Slow Beam Extraction Research Articles

Simulation study on the slow extraction for the improvement of the beam shill structure at J-PARC Main Ring

J-PARC Main Ring (MR) delivers a slow extracted 30 GeV proton beam to the Hadron Experimental Facility using third-order resonance. One of the critical properties required for the proton beam is the flatness of the time structure of the extracted beam (spill structure). We performed a simple beam simulation of the MR slow beam extraction to investigate the effect of the current ripples of the main magnet power supplies on the beam spill structure. In addition, we investigated in the simulation the effects of the feedback control system on the betatron tune using fast Q magnets and the transverse RF system to improve the spill structure. The simulation qualitatively reproduced the measured spill structures. Now the attempts to optimize their parameters for better spill structure are ongoing.

Slow beam extraction method from synchrotron for uniform spill and fast beam switching using an RF knockout method of multi-band colored noise signal—POP Experiment and simulation

A proof of principle experiment (POP) was performed at the WERC synchrotron on the innovative slow beam extraction method with use of RF-knockout. The goal of experiment was to demonstrate the usefulness of the concept of colored noise signals including many frequency bands around the betatron resonances to obtain the uniform beam spill and the fast beam switching off time. The beam experiment shows that a small standard deviation of spill fluctuation can be attained without the longitudinal beam bunching of circulating particles. It is also shown that a beam switching-off time of around 100 μs could be obtained with a uniform spill. The experimental results are compared with the simulation results.

Reducing Fluctuations in Slow-Extraction Beam Spill Using Transit-Time-Dependent Tune Modulation

Slow extraction of beam from synchrotrons or storage rings as required by many fixed target experiments is performed by controlled excitation and feeding of a structural lattice resonance. Due to the sensitive nature of this resonant extraction process, the temporal structure of the extracted beam is modulated by the minuscule current fluctuations present on the quadrupole magnet power supplies. Such a modulation lead to pile-ups in detectors and a significant reduction in accumulated event statistics. This contribution proposes and experimentally demonstrates that by an introduction of further modulation on quadrupole currents with a specific amplitude and frequency, the inherent power supply fluctuations are mitigated leading to a smoothening of the beam temporal structure. The slow extraction beam dynamics associated with this method are explained along with the operational results.

Reduction of 400 GeV/c slow extraction beam loss with a wire diffuser at the CERN Super Proton Synchrotron

Slow extraction of a quasicontinuous flux of high-energy protons is an important requirement for many high-energy physics experiments. This extraction type is associated with an unavoidable beam loss due to scattering on the thin septum element. The energy deposition of scattering products and resulting activation place performance limits on existing and planned high-power, high-energy fixed-target proton facilities. In the $400\text{ }\text{ }\mathrm{GeV}/c$ Super Proton Synchrotron (SPS) at CERN, a diffuser (or prescatterer), comprising an array of dense wires or ribbon located upstream of the electrostatic septum, has been designed to reduce absolute losses on the septum wires. As part of a concerted effort to investigate loss reduction techniques in the SPS in view of new physics experiments, the diffuser concept was explored in numerical simulation and analytically. A prototype device has been designed, built, installed, and tested in the SPS to prove the feasibility and quantify the performance reach. In this paper, the diffuser concept is briefly recalled and design considerations for the SPS use case are presented, with the analytical considerations and simulation studies for the optimization of the material and geometry. The device design is described, and the experimental results with a beam are presented and analyzed. The results are discussed, and an outlook is given for the operational feasibility and maximum obtainable performance gain. Conclusions are drawn on the implications for the application of the concept.

Slow beam extraction from a synchrotron using a radio frequency knockout system with a broadband colored noise signal

An RF-knockout extraction method to obtain a uniform spill intensity has been proposed using a colored noise including many frequency bands around the betatron resonances. A prototype of the RF-knockout system has been developed for a proof-of-principle experiment at the WERC synchrotron. The beam experiment shows that a uniformity of spill intensity improves with the number of frequency band as predicted in a beam simulation. The standard deviation of spill fluctuation to the average value with ten bands becomes a half of that with one band.

