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Successful explosive material detection in luggage and similar sized containers is a critical issue in securing the safety of all airline passengers. Tensor Technology Inc. has recently developed a methodology that will detect explosive compounds with pulsed fast neutron transmission spectroscopy. In this scheme, tritium beams will be used to generate neutrons with a broad energy spectrum as governed by the T(t,2n)4He fission reaction that produces 0-9 MeV neutrons. Lawrence Berkeley National Laboratory, in collaboration with Tensor Technology Inc., has designed and fabricated a pulsed white-spectrum neutron source for this application. The specifications of the neutron source are demanding and stringent due to the requirements of high yield and fast pulsing neutron emission, and sealed tube, tritium operation. In a unique co-axial geometry, the ion source uses ten parallel rf induction antennas to externally couple power into a toroidal discharge chamber. There are 20 ion beam extraction slits and three concentric electrode rings to shape and accelerate the ion beam into a titanium cone target. Fast neutron pulses are created by using a set of parallel-plate deflectors switching between plusmn750 V and deflecting the ion beams across a narrow slit. The generator is expected to achieve 5 ns neutron pulses at tritium ion beam energies between 80-120 kV. First experiments demonstrated ion source operation and successful beam pulsing.

Without quality historical records that provide the composition of legacy materials, the elemental and/or chemical characterization of such materials requires a manual analytical strategy that may expose the analyst to unknown toxicological hazards. In addition, much of the existing legacy inventory also incorporates radioactivity, and, although radiological composition may be determined by various nuclear-analytical methods, most importantly, gamma-spectroscopy, current methods of chemical characterization still require direct sample manipulation, thereby presenting special problems with broad implications for both the analyst and the environment. Alternately, prompt gamma activation analysis (PGAA) provides a ‘single-shot’ in-situ, non-destructive method that provides a complete assay of all major entrained elemental constituents.1–3 Additionally, neutron activation analysis (NAA) using short-lived activation products complements PGAA and is especially useful when NAA activation surpasses the PGAA in elemental sensitivity.

A high-yield D–T neutron generator has been developed for neutron interrogation in homeland security applications such as cargo screening. The generator has been designed as a sealed tube with a performance goal of producing 5 × 1011 n/s over a long lifetime. The key generator components developed are a radio-frequency (RF) driven ion source and a beam-loaded neutron production target that can handle a beam power of 10 kW. The ion source can provide a 100 mA D+/T+ beam current with a high fraction of atomic species and can be pulsed up to frequencies of several kilohertz for pulsed neutron generator operation. Testing in D–D operation has been started.

The Plasma and Ion Source Technology Group at Lawrence Berkeley National Laboratory has developed various types of advanced neutron generators for wide range of applications. The latest developments include a T–T fusion reaction based point neutron generator for Tensor Technology Inc. for airport cargo screening and a single beam, D–D fusion based axial neutron generator for neutron imaging applications for Adelphi Technology Inc. These neutron generators utilize RF-induction discharge to ionize the deuterium/tritium gas. This discharge method provides high plasma density for high output current, high atomic species from molecular gases, long life operation and versatility for various discharge chamber geometries. Stability of the discharge allows for accurate modeling of the beam dynamics in accelerator section of these neutron generators. Current status of the neutron generator development with experimental data will be presented.

In this work we have studied the generation of EUV light by a novel compact electron cyclotron resonance ion source (CECRIS). The EUV emission diagnostics of the ECR plasma was accomplished by means of a 1.5 m grazing incidence monochromator which was operated in a wavelength range of 4–90 nm under the condition of medium to high resolution to discriminate between spectra arising from different Xe q+ (q = 2–10) charge states. One of the major accomplishments of this study is assignment of numerous new optical transitions for xenon in the 10–80 nm range to create a database for further investigations. High resolution spectra were recorded in the 10–16 nm range confirming significant contributions from highly excited Xe 10+ and Xe 9+ ionic states. Major outcome of this work is that the Xe 10+ ion emission with k = 13.4 nm may occurs with such a simplified and compact ECR source. The EUV emission

