Transverse Target Research Articles

Target-field design of surface permanent magnets

We present a target-field approach to analytically design magnetic fields using permanent magnets. We assume that their magnetization is bound to a two-dimensional surface and is composed of a complete basis of surface modes. By posing the Poisson’s equation relating the magnetic scalar potential to the magnetization using Green’s functions, we derive simple integrals that determine the magnetic field generated by each mode. This approach is demonstrated by deriving the governing integrals for optimizing axial magnetization on cylindrical and circular-planar surfaces. We approximate the governing integrals numerically and implement them into a regularized least-squares optimization routine to design permanent magnets that generate uniform axial and transverse target magnetic fields. The resulting uniform axial magnetic field profiles demonstrate more than a tenfold increase in uniformity across equivalent target regions compared to the field generated by an optimally separated axially magnetized pair of rings, as validated using finite element method simulations. We use a simple example to examine how two-dimensional surface magnetization profiles can be emulated using thin three-dimensional volumes and determine how many discrete intervals are required to accurately approximate a continuously varying surface pattern. Magnets designed using our approach may enable higher-quality bias fields for electric machines, nuclear fusion, fundamental physics, magnetic trapping, and beyond. Published by the American Physical Society 2024

Mechanism studies for relativistic attosecond electron bunches from laser-illuminated nanotargets.

To find a way to control the electron-bunching process and the bunch-emitting directions when an ultraintense, linearly polarized laser pulse interacts with a nanoscale target, we explored the mechanisms for the periodical generation of relativistic attosecond electron bunches. By comparing the simulation results of three different target geometries, the results show that for nanofoil target, limiting the transverse target size to a small value and increasing the longitudinal size to a certain extent is an effective way to improve the total electron quantity in a single bunch. Then the subfemtosecond electronic dynamics when an ultrashort ultraintense laser grazing propagates along a nanofoil target was analyzed through particle-in-cell simulations and semiclassical analyses, which shows the detailed dynamics of the electron acceleration, radiation, and bunching process in the laser field. The analyses also show that the charge separation field produced by the ions plays a key role in the generation of electron bunches, which can be used to control the quantity of the corresponding attosecond radiation bunches by adjusting the length of the nanofoil target.

Collimated terahertz radiation through a laser irradiating on a T-type target

A scheme, applying a linearly polarized laser irradiating on a T-type target which contains a longitudinal target followed by a transverse target, is proposed to collimate the terahertz radiation. The results show that the interaction between the laser and the longitudinal target can effectively reduce the electron transverse divergence while increasing the electron maximum cut-off energy. In this way, the terahertz radiation can be well collimated while enhancing its intensity. By using two-dimensional particle-in-cell simulations, we show that the pointing angle is about −13.6° and 17.5° when the length and thickness of the longitudianl target are 90.0 μm and 4.0 μm, respectively. In addition, the impact of the laser and target parameters on the collimation of terahertz radiation are also investigated separately. Such a scheme may pave a new way for enhancing and collimating the terahertz radiation via laser-solid interactions.

Terahertz Emission Enhanced by a Laser Irradiating on a T-Type Target

The generation of high field terahertz emission based on the interaction between an ultra-intense laser and solid targets has been widely studied in recent years because of its wide potential applications in biological imaging and material science. Here, a novel scheme is proposed to enhance the terahertz emission, in which a linearly polarized laser pulse irradiates a T-type target including a longitudinal target followed by a transverse target. By using two-dimensional particle-in-cell simulations, we find that the electron beam, modulated by the direct laser acceleration via the interaction of the laser with the longitudinal solid target, plays a crucial role in enhancing the intensity of terahertz emission and controlling its spatial distribution. Compared with the single-layer target, the maximum radiated electromagnetic field’s intensity passing through the spatial probe point is enhanced by about one order of magnitude, corresponding to the terahertz emission power increasing by two orders of magnitude or so. In addition, the proposed scheme is robust with respect to the thickness and length of the target. Such a scheme may provide important theoretical and data support for the enhancement of terahertz emission efficiency based on the ultra-intense laser irradiation of solid targets.

