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During the last 36 years researchers have suggested and evaluated a large number of target designs for heavy ion inertial fusion. The different target designs can be classified according to their mode of ignition, their method of implosion, and their size. Ignition modes include hot-spot ignition and fast ignition. Methods of implosion include direct drive and indirect drive. Historically there has been significant work on indirectly driven targets with hot-spot ignition. Recently there has been increasing interest in directly driven targets with ion driven fast ignition. In principle, fast ignition might lead to improved target performance. On the other hand, fast ignition imposes stringent requirements on accelerators and beam physics. Furthermore, fast ignition magnifies the importance of a number of traditional target physics issues associated with ion beam energy deposition and fuel preheat. This paper will discuss the advantages and disadvantages of the various classes of targets. It will also discuss some issues that must be resolved to assess the feasibility of ion fast ignition.

Since the 1970s, high energy heavy ion accelerators have been one of the leading options for imploding and igniting targets for inertial fusion energy production. Following the energy crisis of the early 1970s, a number of people in the international accelerator community enthusiastically began working on accelerators for this application. In the last decade, there has also been significant interest in using accelerators to study high energy density physics (HEDP). Nevertheless, research on heavy ion accelerators for fusion has proceeded slowly pending demonstration of target ignition using the National Ignition Facility (NIF), a laser-based facility at Lawrence Livermore National Laboratory. A recent report of the National Research Council recommends expansion of accelerator research in the US if and when the NIF achieves ignition. Fusion target physics and the economics of commercial energy production place constraints on the design of accelerators for fusion applications. From a scientific standpoint, phase space and space charge considerations lead to the most stringent constraints. Meeting these constraints almost certainly requires the use of multiple beams of heavy ions with kinetic energies >1 GeV. These constraints also favor the use of singly charged ions. This article discusses the constraints for both fusion and HEDP, and explains how they lead to the requirements on beam parameters. RF and induction linacs are currently the leading contenders for fusion applications. We discuss the advantages and disadvantages of both options. We also discuss the principal issues that must yet be resolved.

Critical issues and ion beam requirements are explored for fast ignition using ion beams to provide fuel compression using indirect drive and to provide separate short-pulse ignition heating using direct drive. Several ion species with different hohlraum geometries are considered for both accelerator-produced and laser-produced ion ignition beams. Ion-driven fast ignition targets are projected to have modestly higher gains than with conventional heavy ion fusion and may offer some other advantages for target fabrication and for use of advanced fuels. However, much more analysis and additional experiments are needed before conclusions can be drawn regarding the feasibility for meeting the ion beam transverse and longitudinal emittances, focal spots, pulse lengths, and target standoff distances required for ion-driven fast ignition.

The need to reach high temperatures in an inertial fusion energy (IFE) target (or a target for the study of High Energy Density Physics, HEDP) requires the ability to focus ion beams down to a small spot. System models indicate that within the accelerator, the beam radius will be of the order of centimeters, whereas at the final focal spot on the target, a beam radius of the order of millimeters is required, so radial compression factors of order ten are required. The IFE target gain (and hence the overall cost of electricity) and the HEDP target temperature are sensitive functions of the final spot radius on target. Because of this sensitivity, careful attention needs to be paid to the spot radius calculation. We review our current understanding of the elements that enter into a systems model (such as emittance growth from chromatic, geometric, and non-linear space charge forces) for the final focus based on a quadrupolar magnet system.

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.

A computer model for systems analysis of heavy ion drivers has been developed and used to evaluate driver designs for inertial fusion energy. The present work examines a driver for a close-coupled target design that requires less total beam energy but also smaller beam spots sizes than previous target designs. Design parameters and a cost estimate for a 160 beam, 3.3 MJ driver using rubidium ions ( A =85) are reported, and the sensitivity of the results to variations in selected design parameters is given.

The U.S. Department of Energy has established a new, larger inertial fusion energy (IFE) program. To manage program growth, we have developed a new IFE research plan and we have established a Virtual National Laboratory for Heavy Ion Fusion. There has been significant technical progress. Improvements in target design have reduced the predicted energy requirements by approximately a factor of two. There have also been important experiments on chamber dynamics and other inertial fusion technologies. The accelerator program has completed a number of small-scale experiments. Experiments with driver-scale beams are being designed—including experiments with driver-scale ion sources and injectors. Finally we are developing the technologies needed to build a major research facility known as the Integrated Research Experiment (IRE).

