Strong Space Charge Effects Research Articles

Optimization of low-energy slow extraction efficiency of XiPAF

Xi’an Proton Application Facility (XiPAF) synchrotron provides 10∼200MeV proton beam for the experimental simulation of the space radiation environment. Due to the space charge effect, the slow extraction of 10 MeV proton beam is a work full of challenges. In a past experiment, the total extraction efficiency was over 65% with 4.5 ∽ 6.5×1010 protons stored before extraction but decreased to 52% with 9×1010 protons stored. In order to study the beam loss caused by a strong space charge effect, based on experimental parameters, the beam loss fractions at different positions of XiPAF synchrotron are obtained through the simulation. According to the beam loss analysis, optimized parameters are found for reference in subsequent experiments. It is also noted that negative beam average momentum spread before extraction is beneficial to the improvement of extraction efficiency.

Development of a 1.4-cell RF photocathode gun for single-shot MeV ultrafast electron diffraction devices with femtosecond resolution

The MeV ultrafast electron diffraction (UED) has proven to be a powerful tool for exploring the ultrafast process at the atomic level with femtosecond resolution. However, MeV UED facilities are struggling to achieve sub-100 fs temporal resolution at pC level charges due to the rapid and severe bunch lengthening near the cathode region. Both analytical work and simulation show that the bunch lengthening near the cathode originates from both the strong space charge effect (SCE) within the sub-relativistic electron beam and the bunch tail trailing due to the mirror charge effect (MCE). In this paper, we report the development of a new 1.4-cell RF gun that significantly increases the extraction field at the cathode to suppress both the SCE and the MCE. Compared to the conventional 1.6-cell RF gun, the new 1.4-cell RF gun is more suitable to produce an electron beam with a shorter bunch length and less distorted longitudinal phase space. The shorter bunch length leads directly to a temporal resolution improvement in UEDs. Meanwhile, the beam longitudinal phase space with better linearity ensures a smaller compressed bunch length when the bunch compression schemes are applied.

Transverse confinement of electron beams in a 2D optical lattice for compact coherent x-ray sources

Compact coherent x-ray sources have been the focus of extensive research efforts over the past decades. As a result, several novel schemes like optical and nano-undulators for generating x-ray emissions in ‘table-top’ setups are proposed, developed, and assessed. Despite the extensive efforts in the past decades, there exists no operational FEL based on optical or electromagnetic undulators. By combining the particle confinement capability of optical cavities with wiggling motion inside an optical undulator, this paper proposes a new concept for making a compact coherent x-ray source. The full-wave solution of first-principle equations based on finite-difference time-domain and particle-in-cell is performed to simulate inverse-Compton scattering (ICS) off both free and confined electrons. It is shown that the strong space-charge effect in a low-energy electron beam (5 MeV) is the main obstacle in acquiring coherent gain through the ICS mechanism with a 10 micrometer laser. Subsequently, it is shown that by confining the electron beam at the field nodes of an optical cavity, the space-charge effect is compensated, and additionally, the ultrahigh charge density enables high FEL-gain at confinement spots. The full-wave numerical simulations predict enhancement of about three orders of magnitude in the radiation efficiency when ICS is carried out with confined electrons compared to free electrons. These theoretical results show promising potential as a new scheme for implementing a compact coherent x-ray source.

Longitudinal dynamics study and optimization in the beam commissioning of the rapid cycling synchrotron in the China Spallation Neutron Source

The China Spallation Neutron Source (CSNS) is a high intensity proton accelerator-based facility, and its accelerator complex includes two main parts: a H- linac and a rapid cycling synchrotron (RCS). The RCS accumulates the 80 MeV proton beam, and accelerates it to 1.6 GeV, with a repetition rate of 25 Hz. The beam commissioning of RCS began in May, 2017 and reached the target beam power of 100 kW in February, 2020. The longitudinal beam dynamics study plays the key role in the commissioning. The study and optimization include the synchronicity between the ramping magnet field and the RF system, the mitigation of the high intensity effects to minimize the beam loss and the measurement of the longitudinal dynamics. Through the optimization of the bunch factor, the strong space charge effects with high intensity is mitigated, thus the RCS transmission efficiency arrives mostly at 100 %. The beam distribution is not affected by the phase loop with a new algorithm and the beam loss is smaller than the original one. The beam commissioning in longitudinal plane is reviewed in the paper.

