2006 Vol. 30, No. S1
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Gravitational instability of the distribution of stars in a galaxy is a well-known phenomenon in astrophysics. This work is a preliminary attempt to analyze this phenomenon using the standard tools developed in accelerator physics. By applying this analysis, it is found that a stable nonrotating galaxy would become unstable if its size exceeds a certain limit that depends on its mass density.
The research activities for accelerator structures at SLAC are reviewed including the achievement via the main linac design for the Next Linear Collider (NLC), the program adjustment after the decision of the International Linear Collider (ILC) to be based on superconducting technology, and the work progress for the ILC, photon science at SLAC and basic accelerator structure studies.
A new Separated Function RFQ (SFRFQ) accelerating structure has been proposed and studied. The paper summarizes the study results, concerning the accelerating efficiency, reversed field, cavity and ion beam performance.
As the beam envelope mismatch is the major source of the halo formation and the related emittance growth in high intensity linac, some extensions based on the four-step method are developed, and the causes of beam mismatch in RFQ are analyzed and a matching dynamics method is proposed to minimize the emittance growth and the related beam loss. A dynamics example is given to prove this design method.
The longitudinal coupling impedance of the injection section for the SSRF is analyzed in this paper. The main contributions are coated ceramic chambers and the injection tapers. They are treated with the analysis method and numerical method,respectively. The broad band impedance as well as the narrow band impedance of the cavity like structure, which is formed by the two adjacent tapers is calculated. No trapped mode has been found.The broad band impedance is expressed in terms of effective broad band impedance, which is more convenient for microwave instability analysis.
To calculate the beam transport in the ion optical systems accurately, a beam dynamics computer program of the third order approximation has been developed. Many conventional optical elements have been incorporated in the program. Particle distributions of uniform type or Gaussian type in the 3D dimensional ellipses can be selected by the users. The optimization procedures are provided to make the calculations reasonable and fast. The calculated results can be graphically displayed.
This paper investigates long wavelength radiation from the electron beams passing through Optic Klystron. First, a set of formulas is given to compute the long wavelength radiation by Optic Klystron. Next, the quantities of the formulas are testified by a program based on the basic electron dynamic theory. At the end of the paper, the flux per unit solid angle and the flux of long wavelength radiation, which are from bending magnet and Optic Klystron, respectively,are compared. The result shows that for the radiation in the infrared region, Optic Klystron is superior to bending magnet. This paper shows that the Optic Klystron in the National Synchrotron Radiation Laboratory, which is used for the coherent harmonic generation FEL, can be used as a high brilliance infrared source as well.
With the Monte Carlo method, the performance of X-ray source of a flash X-ray radiographic machine is simulated. It is not true that the smaller the beam radius and the emittance, the better the performance of radiographic image. The results indicate that there is a joint restriction on the beam radius and the beam emittance. If the beam radius on the target is 0.12cm and the exposure inhomogeneity within the azimuthal angle of 2°is not lager than five percentage, the normalized emittance of the beam should not be less than 550cm.mrad.
One of the crucial factors for the beam quality of photocathode RF gun is the relative timing jitter between the laser pulse and the RF phase. This paper introduces the sub-picosecond timing jitter measurement and the feedback control technologies, analyzing beam quality influence caused by the jitter, and acquired practical experience for using a PLL to reduce the laser pulse's phase noise, so as to solve the synchronization problem between the laser beam and the RF phase in the photocathode RF gun.
Dipole field kicks arisen from the construction and alignment of the magnets may cause the particle travels away from the ideal orbit in the transport line. In this paper, orbit distortion corrections of the SSRF BTS lattice are done with the response matrix and SVD algorithm based on AT (matlab) toolbox. Study on the different correctors and BPMs placements are carried out. We also study the orbit distortion correction result which is affected by the interceptive value used in the SVD algorithm.
Application of electron-cooling upgrades the quality of ion beams in the storage rings and brings new problems. The transverse magnetic field distorts the ion orbit while guiding the intense electron beam. The closed-orbit distortion should be and can be localized and controlled well inside the ring acceptance. This paper deals with the field in the e-cool section and concomitant COD of ion orbit and shows the correction scheme.
