Beam Extraction Efficiency Research Articles

An upgrade of the radial probes for HIRFL-SFC

SFC (Sector Focusing Cyclotron) is essential to the Heavy Ion Research Facility in Lanzhou (HIRFL). Its beam extraction efficiency is directly related to the overall operational efficiency of the accelerator. The original radial probes of the SFC, due to its outdated equipment, no longer meet the requirements for beam tuning in terms of mechanical precision, vacuum level, and local noise. Three new sets of radial probes have been developed in phases. These devices were installed at the accelerator site during annual maintenance, providing axial and radial beam distribution during acceleration. Since 2020, the system has been operating without any failures, providing corresponding beam parameters for the accelerator's operation and ensuring the normal functioning of the accelerator.

Enhancement of beam quality and transmission using phase bunching in the central region of a cyclotron

Phase bunching in the central region of an azimuthally varying field (AVF) cyclotron contributed significantly to the improvement of the extracted beam quality. The phase bunching effect was demonstrated by measurements of the accelerated and extracted beam properties and by a theoretical analysis using the upgraded geometric trajectory model of the AVF cyclotron at the facility of Takasaki Ion accelerators for Advanced Radiation Application. The phase bunching effect on the beam extraction efficiency and emittance was estimated by a comparison between the 260 MeV 20Ne7+ beam of harmonic number h = 2 in the phase-bunching condition (PBC) and the 107 MeV 4He2+ beam of h = 1 in the non-phase-bunching condition (NBC). The PBC narrowed beam phase width and produced near-single-turn extraction, resulting in high extraction efficiency more than twice as high as that for the NBC. It was proved by beam current measurements. Reduction of the beam phase width was confirmed by the theoretical and experimental analysis of correlation between the radial positions at the phase-defining slits and the phase distribution of the particles passing through the slits. The theoretical analysis also showed that the beam emittance before extraction under the PBC is reduced to less than half of the NBC case. Furthermore, the measured normalized beam emittance in the horizontal direction after the extraction for the PBC was remarkably improved to 0.054π mm mrad nearly one-fourth of the emittance of 0.20π mm mrad for the NBC.

Analytical study of FEL oscillator saturation state based on longitudinal ponderomotive bucket

Free Electron Laser(FEL) oscillator is the main working mode to produce infrared and THz wavelength range radiation. At FEL saturation state, the interaction between electron beams and radiation becomes nonlinear. Saturation power can be solved by numerical simulation of macro particle motion in longitudinal phase space or by semi-analytical formulae analogous to conventional laser system from previous study. While in this paper, the motions of macro-particle are depicted with analytical formulae in the assumption that energy transfer is mainly from captured electrons of ponderomotive bucket. Then corresponding electron beam extraction efficiency can be achieved due to initial and final state of electron beams. Therefore laser power is confirmed through equilibrium situation inside resonator cavity. These simple analytical formulae can be used to optimize output laser power and offer a better understanding in FEL oscillator saturation. Taking small signal gain regime as an example, the optimum FEL efficiency is obtained at gain to loss ratio around 4.1. This agrees well with the results of three-dimension simulation.

First design of a crystal-based extraction of 6\xa0GeV electrons for the DESY II Booster Synchrotron

A proof-of-principle experimental setup for the extraction of 6 GeV electrons from the DESY II Booster Synchrotron using the channeling effect in a bent crystal is elaborated. Various aspects of the experimental setup were investigated in detail, such as the particle beam dynamics during the extraction process, the manufacturing and characterization of bent crystals, and the detection of the extracted beam. In order to optimize the crystal geometry, the overall process of beam extraction was simulated, taking into account the influence of radiation energy losses. As result it is concluded that the multi-turn electron beam extraction efficiency can reach up to 16%. In principle this crystal-based beam extraction technique can be applied at any electron synchrotron in order to provide multi-GeV electron beams in a parasitic mode. This technique will allow to supply fixed-target experiments by intense high-quality monoenergetic electron beams. Furthermore, electron/positron crystal-based extraction from future lepton colliders may provide an access to unique experimental conditions for ultra-high energy fixed-target experiments including searches for new physics beyond the Standard Model.