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.

The 2002 Fusion Summer Study was conducted July 8–19, 2002, in Snowmass, CO, and carried out a critical assessment of major next steps in the fusion energy sciences program in both magnetic fusion energy (MFE) and inertial fusion energy (IFE). The conclusions of this study were based on analysis led by over 60 conveners working with hundreds of members of the fusion energy sciences community extending over eight months. This effort culminated in two weeks of intense discussion by over 250 U.S. and 30 foreign fusion physicists and engineers present at the 2002 Fusion Summer Study. This is the Executive Summary of the study report. Details are posted at http://web.gat.com/snowmass

Fusion faces three types of challenge: scientific, economic, and environmental. Many scientists believe that both inertial and magnetic fusion can meet the scientific challenge in the sense that th...

In many respects, high-energy accelerators are well suited to inertial fusion power production. Accelerators have long life, good reliability, and high pulse repetition rates. They can also have high efficiency. Nevertheless, existing accelerators have not been designed to be fusion drivers and they have not established that they can produce sufficiently intense beams to drive ICF targets. Establishing that properly designed accelerators can produce the required beams, while retaining the other desirable features of existing accelerators, is the principal scientific goal of the heavy ion fusion program. Until recently, we planned to establish the physics of intense ion beams by building a scaled driver known as ILSE. Because of declining support for fusion research in the US it is not now possible to construct ILSE. Other proposed fusion projects have also been cancelled. Because ILSE will not be built, we have restructured the US heavy ion fusion program. The restructured program is based on a large number of small experiments coupled with an expanded effort in numerical simulation. Experiments on ion sources, injection, matching, beam combining, recirculation, and focusing are underway. The goal of the simulation program is to perform accurate end-to-end simulations of the entire accelerator. The experiments and simulations will establish much of the science of high intensity beams. Reducing cost and increasing accelerator efficiency are also important goals of this scientific research. In addition we are developing key technologies that will reduce cost and increase efficiency. Before the program is in a position to build a full-scale fusion driver, it will be necessary to perform accelerator experiments that are larger than the experiments that are currently in progress. We plan to build a new accelerator to do these experiments. This new accelerator will also be designed to perform experiments on those aspects of target physics that are unique to ions.

A brief review is given of the requirements of inertial fusion energy drivers and their status and prospects in the U.S. Drivers based on lasers (diode-pumped solid-state and KrF) and heavy ions are discussed.

The approach to heavy-ion-driven inertial fusion studied most extensively in the US uses induction modulators and cores to accelerate and confine the beam longitudinally. The intrinsic peak-current capabilities of induction machines, together with their flexible pulse formats, provide a suitable match to the high peak-power requirement of a heavy-ion fusion target. However, as in the RF case, where combinations of linacs, synchrotrons, and storage rings offer a number of choices to be examined in designing an optimal system, the induction approach also allows a number of architectures, from which choices must be made. We review the main classes of architecture for induction drivers that have been studied to date. The main choice of accelerator structure is that between the linac and the recirculator, the latter being composed of several rings. Hybrid designs are also possible. Other design questions include which focusing system (electric quadrupole, magnetic quadrupole, or solenoid) to use, whether or not to merge beams, and what number of beams to use – all of which must be answered as a function of ion energy throughout the machine. Also, the optimal charge state and mass must be chosen. These different architectures and beam parameters lead to different emittances and imply different constraints on the final focus. The advantages and uncertainties of these various architectures will be discussed.

