Slow Beam Research Articles

MuCool: muon cooling for high-brightness μ+ beams

A number of experiments with muons are limited by the poor phase space quality of the muon beams currently available. The muCool project aims at developing a phase-space cooling method to transform a surface \mu^+μ+ beam with 4 MeV energy and 1 cm size into a slow muon beam with eV energy and 1 mm size. In this process the phase space is reduced by a factor of 10^{9}-10^{10}109−1010 with efficiencies of 2\cdot 10^{-5}-2\cdot 10^{-4}2⋅10−5−2⋅10−4. The beam is then re-accelerated to keV-MeV energies. Such a beam opens up new avenues for research in fundamental particle physics with muons and muonium atoms as well as in the field of \muμSR spectroscopy.

Systematic study and uncertainty evaluation of P, T-odd molecular enhancement factors in BaF.

A measurement of the magnitude of the electric dipole moment of the electron (eEDM) larger than that predicted by the Standard Model (SM) of particle physics is expected to have a huge impact on the search for physics beyond the SM. Polar diatomic molecules containing heavy elements experience enhanced sensitivity to parity (P) and time-reversal (T)-violating phenomena, such as the eEDM and the scalar-pseudoscalar (S-PS) interaction between the nucleons and the electrons, and are thus promising candidates for measurements. The NL-eEDM collaboration is preparing an experiment to measure the eEDM and S-PS interaction in a slow beam of cold BaF molecules [P. Aggarwal et al., Eur. Phys. J. D 72, 197 (2018)]. Accurate knowledge of the electronic structure parameters, Wd and Ws, connecting the eEDM and the S-PS interaction to the measurable energy shifts is crucial for the interpretation of these measurements. In this work, we use the finite field relativistic coupled cluster approach to calculate the Wd and Ws parameters in the ground state of the BaF molecule. Special attention was paid to providing a reliable theoretical uncertainty estimate based on investigations of the basis set, electron correlation, relativistic effects, and geometry. Our recommended values of the two parameters, including conservative uncertainty estimates, are 3.13 ±0.12×1024Hzecm for Wd and 8.29 ± 0.12 kHz for Ws.

Slow beam extraction method from synchrotron for uniform spill and fast beam switching using an RF knockout method of multi-band colored noise signal—POP Experiment and simulation

A proof of principle experiment (POP) was performed at the WERC synchrotron on the innovative slow beam extraction method with use of RF-knockout. The goal of experiment was to demonstrate the usefulness of the concept of colored noise signals including many frequency bands around the betatron resonances to obtain the uniform beam spill and the fast beam switching off time. The beam experiment shows that a small standard deviation of spill fluctuation can be attained without the longitudinal beam bunching of circulating particles. It is also shown that a beam switching-off time of around 100 μs could be obtained with a uniform spill. The experimental results are compared with the simulation results.

Fiber coupling technology of high brightness blue laser diode

With the development and application of blue semiconductor lasers, it has become a research hotspot to obtain high brightness blue light source by beam combining technology. In order to obtain high brightness blue light output, 48 single tube semiconductor lasers with wavelength of 450 nm and output power of 3.5 W are focused and coupled into 105 μm/0.22 NA fiber by fast slow axis collimation and spatial beam combination. The blue light with power of 144.7 W and brightness of 11 MW/(cm2str) is obtained. The coupling efficiency is 93.78%, and the optical to optical conversion efficiency of the whole system is 86.13%.

