Lanfa Wang - Academia.edu (original) (raw)

Papers by Lanfa Wang

Physical Review Special Topics - Accelerators and Beams

This paper analyzes the longitudinal space charge (LSC) impedances of a round uniform beam inside... more This paper analyzes the longitudinal space charge (LSC) impedances of a round uniform beam inside a rectangular and parallel plate chambers using the image charge method. This analysis is valid for arbitrary wavelengths and the calculation converges fast. The research shows that only a few of the image beams are needed to obtain a relative error less than 0.1%. The beam offset effect is also discussed in the analysis.

In order to improve the luminosity, crab cavities have been installed in the KEKB HER and LER. Si... more In order to improve the luminosity, crab cavities have been installed in the KEKB HER and LER. Since there is only one crab cavity in each ring, the crab cavity generates a horizontally titled bunch oscillating around the whole ring. The electron cloud in LER (positron beam) may distort the crabbed bunch and cause the luminosity drop. This paper briefly estimates the distortion of positron bunch due to the electron cloud with global crab.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

The effect of surface roughness on the secondary electron emission from a sawtooth surface in a m... more The effect of surface roughness on the secondary electron emission from a sawtooth surface in a magnetic field under electron bombardment is investigated using a Monte-Carlo method. Some of the secondary electrons emitted from the sawtooth surface return to the surface within their first few gyrations, resulting in a low effective secondary electron yield. A sawtooth surface in magnetic field can significantly reduce the secondary emission yield below the multipacting threshold.

Journal of Mechanics Engineering and Automation, 2014

The Linac Coherent Light Source II (LCLS-II) will build on the success of the world's most powerf... more The Linac Coherent Light Source II (LCLS-II) will build on the success of the world's most powerful X-ray laser, the Linac Coherent Light Source (LCLS). It will add two new X-ray laser beams and room for additional new instruments, greatly increasing the number of experiments carried out each year. Multiple operation modes are proposed to accommodate a variety of user requirements. There are a large number of variables and objectives in the design. For each operation mode, Multi-Objective Genetic Algorithm (MOGA) is applied to optimize the machine parameters in order to minimize the jitters, energy spread, collective effects and emittance.

PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268), 2001

A 3-dimensional particle simulation code is developed to study the photoelectron cloud in positro... more A 3-dimensional particle simulation code is developed to study the photoelectron cloud in positron rings. The effects of the various magnetic fields in KEKB LER are presented. The distribution and evolution of the electron-cloud are simulated.

In the beam pipe of the positron damping ring of the International Linear Collider (ILC), an elec... more In the beam pipe of the positron damping ring of the International Linear Collider (ILC), an electron cloud may be first produced by photoelectrons and ionization of residual gases and then increased by the secondary emission process 1. This paper reports the assessment of electron cloud effects in a number of configuration options for the ILC baseline configuration. Careful estimates were made of the secondary electron yield (sometimes in the literature also referred as secondary emission yield SEY or δ, with a peak value δ max) threshold for electron cloud build-up, and the related single-and coupled-bunch instabilities, as a function of beam current and surface properties for a variety of optics designs. When the configuration for the ILC damping rings was chosen at the end of 2005, the results from these studies were important considerations. On the basis of the joint theoretical and experimental work, the baseline configuration currently specifies a pair of 6 km damping rings for the positron beam, to mitigate the effects of the electron cloud that could present difficulties in a single 6 km ring. However, since mitigation techniques are now estimated to be sufficiently mature, a reduced single 6-km circumference is presently under consideration so as to reduce costs.

A short-range wake field caused by the electron cloud has previously been studied for a drift spa... more A short-range wake field caused by the electron cloud has previously been studied for a drift space. In a bending magnet, the cloud electrons undergo cyclotron motion with a small radius (<1 mm) and at a high frequency (>10 GHz) in the horizontal plane due to the strong magnetic field of order 1 T. In this report, we study the motion of electrons under the combined influence of a strong magnetic dipole field and the electric field of the beam on the time scale of the bunch length, discuss the short-range wake field caused by the electrons, and simulate the emittance growth. As expected, the wake field in a bending magnet is very different from that in a drift space. The dipole field almost completely suppresses any horizontal coherent motion and rms-size blow up, and it also slows down the instability in the vertical direction.

