Momentum Spread Of Beam Research Articles

Mixed-size spot scanning with a compact large momentum acceptance superconducting (LMA-SC) gantry beamline for proton therapy

Objective. Lowering treatment costs and improving treatment quality are two primary goals for next-generation proton therapy (PT) facilities. This work will design a compact large momentum acceptance superconducting (LMA-SC) gantry beamline to reduce the footprint and expense of the PT facilities, with a novel mixed-size spot scanning method to improve the sparing of organs at risk (OAR). Approach. For the LMA-SC gantry beamline, the movable energy slit is placed in the middle of the last achromatic bending section, and the beam momentum spread of delivered spots can be easily changed during the treatment. Simultaneously, changing the collimator size can provide spots with various lateral spot sizes. Based on the provided large-size and small-size spot models, the treatment planning with mixed spot scanning is optimized: the interior of the target is irradiated with large-size spots (to cover the uniform-dose interior efficiently), while the peripheral of the target is irradiated with small-size spots (to shape the sharp dose falloff at the peripheral accurately). Main results. The treatment plan with mixed-size spot scanning was evaluated and compared with small and large-size spot scanning for thirteen clinical prostate cases. The mixed-size spot plan had superior target dose homogeneities, better protection of OAR, and better plan robustness than the large-size spot plan. Compared to the small-size spot plan, the mixed-size spot plan had comparable plan quality, better plan robustness, and reduced plan delivery time from 65.9 to 40.0 s. Significance. The compact LMA-SC gantry beamline is proposed with mixed-size spot scanning, with demonstrated footprint reduction and improved plan quality compared to the conventional spot scanning method.

A parametric analysis for maximizing beam quality of muon-based storage ring experiments

The Muon g-2 experiment seeks to measure the anomalous magnetic moment (g-2) of muons to a 0.14 ppm uncertainty. In order to accomplish this, the experiment’s storage ring must be supplied with the largest number of muons with energies within 0.2% of 3.094 GeV/c possible. In this work we perform a parametric analysis for enhancing the experiment’s stored beam intensity. From the accelerator technology side, we discuss the impact in muon flux of both, a passive absorber for tailoring the momentum distribution of the injected beam, and a magnetic inflector for shielding it from the storage ring fringe fields. From the beam parameter side, we examine the interplay between beam energy and momentum spread in maximizing muon storage. We show that with a proper choice of injection beam parameters in conjunction with a wedge-shaped absorber and an open-ended inflector design, the yield of the experiment could increase by over 50% as compared to the current performance. We also find that although the wedge can enhance the stored muon yield, most of the improvement originates from the open-ended inflector design.

Magnetic axis measurement of the high precision coil for the High Intensity heavy-ion Accelerator Facility electron cooler

Electron cooling method is used for the High Intensity heavy-ion Accelerator Facility (HIAF), in order to reduce the beam emittance and momentum spread of heavy ion beams, hence to improve the accuracy and luminosity of nuclear physics and atomic physics experiments. The magnetic field homogeneity of the cooling section is the key parameter related to the cooling effect. A new type of cooling section solenoid composed of several coils was used in the HIAF electron cooling device to produce a high parallelism magnetic field. In this paper, a device for the magnetic field axis measurement of high-precision coils is presented. The geometric symmetrical axis of the coil is measured by a positioning device. The radial and axial magnetic field distribution in the center plane of the coil is measured by the rotating Hall probes. Finally, the relative angle between the coil magnetic field axis and the geometric symmetrical axis is calculated by the measurement results. The accuracy of the measured angle is within ±0.10 mrad. The measured angle of the prototype coil is (1.28±0.10) mrad, which satisfies the physics requirement.

