Search

A barium titanate ferroelectric cylindrical plasma source has been developed, tested and delivered for the Neutralized Drift Compression Experiment NDCX-II at Lawrence Berkeley National Laboratory (LBNL). The plasma source design is based on the successful design of the NDCX-I plasma source. A 7 kV pulse applied across the 3.8 mm-thick ceramic cylinder wall produces a large polarization surface charge density that leads to breakdown and plasma formation. The plasma that fills the NDCX-II drift section upstream of the final-focusing solenoid has a plasma number density exceeding 10 10 cm −3 and an electron temperature of several eV. The operating principle of the ferroelectric plasma source are reviewed and a detailed description of the installation plans is presented. The criteria for plasma sources with larger number density will be given, and concepts will be presented for plasma sources for driver applications. Plasma sources for drivers will need to be highly reliable, and operate at several Hz for millions of shots.

The Neutralized Drift Compression Experiment (NDCX-II) is a user facility located at Lawrence Berkeley National Laboratory which is uniquely designed for ion-beam-driven high energy density laboratory physics and heavy ion fusion research. Construction was completed in March 2012 and the facility is now in the commissioning phase. A significant amount of engineering was carried out in order to meet the performance parameters required for a wide range of target heating experiments while making the most cost-effective use of high-value hardware available from a decommissioned high current electron induction accelerator. The technical challenges and design of this new ion induction accelerator facility are described.

A 10.9 cm diameter lithium alumino-silicate ion source has been chosen as a source of �100 mA lithium ion current for the Neutralized Drift Compression Experiment (NDCX-II) at LBNL. Research and development was carried out on lithium alumino-silicate ion sources prior to NDCX-II source fabrication. Space-chargelimited emission with the current density exceeding 1 mA/cm 2 was measured with 0.64 cm diameter lithium alumino-silicate ion sources at 1275 0 C. The beam current density is less for the first 10.9 cm diameter NDCX-II source, and it may be due to an issue of surface coverage. The lifetime of a thin coated (on a tungsten substrate) source is varied, roughly 40-50 hours, when pulsed at 0.05 Hz and with pulse length of 6 µs each, i.e., a duty factor of 3x10 -7 , at an operating temperature of 1250 to 1275 0 C. The 10.9 cm diameter source lifetime is likely the same as of a 0.64 cm source, but the lifetime of a source with a 2 mm diameter (without a tungsten substrate) is 10-15 hours with a duty factor of one (DC extraction). The lifetime variation is dependent on the amount of deposition of �-eucryptite mass, and the surface temperature. The amount of mass deposition does not significantly alter the current density. More ion source work is needed to improve the large source performance.

The ion accelerator NDCX-II is undergoing commissioning at Lawrence Berkeley National Laboratory (LBNL). Its principal mission is to explore ion-driven High Energy Density Physics (HEDP) relevant to Inertial Fusion Energy (IFE) especially in the Warm Dense Matter (WDM) regime. We have carried out hydrodynamic simulations of beam-heated targets for parameters expected for the initial configuration of NDCX-II. For metal foils of order one micron thick (thin targets), the beam is predicted to heat the target in a timescale comparable to the hydrodynamic expansion time for experiments that infer material properties from measurements of the resulting rarefaction wave. We have also carried out hydrodynamic simulations of beam heating of metallic foam targets several tens of microns thick (thick targets) in which the ion range is shorter than the areal density of the material. In this case shock waves will form and we derive simple scaling laws for the efficiency of conversion of ion energy into kinetic energy of fluid flow. Geometries with a tamping layer may also be used to study the merging of a tamper shock with the end-of-range shock. This process can occur in tamped, direct drive IFE targets.

A novel, induction type linear accelerator, the Neutralized Drift Compression eXperiment (NDCX-II), is currently being commissioned at Berkeley Lab. This accelerator is designed to deliver intense (up to 3x1011 ions/pulse), 0.6 to ~600 ns duration pulses of 0.13 to 1.2 MeV lithium ions at a rate of about 2 pulses per minute onto 1 to 10 mm scale target areas. When focused to mm-diameter spots, the beam is predicted to volumetrically heat micrometer thick foils to temperatures of ~30,000 K. At lower beam power densities, the short excitation pulse with tunable intensity and time profile enables pump-probe type studies of defect dynamics in a broad range of materials. We briefly describe the accelerator concept and design, present results from beam pulse shaping experiments and discuss examples of pump-probe type studies of defect dynamics following irradiation of materials with intense, short ion beam pulses from NDCX-II., Comment: 25th International Conference on Atomic Collisions in Solids, ICACS-25, Kyoto, October 2012

