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

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(30-1)-3980

Plasmas and Controlled Nuclear Fusion

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

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

Guidelines for the Management of Severe Traumatic Brain Injury: 2020 Update of the Decompressive Craniectomy Recommendations

© Congress of Neurological Surgeons 2020. When the fourth edition of the Brain Trauma Foundation\u27s Guidelines for the Management of Severe Traumatic Brain Injury were finalized in late 2016, it was known that the results of the RESCUEicp (Trial of Decompressive Craniectomy for Traumatic Intracranial Hypertension) randomized controlled trial of decompressive craniectomy would be public after the guidelines were released. The guideline authors decided to proceed with publication but to update the decompressive craniectomy recommendations later in the spirit of living guidelines, whereby topics are updated more frequently, and between new editions, when important new evidence is published. The update to the decompressive craniectomy chapter presented here integrates the findings of the RESCUEicp study as well as the recently published 12-mo outcome data from the DECRA (Decompressive Craniectomy in Patients With Severe Traumatic Brain Injury) trial. Incorporation of these publications into the body of evidence led to the generation of 3 new level-IIA recommendations; a fourth previously presented level-IIA recommendation remains valid and has been restated. To increase the utility of the recommendations, we added a new section entitled Incorporating the Evidence into Practice. This summary of expert opinion provides important context and addresses key issues for practitioners, which are intended to help the clinician utilize the available evidence and these recommendations. The full guideline can be found at: https://braintrauma.org/guidelines/guidelines-for-the-management-of-severe-tbi-4th-ed#/