Momentum Spread Research Articles

Improving delivery efficiency using spots and energy layers reduction algorithms based on a large momentum acceptance beamline.

Intensity-modulated proton therapy (IMPT) is a well-known delivery method of proton therapy. Besides higher plan quality, reducing the delivery time is also essential to IMPT plans. It can enhance patient comfort, reduce treatment costs, and improve delivery efficiency. From the perspective of treatment efficacy, it contributes to mitigating the intra-fractional motions and improving the accuracy of radiotherapy, especially for moving tumors. However, there is a tradeoff problem between the plan quality and delivery time. We consider the potential of a large momentum acceptance (LMA) beamline and apply the spots and energy layers reduction method to reduce the delivery time. The delivery time for each field consists of the energy layer switching time, spot traveling time, and dose delivery time. The larger momentum spread and higher intensity beam offered by the LMA beamline contribute to reducing the total delivery time compared to the conventional beamline. In addition to the dose fidelity term, an L1 and logarithm items were added to the objective function to increase the sparsity of the low-weighted spots and energy layers. After that, the low-weighted spots and layers were iteratively excluded in the reduced plan, which reduced the energy layer switching time and spot traveling time. We used the standard, reduced, and LMA-reduced plans to validate the proposed method and tested it on prostate and nasopharyngeal cases. Then, we compared and evaluated the plan quality, treatment time, and plan robustness against delivery uncertainty. Compared with the standard plans, the number of spots in the LMA-reduced plans was on average reduced by 13 400 (95.6%) for prostate cases and by 48 300 (80.7%) for nasopharyngeal cases and the number of energy layers was on average reduced by 49 (61.3%) for prostate cases and by 97 (50.5%) for nasopharyngeal cases. And, the delivery time of the LMA-reduced plans was shortened from 34.5 to 8.6 s for prostate cases and from 163.8 to 53.6 s for nasopharyngeal cases. The LMA-reduced plans had comparable robustness to the spot monitor unit (MU) error compared with the standard plans, but the LMA-reduced plans became more sensitive to spot position uncertainty. The delivery efficiency can be significantly improved using the LMA beamline and spots and energy layers reduction strategies. The method is promising to improve the efficiency of motion mitigation strategies for treating moving tumors.

Suppression of stimulated Raman scattering by angularly incoherent light, towards a laser system of incoherence in all dimensions of time, space, and angle

Laser–plasma instability (LPI) is one of the main obstacles to achieving predictable and reproducible fusion at high gain through laser-driven inertial confinement fusion (ICF). In this paper, for the first time, we show analytically and confirm with three-dimensional particle-in-cell simulations that angular incoherence provides suppression of the instability growth rate that is additional to and much stronger than that provided by the well-known temporal and spatial incoherence usually used in ICF studies. For the model used in our calculations, the maximum field ratio between the stimulated Raman scattering and the driving pulses drops from 0.2 for a Laguerre–Gaussian pulse with a single nonzero topological charge to 0.05 for a super light spring with an angular momentum spread and random relative phases. In particular, angular incoherence does not introduce extra undesirable hot electrons. This provides a novel method for suppressing LPI by using light with an angular momentum spread and paves the way towards a low-LPI laser system for inertial fusion energy with a super light spring of incoherence in all dimensions of time, space, and angle, and may open the door to the use of longer-wavelength lasers for inertial fusion energy.

Design and prototype test of a high-sensitivity reentrant-cavity based Schottky pickup.

Schottky diagnostics is an important measure for the debunched beam during the injection phase of the Xi'an Proton Application Facility (XiPAF). The existing capacitive Schottky pickup has a relatively low sensitivity and a poor signal-to-noise ratio for the low-intensity beam. A resonant Schottky pickup based on the principle of a reentrant cavity is proposed. The effects of cavity geometric parameters on cavity properties are systematically studied. A prototype was built and tested to validate the simulation results. The prototype has a resonance frequency of 24.23MHz, a Q value of 635, and a shunt impedance of 19.75 kΩ. The resonant Schottky pickup has the capability to detect as few as 2.3 × 106 protons with an energy of 7MeV and a momentum spread of about 1% at the injection phase of XiPAF. The sensitivity is two orders of magnitude higher than the existing capacitive pickup.