Due to the errors in all kinds of components of a storage ring, the real optics of the ring is different from the design one. A method that fit the measured response matrix to the model response matrix is developed to calibrate the linear optics. This paper introduces some applications at the BEPC. By analyzing the measured response matrix, we have corrected the local closed orbit successfully. On the other hand, simulation study shows that it is feasible for BEPC to determine the real quadrupole gradients, orbit corrector strengths, and BPM gains using response matrix.
A photocathode RF gun is proposed to generate low emittance, low energy spread and high current electron beam for FEL experiment. In this paper an injector includes a photocathode RF gun, a solenoid, and a 6m long LINAC is simulated with PARMELA. A 1mm.mrad electron beam can be produced from the simulation.
Alpha magnet is an important component of a short-bunch electron beam injector. In order to realize an achromatic transport , the reference particle should be injected into the alpha magnet with a correct angle. This paper describes an attempt to solve the equations of motion of the reference particle and to find the correct angle. The result, including how to determine the trajectory of the reference particle moving in the magnet, can help us understand the process of the achromatic transport of electron beam through the alpha magnet at a deeper level.
The synchro-betatron resonances (SBRs) can be excited by beam-beam kick when there is a crossing angle during collision, which are studied by numerical simulations in the paper. The studies indicate that the SBRs would be excited when νx,π\gtrsim (p+rνs)/q,where p, q and r are integers, νx,π is the horizontal π-mode tune and νs is the synchrotron tune, respectively.
Electron beam longitudinal temperature is an important parameter on electron cooling devise. In this paper, electron beam longitudinal temperature on the HIRFL-CSR electron cooling devise is deduced from four important factors—flattened distribution, electrostatic accelerate, space charge effect and beam scattering.
The dispersion curves of the TM01 and HEM11 modes for the X-band hybrid dielectric-iris-loaded travelling accelerating structure have been calculated. The results show that the cutoff frequency and the propagation constant of HEM11 mode are lower than those of the TM01 mode. We have found that the certain dielectric available with permittivity of 5.81 is applied to the design of the new accelerating structure. The MAFIA code has been used to optimize the model cavities, and the measurements indicate that the resonance frequency is consistent with the design frequency.
The upgrade project of the Beijing Electron Positron Collider (BEPC)-BEPCⅡ is in its construction stage. We review the physics design of the storage ring of the BEPCⅡ, concluding the main focusing accelerator physics issues. The results of these physics problems are given.
Photoneutrons produced in the 15MeV electron accelerator for radiography application were measured and calculated. With passive methods of CR-39 and TE/C ion chamber, the photoneutron dose at the isocenter was 0.19mSv/Gy X-ray and 0.06mSv/Gy X-ray. For comparison, the whole accelerator system was simulated by Monte-Carlo method of MCNP5. The ratio or the neutron dose and the photon dose was 0.092mSv/Gy X-ray, less than the limited value of radiation protection standard. The results of the measurement and the calculation agreed well in the same order.
The booster of the Shanghai Synchrotron Radiation Facility (SSRF) is designed to accelerate the electron beam from 100MeV to 3.5GeV in 250ms,with a repetition frequency of 2Hz. Its circumference is 180m with a periodicity of 28 FODO cell. Energy ramping in the booster synchrotron is the one of the important processes that will affect the beam parameters, the time structure and the injection efficiency of the storage ring. In this paper, the ramping process of the SSRF booster is described in detail, such as ramping curves of magnets and RF voltage, eddy current effect and chromaticity correction, phase space evolution during acceleration, etc.
The Beijing Electron Positron Collider (BEPC) ended its running on July 4th 2005, after 17 years' running since the first collision in 1988. In order to realize the possibility that the BEPC can be run as a collider and as a light source in the same time, the paper describes the commissioning study of the parasitic mode with the permanent magnet wiggler 3W1 on the BEPC and the commissioning study of the in-vacuum wiggler 4W2.
The main subsystems of the Hefei Light Source (HLS) storage ring were upgraded in the Phase II project of the NSRL. Some phenomena, occurred in the commissioning of the HLS storage ring, were simply described and analyzed in this paper. Firstly, the performance of the injection system was analyzed by the numerical tracking study. Then the adjustment of the RF system was explained with the traditional Pederson model. The effects of the octupole system were expressly revealed by the beam stability diagram with and without octupoles. Finally, the linear optics compensation of the super-conducting wiggler magnet was introduced briefly. Generally, these analyses basically agree with the physical phenomena and maybe helpful for the improvement of the HLS storage ring.