Since the last Symposium, the US has restructured its fusion program to emphasize science, enabling technologies, and innovation. A principal goal of the restructured program is to develop new, more attractive fusion options. As part of the restructuring, we have canceled ILSE, an accelerator project described at previous Symposia. Instead of ILSE, we have initiated a program of small experiments, technology development, and end-to-end numerical simulation of accelerators and targets. In addition, we have expanded our effort in chamber dynamics and power-plant technologies. This new program has two goals: (1) the development of a more compelling (less expensive) long-term vision for heavy-ion fusion and (2) the development of the scientific and technological foundation for the construction of an accelerator research facility with far greater capability than ILSE. This accelerator facility (sometimes called the Integrated Research Experiment) together with the National Ignition Facility and the expanded program in chambers and power plant technologies will, if successful, provide a sound basis for a decision to begin construction of a full-scale heavy-ion driver that could be upgraded to drive a demonstration power plant. The National Ignition Facility is expected to demonstrate ignition by 2006. With adequate funding, it would also be possible to complete the Integrated Research Experiment by this time.

The capabilities of adiabatic, current-carrying plasma lenses for the final focus problem in heavy-ion-beam-driven inertial confinement fusion are explored and compared with the performance of non-adiabatic plasma lenses, and with that of conventional quadrupole lenses. A final focus system for a fusion reactor is proposed, consisting of a conventional quadrupole lens to prefocus the driver beams to the entrance aperture of the adiabatic lens, the plasma lens itself, and a high current discharge channel inside the chamber to transport the focused beam to the fusion pellet. Two experiments are described that address the issues of adiabatic focusing, and of transport channel generation and stability for ion beam transport. The test of the adiabatic focusing principle shows a 26-fold current density increase of a 1.5 MeV potassium ion beam during operation of the lens. The lens consist of a discharge of length 300 mm, filled with helium gas at a pressure of 1 Torr and is pulsed with a current between 5 and 15 kA. The investigations of discharge channels for ion beam transport show that preionization of the discharge channels with a UV laser can be an efficient way to direct and stabilize the discharge.

The US Department of Energy is proposing to construct the National Ignition Facility (NIF) to embark on a program to achieve ignition and modest gain in the laboratory early in the next century. The NIF will use a ⩾ 1.8 MJ, 0.35 μm laser with 192 independent beams, a 50-fold increase over the energy of the Nova laser. System performance analyses suggest yields as great as 20 MJ may be achievable. NIF will conduct more than 600 shots per year. The benefits of a micro-fusion capability in the laboratory include essential contributions to defence programs, resolution of important Inertial Fusion Energy (IFE) issues and unparalleled conditions of energy density for basic science and technology research. A start has been made to consider the role the NIF will fill in the development of IFE. While the achievement of ignition and gain speaks for itself in terms of its impact on developing IFE, it is believed there are areas of IFE development, such as fusion power technology, IFE target design and fabrication and understanding chamber dynamics, that would significantly benefit from NIF experiments. In the area of IFE target physics, ion targets will be designed using the NIF laser and the feasibility of high-gain targets will be confirmed. Target chamber dynamics experiments will benefit from X-ray and debris energies that mimic the spatial distribution of neutron heating, activation and tritium breeding in relevant materials. IFE target systems will benefit from evaluating low-cost target fabrication techniques by testing such targets on NIF. Additionally, it is believed that it is feasible to inject up to four targets and engage them with the NIF laser by triggering the beams in groups of ca. 50 separated in time by ca. 0.1 s. Sub-ignition neutron yields would allow an indication of symmetry achieved in such proof-of-principle rep-rate experiments. NIF will be a unique source of data to benchmark predictive capabilities to support affordable IFE technology selections. The total of NIF-IFE experiments may involve several thousands of shots. NIF may support design “certification” for the follow-on facility to NIF, dedicated to IFE, called the Engineering Test Facility.

Induction acceleration is one of two principal approaches for producing ion beams for heavy-ion inertial fusion. This approach was first suggested by the late Denis Keefe of Lawrence Berkeley Laboratory and is the main approach of the U.S. heavy-ion fusion program. Induction accelerators have the ability to handle high beam currents; therefore, accumulation rings or storage rings are not required. This paper reviews the target and accelerator considerations that are important for the design of induction accelerators for fusion. These considerations, including some important assumptions, have led to a standard induction accelerator concept; however, a careful examination of the assumptions and considerations shows that many of them are not truly fundamental. Through improvements in technology, changes in design, and alternate ways of focusing beams, it appears possible to circumvent or relax the constraints imposed by the standard orthodoxy. If it is possible, it will lead to induction accelerators that are more efficient and less costly than the standard concept.

