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Abstract: In a particle accelerator system for heavy ion inertial fusion, space-charge-dominated beam dynamics is investigated during a final beam bunching. While the space charge effect undertakes an important role for the beam dynamics in the regime, the beam instability induced by space charge oscillation may occur, depending on the particle distribution of the beam. Particle simulations present that the instability due to the strong space charge effect may not be serious for realistic particle distributions during the final beam bunching. [Copyright &y& Elsevier]

Abstract: Three-dimensional computer simulations are performed for a heavy ion beam (HIB) irradiation onto a direct-driven spherical fuel pellet in heavy ion fusion (HIF). In addition, the non-uniformity growth due to a little pellet displacement from a reactor chamber center is investigated. The calculation results demonstrate that we can realize a rather low non-uniform energy deposition: for example, less than 2.0% even for a 32-beam irradiation system. Moreover, we developed the above simulation code for more common purposes in the research fields of medical treatment, material processing, indirect-driven HIF and so on. [Copyright &y& Elsevier]

Abstract: Beam dynamics is investigated by multiparticle simulations during final beam bunching and final beam focusing in a driver system for heavy-ion inertial fusion. The particle simulations predict the emittance growth during the longitudinal bunch compression for various particle distributions at initial conditions. Particle distributions in the beam transverse cross-section approach uniform during the final beam bunching. It is found that the distribution has the Gaussian profile at the focal spot in the radial direction after the final focusing. [Copyright &y& Elsevier]

Abstract: Heavy ion beams (HIBs) are transported through a reactor chamber gas to a fuel pellet in heavy ion fusion. Due to the HIB high current, the HIB space charge should be neutralized in a reactor, and promising final transport schemes have been proposed. In this paper, we discuss the final transport in a neutralized ballistic final beam transport scheme, and point out a new mechanism of the HIB divergence by an ambipolar (plasma sheath) field generated by neutralizing electrons. The paper also proposes possible solutions to suppress the HIB divergence by the ambipolar field and presents a transportable window. [Copyright &y& Elsevier]

Abstract: In order to realize an effective implosion, beam illumination non-uniformity on a fuel target must be suppressed less than a few percent. In this study, a direct–indirect mixture implosion mode is proposed and discussed in heavy ion beam (HIB) inertial confinement fusion (HIF) in order to release sufficient fusion energy in a robust manner. On the other hand, the HIB illumination non-uniformity depends strongly on a target displacement dz from the center of a fusion reactor chamber. In a direct-driven implosion mode, dz of ∼20μm was tolerable, and in an indirect-implosion mode, dz of ∼100μm was allowable. In the direct–indirect mixture mode target, a low-density foam layer is inserted, and the radiation energy is confined in the foam layer. In the foam layer, the radiation transport is expected to smooth the HIB illumination non-uniformity in the lateral direction. Two-dimensional implosion simulations are performed, and show that the HIB illumination non-uniformity is well smoothed in the direct–indirect mixture target. Our simulation results present that a large pellet displacement of approximately a few hundred microns is allowed in order to obtain a sufficient fusion energy output in HIF. [Copyright &y& Elsevier]

Abstract: In heavy ion beam (HIB) inertial confinement fusion (HIF), implosion asymmetry should be less than a few percent in order to compress a fuel sufficiently and release fusion energy effectively. It is known that the HIB illumination nonuniformity and implosion symmetry are sensitive to a little pellet displacement from a reactor chamber center. We present a new HIB illumination scheme which is robust against the displacement of a direct-driven fuel pellet in an HIF reactor chamber. In conventional HIB illumination schemes a pellet displacement of 25–100μm was tolerable. The new robust HIB illumination scheme is examined by three-dimensional computer simulations. In the new HIB illumination scheme the tolerable pellet displacement is about 200–300μm. [Copyright &y& Elsevier]

Abstract: In this paper, significant progresses of Japanese research activities are presented in heavy ion fusion (HIF) and high energy density physics (HEDP). Heavy ion beam (HIB) is a prominent tool to study HEDP and HIF, and HIBs may be a promising inertial fusion driver. HIB accelerators have been studied intensively for a long time; HIB pulse profile, a particle energy and a HIB quality are controllable. A HIB energy deposition profile is also well defined, and HIB energy is deposited inside a material. By focusing and using the HIB excellent properties, Japanese HIF and HEDP activities have covered a wide variety of subjects ranging from new accelerators to future HIF studies: ion source, new inductive accelerator, beam physics, beam bunching, beam instabilities, HIB interactions with gas or materials, laser ion acceleration, HIB transport, HIB-based warm dense (WD) state generation, new measurement of HED or WD matters, HIB stopping power, atomic physics, multi-HIBs illumination on a target, HIF target implosion, impact ignition scheme, HIB-radiation conversion, radiation confinement and transport in HED matter or in HIF, and so on. [Copyright &y& Elsevier]