S5: Probing the Milky Way and Magellanic Clouds potentials with the 6D map of the Orphan–Chenab stream

ABSTRACTWe present a 6D map of the Orphan–Chenab (OC) stream by combining the data from Southern Stellar Stream Spectroscopic Survey (S5) and Gaia. We reconstruct the proper motion, radial velocity, distance, on-sky track, and stellar density along the stream with spline models. The stream has a total luminosity of MV = −8.2 and metallicity of [Fe/H] = −1.9, similar to classical Milky Way (MW) satellites like Draco. The stream shows drastic changes in its physical width varying from 200 pc to 1 kpc, but a constant line-of-sight velocity dispersion of 5 $\mathrm{km\, s^{-1}}$. Despite the large apparent variation in the stellar number density along the stream, the flow rate of stars along the stream is remarkably constant. We model the 6D stream track by a Lagrange-point stripping method with a flexible MW potential in the presence of a moving extended Large Magellanic Cloud (LMC). This allows us to constrain the mass profile of the MW within the distance range 15.6 < r < 55.5 kpc, with the best measured enclosed mass of $(2.85\pm 0.1)\times 10^{11}\, \mathrm{\, M_\odot }$ within 32.4 kpc. Our stream measurements are highly sensitive to the LMC mass profile with the most precise measurement of its enclosed mass made at 32.8 kpc, $(7.02\pm 0.9)\times 10^{10}\, {\rm M}_\odot$. We also detect that the LMC dark matter halo extends to at least 53 kpc. The fitting of the OC stream allows us to constrain the past LMC trajectory and the degree of dynamical friction it experienced. We demonstrate that the stars in the OC stream show large energy and angular momentum spreads caused by LMC perturbation.

XUV Fluorescence Detection of Laser-Cooled Stored Relativistic Ions

An improved moveable in vacuo XUV fluorescence detection system was employed for the laser cooling of bunched relativistic (β = 0.47) carbon ions at the Experimental Storage Ring (ESR) of GSI Helmholtzzentrum Darmstadt, Germany. Strongly Doppler boosted XUV fluorescence (∼90 nm) was emitted from the ions in a forward light cone after laser excitation of the 2s–2p transition (∼155 nm) by a new tunable pulsed UV laser system (257 nm). It was shown that the detected fluorescence strongly depends on the position of the detector around the bunched ion beam and on the delay (∼ns) between the ion bunches and the laser pulses. In addition, the fluorescence information could be directly combined with the revolution frequencies of the ions (and their longitudinal momentum spread), which were recorded using the Schottky resonator at the ESR. These fluorescence detection features are required for future laser cooling experiments at highly relativistic energies (up to γ∼ 13) and high intensities (up to 1011 particles) of ion beams in the new heavy ion synchrotron SIS100 at FAIR.

Complete beam optics analysis along the Muon Campus External Beamline

The Fermilab Mu2e experiment aims to measure the event ratio of the neutrinoless coherent conversion of muons to electrons in the field of an aluminum nucleus to ordinary capture as a means to probe the possibility of charged lepton flavor violation. Since the number of muons at the Mu2e production target is highly correlated to the upstream beam Twiss parameters, knowledge of these parameters is critical. Such measurement is not trivial since the accelerator line contains several bending magnets which can induce non-negligible dispersion. We discuss a methodology that in addition to the Twiss parameters can extract dispersion, slope of dispersion and momentum spread using only a set of beam profiles. We then apply this technique along the Fermilab Muon Campus and show it can play a significant role in maximizing the muon flux of the Mu2e Experiment.

Orbital angular momentum spectra of twisted Laguerre-Gaussian Schell-model beams propagating in weak-to-strong Kolmogorov atmospheric turbulence.

The presence of atmospheric turbulence in a beam propagation path results in the spread of orbital angular momentum (OAM) modes of laser beams, limiting the performance of free-space optical communications with the utility of vortex beams. The knowledge of the effects of turbulence on the OAM spectrum (also named as spiral spectrum) is thus of utmost importance. However, most of the existing studies considering this effect are limited to the weak turbulence that is modeled as a random complex "screen" in the receiver plane. In this paper, the behavior of the OAM spectra of twisted Laguerre-Gaussian Schell-model (TLGSM) beams propagation through anisotropic Kolmogorov atmospheric turbulence is examined based on the extended Huygens-Fresnel integral which is considered to be applicable in weak-to-strong turbulence. The discrepancies of the OAM spectra between weak and strong turbulence are studied comparatively. The influences of the twist phase and the anisotropy of turbulence on the OAM spectra during propagation are investigated through numerical examples. Our results reveal that the twist phase plays a crucial role in determining the OAM spectra in turbulence, resisting the degeneration of the detection mode weight by appropriately choosing the twist factor, while the effects of the anisotropic factors of turbulence on the OAM spectra seem to be not obvious. Our findings can be applied to the analysis of OAM spectra of laser beams both in weak and strong turbulence.