Septum shadowing by means of a bent crystal to reduce slow extraction beam loss

The flux of high-energy protons slow-extracted from the CERN Super Proton Synchrotron (SPS) is limited by the induced radioactivity caused by the beam loss intrinsic to the extraction process. Methods to substantially increase the efficiency of the extraction process are of great interest to fulfill requests for an increasing flux of 400 GeV protons to the present experiments, located in the North Area of the SPS, and also for potential future experiments with very high demanded protons on target. A crystal shadowing technique to significantly reduce the beam scattered and lost on the electrostatic extraction septum during the third-integer resonant slow extraction process has been developed and a prototype system tested with beam. The technique is based on the use of a thin, bent silicon crystal to coherently channel or volume reflect the portion of beam that would otherwise impinge the wire array of the electrostatic septum and instead eject it into the transfer line toward the production targets of the experiments. In this paper, the concept is described and applied to the SPS machine in order to specify the requirements of the prototype crystal shadowing system. Beam dynamics simulations of the prototype system are compared and benchmarked to the results obtained through beam tests, before being exploited to understand the characteristics of the present system and the potential performance reach of an optimized, future operational configuration. The remaining challenges faced to bring the system into operation, the optimization possibilities and other potential applications are discussed.

A state of the art current-septum dipole magnet

The acceleration process of charged particle beams often requires the use of few acceleration stages to provide the beam with the desired energy. The extraction of the beam from one acceleration stage and the injection to the next, both require a special type of magnet which comes under the name septum magnet. Such a magnet generates a strong field in one region and a very low field in another region with the two regions separated by a very thin material (septum). The septum thickness of such a magnet should be as thin as possible to reduce the strength of other devices, like kickers, which are involved in the extraction or injection processes. A thin septum is also advantageous during the slow beam extraction process to reduce the beam losses at the septum. One of the methods which in theory can generate very large differences in field strength in adjacent field regions separated by a thin septum, is the use of two thin parallel current sheets of infinite dimensions. In practice we use other devices that can approximate such an abrupt change of the magnetic field within the septum thickness. In this paper we describe such a device, the DC current septum, we present results from the study of its electromagnetic properties, and we discuss a method to minimize the magnetic field in the region which requires a very small magnetic field. We also provide some results from the experimental measurements of the magnetic field generated by the “D6” current septum magnet which is installed in the experimental beam line of the NASA’s Space Radiation Laboratory (NSRL) facility (Tsoupas et al., 2007; Brown et al., 2010) at Brookhaven National Laboratory (BNL). This septum magnet is part of the beam’s extraction system from the AGS-Booster into the NSRL beam line for material and biological studies.

Positive features of crystal extraction of protons and carbon ions from the U-70 on basis of long-term experience

Works on the steering of particle beams using channeling in aligned bent crystals have been carried out at IHEP over a number of years. Comprehensive theoretical and experimental studies have led to the creation of actually operating systems on the U-70 accelerator. In particular, a slow proton beam extraction with unprecedentedly high parameters, an extraction efficiency of about 85% at a beam intensity of 10[Formula: see text] particles per cycle, has been realized on U-70 using particle channeling in short bent crystals. In recent years, successful experiments on the extraction of carbon ions were performed. At present, crystal elements are used in regular U-70 runs and provide half of the particle beams for physical experiments. Here, we summarize the results of this unique experience in the world practice of accelerators and outline its prospects.

Application of Crystal Elements for Charged Particle Beam Steering and Radiation Beam Generation on the U-70 Synchrotron

Works on the formation of particle and radiation beams using particle channeling and reflection in oriented crystals have been carried out at IHEP over a number of years. Comprehensive theoretical and experimental studies have led to the creation of actually operating systems on the U-70 accelerator. In particular, a slow proton beam extraction with unprecedentedly high parameters, an extraction efficiency of about 85% at a beam intensity of 1012 particles per cycle, has been realized on U-70 using particle channeling in short bent crystals. Experiments to implement the method of particle reflection in crystals for beam extraction and collimation have been carried out on U-70. At present, crystal elements are used in regular U-70 runs and provide half of the particle beams for physical experiments. We summarize the results of this unique experience in the world practice of accelerators and outline its prospects.

