Generation of high intensity rf pulses in the ionosphere by means of in situ compression

We demonstrate, using a simple model, that high intensity pulses can be generated from a frequency-chirped modifier of much lower intensity by making use of the dispersive properties of the ionosphere. We show that a frequency-chirped pulse can be constructed so that its various components overtake each other at a prescribed height, resulting in large (up to one hundred times) transient intensity enhancements as compared to those achievable from a steady modifier operating at the same power. We examine briefly one possible application: the enhancement of plasma wave amplitudes which occurs as a result of the interaction of such a compressed pulse with pre-generated turbulence

Xenon treatment after severe traumatic brain injury improves locomotor outcome, reduces acute neuronal loss and enhances early beneficial neuroinflammation: a randomized, blinded, controlled animal study

Background Traumatic brain injury (TBI) is a major cause of morbidity and mortality, but there are no clinically proven treatments that specifically target neuronal loss and secondary injury development following TBI. In this study, we evaluate the effect of xenon treatment on functional outcome, lesion volume, neuronal loss and neuroinflammation after severe TBI in rats. Methods Young adult male Sprague Dawley rats were subjected to controlled cortical impact (CCI) brain trauma or sham surgery followed by treatment with either 50% xenon:25% oxygen balance nitrogen, or control gas 75% nitrogen:25% oxygen. Locomotor function was assessed using Catwalk-XT automated gait analysis at baseline and 24 h after injury. Histological outcomes were assessed following perfusion fixation at 15 min or 24 h after injury or sham procedure. Results Xenon treatment reduced lesion volume, reduced early locomotor deficits, and attenuated neuronal loss in clinically relevant cortical and subcortical areas. Xenon treatment resulted in significant increases in Iba1-positive microglia and GFAP-positive reactive astrocytes that was associated with neuronal preservation. Conclusions Our findings demonstrate that xenon improves functional outcome and reduces neuronal loss after brain trauma in rats. Neuronal preservation was associated with a xenon-induced enhancement of microglial cell numbers and astrocyte activation, consistent with a role for early beneficial neuroinflammation in xenon’s neuroprotective effect. These findings suggest that xenon may be a first-line clinical treatment for brain trauma

Xenon improves long-term cognitive function, reduces neuronal loss and chronic neuroinflammation, and improves survival after traumatic brain injury in mice

Background.Xenon is a noble gas with neuroprotective properties. We previously showed that xenon improves short and long-term outcomes in young adult mice after controlled cortical impact (CCI). This is a follow-up study investigating xenon’s effect on very long-term outcome and survival. Methods.C57BL/6N (n=72) young adult male mice received single CCI or sham surgery and were treated with either xenon (75%Xe:25%O2) or control gas (75% N2:25%O2). The outcomes used were: 1) 24-hour lesion volume and neurological outcome score; 2)contextual fear-conditioning at 2 weeks and 20 months; 3) corpus callosum white matter quantification; 4) immunohistological assessment of neuroinflammation and neuronal loss; 5) long-term survival. Results.Xenon treatment significantly reduced secondary injury development (p<0.05), improved short-term vestibulomotor function (p<0.01),and prevented development of very late-onset traumatic brain injury (TBI)-related memory deficits. Xenon treatment reducedwhite matter loss in the contralateral corpus callosum and neuronal loss in the contralateral hippocampal CA1 andDG areas at 20 months. Xenon’s long-term neuroprotective effects were associated with a significant (p<0.05) reduction in neuroinflammation in multiple brain areas involved in associative memory, including reduction in reactive astrogliosis and microglial cell proliferation. Survival was improved significantly (p<0.05) in xenon-treated animals, compared to untreated animals up to 12 months after injury.Conclusions.These results show that xenon treatment after TBI results in very long-term improvements in clinically relevant outcomes and survival. Our findings support the idea that xenon treatment shortly after TBI may have long-term benefits in the treatment of brain trauma patients

