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Parameters and requiremets involving development of superconducting magnets, having to do with the U.S. Heavy Ion Fusion Program, are described and discussed.

The development of quadrupole arrays for heavy ion fusion is described, based on NbTi mini-cable enabling cost effective and highly automated manufacturing.

A superconducting 3X3 quadrupole magnet array for increasing the beam intensity and reducing space charge effects in a Heavy Ion Fusion Driver has been designed and constructed. A single array unit made up of several quadrupole magnets will be installed within a ferromagnetic accelerating core. The operating quadrupole field is 50 T/m across a 78 mm warm bore and the magnetic length is 0.32 m. The overall array size is 900 mm in diameter and 700 mm long including the cryostat.

We describe near-term heavy ion fusion (HIF) research objectives associated with developing an inertial fusion energy demonstration power plant. The goal of this near-term research is to lay the essential groundwork for an intermediate research experiment (IRE), designed to demonstrate all the key driver beam manipulations at a meaningful scale, and to enable HIF relevant target physics experiments. This is a very large step in size and complexity compared to HIF experiments to date, and if successful, it would justify proceeding to a demonstration fusion power plant. With an emphasis on accelerator research, this paper is focused on the most important near-term research objectives to justify and to reduce the risks associated with the IRE. The chosen time scale for this research is 5–10 years, to answer key questions associated with the HIF accelerator drivers, in turn enabling a key decision on whether to pursue a much more ambitious and focused inertial fusion energy research and development program. This is consistent with the National Academies of Sciences Review of Inertial Fusion Energy Systems Interim Report, which concludes that “it would be premature at the present time to choose a particular driver approach…” and encouraged the continued development of community consensus on critical issues, and to develop “options for a community-based roadmap for the development of inertial fusion as a practical energy source.”

The High Current Experiment at Lawrence Berkeley National Laboratory is part of the U.S. program to explore heavy-ion beam transport at a scale representative of the low-energy end of an induction linac 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 intensity (line charge density ∼0.2 μC/m) over long pulse durations (4 μs) in alternating gradient focusing lattices of electrostatic or magnetic quadrupoles. This experiment is testing transport issues resulting from nonlinear space-charge effects and collective modes, beam centroid alignment and steering, envelope matching, image charges and focusing field nonlinearities, halo, and electron and gas cloud effects. We present the results for a coasting 1 MeV K^{+} ion beam transported through ten electrostatic quadrupoles. The measurements cover two different fill factor studies (60% and 80% of the clear aperture radius) for which the transverse phase space of the beam was characterized in detail, along with beam energy measurements and the first halo measurements. Electrostatic quadrupole transport at high beam fill factor (≈80%) is achieved with acceptable emittance growth and beam loss, even though the initial beam distribution is not ideal (but the emittance is low) nor in thermal equilibrium. We achieved good envelope control, and rematching may only be needed every ten lattice periods (at 80% fill factor) in a longer lattice of similar design. We also show that understanding and controlling the time dependence of the envelope parameters is critical to achieving high fill factors, notably because of the injector and matching section dynamics.

Transverse beam combining is a cost-saving option employed in many designs for heavy ion fusion drivers. However, the resultant transverse phase space dilution must be minimized so as not to sacrifice focusability at the target. A prototype combining experiment has been completed employing four 3-mA Cs^{+} beams injected at 160 keV. The focusing elements upstream of the merge consist of four quadrupoles and a final combined-function element (quadrupole and dipole). Following the merge, the resultant single beam is transported in a single alternating gradient channel where the subsequent evolution of the distribution function is diagnosed. The results are in fair agreement with particle-in-cell simulations. They indicate that for some heavy ion fusion driver designs, the phase space dilution from merging is acceptable.