A two-year study of recirculating induction heavy-ion accelerators (recirculators) as low-cost drivers for inertial-fusion energy power plants has recently been completed. A summary of that study and other recent work on recirculators is presented.

The Heavy-Ion Fusion Accelerator Research Program at Lawrence Berkeley Laboratory has proposed building a 10 MeV induction linac systems experiment, ILSE, to investigate accelerator physics and beam manipulations which are needed or desirable for an induction linac driver. This paper describes the experiments proposed for ILSE: transverse beam combining, drift compression, bending of space-charge-dominated beams, final focus, recirculation, and some studies of beam propagation in the environment of the reactor chamber.

A two‐year study of recirculating induction heavy ion accelerators as low‐cost driver for inertial‐fusion energy applications was recently completed. The projected cost of a 4 MJ accelerator was estimated to be about $500 M (million) and the efficiency was estimated to be 35%. The principal technology issues include energy recovery of the ramped dipole magnets, which is achieved through use of ringing inductive/capacitive circuits, and high repetition rates of the induction cell pulsers, which is accomplished through arrays of field effect transistor (FET) switches. Principal physics issues identified include minimization of particle loss from interactions with the background gas, and more demanding emittance growth and centroid control requirements associated with the propagation of space‐charge‐dominated beams around bends and over large path lengths. In addition, instabilities such as the longitudinal resistive instability, beam‐breakup instability and betatron‐orbit instability were found to be controllable with careful design.

Nearly all designs of accelerators for heavy ion fusion rely on a velocity (energy) ramp to compress the beam longitudinally from its length in the accelerator to the length required at the target. The size of the velocity ramp is constrained by the longitudinal emittance of the beam. For example, if the longitudinal emittance is 0.05 eV {center_dot} s and we wish to produce a pulse having a width of {+-}2.5 ns at the target, we must supply an energy tilt such that the energy spread at the target is at least {+-}0.05 eV {center_dot} s/2.5 ns = {+-}2 x 10{sup 7} eV. The minimal value of energy spread occurs when the beam has propagated to the point where there is no correlation between the time and energy variables of the beam particles. (In the simple approximation where the boundary of the longitudinal phase space containing the particles is an ellipse, the ellipse is erect at this point, i.e., not tilted with respect to the axes.) In any case, the energy spread can affect focusing. If, for example, the beam kinetic energy is of the order of 5 GeV, a tilt of {+-}2 x 10{sup 7} eV corresponds to amore » fractional energy spread of 0.004 and it may be possible to focus the beam to the required spot size without using an achromatic optical system. Nevertheless, an optical system that allows larger longitudinal emittance should lead to a less expensive accelerator since the tolerances on acceleration waveforms could be relaxed. Moreover, at lower kinetic energies the problem becomes more serious. If the kinetic energy of our example beam were 1 GeV rather than 5 GeV, the fractional energy spread would be 0.02. This much energy spread would likely produce serious chromatic aberrations leading to an unwanted increase in focal spot size. It is interesting to note that the lower limit on energy spread at the target does not depend on whether the beam is neutralized as it approaches the target. If the beam is not neutralized, it will require a larger initial velocity tilt to overcome longitudinal space-charge forces; but these forces will remove part of the tilt as the beam compresses. Al Maschke suggested that it is possible to reduce the chromatic aberrations by applying a time-dependent transverse focusing correction to the beam upstream of the final focusing lenses [1]. At this point, because of the energy tilt, there is a correlation between longitudinal position in the beam and particle energy. In other words, the average beam energy at the tail of the beam is larger than the average beam energy at the head of the beam. If the beam is completely neutralized as it drifts toward the final focusing lenses, the kinetic energies of the individual particles will remain nearly unchanged during compression. In this case, it is possible, in principle, to apply some 'pre-focusing' to the higher energy particles (those nearer to the tail of the beam) to compensate for their weaker focusing in the final lenses. Although kinetic energies of individual particles are not conserved if the beam is not neutralized, one still expects a positive correlation between the particle energies at the beginning of compression and at the end of compression so correction is still assumed to be possible. It is important that the pulse duration is larger upstream than it is at the final focusing lenses. Larger pulse duration makes it easier, from an engineering standpoint, to supply the power needed to drive the pulsed correction elements. Nevertheless, it still appears impossible or very costly to provide the needed power for some specific cases that have been studied. In the remainder of this paper we ignore this issue and try to determine if there are other fundamental limitations on how well one might correct. We conclude that there are other important limitations.« less

