Clean Beam Research Articles

Hyperons in neutron stars: studies of hyperon spectroscopy and the hyperon-nucleon interaction with the K-long Facility.

Elucidating the role of strange baryons (hyperons) in neutron stars requires detailed knowledge of hyperon-nucleon interactions in the light (u,d,s) quark sector. The structure of the hyperons and their excitation spectra also directly impact, and are an input to, models of big-bang nucleosynthesis. The upcoming K-long Facility will provide a much-needed intense and clean neutral strange meson beam, from which hyperons can be produced at rates where hyperon structure, hyperon-nucleon interactions and higher-order interactions can be studied with a new level of accuracy and for hitherto unreachable measurements. The new facility has the potential to address long-standing questions surrounding the strange sector of the strong force and its relevance to the structure of atomic nuclei, neutron stars and the cosmos at large. This article is part of the theme issue 'The liminal position of Nuclear Physics: from hadrons to neutron stars'.

Cathode etching phenomenon of high beam-anode ion source and its elimination measures

High beam-anode layer ion source can produce high-density ions, and has been widely used in plasma cleaning and assisted deposition. However, when increasing the ion-beams, arcing always occurs inside the ion source and serious etching will take place on the cathode, which results in sample pollution especially in long-time cleaning. In this work, two structures are designed, which are magnetic shielding around the anode and sputtering shielding on the top of the inner cathode and outer cathode, respectively. Based on the particle-in-cell/Monte Carlo collision method and test particle Monte Carlo method, the influence of designed structure on the electromagnetic field and the plasma properties of the ion source are studied through self-established simulation technique. The results show that the magnetic shielding around the anode cuts off the magnetic induction line between the cathode and anode, eliminating the arcing condition in the ion source. The sputtering shielding for the cathode uses alumina ceramic because of its extremely low sputtering yield and high insulation performance. Therefore, the sputtering shields can not only resist the ion sputtering, but also shield the electric field on the outer surface of the cathode. As a result, the plasma discharge region is compressed towards the anode and away from the cathode simultaneously, which provides a stronger electric field force directing to the output region for Ar<sup>+</sup> ions, and also results in a suppressed cathode etching behavior but an improved Ar<sup>+</sup> ion output efficiency. The optimized calculation shows that the best distance from the sputtering shield to the cathode surface is 9 mm. The discharge experiments reveal that the modified ion source can eliminate the inside arcing and provide a clean and strong ion beam with a high efficiency. At the same discharge current, the output efficiency of the modified ion source is 36% higher than that of the original ion source. When used in the plasma cleaning, the glass substrate remains transparent and keeps the original element composition ratio unchanged. The detected Fe content, coming from the cathode sputtering, is only 0.03% after the one-hour plasma cleaning, which is 2 orders of magnitude smaller than that cleaned by the original ion source. The Fe content of the modified ion source is about 0.6% of the original ion source, which is in good agreement with the result of simulation optimization.

Generating ultrashort visible light pulses based on multidimensional solitary states in gas-filled hollow core fiber

Multidimensional solitary states (MDSS) are self-sustaining light wave packets confined in multiple dimensions in multimode fibers. In this work, we experimentally demonstrate the generation of MDSS, driven by a few hundreds of femtoseconds (fs) of long frequency doubled pulses from a Titanium:Sapphire chirped pulsed amplifier in a nitrous oxide-filled hollow core fiber (HCF). The MDSS output, resulting from intermodal interactions in a Raman-active gas-filled large core diameter HCF, features a broadband, red-shifted spectrum in the visible spectral region with a characteristic negative quadratic spectral phase. Therefore, the output with broadband spectra and negative chirp results in the generation of sub-30 fs pulses upon propagation through glass windows and a spectral filter. Backed with experimental observations and multidimensional simulations, we demonstrate that the sign of the frequency chirp of input pulses influences the spectral broadening in the HCF in the high gas-dispersion regime. We observed that the MDSS red-shifted pulses have a clean spatial profile. Therefore, the experimental requirements on the input beam size and quality to achieve a clean MDSS beam profile at the output of large core HCFs can be relaxed. Hence, this work extends the validation of the MDSS phenomenon toward the ultraviolet-visible region of the electromagnetic spectrum, thus providing an alternate source with a clean spatial beam profile for various applications in the field of ultrafast spectroscopy.

