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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.

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.

Significant experimental and theoretical progress has been made in the US heavy-ion fusion program on high-current sources, injectors, transport, final focusing, chambers and targets for high-energy density physics (HEDP) and inertial fusion energy (IFE) driven by induction linac accelerators. One focus of present research is the beam physics associated with quadrupole focusing of intense, space–charge dominated heavy-ion beams, including gas and electron cloud effects at high currents, and the study of long-distance-propagation effects such as emittance growth due to field errors in scaled experiments. A second area of emphasis in present research is the introduction of background plasma to neutralize the space charge of intense heavy-ion beams and assist in focusing the beams to a small spot size. In the near future, research will continue in the above areas, and a new area of emphasis will be to explore the physics of neutralized beam compression and focusing to high intensities required to heat targets to high-energy density conditions as well as for inertial fusion energy.

We report on an ongoing study on modular Heavy Ion Fusion (HIF) drivers. The modular driver is characterized by {approx}20 nearly identical induction linacs, each carrying a single high current beam. In this scheme, one of the full size induction linacs can be tested as an 'integrated Research Experiment' (IRE). Hence this approach offers significant advantages in terms of driver development path. For beam transport, these modules use solenoids, which are capable of carrying high line charge densities, even at low energies. A new injector concept allows compression of the beam to high line densities right after the source. The final drift compression is performed in a plasma in which the large repulsive space charge effects are neutralized. Finally, the beam is transversely compressed onto the target, using either external solenoids or current-carrying channels (in the assisted pinch mode of beam propagation). We report on progress towards a self-consistent point design from injector to target. Considerations of driver architecture, chamber environment as well as the methodology for meeting target requirements of spot size, pulse shape and symmetry are also described. Finally, some near-term experiments to address the key scientific issues are discussed.

Significant experimental and theoretical progress has been made in the U.S. heavy ion fusion program on high-current sources, injectors, transport, final focusing, chambers and targets for high energy density physics (HEDP) and inertial fusion energy (IFE) driven by induction linac accelerators. One focus of present research is the beam physics associated with quadrupole focusing of intense, space-charge dominated heavy-ion beams, including gas and electron cloud effects at high currents, and the study of long-distance-propagation effects such as emittance growth due to field errors in scaled experiments. A second area of emphasis in present research is the introduction of background plasma to neutralize the space charge of intense heavy ion beams and assist in focusing the beams to a small spot size. In the near future, research will continue in the above areas, and a new area of emphasis will be to explore the physics of neutralized beam compression and focusing to high intensities required to heat targets to high energy density conditions as well as for inertial fusion energy.

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 miniature multiple beamlet approach to an injector system was recently proposed in order to reduce the size, cost, and power requirements of the injector. The beamlets of very high current density are needed to meet the brightness requirement. Besides vacuum arc ion sources, cold-cathode gas ion sources are candidates for this application. Vacuum-arc metal ion sources and vacuum-arc-like gas ion sources are discussed. Experiments are presented that focus on the short-pulse plasma composition and ion charge state distribution. Mg and Sr have been identified as the most promising metals leading to mono-species beams when 20 {mu}s arc pulses are used. It is shown that the efficient production of gas ions requires the presence of a magnetic field.

Typical designs for a Heavy Ion Fusion Power Plant require the source injector to deliver 100 beams, packed into an array with a spacing of 7 cm. When designing source injectors using a single large aperture source for each beam, the emitter surfaces are packed into an array with a spacing of 30 cm. Thus, the matching section of the source injector must not only prepare the beam for transport in a FODO lattice, but also funnel the beams together. This can be accomplished by an ESQ matching section in which each beam travels on average at a slight angle to the axis of the quadrupoles and uses the focussing effect of the FODO lattice to maintain the angle. At the end of the matching section, doublet steering is used to bring the beams parallel to each other for injection into the main accelerator. A specific solution of this type for an 84-beam source injector is presented. PACS: 41.75.Ak,41.85.Ar, 41.85.Ja

We describe the goals and research program leading to the Heavy Ion Integrated Research Experiment (IRE). We review the basic constraints which lead to a design and give examples of parameters and capabilities of an IRE. We also show design tradeoffs generated by the systems code IBEAM.

