Showing papers on "Perveance published in 2004"

Design and characterization of a neutralized-transport experiment for heavy-ion fusion

Abstract: In heavy-ion inertial-confinement fusion systems, intense beams of ions must be transported from the exit of the final-focus magnet system through the fusion chamber to hit spots on the target with radii of about 2 mm For the heavy-ion-fusion power-plant scenarios presently favored in the US, a substantial fraction of the ion-beam space charge must be neutralized during this final transport The most effective neutralization technique found in numerical simulations is to pass each beam through a low-density plasma after the final focusing To provide quantitative comparisons of these theoretical predictions with experiment, the Virtual National Laboratory for Heavy Ion Fusion has completed the construction and has begun experimentation with the neutralized-transport experiment The experiment consists of three main sections, each with its own physics issues The injector is designed to generate a very high-brightness, space-charge-dominated potassium beam, while still allowing variable perveance by a beam aperturing technique The magnetic-focusing section, consisting of four pulsed quadrupoles, permits the study of magnet tuning, as well as the effects of phase-space dilution due to higher-order nonlinear fields In the final section, the converging ion beam exiting the magnetic section is transported through a drift region with plasma sources for beam neutralization, and the final spot size is measured under various conditions of neutralization In this paper, we discuss the design and characterization of the three sections in detail and present initial results from the experiment

Electron gun design for fundamental mode S-band multiple-beam amplifiers

Abstract: This paper describes the detailed design of an eight-beam electron gun for use in S-band multiple-beam amplifiers operating in the fundamental mode. The gun operating voltage is 45 kV with a total beam current of 32 A, evenly divided among the beamlets. Each individual beam has a perveance of 0.42 mpervs making a total beam perveance of 3.35 mpervs. The optimized electron gun is singly convergent using a four-fold symmetry with the four inner and four outer emitters interlaced 90/spl deg/ apart. The emitter current density has been kept below 10 A/cm/sup 2/ (space-charge limited). The cathode is magnetically shielded and the longitudinal magnetic field in the interaction region is in the range of 1.1-1.8 kG. The design of the magnetic focusing system minimizes beam corkscrewing as well as electron interception on the tunnel walls. Beam optics simulations of the gun indicate excellent beam transport characteristics with a final beam-to-tunnel radial fill factor of less than 0.45. The primary computational tools used in the design process were the three-dimensional gun code MICHELLE, and the magnetostatics code MAXWELL-3D.

Performance Characterization and Vibration Testing of 30-cm Carbon-Carbon Ion Optics

Abstract: Carbon-based ion optics have the potential to significantly increase the operable life and power ranges of ion thrusters because of reduced erosion rates compared to molybdenum optics. The development of 15-cm and larger diameter grids has encountered many problems, however, not the least of which is the ability to pass vibration testing. JPL has recently developed a new generation of 30-cm carbon-carbon ion optics in order to address these problems and demonstrate the viability of the technology. Perveance, electron backstreaming, and screen grid transparency data are presented for two sets of optics. Vibration testing was successfully performed on two different sets of ion optics with no damage and the results of those tests are compared to models of grid vibrational behavior. It will be shown that the vibration model is a conservative predictor of grid response and can accurately describe test results. There was no change in grid alignment as a result of vibration testing and a slight improvement, if any change at all, in optics performance.

Circular-to-planar transformations of high-perveance electron beams by asymmetric solenoid lenses

Abstract: The generation and transport of planar electron beams is a topic of increasing interest for applications to high-power, high-frequency microwave devices. This paper describes the use of solenoid lenses with elliptical pole apertures to transform a circular high-perveance beam to a planar configuration. The resulting transformation system has a short axial length and is easily fabricated. Furthermore, the approach allows use of a conventional electron gun. We designed lenses and simulated the dynamics of a beam system to drive a 95 GHz, traveling-wave tube experiment at Los Alamos National Laboratory. The three-dimensional self-consistent calculations indicate that a $0.5\text{ }\ensuremath{\mu}\mathrm{perv}$ beam can be compressed to a height of less than 0.5 mm with sufficiently low emittance for transport through periodic-permanent-magnet or wiggler arrays.

