Plasmas and Controlled Nuclear Fusion

Contains reports on one research project.U. S. Atomic Energy Commission (Contract AT(11-1)-3070

Effects of low Z impurities during the startup phase of a large tokamak

The requirements placed on a tokamak ohmic heating system (i.e. loop voltage) to initiate the plasma become more severe as the size increases because of the current density decrease. During the startup phase even small concentrations of low Z impurities can affect the plasma energy balance very substantially and have very important effects on the evolution of the discharge. The startup phase has been studied using a simple zero dimensional computer code. Because the dominant energy loss mechanisms during startup, radiation, and ionization are a volume effect, the zero dimensional code was adequate to treat this phase. The results of this study which have been applied to TFTR indicate that the plasma evolution is a sensitive function of the applied loop voltage, impurity concentration, initial filling pressure and the manner in which gas is fed into the discharge. (auth

Plasmas and Controlled Nuclear Fusion

Contains reports on three research projects.U. S. Atomic Energy Commission (Contract AT(30-1)-3980

R.F. heating near the lower hybrid frequency in the FM-1 spherator

Plasma heating experiments at frequencies near the lower hybrid frequency have been carried out at modest powers (.05 to 4kW). The antenna structure operating at 68 MHz was comprised of two plates driven out of phase on the exterior of the plasma. High electron heating efficiency (greater than 40 percent) in both helium and argon plasmas was observed with only a weak density dependence. At low densities (n/sub e/ less than or equal to 1 x 10$sup 11$ cm$sup -3$), the heating was uniform across the plasma while at higher densities the heating was preferentially on the exterior portion of the plasma. The heating of the exterior of the plasma was found not to correspond to absorption at the lower hybrid resonance layer. The electron heating efficiency was found to be a weak function of rf power when the incident rf power was varied from 1 to 15 times the experimentally observed threshold power for parametric instabilities. Ion temperatures were determined by measuring the Doppler broadening of an Argon ion line using a Fabry-Perot interferometer. Low efficiency main body ion heating (1 to 3 percent) was observed. (auth

Plasmas and Controlled Nuclear Fusion

Contains reports on three research projects.U. S. Atomic Energy Commission (Contract AT(11-1)-3070

Efficacy and safety of methylprednisolone sodium succinate in acute spinal cord injury: a systematic review

Study Design: Systematic review and meta-analysis. Objective: The objective of this study was to conduct a systematic review to assess the comparative effectiveness and safety of high-dose methylprednisolone sodium succinate (MPSS) versus no pharmacological treatment in patients with traumatic spinal cord injury (SCI). Methods: A systematic search was performed in PubMed and the Cochrane Collaboration Library for literature published between January 1956 and June 17, 2015. Included studies ere critically appraised, and Grades of Recommendation Assessment, Development and Evaluation methods were used to determine the overall quality of evidence for primary outcomes. Previous systematic reviews on this topic were collated and evaluated using the Assessment of Multiple Systematic Reviews scoring system. Results: The search yielded 723 citations, 13 of which satisfied inclusion criteria. Among these, 6 were primary research articles and 7 were previous systematic reviews. Based on the included research articles, there was moderate evidence that the 24-hour NASCIS II (National Acute Spinal Cord Injury Studies) MPSS regimen has no impact on long-term neurological recovery when all postinjury time points are considered. However, there is also moderate evidence that subjects receiving the same MPSS regimen within 8 hours of injury achieve an additional 3.2 points (95% confidence interval = 0.10 to 6.33; P = .04) of motor recovery compared with patients receiving placebo or no treatment. Conclusion: Although safe to administer, a 24-hour NASCIS II MPSS regimen, when all postinjury time points are considered, has no impact on indices of long-term neurological recovery. When commenced within 8 hours of injury, however, a high-dose 24-hour regimen of MPSS confers a small positive benefit on long-term motor recovery and should be considered a treatment option for patients with SCI

Modeling of lithium granule injection in NSTX using M3D-C1

In this paper, we present simulations of pedestal control by lithium granule injection (LGI) in NSTX. A model for small granule ablation has been implemented in the M3D-C1 code (Jardin et al 2012 Comput. Sci. Discovery 5 014002), allowing the simulation of realistic lithium granule injections. 2D and 3D simulations of Li injections in NSTX H-mode plasmas are performed and the effect of granule size, injection angle and velocity on the pedestal gradient increase is studied. The amplitude of the local pressure perturbation caused by the granules is found to be highly dependent on the solid granule size. Adjusting the granule injection velocity allows one to inject more particles at the pedestal top. 3D simulations show the destabilization of high order MHD modes whose amplitude is directly linked to the localized pressure perturbation, which is found to depend on the toroidal localization of the granule density source

Density Gradient Stabilization of Electron Temperature Gradient Driven Turbulence in a Spherical Tokamak

In this letter we report the first clear experimental observation of density gradient stabilization of electron temperature gradient driven turbulence in a fusion plasma. It is observed that longer wavelength modes, k⊥ρs ≤10, are most stabilized by density gradient, and the stabilization is accompanied by about a factor of two decrease in the plasma effective thermal diffusivity