Most of the future accelerators will be high intensity machines delivering mega-watt beams for applications such as spallation neutron production, muon colliders, neutrino factories, nuclear-waste transmutation or inertial confinement fusion energy (IFE). Especially in the field of heavy ion driven inertial confinement fusion, where space charge dominated multi kilo-ampere beams have to be transported over several meters through a reactor chamber to a mm-size target, some kind of beam neutralization is required. Among the possible solutions is the plasma-channel based final transport. High-current discharge channels offer unique properties for ion-beam transport. They can neutralize both current and space charge of very intense ion beams and provide a strong azimuthal magnetic field all the way along the channel. This work describes experiments performed at the Gesellschaft fuer Schwerionenforschung (GSI) in Darmstadt and the Lawrence Berkeley National Laboratory (LBNL) to create and diagnose high current discharge channels designed for the transport of intense ion beams. In both experiments, stable channels are created by a laser pulse which is fired into the chamber along the desired path of breakdown before the discharge is triggered. While in Berkeley a UV-laser creates an initial seed of electrons by two-photon ionization of a small admixture of Benzene molecules to the background gas, at GSI an IR-laser is used to heat ammonia gas by resonant absorption and to produce a gas-rarefaction channel with preferred conditions for a breakdown. An alternate technique, using an ion beam to initiate stable, free-standing channels has been tested successfully for the first time at the UNILAC- linear accelerator at GSI. All channels, created by either of these three methods show no signs of hydrodynamic instabilities in a wide parameter range. Several plasma diagnostics were developed and used to gain a deeper understanding of the dynamics and stability of the discharges. In order to measure the electron density with spatial resolution a two-color imaging interferometer was developed. Peak densities around 1017 to 1018 cm-3 were inferred, depending on the discharge conditions. The interferometer also showed the existence of a rarefaction channel and a radially expanding gas wall which is believed to enhance the stability of the discharge. This pressure wave was studied in detail by means of schlieren diagnostics. In Berkeley a Faraday polarimeter was developed to determine the current density distribution and thus the magnetic field inside the plasma, from the rotation of the plane of polarization of a CO2 laser beam passing through the plasma. The plasma-self emission was investigated by spectroscopy in the visible wavelength range. Measurements of the Stark broadening of hydrogen Balmer lines were used for an alternate electron-density measurement. To fit theoretical spectra to the measurements, a rate model for a nitrogen plasma was developed and a maximum electron temperature of 7 eV was derived. For an application of plasma channels to the final focus and transport inside an inertial-confinement fusion reactor with two-sided target illumination it is required to produce intersecting discharges to provide a focusing magnetic field for two ion beams propagating from opposite sides towards the target. Experiments at GSI demonstrated that X-shaped, T-shaped and L-shaped discharges can be produced by CO2 laser initiation. The ion optical properties of such T-discharges were investigated with a 660 MeV Ni+12 heavy-ion beam from the UNILAC-linear accelerator at GSI.

Plasma diagnostics of discharge channels for neutralized ion beam transport

The design of the heavy-ion beam and the HYLIFE-II reactor chamber interface must provide final focusing quadruple triplets, neutron shielding, fast shutters, vapor condensation and pumping, thermal insulation, and blast resistant structures. The smallest half angle encompassing all beams striking the target might be {plus minus}14{degrees} for an array of 4 {times} 4 beams or {plus minus}9{degrees} if the four corner beams are eliminated, giving a 12-beam array. The target gain drops considerably from the 0{degree} published values because of this finite angle. The assumed one-sided irradiation reduces the number of bending magnets. A 350-MJ yield might be achieved with a 6-MJ driver (gain of 58) (nominal 1000 MWe net power with a repetition rate of 8 Hz). For either lower repetition rate or lower gain the yield must be increased by increasing the driver energy. The beam ports are protected from radiation by an array of vertical and horizontal, neutronically-thick, liquid jets. 6 refs., 7 figs.

Heavy ion beam and reactor chamber interface design

Plasma irradiation experiment on the metal pebble flow in the TPDsheet-U

The performance (cost/kWe and efficiency) of generic compact fusion advanced Rankine (CFARII) power conversion is investigated for various working fluids, operating temperatures and pressures, and thermal power levels. Good CFARII performance is found for a remarkably broad range of materials, temperatures, pressures and power levels, which gives considerable flexibility to future design studies which may apply CFARII energy conversion to specific fusion energy sources such as ICF (inertial confinement fusion), MICF, and Mini-PACER. Specifically, in future designs that would apply CFARII power conversion to particular reactor designs, there is considerable flexibility to choose combinations of materials and operating conditions to accommodate other reactor design constraints, and therefore, a greater chance of finding a combination that meets all engineering and physics constraints while still achieving attractive efficiency and low cost. The economic robustness of CFARII is directly related to its extremely high mass power density, and the high efficiency ( eta /sub MHD/>or approximately=50%) of CFARII relative to previous MHD (magnetohydrodynamic) generator design and experiments is due to the higher temperatures of 1 to 3 eV made possible by direct coupling of nuclear energy release to the working fluid material. >