Drift compression and final focus for intense heavy ion beams with nonperiodic, time-dependent lattice

Abstract: In the currently envisioned configurations for heavy ion fusion, it is necessary to longitudinally compress the beam bunches by a large factor after the acceleration phase. Because the space-charge force increases as the beam is compressed, the beam size in the transverse direction will increase in a periodic quadrupole lattice. If an active control of the beam size is desired, a larger focusing force is needed to confine the beam in the transverse direction, and a nonperiodic quadrupole lattice along the beam path is necessary. In this paper, we describe the design of such a focusing lattice using the transverse envelope equations. A drift compression and final focus lattice should focus the entire beam pulse onto the same focal spot on the target. This is difficult with a fixed lattice, because different slices of the beam may have different perveance and emittance. Four time-dependent magnets are introduced in the upstream of drift compression to focus the entire pulse onto the same focal spot. Drift compression and final focusing schemes are developed for a typical heavy ion fusion driver and for the integrated beam experiment being designed by the Heavy Ion Fusion Virtual National Laboratory.

Performance and Vibration of 30 cm Pyrolytic Ion Thruster Optics

Abstract: Carbon has a sputter erosion rate about an order of magnitude less than that of molybdenum, over the voltages typically used in ion thruster applications. To explore its design potential, 30 cm pyrolytic carbon ion thruster optics have been fabricated geometrically similar to the molybdenum ion optics used on NSTAR. They were then installed on an NSTAR Engineering Model thruster, and experimentally evaluated over much of the original operating envelope. Ion beam currents ranged from 0.51 to 1.76 Angstroms, at total voltages up to 1280 V. The perveance, electron back-streaming limit, and screen-grid transparency were plotted for these operating points, and compared with previous data obtained with molybdenum. While thruster performance with pyrolytic carbon was quite similar to that with molybdenum, behavior variations can reasonably be explained by slight geometric differences. Following all performance measurements, the pyrolytic carbon ion optics assembly was subjected to an abbreviated vibration test. The thruster endured 9.2 g(sub rms) of random vibration along the thrust axis, similar to DS 1 acceptance levels. Despite significant grid clashing, there was no observable damage to the ion optics assembly.

Three-Dimensional Divergence Characteristics of Ion Beamlets in an Ion Thruster

Abstract: Three-dimensional divergence characteristics of ion beamlets in an ion thruster were investigated using numerical simulation. A three-dimensional particle-in-cell code was developed to explain the formation mechanism of non-circular grid hole erosion observed in an endurance test of a thruster. Calculation results demonstrated that the ion beamlets cross over the hole axis and possess a sub-hexagonal cross-section in the downstream of the crossover point under low perveance condition. This beamlet shape is formed because of the hexagonally symmetric hole arrangement of ion optics. The calculation results also showed that the calculated beamlet cross-sections were similar to the sub-hexagonal erosion patterns observed in the experiment. This agreement indicates that the non-circular erosion patterns were caused by the direct impingement of the diverged ion beamlets possessing the subhexagonal cross-section.

Perveance monitor for measuring an 80-mw klystron characteristics*

Abstract: The high power klystron-modulator (K&M) system is a main pulse and microwave source for the PLS linac. The peak powers of the modulator and the klystron have 200 MW and 80 MW, respectively. The total heater run time of an oldest klystron system has been accumulated over 75,000-hours as of now. This klystron must operate efficiently and stably in the linear gain region within a band of frequencies. The micro-perveance will change as the tube ages. It is believed that a change in the perveance of the klystron may be a predictor of when a klystron is about to fail. Therefore, it is necessary to monitor the klystron operational status for stable beam operation. It can be achieved by measuring the klystron micro- perveance to diagnose characteristics of klystron. Up to now, the operator manually performs it. The prototype perveance monitor system has been designed by processing the sensing signal of a beam voltage and current of the klystron. In this paper, the design concept and experimental results for application will be presented.