Highly Stable Vibration Measurements by Common-path off-axis Digital Holography

Measurements of vibration and dynamic deformation with high resolution and accuracy by non-destructive techniques are of great interest in many branches of engineering. We report a non-destructive method based on digital holographic interferometry for high-precision micro-vibration measurement of a 3D object. Herein, a new and simple configuration of a common-path off-axis digital holographic system, with high mechanical stability and compact in size, is proposed. The simplicity, compactness, and high stability of the proposed setup are provided by employing a wedge plate in-line with the test object to create a clean reference beam. The object and reference beams propagate the same path, without the need for any specialized optical component or arrangement, and these beams allow to interfere on the faceplate of the image sensor to form a digital hologram. The feasibility of the proposed system is demonstrated by measuring the vibration of the objects driven by different excitation signals. A series of digital holograms of a vibrating object is recorded by the use of a high-speed image sensor. The result of the reconstruction of the recorded holograms is an array of complex numbers containing the complete amplitude and phase profile of the object, which in turn provides displacement and vibration information. Due to its simple geometry and significant outcomes, the proposed system could be established as a powerful tool for a wide range of optical imaging and measurement investigations.

Beta spectrum shape studies for the predictions of the antineutrino spectrum from reactors

Nuclear reactors antineutrino measurements at short baselines do not fully agree with model predictions calculated with the Conversion Method. An alternative method to calculate the antineutrino spectra is theSummation Method. Both methods require the shapes of beta spectra as inputs. For that reason a new setup to measure the shape of the beta spectrum of relevant fission products for the calculation of the antineutrino spectra of reactors has been developed. Some preliminary measurements performed at IGISOL with isotopically clean beams are presented in this contribution.

A fast deconvolution method for multiple sound source localization based on Hilbert curve

To improve the resolution and efficiency of the multiple sound source localization, a fast deconvolution method based on the Hilbert curve, called CLEAN-VH, is developed in this paper. Firstly, the initial cross-spectral matrix of the measured array signal is decomposed by eigenvalue decomposition, and a new cross-spectral matrix function is constructed using the eigenvalues and eigenvectors. Then, the function is used to update the cross-spectral matrix in the process of deconvolution iteration (CLEAN), and the Hilbert curve is introduced to improve the computational efficiency of the output power in the monitoring area. Finally, the distribution of multiple sound sources can be obtained by superimposing the clean beams and residual power spectrum. The superiority of CLEAN-VH is proved by analyzing the key parameters of the method. The search area optimization based on Hilbert curve greatly alleviates the grid mismatch problem and improves the performance of the proposed method. Through the simulation and experimental comparisons with the other three algorithms, such as CLEAN, FB and CLEAN-SC, the proposed CLEAN-VH achieves high-resolution localization of multiple sound sources, better dynamic range and higher computation efficiency. The proposed method provides another choice for the localization of multiple sound sources.

EXPERIMENTAL STUDY ON BEHAVIOR OF SALT-CONTAMINATED SAND CONCRETE BEAM WITH EPOXY COATED REINFORCEMENT

This paper presents the results of comparing the instantaneous working performance in the period before the plastic reinforcement, of the saline aggregate reinforced concrete beams and the clean sand aggregate reinforced concrete beams. The authors performed theoretical and experimental calculations on the bearing capacity of three pairs of beams (salinated sand beams – clean sand beams) corresponding to concrete with strength levels B20, B30 and B45. Concrete with salt-contaminated sand aggregates using corrosion inhibitors and reinforced steel is coated with epoxy coating with thickness 175±18µm. Saline sand aggregates Thuan An - Hue, Tra Khuc - Quang Ngai and Bai Dai - Van Don (Quang Ninh), clean sand aggregates are Song Lo yellow sand. Concrete beams are calculated according to TCVN 5574-2018 standard and tested according to TCVN 9347-2012.

