Large Momentum Spread Research Articles

Heavy Ion Injection of Fixed-Field Alternating Gradient Accelerator

Abstract Much research in recent years has focused on circular accelerators that accelerate and store secondary particles with a large momentum spread, such as muons, unstable nuclei, and heavy ions with different charge states. A fixed-field alternating gradient (FFAG) accelerator with large transverse and momentum acceptance has obvious advantages for such requirements. A versatile beam injection method is required to accelerate secondary particles with a large momentum spread and different charge states with an FFAG accelerator. In the present study, a method for charge exchange injection of positive heavy ions using the large momentum acceptance of an FFAG accelerator is proposed. A charge injection system, which converts a He1+ beam to a He2+ beam, is developed for a 150 MeV FFAG accelerator at the Center for Accelerator and Beam Applied Science (CABAS) of Kyushu University. As the first step to verify the injection method, an orbit shift from one charge state to the other is demonstrated. This is the first demonstration of heavy ion injection using an FFAG accelerator.

Demonstration of momentum cooling to enhance the potential of cancer treatment with proton therapy

In recent years, there has been a considerable push towards ultrahigh dose rates in proton therapy to effectively utilize motion mitigation strategies and potentially increase the sparing of healthy tissue through the so-called FLASH effect. However, in cyclotron-based proton therapy facilities, it is difficult to reach ultrahigh dose rates for low-energy beams. The main reason for this lies in the large momentum spread that such beams have after reducing their energy to levels required for proton therapy, incurring large losses in conventionally used momentum or energy selection slits. Here we propose momentum cooling by using a wedge in the energy selection system (instead of a slit) to reduce the momentum spread of the beam without introducing substantial beam losses. We demonstrate this concept in our eye treatment beamline and obtain a factor of two higher transmission, which could eventually halve the treatment delivery time. Furthermore, we show that with a gantry design incorporating this feature, we can achieve almost a factor of 100 higher transmission for a 70 MeV beam compared with conventional cyclotron-based facilities. This concept could enhance the potential of proton therapy by opening up possibilities of treating new indications and reducing the cost.

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.

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.

(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).

Buy-Side Competition and Momentum Profits

Abstract We show that a new measure of buy-side competition explains momentum profits. The momentum quintile spread is 1.11% when competition is low and negligible when competition is high. Better alphas are attained with superior Sharpe and Sortino ratios, with no negative skewness, and in more investible strategies featuring value-weighted portfolios and large capitalization stocks. Stock characteristics traditionally related to momentum do not explain our results. Tests based on long-term reversals, the trading patterns of funds, their style peers, distant funds, and retail investors suggest that slow information diffusion explains the large momentum spreads and momentum reversals in low competition markets.

Stochastic cooling simulation of rare isotope beam and its secondary beam

Stochastic cooling is a broadband feedback system, which is very effective for reducing the beam size without beam loss [1]. It has advantage over electron cooling in cooling low intensity beam with large emittance and momentum spread, and is required for precise study of the decay properties of RIB (Radioactive Ion Beam) by use of the SMS (Schottky Mass Spectrometry) method [2]. This paper mainly concerns on cooling of primary beam and its secondary beam, pointing out the range of mass-to-charge spread that could be cooled for secondary particles. Meanwhile, TOF cooling combined with filter cooling was also studied. The simulation results provide theoretical supports for analysing different ions circulating in the ring at the same time in the experiments.

Buy-Side Competition and Momentum Profits

We show that a new measure of buy-side competition explains momentum profits. The momentum quintile spread is 1.11% when competition is low and negligible when competition is high. Better alphas are attained with superior Sharpe and Sortino ratios, no negative skewness and in more investible strategies featuring value-weighted portfolios and large capitalization stocks. Stock characteristics traditionally related to momentum do not explain our results. Tests based on long-term reversals, the trading patterns of funds, their style peers, distant funds, and retail investors suggest that slow information diffusion explains the large momentum spreads and momentum reversals in low competition markets.

Simulation of longitudinal dynamics of laser-cooled and RF-bunched C3+ ion beams at heavy ion storage ring CSRe**Supported by National Natural Science Foundation of China (11405237, 11504388)

Laser cooling of Li-like C3+ and O4+ relativistic heavy ion beams is planned at the experimental Cooler Storage Ring (CSRe). Recently, a preparatory experiment to test important prerequisites for laser cooling of relativistic 12C3+ ion beams using a pulsed laser system has been performed at the CSRe. Unfortunately, the interaction between the ions and the pulsed laser cannot be detected. In order to study the laser cooling process and find the optimized parameters for future laser cooling experiments, a multi-particle tracking method has been developed to simulate the detailed longitudinal dynamics of laser-cooled ion beams at the CSRe. Simulations of laser cooling of the 12C3+ion beams by scanning the frequency of the RF-buncher or continuous wave (CW) laser wavelength have been performed. The simulation results indicate that ion beams with a large momentum spread could be laser-cooled by the combination of only one CW laser and the RF-buncher, and show the requirements of a successful laser cooling experiment. The optimized parameters for scanning the RF-buncher frequency or laser frequency have been obtained. Furthermore, the heating effects have been estimated for laser cooling at the CSRe. The Schottky noise spectra of longitudinally modulated and laser-cooled ion beams have been simulated to fully explain and anticipate the experimental results. The combination of Schottky spectra from the highly sensitive resonant Schottky pick-up and the simulation methods developed in this paper will be helpful to investigate the longitudinal dynamics of RF-bunched and ultra-cold ion beams in the upcoming laser cooling experiments at the CSRe.