Analysis of a Possible 20A Electron Gun and Collector Design for the RHIC EBIS

Abstract: Successful operation of the BNL EBIS with electron current up to 10 A provides optimism that EBIS operation with even higher electron current should be possible. We are now considering key aspects of the design for an EBIS operating with electron current 20 A. Several technical problems need to be resolved, including generation of a 20 A electron beam and dissipation of this electron beam power on the electron collector. Since we already have a tested concept of electron beam generation with the gun immersed in a magnetic field and subsequent purely magnetic compression of the electron beam, it makes sense to develop the new electron gun with immersed cathode but with higher perveance. To distribute the electron beam power on the surface of the electron collector more evenly, the emission current density from the cathode can be made bell-shaped with minimum close to zero on the periphery of the electron beam. With the already high requirements to the emission current density, and since such shaping of the electron beam makes these requirements even higher, perhaps the only available cathode material that can satisfy these requirements is IrCe. The problems of power dissipation on the electron collector (EC) include heat removal with cooling water and fatigue of the EC material. The first step in the EC design was electron beam transmission simulation with the goal to reduce `spikes' of power density on EC surface as much as possible. With the geometry of EC thus defined, the conditions of heat exchange for several modes of EBIS operation have been analyzed and cooling parameters, which provide adequate heat removal were found. The last step was stress analysis of several EC materials with ANSYS to find the material suitable for this application. Details of the 20 A electron gun and collector are presented.

Extraction of space-charge-dominated ion beams from an ECR ion source: Theory and simulation

Abstract: Extraction of high quality space-charge-dominated ion beams from plasma ion sources constitutes an optimization problem centered about finding an optimal concave plasma emission boundary that minimizes half-angular divergence for a given charge state, independent of the presence or lack thereof of a magnetic field in the extraction region. The curvature of the emission boundary acts to converge/diverge the low velocity beam during extraction. Beams of highest quality are extracted whenever the half-angular divergence, ω, is minimized. Under minimum half-angular divergence conditions, the plasma emission boundary has an optimum curvature and the perveance, P, current density, j+ext, and extraction gap, d, have optimum values for a given charge state, q. Optimum values for each of the independent variables (P, j+ext and d) are found to be in close agreement with those derived from elementary analytical theory for extraction with a simple two-electrode extraction system, independent of the presence of a magn...

Physics of non-thermal Penning-trap electron plasma and application to ion trapping

Abstract: A modified Penning–Malmberg trap is used to produce a reflexing beam electron distribution. Positive ions are trapped in the electron space charge within a shaped anode at the center of the beam. Electron reflexing of greater than 106 circuits is observed, with a perveance several times that of earlier single pass devices. Classical slowing of the electron beams is observed. Two-stream instability is avoided because the emission limited space charge is subcritical. Trapped ions are observed in two modes of operation; a quiescent mode in which ions are directly counted after destroying the space charge configuration, and a rf mode in which the ion resonance instability is active. Ion inventory up to quasineutral conditions is implied for the quiescent trapping mode.

Low convergent confined-flow Pierce gun for a space TWT

Abstract: An approach for designing an electron gun for a high efficiency, high linearity space traveling wave tube (TWT), has been presented. A low convergent (<10 : 1) Pierce electron gun of beam perveance 0.43 μP has been designed for a high gain, high linearity and high efficiency C-band 60 W Space TWT using in-house developed two-dimensional FDM based gun and collector simulation code PIERCE. In this gun, the first anode (isolated from the ground anode) has been kept nearly 100 V above the ground anode to act as an ion barrier for increasing cathode life and to regulate beam current over the lifetime of the tube. An M-type dispenser cathode of diameter 3.20 mm has been used for cathode loading of less than 1.0 A/cm2 and heater wattage around 3.0 W. The magnetic focusing with integral-pole-piece barrel assembly and periodic-permanent magnets (PPM) have been designed using in house developed two-dimensional FDM based code SUNMAG. The practical problem of linking requisite cathode flux to the cathode for confined...

A simple model and MAFIA simulation for studying the beam-wave interaction in the output gap of a klystron

Abstract: In this paper, a simple model for studying the beam-wave interaction in the output gap of a klystron was developed using MathCad. The output parameter could be obtained, with the advantage of simplicity and speed compared with traditional disc and ring model. The calculated results were compared with those from MAFIA simulation and the errors for efficiency are within half decibel. The model is also used to investigate the dependence of efficiency on perveance and bunch parameters.

