The parallel ion flow in a high-density helicon source plasma expanding into a region of weaker magnetic field is measured as a function of neutral pressure, magnetic field strength, rf power and rf driving frequency. The dependence of the parallel ion flow and parallel ion temperature, measured by laser induced fluorescence, on the plasma density, electron temperature and floating potential, measured with an rf-compensated Langmuir probe, is also examined. At the end of the helicon plasma source, the ion velocity space distribution changes from a single subsonically drifting Maxwellian population to a supersonic ion beam (≈15 eV) plus a cold, subsonically drifting background ion population. At 38 cm into the expansion region beyond the end of the plasma source, the supersonic ion beam is not observed.

Measurements of the three-dimensional ion flow field and the ion temperature in a cross section of a cylindrical, argon, helicon plasma are presented. When these measurements are combined with radially resolved measurements of the plasma density, electron temperature, neutral density, and neutral temperature, the radial profiles of the ion viscosity and ion-neutral momentum transfer rate can be calculated. The ion viscosity and ion-neutral momentum transfer rate profiles are important input parameters for theoretical models of azimuthal flows arising from the nonlinear interaction of drift waves in helicon sources. The experimentally determined magnitudes and radial profiles reported in this work are significantly different than those used in recent theoretical studies. Measurements of the radial flow of argon neutrals and helium neutrals are also presented for a helicon plasma.

We present ion velocity distribution function (IVDF) measurements obtained with a five grid retarding field energy analyzer (RFEA) and IVDF measurements obtained with laser induced fluorescence (LIF) for an expanding helicon plasma. The ion population consists of a background population and an energetic ion beam. When the RFEA measurements are corrected for acceleration due to the electric potential difference across the plasma sheath, we find that the RFEA measurements indicate a smaller background to beam density ratio and a much larger parallel ion temperature than the LIF. The energy of the ion beam is the same in both measurements. These results suggest that ion heating occurs during the transit of the background ions through the sheath and that LIF cannot detect the fraction of the ion beam whose metastable population has been eliminated by collisions.

We report observations that confirm a theoretical prediction that formation of a current-free double layer in a plasma expanding into a chamber of larger diameter is accompanied by an increase in ionization upstream of the double layer. The theoretical model argues that the increased ionization is needed to balance the difference in diffusive losses upstream and downstream of the expansion region. In our expanding helicon source experiments, we find that the upstream plasma density increases sharply at the same antenna frequency at which the double layer appears.

The variability in frequency of allogeneic blood transfusion during coronary artery bypass surgery (CABG) is a concern. Evidence-based guidelines support minimizing the use of blood during open heart surgery. The Hospital Clinical Services Group quality indicator database was queried for intraoperative red blood cell (RBC) transfusions in 17 252 isolated CABG surgery cases during 2007. Institutional variability was observed in the frequency of intraoperative RBC transfusion rates, which ranged from 0% to 85.7%. The institution mean RBC transfusion rate was 40.8%. Regional geographic and cardiac program size variations were observed in RBC transfusion rates and volume with significant variation. Notable institutional variability persists with respect to intraoperative RBC transfusion in isolated CABG surgery despite clear evidence and guidelines to support techniques to minimize RBC transfusion. Such results support the hypothesis that incorporating evidence-based transfusion-related practices in open heart surgery are not uniformly adopted.