The plasma and ion source technology group in Lawrence Berkeley National Laboratory is developing advanced, next generation D-D neutron generators. There are three distinctive developments, which are discussed in this presentation, namely, multi-stage, accelerator-based axial neutron generator, high-output co-axial neutron generator and point source neutron generator. These generators employ RF-induction discharge to produce deuterium ions. The distinctive feature of RF-discharge is its capability to generate high atomic hydrogen species, high current densities and stable and long-life operation. The axial neutron generator is designed for applications that require fast pulsing together with medium to high D-D neutron output. The co-axial neutron generator is aimed for high neutron output with cw or pulsed operation, using either the D-D or D-T fusion reaction. The point source neutron generator is a new concept, utilizing a toroidal-shaped plasma generator. The beam is extracted from multiple apertures and focus to the target tube, which is located at the middle of the generator. This will generate a point source of D-D, T-T or D-T neutrons with high output flux. The latest development together with measured data will be discussed in this article.

Author(s): Firestone, R.B.; English, G.A.; Reijonen, J.; Gicquel, F.; Leung, K.-N.; Perry, D.L.; Garabedian, G.; Bandong, B.; Revay, Zs.; Molnar, G.L. | Abstract: Thermal neutrons from the Budapest Research Reactor and fast neutrons from the Berkeley Neutron Generator Facility have been used to analyze uranium. It has been shown that both prompt and delayed gamma rays from neutron capture and fission product decay can be used to analyze uranium concentrations and 235U enrichment. Detection of neutrons from the spontaneous fission of 238U has also been demonstrated for uranium analysis. The observation of high-energy gamma rays following the decay of short-lived fission products is a sensitive indication of fissile material, and the ratio of fission product gamma ray intensities can uniquely determine the concentrations of fission isotopes.

High neutron output D–D neutron generators have been developed in the Plasma and Ion Source Technology Group in LBNL. A new facility has been build to enable testing and running these powerful generators. The co-axial neutron generator and the shielding/moderator structure are described in this presentation. Also presented are the first PGAA (Prompt Gamma Activation Analysis) and NAA (Neutron Activation Analysis) results measured in this neutron facility.

To characterize legacy radioactive materials, it is necessary to determine both the radioactive and, in the case of carrier-based materials, the stable, non-radioactive chemical constituents. Reputable process knowledge may afford some insight but, absent such information, gamma spectroscopy and (non-destructive) prompt gamma activation analysis (PGAA) cover essentially all of the analytical needs, with the former addressing most radionuclides with the exception of the pure β−-emitters and the latter addressing the stable chemical constituents. This paper integrates both methods into a general analytical protocol based upon radioanalytical work performed at Lawrence Berkeley National Laboratory (LBNL) and PGAA work performed collaboratively by the various groups. A new LBNL-developed neutron generator is also discussed.