Testing of the Ti foil with TiN coating as an exit window of a pulsed electron accelerator

Increasing the efficiency of electron beam extraction from a vacuum diode is an urgent problem for the practical use of accelerators. In the general case, the given problem is reduced to decreasing the mass thickness (g/cm2) of the exit window membrane while ensuring sufficient mechanical properties. The paper presents the results of testing an exit window 85 mm in diameter with a 25 μm Ti membrane and a 0.8 μm TiN coating. When tested, the coated membrane exhibited mechanical characteristics comparable to those of a 60 μm Ti membrane, which deteriorated upon repeated pumpings of the accelerator chamber volume due to the appearance of cracks in the coating. The energy loss of the electron beam in the exit window of the accelerator was decreased by 18%, as compared to the Ti 60 μm membrane. The use of a 25 μm Ti membrane with a 0.8 μm TiN coating provided 16 J per pulse energy output of more than 104 pulses of the electron beam (50–275 keV) with a repetition rate of 1–10 pulses per second. The obtained results will be used to further improve the electron beam extraction systems in the field of high-pressure applications.

Efficiency of electron beam extraction to the atmosphere in an accelerator based on ion-electron emission

The use of a modern element base makes it possible to create power supplies with a transition from a direct mode of generation of an auxiliary discharge to a pulse-periodic mode with a pulse repetition rate at the level of several tens of kHz. This allows for a more flexible adjustment of the discharge parameters, keeping the average value of its current, but changing its amplitude with a corresponding change in the pulse duty cycle. In this work, using an electron accelerator based on ion-electron emission, generating a wide-aperture electron beam, we research the effect of auxiliary discharge generation mode (direct and pulse-periodic) on the efficiency of electron beam extraction into the ambient atmosphere. It is shown that, in a direct mode of electron beam generation at an accelerating voltage of 150 kV, the beam extraction coefficient does not exceed 0.25. The possibility of increasing the extraction coefficient to K = 0.55 at the same accelerating voltage of 150 kV was demonstrated without making changes to the design of the accelerator, but switching to a pulsed-periodic mode of emission plasma generation.

The CERN-MEDICIS Isotope Separator Beamline.

CERN-MEDICIS is an off-line isotope separator facility for the extraction of radioisotopes from irradiated targets of interest to medical applications. The beamline, between the ion source and the collection chamber, consists of ion extraction and focusing elements, and a dipole magnet mass spectrometer recovered from the LISOL facility in Louvain-la-Neuve. The latter has been modified for compatibility with MEDICIS, including the installation of a window for injecting laser light into the ion source for resonance photo-ionization. Ion beam optics and magnetic field modeling using SIMION and OPERA respectively were performed for the design and characterization of the beamline. The individual components and their optimal configuration in terms of ion beam extraction, mass separation, and ion transport efficiency is described, along with details of the commissioning and initial performance assessment with stable ion beams.

Comparison of Large-Area Low-Energy Electron Accelerators Based on a High-Voltage Glow Discharge with Accelerators Based on Longitudinal Filaments

Abstract—A wide-aperture low-energy electron accelerator based on a high-voltage glow discharge (HVGD) is considered in comparison with accelerators based on a number of longitudinal filaments. The basic design features and advantages of HVGD-based accelerators are presented. These studies showed that it is possible to obtain high values of the density of the electron beam current extracted from the foil (56 µA/cm2) and rather high values of the beam extraction efficiency (35%) in comparison with the previously attained results. The obtained characteristics are comparable with the parameters of the accelerators based on a number of longitudinal filaments. The ability of the accelerator to operate with HVGD is demonstrated both in continuous and pulse–periodic modes without a change in its design. Various ion–electron optical systems of HVGD accelerators have been studied and the advantages of slit-type systems are shown.

Numerical model of EOS with large-area plasma cathode with mesh stabilization of the emission plasma boundary

The source of electrons that generates a beam of a large cross section (BLCS) with the beam release into the atmosphere through a thin metal foil has been developed in the IHCE SB RAS. The electronic BLCS in this case is a superposition of elementary beams formed by separate emission structures. Their plasma boundary is stabilized by a fine-grained metal mesh, covered by a mask with round holes. The configuration of holes repeats the configuration of the holes in the support grid of the outlet foil window having a slightly larger diameter. In preliminary experiments, the maximum current-to-atmosphere output coefficient reached ∼70% of the current in the accelerating gap. The objective of this paper is to select a numerical model of the electron-optical system (EOS) for computer simulation and analysis of the characteristics of the formed elementary beams for further optimization of the source and increase the efficiency of beam extraction into the atmosphere.

