Interferometry in an Atomic Fountain with Ytterbium Bose–Einstein Condensates

We present enabling experimental tools and atom interferometer implementations in a vertical “fountain” geometry with ytterbium Bose–Einstein condensates. To meet the unique challenge of the heavy, non-magnetic atom, we apply a shaped optical potential to balance against gravity following evaporative cooling and demonstrate a double Mach–Zehnder interferometer suitable for applications such as gravity gradient measurements. Furthermore, we also investigate the use of a pulsed optical potential to act as a matter wave lens in the vertical direction during expansion of the Bose–Einstein condensate. This method is shown to be even more effective than the aforementioned shaped optical potential. The application of this method results in a reduction of velocity spread (or equivalently an increase in source brightness) of more than a factor of five, which we demonstrate using a two-pulse momentum-space Ramsey interferometer. The vertical geometry implementation of our diffraction beams ensures that the atomic center of mass maintains overlap with the pulsed atom optical elements, thus allowing extension of atom interferometer times beyond what is possible in a horizontal geometry. Our results thus provide useful tools for enhancing the precision of atom interferometry with ultracold ytterbium atoms.

Resonance overlap and nonlinear features of the beam–plasma system

The beam–plasma instability can be addressed as a reduced model in several contexts of plasma physics, from space to fusion plasma. In this paper, we review and refine some nonlinear features of this model. Specifically, by analysing the dependence of the nonlinear velocity spread as a function of the linear growth rate, we discuss the effective size of the resonance in view of its role in the spectral overlap at saturation. The relevance of this characterization relies on the necessity of a quantitative determination of the overlap degree to discriminate among different transport regimes of the self-consistent dynamics. The analysis is enriched with a study of the phase-space dynamics by means of the Lagrangian coherent structure technique, in order to define the transport barriers of the system describing the relevant features of the overlap process. Finally, we discuss relevant features related to the mode saturation levels.

Colliding winds in and around the stellar group IRS 13E at the galactic centre

ABSTRACT IRS 13E is an enigmatic compact group of massive stars located in projection only 3.6 arcsec away from Sgr A*. This group has been suggested to be bounded by an intermediate-mass black hole (IMBH). We present a multiwavelength study of the group and its interplay with the environment. Based on Chandra observations, we find the X-ray spectrum of IRS 13E can be well characterized by an optically thin thermal plasma. The emission peaks between two strongly mass-losing Wolf–Rayet stars of the group. These properties can be reasonably well reproduced by simulated colliding winds of these two stars. However, this scenario underpredicts the X-ray intensity in outer regions. The residual emission likely results from the ram-pressure confinement of the IRS 13E group wind by the ambient medium and is apparently associated with a shell-like warm gas structure seen in Pa α and in ALMA observations. These latter observations also show strongly peaked thermal emission with unusually large velocity spread between the two stars. These results indicate that the group is colliding with the bar of the dense cool gas mini-spiral around Sgr A*. The extended X-ray morphology of IRS 13E and its association with the bar further suggest that the group is physically much farther away than the projected distance from Sgr A*. The presence of an IMBH, while favourable to keep the stars bound together, is not necessary to explain the observed stellar and gas properties of IRS 13E.

Identifying and predicting multiples based on spread of velocity spectrum

The genesis of internal multiples is complicated and identification is difficult as their velocities are similar to the velocity of primaries, so their residual time is short. The existing conventional methods for identifying multiples are mainly used on a single-common mid-point (CMP) or single line, so the result is indistinct and inaccurate. The concept of velocity spread is proposed, whereby multiples are identified by obtaining the lateral spread of energy clusters on the velocity spectrum. The proposed method uses image segmentation to binarise the velocity spectrum, obtain the spread of velocity, and identify and predict multiples on the plane via attribute spread slicing. In a 3D seismic of Sichuan, the multiples predicted are in good agreement with the known wells. The case shows that velocity spread analysis can quantitatively identify and predict multiples interference, and is complementary to the existing multiples identification method. It can be used to monitor the multiples suppression effect in seismic processing and analyse the interference of multiples in interpretation. In addition, the method has good practicability for evaluating the reliability of reservoir prediction results and reduces the risk of well location deployment during exploration.

Mass separated particle flux from a laser-ablation metal cluster source

Flux waveforms of aluminum cluster beams supplied from a laser-ablation cluster source were precisely investigated under various source conditions such as background pressure, ablation laser intensity, and nozzle structure. A time-of-flight mass spectroscopy revealed that aluminum clusters with sizes up to 200 were generated and the amount of the clusters could be maximized by choosing a proper background pressure (~2 MPa) and an ablation laser fluence (~40 mJ/cm2). Flux waveforms of clusters having specific sizes were carefully reconstructed from the observed mass spectra. It is found that the pulse widths of the aluminum cluster beams were typically about 100 µs and much smaller than that of the monoatomic aluminum beam, indicating that the cluster formation was limited in a relatively small volume in the laser-ablated vapor. Introducing a conical nozzle having a large open angle was also found to enhance the cluster beam velocity and reduce its pulse width. A velocity measurement of particles in the cluster beam was conducted to examine the velocity spread of the supplied clusters. We found that the aluminum clusters were continuously released from the source for about 100 µs and this release time mainly determined the pulse width of the cluster beam, suggesting that controlling the behavior of an ablated vapor plume in the waiting room of the cluster source holds the key to drastically improving the cluster beam flux.

Axial modes in terahertz high-harmonic large-orbit gyrotrons

Terahertz (THz) gyrotrons can operate with a lower applied magnetic field in harmonic operation, but the weakened harmonic interactions in harmonic gyrotrons can introduce serious challenges when mode competition occurs. The use of an axis-encircling electron beam can greatly alleviate mode competition in a harmonic gyrotron. In this paper, we study axial modes for third-harmonic [Formula: see text]-mode large-orbit gyrotrons. Simulation results reveal that the minimum current for oscillation to begin in each axial mode in the gyrotron regime is associated with a specific range of applied magnetic field. To avoid mode competition, tapered applied magnetic fields and waveguide radii are employed to enhance the high-order axial modes and suppress the low-order axial modes. Furthermore, spurious transverse modes in a THz gyrotron are discussed below. A stable third-harmonic [Formula: see text]-mode large-orbit gyrotron at the third-order axial mode is predicted to yield peak output power of 6.5 kW at 768.1 GHz with an efficiency of 10% for a 75-kV, 0.85-A electron beam with an axial velocity spread of 3%.