Spatial and Wavenumber Resolution of Doppler Reflectometry

Doppler reflectometry spatial and wavenumber resolution is analyzed within the framework of the linear Born approximation in slab plasma model. Explicit expression for its signal backscattering spectrum is obtained in terms of wavenumber and frequency spectra of turbulence which is assumed to be radially statistically inhomogeneous. Scattering efficiency for both back and forward scattering (in radial direction) is introduced and shown to be inverse proportional to the square of radial wavenumber of the probing wave at the fluctuation location thus making the spatial resolution of diagnostics sensitive to density profile. It is shown that in case of forward scattering additional localization can be provided by the antenna diagram. It is demonstrated that in case of backscattering the spatial resolution can be better if the turbulence spectrum at high radial wavenumbers is suppressed. The improvement of Doppler reflectometry data localization by probing beam focusing onto the cut-off is proposed and described. The possibility of Doppler reflectometry data interpretation based on the obtained expressions is shown.Comment: http://stacks.iop.org/0741-3335/46/114

A new quasilinear formulation for ICRF plasmas in a toroidal geometry

We present a new formulation for quasilinear velocity space diffusion for ICRF plasmas that considers two different aspects: (1) finite Larmor radius approximation and (2) includes the effect of toroidal geometry and constructs a positive definite form. In the first aspect, the Kennel-Engelmann (K-E) quasilinear diffusion coefficients are successfully approximated in a small Larmor radius limit and implemented for the numerical codes (TORIC-CQL3D). In the second aspect, the quasilinear diffusion is reformulated in a toroidal geometry in order to include the parallel dynamics in the inhomogeneous plasmas and magnetic fields. We use these two quasilinear formulations to simulate ITER plasmas with ICRF injection for minority fundamental heating and Tritium second harmonic cyclotron heating

HHFW Heating and Current Drive Studies of NSTX H-Mode Plasmas

30 MHz high-harmonic fast wave (HHFW) heating and current drive are being developed to assist fully non-inductive plasma current (I{sub p}) ramp-up in NSTX. The initial approach to achieving this goal has been to heat I{sub p} = 300 kA inductive plasmas with current drive antenna phasing in order to generate an HHFW H-mode with significant bootstrap and RF-driven current. Recent experiments, using only 1.4 MW of RF power (P{sub RF}), achieved a noninductive current fraction, f{sub NI} {approx} 0.65. Improved antenna conditioning resulted in the generation of I{sub p} = 650 kA HHFW H-mode plasmas, with f{sub NI} {approx} 0.35, when P{sub RF} {ge} 2.5 MW. These plasmas have little or no edge localized mode (ELM) activity during HHFW heating, a substantial increase in stored energy and a sustained central electron temperature of 5-6 keV. Another focus of NSTX HHFW research is to heat an H-mode generated by 90 keV neutral beam injection (NBI). Improved HHFW coupling to NBI-generated H-modes has resulted in a broad increase in electron temperature profile when HHFW heating is applied. Analysis of a closely matched pair of NBI and HHFW+NBI H-mode plasmas revealed that about half of the antenna power is deposited inside the last closed flux surface (LCFS). Of the power damped inside the LCFS about two-thirds is absorbed directly by electrons and one-third accelerates fast-ions that are mostly promptly lost from the plasma. At longer toroidal launch wavelengths, HHFW+NBI H-mode plasmas can have an RF power flow to the divertor outside the LCFS that significantly reduces RF power deposition to the core. ELMs can also reduce RF power deposition to the core and increase power deposition to the edge. Recent full wave modeling of NSTX HHFW+NBI H-mode plasmas, with the model extended to the vessel wall, predicts a coaxial standing mode between the LCFS and the wall that can have large amplitudes at longer launch wavelengths. These simulation results qualitatively agree with HHFW+NBI H-mode data that show decreasing core RF heating efficiency and increasing RF power flow to the lower divertor at longer launch wavelengths