We wish to report preliminary results of a measurement of the cascade time of n~ mesons in liquid helium, and to discuss some possible implications of the result. We mean by cascade time the period between initial atomic capture of the meson and its absorption by the nucleus. It is important to understand the mechanism of the cascade since it determines not only the cascade time, but other important effects such as the angular momentum states from which mesons are absorbed by the nucleus.If channel k is one of r channels through which the meson cascades in average time T^ from initial atomic capture to nuclear absorption, and if Nfe is the number of mesons cascading through channel k, then we define the average cascade time to be This is equivalent towhere T^ is the mean life against decay of the meson, N^ is the number of mesons observed to decay at rest, from a total sample, N s , of mesons observed to stop in liquid helium.The technique used to determine the cascade time, T^, is exactly the same as that used by Fields et _al. x in liquid hydrogen. In the present case, TT~ mesons were stopped in a 1.3-liter liq-9 -uid helium bubble chamber, 2 and the range and angle of all backward 7T-JUL decays were measured to determine the velocity of the pion at the instant of decay. We observe 11 decays at rest with 0^ > |ir for a sample of 2255 7r~ stops in the chamber. Because of range straggling, we cannot distinguish pions slower than 0^ a 0.01 from stopped pions; i, however, the time taken by the pion to go from Py = 0. 01 to atomic capture has been estimated 3 to be much shorter than the cascade time measured here. From ordinary stopping power theory we calculate that the number of events between E^ = 0.175 MeV and E n = 1 MeV with 0^ > | TT should be 0.8, We observe none. From the observed number of backward decays at rest we calculate the cascade time to be T =[2N(6 >\*)/N ]r =(2.5±1.0)xl0~1 0 sec.Day 4 has made theoretical estimates of the magnitudes of several effects which might be of importance in determining the history of a typical K~ meson during its cascade. Day assumes that the meson is initially captured from the continuum into a bound orbit with principal quantum number n a 30, ejecting one of the atom's electrons in the process. Because of the strong binding of electrons in helium, the (K~ He ++ ) ion cannot capture electrons from neighboring atoms, and therefore only one ordinary Auger transition of the K~ meson is possible. In addition to ordinary radiative transitions, Day considers three other mecha-

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The quench performance and ramp rate sensitivity of eighteen 5-cm-aperture, 15-m-long SSC dipole magnet prototypes are discussed. All the magnets appear to reach a quench plateau near their extrapolated short sample current limit and well in excess of the operating current with very little training. Most of the magnets, however, exhibit a dramatic degradation of their quench current as a function of ramp rate, which for the most part, can be attributed to large cable eddy currents.

The interactions of 142-MeV iT mesons with deuterium has been studied using a 15-cm bubble chamber in a 12.7-kG field. The angular distributions for elastic and inelastic scattering were measured. The elastic differential cross section for scattering angles greater than 90° is not in agreement with theoretical calculations based on the impulse approximation. The total cross section for neutral products {In, 2n+y, 2n-\-ir Q ) was measured to be 37.2±2.8 mb. The sum of the separate cross sections gave the ir~+d total cross section to be 183±7 mb.

Eighteen 5-cm-aperture, 15-m-long SSC dipole magnet prototypes have b&n produced and cold tested. On each prototype, the dependence of harmonic field coefficients on magnet current was measured as part of a study of the magnetic field quality. For most of the magnets, the observed behavior conforms to what can be expected from the effects of persistent magnetization currents and iron yoke saturation. A few prototypes, however, exhibited anomalies during current ramp at 4 Ah which can be attributed to large cable eddy currents.