Inertial Fusion Energy Driver Research Articles

2-MV electrostatic quadrupole injector for heavy-ion fusion

High current and low emittance are principal requirements for heavy-ion injection into a linac driver for inertial fusion energy. An electrostatic quadrupole injector is capable of providing these high charge density and low emittance beams. We have modified the existing 2-MV injector to reduce beam emittance and to double the pulse length. We characterize the beam delivered by the modified injector to the High Current Transport Experiment and the effects of finite rise time of the extraction voltage pulse in the diode on the beam head. We demonstrate techniques for mitigating aberrations and reducing beam emittance growth in the injector.

Development of Diode-Pumped Solid-State Laser HALNA for Fusion Reactor Driver

The diode-pumped slab laser for inertial fusion energy driver has been demonstrated, which produces the 1053-nm output energy of 10 J at 10 Hz. The glass slab laser amplifier has been pumped by quasi-CW 290 kW AlGaAs laser-diode arrays at 803 nm. The optical system can compensate for thermal effects by use of zig-zag optical propagation, image-relayed telescope, and 45° Faraday rotator. The output energy of 10.6 J at 1 Hz with the optical to optical conversion efficiency of 19.9% has been successfully obtained. Also the 10 Hz operation has been performed with a 5.1 J output eneregy.

Design and Performance of a Diode-Pumped Nd:Silica-Phosphate Glass Zig-Zag Slab Laser Amplifier for Inertial Fusion Energy

A high-energy, high beam quality, diode-pumped 1053-nm Nd:silica-phosphate glass laser amplifier has been designed, constructed and tested in order to verify the conceptual design of HALNA (high average-power laser for nuclear-fusion application): a diode-pumped solid-state laser based on a water-cooled zig-zag slab optical geometry. This amplifier yields an 8.5 J output energy per pulse at 0.5 Hz in a 20 ns pulse of two times the diffraction limit beam quality with an optical-to-optical conversion efficiency of 10.9%. This is the first demonstration of a diode-pumped solid-state laser amplifier for the inertial fusion energy (IFE) driver. The detailed considerations on the optical and thermal designs of the novel amplifier architecture are discussed. The experimental results revealed that the primary requirements for the IFE driver, such as diode-pumping, energy storage and extraction efficiencies, and beam quality have been fulfilled.

Transport of electron beams and stability of optical windows in high-power e-beam-pumped krypton fluoride lasers

Two of the key issues of a krypton fluoride (KrF) laser driver for inertial fusion energy are the development of long life, high transparency pressure foils (to isolate vacuum in the electron beam diode from a working gas in the laser chamber), and the development of durable, stable, optical windows. Both of these problems have been studied on the single-pulse e-beam-pumped KrF laser installation GARPUN. We have measured the transport of electron beams (300 keV, 50 kA, 100 ns, 10 × 100 cm) through aluminum-beryllium and titanium foils and compared them with Monte Carlo numerical calculations. It was shown that 50-μm thickness Al-Be and 20-μm Ti foils had equal transmittance. However, in contrast to Ti foil, whose surface was strongly etched by fluorine, no surface modification nor fatal damages were observed for Al-Be foils after ∼1000 laser shots and protracted fluorine exposure. We also measured the 8% reduction in the transmission of CaF2 windows under irradiation by scattered electrons when they were set at 8.5 cm apart from the e-beam-pumped region. However an applied magnetic field of ∼0.1 T significantly reduced electron scattering both across and along the laser cell at typical pumping conditions with 1.5 atm pressure working gas. Thus the e-beam-induced absorption of laser radiation in optical windows might be fully eliminated in an e-beam-pumping scheme with magnetic field guiding.

Review of light-ion driver development for inertial fusion energy

The concept of a light ion beam driver for Inertial Fusion Energy (IFE) is based on multi-terawatt, multi-megavolt pulsed power generators, two-stage ion acceleration and charge neutralised transport. In this paper we discuss the present status for each of these components and identify the main issues for research. Only modest extrapolations from presently available technologies seem necessary for the high voltage pulse generator. The greatest challenge of this approach is the accelerator, which will consist of two stages, the injector and the post-accelerator. Large progress has been made in understanding the physical phenomena occurring in the injector gap. This progress has become possible by new sophisticated diagnostics that allowed detailed temporally and spatially resolved measurements of field and particle densities in the acceleration gap and by relativistic fully electromagnetic PIC-simulation tools, that stimulated analytic models. The conclusions drawn from these studies, namely limiting the ion current density to small enhancements to reduce the beam divergence need still to be verified experimentally. Systematic experimental research on post-acceleration at high power and voltage must aim at a complete understanding of instabilities coupling from the injector to the post-accelerator and at limiting voltages and barriers for the extraction of unwanted ions from plasmas at the injection side. Ultimately the light ion approach requires rep-rateable large area ion sources with ion masses greater than 1 and particle energies around 30 MeV. Although different cleaning protocols were able to reduce the amount of parasitic ions in the Li beam from a LiF field emission source the achievements are still insufficient. A field of common interest between light and heavy ion beam driven fusion is beam transport from the accelerator to the target. Supposedly the most favourable concept for both approaches is self-pinched transport. Experimental evidence for self-pinched transport has recently been achieved in an experiment at NRL. Further experiments are needed to determine the dynamics and magnitude of net current formation, the efficiency of transport and the effect of bunching.

