ICF Driver Research Articles

Microscopic characterization of bulk damage resistance of DKDP nonlinear crystals

DKDP nonlinear crystals in ICF drivers are susceptible to laser-induced bulk damage, therefore it is significant important to characterize bulk damage in order to prevent, reduce, and/or manage bulk damage. This work presents a method evaluating the bulk damage resistance of DKDP crystals, directly providing pinpoints density, size distribution, and three-dimensional (3D) distribution of pinpoints. This technique can be used for characterizing the crystal inhomogeneity, and the result demonstrates that crystal inhomogeneity have a strong and negligible impact on pinpoints density and the size distribution of pinpoints respectively, suggesting two distinct energy deposition mechanisms governing the damage initiation and the growth of the pinpoints.

Fast heating of fuel assembled in a spherical deuterated polystyrene shell target by counter-irradiating tailored laser pulses delivered by a HAMA 1 Hz ICF driver

Fast heating is a method of heating an assembled high-density plasma into a hot state by irradiating it with short-duration (sub-picosecond), high-intensity ( W ) laser pulses before the plasma expands and dissolves hydrodynamically. In this paper, we present detailed experimental results of fast heating fuel assembled in a spherical deuterated polystyrene shell target of 500 m diameter and 7 μm thickness with counterbeam illumination by using a HAMA 1 Hz, 5.9 J inertial confinement fusion laser driver with pulse tailoring. These tailored pulses contain three pulses in sequence: a ‘foot’ pulse of 2.4 J/25 ns, a ‘spike’ pulse of 0.5 J/300 ps and a ‘heater’ pulse of 0.4 J/110 fs; these pulses are designed to assemble the fuel and heat it. By varying the energy of the foot pulse, we find that fast heating the fuel is achieved only if the fuel is weakly ablated by the foot pulse and then shock-assembled by the spike pulse into the target centre so that the heater pulse can access the fuel with a focal intensity greater than W . Without a foot pulse, the heater pulse contributes to assembling the fuel. For higher foot-pulse energies, the heater pulse drives a hydrodynamic motion with speeds of the order 107 cm with intensities of the order W , resulting in re-assembling and additional heating of the pre-assembled fuel. Once a shock-assembled core is achieved at the target centre, we succeed qualitatively in fast heating the core for shots in sequence with variations of laser energy within 18%. The coupling efficiency from the heating laser to the core is inferred to be % in total: % for the ionized bulk electrons and % for the bulk ions. The fusion neutron spectrum detected on the laser axis exhibits peaks at 1.0 MeV, 1.7 MeV and 3.8 MeV. These peaks are attributed to the N and He reactions induced by counterpropagating fast deuterons accelerated by the photon pressure of the heating pulses.

The Numerical Simulation and Experiment on Temperature Field in ICF Driver’s Target Building

The spatial temperature distribution in the target range of the ICF driver is one of the key factors, which affects the precision optical components and equipment for normal operation. Application of the basic theory of heat transfer, this paper has discussed the fluid motion mathematical model in ICF driver middle target range. With the aid of finite element analysis software FLUENT, the temperature Numerical Analysis Model has been established. In accordance with assuming the numerical simulation boundary condition, spatial temperature field distribution in the target range intermediate level has calculated. The results indicate that the target range intermediate level temperature field is uniform basically. The temperature fluctuation scope is in a tiny range around 23°C about in the entire space. Although the maximum gradient of temperature achieves 1.2°C in existence heat source region, it is in the range of temperature indicators. This indicates that the present HVAC system can satisfy the request. By analyzing, the results of numerical analysis are in good agreement with experimental results, because the error is only 0.2%.

用于ICF驱动器谐波分离的亚波长光栅优化设计

用于ICF驱动器谐波分离的亚波长光栅优化设计

惯性约束聚变靶场编组站大口径光学元件的热变形分析

惯性约束聚变靶场编组站大口径光学元件的热变形分析

Measurements of source divergence angle of pulsed nitrogen ion beams

Singly or doubly ionized nitrogen beams, including a small part of oxygen ion beams, were extracted from a cryogenic diode with N 2O ice on the anode surface. The nominal diode voltage was 100–360 kV, and the peak ion current was 300 A. With a one-dimensional arrayed pinhole camera with 5 pinholes, very small divergence angle at the beam source was measured. Although, we used a very rough apparatus (not being as sophisticated as the modern version), the absolute value (measured) of the divergence angle was 5–6 mrad. This value was small enough for us to recommend this beam as one of the candidates for the future ICF or IFE driver. With the same apparatus, we observed a rather large angle of 25–60 mrad for the proton beam in our former experiment. These results indicated that this kind of medium-mass ion beam must be investigated in more detail to make clear the potential of the beam. We also developed a Thomson ion spectometer with a CCD detector, which could be applicable to the above ion beams. The energy spectrum of a proton beam was measured as the early stage preparation of the spectometer development.