In a new approach to develop high current beams for heavy ion fusion, beam current at about 0.5 ampere per channel can be obtained by merging an array of high current density beamlets of 5 mA each. We have done computer simulations to study the transport of high current density beamlets and the emittance growth due to this merging process. In our radio frequency (rf) multicusp source experiment, we have produced a cluster of 61 beamlets using minimum gas flow. The current density from a 0.25 cm diameter aperture reached 100 mA/cm2. The normalized 4 rms emittance of 0.0186π mm mrad corresponds to an equivalent ion temperature of 2.08 eV. These results showed that the rf argon plasma source is suitable for producing high current density beamlets that can be merged to form a high current high brightness beam for heavy ion fusion application.

Neutral beams for the next generation tokamaks will be based on multiampere negative ion beams with a beam energy of about 1.0 MeV and pulse lengths of a thousand seconds. High intensity dc beams at these levels of beam energy will require extensive development in electrostatic accelerators. At Lawrence Berkeley Laboratory, a two‐module electrostatic quadrupole (ESQ) accelerator was built to accelerate ions to 200 keV. In this experiment, up to 100 mA of H− beam current was obtained from a Japan Atomic Energy Research Institute cesiated volume source using a multiaperture preaccelerator which merged 19 beamlets into a single circular beam at the entrance to the ESQ accelerator. The H− beam was accelerated by the ESQ to accelerate 200 keV without any significant beam loss or emittance growth.

Development and testing of a lithium ion source and injector P. A. Seidl,1 w.w. Greenway,1 D. P. Grote,2 J—Y. Jung,‘ J. w. Kwan,' S.M. Lidia,‘ P. K. Roy,1 J. Takakuwa,' J-L. Vay,l and W. L. Waldronl ‘Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA zlawrence Livermore National laboratory, Livermore, California 94550, USA (Received 30 January 2012; published 11 April 2012) We report on the development and testing of an intense lithium ion source and injector for an ion induction accelerator designed for warm, dense matter target heating experiments. The source is a 10.9-cm diameter aluminosilicate emitter on a porous tungsten substrate. For an injector voltage pulse of 120 kV, pulse duration of 1.0- ,u,s FWHM, and an operating temperature of 1250°C, the source emits 35 mA of Li‘“ ions. The results follow experimental studies with much smaller sources. The key challenges included beam quality, source lifetime, and heat management. I. INTRODUCTION Recently, low-energy ion beams are being applied to the field of warm, dense matter physics, that is, the exploration of matter at or near solid density and temperature from 1 eV to several eV. In order to achieve this transient state of matter, the target material, or sample, must be heated faster than the characteristic thermodynamic expansion time of the target, ~ 1 ns. Ion beams complement laser heating experiments, because ion beams deposit their energy volu- metrically in the target material. In particular, low to medium mass ions (ion mass in the approximate range 4 l A l 23) with ion kinetic energy of 1-20 MeV deposit most of their energy near the peak of dE/dx vs E, which is particularly effective for uniform heating [1]. The new neutralized drift compression experiment (NDCX—ll) is based on a Li+ beam accelerated to 1-3 MeV. The ~ 0.1 A beam current at injection (E = 0.1 MeV) is accelerated and compressed to a much higher current and focused to an intense millimeter-sized beam radius at the target [2]. The injector and source are designed for = 1 mA/cm2 space—charge limited extraction from a l0.9—cm diameter emitter. An acceleration electrode follows the main extraction electrode. The potential of the accelerating electrode is used to tune the transverse envelope of the beam within the injector. The injector is designed to create 60 nC, or 4 X 10q ions in a l-/L sec bunch. II. ION SOURCE Various methods for the production of alkali ions, and specifically lithium have been demonstrated, for example, aluminosilicate, vapor spark sources, and contact ionizers from refractory metals. The choice of aluminosilicate was driven by the need for high intensity and repetition rate, coupled with low emittance and low impurities in a single charge state. Very high lithium current has been demon- strated, for example, with LiCl dielectric surface flashover sources [3], operating at injector voltage of 500 kV and creating a Li+ current density of 120 A/cmz. However, the charge state impurities were 25%—35%, greater than that required for our application. Very high current has been demonstrated with vapor Li+ sources ionized by high-power lasers [4], generally at low repetition rate. Contact ionizer sources have shown ion current densities in an acceptable range [5] with very low emittance. The expected lower ionization efficiency for lithium and asso- ciated higher neutral emission from these sources are a concern. The choice of aluminosilicate is based on successes with other alkalis such as K+ [6] which have shown good reproducibility, low emittance, and high current from large surface area sources capable of operating at g1 Hz. Also, there have been demonstrated reliable Li+ sources devel- oped as tokamak plasma diagnostics [7,8]. The results here follow on that work to much larger area lithium sources, at ~ 1 mA/cmz. Ion source preparation Earlier experiments with 6.35-mm emitters [9] estab- lished the sintering temperature, emitter heating and cool- ing rate, extracted current density, and source lifetime. In preparing the large emitters, we have followed most of the steps as described in Ref. [9], with a few changes. (i) High-purity chemicals (AIZCO3, 99.7%; SiO2, 99%; 7Li2CO3, 99.7% isotopically pure, 99.9% chemically pure) are mixed in a stoichiometric ratio (7Li2CO3: AIZCO3: 2 - SiO2) for ,8 eucryptite (LiAlSiO4) and heated to 600°C for one hour, which liberates C02. The chemicals are then thoroughly mixed with a mortar and pestle.

