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THE STORY OF SIGMA HYPERNUCLEI - A MODERN FABLE.
No full textThe reality of {Sigma} hypernuclei has been the subject of intense concern among experimenters and theoreticians for more than 20 years. The possible existence of {Sigma} hypernuclei was first suggested by a pioneering experiment on a {sup 9}Be target at the CERN PS. There were reported to be two narrow ({Gamma} < 8 MeV) peaks in the continuum region. This finding was quite unexpected since the widths of {Sigma} states were believed to be large due to the strong conversion process. It is obvious that if such relatively long-lived systems were confirmed unambiguously by experiment, their masses and widths provide important constraints on the {Sigma}N effective interaction and its relation to the {Lambda}N and NN interactions. Since the {Sigma} carries isospin, the role of isospin and isospin conservation in hadronic reactions could be explored. This report stimulated a number of subsequent experiments at the BNL-AGS and KEK, along with further experiments with a specially created short kaon beam at the CERN PS. Experimental data were reported for different targets at different momenta and at different conditions. Various tagging techniques were employed to suppress backgrounds, but always at the expense of a reduction in statistical quality. Because of problems with resolution and statistics, contradictions among the different sets of data resulted more often in clouding the issues than clarifying them. Thus, up until a few years ago, there was no statistically clear confirmation of this surprising finding. In the last few years, however, a series of definitive experiments has been performed at the BNL-AGS in an effort to resolve the discrepancies and settle the controversy. Besides repeating the initial experiment on Be, a target of {sup 6}Li was run. The earlier stopped kaon data on {sup 4}He was repeated in an in-flight experiment, and the suggestion of a {Sigma} bound state, with virtually pure isospin, confirmed. We now have a better understanding of the role of isospin in the nucleon-hyperon interaction and the importance of three body forces in hyper-nuclei. According to that understanding, it is unlikely that {Sigma} states for A > 5 will ever be seen. In this review, a critique of the past BNL experiments is presented and conclusions on the status of the {Sigma} database drawn
Observation of d(d,p)t reactions in the Princeton Large Torus
No full textProtons from d(d,p)t fusion reactions have been observed in the Princeton Large Torus (PLT) using a surface-barrier detector. The time evolution of the escaping protons agrees with the d-d neutron evolution. The proton energy spectrum was measured during ohmic, lower-hybrid, and ICRF heating. The proton spectrum during lower-hybrid heating indicates non-thermal enhancement of the d-d fusion rate
d-/sup 3/He reaction measurements during fast wave minority heating in PLT
No full textTime- and energy-resolved d-/sup 3/He fusion reactions have been measured to infer the energy of the d/sup +/ or He/sup + +/ minority ions heated near their cyclotron frequency by the magnetosonic fast wave. The average energy of the reacting /sup 3/He ions during /sup 3/He minority heating is in the range of 100 to 400 keV, as deduced from the magnitude of the reaction rate, its decay time, and the energy spread of the proton reaction products. The observed reaction rate and its scaling with wave power and electron density and temperature are in qualitative agreement with a radial reaction rate model using the minority distribution predicted from quasilinear velocity space diffusion. Oscillations in the reaction rate are observed concurrent with sawtooth and m = 2 MHD activity in the plasma
Fast-wave heating in the two-ion hybrid regime on PLT
No full textPlasma heating using the fast magnetosonic wave in the ion cyclotron range of frequencies is being studied both experimentally and theoretically in order to evaluate its potential for heating reactor plasmas. RF pulses at power levels up to 800 kW and length >130 ms have been delivered to a set of two parallel 1/2 turn loop antennae with 80% of the power coupled to the plasma. The parallel antennae have been driven both in and out-of-place so that the k/sub phi/ dependence of the antenna coupling and plasma heating can be determined. The heating experiments were conducted in the two-ion hybrid regime where the deuterium plasma contained a small component of a second ion species (hydrogen or /sup 3/He). A bulk ion temperature increase of up to 1.2 keV has been achieved at the 620 kW power level with /sup 3/He as the minority species and anti n/sub e/ = 2.9 x 10/sup 13/ cm/sup -3/. Energetic minority distributions have been detected consistent with theory
Burn-up of fusion-produced tritons and<sup>3</sup>He ions in PLT and PDX
No full textThe d(d, p)t and d(d, n) 3He fusion reactions produce 1 MeV tritons and 0.8 MeV 3He ions which can subsequently undergo d(t, n) α and d(3He, p) α fusion reactions. The magnitude of this triton and 3He ion ‘burn-up’ was measured on the PLT and PDX tokamaks by detection of the 14 MeV neutron and 15 MeV proton emission. In discharges with Bφ > 2 T, the measured 3He and triton burn-up is consistent (within a factor of three) with predictions based on classical theories of ion confinement and slowing down. In discharges with weaker toroidal fields but constant plasma current, the burn-up of both ions fell by more than a factor of ten so that the observed burn-up was significantly less than expected classically. © 1983 IOP Publishing Ltd
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