Predicting the sinϕS single-spin asymmetry of Λ production off a transversely polarized nucleon in SIDIS

We investigate the transverse target spin asymmetry $A^{\sin\phi_{S}}_{UT}$ for the unpolarized $\Lambda$ production in semi-inclusive deep inelastic scattering with the transverse momentum of the final-state lambda hyperon being integrated out. The asymmetry is contributed by the product of the transversity distribution function $h_1(x)$ of the nucleon and the collinear twist-3 fragmentation function $\tilde{H}(z)$ of the $\Lambda$ hyperon. The later one originates from the quark-gluon-quark correlation and is a naive time-reversal-odd function. We calculate $\tilde{H}$ of the $\Lambda$ hyperon by adopt a diquark spectator model. Using the numerical result of $\tilde{H}(z)$ and the available parametrization of $h_1(x)$ from SIDIS data, we predict the $\sin\phi_{S}$ asymmetry in the electroproduction of the $\Lambda$ hyperon in the kinematical region of EIC, EicC and COMPASS. In the phenomenological analysis we include the evolution effect of the distribution functions and the fragmentation functions. The results show that the asymmetries for the $\Lambda$ production SIDIS process is around 0.1 and may be accessible at EIC, EicC and COMPASS. We also find that the evolution of fragmentation function can affect the size of asymmetry.

Suspecting Intussusception and Recurrence Risk Stratification Using Clinical Data and Plain Abdominal Radiographs.

PurposeAlthough ultrasonography is the gold standard of diagnosing intussusception, plain abdomen radiograph (AXR) is often used to make differential diagnosis for pediatric patients with abdominal pain. In intussusception patients, we aimed to analyze the AXR and clinical data to determine the characteristics of early AXR findings associated with diagnosis of intussusception and recurrence after reduction.MethodsBetween January 2011 and June 2018, 446 patients diagnosed with intussusception based on International Classification of Diseases-10 code of K56.1 were admitted. We retrospectively reviewed medical records of 398 patients who received air reduction; 51 of them have recurred after initial reduction. We evaluated six AXR features including absent ascending colon gas, absent transverse colon gas, target sign, meniscus sign, mass, and ileus. Clinical data and AXR features were compared between single episode and recurrence groups.ResultsTwo groups did not show significant differences regarding clinical data. Mean time to recurrence from air reduction was 3.4±3.2 days. Absent ascending colon gas (63.9%) was the most common feature in intussusception, followed by mass (29.1%). All of six AXR features were observed more frequently in the recurrence group. Absent transverse colon gas was the most closely associated AXR finding for recurrence (odds ratio, 2.964; 95% confidence interval, 1.327–6.618; p=0.008).ConclusionIn our study, absence of ascending colon gas was the most frequently seen AXR factor in intussusception patients. Extended and careful observation after reduction may be beneficial if such finding on AXR is found in intussusception patients.

First Measurements of the Double-Polarization Observables F, P, and H in ω Photoproduction off Transversely Polarized Protons in the N^{*} Resonance Region.

First measurements of double-polarization observables in ω photoproduction off the proton are presented using transverse target polarization and data from the CEBAF Large Acceptance Spectrometer (CLAS) FROST experiment at Jefferson Lab. The beam-target asymmetry F has been measured using circularly polarized, tagged photons in the energy range 1200-2700MeV, and the beam-target asymmetries H and P have been measured using linearly polarized, tagged photons in the energy range 1200-2000MeV. These measurements significantly increase the database on polarization observables. The results are included in two partial-wave analyses and reveal significant contributions from several nucleon (N^{*}) resonances. In particular, contributions from new N^{*} resonances listed in the Review of Particle Properties are observed, which aid in reaching the goal of mapping out the nucleon resonance spectrum.

Feasibility and relevance of discrete vasculature modeling in routine hyperthermia treatment planning

