An investigation of combustion instability in aircraft-engine reheat systems

The principal objective of this study was to examine experimentally the effects of upstream temperature, velocity, gutter blockage, tailpipe length, and main and pilot fuel flows, on the form of combustion instability encountered in aircraft reheat systems which is sometimes referred to as 'buzz'. Tests were carried out at atmospheric pressure for upstream temperatures of between 200 and 500°C, and upstream velocities ranging from 140 to 200 ft/sec. Three values of stabilizer blockage were employed, namely 25, 30 and 35%. The tailpipe length was varied between 9 and 45 inches. Auto-correlation techniques were used in the frequency analysis of the buzz waveforms. It was found that a certain minimum tailpipe length is necessary in order to produce buzz which is then strengthened as the tailpipe length is increased. Buzz also becomes more pronounced with an increase in gas velocity but stabilizer blockage appears to have no discernible effect … [cont.]

Quasimonoenergetic electron beams produced by colliding cross-polarized laser pulses in underdense plasmas

The interaction of two laser pulses in an underdense plasma has proven to be able to inject electrons in plasma waves, thus providing a stable and tunable source of electrons. Whereas previous works focused on the "beatwave" injection scheme in which two lasers with the same polarization collide in a plasma, this present letter studies the effect of polarization and more specifically the interaction of two colliding cross-polarized laser pulses. It is shown both theoretically and experimentally that electrons can also be pre-accelerated and injected by the stochastic heating occurring at the collision of two cross-polarized lasers and thus, a new regime of optical injection is demonstrated. It is found that injection with cross-polarized lasers occurs at higher laser intensities.Comment: 4 pages, 4 figure

Mott transition, antiferromagnetism, and unconventional superconductivity in layered organic superconductors

The phase diagram of the layered organic superconductor $\kappa$-(ET)$_{2}$Cu[N(CN)$_{2}$]Cl has been accurately measured from a combination of $^{1}$H NMR and AC susceptibility techniques under helium gas pressure. The domains of stability of antiferromagnetic and superconducting long-range orders in the pressure {\it vs} temperature plane have been determined. Both phases overlap through a first-order boundary that separates two regions of inhomogeneous phase coexistence. The boundary curve is found to merge with another first order line related to the metal-insulator transition in the paramagnetic region. This transition is found to evolve into a crossover regime above a critical point at higher temperature. The whole phase diagram features a point-like region where metallic, insulating, antiferromagnetic and non s-wave superconducting phases all meet.Comment: 4 pages, 6 figures, Revte

Early out-of-equilibrium beam-plasma evolution

We solve analytically the out-of-equilibrium initial stage that follows the injection of a radially finite electron beam into a plasma at rest and test it against particle-in-cell simulations. For initial large beam edge gradients and not too large beam radius, compared to the electron skin depth, the electron beam is shown to evolve into a ring structure. For low enough transverse temperatures, the filamentation instability eventually proceeds and saturates when transverse isotropy is reached. The analysis accounts for the variety of very recent experimental beam transverse observations.Comment: to appear in Phys. Rev. Letter