In testing a cesiated volume‐production negative ion source, we have obtained 75 mA of H− beam current in a 270 ms pulse length delivered downstream of the 87 keV preaccelerator. Optimum pressure in the source was less than 8 mT and the electron‐to‐ion ratio in the beam was less than 4. With future improvements in the electron trap, it is anticipated that higher H− current can be obtained by operating with a higher discharge power and a lower plasma electrode bias.

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.

This study group was initiated to consider whether there were any ''show-stopper'' issues with accelerators for heavy-ion warm-dense matter (WDM) and heavy-ion inertial fusion energy (HIF), and to prioritize them. Showstopper issues would appear as limits to beam current; that is, the beam would be well-behaved below the current limit, and significantly degraded in current or emittance if the current limit were exceeded at some region of an accelerator. We identified 14 issues: 1-6 could be addressed in the near term, 7-10 are potentially attractive solutions to performance and cost issues but are not yet fully characterized, 11-12 involve multibeam effects that cannot be more than partially studied in near-term facilities, and 13-14 involve new issues that are present in some novel driver concepts. Comparing the issues with the new experimental, simulation, and theoretical tools that we have developed, it is apparent that our new capabilities provide an opportunity to re-examine and significantly increase our understanding of the number one issue--halo growth and mitigation.

A folded tandem, with 1.25 MV terminal voltage, combined with an ElectroStatic Quadrupole (ESQ) chain is being proposed as a machine for Accelerator‐Based Boron Neutron Capture Therapy (AB‐BNCT). The machine is shown to be capable of accelerating a 30 mA proton beam to 2.5 MeV. These are the specifications needed to produce sufficiently intense and clean epithermal neutron beams, based on the on the 7Li(p,n)7Be reaction, to perform BNCT treatment for deep seated tumors in less than an hour.

A two‐stage ion source concept was presented a few years ago, consisting of a proven H− ion source and a 2.45‐GHz Electron Cyclotron‐Resonance (ECR) type ion source, here used as a plasma cathode. This paper describes the experimental development path pursued at Lawrence Berkeley National Laboratory, from the early concept to a working unit that produces plasma in both stages and creates a negative particle beam. Without cesiation applied to the second stage, the H− fraction of this beam is very low, yielding 75 micro‐amperes of extracted ion beam current at best. The apparent limitations of this approach and envisaged improvements are discussed.