Electron gun and collector simulations for RHIC EBIS at BNL

Abstract: Based on the successful experience of the Brookhaven National Laboratory test electron beam ion sources (EBIS), the relativistic heavy ion collider (RHIC) EBIS design utilizes a 10 A electron beam to produce the required ion source output intensity of 3.4×109 of Au32+ ions per 10–40 μs pulse. In order to provide increased cathode lifetime and reliability at the required 10 A, and accommodate future upgrades of RHIC EBIS ion intensity, it is desirable to upgrade the electron gun. Simulations have been made for a new electron gun and electron collector capable of generating and dissipating an electron beam with current up to 20 A. The method of forming the electron beam using magnetic compression and inverse magnetron geometry of the electron gun are the same as has been tested successfully on the electron beam test stand. The new gun has higher perveance and partially shielded spherical cathode. A bell-shaped radial current density distribution with reduced current density on a periphery of the beam, combi...

Study of a final focus system for high intensity beams

Abstract: STUDY OF A FINAL FOCUS SYSTEM FOR HIGH INTENSITY BEAMS Enrique Henestroza, Shmuel Eylon, Prabir K. Roy, Simon S. Yu, Frank M. Bieniosek, Derek B. Shuman and William L. Waldron Lawrence Berkeley National Laboratory, CA 94720 Abstract The NTX experiment at the Heavy Ion Fusion Virtual National Laboratory is exploring the performance of neutralized final focus systems for high perveance heavy ion beams. The final focus scenario in an HIF driver consists of several large aperture quadrupole magnets followed by a drift section in which the beam space charge is neutralized by a plasma. This beam is required to hit a millimeter-sized target spot at the end of the drift section. The objective of the NTX experiments and associated theory and simulations is to study the various physical mechanisms that determine the final spot size (radius r s ) at a given distance (f) from the end of the last quadrupole. In a fusion driver, f is the standoff distance required to keep the chamber wall and superconducting magnets properly protected. The NTX final quadrupole focusing system produces a converging beam at the entrance to the neutralized drift section where it focuses to a small spot. The final spot is determined by the conditions of the beam entering the quadrupole section, the beam dynamics in the magnetic lattice, and the plasma neutralization dynamics in the drift section. The main issues are the control of emittance growth due to high order fields from magnetic multipoles and image fields. In this paper, we will describe the theoretical and experimental aspects of the beam dynamics in the quadrupole lattice, and how these physical effects influence the final beam size. In particular, we present theoretical and experimental results on the dependence of final spot size on geometric aberrations and perveance. I. INTRODUCTION The topic of final focus systems for high intensity beams has been an important subject of analytical [1-4], and experimental [5] efforts since the beginning of the Heavy Ion Fusion project in 1976. The first designs were derived from systems already in use in particle accelerators for high energy physics where space-charge is negligible, and which incorporated sextupoles and octupoles elements for the correction of chromatic and geometric aberrations. Chromatic aberrations affect the focal spot radius due to deviations from the nominal ion momentum causing a variation in the focal length produced by the magnet system. These aberrations may result from initial transients in the injector, from residual momentum tilt due to beam compression, or from the momentum spread, or longitudinal emittance produced along the beam line. Geometric aberrations are due to nonlinear external fields and also from deviations from paraxial ray optics. In a possible scenario of a final focus system for an HIF driver, the beam is transported in the final focus section through several strong large aperture magnetic quadrupoles, and is then allowed to drift ballistically through neutralizing plasma in a low-density (millitorr) gas onto the target. There are nonlinear processes both in the magnetic section as well as in the neutralized transport section. To investigate these phenomena, the Neutralized Transport Experiment (NTX) has begun at LBNL [6]. The NTX beamline (Fig. 1) consists of 4 large bore quadrupoles followed by a neutralized drift section. A low emittance K+ beam is made to traverse this 4-quad lattice, at the exit of which, the beam enters a 1-meter long drift section with injected plasma. The beam is diagnosed at the exit of the 4-quad section as well as the end of the drift section. The relevance of NTX to the fusion driver is derived from the observation that the key scaling parameter is perveance, defined as Q = 2 ZeI b 4 πe 0 m i v i 3