Accurate Calibration of Nuclear Recoils at the 100 eV Scale Using Neutron Capture

Searches for light dark matter (DM) and studies of coherent elastic neutrino-nucleus scattering (CEvNS) imply the detection of nuclear recoils in the 100 eV range. However, an absolute energy calibration in this regime is still missing. The CRAB project proposes a method based on nuclear recoils induced by the emission of an MeV gamma following thermal neutron capture. A detailed feasibility study has shown that this method yields distinct nuclear recoil calibration peaks at 112 eV and 160 eV above background for tungsten. In the first phase, the CRAB project foresees to perform a nuclear recoil calibration of cryogenic CaWO4 detectors read-out by TES, similar to the detectors used in CRESST and NUCLEUS. The low-power TRIGA reactor in Vienna provides a clean beam of thermal neutrons well suited for such a measurement. Newly developed and compact sub-keV calibration sources based on x-ray fluorescence (XRF) provide an absolute energy calibration during operation at the research reactor as well as in the DM/CEvNS experiments. In the second phase, additional tagging of the photons produced in the de-excitation process will allow extending the calibration method to even lower energies and to a wider range of detector materials, such as Ge. Combined with the XRF source, CRAB may allow measuring energy quenching in the sub-keV regime.

Quantitative dynamic evolution of physiological parameters of RBC by highly stable digital holographic microscopy

Digital holographic microscopy (DHM) is a powerful label-free imaging tool that provides three-dimensional (3D) quantitative information of a specimen. In this work, the evaluation of morphological and quantitative parameters of human red blood cells (RBCs) by a new single-shot common-path off-axis digital holographic microscopic system is demonstrated. The proposed system is accomplished by employing a wedge plat, silver-coated at its back surface, into the object beam path generating two beams: one from the front surface and another from the back surface of the wedge plate. One of the beams is spatially filtered by using a pinhole to completely erase the object information from it and serving the clean reference beam, which on interfering with the object beam, creates the hologram. The proposed system, owing to common-path configuration, offers higher temporal phase stability, therefore, making it more suitable for the investigation of small cell thickness fluctuation. Moreover, the system is simple, compact, less expensive, and less vibration sensitive. The measurements of morphological and quantitative parameters, and membrane fluctuations of the human RBCs by the proposed system are reported. The experimentally calculated parameters of the RBC are obtained in good agreement with their normal physiological range.

ALMA Super-resolution Imaging of T Tau: r = 12 au Gap in the Compact Dust Disk around T Tau N

Abstract Based on Atacama Large Millimeter/submillimeter Array (ALMA) observations, compact protoplanetary disks with dust radii of r ≲ 20–40 au were found to be dominant in nearby low-mass star formation regions. However, their substructures have not been investigated because of the limited spatial resolution achieved so far. We apply a newly developed super-resolution imaging technique utilizing sparse modeling (SpM) to explore several au-scale structures in such compact disks. SpM imaging can directly solve for the incomplete sampling of visibilities in the spatial frequency and potentially improve the fidelity and effective spatial resolution of ALMA images. Here we present the results of the application to the T Tau system. We use the ALMA 1.3 mm continuum data and achieve an effective spatial resolution of ∼30% (5 au) compared with the conventional CLEAN beam size at a resolution of 17 au. The reconstructed image reveals a new annular gap structure at r = 12 au in the T Tau N compact disk, with a dust radius of 24 au, and resolves the T Tau Sa and Sb binary into two sources. If the observed gap structure in the T Tau N disk is caused by an embedded planet, we estimate a Saturn-mass planet when the viscous parameter of the disk is 10−3. Ultimately, ALMA observations with enough angular resolution and sensitivity should be able to verify the consistency of the super-resolution imaging and definitely confirm the existence of this disk substructure.

High-peak-power structured beams by an Nd:YAG/Cr4+:YAG laser in a near-hemispherical cavity.

An Nd:YAG/Cr4+:YAG passively Q-switched (PQS) laser in a near-hemispherical cavity is exploited to generate high-order structured pulsed fields. Under tightly focused on-axis pumping, radial-order Laguerre-Gaussian (LG) modes with controllable mode orders by the input pump power are realized to exhibit quite stable temporal behavior. The pulse repetition rates of radial-LG modes can reach up to 78 kHz with an average output power of 0.57 W and peak power beyond 300 W under a 5-W pump level. Furthermore, by introducing 1D off-axis pumping into the PQS laser, various structured pulsed fields with transverse morphologies as high-order Ince-Gaussian (IG) modes are further created. With clean and well-defined beam structures, the IG pulsed fields can be nicely reconstructed by the resonant modes of the inhomogeneous Helmholtz equation for spherical cavities. More importantly, these high-order PQS IG modes reveal highly regular pulse trains with the maximum pulse repetition rate beyond 20 kHz and overall peak power higher than 1.5 kW.

