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Irradiation response of ODS ferritic steels to high-energy Ne ions at HIRFL
No full textTwo kinds of ODS high-Cr ferritic steels (commercial MA956 and an Al-free 16Cr-0.1Ti ODS ferritic steel) and one conventional ferritic/martensitic steel (T122) were irradiated at about 440 degrees C with high-energy Ne-20-ions in HIRFL. Successively increasing doses from 350 to 900 appm of Ne concentration, corresponding to atomic displacement levels from 0.7 to 1.8 dpa, were approached. A nearly uniform distribution of Ne concentration and atomic displacement damage was produced through the thickness of 60 mu m of the specimens by using an energy degrader. Mechanical properties of the specimens were tested with the small-ball punch technique. The test at room temperature shows a less significant ductility loss in the ODS ferritic steel MA956 than in the T122 irradiated to the same dose of 350 appm Ne/0.7 dpa. The test at 500 degrees C shows that the Al-free 16Cr-0.1Ti ODS ferritic steel does not exhibit observable loss of ductility even to the highest dose level (900 appm Ne/1.8 dpa). An investigation with transmission electron microscopy (TEM) shows that voids with a diameter up to 70 nm were formed at grain boundaries in the conventional ferritic/martensitic steel T122 while only smaller bubbles were formed at the oxides/substrate interfaces in the ODS ferritic steel MA956. Mechanisms underlying the difference of irradiation response of the steels are discussed. (C) 2014 Elsevier B.V. All rights reserved
Dynamics of He2+ + H ionization with exponential cosine-screened Coulomb potential
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">Dynamics of He2+ + H ionization in dense quantum plasmas (DQPs) has been studied by the classical trajectory Monte Carlo method. The interactions between charged particles have been described by the exponential cosine-screened Coulomb potential. It is found that ionization cross sections in plasma environments are obviously larger than those in plasma-free environments due to the screening effects. Cross sections for H+ also have been calculated for comparison. For H+, cross sections increase with the increase of screening effects. However, for He2+, cross sections begin to decrease in strong screening effects at intermediate energies. Furthermore, He2+ impact ionization cross sections in weakly coupled plasmas (WCPs) also have been calculated. The interactions have been described by the static screened Coulomb potential. It is found that when screening effects are weak, cross sections in DQPs and WCPs are approximately the same. As screening effects increase, cross sections in DQPs become larger than those in WCPs at high energies. However, when screening effects are strong enough, cross sections in DQPs become smaller than those in WCPs at low and intermediate energies.</span
Experimental reconstruction of primary hot isotopes and characteristic properties of the fragmenting source in heavy-ion reactions near the Fermi energy
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">The characteristic properties of the hot nuclear matter existing at the time of fragment formation in multifragmentation events produced in the reaction Zn-64 + Sn-112 at 40 MeV/nucleon are studied. A kinematical focusing method is employed to determine the multiplicities of evaporated light particles, associated with isotopically identified intermediate-mass fragments. From these data the primary isotopic yield distributions are reconstructed using a Monte Carlo method. The reconstructed yield distributions are in good agreement with the primary isotope distributions obtained from antisymmetrized molecular dynamics transport model simulations. Utilizing the reconstructed yields and power distribution, characteristic properties of the emitting source are examined. The primary mass distribution exhibits a power-law distribution with the critical exponent A(-2.3) for A >= 15 isotopes but significantly deviate from that for lighter isotopes. Based on the modified Fisher model, the ratios of the Coulomb and symmetry energy coefficients relative to the temperature, a(c)/T and a(sym)/T, are extracted as a function of A. The extracted a(sym)/T values are compared with results of the antisymmetrized molecular dynamics simulations using Gogny interactions with different density dependencies of the symmetry energy term. The calculated a(sym)/T values show a close relation to the symmetry energy at the density at the time of fragment formation. From this relation the density of the fragmenting source is determined to be rho/rho(0) = 0.63 +/- 0.03. Using this density, the symmetry energy coefficient and the temperature of fragmenting source are determined in a self-consistent manner as a(sym) = 24.7 +/- 3.4 MeV and T = 4.9 +/- 0.2 MeV.</span
Mass dependence of transverse flow in heavy ion collisions at intermediate energies
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">The mass dependence of the transverse flow in the reactions of Ca-40 + Ca-40 at 35 MeV/nucleon has been determined for emitted isotopes with Z = 1 to 9. The observed flow is compared with that calculated using a constrained molecular dynamics (CoMD) simulation. With the application of the appropriate experimental filter, the general trend of the experimental mass-dependent flow is well reproduced by the simulation employing an effective interaction corresponding to a soft equation of state (K = 200 MeV). The CoMD events are further utilized to study the mechanism of generation of the mass-dependent flow. It is found that the mass-dependent flow is generated by the interplay between the thermal and collective motions under a momentum conservation in the fragmenting system. With the help of the collective-thermal-interplay model, the mass-dependent flow scaled by the reduced mass of fragments A/A(sys) is found to be almost independent of the size of the system.</span
