Strong Space Charge Research Articles

ORBIT Simulation, Measurement and Mitigation of Transverse Beam Instability in the Presence of Strong Space Charge in the 3-GeV RCS OF J-PARC

The transverse impedance of eight extraction pulse kicker magnets (KM) is a strong beam instability source in the 3-GeV RCS (Rapid Cycling Synchrotron) at J-PARC (Japan Proton Accelerator Research Complex). Significant beam instability occurs even at a half of the designed 1 MW beam power when the chromaticity (ξ) is fully corrected for the entire acceleration cycle up to 3 GeV, but no beam instability occurs if the ξ is fully corrected only at the injection energy of 0.4 GeV. To realize the designed 1 MW beam power, collective beam dynamics with including the space charge effect for the coupled bunch instabilities excited by the KM impedance and associated measures were studied by incorporating all realistic time-dependent machine parameters in the ORBIT 3-D particle tracking code. The simulation results for systematic beam instability studies and its mitigation measures were found to be very consistent with measurements and, as a consequence, an acceleration of 1 MW beam power has been successfully achieved.

ORBIT Simulation, Measurement and Mitigation of Transverse Beam Instability in the Presence of Strong Space Charge in the 3-GeV RCS of J-PARC

ORBIT Simulation, Measurement and Mitigation of Transverse Beam Instability in the Presence of Strong Space Charge in the 3-GeV RCS of J-PARC

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 $$>1.2\,\hbox {kV}$$ .

Stochastic behavior of electrons in high intensity laser–plasma interaction

The stochastic behavior of electrons during the interaction of an intense short laser pulse with under-dense plasma is investigated by employing a fully kinetic 1D-3V particle-in-cell (PIC) simulation. The development of chaos in the involved nonlinear regime and in the presence of plasma space charge is examined. Though the electron Lagrangian is extremely complicated in this case, our analyses suggest some potential ways for chaos development. In this regard, our simulation results show that chaotic motion can develop in three different ways. When the space charge field is weak, the scattered fields can provide the necessary condition for chaos to occur. When a strong space charge field is presented, the creation of chaos is initiated by wave breaking. The third procedure for creating chaos originates from the inhomogeneity of the density on the vacuum–plasma surface. In this case, a new electrostatic mode without any phase relation with the space charge electrostatic mode is generated.

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.

Generation of high-power, tunable terahertz radiation from laser interaction with a relativistic electron beam

We propose a method based on the slice energy spread modulation to generate strong subpicoseond density bunching in high-intensity relativistic electron beams. A laser pulse with periodic intensity envelope is used to modulate the slice energy spread of the electron beam, which can then be converted into density modulation after a dispersive section. It is found that the double-horn slice energy distribution of the electron beam induced by the laser modulation is very effective to increase the density bunching. Since the modulation is performed on a relativistic electron beam, the process does not suffer from strong space charge force or coupling between phase spaces, so that it is straightforward to preserve the beam quality for further applications, such as terahertz (THz) radiation and resonant excitation of plasma wakefield. We show in both theory and simulations that the tunable radiation from the beam can cover the frequency range of 1-10 THz with high power and narrow-band spectra.

Tracking Based Courant-Snyder Parameter Matching in a Linac with a Strong Space-Charge Force

Tracking Based Courant-Snyder Parameter Matching in a Linac with a Strong Space-Charge Force

CERN Proton Synchrotron booster space charge simulations with a realistic model for alignment and field errorsn1

The CERN Proton Synchrotron booster (PSB) is one of the machines of the LHC injector chain which will be upgraded within the LHC Injectors Upgrade (LIU) project. The injection energy of the PSB will be increased to 160 MeV in order to mitigate direct space charge effects, considered to be the main performance limitation, aiming to double the brightness for the LHC beams. In order to better predict the gain to be expected, space charge simulations are being carried out. As a first step, benchmarking between simulations and measurements is needed. Efforts to establish a realistic modeling of field and alignment errors aim at extending the basic model of the machine toward a more realistic one. Simulations of beam dynamics with strong space charge and realistic errors are presented and analyzed in this paper.

Sub-nanosecond time resolved light emission study for diffuse discharges in air under steep high voltage pulses

Pin-to-plane discharges in centimetre air gaps and standard conditions of pressure and temperature are generated under very high positive nanosecond scale voltage pulses. The experimental study is based on recordings of sub-nanosecond time resolved and Abel-processed light emission profiles and their complete correlation to electrical current waveforms. The effects of the voltage pulse features (amplitude between 20 and 90 kV, rise time between 2 and 5.2 ns, and time rate between 4 and 40 kV · ns−1) and the electrode configuration (gap distance between 10 and 30 mm, pin radius between 10 and 200 µm, copper, molybdenum or tungsten pin material) are described. A three time period development can be found: a glow-like structure with monotonic light profiles during the first 1.5 ns whose size depends on time voltage rate, a shell-like structure with bimodal profiles whose duration and extension in space depends on rise time, and either diffuse or multi-channel regime for the connection to the cathode plane according to gap distance. The transition of the light from monotonic to bimodal patterns reveals the relative effects and dynamics of streamer space charge and external laplacian field. A classical 2D-fluid model for streamer propagation has been used and adapted for very high and steep voltage pulses. It shows the formation of a strong space charge (streamer) very close to the pin, but also a continuity of emission between the pin and the streamer, and electric fields higher than the critical ionization field (28 kV · cm−1 in air) almost in the whole gap and very early in the discharge propagation.

