Light Ion Fusion Research Articles

Light ion fusion in deformation model

Experiments with heavy ions at moderate energies show the importance of deformation in heavy ion collisions. A deformation model which takes deformation dynamically into account is developed. Having described fusion and deep inelastic collision for a very heavy system (Xe + Bi) and a medium heavy system (Ar + Th) at various energies successfully, we turn to some comparatively lighter heavy ions where fusion is the most dominant feature. Fusion cross-sections for six pairs of lighter systems (35Cl +116Sn,58Ni+62Ni,35Cl+62Ni,32S+24Mg,24Mg+24Mg and12C+27Al) have been obtained using our deformation model which agree well with experiment. The two-slope-behaviour of fusion excitation function which is an important feature of light ion fusion systematics is also obtained, in our model calculations for all the systems studied.

Equilibrium and non-equilibrium microfireball behaviour in light-ion fusion systems

Light-ion fusion reactors and high-yield target testing facilities will have a gas-filled reaction vessel. The target microexplosion will create a microfireball in this gas. The behaviour of this microfireball as it propagates and reflects from the reaction vessel wall is critical to the design of the vessel. The type of gas and the modelling assumptions used for analysis can significantly affect the prediction of this behaviour. The effects of two-temperature and multifrequency radiative transfer models are investigated for nitrogen and argon gases. The isothermal sphere model and the target X-ray attenuation model for microfireball creation are compared. The computational results are related to the analytic strong-shock theory.

Neutron Activation and Shielding of the Light ion Fusion Target Development Facility

Neutron Activation and Shielding of the Light ion Fusion Target Development Facility

Light lon Fusion Target Development Facility Pre-Conceptual Design

The light ion fusion target development facility will be used to test high yield ICF targets (50200 MJ) at the rate of 10 shots per day. The 6 meter diameter cylindrical target chamber is designed as a first wall supported by a structural frame and is capable of withstanding 15,000 full yield shots over a 5 year lifetime. It is made from Al 6061, thus greatly reducing induced activity. The chamber is shielded by a water pool to allow easy access.

Dynamic Stress Analysis of Light Ion Fusion Target Development Facility Reaction Chambers

Preliminary structural analysis and design is presented for the reaction chamber of a preconceptual light ion beam target development facility (TDF). The chamber consists of a capped, reinforced cylindrical shell submerged in a water shield. Axisymmetric response is determined for blast waves generated by target ignition. From the analysis, design curves are developed for dynamic displacements and flexural stresses of the shell wall. It is shown that the added mass effect of the water can substantially reduce the response and that a practical design is possible for a range of geometric parameters and materials.

Heating of cryogenic targets in a light ion fusion cavity

Survivability of cryogenic targets in single-shot and reactor cavity environments is an essential prerequisite for high gain (>25) target experimentation, target development, and power production. Heat sources in a gas-filled light ion beam cavity include radiative, convective, and viscous heating by the cavity fill gas, heating due to laser radiation used to initiate low-density plasma channels for beam propagation, and heating due to ohmic dissipation of channel currents near the target. Prior to injection of the target into the cavity, tritium decay and target acceleration are the sources of heat. In this paper the parametric dependence, time scale, and magnitude of each of these thermal sources are discussed. Potential thermal protection techniques which may be applicable to long (>0.1 s), intermediate (∼ ms), and short-duration (∼ μs) heat loads are described, and remaining concerns are noted.

Ion beam propagation and focusing

Inertial confinement fusion with ion beams requires the efficient delivery of high energy (≳1 MJ), high power (≳100 TW) ion beams to a small fusion target. The propagation and focusing of such beams is the subject of this paper. Fundamental constraints on ion beam propagation and focusing are discussed, and ion beam propagation modes are categorized. For light ion fusion (LIF), large currents (2–33 MA) of moderate energy (3–50 MeV) ions of low atomic number (1⩽A≲12) must be directed to a target of radius ≲1 cm. The development of pulsed power ion diodes for LIF is discussed, and the necessity for virtually complete charge neutralization during transport and focusing is emphasized. Fornear-term LIF experiments, the goal is to produce pellet ignition without the standoff needed for the ultimate reactor application. Ion diodes for use on Sandia National Laboratories Particle Beam Fusion Accelerators PBFA-I (2–4 MV, 1 MJ, 30 TW, operational) and PBFA-II (2–16 MV, 3.5 MJ, 100 TW, scheduled for operation in 1985) are discussed. Ion beam transport from these diodes to the pellet is examined in reference to the power brightness ℬ. While values of ℬ=2–5 TW/cm2/sr have been achieved to date, a value of ℬ≈100 TW/cm2/sr is needed for breakeven. Research is now directed toward increasing ℬ, and means already exist (e.g., scaling to higher voltages, enhanced ion diode current densities, and bunching), which indicate that the required goal should be attainable. Forfar-term LIF applications, the goal is to produce net energy gain with standoff suitable for a reactor. This may be achieved by ion beam transport in preformed, current-carrying plasma channels. Channel transport research is discussed, including experiments with wire-initiated, wall-initiated, and laser-initiated discharge channels, all of which have demonstrated transport with high efficiency (50–100%). Alternate approaches to LIF are also discussed, including comoving electron beam schemes and a neutralized beam scheme. For heavy ion fusion (HIF), moderate currents (∼10 kA) of high energy (∼10 GeV) ions of high atomic number (A≳200) must be directed to a target of radius ≲0.3 cm. Conventional accelerator drivers for HIF are noted. For a baseline HIF reactor system, the optimum transport mode for low charge state beams is ballistic transport in near vacuum (10−4–10−3 Torr lithium), although a host of other possibilities exists. Development of transport modes suitable for higher charge state HIF beams may ultimately result in more economical HIF accelerator schemes. Alternate approaches to HIF are also discussed which involve collective effects accelerators. The status of the various ion beam transport and focusing modes for LIF and HIF are summarized, and the directions of future research are indicated.