Induction core alloys are evaluated that are appropriate for heavy-ion induction accelerators to drive heavy-ion inertial fusion (HIF) power plants. Parameters evaluated include the usable flux swing and the energy loss over a range of magnetization rates of ∼10^{5}–10^{7} T/s, corresponding to pulse durations of ∼20 to 0.2 μs, respectively. The usable flux swing, for minimum core losses, extends from near the reversed remanent field to about 80% of the saturation field. The usable flux swing is enhanced, with little increase in losses, by annealing the core after winding. Maintaining low energy loss at high magnetization rates requires insulation to block interlaminar eddy currents. To obtain annealed cores with a high ratio of remanent to saturation magnetic field, the insulation must withstand annealing temperatures and apply minimum mechanical stress to the core during cooldown. We find that commercially available insulating coatings for amorphous metals either break down near 10^{6} T/s (a factor of 10 below the requirement), or do not achieve the maximum remanent field and hence the usable flux swing after annealing. More satisfactory coatings are available for silicon steel and nanocrystalline alloys, which could have applications in HIF. Amorphous alloys are capable of meeting most HIF needs, especially with improved coatings.

A simple polyaniline nanofiber chemical sensor was constructed to introduce both high school and college students to application of nanoscale science. The laboratory exercise introduces students to the fundamentals of sensors and the advantages of using nanoscale fibers for sensing.

Discusses a study which detailed the measurement of the time evolution of the line charge density and energy at the ends of an initially rectangular ion bench due to the space charge of the bunch. Composition of the SBTE machine; Approximation commonly used in describing a drifting bunch for heavy-ion driven; Limitation in the SBTE setup.

Focuses on a study which investigated the direct current and pulsed magnetic properties of Metglas alloys in the as-cast, box annealed and rewound conditions. Background to the study; Results; Conclusions.

Oxygen Isotope Effect In High-Temperature Oxide Superconductors THE BEHAVIOR OF MOST KNOWN SUPERCONDUCTORS is best described by the phonon-mediated Bardeen-Cooper-Schrieffer (BCS) theory (1). According to this theory, electron-phonon interactions couple [...]

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 neutralized compression onto the target. This paper describes the discrete-particle simulation models (one-, two-, and three-dimensional) employed and the space-charge-dominated beam dynamics being realized. [ABSTRACT FROM AUTHOR]

In a heavy ion fusion driver, arrays of superconducting quadrupoles will transport parallel beams through a sequence of induction acceleration cells. The development of such arrays is a unique and challenging task. Since magnetic transport is one of the most expensive subsystems, economy of fabrication is a primary consideration. A compact design is essential to limit the size and cost of induction cores. Special edge coils have to be implemented to adjust the field in outer cells and terminate the magnetic flux. The development of superconducting magnets for both near term experiments and the ultimate driver application is actively pursued by the U.S. Heavy Ion Fusion Program. The main parameters and requirements are discussed, and the R&D status and plans are presented. [ABSTRACT FROM AUTHOR]

A one-tenth-scale version of a final focus subsystem for a heavy-ion-fusion driver has been built and used for experimental tests of concept. By properly scaling the parameters that relate ion energy and mass, current, emittance, and focusing fields, the transverse dynamics of a representative driver final focus have been replicated in a small laboratory beam. Whereas the driver beam parameters considered are 10 GeV Bi[sup +] at 1.25 kA, the scaled experiment used a 95 μA beam of 160 keV Cs[sup +] ions brought to a ballistic focus through a series of six quadrupole magnets. The measured focal spot size was consistent with calculations in the report of the design on which the experiment is based. In a second experimental program, a 400 μA beam was propagated through the focal system and partially neutralized after the last magnet using electrons released from a hot tungsten filament to test the predictions of the benefits of neutralization. The increase in beam current resulted in a corresponding increase in spot radius in the absence of electrons. A reduction of the spot radius and modification of its shape were observed in the presence of neutralizing electrons. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on the development of superconducting quadrupole arrays for heavy-ion fusion accelerators. Description of the individual quadrupole cell; Layout of the arrays; Operation using the cryostat concept.