Electron cloud simulations for the main ring of J-PARC

The simulation of beam instabilities is a helpful tool to evaluate potential threats against the machine protection of the high intensity beams. At Main Ring (MR) of J-PARC, signals related to the electron cloud have been observed during the slow beam extraction mode. Hence, several studies were conducted to investigate the mechanism that produces it, the results confirmed a strong dependence on the beam intensity and the bunch structure in the formation of the electron cloud, however, the precise explanation of its trigger conditions remains incomplete. To shed light on the problem, electron cloud simulations were done using an updated version of the computational model developed from previous works at KEK. The code employed the signals of the measurements to reproduce the events seen during the surveys.

Simulation study on control of spill structure of slow extracted beam from a medical synchrotron with feed-forward and feedback using a fast quadruple magnet and RF-knockout system

A feedback control of the spill structure for the slow beam extraction from the medical synchrotron using a fast quadruple and radio frequency (RF)-knockout (QAR method) is studied to obtain the designed spill structure. In addition the feed-forward control is used so that the feedback control is performed effectively. In this extraction method, the spill of several ms are extracted continuously with an interval time of less than 1ms. Beam simulation showed that a flat spill structure was effectively obtained with feed-forward and feedback control system as well as a step-wise structure which is useful for the shortening of an irradiation time in a spot scanning operation. The effect of current ripples from main quadruple magnet's power supplies could be also reduced with the feedback control application.

Practical application of noise diffusion in U-70 synchrotron

This paper briefly outlines the physical substantiation and the engineering implementation of technological systems in the U-70 synchrotron based on controllable noise diffusion of the beam. They include two systems of stochastic slow beam extraction (for high and intermediate energy) and the system of longitudinal noise RF gymnastics designated for flattening the bunch distribution over the azimuth.

SU‐F‐J‐190: Time Resolved Range Measurement System Using Scintillator and CCD Camera for the Slow Beam Extraction

Purpose:To investigate the time structure of the range, we have verified the rang shift due to the betatron tune shift with several synchrotron parameters.Methods:A cylindrical plastic scintillator block and a CCD camera were installed on the black box. Using image processing, the range was determined the 80 percent of distal dose of the depth light distribution. The root mean square error of the range measurement using the scintillator and CCD system is about 0.2 mm. Range measurement was performed at interval of 170 msec. The chromaticity of the synchrotron was changed in the range of plus or minus 1% from reference chromaticity in this study. All of the particle inside the synchrotron ring were extracted with the output beam intensity 1.8×108 and 5.0×107 particle per sec.Results:The time strictures of the range were changed by changing of the chromaticity. The reproducibility of the measurement was sufficient to observe the time structures of the range. The range shift was depending on the number of the residual particle inside the synchrotron ring.Conclusion:In slow beam extraction for scanned carbon‐ion therapy, the range shift is undesirable because it causes the dose uncertainty in the target. We introduced the time‐resolved range measurement using scintillator and CCD system. The scintillator and CCD system have enabled to verify the range shift with sufficient spatial resolution and reproducibility.

Energy compensation of slow extracted beams with RF acceleration

In a conventional carbon-ion radiotherapy facility, a carbon-ion beam is typically accelerated up to an optimum energy, slowly extracted from a synchrotron ring by a resonant slow extraction method, and ultimately delivered to a patient through a beam-delivery system. At Japan’s Gunma University, a method employing slow-beam extraction along with beam-acceleration has been adopted. This method slightly alters the extracted-beam’s energy owing to the acceleration component of the process, which subsequently results in a residual-range variation of approximately 2mm in water-equivalent length. However, this range variation does not disturb a distal dose distribution with broad-beam methods such as the single beam-wobbling method. With the pencil-beam 3D scanning method, however, such a range variation disturbs a distal dose distribution because the variation is comparable to slice thickness. Therefore, for pencil-beam 3D scanning, an energy compensation method for a slow extracted beam is proposed in this paper. This method can compensate for the aforementioned energy variances by controlling net energy losses through a rotatable energy absorber set fixed between the synchrotron exit channel and the isocenter. Experimental results demonstrate that beam energies can be maintained constant, as originally hypothesized. Moreover, energy-absorber positions were found to be significantly enhanced by optimizing beam optics for reducing beam-size growth by implementation of the multiple-scattering effect option.