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%.

Nonlinear resonance and envelope instability of intense beam in axial symmetric periodic channel

When an intense charged particle beam propagates through a given periodic focusing channel, it will experience the phenomena of nonlinear resonance, collective instability or chaotic motion with different conditions. In this paper, the collective envelope instability mechanisms are studied for symmetric beam propagation in an axially symmetric periodic channel. The beam is characterized as collectively stable if there exists a stable fixed point (SFP) located at the matched beam condition (rm,0) in (r,pr) phase space. It is found that the well-known collective envelope instability is dynamically related to the period-two orbits bifurcation of the matched SFP, meanwhile the unique stable SFP turns into an unstable saddle-node, surrounded by 1/2 resonance islands. However, higher orders of resonance (l/n, n>2) coming from period-n bifurcation will not lead to collective beam instability because a new SFP emerges immediately upon the bifurcation process. The orders of SFP bifurcation is numerically depicted by the envelope tune ν=ϕ/360, where ϕ is the eigenphase of the Poincaré tangent map T(s) in one focusing period at SFP, as functions of depressed phase advance. With strong space charge, due to these resonances from SFP bifurcation could be overlapped, mismatched beam would even show chaotic motion. For specific parameters, regular orbits, resonance islands, chaotic regions formed by resonance overlapping are clearly depicted with frequency analysis and Lyapunov spectral exponents, a method that may prove useful when extended to higher phase-space dimensions.

Correction of the deterministic part of space–charge interaction in momentum microscopy of charged particles

Ultrahigh spectral brightness femtosecond XUV and X-ray sources like free electron lasers (FEL) and table-top high harmonics sources (HHG) offer fascinating experimental possibilities for analysis of transient states and ultrafast electron dynamics. For electron spectroscopy experiments using illumination from such sources, the ultrashort high-charge electron bunches experience strong space–charge interactions. The Coulomb interactions between emitted electrons results in large energy shifts and severe broadening of photoemission signals. We propose a method for a substantial reduction of the effect by exploiting the deterministic nature of space–charge interaction. The interaction of a given electron with the average charge density of all surrounding electrons leads to a rotation of the electron distribution in 6D phase space. Momentum microscopy gives direct access to the three momentum coordinates, opening a path for a correction of an essential part of space–charge interaction. In a first experiment with a time-of-flight momentum microscope using synchrotron radiation at BESSY, the rotation in phase space became directly visible. In a separate experiment conducted at FLASH (DESY), the energy shift and broadening of the photoemission signals were quantified. Finally, simulations of a realistic photoemission experiment including space–charge interaction reveals that a gain of an order of magnitude in resolution is possible using the correction technique presented here.

Enhanced electromagnetic shielding behavior of multi-walled carbon nanotube entrenched poly (3,4-ethylenedioxythiophene) nanocomposites

Exceptionally high electromagnetic shielding behavior shown by composites of poly (3,4-ethylenedioxythiophene)/multi-walled carbon nanotube (PCNT) which showed maximum shielding attenuation of 58 dB in the Ku-band. The electron micrographs confirm the wrapping of poly (3,4-ethylenedioxthiophene) (PEDOT) over multiwalled carbon nanotubes (MWCNTs) resulting in strong interfacial, electronic and space charge polarizations. The EMI shielding results showed that shielding by PCNT composites are mainly due to shielding effectiveness by absorption rather than shielding attenuation by reflection. Complex permittivity and permeability of composites have been calculated using scattering parameters (S11 and S21) based on theoretical calculations given in the Nicolson–Ross–Weir method. The composites were further characterized by Raman spectroscopy, TGA, XRD, and FTIR.

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.

Identification and ranging of lightning flashes using co-located antennas of different geometry

A new technique for detecting and ranging lightning flashes up to approximately 100 km away is described. The technique uses a novel method of discriminating between lightning and non-lightning sources of quasi-electrostatic field change by comparison of the signal strength measured simultaneously on two co-located antennas, which is a function of their different geometry and exposure to the atmospheric electric field. In addition to detection of all types of lightning within range, the system also has the capability of detecting and classifying other sources of rapid electric field change associated with thunderstorm or shower cloud activity, such as from nearby corona brush discharge, strong space charge variability and charged precipitation. Real-time lightning flash detection and ranging combined with monitoring of initial storm electrification processes provides a comprehensive method of local severe weather warning. Since the operating frequency of 1–50 Hz lies below man-made sources of radio signals, the technique is considered especially useful for sites with strong radio interference.

