Target Fabrication Research Articles

Hydrodynamic instability growth of three-dimensional, “native-roughness” modulations in x-ray driven, spherical implosions at the National Ignition Facility

Hydrodynamic instability growth experiments with three-dimensional (3-D) surface-roughness modulations were performed on plastic (CH) shell spherical implosions at the National Ignition Facility (NIF) [E. M. Campbell, R. Cauble, and B. A. Remington, AIP Conf. Proc. 429, 3 (1998)]. The initial capsule outer-surface roughness was similar to the standard specifications (“native roughness”) used in a majority of implosions on NIF. The experiments included instability growth measurements of the perturbations seeded by the thin membranes (or tents) used to hold the capsules inside the hohlraums. In addition, initial modulations included two divots used as spatial fiducials to determine the convergence in the experiments and to check the accuracy of 3D simulations in calculating growth of known initial perturbations. The instability growth measurements were performed using x-ray, through-foil radiography of one side of the imploding shell, based on time-resolved pinhole imaging. Averaging over 30 similar images significantly increases the signal-to-noise ratio, making possible a comparison with 3-D simulations. At a convergence ratio of ∼3, the measured tent and divot modulations were close to those predicted by 3-D simulations (within ∼15%–20%), while measured 3-D, broadband modulations were ∼3–4 times larger than those simulated based on the growth of the known imposed initial surface modulations. In addition, some of the measured 3-D features in x-ray radiographs did not resemble those characterized on the outer capsule surface before the experiments. One of the hypotheses to explain the results is based on the increased instability amplitudes due to modulations of the oxygen content in the bulk of the capsule. As the target assembly and handling procedures involve exposure to UV light, this can increase the uptake of the oxygen into the capsule, with irregularities in the oxygen seeding hydrodynamic instabilities. These new experimental results have prompted looking for ways to reduce UV light exposure during target fabrication.

Actinide targets for the synthesis of super-heavy elements

Since 2000, six new super-heavy elements with atomic numbers 113 through 118 have been synthesized in hot fusion reactions of 48Ca beams on actinide targets. These target materials, including 242Pu, 244Pu, 243Am, 245Cm, 248Cm, 249Cf, and 249Bk, are available in very limited quantities and require specialized production and processing facilities resident in only a few research centers worldwide. This report describes the production and chemical processing of heavy actinide materials for super-heavy element research, current availabilities of these materials, and related target fabrication techniques. The impact of actinide materials in super-heavy element discovery is reviewed, and strategies for enhancing the production of rare actinides including 249Bk, 251Cf, and 254Es are described.

Recent target development activities at Inter-University Accelerator Centre

The target development laboratory at Inter-University Accelerator Centre (IUAC) is one of the main facilities for the fabrication of nuclear physics targets in India. Vacuum evaporation and cold rolling technique are mainly used for the production of isotopically pure targets at IUAC. Targets of Gd, Pt, W, Mo, Ta, Ni, Ag and Sn have been developed in the form of self-supporting targets and with thin carbon backing. Recent progress in target development laboratory at IUAC will be discussed in the report.

Target fabrication for the POLAR experiment on the Orion laser facility

This article describes the fabrication of a suite of laser targets by the Target Fabrication group in the Central Laser Facility (CLF), STFC Rutherford Appleton Laboratory for the first academic-access experiment on the Orion laser facility (Hopps et al., Appl. Opt. 52, 3597–3601 (2013)) at Atomic Weapons Establishment (AWE). This experiment, part of the POLAR project (Falize et al., Astrophys. Space Sci. 336, 81–85 (2011); Busschaert et al., New J. Phys. 15, 035020 (2013)), studied conditions relevant to the radiation-hydrodynamic processes occurring in a remarkable class of astrophysical star systems known as magnetic cataclysmic variables. A large number of complex fabrication technologies and research and development activities were required to field a total of 80 high-specification targets. Target design and fabrication procedures are described and initial alignment and characterization data are discussed.