Microwave Ion Source for Low Charge State Ion Production * J. Reijonen † , M. Eardley, R. Gough, K. Leung, R. Thomae Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 5-119, Berkeley, CA 94720, USA Abstract. The Plasma and Ion Source Technology Group at LBNL have developed a microwave ion source. The source consists of a stainless-steel plasma chamber, a permanent-magnet dipole structure and a coaxial microwave feed. Measurements were carried out to characterize the plasma and the ion beam produced in the ion source. These measurements included current density, charge state distribution, gas efficiency and accelerated beam emittance measurements. Using a computer controlled data acquisition system a new method of determining the saturation ion current was developed. Current density of 3-6 mA/cm 2 was measured with the source operating at the over dense mode. The highest measured charge-states were Ar 5+ , O 3+ and Xe 7+ . Gas efficiency was measured using a calibrated argon leak. Depending on the source pressure and discharge power, more than 20% total gas efficiency was achieved. The emittance of the ion beam was measured by using a pepper-pot device. Certain spread was noticed in the beam emittance in the perpendicular direction to the source dipole field. For the parallel direction to the magnetic field, the normalized rr’ emittance of 0.03 π-mm-mrad at 13 kV of acceleration voltage and beam exit aperture of 3-mm-in-diameter was measured. This compares relatively well with the simulated value of 4rms, normalized emittance value of 0.024 π-mm- mrad. INTRODUCTION Single to low charge state ion beams with good beam quality and ion sources with good gas efficiency are needed in various applications, ranging from radio- active ion beam production to high energy ion implanters. A simple permanent-magnet microwave ion source has been developed to fulfill the various requirements. 1. SOURCE DESIGN The plasma chamber of the microwave ion source was made from stainless-steel. Three vacuum feed- through ports were designed: one to the opposite side of the extraction and two facing each other in the middle of the magnet-rings. The two facing ports were designed to be different in length. This enabled one to test different lengths of the coaxial antenna inside the source. The other two ports were used for gas feed and for a window port. The magnets were attached around the source using an iron yoke. They were floating around the source chamber so that the cooling air was flowing between the source body and the magnets. This arrangement maintained the temperature of the magnets reasonably low. The magnet rings were constructed from a SmCo magnet blocks measuring 1.3 cm, 2.5 cm and 3.8 cm in width, height and depth respectively. To have a ring configuration, using bar magnets, the bar ends close to the feed-trough port were touching each other, but the other ends of the magnet bars were separated. To achieve a fairly uniform field, the magnet poles of the opposite sides were rotated slightly so that the magnets in the poles did not face each other. In figure 1 a schematic drawing of the micro-wave ion source is shown. Initially the magnetic field (B dip (d)) using a yoke, as a function of the distance between the poles was approximately given by This Work was supported by Department of Energy under Contract No. DE-AC03-76SF00098 email: jreijonen@lbl.gov

Negative light ion beams have been used widely in many applications over the past decades. One of the most popular methods of producing H− and D− beams is the so-called volume production, in which a plasma is contained in a multicusp magnetic field. The beam is extracted using an electric field applied in the extraction gap. Accompanying the negative ions is up to 100 times greater number of electrons, which have to be removed from the beam. This is usually done by placing a transverse magnetic field in the extraction region. With this method the electrons can be quite effectively removed from the beam. The problem is that we dump a high intensity, high energy electron beam in the extraction electrode and dissipate a lot of power in the process. The negative ion beam is also deflected in this strong magnetic field which has to be corrected either by tilting the source compared to the extraction or by adding an opposite transverse magnetic field. In the latter method the beam is laterally displaced from th...

The H− ion source for the Spallation Neutron Source (SNS) is a cesiated, radio-frequency driven multicusp volume source which operates at a duty cycle of 6%. In pulsed rf driven plasma sources, ignition of the plasma affects the stability of source operation and the antenna lifetime. We report on ignition schemes, based on secondary electron generation by UV light, a hot filament, a low power rf plasma (cw, 13.56 MHz), as well as source operation solely with the high power 2 MHz rf. We find that the dual frequency, single antenna scheme is most attractive for the operating conditions of the SNS H− source.

The front-end systems (FES) of the spallation neutron source project are being built by Berkeley Lab and will deliver a pulsed 40 mA H− ion beam at 2.5 MeV energy to the subsequent drift-tube linac. The FES accelerator components comprise a rf driven, volume-production, cesium-enhanced, multicusp ion source; an electrostatic low-energy beam transport (LEBT) that includes provisions for transverse focusing, steering, and beam chopping; a radio-frequency quadrupole accelerator; and a medium-energy beam transport line. The challenges for ion source and LEBT design are the generation of a plasma suitable for creating the required high H− ion density, lifetime of the rf antenna at 6% duty factor, removal of the parasitic electron population from the extracted negative ions, and emittance conservation. The article discusses these issues in detail and highlights key experimental results obtained so far.