Low-pressure pseudospark switches for ICF pulsed power

Hollow-electrode pseudospark switches are gas-filled, low-pressure, high-current plasma switches which are based on cold cathode emission. They have the capability to satisfy at least a part of switching requirements for different applications in ICF drivers. The main purpose of the submitted paper is therefore to discuss the following realistic ways for the use of pseudospark switches. There are intense international activities aimed at investigating different approaches for the ignition of an ICF capsule. Most of these efforts utilize lasers of varying wavelengths to deliver the energy to initiate the ablation of the target, the compression and ignition of the fuel, and the propagation of the fusion burn. One alternative to this scheme is to provide the drive energy in form of a light ion beam produced by an efficient pulse power accelerator. A related method uses beams of heavy ion beams from high intensity versions of traditional high-energy accelerators. Dependent on the ICF driver for the power conditioning unit (PCU) arise totally different demands. These extremely different requirements mainly rely on the very specific character of the load. Flashlamps, pumping high power lasers represent a non-linear, low-impedance load. Relatively low switching voltage is necessary, but a high charge-transfer capability. Induction cells or magnetic compression units have a high impedance. Consequently high voltage (up to several 100 kV) is required to feed the energy in Marx modules and the following voltage adders produce megavolt voltages, which determines likewise the specific data of the used switch.

Pulsed, high-current and iron-free ion optical systems for beam transport in ICF driver accelerators

To drive ICF implosion targets, pulsed ion beams will be used. Therefore the corresponding beam guiding systems do not have to provide the magnetic flux density in a d.c. mode, but only in a pulsed mode on a short time scale. The operation of steady-state magnetic fields in accelerator-based ICF driver scenarios as outlinede.g. in the HIBALL reactor study would lead to a waste of a significant fraction of the produced electrical energy. We suggest making use of pulsed, high-current and iron-free magnetic lenses for this purpose. In a number of experiments at the UNILAC accelerator at GSI-Darmstadt, pulsed quadrupole lenses have already proven their ability and reliability to focus and transport highly energetic heavy-ion beams.

The NIKE KrF laser fusion facility

NIKE is a second generation high power KrF laser now under construction at the Naval Research Laboratory. The project is a collaborative effort between NRL and Los Alamos National Laboratory. NIKE is designed to deliver more than 2 kJ of energy to target in a 600-μm focal spot and a 4-ns pulse duration. Echelon free induced spatial incoherence (ISI) will be used to produce uniform target illumination. Flat targets will be ablatively accelerated to study both Rayleigh-Taylor and parametric instabilities. These results will have direct implications to direct-drive inertial confinement fusion for commercial energy applications. Reliable operation of a high power KrF laser is also an important goal of the NIKE laser, with the objective of 1000 target shots per year. This would be an important step in the development of the KrF laser as an ICF driver. NIKE is cheduled to begin target experiments in early 1994. If successful, these experiments will provide a technical basis to proceed with construction of an ignition facility.

Heavy Ion Induction Linac Drivers for Inertial Confinement Fusion

Intense beams of high energy heavy ions (e.g., 10 GeV Hg) are an attractive option for an ICF driver because of their favorable energy deposition characteristics. The accelerator systems to produce...

Nuclear Pumped Laser for Next Step ICF Driver

A conceptual design for an alternative laser driver for the Laboratory Microfusion Facility (LMF) is presented. A pulsed fission reactor is used to excite an oxygen-iodine laser in this study based on preliminary data on nuclear pumping of O/sub 2/(/sup 1/..delta..). Although a working NPL of this specific type has not yet been assembled, the authors believe this concept holds great potential both as a test facility driver and as a future power reactor.

Spin polarized ICF targets

Parallel spin polarization of D and T increases the fusion cross-section by 50%, which may lead to a reduction in the ICF driver energy requirement by a factor of about two. The non-isotropic emission of fusion products may help in prolonging the life of the sensitive parts of the ICF reactor system. After briefly explaining the basic principles responsible for these effects, the paper examines the feasibility of polarizing solid D-T targets. It is shown that this may be accomplished with the technology available at present, provided pure D-T is available. The spin polarized ICF target will not experience any noticeable depolarization during the compression and burn phases. This is shown on the example of the HIBALL target.

Future Developments and Applications of KrF Laser-Fusion Systems

Two different types of KrF lasers currently being analyzed as potential laser-fusion drivers: large electron-beam (e-beam)- pumped amplifiers using pure optical multiplexing for pulse compression and small e-beam sustained discharge lasers using a hybrid pulse compression technique. Both types of KrF lasers appear able to satisfy all of the requirements for commercial-applications ICF drivers, including cost, efficiency, pulse shaping, energy scaling, repetition rate, reliability, and target coupling. The KrF driver can effectively operate at efficiencies > 10% and can contribute < 10 mill/kWh to the cost of electric power production, with the total estimated cost of electricity from either KrF laser system being comparable (25 to 50 mill/kWh, 1985 dollars) with the cost from other methods of electric power production. The Aurora facility is described.