Purpose: To investigate the effect of patient specific vessel cooling on head and neck hyperthermia treatment planning (HTP).Methods and materials: Twelve patients undergoing radiotherapy were scanned using computed tomography (CT), magnetic resonance imaging (MRI) and contrast enhanced MR angiography (CEMRA). 3D patient models were constructed using the CT and MRI data. The arterial vessel tree was constructed from the MRA images using the ‘graph-cut’ method, combining information from Frangi vesselness filtering and region growing, and the results were validated against manually placed markers in/outside the vessels. Patient specific HTP was performed and the change in thermal distribution prediction caused by arterial cooling was evaluated by adding discrete vasculature (DIVA) modeling to the Pennes bioheat equation (PBHE).Results: Inclusion of arterial cooling showed a relevant impact, i.e., DIVA modeling predicts a decreased treatment quality by on average 0.19 °C (T90), 0.32 °C (T50) and 0.35 °C (T20) that is robust against variations in the inflow blood rate (|ΔT| < 0.01 °C). In three cases, where the major vessels transverse target volume, notable drops (|ΔT| > 0.5 °C) were observed.Conclusion: Addition of patient-specific DIVA into the thermal modeling can significantly change predicted treatment quality. In cases where clinically detectable vessels pass the heated region, we advise to perform DIVA modeling.

Simplified seismic resistant design of base isolated single pylon cable-stayed bridge

The seismic vulnerability of single pylon cable-stayed bridges under strong ground motions in the transverse direction is of great concern to earthquake engineering researchers and bridge engineers. Introduction of base isolation to cable-stayed bridges has been proved very effective in reducing seismic forces in the bridges in previous studies. This paper proposes a direct displacement based seismic design (DDBD) procedure for base isolated cable-stayed bridge under transverse seismic excitation. One of the key aspects of the DDBD is the realization of a uniform transverse target displacement of the deck under seismic excitation, which is achieved by appropriate design of the isolator stiffness at the bottom of the pylon and the ends of the deck. The proposed DDBD procedure is applied in this paper to the seismic design of a single pylon cable-stayed bridge isolated by friction pendulum bearings. The effectiveness and the accuracy of the resulting design are checked by nonlinear time history analyses. The numerical results indicate that the proposed DDBD procedure can predict the deck displacement profile and amplitudes, as well as the base shear within a reasonable degree of accuracy. The case study demonstrates that the proposed DDBD procedure is sufficiently accurate and practical for the seismic design of base isolated single pylon cable-stayed bridges.

Extraction of helicity amplitude ratios from exclusive ρ0-meson electroproduction on transversely polarized protons

Exclusive ρ0-meson electroproduction is studied by the HERMES experiment, using the 27.6 GeV longitudinally polarized electron/positron beam of HERA and a transversely polarized hydrogen target, in the kinematic region 1.0 GeV2 < Q2 < 7.0 GeV2, 3.0 GeV < W < 6.3 GeV, and −t′ < 0.4 GeV2. Using an unbinned maximum-likelihood method, 25 parameters are extracted. They determine the real and imaginary parts of the ratios of certain helicity amplitudes (describing ρ0-meson production by a virtual photon) and the dominant amplitude without the nucleon-helicity flip. The latter amplitude describes the production of a longitudinal ρ0 meson by a longitudinal virtual photon. The transverse target polarization allows for the first time the extraction of ratios of a number of nucleon-helicity-flip amplitudes to . The ratios of nucleon-helicity-non-flip amplitudes to are found to be in good agreement with those from the previous HERMES analysis. A comparison of the extracted amplitude ratios with the Goloskokov-Kroll model shows the necessity to add pion exchange amplitudes with positive πρ form factor to the amplitudes based on generalized parton distributions to improve the HERMES data description.

Quark-photon-quark correlation and transverse target single spin asymmetry in inclusive DIS

We calculate the q q correlation function associated to transverse target lepton-nucleon inclusive deep-inelastic scattering by direct evaluation of the corresponding matrix element. We use the electromagnetic impact parameter potential for a transversely polarized nucleon to define the q q correlation function for each avor in terms of the field components of that avor. The results are compared with the two existing models for the q q correlator. Using the calculated q q correlation function, we estimated the transverse target SSA in IDIS process.

Developments towards a transverse free-electron target for the storage ring CRYRING@ESR

SynopsisA transverse free-electron target for crossed-beams collision studies is currently being developed. The target will be installed in the main experimental section of the FAIR storage ring CRYRING@ESR. The setup will allow for electron-ion collision studies with highly charged ions on an unprecedented level of detail that comprises, e.g., the angle-differential observation of photon emission.