As part of the international Linear Collider (ILC) collaboration, we have compared the electron c... more As part of the international Linear Collider (ILC) collaboration, we have compared the electron cloud (EC) effect for different Damping Ring (DR) designs respectively with 6.4 km and 3.2 km circumference and investigated the feasibility of a shorter damping ring with respect to the electron cloud build-up and related beam instability. The studies for a 3.2 km ring were carried out with beam parameters of the ILC Low Power option. A reduced damping ring circumference has been proposed for the new ILC baseline design SB2009 [1] and would allow to considerably reduce the number of components, wiggler magnets and costs. We discuss the impact of the proposed operation of the ILC at high repetition rate 10 Hz and address the necessary modifications for the DRs. We also briefly discuss the plans for future studies including the luminosity upgrade option with shorter bunch spacing, the evaluation of mitigations and the integration of the CesrTA results into the Damping Ring design.

The Cornell Electron Storage Ring (CESR) has been reconfigured as an ultra low emittance damping ... more The Cornell Electron Storage Ring (CESR) has been reconfigured as an ultra low emittance damping ring for use as a test accelerator (CesrTA) for International Linear Collider (ILC) damping ring R&D [1]. One of the primary goals of the CesrTA program is to investigate the interaction of the electron cloud with low emittance positron beam to explore methods to suppress the electron cloud, develop suitable advanced instrumentation required for these experimental studies and benchmark predictions by simulation codes. This paper reports the simulation of the electron-cloud formation in the wiggler and quadrupole magnets using the 3D code CLOUDLAND. We found that electrons can be trapped with long lifetime in a quadrupole magnet due to the mirror field trapping mechanism and photoelectrons produced in the wiggler zero field zone have long lifetime due to their complicated trajectory.

The mechanism of electron multipacting in long bunched proton machine has been quantitatively des... more The mechanism of electron multipacting in long bunched proton machine has been quantitatively described by the electron energy gain and electron motion. Some important parameters related to electron multipacting are investigated in detail. It is proved that multipacting is sensitive to beam intensity, longitudinal beam profile shape and transverse beam size. Agreements are achieved among our analysis, simulation and experiment. The possible remedies to clearing electron cloud are also investigated.

Trapping is a general phenomenon of photoelectron cloud. Photoelectron can be strongly trapped by... more Trapping is a general phenomenon of photoelectron cloud. Photoelectron can be strongly trapped by the positron/proton beam electric field and mirror magnetic field. The electron cloud density increases due to the trap and the trap causes the lifetime of the electron cloud longer. The photoelectrons in drift region can be strongly trapped by the positron or proton beam electric field. There is a novel photoelectron-trapping phenomenon in the quadrupole and sextupole magnetic fields. The trapping phenomenon is strongly beam-dependent, especially on the bunch length. The trapped electron cloud can cause multi-bunch instability due to the long trapping time. The phenomenon and mechanism of photoelectron trapping in different magnetic and electric fields are studied.

In this paper we describe a mechanism using the clearing electrodes to remove the electron cloud ... more In this paper we describe a mechanism using the clearing electrodes to remove the electron cloud in the Spallation Neutron Source (SNS) accumulator ring, where strong multipacting could happen at median clearing fields. A similar phenomenon was reported in an experimental study at Los Alamos laboratory's Proton Synchrotron Ring (PSR). We also investigated the effectiveness of the solenoid's clearing mechanism in the SNS, which differs from the short bunch case, such as in B-factories. The titanium nitride (TiN) coating of the chamber walls was applied to reduce the secondary electron yield (SEY).

The operation at high current of high-energy proton machines like the SPS at CERN is affected by ... more The operation at high current of high-energy proton machines like the SPS at CERN is affected by transverse single-bunch instabilities due to the Electron Cloud effect [1]. As a first step toward modeling a realistic feedback control system to stabilize the bunch dynamics, we investigate the use of a Finite Impulse Response (FIR) filter to represent the processing channel. The effect of the processing channel on the bunch dynamics is analyzed using the macro-particle simulation package Wart-Posinst. We discuss the basic features of the feedback model, report on simulation results, and present our plans for further development of the numerical model.

The multibunch collision by means of pretzel scheme to enhance the luminosity in BEPC have been s... more The multibunch collision by means of pretzel scheme to enhance the luminosity in BEPC have been studied. The modification of the lattice is carried out, the solenoid compensation and chromaticity correction are studied, the physical aperture is examined, the long range beam-beam interaction and coupled bunch instabilities are investigated. The results show that the pretzel scheme with six bunches per beam is feasible.