Schlumberger is an international oilfield service company with nearly 80,000 employees of 140 nationalities, operating globally in 80 countries. As a market leader in oilfield services, Schlumberger has developed a suite of technologies to assess the downhole environment, including, among others, electromagnetic, seismic, chemical, and nuclear measurements. In the past 10 years there has been a radical shift in the oilfield service industry from traditional wireline measurements to logging‐while‐drilling (LWD) analysis. For LWD measurements, the analysis is performed and the instruments are operated while the borehole is being drilled. The high temperature, high shock, and extreme vibration environment of LWD imposes stringent requirements for the devices used in these applications. This has a significant impact on the design of the components and subcomponents of a downhole tool. Another significant change in the past few years for nuclear‐based oilwell logging tools is the desire to replace the sealed radioisotope sources with active, electronic ones. These active radiation sources provide great benefits compared to the isotopic sources, ranging from handling and safety to nonproliferation and well contamination issues. The challenge is to develop electronic generators that have a high degree of reliability for the entire lifetime of a downhole tool. LWD tool testing and operations are highlighted with particular emphasis on electronic radiation sources and nuclear detectors for the downhole environment.

At Lawrence Berkeley National Laboratory different antenna protection schemes have been investigated for the radio frequency-driven multicusp ion source. It was found that the antenna lifetime can be greatly enhanced by an additional shielding, which consists of porcelain, quartz or boron nitride. Different antenna configurations and their influence on the plasma generation will be discussed. Antenna life time greater than 500 hours continuous wave operation has been demonstrated in hydrogen plasma using a novel quartz antenna design.

This research and development program was designed to improve nondestructive evaluation of large mechanical objects by providing both fast and thermal neutron sources for radiography. Neutron radiography permits inspection inside objects that x-rays cannot penetrate and permits imaging of corrosion and cracks in low-density materials. Discovering of fatigue cracks and corrosion in piping without the necessity of insulation removal is possible. Neutron radiography sources can provide for the nondestructive testing interests of commercial and military aircraft, public utilities and petrochemical organizations. Three neutron prototype neutron generators were designed and fabricated based on original research done at the Lawrence Berkeley National Laboratory (LBNL). The research and development of these generators was successfully continued by LBNL and Adelphi Technology Inc. under this STTR. The original design goals of high neutron yield and generator robustness have been achieved, using new technology developed under this grant. In one prototype generator, the fast neutron yield and brightness was roughly 10 times larger than previously marketed neutron generators using the same deuterium-deuterium reaction. In another generator, we integrate a moderator with a fast neutron source, resulting in a high brightness thermal neutron generator. The moderator acts as both conventional moderator and mechanical and electrical support structuremore » for the generator and effectively mimics a nuclear reactor. In addition to the new prototype generators, an entirely new plasma ion source for neutron production was developed. First developed by LBNL, this source uses a spiral antenna to more efficiently couple the RF radiation into the plasma, reducing the required gas pressure so that the generator head can be completely sealed, permitting the possible use of tritium gas. This also permits the generator to use the deuterium-tritium reaction to produce 14-MeV neutrons with increases of yield of two orders of magnitude. The first fast neutron radiographic images were obtained using neutron cameras and a new fast neutron generator. These early images demonstrated the feasibility of using fast neutrons for imaging and penetrating thick objects of high density and imaging. Fast neutrons can be used to image low atomic number materials (e.g. plastics, explosives, lubricants and ceramics) that are shielded by high density materials (e.g. lead, tungsten and uranium). Fast neutron radiography could be used as a means to screen weapons for flaws and chemical stability. X-ray radiography can not easily do this. Fast neutron imaging is technically difficult and, consequently, a completely undeveloped market. Two of the generators were designed to have small source size and high brightness, ideal for fast-neutron imaging. With these generators we successfully used two fast neutron cameras: one developed by us, and another developed by a collaborator, Commonwealth Scientific and Industrial Research Organization, CSIRO. We have successfully used these cameras to obtain low resolution images of various objects such as pipe fittings filled with water and other mechanical objects. Higher resolution and contrast images are expected by decreasing the source size and increasing generator yield.« less