Experimental observation of Kerr beam self-cleaning in graded-index multimode fiber from higher-order mode to fundamental mode

We experimentally demonstrate Kerr beam self-cleaning in 90 m long standard graded-index (GRIN) multimode fiber (MMF) for normal and oblique launching conditions. Sub-nanosecond pump pulses are launched in the normal dispersion regime of the GRIN MMF. We measure the simultaneous evolution of the near field modal profile and the output spectrum for various pump powers under different launching conditions. Experimental findings establish that the nonlinear coupling among the guided modes leads to reshaping the output speckle pattern into a bell shape (LP01) or higher-order (LP11 and LP21) spatially clean beam profile at very low input pump powers, whereas the spectral domain exhibits generation of modulation instability peaks. Threshold power for the self-cleaning process increases effectively for higher-order modes.

Comparison of classical and Bayesian imaging in radio interferometry

CLEAN, the commonly employed imaging algorithm in radio interferometry, suffers from a number of shortcomings: In its basic version, it does not have the concept of diffuse flux, and the common practice of convolving the CLEAN components with the CLEAN beam erases the potential for super-resolution; it does not output uncertainty information; it produces images with unphysical negative flux regions; and its results are highly dependent on the so-called weighting scheme as well as on any human choice of CLEAN masks for guiding the imaging. Here, we present the Bayesian imaging algorithm resolve , which solves the above problems and naturally leads to super-resolution. We take a VLA observation of Cygnus A at four different frequencies and image it with single-scale CLEAN, multi-scale CLEAN, and resolve. Alongside the sky brightness distribution, resolve estimates a baseline-dependent correction function for the noise budget, the Bayesian equivalent of a weighting scheme. We report noise correction factors between 0.4 and 429. The enhancements achieved by resolve come at the cost of higher computational effort.

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.

Sound wave detection by common-path digital holography

The sound wave has been recorded and visualized by optical means such as digital holography (DH), where light wave carries the sound information. However, in DH, an additional reference beam is required, which can create problems in the applications where long-distance propagations are required for sound field studies. In this work, we present a new way of sound wave recording and visualization by a common-path DH in which a single light beam can carry the sound information and near the recording device, this single light beam is divided into the object and reference beams by using a beam splitter. One of the beams is filtered to generate a clean reference beam. Therefore, this configuration of DH eliminates the need of a reference beam from the starting point and makes the system simpler, compact, and stable, in comparison to the optical sound wave recording setup of traditional DH. The presented optical system of sound wave recording is suitable for applications where the single beam is required to observe invisible sound phenomena at far position. We present experimental results of vibration frequency and voice information visualization to demonstrate the proposed system.

Baryon acoustic oscillations from Integrated Neutral Gas Observations: Broadband corrugated horn construction and testing

The Baryon acoustic oscillations from Integrated Neutral Gas Observations (BINGO) telescope is a 40-m~class radio telescope under construction that has been designed to measure the large-angular-scale intensity of HI emission at 980--1260 MHz and hence to constrain dark energy parameters. A large focal plane array comprising of 1.7-metre diameter, 4.3-metre length corrugated feed horns is required in order to optimally illuminate the telescope. Additionally, very clean beams with low sidelobes across a broad frequency range are required, in order to facilitate the separation of the faint HI emission from bright Galactic foreground emission. Using novel construction methods, a full-sized prototype horn has been assembled. It has an average insertion loss of around 0.15 dB across the band, with a return loss around -25 dB. The main beam is Gaussian with the first sidelobe at around $-25 dB. A septum polariser to separate the signal into the two hands of circular polarization has also been designed, built and tested.