Fabrication of self-supporting targets of lead (206,208Pb) using evaporation technique

The self-supporting 206,208Pb enriched isotopic targets of thicknesses varying from 500μg/cm2 to 800μg/cm2 have been prepared in the high vacuum environment at the target laboratory of Inter University Accelerator Centre (IUAC), by using the resistive heating method. The limited amount of the target material, selection of the parting agent, highly oxidizing tendency of the Pb in the atmosphere and the separation of the lead film from the glass slides were the few major challenges faced in the fabrication of the targets. A limited amount of isotopic material (100mg) was utilized for the preparation of more than 20 thick self-supporting targets of 206Pb and 208Pb isotopes. Several attempts were made to overcome the difficulty of finding a suitable parting agent to avoid direct contact of water with the target material are discussed, along with the methods adopted for the fabrication of the targets. Further Energy Dispersive X-ray (EDX) analysis was performed to check the elemental purity of the foils. These targets have been successfully used for several nuclear physics experiments using the neutron detector setup known as National Array of Neutron Detectors (NAND) at IUAC, New Delhi.

Fabrication of calcium-gold and calcium-lead targets for ion beam experiments at TRIUMF ISAC-II

Multi-layer thin targets are vital in low-energy nuclear physics experiments employing the use of accelerated beams. In this paper, we describe the fabrication of encapsulated calcium targets produced by evaporation on gold and lead backings for radioactive beam experiments at TRIUMF’s ISAC-II facility.

Metallurgical considerations for the fabrication of low-enriched uranium dispersion targets with a high density for 99Mo production

It is necessary to develop high-uranium-density targets with low enriched uranium in order to improve 99Mo production efficiency. In order to investigate the use of high density low enriched uranium (LEU) dispersion targets using atomized U–Al alloy powder, U–10 wt% Al and U–20 wt% Al powders were fabricated by centrifugal atomization. Metallurgical reactions between uranium and aluminum during the hot working were investigated in order to minimize changes in the established chemical processes for 99Mo extraction. It is concluded that LEU based dispersion target plates with increased uranium density can be fabricated by controlling the chemical reactions between U and Al in atomized U–Al alloy powders.

Fabrication of 94Zr thin target for recoil distance doppler shift method of lifetime measurement

A thin isotopic 94Zr target of thickness 520μg/cm2 has been prepared for recoil distance Doppler shift method (RDM) lifetime measurement by using an electron beam deposition method on tantalum backing of 3.5mg/cm2 thickness at Inter University Accelerator Center (IUAC), New Delhi. To meet the special requirement of smoothness of surface for RDM lifetime measurement and also to protect the outer layer of 94Zr from peeling off, a very thin layer of gold has been evaporated on a 94Zr target on a specially designed substrate holder. In all, 143mg of 99.6% enriched 94Zr target material was utilized for the fabrication of 94Zr targets. The target has been successfully used in a recent RDM lifetime measurement experiment at IUAC.

Design of a supernova-relevant Rayleigh–Taylor experiment on the National Ignition Facility. I. Planar target design and diagnostics

We present a feasability study for a laser-driven shock experiment on the National Ignition Facility (NIF) to study the evolution of the Rayleigh-Taylor instability in the non-linear regime. The experiment is relevant to the problem of material mixing in core-collapse supernovae and is intended to serve as a stepping stone for more realistic Rayleigh–Taylor experiments using spherical geometry.The radiation hydrodynamics simulations described here are done using the CRASH code and include the actual NIF laser drive. It is shown that the simulations are converged with respect to numerical resolution effects. Small-scale imperfections, such as they might be introduced during the process of target fabrication, are found to have negligible impact, provided that their size is smaller than 1 μm. The simulation results are in excellent agreement with a buoyancy-drag model, and the mix layer width is found to increase at higher drive energies.