The conceptual design of a heavy ion fusion driver system is described, including all major components. Particular issues emerging from this exercise are identified and discussed. The most important conclusion of our study is that due to stringent requirements on ion pulse phase space, we are unable to find a credible accelerator design that meets the requirements of the example target. Either the target design must be modified to accept larger ion ranges and larger focal spot sizes, or we must consider other target options.

Fusion is potentially a safe clean source not limited by political boundaries. Magnetic and inertial fusion share this promise, but there are differences between them. An inertial fusion power plant is based on different physics and technology from a magnetic fusion power plant and therefore presents somewhat different benefits and challenges. The facilities required to demonstrate inertial fusion power are potentially much smaller. In this article we describe concepts for such a power plant, its beneficial features and a low‐cost reactor test facility for developing practical fusion power.

In his paper in this issue, Dr. David Crandall of the Office of Fusion Energy presented DOE budget figures for magnetic fusion energy (MFE) and inertial fusion energy (IFE). Funding for IFE decreased from about $9M in FY91 and FY92 to $7.7M in FY93. The Bush budget for FY94 allocated $6.5M for IFE. Clearly the trend is down. In contrast, the FY93 budget for MFE is $330.7M and the Bush budget allocated $416.6M for FY94. These trends force one to ask if there should be an IFE program. In the authors opinion the answer to this question is emphatically affirmative. The remainder of this paper explaines the reasons for this opinion. The paper will emphasize heavy ion inertial fusion (HIF), but many of the reasons apply to any inertial fusion system. There are numerous studies, detailed calculations, and experiments that support the conclusion that HIF is promising: however, enough `promising` fusion schemes have come and gone that many fusion researchers (and politicians) have developed some skepticism about the results and projections of studies, calculations, and even some experiments. To be believable, results and projections must be consistent with scientific, technological, and industrial experience. Therefore this paper will not emphasize detailedmore » studies, but rather plausibility arguments based on experience with large high-energy accelerators and common industrial practice.« less

A source-to-target model for an induction linac driver for heavy ion fusion has been developed and is described here. Design features for a reference case driver that meets the requirements of one current target design are given, and the systems analyses supporting the point design are discussed. Directions for future work are noted.

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 High Current Experiment (HCX) is being built to explore heavy-ion beam transport at a scale appropriate to the low-energy end of a driver for fusion energy production. The primary mission of this experiment is to investigate aperture fill factors acceptable for the transport of space-charge dominated heavy-ion beams at high space-charge intensity (line-charge density /spl sim/0.2 /spl mu/C/m) over long pulse durations (3-10 /spl mu/sec). A single beam transport channel will be used to evaluate scientific and technological issues resulting from the transport of an intense beam subject to applied field nonlinearities, envelope mismatch, misalignment-induced centroid excursions, imperfect vacuum, halo, background gas and electron effects resulting from lost beam ions. Emphasis will be on the influence of these effects on beam control and limiting degradations in beam quality (emittance growth). Electrostatic (Phase I) and magnetic (Phase II) quadrupole focusing lattices have been designed and future phases of the experiment may involve acceleration and/or pulse compression. The Phase I lattice is presently under construction and simulations to better predict machine performance are being carried out. Here we overview: the scientific objectives of the overall project, processes that will be explored, and transport lattices developed.