On Fabry–Pérot Etalon-based Instruments. IV. Analytical Formulation of Telecentric Etalons

Abstract Fabry–Pérot etalons illuminated with collimated beams have been analytically characterized in detail since their invention. Meanwhile, most of the features of etalons located in telecentric planes have been studied only numerically, despite the wide use of this configuration in astrophysical instrumentation for decades. In this work we present analytical expressions for the transmitted electric field and its derivatives that are valid for etalons placed in slow telecentric beams, like the ones commonly employed in solar instruments. We use the derivatives to infer the sensitivity of the electric field to variations in the optical thickness for different reflectivities and apertures of the incident beam, and we compare them to the collimated case. This allows us to estimate the wavefront degradation produced by roughness errors on the surfaces of the Fabry–Pérot etalons and to establish the maximum allowed rms value of the cavity irregularities across the footprint of the incident beam on the etalons that ensures diffraction-limited performance. We also evaluate the wavefront degradation intrinsic to these mounts, which is produced only by the finite aperture of the beam and that must be added to the one produced by defects. Finally, we discuss the differences in performance of telecentric and collimated etalon-based instruments and we generalize our formulation to anisotropic etalons.

Wave propagation with degenerate electron–positron in magnetically quantised ion beam plasma

In an ion beam plasma system, the effect of magnetically quantised degenerate trapped electron and positron, on small-amplitude ion-acoustic solitary waves are studied with the help of Korteweg–de Vries (KdV) equation. Here the magnetised positive ions and beam ions are considered as non-degenerate. The effect of magnetic quantisation, degenerate temperature, normalised positron concentration, normalised ion beam concentration along with other relevant physical plasma parameters of the origin of astrophysical plasma environment, on solitary wave propagation is studied especially in the nonlinear regime. On the other hand, in the linear regime, the dependency of frequency and wavenumber on the aforementioned plasma parameters are discussed. It is found that both compressive and rarefactive type solitary waves can exist in such a plasma environment. Three different modes of propagation, the fast beam and slow beam modes and the inherent ion-acoustic mode coexist in such plasma systems and the role of different degenerate plasma parameters on these wave modes are also discussed in detail. The normalised positron concentration and velocity, as well as the normalised ion beam concentration along with different degenerate plasma parameters, has an astounding control on the amount of compression and rarefaction, a typical plasma wave mode is supposed to undergo. Within the chosen degenerate and non-degenerate plasma parameters, for a compressive (rarefactive) fast beam mode, the slow mode appears as rarefactive (compressive). For some typical combinations of degenerate parameters, the fast mode can propagate with a hypersonic phase velocity which shows distinctive characteristics with positron density.

Lithium-cesium slow beam from a two-dimensional magneto-optical trap

We present the creation of a lithium-cesium slow beam using a two-dimensional magneto-optical trap. The two-species atomic beam is directed to load a three-dimensional magneto-optical trap in ultrahigh vacuum. We achieve a loading rate of 1.3$\times$10$^{7}$ lithium atoms/s with the lithium oven temperature at 370~$^{\circ}$C and 2.2$\times$10$^{7}$ cesium atoms/s with the Cs oven temperature at 20~$^{\circ}$C. The maximum numbers of lithium and cesium atoms in the trap are 1.0$\times$10$^{9}$ and 1.4$\times$10$^{8}$, respectively. Our results show that the simple and compact two-dimensional magneto-optical trap is suitable for producing an atomic beam of two species that have a large mass ratio and very different volatilities.

Fast and slow beam mode ion-acoustic solitons in plasmas with counterstreaming cold protons

It was recently shown (Lakhina et al (2020), Physica Scr. 95, 105601) that in a plasma of hot electrons and two counterstreaming warm proton beams, a slow ion-acoustic solitary mode occurred, where the soliton speeds decreased from the critical acoustic speeds, while the amplitudes increased. This contradicts conventional wisdom that solitons are inherently ‘super-acoustic’, the soliton speeds exceeding the linear acoustic speed, and that amplitudes grow with soliton speed. To elucidate and further elaborate on these findings, a simpler model is considered, in which the ion beam species are cold, neglecting their thermal effects. This retains the essence of the physics, but simplifies the analysis. It permits a full parametric discussion of the existence ranges for such solitons, not only for the critical Mach numbers, but also for the limit amplitudes, by using fluid density restrictions for the ions. If the beam speed exceeds a threshold, two acoustic regimes are found: a fast beam mode with the usual super-acoustic solitons, and a slow beam mode, where solitons are sub-acoustic, at least in the laboratory frame. This confirms the earlier result, but shows that it is primarily a beam effect, rather than an ion thermal effect. The observation can be explained: in the ion beam frame, the solitons are indeed super-acoustic. However, those travelling in the negative direction are swept forwards by the fast beam and hence are observed in the laboratory frame as being sub-acoustic. A similar approach is used for a case of asymmetric proton beams, with unequal ion densities and beam speeds.