Ratios of helicity amplitudes for exclusive rho ^0 electroproduction on transversely polarized protons

Exclusive rho ^0-meson electroproduction is studied by the HERMES experiment, using the 27.6 GeV longitudinally polarized electron/positron beam of HERA and a transversely polarized hydrogen target, in the kinematic region 1.0 GeV^2<Q^2< 7.0 GeV^2, 3.0 GeV <W< 6.3 GeV, and -t^prime < 0.4 GeV^2. Using an unbinned maximum-likelihood method, 25 parameters are extracted. These determine the real and imaginary parts of the ratios of several helicity amplitudes describing rho ^{0}-meson production by a virtual photon. The denominator of those ratios is the dominant amplitude, the nucleon-helicity-non-flip amplitude F_{0frac{1}{2}0frac{1}{2}}, which describes the production of a longitudinal rho ^{0}-meson by a longitudinal virtual photon. The ratios of nucleon-helicity-non-flip amplitudes are found to be in good agreement with those from the previous HERMES analysis. The transverse target polarization allows for the first time the extraction of ratios of a number of nucleon-helicity-flip amplitudes to F_{0frac{1}{2}0frac{1}{2}}. Results obtained in a handbag approach based on generalized parton distributions taking into account the contribution from pion exchange are found to be in good agreement with these ratios. Within the model, the data favor a positive sign for the pi -rho transition form factor. By also exploiting the longitudinal beam polarization, a total of 71 rho ^0 spin-density matrix elements is determined from the extracted 25 parameters, in contrast to only 53 elements as directly determined in earlier analyses.

Ratios of helicity amplitudes for exclusiveρ0electroproduction on transversely polarized proton

Exclusive ρ 0 -meson electroproduction is studied by the HERMES experiment, using the 27.6 GeV longitudinally polarized electron/positron beam of HERA and a transversely polarized hydrogen target, in the kinematic region 1.0 GeV 2 Q 2 2 , 3.0 GeV t ′ 2 . Using an unbinned maximum-likelihood method, 25 parameters are extracted. They determine the real and imaginary parts of the ratios of certain helicity amplitudes describing ρ 0 -meson production by a virtual photon, where the denominator is the dominant amplitude . The latter is the nucleon-helicity-non-flip amplitude, which describes the production of a longitudinal ρ 0 meson by a longitudinal virtual photon. The transverse target polarization allows for the first time the extraction of ratios of a number of nucleon-helicity-flip amplitudes to . The ratios of nucleon-helicity-non-flip amplitudes are found to be in good agreement with those from the previous HERMES analysis.

Timelike Compton Scattering off the nucleon: observables and experimental perspectives for JLab at 12 GeV

Hard exclusive processes such as photoproduction or electroproduction of photon or meson off the nucleon provide access to the Generalized Parton Distributions (GPDs), in the regime where the scattering amplitude is factorized into a hard and a soft part. GPDs contain the correlation between the longitudinal momentum fraction and the transverse spatial densities of quarks and gluons in the nucleon. Timelike Compton Scattering (TCS) correspond to the reaction γN → γ*N → e + e − N , where the photon is scattered off a quark. It is measured through its interference with the associated Bethe-Heitler process, which has the same final state. TCS allows to access the GPDs and test their universality by comparison to the results obtained with the DVCS process ( eN → eγN ). Also, results obtained with TCS provide additional independent constrains to the GPDs parameterization.We will present the physical motivations for TCS, with our theoretical predictions for TCS observables and their dependencies. We calculated for JLab 12 GeV energies all the single and double beam and/or target polarization observables off the proton and off the neutron. We will also present the experimental perspectives for the next years at JLab. Two proposals were already accepted at JLab: in Hall B, with the CLAS12 spectrometer, in order to measure the unpolarized cross section and in Hall A, with the SoLID spectrometer, in order to measure the unpolarized cross section and the beam spin asymmetry at high intensity. A Letter Of Intent was also submitted in order to measure the transverse target spin asymmetries in Hall C. We will discuss the merits of this different experiments and present some of the expected results.