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Compact fusion advanced Rankine (CFARII) power cycle-operating regimes

The Neutralized Drift Compression eXperiment (NDCX-II), a newly completed accelerator facility at LBNL, will produce nanosecond Li ion beam bunchs at ~1.2 MeV energy for volumetric heating of thin foils. Using specialized acceleration voltage waveforms, a beam bunch is compressed >500-fold longitudinally to ns time scale. Planned experiments on NDCX-II to study warm dense matter include: measuring dE/dx, equation of state, conductivity, and shock generation. Theoretically, we have studied transverse and longitudinal beam compression; transverse gradients and profile shapes on beam-plasma instabilities; nonlinear effects of beamplasma instabilities on beam current neutralization; and beam “wobbler” as a beam smoothing technique. The HIF X-target design was improved to achieve a gain of 300. It uses multiple heavy ion beams to illuminate the target axially from only one side such that the fuel can be compressed and ignited at the X-vertex, with negligible RT growth thus providing a central clean DT ignition zone. 1. The Heavy Ion Beam-Driven IFE Approach and Development The Heavy Ion Fusion approach for IFE is promising because its attributes are well matched to IFE driver requirements. Accelerators routinely demonstrate repetition rates higher than the required 5-10 Hz range, and efficiencies up to 40% are projected. Final ion beam optics (facing the target) is robust because the focusing magnet is shielded from line-of-sight radiation or debris from the targets [1]. Heavy ions are found to strip minimally in vapor of molten FLiBe, thus enabling the use of liquid protection of the inner chamber wall. With such protection, chamber materials would enjoy a thirty-year lifetime and qualify for shallow burial when the power plant is decommissioned. In comparison to photon beams, heavy ions have a stopping range exceeding the mean-freepath of thermal x-rays, so that they can penetrate and deposit most of their energy deep inside the targets. This implies that no “entrance hole” is needed for indirect-driven targets, and likewise volumetric deposition is possible for directly driven targets. Second, the range of heavy ion beams in dense plasma targets is determined primarily by Coulomb collisions with the target electrons. The ions slow down with minimal side-scattering, and their energy deposition has a pronounced peak in the rate of energy loss (dE/dx) that increases with the beam ion charge state, Z. Third, velocity-ramping of heavy ion beams that interact with dense target plasmas may suppress or reduce beam plasma instabilities that could otherwise generate unwanted hot electrons and cause target preheat. These unique properties make heavy ion beams an excellent choice for studies of high energy density physics and fusion target physics that can eventually lead to the design of very attractive high-gain HIF targets.

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Summary of Progress in U.S. Heavy Ion Fusion Science Research

The HYLIFE-II inertial fusion power plant design study uses a liquid fall, in the form of jets, to protect the first structural wall from neutron damage, x rays, and blast to provide a 30-y lifetime. HYLIFE-I used liquid lithium. HYLIFE-II avoids the fire hazard of lithium by using a molten salt composed of fluorine, lithium, and beryllium (Li 2BeF4) called" Flibe". Access for heavy-ion beams is provided. Calculations for assumed heavy-ion beam performance show a nominal gain of 70 at 5 MJ, producing 350 MJ, about 5.2 times less yield than the 1.8 GJ from a driver energy of 4.5 MJ with gain of 400 for HYLIFE-I. The nominal 1 gigawatt electrical (GWe) of power can be maintained by increasing the repetition rate by a factor of about 5.2, from 1.5 to 8 Hz. A higher repetition rate requires faster re-establishment of the jets after a shot, which can be accomplished in part by decreasing the jet fall height and increasing the jet flow velocity. Multiple chambers may be required. In addition, although not adequately considered for HYLIFE-I, there is undoubtedly liquid splash that must be forcibly cleared because gravity is too slow, especially at high repetition rates. Splash removal can be accomplished by either pulsed or oscillating jet flows. The cost of electricity is estimated to be 0.09 $/kWh in constant 1988 dollars, about twice that offuture coal and light-water-reactor nuclear power. The driver beam cost is about one-halfthe total cost.

Hylife-ii inertial confinement fusion power plant design

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Ralph W. Moir

Papers

Hylife-ii inertial confinement fusion power plant design

Hylife-II inertial confinement fusion power plant design