Experimental investigation of the package of diode laser chip based on lateral heat flow suppression

To improve slow axis beam quality of diode laser (LD) and decrease slow axis divergence angle, a new package with lateral heat flow suppression was designed utilizing the difference in thermal conductivity between air and heat sink. The finite element analysis software was used to analyze the temperature distribution with lateral flow suppression package. It is shown that diode laser chip soldered on trough heat sink with width W=120 μm and length L=4000 μm can reduce slow axis divergence angle about 14%, from 12.25° to 10.49°, when working current was 15A. Correspondingly, beam parameter product (BPP) can reduce from 5.344 mm·mrad to 4.5763 mm·mrad and the brightness of slow axis increased about 5.5% than before. According to the result, the lateral flow suppression package can weaken higher order mode caused by thermal lens effect of diode laser so that decrease slow axis divergence angle effectively.

A slow and clean fluorine atom beam source based on ultraviolet laser photolysis

A slow and clean fluorine atom beam source is one of the essential components for the low-collision energy scattering experiment involving fluorine atom. In this work, we describe a simple but effective photolysis fluorine atom beam source based on ultraviolet laser photolysis, the performance of which was demonstrated by high-resolution time-of-flight spectra from the reactive scattering of F+HD. This beam source paved the way for studies of low energy collisions with fluorine atoms.

Methods for measuring the electron’s electric dipole moment using ultracold YbF molecules

Measurements of the electron’s electric dipole moment (eEDM) are demanding tests of physics beyond the standard model. We describe how ultracold YbF molecules could be used to improve the precision of eEDM measurements by two to three orders of magnitude. Using numerical simulations, we show how the combination of magnetic focussing, two-dimensional transverse laser cooling, and frequency-chirped laser slowing, can produce an intense, slow, highly-collimated molecular beam. We show how to make a magneto-optical trap of YbF molecules and how the molecules could be loaded into an optical lattice. eEDM measurements could be made using the slow molecular beam or using molecules trapped in the lattice. We estimate the statistical sensitivity that could be reached in each case and consider how sources of noise can be reduced so that the shot-noise limit of sensitivity can be reached. We also consider systematic effects due to magnetic fields and vector light shifts and how they could be controlled.

A Blinking Mesoporous TiO2−x Composed of Nanosized Anatase with Unusually Long‐Lived Trapped Charge Carriers

AbstractA mesoporous TiO2−x material comprised of small, crystalline, vacancy‐rich anatase nanoparticles (NPs) shows unique optical, thermal, and electronic properties. It is synthesized using polymer‐derived mesoporous carbon (PDMC) as a template. The PDMC pores serve as physical barriers during the condensation and pyrolysis of a titania precursor, preventing the titania NPs from growing beyond 10 nm in size. Unlike most titania nanomaterials, during pyrolysis the NPs undergo no transition from the anatase to rutile phase and they become catalytically active reduced TiO2−x. When exposed to a slow electron beam, the NPs exhibit a charge/discharge behavior, lighting up and fading away for an average period of 15 s for an extended period of time. The NPs also show a 50 nm red‐shift in their UV/Vis absorption and long‐lived charge carriers (electrons and holes) at room temperature in the dark, even long after UV irradiation. The NPs as photocatalysts show a good activity for CO2 reduction.

A Blinking Mesoporous TiO2-x Composed of Nanosized Anatase with Unusually Long-Lived Trapped Charge Carriers.

