Heavy Ion Fusion Research Research Articles

Recent developments in heavy-ion fusion reactions

In this review the main advances in heavy-ion fusion research that have taken place over the last decade are addressed. During this period, experimental studies have been extended to deep subbarrier energies to reveal the unexpected phenomenon of fusion hindrance. The coupled-channels descriptions have been refined to include the effects of nucleon transfer and to account for the fusion hindrance in terms of the ion-ion potential in the strongly overlapping region. Substantial progress has been made in time-dependent Hartree-Fock theory to the point that this approach now can make parameter-free predictions of heavy-ion fusion excitation functions. As several heavy-ion fusion reactions are of crucial importance in late-stage giant-star evolution, these reactions continue to be studied with better experimental and theoretical tools in order to provide improved input to astrophysical models. The effects of loosely bound valence nucleons on the fusion cross sections are the focus of a number of experimental studies involving radioactive beams, which have only recently become available. And finally, as the active field of synthesizing superheavy elements relies on heavy-ion fusion to reach the nuclei of interest, it is important to understand the fusion dynamics that plays a crucial role in both the “cold-fusion” and “hot-fusion” approaches to the superheavy island of stability. Also this area has seen significant progress in several different approaches to the problem of predicting the cross sections for formation and survival of these rare nuclei.

The NDCX-II engineering design

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.

The electromagnetic Darwin model for intense charged particle beams

The theoretical and numerical properties of the electromagnetic Darwin model for intense charged particle beams are investigated. The model neglects the transverse displacement current in Ampere's law and results in the elimination of high-frequency transverse electromagnetic waves and the associated retardation effects in the Vlasov–Maxwell equations. In this paper, two numerical schemes are presented for the purpose of circumventing the numerical instabilities associated with the presence of E T [ ≡ - ( 1 / c ) ∂ A / ∂ t ] in the equations of motion for particle codes, where A is the vector potential. The first relies on higher-order velocity moments for closure, and the other replaces the mechanical momentum, p = γ m v , by the canonical momentum, P = p + ( q / c ) A , as the phase-space variable. The properties of these simulations schemes in the laboratory frame as well as in the beam frame are also discussed. These new numerical methods are most suitable for studying Weibel and two-stream instabilities in heavy ion fusion research.

Simulation of intense beams for Heavy Ion Fusion

Computer simulations of intense ion beams play a key role in the Heavy Ion Fusion research program. Along with analytic theory, they are used to develop future experiments, guide ongoing experiments, and aid in the analysis and interpretation of experimental results. They also afford access to regimes not yet accessible in the experimental program. The U.S. Heavy Ion Fusion Virtual National Laboratory and its collaborators have developed state-of-the art computational tools, related both to codes used for stationary plasmas and to codes used for traditional accelerator applications, but necessarily differing from each in important respects. These tools model beams in varying levels of detail and at widely varying computational cost. They include moment models (envelope equations and fluid descriptions), particle-in-cell methods (electrostatic and electromagnetic), nonlinear-perturbative descriptions (“ δ f ”), and continuum Vlasov methods. Increasingly, it is becoming clear that it is necessary to simulate not just the beams themselves, but also the environment in which they exist, be it an intentionally created plasma or an unwanted cloud of electrons and gas. In this paper, examples of the application of simulation tools to intense ion beam physics are presented, including support of present-day experiments, fundamental beam physics studies, and the development of future experiments. Throughout, new computational models are described and their utility explained. These include Mesh Refinement (and its dynamic variant, Adaptive Mesh Refinement); improved electron cloud and gas models, and an electron advance scheme that allows use of larger time steps; and moving-mesh and adaptive-mesh Vlasov methods.

Tests of prototype quadrupole magnets for heavy ion fusion beam transport

Four NbTi superconducting prototype quadrupole magnets have been built for the High Current Transport Experiment (HCX) as part of the multi-beam heavy-ion fusion research activity, led by the Lawrence Berkeley National Laboratory (LBNL). MIT performed quench training and ramp rate tests of the two prototype magnets that were designed and built by the Advanced Magnet Lab, Inc. (AML), based on a novel concept featuring cable-in-groove and multi-layer stacking. Both magnets are splice-free without inter-layer or inter-quadrant joint. Each coil was wound with a continuous NbTi round cable, placed in precise grooves machined in G-11 plates. The two magnets differ in their cable construction and their coil and yoke configuration. Each magnet was tested more than once in liquid helium bath with a room temperature thermal cycle between cold tests. This paper describes the results of the performance tests as well as the instrumentation and the quench protection system. Possible improvements for future coil winding are discussed.

Status of heavy ion fusion

An overview of ongoing activities on heavy ion fusion (HIF) in Russia, Europe, the USA and Japan is presented. In this phase, the activities are oriented towards theoretical and experimental investigations of the state of matter under extreme conditions, experimental and theoretical study on heavy ion beam-plasma interaction, powerful driver issues and development of computer codes for comprehensive numerical simulations of heavy ion driven inertial fusion. In the context of the new-generation facilities at GSI-Darmstadt and ITEP-Moscow, considerations are focused on large synchrotron rings and high current accumulator rings which would be important tools for investigations in the physics of dense plasmas and inertial fusion. Numerous national and international collaborations on HIF research are proceeding effectively towards development of a new energy source that is abundant, safe, environmentally acceptable and economical.