Design of a high efficiency relativistic backward wave oscillator with low guiding magnetic field

A high efficiency relativistic backward wave oscillator working at a low guiding magnetic field is designed and simulated. A trapezoidal resonant reflector is used to reduce the modulation field in the resonant reflector to avoid overmodulation of the electron beam which will lead to a large momentum spread and then low conversion efficiency. The envelope of the inner radius of the slow wave structure (SWS) increases stepwise to keep conformal to the trajectory of the electron beam which will alleviate the bombardment of the electron on the surface of the SWS. The length of period of the SWS is reduced gradually to make a better match between phase velocity and electron beam, which decelerates continually and improves the RF current distribution. Meanwhile the modulation field is reduced by the introduction of nonuniform SWS also. The particle in cell simulation results reveal that a microwave with a power of 1.8 GW and a frequency of 14.7 GHz is generated with an efficiency of 47% when the diode voltage is 620 kV, the beam current 6.1 kA, and the guiding magnetic field 0.95 T.

Transverse Dynamics for Super-Rapid Acceleration in Circular High-Energy Particle Accelerators

A new particle acceleration concept had been presented to realize a short acceleration time of µs to produce high-energy muons in circular accelerators. The acceleration method is also expected to accelerate heavy-mass particles with large momentum spread: protons, deuterons, and various heavy ions. It is most important to develop a beam injection method into a main accelerator and to investigate the vertical motion of particles, especially for heavy ion acceleration. The outlines of beam injection method and beam focusing method to solve the vertical divergence problem, which causes the beam loss, are shown in this paper. In addition, a new compact magnet system, which produces magnetic field like a quadrupole field for beam focusing especially in wide aperture accelerators, is also described here.

Time-resolved momentum and beam size diagnostics for bunch trains with very large momentum spread

We propose a novel method to measure the time-resolved momentum distribution and size of beams with very large momentum spread. To demonstrate the principle we apply the method to the beam at the end of a Compact Linear Collider decelerator, where conventional diagnostic methods are hampered by the large energy spread of the drive beam after up to 90% of its kinetic energy is converted into microwave power. Our method is based on sweeping the beam in a circular pattern to determine the momentum distribution and recording the beam size on a screen using optical transition radiation. We present an algorithm to extract the time-resolved momentum distribution. Furthermore, the beam size along the bunch train can be extracted from the image left on a screen by sweeping the beam linearly. We introduce the analysis technique and show simulation results that allow us to estimate the applicability. In addition, we present a conceptual design of the technical realization.

Laser cooling of stored relativistic ion beams with large momentum spreads using a laser system with a wide scanning range

New results on laser cooling of stored, bunched, relativistic ion beams are presented. For the first time it has been possible to cool an ion beam with large momentum spread without initial electron cooling or scanning of the bunching frequency by using a single cw laser system.

Beam profile monitoring at the test beam line at the Compact Linear Collider test facility

Following the discovery of the Higgs-like boson at the Large Hadron Collider, there is demand for precision measurements on recent findings. The Compact Linear Collider, CLIC, is a candidate for a future linear electron-positron collider for such precision measurements. In CLIC, the beams will be brought to collisions in the multi-TeV regime through high gradient acceleration with high frequency RF power. A high intensity electron beam, the so-called drive beam, will serve as the power source for the main beam, as the drive beam is decelerated in special structures, from which power is extracted and transfered to the main beam. When the drive beam is decelerated the beam quality deteriorates and the momentum spread increases, which makes the beam transport challenging. Dedicated diagnostics to monitor the momentum profile along each bunch train and transverse profile diagnostics will be needed to guarantee the reliability of the decelerator and consequently the power source of the main beam acceleration.A test facility, CTF3, has been constructed at CERN to validate key technical aspects of the CLIC concept. The beam quality in the decelerator will be investigated in the test beam line, TBL, where several power extraction structures reduce the drive beam energy by up to 55%. At the same time, the single-bunch rms energy spread grows from the initial value of 1% to almost 6%. To monitor the parameters of such a beam is challenging but crucial for the optimization of the beamline. In this thesis we report on progress made on adapting generally used methods for beam profile measurements to the demanding conditions of a wide momentum profile. Two detector technologies are used for measuring transverse profile and momentum profile and we discuss the performance of these instruments, in the view of the large momentum spread and with the outlook towards equivalent beam profile monitors in the CLIC decelerator.