This report collects information on cathode contaminants we have gathered in the process of operating the LBNL DARHT cathode test stand. Information on contaminants is compiled from several sources. The attachment, ''Practical Aspects of Modern Dispenser Cathodes'', is from Heat Wave Corp. (TB-134) and was originally published in Microwave Journal, September 1979. Cathode contamination depends on both material choices and residual gases. Table 1 of TB-134 lists materials that can poison dispenser cathodes. These include reactive residual gases or vapors such as oxygen, water vapor, benzene, chlorine, fluorine, sulfur, silicon, and most metals other than molybdenum, rhenium, tungsten, and copper. The metals interact with the cathode surface through their vapor pressure. A paper by Nexsen and Turner, J. Appl. Phys. 68, 298-303 (1990) shows the threshold effects of some common residual gases or vapors on cathode performance. The book by Walter H. Kohl, Handbook of Materials and Techniques for Vacuum Devices, also contains useful information on cathodes and poisoning agents. A plot of the vapor pressures and poisoning effect of certain metals (from Kohl) is shown below. Note that the vapor pressure of zinc is 1.1 x 10{sup -8} Torr at 400 K = 127 C, and 2.7 x 10{supmore » -5} at 500 K = 227 C. By contrast iron reaches a vapor pressure 1 x 10{sup -8} between 800 and 900 C. Therefore it is important to eliminate any brass parts that could exceed a temperature of 100 C. Many structural components of the cathode assembly contain steel. At 500-600 C in an oxygen atmosphere chromium oxide may outgas from the steel. [Cho, et.al., J. Vac. Sci. Technol. A 19, p. 998 (2001)]. Steel may also contain silicon, and sulfur at low concentrations. Therefore use of steel should be limited or avoided at high temperature near the cathode. Materials that should be avoided in the vicinity of the cathode include brass, silver, zinc, non-OFHC copper, silicates, and sulfur-containing lubricants such molybdenum disulfide. Macor is an aluminosilicate-based insulator that is not stable at high temperature. Macor near the cathode should be replaced by a high-temperature insulator such as alumina ceramic. Other insulating materials that contain silicates, such as fiber insulating sleeves, should be avoided. Copper that is not OFHC contains oxygen and other impurities and should be avoided. Lubricating screw coatings should be chosen carefully to have no sulfur content. Common sources of contamination that can cause low emission include water, saliva, silicates such as glass dust, etc. Cathodes should be handled in near clean-room conditions to minimize the amount of water vapor on the cathode surface from breathing, etc. Cathodes should also be stored in such as a way as to avoid contact with materials such as glass dust and water vapor. Attached are plots of SEM data for several test pieces that were taken from the LBNL test stand after activation of the 311x scandate DARHT cathode. Several copper pieces in the anode region were tested, showing the presence of zinc. Two stainless steel nuts coated with a contaminant were also tested. The SEM data indicates the presence of zinc and some sulfur. The zinc has been traced to a brass piece, and the sulfur to the possible use of molybdenum disulfide lubricant on a nut in the system. Finally a swipe of contaminant on the vacuum vessel wall analyzed by a commercial testing laboratory shows again the presence of zinc. In order to improve system cleanliness, we have implemented the following modifications to the test stand: replaced the brass piece with copper-tungsten; replaced Macor insulators with alumina ceramic; used boron nitride lubricant; replaced copper beam stop with OFHC copper; and replaced steel pieces near the cathode where possible with copper or copper-tungsten. A clean fire of high-temperature components and a high-current filament test have shown no evidence to date for contaminants since the modifications.« less

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 purpose of this report is to describe the activation of the fourth cathode installed in the DARHT-II Injector. Appendices have been used so that an extensive amount of data could be included without danger of obscuring important information contained in the body of the report. The cathode was a 612 M type cathode purchased from Spectra-Mat. Section II describes the handling and installation of the cathode. Section III is a narrative of the activation based on information located in the Control Room Log Book supplemented with time plots of pertinent operating parameters. Activation of the cathode was performed in accordance with the procedure listed in Appendix A. The following sections provide more details on the total pressure and constituent partial pressures in the vacuum vessel, cathode heater power/filament current, and cathode temperature.

High current and low emittance are principal requirements for heavy-ion injection into a linac driver for inertial fusion energy. An electrostatic quadrupole injector is capable of providing these high charge density and low emittance beams. We have modified the existing 2-MV injector to reduce beam emittance and to double the pulse length. We characterize the beam delivered by the modified injector to the High Current Transport Experiment and the effects of finite rise time of the extraction voltage pulse in the diode on the beam head. We demonstrate techniques for mitigating aberrations and reducing beam emittance growth in the injector.

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.

Negative halogen ion beams have recently been proposed as heavy ion fusion drivers. They would avoid the problem of electron accumulation in positive ion beams, and could be efficiently photodetached to neutrals if desired [1]. Initial experiments using chlorine produced a current density of 45 mA/cm{sup 2} of 99.5% atomic negative Cl with an e/Cl{sup -} ratio as low as 7:1 and good emittance.