Diagnostics of target inhomogeneity and influence of YBCO target oxygen content on properties of HTSC 2G samples fabricated by PLD technique

The pulsed laser deposition (PLD) targets used for HTSC 2G fabrication should be uniform and chemically suitable to make long tapes with reproducible critical properties. We investigated inner density distribution of flat YBCO targets using non-destructive neutron introscopy and tomography techniques. The methods are based on absorption of monochromatic neutron beam which is going through the specimen. In first set of targets we measured variance of material density (up to 10-25%) with maxima density located in central layer of the target body. After updating of target fabrication technology no significant density inhomogeneity were detected. The dependence of critical current of superconducting films with thickness of 300 nm deposited on sapphire substrate with appropriate buffer layers using PLD YBCO targets with various oxygen content was also investigated. Oxygen index of YBCO targets vary from 6.12 to 6.85. No significant influence of target oxygen index on critical current density of fabricated films was detected.

Fabrication of hydroxyapatite targets in radio frequency sputtering for surface modification of titanium dental implants

The purpose of this study was to explore the properties of sintered hydroxyapatite specimens for developing a suitable hydroxyapatite target and a fabrication process for the radio frequency sputtering of implants. Using a compound surface treatment of sand blasting and acid etching followed by hydroxyapatite radio frequency sputtering, this work planned to develop a commercial dental implant system in the near future. First, in addition to producing hydroxyapatite parts using hot isostatic pressing, this study examined the properties of hydroxyapatite parts produced through cold pressing followed by sintering in vacuum and air. The experimental results showed that the index of crystallization, density, and Vickers hardness of the parts sintered in air were more favorable than those of parts sintered in vacuum, and that the parts sintered in vacuum could crack or break. Second, hydroxyapatite sputtering was performed on the hot isostatic pressing–produced and cold pressing–produced targets on titanium dental implant surfaces at power levels of 50 and 90 W. The results showed no cracks in the cold pressing–produced hydroxyapatite targets when the sintering condition was at 1050 °C. By contrast, cracks occurred in the hot isostatic pressing hydroxyapatite targets at a relative density in excess of 93.35%. Observing scanning electron microscopy cross-sectional images revealed that the sputtering deposition rate was approximately 0.456 nm/min at the sputtering power level of 50 W and 1.139 nm/min at 90 W.

Electrothermal instability mitigation by using thick dielectric coatings on magnetically imploded conductors.

Recent experiments on Sandia's Z facility have confirmed simulation predictions of dramatically reduced instability growth in solid metallic rods when thick dielectric coatings are used to mitigate density perturbations arising from an electrothermal instability. These results provide further evidence that the inherent surface roughness as a result of target fabrication is not the dominant seed for the growth of magneto-Rayleigh-Taylor instabilities in liners with carefully machined smooth surfaces, but rather electrothermal instabilities that form early in the electrical current pulse as Joule heating melts and vaporizes the liner surface. These results suggest a new technique for substantially reducing the integral magneto-Rayleigh-Taylor instability growth in magnetically driven implosions, such as cylindrical dynamic material experiments and inertial confinement fusion concepts.

Efficient multi-keV x-ray source generated by nanosecond laser pulse irradiated multi-layer thin foils target

A new target configuration is proposed to generate efficient multi-keV x-ray source using multiple thin foils as x-ray emitters. The target was constructed with several layers of thin foils, which were placed with a specific, optimized spacing. The thin foils are burned though one by one by a nanosecond-long laser pulse, which produced a very large, hot, underdense plasma. One-dimensional radiation hydrodynamic simulations show that the emission region and the multi-keV x-ray flux generated by multi-layer thin foil target are similar to that of the low-density gas or foam target, which is currently a bright multi-keV x-ray source generated by laser heating. Detailed analysis of a range of foil thicknesses showed that a layer-thickness of 0.1 μm is thin enough to generate an efficient multi-keV x-ray source. Additionally, this type of target can be easily manufactured, compared with the complex techniques for fabrication of low-density foam targets. Our preliminary experimental results also verified that the size of multi-keV x-ray emission region could be enhanced significantly by using a multi-layer Ti thin foil target.