Estimation of longitudinal bunch characteristics in the LHC using Schottky-based diagnostics

The Large Hadron Collider (LHC) Schottky monitors have been designed to measure various parameters of relevance to beam quality, namely tune, momentum spread, and chromaticity. In this work, we present how this instrument can be used to estimate longitudinal bunch characteristics, such as longitudinal bunch profile or synchrotron frequency distribution. Under the assumption of bunched beams with no intrabunch coherent motion, we start by deriving the relation between the distribution of synchrotron amplitudes within the bunch population and the longitudinal bunch profile from probabilistic principles. Subsequently, we fit the cumulative power density of acquired Schottky spectra with the underlying distribution of synchrotron amplitudes. Finally, the result of this fit is used to reconstruct the bunch profile using the derived model. The results obtained with this method are verified by comparison with longitudinal profile measurements from the LHC wall current monitors.

Realistic modeling of a particle–matter-interaction system for controlling the momentum spread of muon beams

The goal of the Muon g-2 Experiment is to measure the anomalous magnetic moment of the muon with a precision of 140 ppb; this is achieved by observing the polarization of muon decays in a precisely designed storage ring. Unfortunately, 90% of the injected beam is lost in apertures since it has a rms momentum spread that is an order of magnitude larger than the ring’s acceptance. In this study, we investigate the use of a wedge absorber for reducing the momentum spread of a muon beam. This technique relies on an interplay between ionization cooling and emittance exchange. We present the outcomes of tracking simulations and examine in detail the impact of the absorber length in reducing the momentum spread of the beam. Overall, we illustrate that the wedge has a positive impact on the Muon g-2 Experiment as it can increase the intensity of the storable beam. The technique discussed here may serve as an important a tool for momentum control of next generation secondary-beam-based experiments.

Beam momentum spread measurement using two beam position monitors at Xi’an Proton Application Facility

Beam momentum spread is a key parameter of the linac injector at the Xi’an Proton Application Facility (XiPAF), China. A momentum spread measurement method using multiple beam position monitors (BPM) was successfully developed recently at Tsinghua University, China. This work is an extension of the method. The original method requires at least three BPMs to perform the measurement, and the BPMs should be installed far from the accelerator exit, causing long measurement space and low BPM signals. The new method only needs two BPMs, and a much shorter measurement space is proposed for the low-current linac in this paper. The new method was successfully tested at XiPAF. The measured rms momentum spread at the Radio Frequency Quadrupole exit is (5.05 ± 0.06) × 10−3, which agrees well with the spectrometer measured value (5.09 ± 0.05) × 10−3.

An online bunch length and momentum spread measurement method based on multiple BPMs

Bunch length and momentum spread are two crucial parameters in proton and ion linacs. A non-destructive model-independent rms bunch length and momentum spread measurement method that uses button BPMs is presented in this paper. By using the exponential relation between BPM signal amplitude and rms bunch length, as well as the linear relation between rms bunch length and drift time, rms bunch length and rms momentum spread are derived from several BPMs (three at least) located along the beam line. The effects of beam displacement, beam size, and BPM quantity on the measurement are analyzed. The rms bunch length and the rms momentum spread of the 3-MeV proton beam at the Compact Pulsed Hadron Source (CPHS) of Tsinghua University were successfully measured using this method. The measured rms momentum spread 0.54% is consistent with the simulation value. In addition, the resolution for the rms bunch length and the rms momentum spread measurements were ±0.017 ns and ±0.016%, respectively.

Helium ions at the heidelberg ion beam therapy center: comparisons between FLUKA Monte Carlo code predictions and dosimetric measurements

In the field of particle therapy helium ion beams could offer an alternative for radiotherapy treatments, owing to their interesting physical and biological properties intermediate between protons and carbon ions. We present in this work the comparisons and validations of the Monte Carlo FLUKA code against in-depth dosimetric measurements acquired at the Heidelberg Ion Beam Therapy Center (HIT). Depth dose distributions in water with and without ripple filter, lateral profiles at different depths in water and a spread-out Bragg peak were investigated. After experimentally-driven tuning of the less known initial beam characteristics in vacuum (beam lateral size and momentum spread) and simulation parameters (water ionization potential), comparisons of depth dose distributions were performed between simulations and measurements, which showed overall good agreement with range differences below 0.1 mm and dose-weighted average dose-differences below 2.3% throughout the entire energy range. Comparisons of lateral dose profiles showed differences in full-width-half-maximum lower than 0.7 mm. Measurements of the spread-out Bragg peak indicated differences with simulations below 1% in the high dose regions and 3% in all other regions, with a range difference less than 0.5 mm. Despite the promising results, some discrepancies between simulations and measurements were observed, particularly at high energies. These differences were attributed to an underestimation of dose contributions from secondary particles at large angles, as seen in a triple Gaussian parametrization of the lateral profiles along the depth. However, the results allowed us to validate FLUKA simulations against measurements, confirming its suitability for 4He ion beam modeling in preparation of clinical establishment at HIT. Future activities building on this work will include treatment plan comparisons using validated biological models between proton and helium ions, either within a Monte Carlo treatment planning engine based on the same FLUKA code, or an independent analytical planning system fed with a validated database of inputs calculated with FLUKA.

