High-power Target Research Articles

Laser time fiducial for precise physical experiment in Shenguang-Ⅲ prototype facility

Using comb laser pulses synchronized with the main pulse output by large laser facility as time fiducial to scale the reaction process between high power laser pulse and target is very important for the realization of precise measurement and simulation in the intense field experiment. We demonstrate a fiber multiharmonic time fiducial laser pulse generation system using optic-electric modulation and optical pulse stacking. A unit optical pulse with a width of 150 ps generated by modulation was stacked in a fiber stacker to form a 1053 nm comb pulse. The pulse was then amplified and frequency-converted to generate green (527 nm) and UV (351 nm) fiducials. The system can stably provide Shenguang-Ⅲ prototype facility with multi-frequency laser time fiducials which is essential for the precise physical experiment. In addition, the system is highly adaptive since it can generate fiducial signals with variable pulse intervals and amplitudes flexibly according to the requirements of different physical experiments.

The extendedQ-range small-angle neutron scattering diffractometer at the SNS

The extendedQ-range small-angle neutron scattering diffractometer (EQ-SANS) at the Spallation Neutron Source (SNS), Oak Ridge, is designed for wide neutron momentum transfer (Q) coverage, high neutron beam intensity and good wavelength resolution. In addition, the design and construction of the instrument aim to achieve a maximum signal-to-noise ratio by minimizing the background. The instrument is located on the high-power target station at the SNS. One of the key components in the primary flight path is the neutron optics, consisting of a curved multichannel beam bender and sections of straight neutron guides. They are optimized to minimize neutron transport loss, thereby maximizing the available flux on the sample. They also enable the avoidance of a direct line of sight to the neutron moderator at downstream locations. The instrument has three bandwidth-limiting choppers. They allow a novel frame-skipping operation, which enables the EQ-SANS diffractometer to achieve a dynamicQrange equivalent to that of a similar machine on a 20 Hz source. The two-dimensional low-angle detector, based on3He tube technologies, offers very high counting rates and counting efficiency. Initial operations have shown that the instrument has achieved its design goals.

Mitigation Technologies for Damage Induced by Pressure Waves in High-Power Mercury Spallation Neutron Sources (II)—Bubbling E.ect to Reduce Pressure Wave—

Liquid mercury was suggested to be used as target material for high-power pulsed spallation neutron sources. In order to realize the high-power target, however, the pressure wave is a critical issue, which is caused by the thermal shock in mercury and causes cavitation at the moment when highly intense proton beams bombard mercury. R&D on pressure wave mitigation technologies is carried out for Japan Spallation Neutron Source (JSNS; 1MW/25 Hz). Microbubble injection into the mercury is one of prospective technologies to mitigate the pressure wave. The microbubble effect was experimentally investigated from the viewpoint of pitting damage due to the cavitation in the mercury loop with an electro-magnetic impact testing machine (MIMTM) and numerically examined from the viewpoint of bubble dynamics. In the present study, we confirmed that the microbubble injection is very effective to reduce pitting damage and the amplitude of negative pressure, which causes explosive growth of cavitation bubble.

EURISOL High Power Targets

Modern Nuclear Physics requires access to higher yields of rare isotopes, that relies on further development of the In-flight and Isotope Separation On-Line (ISOL) production methods. The limits of the In-Flight method will be applied via the next generation facilities FAIR in Germany, RIKEN in Japan, and RIBF in the United States. The ISOL method will be explored at facilities including ISAC-TRIUMF in Canada, SPIRAL-2 in France, SPES in Italy, ISOLDE at CERN, and eventually at the very ambitious multi-MW EURISOL facility [1]. ISOL and in-flight facilities are complementary entities. While in-flight facilities excel in the production of very short lived radioisotopes independently of their chemical nature, ISOL facilities provide high Radioisotope Ion Beam (RIB) intensities and excellent beam quality for 70 elements. Both production schemes are opening vast and rich fields of nuclear physics research.