A mesoporous TiO2-x material comprised of small, crystalline, vacancy-rich anatase nanoparticles (NPs) shows unique optical, thermal, and electronic properties. It is synthesized using polymer-derived mesoporous carbon (PDMC) as a template. The PDMC pores serve as physical barriers during the condensation and pyrolysis of a titania precursor, preventing the titania NPs from growing beyond 10 nm in size. Unlike most titania nanomaterials, during pyrolysis the NPs undergo no transition from the anatase to rutile phase and they become catalytically active reduced TiO2-x . When exposed to a slow electron beam, the NPs exhibit a charge/discharge behavior, lighting up and fading away for an average period of 15 s for an extended period of time. The NPs also show a 50 nm red-shift in their UV/Vis absorption and long-lived charge carriers (electrons and holes) at room temperature in the dark, even long after UV irradiation. The NPs as photocatalysts show a good activity for CO2 reduction.

Reducing Fluctuations in Slow-Extraction Beam Spill Using Transit-Time-Dependent Tune Modulation

Slow extraction of beam from synchrotrons or storage rings as required by many fixed target experiments is performed by controlled excitation and feeding of a structural lattice resonance. Due to the sensitive nature of this resonant extraction process, the temporal structure of the extracted beam is modulated by the minuscule current fluctuations present on the quadrupole magnet power supplies. Such a modulation lead to pile-ups in detectors and a significant reduction in accumulated event statistics. This contribution proposes and experimentally demonstrates that by an introduction of further modulation on quadrupole currents with a specific amplitude and frequency, the inherent power supply fluctuations are mitigated leading to a smoothening of the beam temporal structure. The slow extraction beam dynamics associated with this method are explained along with the operational results.

Guiding a 7.5 keV Ar3+ ion beam using a cylindrical glass channel

Although guiding slow multi-charge ion beams using insulator capillaries has been vigorously studied for the last two decades, controlling the shape and surface condition of the inner wall of the capillary has been an issue. We attempted to guide 7.5 keV Ar3+ ion beams using a channel formed by a pair of cylindrical convex glass and a cylindrical concave glass to resolve this issue. We measured both the charge state and the kinetic energy of the exiting ions from the cylindrical glass channel. The ions kept both their initial charge state and initial kinetic energy during transportation in the channel, even at tilt angles from ‒3° to +3°. Guiding using a pair of curved glass surfaces has the advantage of more easily controlling the shape and surface condition of the capillary. This technique can make it easy to precisely adjust the incident angle of the ion beam onto various targets.

Three-Dimensional Cooling of an Atom-Beam Source for High-Contrast Atom Interferometry

We present a compact, two-stage atomic beam source that produces a continuous, narrow, collimated and high-flux beam of rubidium atoms with sub-Doppler temperatures in three dimensions, which features very low emission of near-resonance fluorescence along the atomic trajectory. The atom beam source originates in a pushed two-dimensional magneto-optical trap (2D$^+$ MOT) feeding a slightly off-axis three-dimensional moving optical molasses stage that continuously cools and redirects the atom beam. The capture velocity of the moving optical molasses is deliberately chosen to be low, $\sim 3$ m/s, to reduce fluorescence, and the cooling light is detuned by several atomic linewidths from resonance to reduce the absorption cross-section of cooling-induced fluorescence. Near-resonance light from the 2D$^+$ MOT and the push beam does not propagate to the output atomic trajectory due to a 10 degree bend in the atomic trajectory. The atomic beam emitted from the two-stage source has a flux up to $1.6(3)\times 10^9\;\textrm{atoms/s}$, with an optimized temperature of $15.0(2)\;\mu$K. We employ continuous Raman-Ramsey interference measurements at the atom beam output to study the sources of decoherence in the presence of continuous cooling, and demonstrate that the atom beam source effectively preserves high fringe contrast even during cooling. This cold-atom beam source is appropriate for use in atom interferometers and clocks, where continuous operation eliminates dead time, the slow atom beam velocity (6 - 16 m/s) improves sensitivity, the narrow 3D velocity distribution improves fringe contrast, and the low reabsorption of scattered light mitigates decoherence caused by the continuous cooling process.