A 100 kV ion source test stand formerly operated at Lawrence Livermore National Laboratory has been relocated to Princeton Plasma Physics Laboratory, where it is being installed and prepared for operation. A variety of topics relevant to ion-beam-driven high energy density physics and heavy ion fusion will be explored at this facility. The practicality of magnetic insulation to improve the performance of electrostatic accelerators will be investigated by determining whether a pair of parallel plates forming a high-voltage gap can sustain higher electric field gradients, when an electric current is passed through the electrode at the cathode potential so as to produce a magnetic field, which is everywhere parallel to the surface. The facility will also be used to develop and characterize improved plasma sources for space charge neutralization of intense ion beam systems such as the Neutralized Drift Compression Experiment-II facility. The negative halogen ion beam and ion-ion plasma studies previously initiated when this test facility was located at Lawrence Livermore National Laboratory will be resumed, and other experimental topics are also under consideration.

Some years ago it was suggested that halogen negative ions [L.R. Grisham, Nuclear Instruments and Methods in Physics Research A 464 (2001) 315] could offer a feasible alternative path to positive ions as a heavy ion fusion driver beam, which would not suffer degradation due to electron accumulation in the accelerator and beam transport system, and which could be converted to a neutral beam by photodetachment near the chamber entrance if desired. Since then, experiments have demonstrated that negative halogen beams can be extracted and accelerated away from the gas plume near the source with a surviving current density close to what could be achieved with a positive ion of similar mass, and with comparable optical quality. In demonstrating the feasibility of halogen negative ions as heavy ion driver beams, ion–ion plasmas, an interesting and somewhat novel state of matter, were produced. These plasmas, produced near the extractor plane of the sources, appear, based upon many lines of experimental evidence, to consist of almost equal densities of positive and negative chlorine ions, with only a small component of free electrons. Serendipitously, the need to extract beams from this plasma for driver development provides a unique diagnostic tool to investigate the plasma, since each component – positive ions, negative ions, and electrons – can be extracted and measured separately. We discuss the relevance of these observations to understanding negative ion beam extraction from electronegative plasmas such as halogens, or the more familiar hydrogen of magnetic fusion ion sources. We suggest a concept that might improve negative hydrogen extraction by the addition of a halogen. The possibility and challenges of producing ion–ion plasmas with thin targets of halogens or, perhaps, salt is briefly addressed.

Advanced neutron interrogation systems for the screening ofsea-land cargo containers for shielded special nuclear materials (SNM)require a high-yield neutron source to achieve the desired detectionprobability, false alarm rate, and throughput. An accelerator-drivenneutron source is described that produces a forward directed beam ofhigh-energy (up to 8.5 MeV) neutrons utilizing the D(d,n)3He reaction atdeuteron beam energies of up to 6 MeV. The key components of the neutronsource are a high-current RFQ accelerator and an innovative neutronproduction target. A microwave-driven deuteron source is coupled to anelectrostatic LEBT that injects a 40 mA D+-beam into a 6 MeV, 5.1meter-long, 200 MHz RFQ. The RFQ is based on an unusual beam dynamicsdesign and is capable of operating at a duty factor that produces morethan 1.2 mA timeaverage beam current. The beam is transported to a2-atmosphere deuterium gas target with a specially-designed, thinentrance window. A high-frequency dipole magnet is used to spread thebeam over the long dimension of the 4 by 35 cm target window. The sourcewill be capable of delivering a neutron flux of ~;2 x 107 n/(cm2 x s) tothe center of a sea-land cargo container and is expected t o satisfy therequirements for full testing and demonstration of advanced neutroninterrogation techniques based on more » stimulated SNM signatures. « less

A project to develop a Tandem-electrostatic-quadrupole (TESQ) accelerator for accelerator-based boron neutron capture therapy (AB-BNCT) is described. A folded Tandem, with 1.25 MV terminal voltage, combined with an electrostatic quadrupole (ESQ) chain is being proposed. The project goal is a machine capable of delivering 30 mA of 2.5 MeV protons to be used in conjunction with a neutron production target based on the 7Li(p, n)7Be reaction slightly beyond its resonance at 2.25 MeV. This machine is conceptually 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 7Li(p, n)7Be reaction, to perform BNCT treatment for deep-seated tumors in less than an hour. This electrostatic machine is the technologically simplest and cheapest solution for optimized AB-BNCT.