Dispersion-matched spectrometer in the low-energy branch of the Super-FRS for high-resolution measurements with large-emittance relativistic fragment beams

Precision measurements with an incident ion beam characterized by a large phase space represent a great challenge for in-flight rare-isotope facilities. Projectile fragments and fission products separated in flight have an inevitable large angular and momentum spread due to their stochastic creation processes and the atomic interactions in the production target, degrader and detector materials. A solution is to use dedicated ion-optical spectrometers with a high-resolution which can be obtained by circumventing the influence of the inherent large transverse and longitudinal emittance of the fragment beams. We demonstrate the method by coupling the different ion-optical sections of the magnetic in-flight separator Super-FRS in the Low-Energy Branch and show that the required high resolution can be achieved via dispersion-matched modes.

Effect of large momentum spread on emittance measurements

We discuss the systematic errors in emittance measurements with quadrupole scans and four screens due to large momentum spread in the beam. This is particularly relevant in the drive beam complex of CLIC and the test beam line TBL in the CTF3 facility at CERN. We also discuss methods to adapt the model to correct for the systematic errors.

Magnetic field measurement of large aperture FFAG magnet for muon-phase-rotation ring

The PRISM–FFAG ring, which consists of 10 scaling-radial-sector magnets, has been designed to store muons with large emittance and momentum spread. The FFAG magnets differ from conventional dipole magnets in that they have a magnetic field that varies strongly with radius and the vertical direction of the magnetic field alternates. Each magnet is composed of three sets of coils to produce a defocussing (outward bending)–focussing–defocussing triplet. After careful design, the PRISM–FFAG magnets were constructed and magnetic field measurements were made. The field maps in the fiducial volume show satisfactory agreement with the design fields based on OPERA 3D/TOSCA calculations.

Broadband single-shot electron spectrometer for GeV-class laser-plasma-based accelerators

Laser-plasma-based accelerators can provide electrons over a broad energy range and/or with large momentum spread. The electron beam energy distribution can be controlled via accurate control of laser and plasma properties, and beams with energies ranging from approximately 0.5 to 1000 MeV have been observed. Measuring these energy distributions in a single shot requires the use of a diagnostic with large momentum acceptance and, ideally, sufficient resolution to accurately measure narrow energy spread beams. Such a broadband single-shot electron magnetic spectrometer for GeV-class laser-plasma-based accelerators has been developed at Lawrence Berkeley National Laboratory. Detailed descriptions of the design concept and hardware are presented, as well as a performance evaluation of the spectrometer. The spectrometer covered electron beam energies raging from 0.01 to 1.1 GeV in a single shot, and enabled the simultaneous measurement of the laser properties at the exit of the accelerator through the use of a sufficiently large pole gap. Based on measured field maps and third-order transport analysis, a few percent-level resolution and determination of the absolute energy were achieved over the entire energy range. Laser-plasma-based accelerator experiments demonstrated the capability of the spectrometer as a diagnostic and its suitability for measuring broadband electron sources.

Decrease of the tunneling time and violation of the Hartman effect for large barriers

The explicit formulation of the initial conditions of the definition of the wave-packet tunneling time is proposed. This formulation takes adequately into account the irreversibility of the wave-packet space-time spreading. Moreover, it explains the violations of the Hartman effect, leading to a strong decrease of the tunneling times up to negative values for wave packets with large momentum spreads due to strong wave-packet time spreading.

Therapeutic purpose 9C beams produced in the secondary beam line at HIMAC

Due to the favorable characteristics of heavy-ion beams such as dose localization as well as high relative biological effectiveness, heavy-ion cancer therapy is attracting growing interests all over the world. The application of β-delayed particle decay beams like 9C ions in cancer therapy is expected to further improve the treatment efficacy of the modality of heavy-ions. For the first time 9C beams were produced in the secondary beam line (SBL) of the HIMAC facility with a primary 12C beam of 430 MeV/n. The production conditions providing a 9C beam with higher production rate and purity were optimized using different thick production targets and degraders. The results show setting the momentum acceptance to the full value of 5% the production rate is 9.07 × 10 −6 and the purity is 82.88% for the produced 9C beam under the optimal condition. Because of the large momentum spread for a secondary beam, the momentum distribution of the produced 9C beam at the optimal condition was measured. The momentum among the beam had a nearly Gaussian profile with a standard deviation of 26.1 MeV/c/n and the largest component of the momenta appeared around 838.9 MeV/c/n. In order to form a relatively large uniform irradiation field being appropriate to further biological experiments for the produced 9C beam, the scanning magnets in the irradiation system of the SBL, operating in a wobbling mode, was used. A uniform irradiation field of 20 mm in diameter could be achieved with homogeneity of 93.8%. The work presented in this paper provides a substantial basis for the further studies with 9C beams for the therapeutic purpose.