In this article the effects of different engineering parameters of rf-driven ion sources with an external spiral antenna and a quartz rf window are studied. This article consists of three main topics: the effect of source geometry on the operation gas pressure, the effect of source materials and magnetic confinement on extracted current density and ion species, and the effect of different antenna geometries on the extracted current density. The effect of source geometry was studied using three cylindrical plasma chambers with different inner diameters. The chamber materials were studied using two materials, aluminum (Al) and alumina (Al(2)O(3)). The removable 14 magnet multicusp confinement arrangement enabled us to compare the effects of the two wall materials with and without the magnetic confinement. The highest measured proton fractions were measured using Al(2)O(3) plasma chamber and no multicusp confinement. For the compared ion sources the source with multicusp confinement and Al(2)O(3) plasma chamber yields the highest current densities. Multicusp confinement increased the maximum extracted current by up to a factor of 2. Plasma production with different antenna geometries were also studied. The highest current density was achieved using 4.5 loop solenoid antenna with 6.0 cm diameter. A slightly lower current density with lower pressure was achieved using a tightly wound 3 loop spiral antenna with 3.3 cm inner diameter and 6 cm outer diameter.

We report here on the development of neutron and photon sources for use in imaging and active interrogation applications, where there is a growing urgency for more advanced interrogation tools. These devices include high yield D-D, D-T and T-T fusion reaction based neutron generators and also low energy nuclear reaction based high-energy gamma generators. One common feature in these various devices is the use of a high-efficiency, RF-induction discharge ion source. This discharge method provides high plasma density for high output current, high atomic species from molecular gases for high efficiency neutron or gamma generation and long lifetime. Predictable discharge characteristics of these plasma generators allow accurate modeling for both the beam dynamics and for the heat loads at the target spot. Current status of the neutron and gamma generator development with experimental data will be presented.

The Plasma and Ion Source Technology Group at Lawrence Berkeley National Laboratory has developed various types of advanced D-D (neutron energy 2.5 MeV), D-T (14 MeV) and T-T (0 – 9 MeV) neutron generators for wide range of applications. These applications include medical (Boron Neutron Capture Therapy), homeland security (Prompt Gamma Activation Analysis, Fast Neutron Activation Analysis and Pulsed Fast Neutron Transmission Spectroscopy) and planetary exploration with a sub-surface material characterization on Mars. These neutron generators utilize RF induction discharge to ionize the deuterium/tritium gas. This discharge method provides high plasma density for high output current, high atomic species from molecular gases, long life operation and versatility for various discharge chamber geometries. Four main neutron generator developments are discussed here: high neutron output co-axial neutron generator for BNCT applications, point neutron generator for security applications, compact and sub-compact axial neutron generator for elemental analysis applications. Current status of the neutron generator development with experimental data will be presented.

A permanent magnet 6.4 GHz microwave plasma generator has been designed and constructed at Plasma and Ion Source Technology group at Lawrence Berkeley National Laboratory for applications in Extreme Ultraviolet Lithography (EUVL). In order to produce 13.5 nm EUV light, Xenon plasma was formed with the goal of producing Xe10+ ions, which are associated with the formation of 13.5 nm radiation. The goal was to diagnose the source plasma by extracting Xe‐ ions from the source plasma and by measuring the EUV light spectrum with a grazing incidence monochromator. 13.5 nm light was observed in the measurements indicating that Xe10+ existed in the plasma.