Discharge electrode geometry and energy efficiency in a one-stage wire–tube electrostatic precipitator operating at high concentrations of submicron liquid aerosol

ABSTRACTIn order to help answering the question ‘Which electrode design is the best?’, the precipitation performance of a tubular electrostatic precipitator was determined for different electrode designs with special attention to specific energy consumption. Experiments were conducted in a wire–tube arrangement with a high loading of liquid submicron particles causing strong space charge effects, also known as corona quenching. The experiments are supplemented by numerical simulation results showing the effect of residence time and power consumption on separation efficiency.

Design and test of an RF acceleration system loaded with magnetic alloy for the proton synchrotron of the Xi’an Proton Application Facility

The Xi’an Proton Application Facility (XiPAF) is a facility dedicated to the experimental simulation of the space radiation environment. The facility uses a compact synchrotron as its final-stage accelerator. The synchrotron can accelerate a proton beam from 7 to $$230\,\hbox {MeV}$$ . Physical design results show that the radio frequency (RF) acceleration system should work in the frequency range of $$1{-}6\,\hbox {MHz}$$ and provide a maximum voltage of $$>800\,\hbox {V}$$ . To dilute the strong space charge effect during the injection period, we also aim to achieve multiharmonic acceleration. A compact RF acceleration system loaded with magnetic alloy cores has been designed and developed to fulfill these requirements. The preliminary test results show that the system can work normally with a gap voltage of $$800\,\hbox {V}$$ . With a further RF power upgrade, the voltage can be improved to $$>1.2\,\hbox {kV}$$ .

Two-plane painting injection scheme for BRing of HIAF

The high-intensity heavy-ion accelerator facility (HIAF) is under design at the Institute of Modern Physics (IMP) and will provide an intense ion beam for nuclear physics, atomic mass measurement research, and other applications. As the main ring of HIAF, the BRing accumulates beams to high intensity and accelerates them to high energy. To achieve high intensities up to $$1\times 10^{11}$$ ( $$^{238}$$ U $$^{34+}$$ ), the injection gain of the BRing must be as high as 88. However, multiple multiturn injection supported by the electron cooling system takes a long time, causing substantial beam loss under a strong space charge effect. Hence, a two-plane painting injection scheme is proposed for beam accumulation in the BRing. This scheme uses a tilted injection septum and horizontal and vertical bump magnets to paint the beam into horizontal and vertical phase space simultaneously. In this paper, the two-plane painting injection parameters are optimized, and the resulting injection process is simulated using the Objective Ring Beam Injection and Tracking (ORBIT) code. An injection gain of up to 110.3 with a loss rate of $$2.3\%$$ is achieved, meeting the requirements of BRing.

Beam Dynamics Design of a 50 mA D+ RFQ**Supported by the National Basic Research Program of China under Grant No 2014CB845503.

A new 973 project was proposed by Peking University and Institute of Modern Physics of Chinese Academy of Sciences recently. The project requires a 50 mA, 162.5 MHz, cw mode radio frequency quadrupole (RFQ) to accelerate the D+ to 1 MeV. In a high-current linear accelerator, the strong space charge effect causes the growth of envelope and emittance along with heavy beam losses. In the beam dynamics design of this RFQ, beam envelope mismatching is discussed and a matching dynamics method is proposed to minimize the envelope and emittance growth. The influence of limiting current on the beam transmission is discussed and used in the optimization of transverse and longitudinal parameters. After the optimization, the beam transmission efficiency reaches higher than 98%.

Systematic studies on the effect of linear lattice optics for space-charge limited beams

The HL-LHC (High Luminosity LHC) project aims to an increase of the luminosity of the LHC by a factor of 10. In order to realize this ambitious goal, the LHC itself has to undergo a major upgrade accompanied by an extensive upgrade of the complete injector complex referred to as LHC injector upgrade (LIU). In the framework of the LIU project, a new rapid cycling synchrotron (RCS) as an alternative to the energy upgrade of the existing PS Booster has been proposed. Motivated by the optics studies conducted for this RCS, the more general question of the influence of the linear optics on the machine performance has been raised. In this paper, we want to investigate this question by comparing different lattices with the final aim of identifying lattice characteristics advantageous under strong space-charge effects.