Over the past two years noteworthy experimental and theoretical progress has been made towards the top-level scientific question for the US programme on heavy-ion-fusion-science and high energy density physics: ‘How can heavy-ion beams be compressed to the high intensity required to create high energy density matter and fusion conditions?’ New results in transverse and longitudinal beam compression, high-brightness transport and beam acceleration will be reported. Central to this campaign is final beam compression. With a neutralizing plasma, we demonstrated transverse beam compression by an areal factor of over 100 and longitudinal compression by a factor of >50. We also report on the first demonstration of simultaneous transverse and longitudinal beam compression in plasma. High beam brightness is key to high intensity on target, and detailed experimental and theoretical studies on the effect of secondary electrons on beam brightness degradation are reported. A new accelerator concept for nearterm low-cost target heating experiments was invented, and the predicted beam dynamics validated experimentally. We show how these scientific campaigns have created new opportunities for interesting target experiments in the warm dense matter regime. Finally, we summarize progress towards heavy-ion fusion, including the demonstration of a compact driver-size high-brightness ion injector. For all components of our high intensity campaign, the new results have been obtained via tightly coupled efforts in experiments, simulations and theory.

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.

During the past two years, significant experimental and theoretical progress has been made in the US heavy ion fusion science program in longitudinal beam compression, ion-beam-driven warm dense matter, beam acceleration, high brightness beam transport, and advanced theory and numerical simulations. Innovations in longitudinal compression of intense ion beams by >50X propagating through background plasma enable initial beam target experiments in warm dense matter to begin within the next two years. We are assessing how these new techniques might apply to heavy ion fusion drivers for inertial fusion energy.

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

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

Heavy ion beam driven inertial fusion requires short ion beam pulses with high current and high brightness. Depending on the beam current and the number of beams in the driver system, the injector can use a large diameter surface ionization source or merge an array of small beamlets from a plasma source. In this paper, we review the scaling laws that govern the injector design and the various ion source options including the contact ionizer, the aluminosilicate source, the multicusp plasma source, and the metal vapor vacuum arc (MEVVA) source.

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 (Nucl. Instr. and Meth. A 464 (2001) 315; Fusion Sci. Technol. 43 (2003) 191; Laser Part. Beams 21 (2003) 545). 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 2 was obtained under the same conditions that gave 57 mA/cm 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 − 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 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.

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.

In this paper we report on two Heavy Ion Fusion (HIF) driver point design studies. The Robust Point Design (RPD) was completed over a year ago, and the Modular Point Design (MPD) is still in progress. The goal of any point design study is to construct a detailed design that is self-consistent and integrated from injector to target. This has been the primary theme of both studies.

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.

Radio frequency driven multicusp source was set up to run chlorine plasma and the source performance was compared between positive and negative chlorine ion production. A maximum Cl− current density of 45 mA/cm2 was achieved at 2.2 kW of rf power with electron to negative ion ratio of 7 and positive to negative ion ratio of 1.3. 99.8% of the total negative chlorine beam was atomic Cl−. To produce negative boron ions for semiconductor manufacturing applications, a noncesiated, sputtering-type surface production ion source was constructed. An external rf antenna geometry and large LaB6 converter were implemented in the source design. Maximum B2− ion current density of 1 mA/cm2 was achieved at 800 W of rf power and −600 V converter voltage. Total B2− ion current was 1.8 mA.

We describe the next set of experiments proposed in the U.S. Heavy Ion Fusion Virtual National Laboratory, the so-called Integrated Beam Experiment (IBX). The purpose of IBX is to investigate in an integrated manner the processes and manipulations necessary for a heavy ion fusion induction accelerator. The IBX experiment will demonstrate injection, acceleration, compression, bending, and final focus of a heavy ion beam at significant line charge density. Preliminary conceptual designs are presented and issues and trade-offs are discussed. Plans are also described for the step after IBX, the Integrated Research Experiment (IRE), which will carry out significant target experiments.

Use of high mass atomic neutral beams produced from negative ions as drivers for inertial confinement fusion has been suggested recently. Best candidates for the negative ions would be bromine and iodine with sufficiently high mass and electron affinity. These materials require a heated vapor ion source. Chlorine was selected for initial testing because it has similar electron affinity to those of bromine and iodine, and is available in gaseous form. An experiment was set up by the Plasma and Ion Source Technology Group in Lawrence Berkeley National Laboratory to measure achievable current densities and other beam parameters by using a rf driven multicusp ion source [K. N. Leung, Rev. Sci. Instrum. 65, 1165 (1994); Q. Ji et al., Rev. Sci. Instrum. 73, 822 (2002)]. Current density of 45 mA/cm2 was achieved with 99.5% of the beam as atomic negative chlorine at 2.2 kW of rf power. An electron to negative ion ratio as low as 7 to 1 was observed, while the ratio of positive and negative chlorine ion currents w...