Design and beam dynamics study of disk-loaded structure for muon LINAC

The disk-loaded structures (DLS) in the muon LINAC are under development for the J-PARC muon g–2/EDM experiment. Four DLSs with an accelerating gradient of 20 MV/m take charge of muon acceleration from 40 MeV to 212 MeV, which corresponds to 70% to 94% of the speed of light. The quasi-constant gradient type TM01-2π/3 mode DLSs with gradually varying disk spacing was designed and it was confirmed that the cumulative phase slip due to the mismatch between muon and phase velocity can be suppressed to less than 2 degrees at the frequency of 2592 MHz. In addition, the optimum synchronous phase and the lattice were investigated to satisfy the requirements of the total emittance less than 1.5π mm mrad and the momentum spread less than 0.1% in RMS.

Nonlinear field effects in the collector ring due to large-amplitude particle oscillations

In the frame of the FAIR project, the Collector Ring (CR) is planned to be built for efficient cooling of antiprotons and rare isotope beams [1]. In order to accept hot beam from separators large acceptances are required. This paper examines the effects which can influence the beam dynamics due to large betatron oscillation amplitude and momentum spread. Using analytic expressions, the amplitude-dependent tune shifts driven by sextupole magnets, the fringe field of quadrupole magnets, and kinematics effects have been calculated. The obtained results have been compared with numerical simulations by means of precise multi-turn particle tracing. The tracking analysis for the CR has been performed considering the real shape of the magnetic field of the wide aperture quadrupole. We report on quantitative studies of the effects on the dynamic aperture of the rings.

Dispersion of Ultrarelativistic Tardyonic and Tachyonic Wave Packets on Cosmic Scales

We investigate the time propagation of tachyonic (superluminal) and tardyonic (subluminal, ordinary) massive wave packets on cosmic scales. A normalizable wave packet cannot be monochromatic in momentum space and thus acquires a positional uncertainty (or packet width) that increases with travel distance. We investigate the question of how this positional uncertainty affects the uncertainty in the detection time for cosmic radiation on Earth. In the ultrarelativistic limit, we find a unified result, δx(t)/c3=m2δpt/p03, where δx(t) is the positional uncertainty, m is the mass parameter, δp is the initial momentum spread of the wave function, and p0 is the central momentum of the wave packet, which, in the ultrarelativistic limit, is equal to its energy. This result is valid for tachyons and tardyons; its interpretation is being discussed.

Methods for Monitoring the Longitudinal Momentum Spread of Ions within a Bunch during an Injection into a Synchrotron

Methods for Monitoring the Longitudinal Momentum Spread of Ions within a Bunch during an Injection into a Synchrotron

Tailored ion beam for precise colour centre creation.

We present an invariant-based quantum control scheme leading to a highly monochromatic ion beam from a Paul trap. Our protocol is implementable by supplying the segmented electrodes in the trap with voltages of the order of volts. This mitigates the impact of fluctuations in previous designs and leads to a low-dispersion beam of ions. Moreover, our proposal does not rely on sympathetically cooling ions, which bypasses the need of loading different species in the trap-namely, the propelled ion and, e.g. a [Formula: see text] to exert sympathetic cooling-significantly incrementing the repetition rate of the launching procedure. Our scheme is based on an invariant operator linear in position and momentum, which enables us to control the average extraction energy and the outgoing momentum spread. In addition, we propose a sequential operation to tailor the transversal properties of the beam before the ejection to minimize the impact spot and to increase the lateral resolution of the implantation. This article is part of the theme issue 'Shortcuts to adiabaticity: theoretical, experimental and interdisciplinary perspectives'.