A conceptual design of a high-efficiency rep-rated pulsed power system for KrF laser drivers of inertial fusion energy

A conceptual design of a high efficiency, high repetition-rated (rep-rated) pulsed power system for an electron-beam (e-beam) pumped KrF laser driver for inertial fusion energy (IFE) is presented. The proposed pulsed power circuit incorporates linear induction voltage adders to charge pulse forming lines for the generation of 900 kV, 260 ns e-beamsat several Hz. This rep-rated power system meets the pulsed power requirements of the future IFE drivers that necessitate high amplifier efficiency as well as high laser energy.

Conceptual Design of Laser-Diode-Pumped Water-Cooled Nd:Glass Slab Laser Driver for Inertial Fusion Energy.

We have proposed and designed a laser-diode-pumped laser driver for inertial fusion energy (IFE) which consists of water-cooled zig-zag path Nd: glass (HAP-4) slab amplifiers. A driver module was designed under the several operational constraints and has 10 kJ total output energy at 351 nm and operates at 12 Hz with 9-12% overall efficiency. The laser driver producing 4 MJ blue output for IFE will consist of 400 modules

The role of the National Ignition Facility in energy production from inertial fusion

The 1993 declassification of virtually all inertial confinement fusion (ICF) target information relevant to fusion energy development, and demonstrable successes in the physics and technology related to ICF, have laid the ground work for a development plan for an Inertial Fusion Energy (IFE) programme. The ICF programme, funded by the Defense Program in the USA, has clearly demonstrated there is sufficient confidence in ignition and gain to proceed with construction of the National Ignition Facility, which will test the detailed physics of targets suitable for IFE. In September 1998, the facility was about 40% complete and on schedule and within budget for completion in 2003. X–ray–drive ignition is planned for 2007, followed by direct–drive ignition experiments. The other major elements of an IFE development programme, namely, driver, target factory, and target chamber developments can be investigated separately in affordable programmes. Although much work remains, there are concepts for adequately high driver efficiency and target gain, target cost and target chamber survivability to make an exploratory programme in IFE attractive.

Conceptual design of a laser-diode-pumped Nd:glass slab laser driver for inertial fusion energy

We have proposed and designed a laser-diode-pumped laser driver for inertial fusion energy (IFE) which consists of water-cooled zig-zag path Nd:glass slab amplifiers. A driver module was designed under the several operational constraints and has 10 kJ total output energy at 351 nm and operates at 12 Hz with 10.4% overall efficiency. The laser driver producing 4 MJ blue output for IFE will consist of 400 modules.

A rep rate KrF system to address issues relevant to inertial fusion energy

We present a conceptual design for a rep-rate krypton-fluoride (KrF) laser facility that will allow us to develop the technologies required for an inertial fusion energy (IFE) driver. Most of these have been partially developed elsewhere, but they have not been combined in a single integrated test. The facility we are evaluating would be modest in size (about 400 J laser output) and would run at 5 Hz. If this facility was built it would significantly improve our ability to assess the potential of direct drive KrF.

Driver Technology for Inertial Fusion Research Introduction. 2. Inertial Fusion Driver development and Future Prospects in the United States.

A brief review is given of the requirements of inertial fusion energy drivers and their status and prospects in the U.S. Drivers based on lasers (diode-pumped solid-state and KrF) and heavy ions are discussed.

Systems Modeling and Analysis of Heavy Ion Drivers for Inertial Fusion Energy

A computer model for systems analysis of heavy ion drivers based on induction linac technology has been used to evaluate driver designs for inertial fusion energy (IFE). Design parameters and estimated costs have been determined for drivers with: various ions; different charge states; different front-end designs; with and without beam merging; and various pulse compression and acceleration schedules. We have examined the sensitivity of the results to variations in component cost assumptions, design constraints, and selected design parameters.