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...

Kapton film is used to image K+ ion beams in the 0.4 to 2 MeV energy range. Dose response is shown to be linear and to follow a simple model for a range of exposures. The measured profiles agree with profiles obtained with a slit scanner. Kapton has excellent spatial resolution, dynamic range, and discrimination against stray low energy and low mass particles.

Significant experimental and theoretical progress has been made in the U.S. heavy ion fusion program on high-current sources, transport, and focusing. Currents over 200 mA have been transported through a matching section and 10 half-lattice periods with electric quadrupoles. An experiment shows control of high-beam current with an aperture, while avoiding secondary electrons. New theory and simulations of the neutralization of intense beam space charge with plasma in various focusing chamber configurations predict that near-emittance-limited beam focal spot sizes can be obtained even with beam perveance (ratio of beam space potential to ion energy) >10× higher than in earlier HIF focusing experiments. Progress in a new focusing experiment with plasma neutralization up to 10−3 perveance, and designs for a next-step experiment to study beam brightness evolution from source to target are described.

An overview of experiments is presented, in which the physical dimensions, transverse emittance and generalized perveance are scaled to explore driver-relevant beam dynamics. Among these are beam merging, focusing to a small spot, and bending and recirculating beams. The Virtual National Laboratory for Heavy Ion Fusion (VNL) is also developing two driver-scale beam experiments involving heavy-ion beams with I beam ∼1 A to provide guidance for the design of an Integrated Research Experiment (IRE) for driver system studies within the next 5 years. Multiple-beam sources and injectors are being designed and a one-beam module will be built and tested. Another experimental effort will be the transport of such a beam through ∼100 magnetic quadrupoles. The experiment will determine transport limits at high aperture fill factors, beam halo formation, and the influence on beam properties of secondary electron production and neutral atom desorption from the vacuum pipe wall. Research into driver technology will be briefly presented, including the development of ferromagnetic core materials, induction core pulsers, multiple-beam quadrupole arrays and plasma channel formation experiments for pinched transport in reactor chambers.

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.

One of the most challenging aspects of ion beam driven inertial fusion energy is the reliable and efficient generation of low emittance, high current ion beams. The primary ion source requirements include a rise time of order 1-msec, a pulse width of at least 20-msec, a flattop ripple of less than 0.1 percent and a repetition rate of at least 5-Hz. Naturally, at such a repetition rate, the duty cycle of the source must be greater than 108 pulses. Although these specifications do not appear to exceed the state-of-the-art for pulsed power, considerable effort remains to develop a suitable high current ion source. Therefore, we are constructing a 500-kV test stand specifically for studying various ion source concepts including surface, plasma and metal vapor arc. This paper will describe the test stand design specifications as well as the details of the various subsystems and components.

Depending on the type of beam transport selected at the front end of a heavy ion fusion driver, the optimum injector current (per beam) can vary from 0.5 to 25 A of cesium ions. The average current density should be ≥10 mA/cm 2 . So far, surface ionization sources have been used in most HIF driver designs. These sources can efficiently produce singly charged alkali ions such as Cs + and K + . Nevertheless, the gas sources and the metal vapor vacuum arc (MEVVA) sources are also potentially useful for HIF applications. Recent experimental results on ion source development are summarized.

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.

The high power ion beams used in the next generation thermonuclear fusion reactors require high current negative ion beams accelerated to high energy, with high efficiency. One way to meet these requirements is to merge multiple low current density H− beamlets into a single high current beam. The feasibility of a high current merging preaccelerator was demonstrated in this experiment by merging 19 beamlets of H− ions distributed over a circular area 80 mm in diameter from a Japan Atomic Energy Research Institute negative ion source. H− ions were extracted at a current density exceeding 10 mA/cm2 at the ion source which operates at 0.13 Pa (1 mTorr), with a low arc power density (70 V×250 A). Spherically curved grids (with built‐in magnetic electron suppression) were used in the preaccelerator to focus the extracted beamlets into a single 104 mA, 100 keV beam. The merged beam has a diameter of 23 mm and a converging angle of ±30 mrad at the beam envelope. The rms emittance of the 104 mA merging beam was 1.00 π mrad cm, which is a condition acceptable to the electrostatic quadropole accelerator for further acceleration.

