycles, and a comparison between different RF processing methods.

Presents the design of a W-band LiGA (a German acronym for lithographe, galvanoformung, und abformung) fabricated three-dimensional five-gap coupled cavity. This paper focuses on analyzing the coupling slot effects on such a periodic structure's dispersion characteristics using the three-dimensional code MAFIA (Maxwell equation using finite integration algorithm). The different coupling slot sizes corresponding to LiGA fabrication and EDM (electric discharge machining) fabrication constraints have been modeled and discussed in detail. The equivalent circuit model of such a coupling slot in two-dimensional MAGIC code also has been studied.