Design study for a 500 MeV positron beam at the Mainz Microtron MAMI

A design study has been performed for a positron beam with an energy of 500 MeV to be realized at the applied physics area of the Mainz Microtron MAMI. Positrons will be created after pair conversion of bremsstrahlung, produced by the 855 MeV electron beam at MAMI in a tungsten converter target. From the two conceivable geometries (1) pair conversion in the bremsstrahlung converter target itself, and (2) bremsstrahlung pair conversion in a separated lead foil, the former was considered in detail. Positrons will be energy selected within an outside open electron beam-line bending magnet, and bent back by an additional sector magnet. Magnetic focusing elements in between are designed to prepare in a well shielded positron target chamber about 6 m away from the target a beam with horizontal and vertical emittances of epsilon _mathrm{v} = 0.055 pi mm mrad (1 sigma ), and epsilon _mathrm{h} = 0.12, pi mm mrad (1 sigma ), respectively, for a 10 upmu m thick amorphous tungsten target and negligible momentum spread. At an accepted positron band width of 1 MeV, spots are expected vertically with an angular spread of 0.064 mrad and a size of 5.0 mm (FWHM), and horizontally with an angular spread of 0.64 mrad and a size of 7.7 mm (FWHM). The positron yield amounts to 13.1 per second, 1 MeV positron energy band width, and 1 nA electron beam current.Graphic abstract

Commissioning of the 7 MeV H[formula omitted] linac injector for a 200 MeV proton synchrotron

This paper describes the beam commissioning progress of the 7 MeV H− linac injector for the proton synchrotron of Xi’an 200 MeV Proton Application Facility (XiPAF). To fulfill a flux of 105∼108p/cm2/s with a uniformity better than 90% on a 3 cm × 3 cm sample size at the experimental station, the number of the accumulated protons in each cycle in the synchrotron is designed to be larger than 2 × 1011. The protons are acquired from the H− beam stripped by the carbon foil, which enables transverse space painting during injection. The maximum pulse length of the injected beam is 40μs. With an estimation of 40 for the intensity gain factor, the injected beam is required to have a peak current of higher than 1 mA, with the normalized transverse emittance of 90% particles less than 6 and 4 πmm mrad for the horizontal and vertical planes, respectively, and the momentum spread of 90% particles within ±0.45%. The injector mainly consists of an H− ion source, a low energy beam transport line (LEBT), a 3 MeV radio frequency quadrupole (RFQ) accelerator, a 7 MeV interdigital H-mode drift tube linac (IH-DTL), and an injection beam transport line. After several stages of beam commissioning, the linac injector has reached a pulsed peak current of 2.5 mA, with normalized emittance (90% particles) less than 4.4 and 2.2 πmm mrad, 90% momentum spread less than ±0.55%, which lays a good foundation for the beam commissioning of the synchrotron.

Upgrading the beam telescopes at the DESY II Test Beam Facility

The DESY II Test Beam Facility is a key infrastructure for modern high energy physics detector development, providing particles with a small momentum spread in a range from 1 to 6GeV to user groups e.g. from the LHC experiments and Belle II as well as generic detector R&D. Beam telescopes are provided in all three test beam areas as precise tracking reference without time stamping, with triggered readout and a readout time of > 115 μs . If the highest available rates are used, multiple particles are traversing the telescopes within one readout frame, thus creating ambiguities that cannot be resolved without additional timing layers. Several upgrades are currently investigated and tested: Firstly, a fast monolithic pixel sensor, the TelePix, to provide precise track timing and triggering on a region of interest is proposed to overcome this limitation. The TelePix is a 180nm HV-CMOS sensor that has been developed jointly by DESY, KIT and the University of Heidelberg and designed at KIT. In this publication, the performance evaluation is presented: The difference between two amplifier designs is evaluated. A high hit detection efficiency of above 99.9% combined with a time resolution of below 4ns at negligible pixel noise rates is determined. Finally, the digital hit output to provide region of interest triggering is evaluated and shows a short absolute delay with respect to a traditional trigger scintillator as well as an excellent time resolution. Secondly, a fast LGAD plane has been proposed to provide a time resolution of a few 10 ps, which is foreseen to drastically improve the timing performance of the telescope. Time resolutions of below 70 ps have been determined in collaboration with the University of California, Santa Barbara.

(Invited, Digital Presentation) High Quality 2-D Materials Characterized Paradoxically from Broad Diffraction Features