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.

Presently the Heavy Ion Fusion Virtual National Laboratory is researching ion sources and injector concepts to understand how to optimize beam brightness over a range of currents (50–2000 mA argon equivalent). One concept initially accelerates millimeter size, milliamp beamlets to 1 MeV before merging them into centimeter size, ampere beams. Computer simulations have shown the final brightness of the merged beams is dominated by the emittance growth of the merging process, as long as the beamlets’ ion temperature is below a few electron volts. Thus, a radio frequency multicusp source capable of high current density can produce beams with better brightness compared to ones extracted from a colder source with a large aperture and lower current density. Initial experiments with such a source have successfully demonstrated simultaneously high current density, ∼100 mA/cm2, and fast turn on, ∼1 μs. Results from these experiments are presented as well as progress and plans for the next set of experiments for the...

Heavy ion beam inertial fusion driver concepts depend on the availability and performance of high-brightness high-current ion sources. Surface ionization sources have relatively low current density but high brightness because of the low temperature of the emitted ions. We have measured the beam profiles at the exit of the injector diode, and compared the measured profiles with EGUN and WARP-3D predictions. Spherical aberrations are significant in this large aspect ratio diode. We discuss the measured and calculated beam size and beam profiles, the effect of aberrations, quality of vacuum, and secondary electron distributions on the beam profile.

We report results on lithium alumino-silicate ion source development in preparation for warm dense matter heating experiments on the new neutralized drift compression experiment II. The practical limit to the current density for a lithium alumino-silicate source is determined by the maximum operating temperature that the ion source can withstand before running into problems of heat transfer, melting of the alumino-silicate material, and emission lifetime. Using small prototype emitters, at a temperature of ≈1275 °C, a space-charge limited Li(+) beam current density of J ≈1 mA/cm(2) was obtained. The lifetime of the ion source was ≈50 h while pulsing at a rate of 0.033 Hz with a pulse duration of 5-6 μs.

HIFAN 1748 Neutralized Drift Compression Experiment (NDCX) - II DE-AC02-05CH11231 OFES Project Manager: Dave Goodwin Quarterly Progress Report Issued: 10/08/2009 Recovery Act Project: High Energy Density Laboratory Plasma - Neutralized Drift Compression Experiment (NDCX-II) by J.W. Kwan LBNL Accelerator Fusion Research Division Ernest Orlando Lawrence Berkeley National Laboratory University of California Berkeley, California 94720 October 2009 This work was supported by the Director, Office of Science, Office of Fusion Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02- 05CH11231.

Study of the projectional emittance is an efficient way of probing the quality of a particle beam. In this work we deal with some computational aspects of the problem. We present the argument that in a beam optic code for the design or evaluation of the performance of electrostatic extractors/accelerators which produce such (round) beams, one must include in the calculation beamlets with skew angles. This is necessary if one wants to compare calculations with emittance measurements for a beam with transverse temperature. We have developed new steps and modified an existing code for such a purpose and produced calculated results of emittance plots that can be compared with experimental observations.

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.

Based on recent experimental results made on the large and small multicusp volume H− sources, a new multicusp source has been designed to generate high‐brightness H− or D− beams for high duty factor or dc operations. Cesium will be introduced into the source plasma to enhance the H− output current. Arrangements for reducing the electrons as well as capturing them in the preaccelerator electrodes will be incorporated into the new source geometry.

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.

An over-dense microwave driven ion source capable of producing deuterium (or hydrogen) beams at 100-200 mA/cm2 and with atomic fraction > 90 percent was designed and tested with an electrostatic low energy beam transport section (LEBT). This ion source was incorporated into the design of an Accelerator Driven Neutron Source (ADNS). The other key components in the ADNS include a 6 MeV RFQ accelerator, a beam bending and scanning system, and a deuterium gas target. In this design a 40 mA D+ beam is produced from a 6 mm diameter aperture using a 60 kV extraction voltage. The LEBT section consists of 5 electrodes arranged to form 2 Einzel lenses that focus the beam into the RFQ entrance. To create the ECR condition, 2 induction coils are used to create ~; 875 Gauss on axis inside the source chamber. To prevent HV breakdown in the LEBT a magnetic field clamp is necessary to minimize the field in this region. Matching of the microwave power from the waveguide to the plasma is done by an autotuner. We observed significant improvement of the beam quality after installing a boron nitride liner inside the ion source. The measured emittance data are compared with PBGUNS simulations.

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.