Core-halo issues for a very high intensity beam

The relevance of classical parameters like beam emittance and envelope used to describe a particle beam is questioned in case of a high intensity accelerator. In the presence of strong space charge effects that affect the beam differently following its density, the much less dense halo part behaves differently from the much denser core part. A method for precisely determining the core-halo limit is proposed, that allows characterizing the halo and the core independently. Results in 1D case are given and discussed. Expected developments extending the method to 2D, 4D, or 6D phase spaces are examined.

Microanalysis of a Grain Boundary’s Blocking Effect in Lanthanum Silicate Electrolyte for Intermediate-Temperature Solid Oxide Fuel Cells

In order to study the grain boundary's (GB's) blocking effect in lanthanum silicate electrolyte, high density Al-doped apatite-type lanthanum silicate was synthesized and characterized by impedance spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Microstructural characterization indicated that the GB's blocking effect was an intrinsic effect. Further microanalysis shows that the GB region is rich in La and poor in Si in comparing with the grain interior (GI). Our discussion suggested that the chemical variation from GI to GB, on the one hand, could degrade the GB region's conductivity; on the other hand, it introduced a strong space-charge effect at GBs. The latter was believed to play a dominant role in the GB's blocking effect.

Influence of diode gap distance on space charge effects in field emission

Under intense electric field, the electrons emitted from the cathode by field emission have strong space charge effects, so the space charge limited current of a diode is an important parameter in the design of many intense electron beam apparatus, such as the high power microwave source devices. The field emission current density depends on cathode material and electric field at the cathode surface, while the space charge limited current density is a function of applied voltage and diode gap distance. To investigate the influence of the diode gap distance on space charge effect in field emission, in the paper we build a model of a planar vacuum diode operating with a field emission cathode. The time evolutions of the electric field at the cathode surface with various diode gap distance and applied voltage are studied using the particle-in-cell method, and the steady value of the electric field at the cathode surface is obtained. The electric field at the cathode surface first oscillates and finally reaches a steady state. At a given applied electric field, the longer the diode gap distance, the higher the absolute value of the electric field at the cathode surface is, and it takes more time to reach the steady state for longer diode gap distance; the distribution of the electric field in the diode gap region is steeper for shorter diode gap distance after the electric field at the cathode surface has reached a steady state.

The compensation of quadrupole errors and space charge effects by using trim quadrupoles

The China Spallation Neutron Source (CSNS) accelerators consist of an H-linac and a proton Rapid Cycling Synchrotron (RCS). RCS is designed to accumulate and accelerate proton beam from 80 MeV to 1.6 GeV with a repetition rate of 25 Hz. The main dipole and quadruple magnet will operate in AC mode. Due to the adoption of the resonant power supplies, saturation errors of magnetic field cannot be compensated by power supplies. These saturation errors will disturb the linear optics parameters, such as tunes, beta function and dispersion function. The strong space charge effects will cause emittance growth. The compensation of these effects by using trim quadruples is studied, and the corresponding results are presented.

Gain length fitting formula for free-electron lasers with strong space-charge effects

We present a power-fit formula, obtained from a variational analysis using three-dimensional free-electron laser theory, for the gain length of a high-gain free-electron laser's fundamental mode in the presence of diffraction, uncorrelated energy spread, and longitudinal space-charge effects. The approach is inspired by the work of Xie [Nucl. Instrum. Methods Phys. Res., Sect. A 445, 59 (2000)], and provides a useful shortcut for calculating the gain length of the fundamental Gaussian mode of a free-electron laser having strong space-charge effects in the 3D regime. The results derived from analytic theory are in good agreement with detailed numerical particle simulations that also include higher-order space-charge effects, supporting the assumptions made in the theoretical treatment and the variational solutions obtained in the single-mode limit.