Recent results from COMPASS on exclusive muoproduction

The 160 GeV polarised muon beam available at CERN, with positive or negative charge, makes COMPASS a unique place for GPD studies. The first GPD related COMPASS results come from exclusive vector meson production on transversely polarised protons and deuterons. The data were taken in 2003-2010 with large solid-state polarised targets, although without detection of recoil particles. Results on various transverse target spin dependent azimuthal asymmetries are presented and their relations to GPDs are discussed. The dedicated COMPASS GPD program started in 2012 with commissioning of a new long liquid hydrogen target and new detectors such as the large recoil proton detector and the large-angle electromagnetic calorimeter. It was followed by a short pilot 'DVCS run'. The performance of the setup and first results on DVCS and exclusive π0 channels have been demonstrated. The full data taking for the GPD program approved within COMPASS-II proposal is planned for 2016 and 2017.

Shape error prediction and compensation of three-dimensional surface in flexibly-reconfigurable roll forming

The Flexibly-reconfigurable roll forming (FRRF) scheme as one of the advanced continuous roll forming processes consists of upper and lower flexible rollers that can be controlled by each reconfigurable punch module. The shape error in the FRRF process often results in undesirable changes in the shape of the deformed surface and brings about a deviation in the precision of the deformed product. This study considers the changes in the shape error of a deformed configuration by controlling the non-uniform gap between both flexible rollers in the transverse direction. A Non-uniform rational B-spline (NURBS) type control methodology is introduced based on the transverse target curve and the thickness reduction ratio. The function for the transverse target curve is reconstructed by using a NURBS curve, and the function of the reduction ratios of the thickness is assumed to have linear increments. Finite element simulations are conducted for the FRRF process with the AA5052-H32 sheet material by applying NURBS-type control methodology for both flexible rollers. The transverse shape error of the three-dimensional surface is predicted by using a numerical approach, and its results are experimentally verified. A Reverse displacement compensation (RDC) method is adopted to compensate the transverse shape error of the deformed surface. Consequently, the proposed RDC method is validated as a suitable approach to address the transverse shape error. This method contributes to further developing capabilities to modify the profiles of the upper and lower flexible rollers in the flexibly-reconfigurable roll forming process for various 3D surface parts.

Threshold [formula omitted] photoproduction on transverse polarised protons at MAMI

Polarisation-dependent differential cross sections σT associated with the target asymmetry T have been measured for the reaction γp→→pπ0 with transverse target polarisation from π0 threshold to photon energies of 190 MeV. The data were obtained using a frozen-spin butanol target with the Crystal Ball / TAPS detector set-up and the Glasgow photon tagging system at the Mainz Microtron MAMI. Results for σT have been used in combination with our previous measurements of the unpolarised cross section σ0 and the beam asymmetry Σ for a model-independent determination of S- and P-wave multipoles in the π0 threshold region, which includes for the first time a direct determination of the imaginary part of the E0+ multipole.

A Bulk Superconducting Magnetic System for the CLAS12 Target at Jefferson Lab

A feasibility study of a bulk magnetic system for the target of an experiment to measure the transverse spin effects in semi-inclusive deep inelastic scattering (SIDIS) at 11 GeV with a transversely polarized target using the CLAS12 detector is presented. An experiment has been approved with the highest priority rating to study spin azimuthal asymmetries in SIDIS using 11-GeV polarized electron beams from the upgraded CEBAF facility and the CLAS12 detector equipped with a transversely polarized target. The transverse target in CLAS12 requires the shielding of a volume inside the longitudinal field of the main solenoid. In the shielded region, a transverse target magnet can operate; for the proposed magnetic configuration, the main solenoid maximum magnetic induction is 2 T. A bulk MgB 2 cylinder cooled in liquid helium is proposed both to shield the longitudinal field of the main solenoid and to provide a transverse field induction up to 1.2 T for the hydrogen deuteride ice (HD-ice)target. The installation and magnetization procedure will be described: The magnetization procedure has to be compatible with the polarization and installation procedure of the HD-ice target. The design of a test bench to measure the transverse magnetization of a MgB2 bulk cylinder cooled by a coldhead is presented together with the scheduled measurements.

Measurement of the transverse target and beam-target asymmetries in η meson photoproduction at MAMI.

We present new data for the transverse target asymmetry T and the very first data for the beam-target asymmetry F in the γ[over →]p[over →]→ηp reaction up to a center-of-mass energy of W=1.9 GeV. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. All existing model predictions fail to reproduce the new data indicating a significant impact on our understanding of the underlying dynamics of η meson photoproduction. The peculiar nodal structure observed in existing T data close to threshold is not confirmed.