SU‐E‐T‐470: Beam Performance of the Radiance 330 Proton Therapy System

Purpose:The ProTom Radiance 330 proton radiotherapy system is a fully functional, compact proton radiotherapy system that provides advanced proton delivery capabilities. It supports three‐dimensional beam scanning with energy and intensity modulation. A series of measurements have been conducted to characterize the beam performance of the first installation of the system at the McLaren Proton Therapy Center in Flint, Michigan. These measurements were part of the technical commissioning of the system. Select measurements and results are presented.Methods:The Radiance 330 proton beam energy range is 70–250 MeV for treatment, and up to 330 MeV for proton tomography and radiography. Its 3‐D scanning capability, together with a small beam emittance and momentum spread, provides a highly efficient beam delivery. During the technical commissioning, treatment plans were created to deliver uniform maps at various energies to perform Gamma Index analysis. EBT3 Gafchromic films were irradiated using the Planned irradiation maps. Bragg Peak chamber was used to test the dynamic range during a scan in one layer for high (250 MeV) and Low (70 MeV) energies. The maximum and minimum range, range adjustment and modulation, distal dose falloff (80%–20%), pencil beam spot size, spot placement accuracy were also measured. The accuracy testing included acquiring images, image registration, receiving correction vectors and applying the corrections to the robotic patient positioner.Results:Gamma Index analysis of the Treatment Planning System (TPS) data vs. Measured data showed more than 90% of points within (3%, 3mm) for the maps created by the TPS. At Isocenter Beam Size (One sigma) < 3mm at highest energy (250 MeV) in air. Beam delivery was within 0.6 mm of the intended target at the entrance and the exit of the beam, through the phantom.Conclusion:The Radiance 330 Beam Performance Measurements have confirmed that the system operates as designed with excellent clinical performance specifications.Hovakim Nazaryan, Vahagn Nazaryan and Fuhua Wang are employees of ProTom International, Inc. who contributed to the development and completed the technical commissioning of the Radiance 330 proton therapy delivery system manufactured by ProTom International.

Dielectronic recombination experiment of P-like Tin on HIRFL-CSRm at Lanzhou

Total recombination rate coefficients of 112Sn35+ ions have been firstly measured by employing the electron-ion merged-beams technique on the main cooler storage ring at Lanzhou. Using an electron beam energy detuning system, we precisely tuned the relative energies from 0 to 6.0 eV between the electron beam and the ion beam (momentum spread Δp/p ~ 5 × 10−4). A multi-configuration Breit-Pauli calculation utilizing kappa-averaged relativistic orbitals has been carried-out for the recombination rate coefficients. We find that there are obvious differences between the experimental total rate coefficients and the theoretical calculations.

Simulation and Design of Tentative Muon Source Based on CSNS

This paper presents a conceptual design for the first tentative surface muon source based on the proton beam provided by China Spallation Neutron Source (CSNS). We have calculated the optimal parameters of solid muon target, in which the method of Monte Carlo simulation is used to obtain the optimal muon beam parameters, such as beam fluence rate, momentum spread and phase space distribution. A simple muon transport beamline system was also designed, which could transport the muons emitted from the muon target into the experimental area, where positrons from muon decay in a test sample are detected by a spectrometer. The beam optics of this new beam line is also described.