Negative halogen ions have recently been proposed as a possible alternative to positive ions for heavy ion fusion drivers because electron accumulation would not be a problem in the accelerator, and if desired, the beams could be photodetached to neutrals [1,2,3]. To test the ability to make suitable quality beams, an experiment was conducted at Lawrence Berkeley National Laboratory using chlorine in an RF-driven ion source. Without introducing any cesium (which is required to enhance negative ion production in hydrogen ion sources) a negative chlorine current density of 45 mA/cm{sup 2} was obtained under the same conditions that gave 57 mA/cm{sup 2} of positive chlorine, suggesting the presence of nearly as many negative ions as positive ions in the plasma near the extraction plane. The negative ion spectrum was 99.5% atomic chlorine ions, with only 0.5% molecular chlorine, and essentially no impurities. Although this experiment did not incorporate the type of electron suppression technology that is used in negative hydrogen beam extraction, the ratio of co-extracted electrons to Cl{sup -} was as low as 7 to 1, many times lower than the ratio of their mobilities, suggesting that few electrons are present in the near-extractor plasma. This, along with the near-equivalence of the positive and negative ion currents, suggests that the plasma in this region was mostly an ion-ion plasma. The negative chlorine current density was relatively insensitive to pressure, and scaled linearly with RF power. If this linear scaling continues to hold at higher RF powers, it should permit current densities of 100 mA/cm{sup 2}, sufficient for present heavy ion fusion injector concepts. The effective ion temperatures of the positive and negative ions appeared to be similar and relatively low for a plasma source.

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.

In Heavy-Fusion and in other applications, there is a need for high brightness sources with both high current and low emittance. The traditional design with a single monolithic source, while very successful, has significant constraints on it when going to higher currents. With the Child-Langmuir current-density limit, geometric aberration limits, and voltage breakdown limits, the area of the source becomes a high power of the current, A/spl sim/I?8/3. We are examining a multi-beamlet source, avoiding the constraints by having many beamlets each with low current and small area. The beamlets are created and initially accelerated separately and then merged to form a single beam. This design offers a number of potential advantages over a monolithic source, such as a smaller transverse footprint, more control over the shaping and aiming of the beam, and more flexibility in the choice of ion sources. A potential drawback, however, is the emittance that results from the merging of the beamlets. We have designed injectors using simulation that have acceptably low emittance and are beginning to examine them experimentally.

A test of intense beam production with a JAERI negative ion source and an ESQ accelerator is in progress under US-JAPAN collaborative program between JAERI and LBL. In the first series of the experiments, a merging beam system with an extractor composed of spherical shaped curved grids are used to merge multiple-beams into a single high current beam to be accelerated by an ESQ accelerator. The H/sup -/ ions of 104 mA were extracted from nineteen apertures (10 mm dia.) drilled in an area of 80 mm/spl phi/. Using the merging beam system with a focal length of 150 mm, the beamlets were successfully focused and the beam envelope diameter was compressed to 23 mm. Focusing angle of the merging beam envelope at the entrance of the accelerator could be reduced within the range of -30 (converging)/spl sim/+30 (diverging) mrad, which is acceptable in the ESQ accelerator to obtain a high energy beam.

A high current DC electrostatic quadrupole (ESQ) accelerator is being developed for negative-ion-based neutral beam heating and current drive on the next generation tokamak. Beam energy and current will eventually be in the megaelectronvolt and multiampere range. This constant-current variable-voltage (CCVV) accelerator uses a series of identical ESQ modules. The authors have successfully tested a prototype CCVV accelerator up to 200 keV with a 100-mA He/sup +/ beam (with space charge equivalence of 140 mA of D/sup -/) for a pulse length of 1 s. Testing was also done with a 42-mA H/sup -/ beam (H/sup -/ beam current was limited by source performance). There was almost no beam loss in the ESQ accelerator. >

A heavy ion fusion driver must be capable of accelerating an intense ion beam to GeV beam energies. The final beam pulse current can be as high as a few kA using beam compression in an induction linac. Combining beamlets at low energy may prove to be economical as long as there is no significant emittance growth. Focusing of the final beam pulse from the reactor chamber wall to the target can be enhanced by using a plasma channel to guide the ion beam. Experiments at LBNL on ion sources, injector, the combiner and plasma channel focusing are discussed. One possible way to reduce the cost of a driver is to use an induction recirculator. Experiments at LLNL are exploring this concept by studying the transport and bending of space-charge-dominated ion beams. At the Univ. of Maryland the behavior of space-charge dominated beams is being simulated with low-energy electrons. They studied emittance growth, halo formation and beam pulse compression.