The solenoidal transport option for IFE drivers and a near-term research facility

Solenoidal magnets have been used as the beam transport system in all high current electron induction accelerators that have been built in the past several decades. They have also been considered for the front end transport system for heavy ion accelerators for Inertial Fusion Energy drivers, but this option has received very little attention in recent years. The analysis reported here was stimulated mainly by the recent effort to define an affordable “Integrated Research Experiment” (IRE) that can meet the near-term needs of the IFE program. Solenoidal transport has a very favorable scaling as the particle mass and kinetic energy are decreased (the main reason why it is preferred for electrons in the region below 50 MeV). A central contention of this paper is that a “front end” design based on solenoidal transport can form the basis of a significantly different overall driver architecture. With a solenoidal front end, we can consider drivers with a much smaller number of beam channels at low energy, and without beam combining. A fast-running code (named SALT) has been developed at LBNL to study the axisymmetric dynamics of a particle beam transported through a sequence of solenoids. The beam is modelled as a set of ringlets, with radius and momentum traced in the axial coordinate. Emittance growth, envelope matching, and phase space evolution are treated. Initial applications to IRE scale parameters are described.

Elise plans and progress

Elise is a heavy-ion induction linear accelerator that will demonstrate beam manipulations required in a driver for inertial fusion energy. With a line charge density similar to that of heavy-ions drivers, Elise will accelerate a beam pulse (duration of 1 μs or more) of K + ions from an initial energy of 2 MeV to a final energy 5 MeV or more. In the present design, the Elise electrostatic quadrupoles (ESQs) will have an aperture of radius 2.33 cm operating at ± 59 kV. The half-lattice periods range from 21 to 31 cm. The entire machine will be approximately 30 m long, half of which is the induction accelerator with the remaining half being the injector (including the Marx generator) and the matching section. Elise will be built in a way that allows future expansion into the full Induction Linear Accelerator Systems Experiments (ILSE) configuration, so it will have an array of four ESQ focusing channels capable of transporting up to a total of 3.2 A of beam current. Elise will also have an active alignment system with an alignment tolerance of less than 0.1 mm. Initially, only one beam channel will be used during nominal Elise operation. At the currently expected funding rate, the construction time will be 4.75 years, with FY95 being an extra year for research and development before construction. Total project cost is estimated to be US$25.9m, including contingency costs.

A diode pumped solid state laser driver for inertial fusion energy

A comprehensive conceptual design for a diode pumped solid state laser (DPSSL) as a driver for an inertial fusion energy (IFE) power plant is presented. This design is based on recent technical advances that offer potential solutions to difficulties previously associated with the use of a laser for IFE applications. The design was selected by using a systems analysis code that optimizes a DPSSL configuration by minimizing the calculated cost of electricity (COE). The code contains the significant physics relevant to the DPSSL driver, but treats the target chamber and balance of plant costs generically using scaling relations published for the Sombrero KrF laser concept. The authors describe the physics incorporated in the code, predict DPSSL performance and its variations with changes in the major parameters, discuss IFE economics and technical risk, and identify the high leverage development efforts that can make DPSSL driven IFE plants more economically competitive. It is believed that this study is a significant advance over previous conceptual studies of DPSSLs for IFE because it incorporates a new cost effective gain medium, applies a potential solution to the `final optics` problem, and considers the laser physics in substantially greater detail. The result is the introduction of an option for an IFE driver that has relatively low development costs and that builds upon the mature laser technology base already developed for Nova and being developed for the proposed National Ignition Facility. The baseline design of the paper has a product of laser efficiency and target gain of ηG~6.6 and a COE of 8.6 cents/kW.h for a 1 GW(e) plant with a target gain of 76 at 3.7 MJ. Higher ηG(≳11) and lower COEs (≲6.6 cents/kW.h) can be achieved with target gains twice as high

5351007 Superconducting magnetic resonance probe coil

Solenoidal magnets have been used as the beam transport system in all high current electron induction accelerators that have been built in the past several decades. They have also been considered for the front end transport system for heavy ion accelerators for Inertial Fusion Energy drivers, but this option has received very little attention in recent years. The analysis reported here was stimulated mainly by the recent effort to define an affordable “Integrated Research Experiment” (IRE) that can meet the near-term needs of the IFE program. Solenoidal transport has a very favorable scaling as the particle mass and kinetic energy are decreased (the main reason why it is preferred for electrons in the region below 50 MeV). A central contention of this paper is that a “front end” design based on solenoidal transport can form the basis of a significantly different overall driver architecture. With a solenoidal front end, we can consider drivers with a much smaller number of beam channels at low energy, and without beam combining. A fast-running code (named SALT) has been developed at LBNL to study the axisymmetric dynamics of a particle beam transported through a sequence of solenoids. The beam is modelled as a set of ringlets, with radius and momentum traced in the axial coordinate. Emittance growth, envelope matching, and phase space evolution are treated. Initial applications to IRE scale parameters are described.