Potential Formation in a Bounded Plasma System which is Terminated by an Electron Emitting Floating Collector Studied by a Particle‐in‐Cell Computer Simulation

AbstractPotential formation in one‐dimensional bounded plasma system terminated by a floating, electron emitting collector is studied by particle‐in‐cell (PIC) computer simulation. Attention is focused to the case of rather strong space charge limited emission. Formation of a potential well (virtual cathode) in front of the collector is observed. As emission increases the floating potential of the electrode and the potential of the bottom of the potential well both increase. The floating potential increases faster than the virtual cathode potential and consequently the depth of the potential well in front of the collector increases also. As long as the emission is not to large (up to approximately 40 times the critical emission) the relation between the depth of the potential well and the normalized emission follows a simple logarithmic formula. For larger emissions the depth of the potential well is larger than predicted by the model. It seems that at very large emission the floating potential of the collector might even exceed the zero reference potential of the source electrode. Such phenomenon has been reported by [A. Marek et al. Contrib. Plasma Phys., 48, 491 (2008)], where it was observed that the floating potential of a strongly emissive probe exceeded the plasma potential determined from the knee of the current‐voltage characteristics when the same probe was used as a Langmuir probe. But before this actually happens the simulation breaks down. When positive ions start to be repelled by the positive collector back towards the source the system becomes unstable so that a steady state can not be reached and no results can be read from the output of the simulations. That electron emission may destabilize the sheath in front of it, was found also in Hall thrusters, see e.g. [Daren Yu et al. Phys. Plasmas, 15, 104501, 2008] and [F. Taccogna et al Appl. Phys. Lett., 94, 251502, 2009]. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

HIGH DIELECTRIC CONSTANT COMPOSITE BASED ON CHLOROPHYLL A ENTRAPPED NANOPOROUS SILICA GEL

Chlorophyll a (naturally occurring Mg porphyrene) has been entrapped in nano/porous silica gel using sol–gel method at room temperature, producing a stable composite. HRTEM observation reveals regular nanoscale [around 15–20 nm diameter] distribution of aggregated polycrystalline chlorophyll a within porous silica matrix. UV-vis study also corroborates the presence of various aggregated chlorophyll a species within the system. Low field measurement shows almost 400 times enhancement of dielectric constant (1700) with incorporation of only 0.125 mg/ml of chlorophyll and the loss is 0.5 at room temperature at 100 Hz. The dielectric constant of the composite reaches 2500 as chlorophyll concentration becomes 1 mg/ml. Observed strong space charge response to the external field and strong frequency dispersion of the dielectric properties of the composite can be attributed to the long-range electron delocalization [nomadic polarization] in chlorophyll a aggregates. The electric modulus (M*) formalism used in this study enabled us to distinguish and separate various relaxation processes. It is found that with increasing chlorophyll concentration D.C. relaxation time decreases exponentially at room temperature. It is shown that observed relaxations do not perfectly follow the Debye response in high frequency region due to heterogeneous distribution of chlorophyll aggregates. The low values of room temperature activation energy calculated from Arrhenius plot reveal that polaronic hopping phenomena is absent at grain-interfacial region due to low thermal energy.

Van de Graaf-based 13.5 nm inverse-Compton light source

We review the factors governing the performance of inverse-Compton light sources in the extreme-ultraviolet (EUV) region. While the use of an optical storage cavity and the minimization of the laser pump focal spot area remain critical to the optimization of power and brightness in the EUV, the appearance of a strong space charge forces at the low electron energies required for operation in the EUV sets an independent lower limit to the focal spot area, and therefore an upper limit to source power and brightness. These limitations are at least partially compensated by the very high average electron currents realizable at these lower electron energies. Based on these considerations, we describe the design and estimated performance of an EUV inverse-Compton scattering light source optimized for average power output and brightness consistent with the limits imposed by the capabilities of existing materials, laser pumps, and radio frequency power sources.

Investigations of space charge limited effects in diode with Coulomb's law

Vacuum diode is a critical component of the apparatus which is the source of electron beams, the emitted electrons from the cathode of the diode have strong space charge limited effects. Based on Coulomb's law, the distributions of electric field in cathode-anode gap for different values of the ratio of radius to gap distance, R/D, are calculated numerically with the model of space charge limited effects in a planar vacuum diode. This method can avoid solving a non-linear differential equation which is used to yield the Child-Langmuir law from Poisson's equation. The results demonstrate that the only difference between the results from Coulomb's law and Child-Langmuir law is a modification factor, which is shown to be related to the potential difference across the gap. The results also show that one-dimensional space charge limited law will be a good approximation for the practical planar diode if the parameter R/D is beyond 10, but it can present a large error if the parameter R/D is small. Therefore it should be cautiously used.

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.