High-current laser ion source for induction accelerators

We have developed a high-current laser ion source for heavy ion fusion research based on induction accelerators. A frequency-doubled Nd:YAG laser irradiated a copper target with an intensity of 10 8–10 9 W/cm 2, producing plasmas composed of Cu + and Cu 2+ ions dominantly. The laser plasma supplied a large number of ions (∼10 14 ions/pulse) during several microseconds, which meets the requirement of heavy ion fusion. An inductive acceleration module extracted high-current ion beams over 0.1 A/cm 2 from a plasma-filled gap.

Vacuum arc ion source for heavy ion fusion

Heavy ion fusion is one approach to the problem of controlled thermonuclear power production, in which a small DT target is bombarded by an intense flux of heavy ions and compressed to fusion temperatures. There is a need in present HIF research and development for a reliable ion source for the production of heavy ion beams with low emittance, low beam noise, ion charge states Q=1+ to 3+, beam current ∼0.5 A, pulse width ∼5–20 μs, and repetition rate ∼10 pulses per second. We have explored the suitability of a vacuum arc ion source for this application. Energetic, high current, gadolinium ion beams were produced with parameters as required or close to those required. The performance parameters can all be improved yet further in an optimized ion source design. Here we describe the ion source configuration used, the experiments conducted, and the results obtained. We conclude that a vacuum arc based metal ion source of this kind could be an excellent candidate for heavy ion fusion research application.

Heavy ion fusion research at GSI

Heavy ion fusion research at GSI is dedicated to accelerator experiments and theory in the r.f. linac-storage ring approach as well as experimental work in ion beam focusing and ion beam plasma interaction. The status of the accelerator-based work is summarized in this paper. Important topics along this line have been the studies on the European Ignition Facility, high current development at the SIS and beam target experiments, experimental and theoretical studies on the longitudinal resistive instability, bunched beam experiments using a streak camera as well as theoretical work on resonance crossing.

Heavy ion fusion research in Spain

The indirect-direct illumination scheme has been investigated, and simulations were performed using the radiation-hydrodynamics code Sara, showing good agreement with experiments performed at CEL-V Limeil (France) in the PHEBUS laser. The use of an externally guided implosion of the fuel has been suggested, where two pellets, each being accelerated from opposite mouths of a cannon barrel, will collide and implode in a central cavity. A detailed opacity model ( Jimena-Dca) has been developed that treats absorption bands that result from many-particle configurations using the original Mozskowski's formalism; our average ion model ( Jimena-Ai) also includes that model. Frequency-dependent opacities for intermediate- and high- Z plasmas have been computed and tested through the WORKOP series. An adaptive mesh scheme has been implemented in the two-dimensional Arwen code based on an implicit Riemann solver and part of a Lagrangian flux-corrected transport staggered-mesh (RMFCT) scheme. The code can handle several materials on a Eulerian mesh, and includes simple ion and laser energy sources. A two-dimensional code for radiation-hydrodynamics ( Multi-2D) has been developed that uses non-structured triangular grids, and includes arbitrary Eulerian-Lagrangian hydrodynamics, radiation transport by discrete ordinates, and laser or heavy ion beam deposition. The inventory and radiological code ACAB has been extensively used to determine the activation in inertial fusion reactors and has been improved to include pulsed regimes and fission process. A molecular dynamics code has been developed in collaboration with LLNL to study neutron damage in SiC. DENIM is actively participating as one of the main proponents of the European Heavy Ion Ignition Facility of the European authorities, together with GSI Darmstadt, ENEA Frascatti and KfK Karlsruhe.

ILSE: The next step in heavy ion fusion research

Induction Linac Systems Experiments is the next experiment planned by the Heavy Ion Fusion Accelerator Research (HIFAR) group at LBL, following the recent completion of the MBE-4 experiment. ILSE at 10 MeV will address many of the key physics and technology issues of HIF such as performance of a multiple beam, high voltage injector, high intensity electrostatically-focused transport, beam combining, high intensity magnetically-focused transport, drift-compression and energy-tilt removal, high intensity transport around a magnetic bend, and, possibly, recirculation. Presuming a “new start” in FY 94, experiments could begin with ILSE in FY 97.

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Applications of the MEVVA high current metal ion source

A new kind of ion source has been developed in which a MEtal Vapor Vacuum Arc (MEVVA) is used to produce the plasma from which the ion beam is extracted. The novel and exciting feture of this source is the very high metal ion beam current attainable. A total ion beam current of over 1 Ae has been extracted from the embodiment of the concept that we are presently using, and this is not a limit of the method. The source was developed to upgrade the uranium ion beam intensity of the Bevatron, LBL's heavy ion synchrotron, for basic nuclear physics research. Other important applications include its use within the Heavy Ion Fusion research effort; for ion implantation; and for other basic research uses. In this paper the source is described briefly, its performance outlined, and its potential and limitations for a variety of applications is discussed.

Preliminary Design Study of the NSWC Proton Induction Linac

A 5 MeV, 100 A, 3 ?sec proton beam is required for the injection into a compact accelerator which uses quadrupole lenses in a betatron-like device at NSWC. As an injector, an induction linac is proposed to utilize technologies developed in magnetic and heavy ion fusion research: A 50 keV, 100 A, 3 ?sec proton beam extracted from an ion source used for the PDX-type neutral beam injector, is accelerated by induction modules. The beam size is reduced by solenoidal lenses in three steps as beam energy is increased. The matching section is followed before injection to the quadrupole channel. We present preliminary design details of the proposed intense, long-pulse proton linac.

The heavy ion fusion research program in the Federal Republic of Germany

Recent progress on accelerator and systems studies carried out in the framework of a national program on heavy ion fusion is reviewed. Plans for future investigations aiming at the basic aspects of inertial confinement with heavy ion beams are discussed.