ILSE Heavy Ion Accelerator

Lawrence Berkeley Laboratory (LBL) and Lawrence Livermore National Laboratory (LLNL) propose to build at LBL the Induction Linac Systems Experiments (ILSE), the next logical step towards the eventual goal of a heavy-ion induction accelerator powerful enough to implode or {open_quotes}drive{close_quotes} inertial-confinement fusion targets. ILSE is a 10 MeV heavy ion accelerator system that will establish the beam dynamics understanding required for a heavy ion IFE driver. Space charge dominated beams with driver scale dimensions will be employed. ILSE, although much smaller than a driver, will be the first experiment at full driver scale in several important parameters. Most notable among these are line charge density and beam cross section. Nearly all accelerator components and beam manipulations needed for an inertial fusion energy (IFE) driver will be tested. The ILSE accelerator and research program will permit experimental study of those beam manipulations required of an induction linac inertial fusion driver that have not been tested sufficiently in previous experiments. ILSE is also an important step in driver technology development for heavy ion drivers.

Design descriptions of the Prometheus-L and -H inertial fusion energy drivers

Abstract Two innovative drivers have been designed for a prototype 1000 MW thermonuclear power plant planned for operation early in the next century. The Prometheus-L driver is a 4 MJ KrF master oscillator power amplifier laser system designed to operate at a 5.6 Hz repetition rate. Output pulses from the KrF master oscillator are synchronized with the pulsed-power excitation of the KrF power amplifiers and the launching of the inertial fusion energy (IFE) deuterium/tritium targets. The Prometheus-L laser architecture features 960 5 kJ electric discharge KrF power amplifiers pumping 60 crossed stimulated rotational Raman scattering H 2 amplifiers serving as beam accumulators. Pulse compression of the 60 accumulator beams is accomplished in 60 chirped, self-seeded SF 6 stimulated Brillouin scattering pulse compressors. Grazing incidence metal focusing mirrors minimize back-streaming radiation damage from the target chamber. This architecture permits the laser driver to deliver spectrally broad-band, temporally complex optical pulses in 60 beam lines to implode the direct-drive IFE targets within a 5 m radius target chamber. The Prometheus-H driver is a 7.8 MJ 4 GeV Pb ++ heavy ion (HI) inertial fusion energy system designed to operate at a 3.5 He repetition rate. The HI driver design is based on a short, ramped gradient, 5 MeV accelerator, followed by a longer, 2 km constant gradient, single beam linear accelerator operated in a 50 kHz burst mode to generate sequentially 18 4 GeV beamlets. A two-sided irradiation geometry was developed for indirect-drive HI targets. Six beamlets are used for the 45 ns precursor HI pulses stored in two superconducting storage rings, 12 superconducting storage rings accumulate the 12 main beamlets, with a final buncher generating the 8 ns HI pulses which arrive at the target chamber simultaneously. Final focusing is accomplished with large aperture triplet focusing magnets through Pb-vapor neutralization cells to reduce the effect of space charge, ballistically focusing onto two Pb stripping jets to create self-pinched Pb +82 beams which propagate along two preformed channels through two small openings in the HI target chamber blanket.

Application of FEL to solid state laser pumping for inertial fusion energy driver

We discuss here a FEL application to pump a solid state laser in order to use it as an inertial fusion energy driver. There is a possibility that this method may meet the requirements of cost, efficiency, repetition rate and lifetime, which are essential issues for an energy driver of the IFE commercial reactor.

Theoretical evaluation of electron-beam-excited KrF lasers using argon-free mixtures of one atmosphere

The output performance of the electron-beam-excited KrF laser operating at one atmosphere is theoretically analyzed because the KrF laser at one atmosphere can greatly reduce the design constraints on the large laser windows and the electron-beam pressure foils in a huge laser system as the inertial confinement fusion energy driver. The KrF laser using the atmospheric pressure, argon-free laser mixture is found to operate with an intrinsic laser efficiency as high as that of high-pressure, aregon-diluted mixtures. This is because three-body collisional quenching is not a detrimental energy-loss channel for the atmospheric pressure operation. By using higher excitation rate and shorter excitation pulse width pumping, higher intrinsic laser efficiency than conventional, argon-diluted, high-pressure mixtures is found to be attainable. Moreover, the specific laser energy (28 J/l, for 1-atm Kr/F2 mixtures pumped by an electron beam of 100 ns, 600 keV, and 150 A/cm2) is comparable to that of two-atm, argon-rich laser gas mixtures under the same excitation condition.