A neutron production target for FRANZ

A high power target for neutron production has been developed for the upcoming intense neutron source FRANZ at the University of Frankfurt. At this facility neutrons will be produced via the 7Li(p,n) 7Be reaction by bombarding layers of a high temperature Li compound with pulsed proton beams of up to 2 mA average current and maximum energies of 2.3 MeV. Cooling is achieved by water flowing under high pressure through capillaries in a 1.2 mm thick copper target. The heat distribution has been calculated with the fluid dynamics code StarCD/3.26, ensuring that the copper surface remains below 500 ∘ C at the maximum beam power of 5 kW. The moderating effect of the cooling water on the neutron spectra was studied by simulations using the GEANT software package. A prototype target was successfully tested at the Karlsruhe Van de Graaff accelerator, confirming stable operation at a thermal load of 5 kW/cm 2.

High intensity targets for ISOL, historical and practical perspectives

The concepts and technical challenges of generating radioactive ion beams from ISOL (isotope separation on line) targets irradiated with high power proton beams are discussed in an historical context. The evolution of potential target designs for high beam power dissipation over the past 20 years is reviewed with respect to effectiveness and practicality. The development of TRIUMF-ISAC high power targets and their successes and problems during on-line operation at elevated proton currents are presented.

Optical diagnostics of mercury jet for an intense proton target

An optical diagnostic system is designed and constructed for imaging a free mercury jet interacting with a high intensity proton beam in a pulsed high-field solenoid magnet. The optical imaging system employs a backilluminated, laser shadow photography technique. Object illumination and image capture are transmitted through radiation-hard multimode optical fibers and flexible coherent imaging fibers. A retroreflected illumination design allows the entire passive imaging system to fit inside the bore of the solenoid magnet. A sequence of synchronized short laser light pulses are used to freeze the transient events, and the images are recorded by several high speed charge coupled devices. Quantitative and qualitative data analysis using image processing based on probability approach is described. The characteristics of free mercury jet as a high power target for beam-jet interaction at various levels of the magnetic induction field is reported in this paper.

Feasibility of Lead-Bismuth-Cooled Accelerator-Driven System for Minor-Actinide Transmutation

The feasibility for the lead-bismuth-cooled accelerator-driven system (ADS) to transmute minor actinides partitioned from high-level radioactive waste is discussed. Since lead-bismuth will cause considerable corrosion and erosion effects at high temperature, the fuel-clad temperature must be kept as low as possible. Moreover, the most critical issue of the ADS design is the engineering viability of the high-power spallation target and the beam window. The thermal-hydraulic and structural analysis was carried out for both the fuel assembly and the beam window. In addition to the analysis in steady state, the transient behaviors were also studied during typical transient and unprotected accidents. The results showed that engineering viability is reasonably achievable in the nominal operation. For the beam trip, which will be the most frequent transient, the number of events to cause the failure of the beam window is estimated as more than 105. For safety aspects of the ADS during unprotected accidents, the estimated results showed that unprotected loss of flow would cause the most significant problem, if the beam operation was kept. Therefore, high reliability of the beam shutdown is required for the ADS safety.

Thermal shock measurements and modelling for solid high-power targets at high temperatures

A description of lifetime shock tests on tantalum and tungsten is given and of modelling studies as part of the research into solid targets for a Neutrino Factory. A fast high current pulse is applied to a thin wire of the sample material and the number of pulses measured before the wire visibly deteriorates. These measurements are made at temperatures up to ∼2000 K. The stress on the wire is calculated and compared to the stress expected in the target using the computer code LS-DYNA. It has been found that tantalum is too weak to sustain prolonged stress at these temperatures but a tungsten wire has reached over 13 million pulses (equivalent to 10 years of operation) at the stress expected in the target. Further work is in progress to study graphite and other materials. Measurement of the surface acceleration of the wire using a VISAR are to be made, which, combined with LS-DYNA modelling, will allow the evaluation of the constitutive equations of state of the materials at high temperature and provide a more accurate model of the stresses in a number of target geometries.