Observation of K- and L-REC in 200 MeV/u Xe 54+-N 2 collisions at HIRFL-CSR

The 200 MeV/u Xe 54+ ions were utilized to collide with N 2 molecules and the K- and L-REC, as well as the Lyman lines of Xe 53+ were observed. After electron cooling, the ion beam momentum spread Δ P/ P ≈ 2.2 × 10 −5 was achieved and the target thickness was stabilized at about 10 13 atom/cm 2. As the first atomic experiment at HIRFL-CSR with the internal target, its feasibility and stability were verified.

Design study of the KINRIS isotope separator with a 270° wide aperture magnet

A new isotope separator KINRIS (Kiev Institute for Nuclear Research Isotope Separator) is being constructed at the Institute for Nuclear Research in Kiev (Ukraine). This paper reviews main features of the electromagnetic separator for stable isotopes production using an analyzing magnet with an inhomogeneous magnetic field. Beam-optical principles of the KINRIS separator and results of beam-optical calculations are discussed. In this paper we consider the influence of a beam emittance, momentum spread and aberrations on the mass resolving power of the KINRIS separator. Results show that this separator can be used for isotopes production with an excellent efficiency for any ion mass.

Unraveling the mystery of enhanced cell-killing effect around the Bragg peak region of a double irradiation source9C-ion beam

An enhanced cell-killing effect at the penetration depths around the Bragg peak of a β-delayed particle decay9C-ion beam has been observed in our preceding radiobiological experiments in comparison with a therapeutic12C beam under the same conditions, and RBE values of the9C beam were revealed to be higher than those of the comparative12C beam by a factor of up to 2. This study is aimed at investigating the biophysical mechanisms underlying the important experimental phenomenon. First of all, a model for calculating the stopping probability density of the experimentally applied9C beam is worked out, where all determinants such as the initial momentum spread of the9C beam, the fluence attenuation with penetration depth due to the projectile-target nuclear reaction and the energy straggling effect are taken into account. On the basis of the calculated9C-ion stopping distribution, it has been found that the area corresponding to the enhanced cell-killing effect of the9C beam appears at the stopping region of the incident9C ions. The stopping9C-ion density in depth, then, is derived from the calculated probability density. Moreover, taking entrance dose 1 Gy for the9C beam as an example, the average stopping9C-ion numbers per cell at various depths are deduced. Meanwhile, the mean lethal damage events induced by the9C and comparative12C beams at the depths with almost equal dose-averaged LETs are derived from the measured cell surviving fractions at these depths for the9C and12C beams. Under the condition of the same absorbed doses, there are indeed good agreements between the average stopping9C-ion number pre cell and the difference of the mean lethal damage events between the9C and12C beams at the depths of similar dose-averaged LETs. It can be inferred that if a9C ion comes to rest in a cell, the cell would undergo dying. In view of the decay property of9C nuclide, clustered damage would be caused in the cell by the emitted low-energy particles. Therefore, the results achieved in this work can be taken as indirect evidence supporting that damage cluster is more efficient in leading to cell lethality.

Simulations of neutralized final focus

In order to drive an inertial fusion target or study high-energy density physics with heavy ion beams, the beam radius must be focused to <3 mm and the pulselength must be compressed to <10 ns. The conventional scheme for temporal pulse compression makes use of an increasing ion velocity to compress the beam as it drifts and beam space charge to stagnate the compression before final focus. Beam compression in a neutralizing plasma does not require stagnation of the compression, enabling a more robust method. The final pulse shape at the target can be programmed by an applied velocity tilt. In this paper, neutralized drift compression is investigated. The sensitivity of the compression and focusing to beam momentum spread, plasma, and magnetic field conditions is studied with realistic driver examples. Using the 3D particle-in-cell code, we examine issues associated with self-field generation, stability, and vacuum-neutralized transport transition and focusing.