Physical Review Special Topics - Accelerators and Beams

This paper analyzes the longitudinal space charge (LSC) impedances of a round uniform beam inside... more This paper analyzes the longitudinal space charge (LSC) impedances of a round uniform beam inside a rectangular and parallel plate chambers using the image charge method. This analysis is valid for arbitrary wavelengths and the calculation converges fast. The research shows that only a few of the image beams are needed to obtain a relative error less than 0.1%. The beam offset effect is also discussed in the analysis.

In order to improve the luminosity, crab cavities have been installed in the KEKB HER and LER. Si... more In order to improve the luminosity, crab cavities have been installed in the KEKB HER and LER. Since there is only one crab cavity in each ring, the crab cavity generates a horizontally titled bunch oscillating around the whole ring. The electron cloud in LER (positron beam) may distort the crabbed bunch and cause the luminosity drop. This paper briefly estimates the distortion of positron bunch due to the electron cloud with global crab.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

The effect of surface roughness on the secondary electron emission from a sawtooth surface in a m... more The effect of surface roughness on the secondary electron emission from a sawtooth surface in a magnetic field under electron bombardment is investigated using a Monte-Carlo method. Some of the secondary electrons emitted from the sawtooth surface return to the surface within their first few gyrations, resulting in a low effective secondary electron yield. A sawtooth surface in magnetic field can significantly reduce the secondary emission yield below the multipacting threshold.

Journal of Mechanics Engineering and Automation, 2014

The Linac Coherent Light Source II (LCLS-II) will build on the success of the world's most powerf... more The Linac Coherent Light Source II (LCLS-II) will build on the success of the world's most powerful X-ray laser, the Linac Coherent Light Source (LCLS). It will add two new X-ray laser beams and room for additional new instruments, greatly increasing the number of experiments carried out each year. Multiple operation modes are proposed to accommodate a variety of user requirements. There are a large number of variables and objectives in the design. For each operation mode, Multi-Objective Genetic Algorithm (MOGA) is applied to optimize the machine parameters in order to minimize the jitters, energy spread, collective effects and emittance.

PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268), 2001

A 3-dimensional particle simulation code is developed to study the photoelectron cloud in positro... more A 3-dimensional particle simulation code is developed to study the photoelectron cloud in positron rings. The effects of the various magnetic fields in KEKB LER are presented. The distribution and evolution of the electron-cloud are simulated.

In the beam pipe of the positron damping ring of the International Linear Collider (ILC), an elec... more In the beam pipe of the positron damping ring of the International Linear Collider (ILC), an electron cloud may be first produced by photoelectrons and ionization of residual gases and then increased by the secondary emission process 1. This paper reports the assessment of electron cloud effects in a number of configuration options for the ILC baseline configuration. Careful estimates were made of the secondary electron yield (sometimes in the literature also referred as secondary emission yield SEY or δ, with a peak value δ max) threshold for electron cloud build-up, and the related single-and coupled-bunch instabilities, as a function of beam current and surface properties for a variety of optics designs. When the configuration for the ILC damping rings was chosen at the end of 2005, the results from these studies were important considerations. On the basis of the joint theoretical and experimental work, the baseline configuration currently specifies a pair of 6 km damping rings for the positron beam, to mitigate the effects of the electron cloud that could present difficulties in a single 6 km ring. However, since mitigation techniques are now estimated to be sufficiently mature, a reduced single 6-km circumference is presently under consideration so as to reduce costs.

A short-range wake field caused by the electron cloud has previously been studied for a drift spa... more A short-range wake field caused by the electron cloud has previously been studied for a drift space. In a bending magnet, the cloud electrons undergo cyclotron motion with a small radius (<1 mm) and at a high frequency (>10 GHz) in the horizontal plane due to the strong magnetic field of order 1 T. In this report, we study the motion of electrons under the combined influence of a strong magnetic dipole field and the electric field of the beam on the time scale of the bunch length, discuss the short-range wake field caused by the electrons, and simulate the emittance growth. As expected, the wake field in a bending magnet is very different from that in a drift space. The dipole field almost completely suppresses any horizontal coherent motion and rms-size blow up, and it also slows down the instability in the vertical direction.