Ion fast ignition, like laser fast ignition, can potentially reduce driver energy for high target gain by an order of magnitude, while reducing fuel capsule implosion velocity, convergence ratio, and required precisions in target fabrication and illumination symmetry, all of which should further improve and simplify IFE power plants. From fast-ignition target requirements, we determine requirements for ion beam acceleration, pulse-compression, and final focus for advanced accelerators that must be developed for much shorter pulses and higher voltage gradients than today's accelerators, to deliver the petawatt peak powers and small focal spots ({approx}100 {micro}m) required. Although such peak powers and small focal spots are available today with lasers, development of such advanced accelerators is motivated by the greater likely efficiency of deep ion penetration and deposition into pre-compressed 1000x liquid density DT cores. Ion ignitor beam parameters for acceleration, pulse compression, and final focus are estimated for two examples based on a Dielectric Wall Accelerator; (1) a small target with {rho}r {approx} 2 g/cm{sup 2} for a small demo/pilot plant producing {approx}40 MJ of fusion yield per target, and (2) a large target with {rho}r {approx} 10 g/cm{sup 2} producing {approx}1 GJ yield for multi-unit electricity/hydrogen plants, allowing internal T-breeding with low T/D ratios, >75 % of the total fusion yield captured for plasma direct conversion, and simple liquid-protected chambers with gravity clearing. Key enabling development needs for ion fast ignition are found to be (1) ''Close-coupled'' target designs for single-ended illumination of both compressor and ignitor beams; (2) Development of high gradient (>25 MV/m) linacs with high charge-state (q {approx} 26) ion sources for short ({approx}5 ns) accelerator output pulses; (3) Small mm-scale laser-driven plasma lens of {approx}10 MG fields to provide steep focusing angles close-in to the target (built-in as part of each target); (4) beam space charge-neutralization during both drift compression and final focus to target. Except for (1) and (2), these critical issues may be explored on existing heavy-ion storage ring accelerator facilities.

An attractive feature of the inertial fusion energy (IFE) approach to commercial energy production is that the fusion driver is well separated from the fusion confinement chamber. This ''standoff'' feature means the driver is largely isolated from fusion reaction products. Further, inertial confinement fusion (ICF) target ignition (with modest gain) is now scheduled to be demonstrated at the National Ignition Facility (NIF) using a laser driver system. The NIF program will, to a considerable extent, validate indirectly-driven heavy-ion fusion (HIF) target designs for IFE. However, it remains that HIF standoff between the final focus system and the fusion target needs to be seriously addressed. In fact, there now exists a timely opportunity for the Office of Fusion Energy Science (OFES) to experimentally explore the feasibility of one of the attractive final transport options in the fusion chamber: the self-pinched transport mode. Presently, there are several mainline approaches for HIF beam transport and neutralization in the fusion chamber. These range from the (conservative) vacuum ballistic focus, for which there is much experience from high energy research accelerators, to highly neutralized ballistic focus, which matches well to lower voltage acceleration with resulting lower driver costs. Alternatively, Z-discharge channel transport and self-pinched transport in gas-filled chambers may relax requirements on beam quality and final focusing systems, leading to even lower driver cost. In any case, these alternative methods of transport, especially self-pinched transport, are unusually attractive from the standpoint of chamber design and neutronics. There is no requirement for low chamber pressure. Moreover, only a minuscule fraction of the fusion neutrons can escape from the chamber. Therefore, it is relatively easy to shield sensitive components, e-g., superconducting magnets from any significant neutron flux. Indeed, self-pinched transport and liquid wall protection endow DT fusion with many of the advantages of aneutronic fusion. The question is: will self-pinched transport work? Early theoretical studies indicated that self-pinched transport was not an option because net currents established in gas during beam injection were too small to cause beam pinching. However, recent numerical simulations using the 3D hybrid code IPROP3, including the effects of non-local ionization, indicate that self-pinched transport may be possible. The capability to test the concept exists today in scaled experiments using a high-current focused proton beam produced by the Gamble II pulsed-power accelerator at the Naval Research Laboratory. This White Paper describes the implications of the self-pinched transport approach to HIF power plant design and the relevance of proton experiments designed to test the concept. Near-term experiments and analysis are also suggested.

HIFAN827 LBNL Perspective on Inertial Fusion Energy Roger Bangerter Lawrence Berkeley National Laboratory presented at the San Diego Meeting of the FEAC Policy Subcommittee December 17, 1995 FEAC 12/17/95

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.