Numerical research of a 2D axial symmetry hybrid model for the radio-frequency ion thruster

Since the high efficiency discharge is critical to the radio-frequency ion thruster (RIT), a 2D axial symmetry hybrid model has been developed to study the plasma evolution of RIT. The fluid method and the drift energy correction of the electron energy distribution function (EEDF) are applied to the analysis of the RIT discharge. In the meantime, the PIC-MCC method is used to investigate the ion beam current extraction character for the plasma plume region. The beam current simulation results, with the hybrid model, agree well with the experimental results, and the error is lower than 11%, which shows the validity of the model. The further study shows there is an optimal ratio for the radio-frequency (RF) power and the beam current extraction power under the fixed RIT configuration. And the beam extraction efficiency will decrease when the discharge efficiency beyond a certain threshold (about 87 W). As the input parameters of the hybrid model are all the design values, it can be directly used to the optimum design for other kinds of RITs and radio-frequency ion sources.

Modernization of electron accelerator with a large cross section beam for radiation effects on materials

The results of the work on the creation of an automated wide-aperture electron accelerator with a grid plasma cathode based on the low-pressure arc discharge and outputting of a large section beam (750×150 mm) in the atmosphere through a outlet foil window. The distinctive feature of such electron accelerator is a weak correlation of beam parameters, as well as a high current beam extraction efficiency to air, reaching ≈ (80 ÷ 90)% of the current in the accelerating gap at an accelerating voltage of 200 kV, beam current amplitude in the atmosphere up to 30A, frequency and pulse duration up to 50 s-1 and 100 μs, respectively. The electron source provides a stable continuous operation for tens of hours in a repetitively pulsed modes at the maximum average beam power in the atmosphere is ≈5 kW. Examples of applications of such accelerator in the radiation-stimulated technology are given, showing the prospects of its using in scientific and technological purposes.

A study of collimation and extraction of the U-70 accelerator beam using an axially oriented crystal

Extraction and collimation of the 50-GeV proton beam with a bent silicon crystal at the U-70 accelerator of the Institute for High Energy Physics (Protvino, Russia) was investigated. Until recently, proton beam extraction (and collimation) from accelerators has been effected using crystals with the (111) or (110) plane orientation, when the beam propagates far from the crystal axes. In the described experiment, the silicon crystal was oriented so that the proton beam was incident on it near the 〈110〉 axis. Under these conditions, a part of the beam was deflected by the crystal owing to the dynamic chaos phenomenon. The maximum beam extraction efficiency was as high as ~80%.

Optimization of Accelerating Grid for EAST Neutral Beam Injector Ion Source

As the first full superconducting non-circular cross section Tokomak in the world, EAST is used to explore the forefront physics and engineering issues on the construction of Tokomak fusion reactor. Neutral beam injection has been recognized as one of the most effective means for plasma heating. According to the research plan of the EAST physics experiment, two sets of neutral beam injector (NBI) (4–8 MW, 10–100 s) will be built and operational in 2014. Each of the NBI system consists of two high-current ion sources. In order to improve the beam extraction efficiency of ion source, the plasma grid of accelerating electrode was optimized. In this paper, the improved method and results after improvement has been reported. Experiment result shows that the beam extraction ability of accelerating electrode and the beam quality has been improved.

Design of the Superconducting Magnet System for a 28-GHz ECR Ion Source of RAON Accelerator

The linear accelerator, RAON, has been being developed as a part of the Rare Isotope Science Project (RISP) at Institute for Basic Science (IBS) in the Republic of Korea. In this paper, it is dealt with the design of a low Tc superconducting magnet system for an electron cyclotron resonance (ECR) ion source to utilize a 28-GHz radio frequency source. The superconducting magnet system for a 28-GHz ECR ion source consists of four solenoid coils and six saddle coils (a sextupole coil) (Taylor et al. IEEE Trans. Appl. Supercond. 10, 224–227, 2000). The detail specifications of each superconducting coil are designed by analyzing magnetic field to enhance the efficiency of beam extraction and electromagnetic force to improve the mechanical stability of a superconducting coil by using finite elements method (FEM) simulation. The definitive design parameters for manufacturing the superconducting magnet system for a 28-GHz ECR ion source of RAON accelerator are suggested considering electromagnetic characteristics.