Recently, a new application of boron neutron capture therapy (BNCT) treatment has been introduced. Results have indicated that liver tumors can be treated by BNCT after removal of the liver from the body. At Lawrence Berkeley National Laboratory, compact neutron generators based on (2)H(d,n)(3)He (D-D) or (3)H(t,n)(4)He (D-T) fusion reactions are being developed. Preliminary simulations of the applicability of 2.45 MeV D-D fusion and 14.1 MeV D-T fusion neutrons for in vivo liver tumor BNCT, without removing the liver from the body, have been carried out. MCNP simulations were performed in order to find a moderator configuration for creating a neutron beam of optimal neutron energy and to create a source model for dose calculations with the simulation environment for radiotherapy applications (SERA) treatment planning program. SERA dose calculations were performed in a patient model based on CT scans of the body. The BNCT dose distribution in liver and surrounding healthy organs was calculated with rectangular beam aperture sizes of 20 cm x 20 cm and 25 cm x 25 cm. Collimator thicknesses of 10 and 15 cm were used. The beam strength to obtain a practical treatment time was studied. In this paper, the beam shaping assemblies for D-D and D-T neutron generators and dose calculation results are presented.

Various types of neutron generator systems have been designed and tested at the Plasma and Ion Source Technology Group at Lawrence Berkeley National Laboratory. These generators are based on a D-D fusion reaction. These high power D-D neutron generators can provide neutron fluxes in excess of the current state of the art D-T neutron generators, without the use of pre-loaded targets or radioactive tritium gas. Safe and reliable long-life operations are the typical features of these D-D generators. All of the neutron generators developed in the Plasma and Ion Source Technology Group are utilizing powerful RF-induction discharge to generate the deuterium plasma. One of the advantages of using the RF-induction discharge is it's ability to generate high fraction of atomic ions from molecular gases, and the ability to generate high plasma densities for high extractable ion current from relatively small discharge volume.

The long list of contributors to the prompt gamma activation analysis (PGAA) project is important because it highlights the broad cast of active PGAA researchers from various facilities and backgrounds. PGAA is basically a simple process in principle that was traditionally difficult in application. It is an old technique that has for years been tied to and associated exclusively with nuclear reactor facilities, which has limited its acceptance as a general, analytical tool for identifying and quantifying elements or, more precisely, isotopes, whether radioactive or nonradioactive. Field use was not a viable option.

A compact neutron generator based on D-D or D-T fusion reactions is being developed at the Lawrence Berkeley National Laboratory. The deuterium or tritium ions are produced in a radio-frequency (RF) driven multicusp plasma source. Seven beamlets are extracted and are accelerated to energy of 100 keV by means of a three-electrode electrostatic accelerator column. The ion beam then impinges on a titanium coated copper target where either the 2.4 MeV D-D or 14 MeV D-T neutrons are generated by fusion reaction. The development of the neutron tube is divided into three phases. First, the accelerator column is operated at hydrogen beam intensity of 15 mA. Second phase consists of deuterium beam runs at pulsed, low duty cycle 150 mA operation. The third phase consists of deuterium or tritium operation at 1.5 A beam current. Phase one is completed and the results of hydrogen beam testing are discussed. Low duty cycle 150 mA deuterium operation is being investigated. Neutron flux will be measured. Finally the phase three operation and the advance neutron generator designs are described.

A novel design for an electron beam focusing column has been developed at LBNL. The design is based on a low-energy spread multicusp plasma source which is used as a cathode for electron beam production. The focusing column is 10 mm in length. The electron beam is focused by means of electrostatic fields. The column is designed for a maximum voltage of 50 kV. Simulations of the electron trajectories have been performed by using the 2-D simulation code IGUN and EGUN. The electron temperature has also been incorporated into the simulations. The electron beam simulations, column design and fabrication will be discussed in this presentation.

rf driven multicusp ion sources have been successfully used in various different applications. Lately the Plasma and Ion Source Technology Group at Lawrence Berkeley National Laboratory has been developing a rf ion source for neutron production and a high current density cw-operated ion source for SIMOX (Separation by Implantation of Oxygen)-application. The group has developed a small ion source, which consists of a quartz plasma chamber, an external rf-antenna, an extraction electrode, and a target assembly, all in a tube that is approximately 25 cm in length and 5 cm in diameter. Another neutron generator currently under development is a multiaperture, high power generator. The neutron generator currently operates at 1% duty cycle, 80 kV, and 150 mA of deuterium beam. The neutron yield measured from the generator is 1.6×107 n/s. For oxygen implantation, the group has been developing a source which could provide a high percentage of O+ at high current density using cw operation. A dual-antenna has been ...