The promise of inertial fusion energy driven by heavy ion beams requires the development of accelerators that produce ion currents (/spl sim/100's Amperes/beam) and ion energies (/spl sim/1 - 10 GeV) that have not been achieved simultaneously in any existing accelerator. The high currents imply high generalized perveances, large tune depressions, and high space charge potentials of the beam center relative to the beam pipe. Many of the scientific issues associated with ion beams of high perveance and large tune depression have been addressed over the last two decades on scaled experiments at Lawrence Berkeley and Lawrence Livermore National Laboratories, the University of Maryland, and elsewhere. The additional requirement of high space charge potential (or equivalently high line charge density) gives rise to effects (particularly the role of electrons in beam transport) which must be understood before proceeding to a large scale accelerator. The first phase of a new series of experiments in the Heavy Ion Fusion Virtual National Laboratory (HIF VNL), the High Current Experiments (HCX), is now beginning at LBNL. The mission of the HCX is to transport beams with driver line charge density so as to investigate the physics of this regime, including constraints on the maximum radial filling factor of the beam through the pipe. This factor is important for determining both cost and reliability of a driver scale accelerator. The HCX will provide data for design of the next steps in the sequence of experiments leading to an inertial fusion energy power plant. The focus of the program after the HCX will be on integration of all of the manipulations required for a driver. In the near term following HCX, an Integrated Beam Experiment (IBX) of the same general scale as the HCX is envisioned. The step which bridges the gap between the IBX and an engineering test facility for fusion has been designated the Integrated Research Experiment (IRE). The IRE (like the IBX) will provide an integrated test of the beam physics necessary for a driver, but in addition will provide target and chamber data. This paper will review the experimental and theoretical progress in heavy ion accelerator driver research from the scaled experiments through the present experiments and will discuss plans for the IRE.

The Source Injector Program for the U.S. Heavy Ion Fusion Virtual National Laboratory is currently exploring the feasibility of using RF gas plasma sources for a HIF driver. This source technology is presently the leading candidate for the multiple aperture concept, in which bright millimeter size beamlets are extracted and accelerated electrostatically up to 1 MeV before the beamlets are allowed to merge and form 1 A beams. Initial experiments have successfully demonstrated simultaneously high current density, /spl sim/100 mA/cm/sup 2/, and fast turn on, /spl sim/1 /spl mu/s. These experiments were also used to explore operating ranges for pressure and RF power. Results from these experiments are presented as well as progress and plans for the next set of experiments for these sources.

Heavy ion fusion (HIF) drivers require large currents and bright beams. In this paper we review the two different approaches for building HIF injectors and the corresponding ion source requirements. The traditional approach uses large aperture, low current density ion sources, resulting in a very large injector system. A more recent conceptual approach merges high current density mini-beamlets into a large current beam in order to significantly reduce the size of the injector. Experiments are being prepared to demonstrate the feasibility of this new approach.

The clinical success of boron neutron capture therapy (BNCT) depends on both the selective concentration of the boron carrying drug in the tumor cells and the quality of the available neutron beam. For the treatment of glioblastoma multiforme (GBM) the ability of the neutron beam to deeply penetrate is of great importance.

In a typical heavy ion fusion driver design, the induction linac requires a multiple beam injector. We present a conceptual design for an 84-beam injector system with each beam channel carrying 0.5 A of beam current. Each channel starts with a 10-cm diameter surface ionization source followed by a 1.7 MV electrostatic Einzel lens-type preaccelerator and an electrostatic quadrupole (ESQ) matching section. The preaccelerator and matching section are 0.7 m and 5.0 m long respectively. The array has an overall diameter of 3.0 m at the ion source end and 1.0 m diameter at the exit.

A compact multiple-beam injector concept is being developed for heavy ion inertial fusion. The design is based on merging high intensity miniature beamlets of a few mA each to form a large beam. In order to minimize emittance growth, the beamlets are kept separated in grids until they are allowed to merge together at 1.2 MeV. With optimized positioning and aiming, the merged beam can quickly match into an electrostatic quadrupole (ESQ) channel. Simulation results have shown that, based on this design, a 1.6 MeV, 0.5 A beam of K/sup +/ ions at the end of the injector has a normalized emittance of approximately 1.0 /spl pi/-mm-mrad which is comparable to that from the previous low current density design. The advantage is a factor of 6 reduction in the combined injector and matching section length.