Magnetocurrent of ballistically injected electrons in insulating silicon

By using ballistic hot-electron injection to achieve lateral conduction through an otherwise fully insulating undoped silicon channel, we are able to study magnetic field suppression of charge transport in a regime normally excluded in Ohmic magnetoresistance measurements. Exceptionally large magnetocurrent changes of >16 000% at 45 K in magnetic fields of ≈2 T are observed, with differential reduction of over 6.2 T−1. Temperature-, electrostatic back-gate-, and magnetic field angle-dependence are presented. This phenomenon is attributed to strong space-charge effects in the dilute three-dimensional electron gas created by nonequilibrium injection.

Beam collimation and transport of laser-accelerated protons by a solenoid field

A pulsed high field solenoid was used in a laser-proton acceleration experiment to collimate and transport the proton beam that was generated at the irradiation of a flat foil by a high intensity laser pulse. 1012 particles at an energy of 2.3 MeV could be caught and transported over a distance of more than 240 mm. Strong space charge effects occur, induced by the high field of the solenoid that forces all co-moving electrons down the the solenoid's axis, building up a strong negative space charge that interacts with the proton beam. This leads to an aggregation of the proton beam around the solenoid's axis and therefore to a stronger focusing effect. The collimation and transport of laser-accelerated protons is the first step to provide these unique beams for further applications like post-acceleration by conventional accelerator structures.

Drift-Diffusion Modeling for Impurity Photovoltaic Devices

A 1-D drift-diffusion modeling for impurity photovoltaics is presented. The model is based on the self-consistent solution of Poisson's equation and carrier continuity equations incorporating generation and recombination mechanisms including the intermediate states. The model is applied to a prototypical solar cell device, where strong space charge effects and reduced conversion efficiency are identified for the case of lightly doped absorption regions. A doping compensation scheme is proposed to mitigate the space charge effects, with optimal doping corresponding to one-half the concentration of the intermediate states. The compensated doping device design provides calculated conversion efficiencies of approximately 40%, which is similar to the maximum expected values from prior 0-D models. The carrier transport between intermediate levels is shown to be noncritical for achieving the efficiency limit predicted by 0-D models. The qualitative behavior of the model is compared to existing experimental data on quantum dot solar cells.

Two-dimensional/three-dimensional simulations for the optimization of an electron-beam-generated-plasma-based-type ion source

To fulfill the need of a plasma ion source for SPIRAL-2 and EURISOL, capable of producing radioactive ion beams under strong radiation, the first prototype of the IRENA (Ionization by Radial Electrons Neat Adaptation) ion source has been designed. For designing an optimized prototype based on the first one, the influence of the geometrical parameters on the electron trajectories is investigated by means of two-dimensional/three-dimensional (3D) simulations. Due to the strong space charge effect in this kind of ion source, 3D simulations help particularly to better estimate effects on ion confinement and extraction. Simulation constructions will be presented and results discussed.

Beam dynamics simulation during final bunching and transport for heavy ion inertial fusion

In a particle accelerator system for heavy ion inertial fusion, space-charge-dominated beam dynamics is investigated during a final beam bunching. While the space charge effect undertakes an important role for the beam dynamics in the regime, the beam instability induced by space charge oscillation may occur, depending on the particle distribution of the beam. Particle simulations present that the instability due to the strong space charge effect may not be serious for realistic particle distributions during the final beam bunching.

Enhanced photoluminescence from Cr3+ centers in α-sapphire coated with LiNbO3(:Fe) and LiTaO3 films

A LiNbO3(:Fe) or LiTaO3 film is sandwiched between a (012)-oriented α-sapphire wafer and an amorphous Al2O3 or SiO2 film using pulsed laser deposition. After annealing at 1000 °C in O2, the film becomes a c-oriented single-domain ferroelectric. This sandwich structure shows an enhanced photoluminescence from trace amounts of Cr3+ centers in the host α-sapphire (R-line emission at 691 nm). Spectral analyses suggest that both strong space-charge and photorefractive effects of the LiNbO3(:Fe) or LiTaO3 film cause a change in the crystal field of the host α-sapphire, which increases the transition probability of Cr3+ and thus leads to an enhancement of the R-line intensity. The result has prospective applications in laser and optical integrated devices.