High-power S-band fundamental-mode eight-beam klystron and gun design

Abstract: Summary form only given. In multiple-beam amplifiers, beamlets are transported in individual beam tunnels but interact with RF fields in a common interaction region. This approach enables the designer to have the best of both worlds: individual beamlets can have low perveance which is conducive to efficient bunching and beam transport, leading to higher gain, electronic efficiencies, and average power, while the aggregate beam current can be high, facilitating high beam and RF power, and also broad bandwidth. A fundamental mode multiple-beam amplifier is described in this paper and we report on the design of a beam forming system for high-average-power broadband S-band multiple-beam amplifiers, developed at the Naval Research Laboratory (NRL). These amplifiers utilize eight individual electron beams and operates in the fundamental TM/sub 01/ mode.

Creation of powerful broadband low-voltage small-sized grid-controlled pulse TWT over decimetre waves

Abstract: Decrease of anode voltage, mass, and dimensions of powerful pulse traveling-wave tube (TWT) with grid modulation, as well as broadening the operating frequency range of signals to be amplified, is achieved by the increase of a perveance of an electron beam formed by the original three-grid electron gun The features of focusing the high-perveance electron beam by PPM system are shown Main parameters of such TWTs are presented

Cathode for x-ray tube of high emission

Abstract: PROBLEM TO BE SOLVED: To provide the electron beam 34 of perveance and beam compression rate substantially larger than that obtained by another method while using a conventional design of a cathode 12. SOLUTION: A device includes a cathode assembly 22 mounted oppositely to an anode 18 at an interval from the anode. The cathode assembly includes an emitter 14 for emitting the electron beam 34 to a focal point on the anode during the operation of the X-ray tube, and a cathode front face member 32 mounted at a first side of the emitter and having an opening 30 formed by the cathode front face member. A backing 36 is mounted at a second side of the emitter, and operatably joined to the cathode front face member through a backing insulating body 42. COPYRIGHT: (C)2004,JPO

High power mini-TWT development at L-3 Communications

Abstract: Summary form only given. This paper provides a hardware-centered status on the progress over the last year in extending wideband mini-TWT performance to 200 W. Over the least year, L-3 has completed two designs demonstrating 200 to 400 W CW over more than an octave, with peak efficiencies of nearly 50% using only a three-stage collector. The mini-TWT gun assembly shares common parts with production TWTs while only requiring a new cathode and beam-forming electrode. The cathode current density is less than 2 A/cm/sup 2/, which results in exceptionally long life. The higher beam perveance of the mini-TWT design allows for wide band operation with good power flatness. This talk presents experimental data and challenges overcome on recent high power designs.

Comparison of experimental data and 3D simulations of ion beam neutralization from the neutralized transport experiment

Abstract: The Neutralized Transport Experiment (NTX) at Lawrence Berkeley National Laboratory has been designed to study the final focus and neutralization of high perveance ion beams for applications in heavy ion fusion (HIF) and high energy density physics (HEDP) experiments. Pre-formed plasmas in the last meter before the target of the scaled experiment provide a source of electrons which neutralize the ion current and prevent the space-charge induced spreading of the beam spot. NTX physics issues are discussed and experimental data is analyzed and compared with 3D particle-in-cell simulations. Along with detailed target images, 4D phase-space data of the NTX at the entrance of the neutralization region has been acquired. This data is used to provide a more accurate beam distribution with which to initialize the simulation. Previous treatments have used various idealized beam distributions which lack the detailed features of the experimental ion beam images. Simulation results are compared with NTX experimental measurements for 250 keV K{sup +} ion beams with dimensionless perveance of 1-7 x 10{sup -4}. In both simulation and experiment, the deduced beam charge neutralization is close to the predicted maximum value.