Final focusing of ion beams and propagation in a reactor chamber are crucial questions for heavy ion beam driven fusion. An alternative solution to ballistic quadrupole focusing, as it is proposed in most reactor studies today, is the utilization of the magnetic field produced by a high current plasma discharge. This plasma lens focusing concept relaxes the requirements for low emittance and energy spread of the driver beam significantly and allows to separate the issues of focusing, which can be accomplished outside the reactor chamber, and of beam transport inside the reactor. For focusing a tapered wall-stabilized discharge is proposed, a concept successfully demonstrated at GSI, Germany. For beam transport a laser pre-ionized channel can be used.

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.

This paper describes an economical program for heavy ion fusion accelerator research. The heavy ion accelerator research program is part of a larger national research program to develop inertial fusion for commercial power production.

Large fusion devices will almost certainly produce net energy. However, a successful commercial fusion energy system must also satisfy important engineering and economic constraints. Inertial confinement fusion power plants driven by multi-stage, heavy-ion accelerators appear capable of meeting these constraints. The reasons behind this promising outlook for heavy-ion fusion are given in this report. This report is based on the transcript of a talk presented at the Symposium on Lasers and Particle Beams for Fusion and Strategic Defense at the University of Rochester on April 17-19, 1985.

Progress since the last Heavy-Ion Fusion Symposium has moved us much closer to demonstrating the scientific and technological requirements for inertial

We present the analysis of 64 000 K/sup -/p..--> sigma../sup -/..pi../sup +/ and 89 000 K/sup -/p..--> sigma../sup +/..pi../sup -/ events obtained with the Berkeley 25-in. hydrogen bubble chamber. Total cross sections and Legendre-polynomial expansion coefficients describing the differential cross sections and polarizations are presented in 10-MeV/c momentum intervals extending from 220 to 470 MeV/c. This paper completes the series devoted to all K/sup -/p final states in this momentum range.

In addition to the role of photoionization in the context of ionizing the gas in the target chamber, the possible importance of photoionization of the

An analysis has been made of 64600 events of the type K/sup -/p ..-->.. K/sup -/p and 22800 events of the type K/sup -/p ..-->.. K/sup 0/n in the Berkeley 25-in. hydrogen bubble chamber. Differential cross sections have been measured in intervals of 10 MeV/c over the momentum range 220 to 470 MeV/c. Legendre-polynomial fits to the distributions have been made, and the coefficients show structure from the resonant D-wave ..lambda..(1520) and background S and P waves. No new structure is observed. The total K/sup -/p cross section determined from measurements of all final states seen in this exposure is also presented. (AIP)

A general method is given for tuning an operating charged-particle beam with maximum efficiency (least number of iterations). The method involves finding the optimum linear combinations of magnet strengths to vary during the tuning process.

An experiment to study the decay ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p\ensuremath{\gamma}$ was performed in the Berkeley 25-in. hydrogen bubble chamber. An analysis was made of 48 000 events of the type ${K}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\Sigma}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$, ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p+\mathrm{neutral}$ with ${K}^{\ensuremath{-}}$ momenta near 400 MeV/c. The $\ensuremath{\Sigma}'\mathrm{s}$ produced in this momentum region are polarized because of the interference of the ${{Y}_{0}}^{*} (1520)$ amplitude with the background amplitudes. We have measured the proton asymmetry parameter $\ensuremath{\alpha}$ for 61 ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p\ensuremath{\gamma}$ events with an average polarization of 0.4. We found $\ensuremath{\alpha}=\ensuremath{-}{{1.03}_{\ensuremath{-}0.42}}^{+0.52}$. $\mathrm{SU}(3)$ predicts a value $\ensuremath{\alpha}=0$. A more restricted sample of events was used to determine the ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p\ensuremath{\gamma}$ branching ratio. From 31 ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p\ensuremath{\gamma}$ events and 11 670 ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{0}$ events, we found $\frac{({\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p\ensuremath{\gamma})}{({\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{0})}=(2.76\ifmmode\pm\else\textpm\fi{}0.51)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$. The result is in agreement with the previous measurements.