Upgrade of a kicker control system for the HIRFL

A kicker system plays an important role in beam extraction and injection for a ring-like accelerator. The kicker system in the Heavy Ion Research Facility in Lanzhou (HIRFL) is used for beam extraction and injection between two cooling storage rings (CSRs). The system consists of two parts: one part is used for beam extraction from the CSR/main (CSRm), and the other is used for beam injection into the CSR/experimental (CSRe). To meet the requirements of special physics experiments, we upgraded the kicker control system. In this upgraded system, the position of the beam bunches can be determined by measuring the phase of the radio frequency (RF) signal in real time because each beam bunch is synchronized with the RF signal. The digital timing control and delay regulatory function, which are based on a new design using ARM+DSP+FPGA technology, achieved a precision of 2.5ns, which is a significant improvement over old system's precision of 5ns. In addition, this system exhibits a better anti-interference capability. Moreover, the efficiency of beam extraction can be enhanced, and the accuracy of the reference voltage setting can reach as low as 0.1%, compared to 2% for the old system.

Optimization of magnetic system parameters for the multipurpose isochronous cyclotron AIC-144

Optimization of the magnetic system parameters for multipurpose isochronous cyclotron aimed at improving the separation of the last two orbits and increasing the ion beam extraction efficiency is described. The optimization involves the adjustment of both the phase of the accelerated ion bunch center at the electrostatic deflector position radius and the first harmonic amplitude and phase of the working magnetic field at the radius of the ejection of the beam into the electrostatic deflector. The adjustment is performed by varying the current in the trim coils and two pairs of harmonic coils to correct the first harmonic of the resulting magnetic field. An inhomogeneous system of nonlinear algebraic equations is also considered. Given the first harmonic amplitude and phase of the working magnetic field and the radius, it allows the inverse problem of calculating currents in two pairs of harmonic coils to be solved. The results of physics experiments conducted at the AIC-144 multipurpose isochronous cyclotron in April 2011 are reported.

Use of a bent crystal with a decreasing curvature to increase the efficiency of the extraction and collimation of a beam in an accelerator

It has been shown that the use of a bent crystal with a variable curvature radius makes it possible to reduce the fraction of dechanneled particles by an order of magnitude. This effect enables the strong reduction of the particle density at the edge of a collimator or the partition of a septum upon the multi-turn extraction of a beam from a ring accelerator. In particular, the beam extraction efficiency at the U-70 synchrotron and Large Hadron Collider can be increased to 95 and 99.65%, respectively.

Crystal-assisted beam extraction and collimation at the U-70 circular accelerator

New crystal devices—an array of bent strips and a fan-type reflector based on thin straight plates—have been used to study extraction and collimation of the beam circulating in the accelerator at energies of 50 and 1.3 GeV. It is shown that these devices allow high-efficiency beam steering in a wide energy range. For 50-GeV protons, the efficiency of beam extraction and collimation is ∼90%, which is the highest efficiency attained for this method to date. It has been observed that the use of different crystals causes the particle loss at the accelerator downstream of the absorber to decrease by a factor of 2–3 in comparison with the standard single-stage scheme of beam collimation by a steel absorber.

Simulation of beam extraction from C235 cyclotron for proton therapy

The extraction of an accelerated beam from C235 cyclotron (IBA, Belgium) for proton therapy is simulated. The results of optimizing the parameters of the extraction system to increase the beam extraction efficiency are presented. Our theoretical results agree well with the experimental data. A new configuration of electrostatic deflector is proposed based on the numerical results; using this configuration essentially increases the efficiency of the cyclotron extraction system.

STUDIES AND APPLICATION OF BENT CRYSTALS FOR BEAM STEERING AT 70 GEV IHEP ACCELERATOR

This report overviews studies accomplished in the U70 proton synchrotron of IHEP-Protvino during the recent two decades. Major attention is paid to a routine application of bent crystals for beam extraction from the machine. It has been confirmed experimentally that efficiency of beam extraction with a crystal deflector of around 85% is well feasible for a proton beam with intensity up to 1012 protons per cycle. Another trend is to use bent crystals for halo collimation in a high energy collider. New promising options emerge for, say, LHC and ILC based on the "volume reflection" effect, which has been discovered recently in machine study runs at U70 of IHEP (50 GeV) and SPS of CERN (400 GeV). Perspectives to use bent crystals for extraction of light ions from the U70 accelerator are also disclosed.