A D− surface‐conversion source using a solid barium converter is designed for steady‐state operation to produce 200 mA of D−. A similar ion source of twice the size as the one discussed here will meet the requirements set by the present US‐ITER neutral beam injector design. Among the possible types of ion sources being considered for the US‐ITER neutral beam design, the barium converter surface‐conversion source is the only kind that does not use cesium in the discharge. This absence of cesium will minimize the number of accelerator breakdowns.

Ion source and injector development is one of the major parts of the HIF program in the USA. Our challenge is to design a cost effective driver-scale injector and to build a multiple beam module within the next couple of years. In this paper, several current–voltage scaling laws are summarized for guiding the injector design. Following the traditional way of building injectors for HIF induction linac, we have produced a preliminary design for a multiple beam driver-scale injector. We also developed an alternate option for a high current density injector that is much smaller in size. One of the changes following this new option is the possibility of using other kinds of ion sources than the surface ionization sources. So far, we are still looking for an ideal ion source candidate that can readily meet all the essential requirements.

The 2-MV Injector consists of a 17-cm-diameter surface ionization source, an extraction diode, and an electrostatic quadrupole (ESQ) accelerator, with maximum current of 0.8 A of potassium beam at 2 MeV. Previous performance of the Injector produced a beam with adequate current and emittance but with a hollow profile at the end of the ESQ section. We have examined the profile of the beam as it leaves the diode. The measured nonuniform beam density distribution qualitatively agrees with EGUN simulation. Implications for emittance growth in the post acceleration and transport phase will be investigated.

Renewed interest by several major university medical centers (UCSF-Standford, UC-Davis) in conducting boron neutron capture therapy (BNCT) led to the investigation of converting the decommissioned 5 mA, 2.5 MV Super HILAC injector to a 50 mA, 2.5 MV proton accelerator for the generation of neutrons. The original high impedance shunt-fed multiplier has been converted to a 55 stage air-coupled transformer with much lower impedance driven by a 200 kW, 50 kHz oscillator. The proton beam will be transported by electrostatic quadrupoles (ESQ) acceleration column housed axially within the power supply stages and biased by connecting sequentially to the desired voltage. The pressure vessel which houses the 2.5 MV power supply and ESQ acceleration column has been moved near the patient treatment rooms in the Bevatron complex. As funds become available, we will finalize the design and assembly of all components required for the generation, transport and conversion of the proton beam to neutrons for patient treatment. Preliminary tests of the power supply and design of the ESQ column will be presented.

In testing a multicusp volume‐production H− ion source (20 cm diameter, 23 cm long), we optimized the gas pressure, the plasma electrode bias potential, and the magnetic filter. At the optimum pressure of 9 mTorr, the H− beam output increased linearly with discharge power. The maximum H− beam, measured with a current transformer downstream of the accelerator, was 100 mA while using a 6.67‐cm2 aperture. Presently we are limited by overheating of the cathodes by the plasma ions. Under similar discharge conditions the maximum H− current density was found to vary as a−0.7, where a is the aperture radius. Results from emittance measurements showed that the effective H− ion temperature increased with a for a>0.8 cm. Thus, the brightness of the beam decreased with increasing aperture radius. Operating the source with cesium would increase the H− output; however, our accelerator must be improved to avoid breakdowns caused by the cesium contamination.

Elise is a heavy-ion induction linear accelerator that will demonstrate beam manipulations required in a driver for inertial fusion energy. With a line charge density similar to that of heavy-ions drivers, Elise will accelerate a beam pulse (duration of 1 μs or more) of K + ions from an initial energy of 2 MeV to a final energy 5 MeV or more. In the present design, the Elise electrostatic quadrupoles (ESQs) will have an aperture of radius 2.33 cm operating at ± 59 kV. The half-lattice periods range from 21 to 31 cm. The entire machine will be approximately 30 m long, half of which is the induction accelerator with the remaining half being the injector (including the Marx generator) and the matching section. Elise will be built in a way that allows future expansion into the full Induction Linear Accelerator Systems Experiments (ILSE) configuration, so it will have an array of four ESQ focusing channels capable of transporting up to a total of 3.2 A of beam current. Elise will also have an active alignment system with an alignment tolerance of less than 0.1 mm. Initially, only one beam channel will be used during nominal Elise operation. At the currently expected funding rate, the construction time will be 4.75 years, with FY95 being an extra year for research and development before construction. Total project cost is estimated to be US$25.9m, including contingency costs.