A new route for laser cooling and trapping of cold molecules: Intensity-gradient cooling of MgF molecules using localized hollow beams

We propose a promising scheme to prepare ultracold MgF molecules from a slowed cold molecular beam by using three-dimensional pure intensity-gradient induced Sisyphus cooling. The cooling is based on a blue-detuned localized hollow beam and a weak repumping beam. We investigate the dynamic process in the trap with the method of the Monte-Carlo simulations, verifying the feasibility. Our results show that achieving sub-Doppler temperature should be possible in such a well-designed trap; the trapped MgF molecules with initial temperature of can be directly cooled to the final equilibrium temperature of about well below the Doppler limit (about for MgF); meanwhile, molecules with initial temperature of can be even cooled to about

Two types of highly efficient electrostatic traps for single loading or multi-loading of polar molecules**Project supported by the National Natural Science Foundation of China (Grant Nos. 11834003, 91536218, 11034002, 11274114, 11504112, and 11874151), the National Key Basic Research and Development Program of China (Grant No. 2011CB921602), the Fundamental Research Funds for the Central Universities, China, Shanghai Pujiang Talents Plan, China

Two novel electrostatic traps named octopole-based disk electrostatic trap (ODET) and tubular-based disk electrostatic trap (TDET) are proposed for trapping cold polar molecules in low-field-seeking states. Using MgF as the target molecule, single loading and multi-loading methods are numerically simulated with varied incident velocities of slow molecular beams in the two types of traps, respectively. In ODET, with an incident velocity of 10 m/s, a highest loading efficiency of 78.4% or 99.9% has been achieved under the single loading or multi-loading operation mode. In TDET, with an incident velocity of 11 m/s, a highest loading efficiency of 81.6% or 106.5% has been achieved using the two loading methods, respectively. With such high loading efficiencies, the trapped cold molecules can be applied in the researches of cold collisions, high precision spectroscopy, and precision measurements. Especially, together with a blue-detuned hollow beam, the new electrostatic traps proposed here offer a new platform for the following gradient-intensity cooling of MgF molecules, which may provide a new way to produce high density ultracold molecules.

Reduction of 400 GeV/c slow extraction beam loss with a wire diffuser at the CERN Super Proton Synchrotron

Slow extraction of a quasicontinuous flux of high-energy protons is an important requirement for many high-energy physics experiments. This extraction type is associated with an unavoidable beam loss due to scattering on the thin septum element. The energy deposition of scattering products and resulting activation place performance limits on existing and planned high-power, high-energy fixed-target proton facilities. In the $400\text{ }\text{ }\mathrm{GeV}/c$ Super Proton Synchrotron (SPS) at CERN, a diffuser (or prescatterer), comprising an array of dense wires or ribbon located upstream of the electrostatic septum, has been designed to reduce absolute losses on the septum wires. As part of a concerted effort to investigate loss reduction techniques in the SPS in view of new physics experiments, the diffuser concept was explored in numerical simulation and analytically. A prototype device has been designed, built, installed, and tested in the SPS to prove the feasibility and quantify the performance reach. In this paper, the diffuser concept is briefly recalled and design considerations for the SPS use case are presented, with the analytical considerations and simulation studies for the optimization of the material and geometry. The device design is described, and the experimental results with a beam are presented and analyzed. The results are discussed, and an outlook is given for the operational feasibility and maximum obtainable performance gain. Conclusions are drawn on the implications for the application of the concept.

Characterization of Neutron Beam Applications

Analytic framework to quantitatively evaluate the performance of existing neutron scattering instruments would be valuable to find out new possibilities and potentials of slow neutron beams. A conceptual sketch of ongoing effort in Japan is described.