Atomic data for highly charged ions: Applications to X-ray laser design and thermonuclear fusion

A detailed understanding of a myriad of atomic processes is proving important for the development of short wavelength lasers and to the achievement of controlled thermonuclear fusion. A brief overview of some X-ray laser design issues is presented along with a discussion of relevant atomic data needs. Special attention is given to the need for experimental verification of rate coefficient data which are important for determining laser kinetics. Approaches to magnetic and inertial confinement fusion are reviewed with emphasis on atomic processes affecting both fuel burn and plasma diagnostics. Recent advances in the development of high power ICF drivers, both lasers and particle beams, are shown to suggest new areas of research involving very highly charged ions in dense hot plasmas.

Conceptual Design of a Large E-Beam-Pumped KrF Laser for ICF Commercial Applications

Two types of KrF lasers appear attractive as a driver for an ICF electric power plant. The original concept uses large electron-beam-pumped amplifiers and pure angular multiplexing to deliver short, shaped pulses to the target. A recently conceived alternate concept uses many small, long-pulse e-beam sustained discharge lasers which transfer their energy through the forward Raman process to a multiplexed set of beams to deliver the energy to target. Preliminary comparisons of the two systems indicate that the original concept has both a lower cost and a lower system efficiency, and both concepts appear to be nearly equally attractive as an ICF driver for an electric power plant. This paper examines a 4.8 MJ, 5 Hz KrF laser system designed using the original concept. The laser uses 24 main amplifiers arranged in eight sets of three amplifiers each. This layout optimizes both the optical system and the gas flow system, and uses a simple target illumination scheme that provides neutron shielding to allow hands-on maintenance in the laser hall.

Properties of a KrF laser with atmospheric-pressure Kr-rich mixture pumped by an electron beam

Atmospheric pressure operation of a KrF laser is suitable for large-aperture laser modules in which several technical limitations on the ICF driver design are overcome by the use of aerodynamic windows instead of the conventional solid optical windows. We experimentally studied atmospheric-pressure operation of the KrF laser pumped by 50-ns electron beams. For a 1-atm mixture of Kr and F2 without diluent, a specific output energy of 4.2 J/1 was obtained with an intrinsic efficiency of 5%, which was comparable to that from normal 10% Kr mixture. According to the results of fluorescence measurements, a large amount of Kr2F* is formed via three-body collisional quenching by high-concentration Kr even in the atmospheric-pressure mixture. Code calculations indicate that a higher excitation rate improves the intrinsic efficiency by reducing three-body quenching especially in Kr-rich mixtures, and that a specific energy in excess of 10 J/1 is realizable.

Numerical Studies of High Current Beam Compression in Heavy Ion Fusion

The process of longitudinal compression of a drifting heavy ion pulse to be used as an ICF driver is examined with the aid of particle simulation. Space charge forces play a vital role in halting compression before the final focus lens system is reached. This must take place with minimal growth of transverse emittance and momentum spread. Of particular concern are the distortion of longitudinal phase space by the rounded transverse profile of the longitudinal self-electric field. For application as an ICF reactor driver, a heavy-ion beam pulse must be longitudinally compressed by 1 to 2 orders of magnitude to achieve the peak power required to ignite a target. This process, among others, will be tested in a facility known as the ''High-Temperature Experiment'' in heavy-ion fusion. Beam compression is a critical element of an accelerator for heavy-ion fusion; it occurs primarily after the main phase of acceleration and before final focus onto target. Here we examine the compression of a drifting heavy-ion pulse with the aid of particle simulations. We describe initial theoretical results for an in-principle solution to this problem. Further refinements including integration into a complete driver system are necessary before the least costly solution can bemore » chosen.« less

Precision Intense Particle Beam Accelerators Using in-Situ Tuning Techniques

Modern superpower accelerators are capable of up to 15 MeV and over 10 TW in 100ns pulses using oil or water insulated pulselines. Previous pulseline accelerators have generally had to accept a pulse shape somewhat different than the design based on computer simulation (due to unpredictable load dynamics in many cases). This paper presents an iterative perturbation theory approach to accelerator design. The approach utilizes a transmission line whose taper can be adjusted in-situ, thereby permitting corrections to the voltage waveform during operation with the actual dynamic particle beam load. Two successful examples of this iterative perturbation theory approach are: (1) the achievement of a ramped voltage pulse to bunch a light ion beam ICF driver. The ORCA-I 1 MeV - 200ns accelerator with ± 1% precision has been tested and is now used in low emittance light ion beam ICF driver research, (2) the suppression of voltage droop in a field emission diode with plasma induced gap closure. A precise (± 1%) voltage plateau is achieved for use in high rep-rate generators for pre-ionizing high energy gas laser chambers.

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.