Paradoxically a very broad diffraction background, named the Bell-Shaped-Component (BSC), has been established as a feature of graphene growth. Recent diffraction studies as a function of electron energy on Gr/SiC have shown that the BSC is not related to scattering interference. The broad background is in-phase with the Bragg component of both the (00) and Gr(10) spots. Instead textbook diffraction states it should be out-of-phase since it should originate from destructive interference between adjacent terraces[1]. Additional experiments were carried out as a function of temperature over the range 1200° C-1300° C that single-layer-graphene (SLG) grows. Quantitative fitting of the profiles shows that the BSC follows the increase of the G(10) spot, proving directly that the BSC indicates high quality graphene[2]. The BSC has been also seen in graphene on metals including Gr/Ir(111) and on h-BN/Ir(111)[3,4]. Its presence in such a wide range of 2-materials suggests its origin must be general and fundamental, related to their unusual single layer uniformity. The BSC can be a diagnostic of high quality in the growth of other 2-d materials. One possible explanation of the BSC relates to electron confinement within a single uniform layer, according to the uncertainty principle, which generates spread in their wavevector as confirmed with ARPES[5]. The transfer of the large momentum spread to the diffracted electrons to generate the BSC requires better theoretical understanding of the graphene electron-beam electron interaction.Work in collaboration with P. A. Thiel (deceased), S. Chen, E. Conrad, M. Horn von Hoegen, M. Petrovic, F.-J. Meyer zu Heringdorf [1] S. Chen, et al. Phys. Rev. B. 100, 155307 (2019).[2] S. Chen, et al. J. Phys. Chem. Lett. 11, 8937 (2020).[3] K. Omambac et al , Appl. Phys. Lett. 118, 241902 (2021)[4]M. Petrovic et al Nanotechnology 32 505706 (2021)[5] T. Ohta et al. Phys. Rev. Lett. 98, 206802 (2007).

Resonance and antiresonance characteristics in linearly delayed Maryland model

The Maryland model is a critical theoretical model in quantum chaos. This model describes the motion of a spin-1/2 particle on a one-dimensional lattice under the periodical disturbance of the external delta-function-like magnetic field. In this work, we propose the linearly delayed quantum relativistic Maryland model (LDQRMM) as a novel generalization of the original Maryland model and systematically study its physical properties. We derive the resonance and antiresonance conditions for the angular momentum spread. The “characteristic sum” is introduced in this paper as a new measure to quantify the sensitivity between the angular momentum spread and the model parameters. In addition, different topological patterns emerge in the LDQRMM. It predicts some additions to the Anderson localization in the corresponding tight-binding systems. Our theoretical results could be verified experimentally by studying cold atoms in optical lattices disturbed by a linearly delayed magnetic field.

Direct reconstruction of the band structure of a one-dimensional optical lattice with thermal atoms

We report on a simple method to reconstruct the band structure of a 1D optical lattice using a thermal cloud with a momentum spread of about two-photon recoils. We image the momentum distribution of a thermal cloud exposed to a standing wave potential using time-of-flight absorption images and observe unique features. With the support of numerical calculations, we explain their appearance and show how they can be used to reconstruct the full band-structure directly. While this can serve as a precise lattice depth calibration tool, we additionally propose a method to estimate the lattice depth in a single-shot manner.

Anomalous correlation between quantum efficiency and transverse momentum spread in semiconductor cathode photoemission

The next generation of accelerator based scientific facilities, such as the megahertz repetition rate free electron laser and electron-ion collider, relies on photoelectron sources of high peak and high average brightness. Therefore, photocathodes with both low transverse momentum spread (TMS) and high quantum efficiency (QE) are required. The conventional positive correlation between QE and TMS leads to a tradeoff between peak and average brightness. In this study, a negative correlation between QE and TMS is experimentally observed for the first time on a semiconductor photocathode (${\mathrm{Cs}}_{2}\mathrm{Te}$). Two models are proposed to explain such an anomalous correlation. One model considers the junction between the semiconductor cathode and the metal substrate in the case of slightly excessive cesium deposition, and the other model considers different Cs-Te composites. Our studies inspire a new way to break the conventional correlation between QE and TMS, and open a new perspective to advance the beam brightness frontiers.

The Impact of Intangible Capital on Factor Performance Efficacy

Prevalent accounting standards require the cost of internally created intangibles to be expensed, disproportionately affecting the book values of high and low intangible intensity (II) companies. We expect this to impact the performance efficacy of various factors contextually, depending on the extent to which intangible capital affects their computation. We compare return spreads for Book to Market, a measure of Value, and Momentum for companies belonging to low and high II industries and find that for Book to Market, they have declined significantly for companies in high II industries compared to spreads for companies in low II industries. We show that this decline is linked to the increasing intangible intensity of companies in high II industries. In contrast, Momentum spreads have increased for companies in high II industries. For investors who use multifactor strategies, the implication is that weighting Book to Market and Momentum according to the II of the company’s industry may be a useful technique for incorporating the effects of intangibles.