Multi-beam klystron development for accelerator applications

Abstract: Summary form only given. The multi-beam klystron (MBK) enjoys high efficiency, a consequence of the low perveance of the individual beamlets, while operating at a low beam voltage due to the high total perveance. The plasma wavelength is less than that of a conventional single beam klystron, allowing a significant reduction in the length of the device. MBKs are, therefore, especially attractive in lower frequency accelerator applications. Described in this paper is the L6102-50 MBK, currently being developed at L-3 Communications Electron Devices, which is designed to the DESY TESLA (Tera electron volt energy superconducting linear accelerator) specification, which calls for a 10 MW peak, 150 kW average power MBK at 1300 MHz.

Extractor configurations for a heavy ion fusion volume source

Abstract: MFAN 981 LBNL-44004 EXTRACTOR CONFIGURATIONS FOR A HEAVY ION FUSION VOLUME SOURCE* O. A . Anderson*, L B N L , Berkeley, C A 94720, U S A Abstract In order for volume sources to deliver the current (e.g., 0.8 A of A r per module) and brightness necessary for heavy ion fusion (HIF), they must operate at high current density. Conventional extractor designs for 1 to 2 M e V run into voltage breakdown limitations and cannot easily produce the required current rise time (about one microsec­ ond). We discuss two systems that can overcome these volume-extraction problems. Each uses multichannel preaccelerators followed by a single channel main accelera­ tor. Fast beam switching is done in the low energy beam- let stages. A new design, utilizing concentric ring preac­ celerators, was recently described for another application [2]. A more conventional design uses a large number of small round beamlets. In either case, the merging beam- lets are angled toward the axis, a feature that dominates other focusing. By suitable adjustment of the individual angles, beam aberrations are reduced. Because of the high current density, the overall structure is compact. Emit­ tance growth from merging of beamlets is calculated and scaling is discussed. The present paper studies extraction of HIF beams from conventional gas sources. The 0.75 A beams of A r are to be injected at -1.5 M e V into an array of E S Q channels spaced about 7 cm in both directions. The proposed system is compact and should fit within these dimensions. As an alternative, we also consider Fig. 2. Detail of an older arrangement [3] using pencil preaccelerators. beams. Figures 3a and 3b compare axial views (before merging) for the old and new designs. In Fig. 3(a) the beamlets are arranged in idealized circular arrays to facilitate the calculations that follow. Section 2 calculates free field energy and asymptotic emittance for both cases; it also compares transparency and brightness. Aberration control and general design considerations are discussed in section 3. (a) INTRODUCTION For extraction of large currents with low emittance for Heavy Ion Fusion (HIF), we consider an arrangement originally proposed for a laser ion source extractor of very high perveance [2]. A s shown in Figs. 1 and 2, the beam- lets from a system of concentric preaccelerators are angled toward the axis. The inward momentum produces a pow­ erful focusing effect, allowing the main M e V accelerator column (Fig. 1) to operate at low gradient. The angling at various radii can be adjusted to compensate for the aber­ rations typically present in high perveance extractors. Fig. 3. Axial view of beamlets emerging from (a) beaded ring and (b) solid ring preaccelerators. Occupancy T| = 50%, number of rings M = 4. 2 EMITTANCE FROM MERGING With X and V the rms values of position and velocity, we define the nonrelativistic normalized rms emittance G = 16P X (V -X' ); G = 4|3XV for a matched beam. Under standard conditions [4], the asymptotic emit- tance G is then given by G —> G . x w, X X X X X F F e pX (2QU ) ' ; i n Fig. 1. Sketch of axial and cross-section views of preacceler- ator grids and two-gap main extractor grids. In practice, more stages would be used in both sections. *This work is supported by the Office of Fusion Energy Science, US DOE under contract No. DE-AC03-76SF00098. Email: OAAnderson@LBL.gov; also affiliated with Particle Beam Consultants, 2910 Benvenue Ave., Berkeley, CA 94705. f G a n d X are initial quantities. The emittance due to merging G t h u s adds in quadrature to the initial emit­ tance G = 4(3X V . Q is the normalized perveance and U is the initial normalized free field energy (beam shape factor) discussed in reference [4]. x i x m X I i xi n 2.1 Round Arrays of Round Beamlets In the type of array shown in F i g . 3(a), the total number N of pencil beamlets is N = 3 M + 3M+ 1, where M is the number of beaded rings. When N is large [4],