Feasibility of high power refractory metal-foil targets for EURISOL

EURISOL foil-targets have to withstand a primary proton beam of 1 GeV kinetic energy and up to 100 μA beam current. These foil targets will be based on previous high-power target concepts, i.e. the RIST target [J.R.J. Bennett et al., Nucl. Instrum. Meth. Phys. Res. B 126, 117 (1997)] or high power targets used at TRIUMF [P. Bricault et al., Nucl. Instrum. Meth. Phys. Res. B 204, 319 (2003), M. Dombsky et al., Nucl. Instrum. Meth. Phys. Res. B 204, 191 (2003)]. A single target unit is capable of dissipating up to 25 kW, hence, several target units can be merged together by individual transfer lines to one common ion source. The single target units will be irradiated by a proton beam in a time sharing mode to distribute the primary proton beam current to the individual target units. In this feasibility study the necessary properties of high-power foil targets are discussed and the requirements to design a foil target according to the proton beam parameters [CITE] for the future EURISOL facility are given.

The status of the Super-FRS at FAIR

The Super-FRS will be a large-acceptance two-stage superconducting fragment separator with three exit branches serving different experimental areas. Due to the high primary-beam intensity of up to 1012 ions/s a challenging design of the target area and the components used in the first dipole Super-FRS is necessary. These efforts include high-power production targets, beam-dumps to catch the remaining primary beam, and radiation resistant magnets. In this contribution we summarize the recent developments on these issues.

Development of a high intensity 26gAl beam from SiC targets for accelerated beam experiments at ISAC

An intense beam of 26gAl has been developed for accelerated beam experiments at TRIUMF’s ISAC facility. Studies of the on-line production of Al radionuclides from thick silicon carbide targets have been performed as part of a program of beam development for astrophysical reaction studies at ISAC. While the release of short-lived Al nuclides from SiC was found to be slow, development of new target material forms and high-power target containers has allowed operation of SiC targets with proton currents of up to 70μA on target. In addition, operation with the TRIUMF resonant ionization laser ion source (TRILIS) has produced 26gAl beam intensities of 5.1×1010s−1.

Plans for an Advanced Exotic Beam facility in the U.S.

The Office of Science of the Department of Energy is currently considering options for an advanced radioactive beam facility in the U.S. A committee, the Rare Isotope Science Assessment Committee, has been formed under the auspices of the Board of Physics and Astronomy of the National Academies of Science and Engineering with the charge of assessing the importance of and prospects for future research in this field world-wide. There is interest in identifying opportunities for a facility in the U.S. that will complement the capabilities that will exist elsewhere. There is an on-going R&D program sponsored by the DOE to develop the technologies that are essential to both the production of and use of beams of intense exotic beams at next-generation facilities. This paper presents the status of planning and options for such a facility, as well as, progress in the R&D. This program is developing concepts and prototypes for high power superconducting heavy ion linacs for rare isotope production and high power targets, ion sources, fragment separators, gas catchers, and reacceleration technologies that support the delivery of high quality, intense beams of exotic isotopes for research.

Measurement of delayed neutron yields and time spectra from 1 GeV protons interacting with thick natPb targets

In this paper we present for the first time the measured delayed neutron (DN) yields and time spectra from high-energy protons interacting with thick natPb targets. The 1GeV protons from the accelerator impinged on targets of different thicknesses producing a huge number of spallation-fission products, some of which can be DN precursors. After the beam is switched off, the DNs were detected with optimized 3He counter. The production yields of light DN precursors as 17N and “usual” fission products as 87Br and 88Br, which dominate the total DN activity, are obtained both for thin and thick targets. These new data are of great interest for the new generation high-power spallation targets based on liquid-metal technologies. Our findings also should help to constrain the physics models within the simulations codes.

A long-wavelength target station for the SNS

A long-wavelength target station (LWTS) [J. M. Carpenter, T. E. Mason, Nucl. Instr. and Meth. A 545 (2001) 1; Technical concepts for a long-wavelength target station for the spallation neutron source, Argonne National Laboratory report ORNL/SNS-TM-2001/163, November, 2002; 〈 http://www.pns.anl.gov/related/〉] will complement the high-power target station (HPTS) facility of the spallation neutron source. The LWTS will at least double the overall scientific capability of the SNS and provide up to an order of magnitude performance gain over the initial HPTS. The fully equipped SNS has the prospect to offer capabilities for neutron-scattering studies that are unparalleled in the world. We describe the principal features of the LWTS concept and illustrate some neutron-scattering instruments suited to exploit the unique features of the LWTS.