Perspectives for low energy antiproton physics at FAIR

The CRYRING accelerator, previously located at the Manne Siegbahn Laboratory of Stockholm University, has been chosen by the FLAIR collaboration as the central accelerator for the planned facility. It has been modified to allow for high-energy injection and extraction and is capable of providing fast and slow extracted beams of antiprotons and highly charged ions. It is currently being installed at the ESR of GSI Darmstadt where it can be used with highly charged ions. The future possibilities for its use with slow antiprotons will be discussed.

RF knock-out extraction in HITFiL

A compact facility for cancer therapy has been designed and is presently under construction. A slow beam extraction system using the RF-Knock Out method and 3rd-order resonance is adopted in the synchrotron of this facility. Eight sextupoles are used, four of them are for correcting the chromaticity and the rest for driving the 3rd-order resonance. In order to save the aperture of vacuum chamber, a 3-magnet bump is adopted during the extraction process. The extraction phase space map and the last 3 turns' particle trajectory before extraction are given. The matching betatron functions with HEBT (high energy beam transport) are also presented.

Simon van der Meer (1925–2011): A Modest Genius of Accelerator Science

Simon van der Meer was a brilliant scientist and a true giant of accelerator science. His seminal contributions to accelerator science have been essential to this day in our quest for satisfying the demands of modern particle physics. Whether we talk of long base-line neutrino physics or antiproton–proton physics at Fermilab or proton–proton physics at LHC, his techniques and inventions have been a vital part of the modern day successes. Simon van der Meer and Carlo Rubbia were the first CERN scientists to become Nobel laureates in Physics, in 1984. Van der Meer's lesser-known contributions spanned a whole range of subjects in accelerator science, from magnet design to power supply design, beam measurements, slow beam extraction, sophisticated programs and controls.

Design Study on Slow Beam Extraction in the 1 GeV Rapid Cycling Synchrotron at the PEFP

in a slow extraction system for a future 1-GeV proton synchrotron the Proton Engineering Frontier Project. This paper describes the properties of the optics design and optimizations for slow extraction in the synchrotron. The eects of the thirdinteger resonance in Rapid Cycle Synchrotron were investigated. We performed beam tracking simulations to observe the motions of particles in phase space by using the Methodical Accelerator Design 8 program. Finally, we performed beam trace simulations at the designed slow extraction line and showed that the proton beam could be stably extracted by using the RCS.

Manufacturing and Operation of the Magnetic Septa for the Slow Beam Extraction From the J-PARC 50 GeV Proton Synchrotron

The magnetic septa have been developed for the slow beam extraction from the 50 GeV Proton Synchrotron to the Hadron Experimental Hall at J-PARC (Japan Proton Accelerator Research Complex). The magnetic septa consist of two thin magnetic septa, four medium thick magnetic septa and four thick magnetic septa. The typical operating current is 3000 A and the total kick angle is 77 mrad with the 30 GeV proton beam. All parts of the thin and of the medium thick septum magnets are made of inorganic materials to resist high radiation environment. The positions of the thin and medium thick septa can be aligned remotely in the horizontal range of ±5 mm, which enables us to minimize the beam loss at the magnetic septum section. The septa were installed in the synchrotron ring in December, 2008, after a test at KEK (High Energy Accelerator Research Organization), and were successfully operated in the beam time for the slow beam extraction in January and February, 2009, which resulted in the first 30 GeV slow extracted beam delivery to the Hadron Experimental Hall.

Lattice Design of a Carbon-Ion Synchrotron for Cancer Therapy

A medical synchrotron for carbon-ion cancer therapy was designed to be compact for a hospital-based therapy facility. The circumference of the synchrotron is only 60 meter, and the lattice is a FODO structure of 6 cells. The lattice satisfies the requirements for resonant slowbeam extraction. An acceleration-driven resonant extraction scheme using betatron core is chosen to offer the smoothest spill of particles to the patients. Particle tracking simulations for injection and extraction are carried out to confirm the lattice design.