Six-dimensional muon beam cooling in a continuous, homogeneous, gaseous hydrogen absorber

The fast reduction of the six-dimensional phase space of muon beams is required for muon colliders and is also of great importance for neutrino factories based on accelerated muon beams. Ionization cooling, where all momentum components are degraded by an energy absorbing material and only the longitudinal momentum is restored by RF cavities, provides a means to quickly reduce transverse beam sizes. However, the beam momentum spread cannot be reduced by this method unless the longitudinal emittance can be transformed or exchanged into the transverse emittance. The best emittance exchange plans up to now have been accomplished by using magnets to disperse the beam along the face of a wedge-shaped absorber such that higher momentum particles pass through thicker parts of the absorber and thus suffer larger ionization energy loss. In the scheme advocated in this paper, it is noted that one can generate a magnetic channel filled with absorber where higher momentum corresponds to a longer path length and therefore larger ionization energy loss. Thus a homogeneous absorber, without any special edge shaping, can provide the desired emittance exchange. An attractive example of a cooling channel based on this principle involves the use of RF cavities filled with a continuous gaseous hydrogen absorber in a magnetic channel composed of a solenoidal field with superimposed helical transverse dipole, quadrupole, and octupole fields. The theory of this helical channel is described to support the analytical prediction of a million-fold reduction in phase space volume in a channel 150m long.

Observations of Ordered Beams in CRYRING

In the CRYRING storage ring weak beams of electron-cooled highly charged ions have been studied. When the intensity of the ion beam decays below a certain limit the momentum spread of the beam show a sudden transition to a state with much lower momentum spread. Similar observations have earlier been made at GSI, and have been interpreted as a one-dimensional ordering of the beam. For a beam of 7.4 MeV/u Xe36+ we have varied the electron density and studied how that affects the particle number at transition, the momentum spread of the ion beam, and the Schottky power. The transition occurs at particle distances between 1 and 35 cm, depending on the cooling rate.

Electron cooling system for ITEP ion storage ring

The main goal of the Tera Watt A Cumulator project (Institute for Theoretical and Experimental Physics, Moscow) is accumulation in the storage ring of an intense ion beam, its longitudinal compression and the use of the extracted beam for plasma experiments. However, beam parameters at the target are decreased because of extreme transverse heating and growth of the beam momentum spread due to intrabeam scattering. These effects can be suppressed by application of the electron cooling system (ECS). Design study of ECS has been performed in the Joint Institute for Nuclear Research. The design project and characteristics of the system are described, as well as analysis of the accumulation kinetics in the presence of the cooling system. Design work has shown that because of the small length of the straight section (2.35 m), the effective length of the cooling system is small (about 55–60 cm). Nevertheless, for long accumulation times (&gt;100 s), the system allows us to significantly improve the beam parameters at the target (specific energy, specific power, and so on) and to suppress the beam losses by an order of magnitude.

Realization of matching conditions for high-resolution spectrometers

For precise measurements of nuclear-reaction spectra using a beam from an accelerator, a high-resolution magnetic spectrometer is a powerful tool. The full capability of a magnetic spectrometer, however, can be achieved only if the characteristics of the beam coming from the accelerator are matched to those required by the spectrometer by properly adjusting the beam line conditions. The matching methods, lateral dispersion matching, focus matching and also the kinematic correction compensate the spectrum line-broadening effects caused by the beam momentum spread and reaction kinematics. In addition, angular dispersion matching should be performed if good resolution of the scattering angle is important. Diagnostic methods developed to realize these matching conditions for the spectrometers K600 at IUCF and Grand Raiden at RCNP are presented.

New methods to derive the optical and beam parameters in transport channels

The standard approach to compute the optical parameters and the beam emittance in a transport channel is based on the analysis of the profiles measured by three monitors. This requires the independent measurement of the dispersion function at the monitor locations and the knowledge of the value of the beam's momentum spread. In this paper different approaches based on the use of more than three beam profiles are presented. These techniques allow the determination of the complete set of four optical parameters, the betatron and dispersion functions and their derivatives, along with the beam emittance and the beam's momentum spread, simultaneously and without varying the physical parameters of the transport channel or the upstream machine. A detailed description of the different methods is carried out with a particular emphasis on their accuracy. Results of numerical simulations are presented.