Solid Target Studies for Muon Colliders and Neutrino Beams

This paper presents preliminary results from an ongoing post-irradiation analysis of materials that have been irradiated at the Brookhaven National Laboratory (BNL) Isotope facility. The effort is part of an experimental study that focuses on how prone to irradiation damage these materials are and thus what is their potential in playing the role of high power targets in the neutrino superbeam and the muon collider initiatives.

Some problems encountered with high-power targets with special reference to neutrino factories

An outline is given of the general problems of high-power targets used in particle accelerators with cw and pulsed beams for a variety of uses, such as neutron and radioactive particle production and in particular for pion production in neutrino factories. The question of heat dissipation and thermal shock with pulsed beams will be examined along with those of the target station, remote handling, replacement of components and maintenance. A discussion of the facilities that may be needed to address these issues and the required R&D will be presented.

Requirements for a high-power target test facility

Future advances in several research areas are being based around accelerator facilities that employ targets for generating neutrons, neutrinos or rare isotopes. The demand for higher neutron intensities and particle or isotope production is driving facilities to higher accelerator powers and more intense beams on targets. The challenges to target development are significant for accepting higher power levels while maintaining reasonable lifetimes. In the case of short-pulse liquid metal spallation targets the most significant issue is cavitation damage erosion. Although research and development is underway, long-term progress is hampered by lack of a test facility that provides prototypic beam in a flexible testing and analysis environment. The requirements of such a facility are significant, but it was recognized by some in the spallation neutron source community that many of its features would be useful for the development of targets in other research areas. This paper outlines the requirements of a desired facility that serves not only the spallation source community, but also those of other research areas. The scope of requirements includes beam parameters, test cell infrastructure, remote handling, post-irradiation examination and waste handling. Discussion and consensus between the potential users is hoped to lead to collaboration towards making the facility a reality.

Status report of the radioactive ion beam production at TRIUMF (invited)

The ISAC radioactive ion beam (RIB) facility has been operational since November 1998. The ISAC Facility at TRIUMF utilizes up to 100μA proton intensity at 500MeV from the existing H− cyclotron to produce RIB using the isotopic separation on-line (ISOL) method. The science programs at ISAC range from nuclear astrophysics to fundamental symmetry. The facility can deliver RIB to the low energy area and a linear accelerator composed of a four-rod radio frequency quadrupole and a linear accelerator can provide beam from A=3to30amu with an energy range from 0.15to1.5AMeV. An accelerator upgrade is underway and will allow us to extend the mass range to A=150amu and the energy up to 6.5AMeV. The target/ion source assembly and heavy-ion optics components are located in a shield canyon under 2m of steel shielding allowing high proton beam intensity on a thick target. At the beginning the production target was operating at 2–5μA but rapidly the proton beam intensity was raised to 40μA. Now, we operate up to nearly 100μA proton beam using the new high power target design equipped with radial fins. While the production target capabilities have improved quite a lot, from 2to100μA, the ion sources development have not followed the same trend. Since the beginning of ISAC most of the RIB production is done using the surface ion source. A 2.45GHz electron cyclotron resonance ion source (ECRIS) was built and used on line with moderate success.

Upgrade status and plans at the Holifield Radioactive Ion Beam Facility

The Holifield Radioactive Ion Beam Facility (HRIBF) is a national user facility dedicated to nuclear structure and astrophysics research with Radioactive Ion Beams (RIBs) using the Isotope Separator On-Line (ISOL) technique. HRIBF also maintains a vibrant development program for ISOL targets, ion sources and diagnostics. As a bridge to RIA, HRIBF continues to expand its technology. Presently, a $4.75M High Power Target Laboratory (HPTL) is being constructed to provide a facility for testing new targets, target geometries, ion sources and beam preparation techniques. HPTL will ultimately be co-located with a second RIB production system (IRIS2). An external axial injection system for the driver cyclotron, ORIC, is planned to provide higher beam intensities, reduce machine activation and eliminate cathode lifetime limitations. A multi-channel residual gas BPM is under development for measuring intensity and position of the driver beam. RIB production via electron-induced photofission is also being explored to attain higher intensities.