As part of the international Linear Collider (ILC) collaboration, we have compared the electron c... more As part of the international Linear Collider (ILC) collaboration, we have compared the electron cloud (EC) effect for different Damping Ring (DR) designs respectively with 6.4 km and 3.2 km circumference and investigated the feasibility of a shorter damping ring with respect to the electron cloud build-up and related beam instability. The studies for a 3.2 km ring were carried out with beam parameters of the ILC Low Power option. A reduced damping ring circumference has been proposed for the new ILC baseline design SB2009 [1] and would allow to considerably reduce the number of components, wiggler magnets and costs. We discuss the impact of the proposed operation of the ILC at high repetition rate 10 Hz and address the necessary modifications for the DRs. We also briefly discuss the plans for future studies including the luminosity upgrade option with shorter bunch spacing, the evaluation of mitigations and the integration of the CesrTA results into the Damping Ring design.

The Cornell Electron Storage Ring (CESR) has been reconfigured as an ultra low emittance damping ... more The Cornell Electron Storage Ring (CESR) has been reconfigured as an ultra low emittance damping ring for use as a test accelerator (CesrTA) for International Linear Collider (ILC) damping ring R&D [1]. One of the primary goals of the CesrTA program is to investigate the interaction of the electron cloud with low emittance positron beam to explore methods to suppress the electron cloud, develop suitable advanced instrumentation required for these experimental studies and benchmark predictions by simulation codes. This paper reports the simulation of the electron-cloud formation in the wiggler and quadrupole magnets using the 3D code CLOUDLAND. We found that electrons can be trapped with long lifetime in a quadrupole magnet due to the mirror field trapping mechanism and photoelectrons produced in the wiggler zero field zone have long lifetime due to their complicated trajectory.

The mechanism of electron multipacting in long bunched proton machine has been quantitatively des... more The mechanism of electron multipacting in long bunched proton machine has been quantitatively described by the electron energy gain and electron motion. Some important parameters related to electron multipacting are investigated in detail. It is proved that multipacting is sensitive to beam intensity, longitudinal beam profile shape and transverse beam size. Agreements are achieved among our analysis, simulation and experiment. The possible remedies to clearing electron cloud are also investigated.

Trapping is a general phenomenon of photoelectron cloud. Photoelectron can be strongly trapped by... more Trapping is a general phenomenon of photoelectron cloud. Photoelectron can be strongly trapped by the positron/proton beam electric field and mirror magnetic field. The electron cloud density increases due to the trap and the trap causes the lifetime of the electron cloud longer. The photoelectrons in drift region can be strongly trapped by the positron or proton beam electric field. There is a novel photoelectron-trapping phenomenon in the quadrupole and sextupole magnetic fields. The trapping phenomenon is strongly beam-dependent, especially on the bunch length. The trapped electron cloud can cause multi-bunch instability due to the long trapping time. The phenomenon and mechanism of photoelectron trapping in different magnetic and electric fields are studied.

In this paper we describe a mechanism using the clearing electrodes to remove the electron cloud ... more In this paper we describe a mechanism using the clearing electrodes to remove the electron cloud in the Spallation Neutron Source (SNS) accumulator ring, where strong multipacting could happen at median clearing fields. A similar phenomenon was reported in an experimental study at Los Alamos laboratory's Proton Synchrotron Ring (PSR). We also investigated the effectiveness of the solenoid's clearing mechanism in the SNS, which differs from the short bunch case, such as in B-factories. The titanium nitride (TiN) coating of the chamber walls was applied to reduce the secondary electron yield (SEY).

The operation at high current of high-energy proton machines like the SPS at CERN is affected by ... more The operation at high current of high-energy proton machines like the SPS at CERN is affected by transverse single-bunch instabilities due to the Electron Cloud effect [1]. As a first step toward modeling a realistic feedback control system to stabilize the bunch dynamics, we investigate the use of a Finite Impulse Response (FIR) filter to represent the processing channel. The effect of the processing channel on the bunch dynamics is analyzed using the macro-particle simulation package Wart-Posinst. We discuss the basic features of the feedback model, report on simulation results, and present our plans for further development of the numerical model.

The multibunch collision by means of pretzel scheme to enhance the luminosity in BEPC have been s... more The multibunch collision by means of pretzel scheme to enhance the luminosity in BEPC have been studied. The modification of the lattice is carried out, the solenoid compensation and chromaticity correction are studied, the physical aperture is examined, the long range beam-beam interaction and coupled bunch instabilities are investigated. The results show that the pretzel scheme with six bunches per beam is feasible.