Generation of strong time compressed light ion beams

Positive light ions (He4) are extracted from a pulsed plasma source and accelerated in two states, first at constant potential and subsequently by a time varying voltage which is programmed to generate a time compressed beam bunch, downstream at a defined distance form the accelerator. Time compression of a 1-μs extracted beam pulse into an 8-ns bunched pulse at a distance of 66 cm from the source has been achieved. The technique provides useful applications for concentrated energy deposition on targets and is part of a proposed Light Ion Fusion Experiment (LIFE) accelerator system where 20:1 axial pulse compression would be programmed to occur during the ballistically focused and neutralized transport of intense ion beams.

Method of Active Charge and Current Neutralization of Intense Ion Beams for ICF

Intense ion beam neutralization by sufficiently cold, co-moving and co-injected electrons is crucial to Light Ion and important to Heavy Ion Inertial Confinement Fusion (ICF) drivers for the ballistically focused propagation onto ~ 5 mm radius targets located some 10 m downstream. Methods of generating the beam neutralization electrons with required properties are given in the context of a Light Ion Fusion Experiment (LIFE) designed accelerator. Recently derived envelope equations for neutralized and ballistically focused intense ion beams are applied to the LIFE geometry in which 10 MeV He+ multiple beamlets coalesce and undergo 45:1 radial compression while beam pulses experience a 20:1 axial compression in the propagation range of 10 m. For these representative conditions, the theoretical analysis produces a requirement of the initial electron temperature neutralizing the ions as Teo ≤ 35 eV where also the initial ion temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">io</sub> is correlated. Both active and auto <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> -neutralization methods are examined and found to produce initial electron temperatures consistent with the requirement of the envelope equation for both radial and axial adiabatic beam pulse compressions. The stability of neutralized beam propagation is also examined concerning the Pierce type electrostatic instability and for the case of LIFE beams it is found to have insignificant effect. A scaled experimental setup is presented which can serve to perform near term tests on the ballistically focused propagation of neutralized light ion beams.

Performance of Intense Pulsed Ion Source

The development of intense pulsed plasma ion sources for high current extraction of He+, Ne+ and Xe+ beams is motivated by several applications. Cold (Ti < 0.2 eV) He+ ions extracted at current density of 1-1.5 A/cm2 across a 1 m radius surface for a total current of 25 kA in 0.5 ?s pulses are required for a Light Ion Fusion Experiment (LIFE) ICF driver based on the neutralized and ballistically focused propagation approach. Moderate temperature (Ti ~, 3 eV) Ne+ and Xe+ ions at 1-1.5 A/cm2 for 1-10 A extracted currents in ms long pulses are required in several recent low s approaches based on multi-aperture quadrupole focused RF acceleration schemes such as the MEQALAC and the RFQ injector. In a test ion source, plasma is induced by ms time pulsing a 0.3 MHz, 0.1 MW RF oscillator with power AC-coupled to an antenna situated inside a 30 cm radius cylindrical vessel where the interior surfaces are lined with cusp-field permanent magnets except for the front extraction face. The plasma parameters Te, Ti, np are characterized by measurements as a function of time during ms long pulses and in the immediate afterglow, the neutral gas density, the RF power and location at the extraction surface, and data are compared with derived scaling relations.

Multi-Stage Intense Ion Beam Electrostatic Accelerator for ICF

The design of a multi-aperture, channel focused, multi-stage low 8 electrostatic accelerator is made to produce well controlled intense light ion beams as drivers of Inertial Confinement Fusion (ICF) targets. Unlike the case of diode accelerators, the Light Ion Fusion Experiment (LIFE) accelerator system contains separate-function elements to launch 3 to 10 MeV, 23 kA accelerated current, He+ beams in 400 ns pulses where 20:1 axial pulse compression would occur during the neutralized and ballistically focused transport. Each beam line would impart 50 kJ implosion energy in ~ 20 ns on 5-6 mm radius targets located 10 m downstream and a system of 40 beam lines would deliver 2 MJ. Methods of producing beam neutralization with initial electron temperature Teo, satisfying analytically derived constraints for both radial (45:1) and axial (20:1) pulse compressions during transport are given separately. Also, the development of a pulsed intense cold plasma ion source capable of producing 1 A/cm2 and Ti ~ 0.15 eV He+ beamlets over large extraction surfaces which is suitable for this application is presented in these proceedings.