The Front-End Systems (FES) of the Spallation Neutron Source (SNS) project have been described in detail elsewhere. They comprise an rf-driven H/sup -/ ion source, electrostatic LEBT, four-vane RFQ, and an elaborate MEBT. These systems are planned to be delivered to the SNS facility in Oak Ridge in June 2002. This paper discusses the latest design features, the status of development work, component fabrication and procurements, and experimental results with the first commissioned beamline elements.

At LBNL we are investigating the use of gaseous ion sources for induction linac applications such as heavy ion inertial fusion. Typical requirements for the ion source is to produce 20 /spl mu/s pulses with a rise-time of 2 /spl mu/s. The current density should be greater than 100 mA/cm/sup 2/ at a duty cycle of 10 Hz. Noble gases such as krypton, neon and xenon will be used. The source used for the measurements described in this paper was a standard 10 cm in diameter multicusp source with RF-discharge.

We report the detection of single ion impacts through monitoring of changes in the source-drain currents of field effect transistors (FET) at room temperature. Implant apertures are formed in the interlayer dielectrics and gate electrodes of planar, micro-scale FETs by electron beam assisted etching. FET currents increase due to the generation of positively charged defects in gate oxides when ions (121Sb12+, 14+, Xe6+; 50 to 70 keV) impinge into channel regions. Implant damage is repaired by rapid thermal annealing, enabling iterative cycles of device doping and electrical characterization for development of single atom devices and studies of dopant fluctuation effects.

High-intensity fast white neutron pulses are needed for pulsed fast neutron transmission spectroscopy (PFNTS). A compact tritium–tritium fusion reaction neutron generator with an integrated ion beam chopping system has been designed, simulated, and tested for PFNTS. The design consists of a toroidal plasma chamber with 20 extraction slits, concentric cylindrical electrodes, chopper plates, and a central titanium-coated beam target. The total ion beam current is 1A. The beam chopping is done at 30keV energy with a parallel-plate deflector integrated with an Einzel lens. Beam pulses with 5ns width can be achieved with a 15ns rise/fall time ±1500V sweep on the chopper plates. The neutrons are produced at 120keV energy. A three-dimensional simulation code based on Vlasov iteration was developed for simulating the ion optics of this system. The results with this code were found to be consistent with other simulation codes. So far we have measured 50ns ion beam pulses from the system.

Fast deuterium (D+) and tritium (T+) ion beam pulses are needed in some neutron-based imaging systems. A compact, integrated fast ion beam extraction and chopping system has been developed and tested at the Lawrence Berkeley National Laboratory for these applications, and beam pulses with 15ns full width at half maximum have been achieved. Computer simulations together with experimental tests indicate that even faster pulses are achievable by shortening the chopper voltage rise time. This chopper arrangement will be implemented in a coaxial neutron generator, in which a small point-like neutron source is created by multiple 120keV D+ ion beams hitting a titanium target at the center of the source.

The Spallation Neutron Source requires an ion source capable of delivering a high-current (∼50 mA) H− beam with a 6% duty cycle continuously for the three weeks between the scheduled maintenance periods. The cesium-enhanced, multicusp volume ion source under development on the integrated test facility at LBNL delivers H− ion currents up to 50 mA, increasing approximately linearly with the rf power. Initial experience using porcelain-coated copper antennas, however, indicates lifetimes will fall below the desired three-week period, mostly limited by antenna failures. In an effort to improve our understanding of the antenna limitations, we are in the process of developing an antenna test dome, which will allow us to visually observe and study the rf-initiated discharge at low-power levels. We hope to be able to test antennas for invisible defects by observing and measuring the onset of the discharge. In addition, we are planning to test different antennas. Results will be presented at the meeting.