HTSC Maglev Systems for IFE Target Transport Applications

A challenge in inertial fusion energy (IFE) research is to deliver the target to the target chamber center at a high repetition rate. Therefore, the problem of target fabrication and delivery is focused on methods that scale to highly repeatable and cost-effective target production. In this paper, we investigate the possibility of using magnetic-levitation (maglev) transport systems for noncontact manipulation, positioning, and delivery of the cryogenic targets. We focus on the development of transport systems based on movement of high-temperature superconductors (HTSC) over a permanent magnet guideway (PMG). Active guidance is achieved using the HTSC ceramics YBa2Cu3O7−X and PMG, where an ordered motion is initiated by a special arrangement of the permanent magnets. At present, significant R&D programs are ongoing in order to fulfill the technical requirements and basic elements of the system’s operation as a maglev target accelerator. We present here the main results of this work along with recent results.

Review of the National Ignition Campaign 2009-2012

The National Ignition Campaign (NIC) was a multi-institution effort established under the National Nuclear Security Administration of DOE in 2005, prior to the completion of the National Ignition Facility (NIF) in 2009. The scope of the NIC was the planning and preparation for and the execution of the first 3 yr of ignition experiments (through the end of September 2012) as well as the development, fielding, qualification, and integration of the wide range of capabilities required for ignition. Besides the operation and optimization of the use of NIF, these capabilities included over 50 optical, x-ray, and nuclear diagnostic systems, target fabrication facilities, experimental platforms, and a wide range of NIF facility infrastructure. The goal of ignition experiments on the NIF is to achieve, for the first time, ignition and thermonuclear burn in the laboratory via inertial confinement fusion and to develop a platform for ignition and high energy density applications on the NIF. The goal of the NIC was to develop and integrate all of the capabilities required for a precision ignition campaign and, if possible, to demonstrate ignition and gain by the end of FY12. The goal of achieving ignition can be divided into three main challenges. The first challenge is defining specifications for the target, laser, and diagnostics with the understanding that not all ignition physics is fully understood and not all material properties are known. The second challenge is designing experiments to systematically remove these uncertainties. The third challenge is translating these experimental results into metrics designed to determine how well the experimental implosions have performed relative to expectations and requirements and to advance those metrics toward the conditions required for ignition. This paper summarizes the approach taken to address these challenges, along with the progress achieved to date and the challenges that remain. At project completion in 2009, NIF lacked almost all the diagnostics and infrastructure required for ignition experiments. About half of the 3 yr period covered in this review was taken up by the effort required to install and performance qualify the equipment and experimental platforms needed for ignition experiments. Ignition on the NIF is a grand challenge undertaking and the results presented here represent a snapshot in time on the path toward that goal. The path forward presented at the end of this review summarizes plans for the Ignition Campaign on the NIF, which were adopted at the end of 2012, as well as some of the key results obtained since the end of the NIC.

ICF流体力学不稳定性实验用柱状激波管的研制

In inertial confinement fusion (ICF) experiments, the surface (interface) roughness and defect of target capsule can lead to hydrodynamic instability when the target capsule is irradiated by high-intensity laser facility. Controlling and understanding the growth of hydrodynamic instability can strongly increase the feasibility of ignition experiment and is of the main importance for achieving ignition and high gain. A new cylindrical shock wave tube was designed and fabricated after consulting relevant references and the parameters of Shenguang Ⅱ laser facility. The cylindrical shock wave tube consisted of rippled polystyrene (CH) film, cylindrical carbonized-resorcinol-formaldehyde (CRF) aerogel and cylindrical CH tube. The cylindrical shock wave tube was obtained by assembling the rippled CH film and cylindrical CRF aerogel into the cylindrical CH tube. The target design and fabrication processes were described while the target parameters were measured. The results indicate that the length, diameter and density of cylindrical CRF aerogel are 1000 m, 730 m and 250 mgcm-3, respectively, the diameter and thickness of the rippled CH film are 15 m and 730 m, while the perturbation period and amplitude on its surface are 100 m and 4.3 m, the maximum axial assembly deviation of the cylindrical shock wave tube is 2 m, while its maximum diameter assembly deviation is 3 m.