Characterization and Simulation of an Adaptable Fan-Beam Collimator for Fast Calibration of Radiation Detectors for PET

Monolithic scintillators for positron emission tomography systems perform best when calibrated individually. We present a fan-beam collimator with which a crystal can be calibrated within less than 1 h when suitable positioning algorithms are applied. The collimator is manufactured from lead, features an easily adaptable slit to tune the beam width and can be operated together with a coincidence detector to select a clean sample of 511-keV annihilation photons. We evaluated the performance of the collimator with a Geant4 simulation for slit widths of 0.25 mm, 0.4 mm, and 1mm and validated the shape of the beam profile experimentally by step-wisely moving a detector into the beam. This shows a clear narrow and box-shaped beam profile even if the collimator is operated without the coincidence set-up. In the latter configuration, the fraction of gammas in the beam region on a $50\times 50$ mm2 large detector is between 48% and 79% which is improved significantly to more than 94% by using only coincidence events. Analyzing the energy distribution shows that the fraction of 511-keV photons is increased from less than 50% to more than 96% by selecting coincidences. This demonstrates that our collimator produces a very defined and clean beam and provides optimal conditions for calibration.

Improving the resolution of underwater acoustic image measurement by deconvolution

The conventional beamforming (CBF) map of underwater acoustic image measurement can be expressed as a convolution of the source distribution and the response of the beamformer to a point source, defined as the beam pattern or the point spread function (PSF). By deconvolving the CBF beamformer’s map, the distribution of the actual sources with a clean beam map can be obtained to improve the resolution. In this paper, the deconvolved conventional beamforming (dCv) is applied to underwater acoustic image measurement to improve the accuracy of sound source localization. Due to the point spread function of the array in near field is dependent on the focused point, which means that the PSF is shift variant, so it is necessary to use shift-variant deconvolution method. In this paper, an extended Richardson-Lucy (Ex-RL) algorithm is applied to the two-dimensional shift-variant deconvolution acoustic image measurement problem to improve resolution. The method is compared with the original-RL, classical deconvolution approach for the mapping of acoustic sources (DAMAS) and non-negative least squares (NNLS). The simulation and the experiment results verify the effectiveness of the algorithm.

Associated production of SM Higgs with a photon in type-II seesaw models at the ILC

We consider the production of a single Standard Model (SM) Higgs boson (h^0) in association with a photon at the future Linear collider (LC) in the context of a type-II seesaw model. The type-II seesaw model extends the SM particle content by adding one triple Higgs where its Higgs coupling is a key parameter of the scalar potential triggering the electroweak symmetry-breaking mechanism in the SM. It is a well motivated model since it provides neutrino masses and mixing. The LC presents a particularly interesting possibility to probe Higgs couplings due to the clean beams in the initial state. We study the one loop processes e^+e^- rightarrow h^0gamma and e^-gamma rightarrow e^- h^0, we show that it is possible to correlate the total cross section predictions with the couplings h^0gamma gamma and h^0gamma Z which are sensitive to the presence of singly and doubly charged Higgs. For parameter points allowed by the current experimental constraints, our numerical results show that the effect of H^pm and H^{pm pm } can be as large as ± 25% with respect to the SM predictions. For both processes, we also present differential cross section for different center of mass energy.

Superresolution Interferometric Imaging with Sparse Modeling Using Total Squared Variation: Application to Imaging the Black Hole Shadow

Abstract We propose a new imaging technique for interferometry using sparse modeling, utilizing two regularization terms: the ℓ 1-norm and a new function named total squared variation (TSV) of the brightness distribution. First, we demonstrate that our technique may achieve a superresolution of ∼30% compared with the traditional CLEAN beam size using synthetic observations of two point sources. Second, we present simulated observations of three physically motivated static models of Sgr A* with the Event Horizon Telescope (EHT) to show the performance of proposed techniques in greater detail. Remarkably, in both the image and gradient domains, the optimal beam size minimizing root-mean-squared errors is ≲10% of the traditional CLEAN beam size for ℓ 1+TSV regularization, and non-convolved reconstructed images have smaller errors than beam-convolved reconstructed images. This indicates that TSV is well matched to the expected physical properties of the astronomical images and the traditional post-processing technique of Gaussian convolution in interferometric imaging may not be required. We also propose a feature-extraction method to detect circular features from the image of a black hole shadow and use it to evaluate the performance of the image reconstruction. With this method and reconstructed images, the EHT can constrain the radius of the black hole shadow with an accuracy of ∼10%–20% in present simulations for Sgr A*, suggesting that the EHT would be able to provide useful independent measurements of the mass of the supermassive black holes in Sgr A* and also another primary target, M87.