Tritium gas handling system for muon catalyzed fusion research at RIKEN-RAL muon facility

For muon catalyzed fusion (μCF) experiments at RIKEN-RAL muon facility, a tritium gas handling system for a high purity D–T target, free from ³ component, has been constructed to perform precise measurements of α-sticking probability in the μCF cycle. The system has been constructed to enable us to purify the target D–T gas by removing ³He component, to adjust the D/T mixing ratio, and to measure the hydrogen isotope components at the experiment site. The whole performance has been confirmed and a tritium gas with the inventory of 56 TBq (1500 Ci) has been operated in the system. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temperature-independent hyperfine field on μ+ in nickel in the temperature range of 0.12–300 K

The hyperfine field on a positive muon at interstitial site in a nickel single crystal has been measured by the muon spin rotation method in the temperature range from 0.12 K to 300 K. The hyperfine field in the low temperature limit was found to be ?640.7±2.2 Gauss. While the saturation magnetization decreases by 7% as the temperature increases from 0.1 K to 300 K, the hyperfine field seen by the muon remains nearly constant. Possible mechanisms for explaining this result are considered.     

Quantum diffusion of positive muon in pure tantalum

Quantum diffusion of positive muons has been studied in high purity Ta by zero and longitudinal field muon spin relaxation techniques. We found that the muon hopping rate in Ta is more or less the same as in pure Cu (i.e., \nu\simeq10⁵\sim10⁶\ s^™1), showing a characteristic temperature dependence proportional to T^™\alpha with \alpha ranging from 2 to 0.2 below 20 K. In addition, a step‐like change of the nuclear dipolar width was observed at 60 K associated with the sharp peak of hopping rate, suggesting a change of stable muon sites. This revised version was published online in August 2006 with corrections to the Cover Date.     

Generation of ultra-slow muons for large-scale future applications

The ideas of providing intense high-quality eV to keV muons (μ⁺μ⁻) proposed in the eighties have been tested during the last five years. Recently, remarkable success was marked for ultra-slow μ⁺, while a promising test result was obtained for ultra-slow μ⁻. The ultimate future of these beams is considered. A possible large-scale application to an eventual μ⁺μ⁻ collider is discussed.     

Magnetic properties of crystalline and amorphous DyAg from μSR measurements

Muon spin relaxation in crystalline and amorphous DyAg has been studied in the paramagnetic and magnetically ordered regimes. In cr-DyAg the critical slowing down of the Dy³⁺ spin fluctuation is seen on approaching T_N = 60 K. In the ordered state we observe a Lorentzian field distribution. The muon spin relaxation in am-DyAg approaches at lower temperatures a root exponential law usually encountered in spin glasses.     

Global finite-energy solutions of the Maxwell-Schrödinger system

The existence of global finite-energy solutions is proved for the initial value problem for the Maxwell-Schrödinger system in the Coulomb, Lorentz and temporal gaugesThis research was done primarily while all three authors were at Brown University. It was supported in part by NSF grant 90-23864 and ARO grant DAAH 04-93-G-0198.     

Ultra slow muons generated by laser resonant ionization of thermal muonium produced by 500‐MeV protons with hot tungsten

We report recent progress to date on the UT‐MSL/KEK “Ultra Slow Muon” project, in which thermal muonium (Mu) atoms are generated from the surface of a hot tungsten target placed at the primary 500 MeV proton beam line and resonantly ionized by intense u.v. lasers synchronized with the emission of the Mu. The positive muon ionization fragments are collected by electrostatic beam optics to form a beam of slow positive muons. This revised version was published online in August 2006 with corrections to the Cover Date.     

Application of a high-performance,special-purpose computer,GRAPE-2A,to molecular dynamics

The special-purpose computer GRAPE-2A accelerates the calculation of pairwise interactions in many-body systems. This computer is a back-end processor connected to a host computer through a Versa Module Europe (VME) bus. GRAPE-2A receives coordinates and other physical data for particles from the host and then calculates the pairwise interactions. The host then integrates an equation of motion by using these interactions. We did molecular dynamics simulations for two systems of liquid water: System 1 (1000 molecules), and System 2 (1728 molecules). The time spent for one step of molecular dynamics was 3.9 s (System l), and 10.2 s (System 2). The larger the molecular system, the higher the performance. The speed of GRAPE-2A did not depend on the formula describing the pairwise interaction. The cost performance was about 20 times better than that of the fastest workstations available today, and GRAPE-2A cost only $22,000. © 1994 by John Wiley & Sons, Inc.