Conceptional design of a heavy ion linac injector for HIRFL-CSRm
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">A room temperature heavy ion linac has been proposed as a new injector of the main Cooler Storage Ring (CSRm) at the Heavy Ion Research Facility in Lanzhou (HIRFL), which is expected to improve the performance of HIRFL. The linac injector can supply heavy ions with a maximum mass to charge ratio of 7 and an injection kinetic energy of 7.272 MeV/u for CSRm; the pulsed beam intensity is 3 emA with the duty factor of 3%. Compared with the present cyclotron injector, the Sector Focusing Cyclotron (SFC), the beam current from linac can be improved by 10 100 times. As the pre-accelerator of the linac, the 108.48 MHz 4-rod Radio Frequency Quadrupole (RFQ) accelerates the ion beam from 4 keV/u to 300 keV/u, which achieves the transmission efficiency of 95.3% with a 3.07 m long vane. The phase advance has been taken into account in the analysis of the error tolerance, and parametric resonances have been carefully avoided by adjusting the structure parameters. Kombinierte Null Grad Struktur Interdigital H-mode Drift Tube Linacs (KONUS IH-DTLs), which follow the RFQ, accelerate ions up to the energy of 7.272 MeV/u for CSRm. The resonance frequency is 108.48 MHz for the first two cavities and 216.96 MHz for the last 5 Drift Tube Linacs (DTLs). The maximum accelerating gradient can reach 4.95 MV/m in a DTL section with the length of 17.066 m, and the total pulsed RF power is 2.8 MW. A new strategy, for the determination of resonance frequency, RFQ vane voltage and DTL effective accelerating voltage, is described in detail. The beam dynamics design of the linac will be presented in this paper.</span
Application of evaporative cooling technology in super-high power density magnet
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">Evaporative cooling technology utilizes phase-change heat transfer mode to achieve the cooling for heating equipment. The heat transfer capacity of evaporative cooling technology is far more than air or water cooling technology. The Electron Cyclotron Resonance ion source magnet is a typical super-high power density magnet, and the evaporative cooling technology is an ideal cooling method for the coils of magnet. In this paper we show the structure and process of coils and the special design of flow channels of coolant for an experiment magnet model. Additionally, the heat transfer circulation is presented and analyzed. By the finite element method, the flow channels are optimized to rationally allocate coolant and to reduce the temperature of coils. For the experiment model, the current density of copper wire of coils is 19 A/mm(2), and the coil-windows current density is larger than 12 A/mm(2). The max temperature of coils is below 80 degrees C, and the total heat is about 200 kW. (C) 2013 AIP Publishing LLC.</span
Irradiation hardening of ODS ferritic steels under helium implantation and heavy-ion irradiation
No full textIrradiation hardening of ODS ferritic steels after multi-energy He-ion implantation, or after irradiation with energetic heavy ions including Xe and Bi-ions was investigated with nano-indentation technique. Three kinds of high-Cr ODS ferritic steels including the commercial MA956 (19Cr-3.5Al), the 16Cr-0.1Ti and the 16Cr-3.5Al-0.1Zr were used. Data of nano-hardness were analyzed with an approach based on Nix-Gao model. The depth profiles of nano-hardness can be understood by the indentation size effect (ISE) in specimens of MA956 implanted with multi-energy He-ions or irradiated with 328 MeV Xe ions, which produced a plateau damage profile in the near-surface region. However, the damage gradient overlaps the ISE in the specimens irradiated with 9.45 Bi ions. The dose dependence of the nano-hardness shows a rapid increase at low doses and a slowdown at higher doses. An 112-power law dependence on dpa level is obtained. The discrepancy in nano-hardness between the helium implantation and Xe-ion irradiation can be understood by using the average damage level instead of the peak dpa level. Helium-implantation to a high dose (7400 appm/0.5 dpa) causes an additional hardening, which is possibly attributed to the impediment of motion dislocations by helium bubbles formed in high concentration in specimens. (C) 2014 Elsevier B.V. All rights reserved
Development of a superconducting solenoid for CADS
No full textA superconducting focusing solenoid has been designed and developed for the China Accelerator Driven System (CADS). In order to meet the requirement of focusing strength and fringe field while minimizing the physical size of the solenoid, the novel optimizing design method based on a linear programming method was employed. In this report, the design of the solenoid including magnetic field optimization, mechanical design and quench protection will be introduced. The solenoid has been fabricated and tested. The testing results show that the central field reached 8.4 T and the stray field was lower than 50 Gauss in the cavity zone.National Natural Science Foundation of Chin