Elise is an electrostatically focused heavy-ion accelerator being designed and constructed at Lawrence Berkeley Laboratory. The machine is intended to be the first half of the four-beam Induction Linac Systems Experiment (ILSE), which ultimately will test the principal beam dynamics issues and manipulations of induction heavy-ion drivers for inertial fusion. Elise will use an existing 2 MeV injector and will accelerate space-charge-dominated pulses to greater than 5 MeV. The design objective of Elise is to maximize the output beam energy within the fixed project budget while allowing for adequate beam diagnostics, flexibility in the acceleration schedule, and beam parameters suitable for ILSE and the experimental program. We review the design equations and ''rules of thumb'' used for choosing beam and lattice parameters for heavy-ion induction accelerators, and we discuss incorporating these relations in a spreadsheet program that generates internally consistent lattice layouts and acceleration schedules. These designs have been tested using a one-dimensional (1-D) particle simulation code, SLIDE, a 3-D fluid/envelope code, CIRCE, and a 3-D particle-in-cell code WARP3D. Sample results from these calculations are presented. Results from these dynamics codes are also shown illustrating sensitivities to beam and lattice errors and testing various strategies for longitudinal confinement of the beam ends.

Intense beams of heavy ions are well suited for heating matter to regimes of emerging interest. A new facility, NDCX-II, will enable studies of warm dense matter at ∼1 eV and near-solid density, and of heavy-ion inertial fusion target physics relevant to electric power production. For these applications the beam must deposit its energy rapidly, before the target can expand significantly. To form such pulses, ion beams are temporally compressed in neutralizing plasma; current amplification factors of ∼50–100 are routinely obtained on the Neutralized Drift Compression Experiment (NDCX) at the Lawrence Berkeley National Laboratory. In the NDCX-II physics design, an initial non-neutralized compression renders the pulse short enough that existing high-voltage pulsed power can be employed. This compression is first halted and then reversed by the beam’s longitudinal space-charge field. Downstream induction cells provide acceleration and impose the head-to-tail velocity gradient that leads to the final neutraliz...

A dual-energy tandem-type gamma generator has been developed at E. O. Lawrence Berkeley National Laboratory and Sandia National Laboratories. The tandem accelerator geometry allows higher energy nuclear reactions to be reached, thereby allowing more flexible generation of MeV-energy gammas for active interrogation applications. Both positively charged ions and atoms of hydrogen are created from negative ions via a gas stripper. In this paper, we show first results of the working tandem-based gamma generator and that a gas stripper can be utilized in a compact source design. Preliminary results of monoenergetic gamma production are shown.

The design and operation of the surface‐conversion H− ion source and the 80‐keV preaccelerator are discussed. Both the source and the preaccelerator, together with the transverse field focusing (TFF) matching and pumping beam transport section (presently being tested), will be parts of a negative‐ion‐based neutral beam line. Results from testing the source and preaccelerator have shown that the system can accelerate more than 1 A of H− ions at 80 keV continuously; the preaccelerator operates at an optimum perveance which matches the one predicted by WOLF code computer simulation. Deconditioning of the preaccelerator due to cesium contamination is a critical problem. A method has been developed to cope with this problem.

High energy neutral beams provide a promising method of heating and driving current in steady-state tokamak fusion reactors. As an example, we have made a conceptual design of a neutral beam system for current drive on the International Thermonuclear Experimental Reactor (ITER). The system, based on electrostatic acceleration of D- ions, can deliver up to 100 MW of 1.6 MeV D o neutrals through three ports. Radiation protection is provided by locating sensitive beamline components 35 to 50 m from the reactor. In an application to a 3300 MW power reactor, a system delivering 120 MW of 2-2.4 MeV deuterium beams assisted by 21 MW of lower hybrid wave power drives 25 MA and provides an adequate plasma power gain (Q = 24) for a commercial fusion power plant.