Characteristics of Diode Perveance and Output Microwave Power in Coaxial Virtual Cathode Oscillator

Abstract: We have investigated numerically and experimentallycharacteristics of diode perveance and output microwave power incoaxial virtual cathode oscillator (vircator). In this experiment, the diode perveance characteristics could be described using thediode voltages and currents. The sheath plasma expansion speed isto be about 7cm/μs under A-K gap distance 4 mm. We have alsoinvestigated an influence of anode-cathode (A-K) gap distance onoutput characteristics of high power microwave from coaxialvircator. In this experiment, the maximum microwave power isobserved to be 244 MW, whose efficiency is about 2.75 %, at theA-K gap distance of 4 mm. The microwave frequencies are alsomeasured to be 5.1 ≤ f ≥ 5.9 GHz from combination ofcoupled line band pass filter with 1 GHz band gap and dispersivedelay line. With microwave reflector, the maximum output microwavepower is observed to be about 400 MW, whose efficiency is about7.1 %, at the A-K gap distance 8 mm and microwave reflectorinner-hole diameter of 7.6 cm. The microwave frequencies are alsomeasured to be 4.8 ≤ f ≥ 5.2 GHz.

Electron gun simulation using MAFIA

Abstract: The paper describes the work of 2D/3D electron gun simulation using MAFIA. The results obtained by EGUN and by MAFIA are almost alike for 2D model. For 3D model, the current and perveance are 5-10% lower than those of EGUN. Multi-beam guns have also been developed.

Charged‐particle Optics

Abstract: The emphasis of this article is on the common fundamentals and techniques on which the wide variety of different beam-optical devices are based. It should give the reader the necessary background to understand the principles of the actual devices described elsewhere in more advanced treatments. Along with the qualitative description of the basic building blocks of charged particle beam optics, enough selected references to monographs and research reports are given to guide the interested reader towards more in-depth studies. Relatively few references to original research papers are given, but extensive bibliographies are included in the listed review articles and textbooks. Topics introduced include: single-particle motion of charged particles in electric and magnetic fields, sources of charged particles, beam handling and transport, magnetic and electric deflection systems, aberrations of charged particle optical systems, and the mathematics of matrix methods for charged particle optical simulation. Keywords: charged particles; ions; electrons; beam optics; beam transport; magnetic spectrometers; magnetic spectrographs; mass analyzers; focussing and deflection; lenses; accelerators; aberrations; matrix optics; ion sources; ray tracing; achromatic; isochronous; phase space; emittance; space charge; brightness; perveance; Lorentz force

High-power S-band fundamental-mode eight-beam klystron and gun design

Abstract: Summary form only given. In multiple-beam amplifiers, beamlets are transported in individual beam tunnels but interact with RF fields in a common interaction region. This approach enables the designer to have the best of both worlds: individual beamlets can have low perveance which is conducive to efficient bunching and beam transport, leading to higher gain, electronic efficiencies, and average power, while the aggregate beam current can be high, facilitating high beam and RF power, and also broad bandwidth. We will report on the design of a beam forming system for high-average-power broadband S-band multiple-beam amplifiers to be developed at the Naval Research Laboratory (NRL). These amplifiers will utilize eight individual electron beams and operates in the fundamental TM/sub 01/ mode. The singly convergent electron gun topology has fourfold symmetry with four inner and four outer emitters, interlaced 90/spl deg/ apart. The operating voltage is 45 kV with a total beam current of 32 A, evenly divided among the beamlets. Each individual beam perveance is 0.42 micro-pervs, for a total beam microperveance of 3.35. Cathode loading is kept below 10 A/cm/sup 2/ (space charge limited) for lifetime considerations. The cathode is magnetically shielded and the magnetic field in the interaction region is 1.1-1.8 kG. A key design feature is the magnetic focusing system, designed to ensure minimal beam corkscrewing, which limits the beam clearance in the beam tunnel. The primary computational tools used in this design were the 3-D gun code, MICHELLE, and the magnetic code, MAXWELL-3D. Beam optics simulations of the gun design demonstrate excellent beam transport characteristics with a final beam-to-tunnel fill factor less than 40%.