皮秒激光在激光状态方程靶制备中的应用

皮秒激光在激光状态方程靶制备中的应用

Fabrication of Bulk Targets of MgB2 with Stoichiometric and Nonstoichiometric Contents

Fabrication of Bulk Targets of MgB2 with Stoichiometric and Nonstoichiometric Contents

Targets for accelerator-based research

This special issue of the Journal of Radioanalytical and Nuclear Chemistry is dedicated to the 26th World Conference of the International Nuclear Target Development Society (INTDS 2012) held from August 19th to 24th, 2012 at the conference center Erbacher Hof in Mainz, Germany with special emphasis on targets for acceleratorbased research. The INTDS 2012 was co-organized by the Johannes Gutenberg-Universitat Mainz and the GSI Helmholtzzentrum fur Schwerionenforschung, Darmstadt. The 4th Target Fabrication Workshop (TFW), dedicated to targets for laser application and hosted by the Technical University Darmstadt, was held in parallel to the INTDS 2012 at the Erbacher Hof with common plenary sessions giving the participants of both events the opportunity of exchanging experiences and know-how. Accordingly, these proceedings contain some contributions presented at the 4th Target Fabrication Workshop. The series of INTDS conferences dates back to 1963 when the ‘‘First Symposium on Research Materials for Nuclear Measurements’’ was held sponsored by the Central Bureau for Nuclear Measurements (CBNM, recently IRMM—Institute for Reference Materials and Measurements) in Belgium. Since then researchers involved in target preparation share experience and discuss related problems during biennial conferences hosted alternatively in Europe, North America and Asia (www.intds.org). It dates back to 1978 and 1988 when the 7th and the 14th INTDS conference were held at Garching, organized by Ludwig-Maximilians-Universitat together with Technische Universitat Munchen and at Darmstadt, organized by GSI, respectively. Thus, it was delightful to meet again in Germany on the occasion of the 26th International INTDS conference. More than 70 participating scientists from 15 countries (Belgium, Canada, France, Germany, India, Italy, Japan, Korea, Poland, Romania, Russia, South Africa, Switzerland, UK, USA), met in Mainz presenting over 50 scientific contributions covering the wide field of ‘‘Targets for Accelerator-bases Research’’. Two complementary visits to GSI and the TRIGA Mainz research reactor operated by the Johannes Gutenberg-Universitat were included in the scientific program to introduce the institutions and laboratories. The conference comprised seven different sessions titled ‘‘Classical Accelerator Targets’’, ‘‘Laser& Accelerator Based Research’’, ‘‘RIB Targets’’, ‘‘Isotope Enrichment and Medical Radioisotopes’’, ‘‘Stripper’’, K. Eberhardt (&) Johannes Gutenberg-Universitat Mainz, 55128 Mainz, Germany e-mail: klaus.eberhardt@uni-mainz.de

Scientific and technological advancements in inertial fusion energy

Scientific advancements in inertial fusion energy (IFE) were reported on at the IAEA Fusion Energy Conference, October 2012. Results presented transect the different ways to assemble the fuel, different scenarios for igniting the fuel, and progress in IFE technologies. The achievements of the National Ignition Campaign within the USA, using the National Ignition Facility (NIF) to indirectly drive laser fusion, have found beneficial the achievements in other IFE arenas such as directly driven laser fusion and target fabrication. Moreover, the successes at NIF have pay-off to alternative scenarios such as fast ignition, shock ignition, and heavy-ion fusion as well as to directly driven laser fusion. This synergy is summarized here, and future scientific studies are detailed.