Diffraction radiation is generated when there are optical inhomogeneities in the presence of which would cause induced currents that give rise to radiation. Diffraction radiation is the most promising candidate for beam characterizations for the 4th generation light source and the next generation linear colliders due to its non-intercepting and multi-parameter features. In this paper, we gave a brief introduction to the principles of diffraction radiation and systematically studied its applications in electron beam diagnostics.
Short and ultra-short bunch length measurement technique is one of the key techniques used to develop the short wavelength FEL and advanced accelerators. Off-line test experiment on a newly-developed bunch-length diagnostic device was implemented with the far-IR radiation emitted from a black body radiator instead of far-IR to mm wave coherent transition radiation generated by a train of micro-bunches, and got a good autocorrelation interferogram. The experiment showed that its hard and soft-ware worked as good as expected. Through a fine collimation, the well-modulated interferogram can be obtained. Further improvements are put forward.
A BNL/KEK/SHI type 1.6cell Photocathode RF gun has been constructed in Tsinghua university. During the tuning process, the relation of the external quality factor to the length of the coupling iris is measured. Mode frequency, single cell frequency and field balance are also measured. Initial high power test results are also presented in this paper.
In order to study the X-ray's parameters produced by Thomson scattering, the beam profile, energy, divergence and emittance of the 16MeV electron beam accelerated by the backward traveling wave electron linac are measured. The simulated results of the Thomson scattering X-ray based on the measured electron beam parameters are also presented.
The technology of diamagnetic loop (DML) diagnosing intense pulse beam radius is a kind of on-line diagnostics. The technologies can diagnose beam emittance and obliquity on-line cooperating with other technologies such as three gradients method. In this paper, we introduce the theory of diamagnetic loop, design and calibrate diamagnetic loop device. And we diagnose the double pulse electron beams radius generated by the 2MeV injector. By the DML, the double beams radii are 6.84mm and 5.63mm, which are accordant with the results of a frame camera.
The 12MeV Linear induction accelerator can generate the pulse electron beam with energy ～12MeV and current 2.2kA.The beam is transported and focused onto the bremsstrahlung converter target(Ta) with about 4mm spot to produce high intensive X-ray.The X-ray detector and the multi-layer attenuation method are designed and applied to measure X-ray bremsstrahlung spectrum.The results show that the maximum energy of the X-ray is about 2MeV.The measurement results are also analyzed and discussed.
One of the advantages of free electron lasers (FEL) compared to the conventional laser is the possibility of changing the radiation wavelength in a wide range. However, a series of problems arise under the realization of this advantage. In this paper, the problems, related with the adjustment of energy of the BFEL linac, are investigated mainly with the method of simulation. Three adjustment means are discussed, including changing the gradient of accelerator section, the beam phase and the beam current.
First lasing of the CAEP FIR-FEL at the center wavelength of 115 microns was observed in March 2005. The facility is based on RF linac, which consists of an RF-gun, an alpha magnet, an L-band SW accelerator, a beam transport line, a wiggler, an optical cavity and a measurement system. In this paper, the main parts of the facility and the main experimental results are introduced.
The Micro-Pulse Electron Gun (MPG) is a new type of microwave electron gun that is based on the multipactor discharge. In this paper, the MPG emission currents at different RF power levels are measured and discussed. The steady-state and transient dynamics of multipactor are used to explain the experiment waveforms. The dependence of the multipactor saturation current on the RF gap voltage is also given by the SEEG code. The experimental results agree with the theory qualitatively.
The Electron Cloud Instability (ECI) may occur in a positively charged particle storage ring when the machine is operated with a multi-bunch beam. The related experiments have been carried out on the Beijing Electron Positron Collider (BEPC) since 1996. The phenomena of the ECI are mainly coupled bunch oscillation and transverse beam size blow up. The ECI studies at the BEPC are reviewed in this paper, both on experiments and on simulations. The potential methods to suppress the ECI in a positron storage ring have been summarized from the studies.
In this paper the studies on the beam measurements developed during the construction of the Dragon-Ⅰ linebreak linear induction accelerator are described. The measurements of the beam profile, emittance and energy spread using Cerenkov radiation and transition radiation are presented. The measurements of the beam position, intensity and root-means-square radius using resistive wall, B-Dot, D-Dot and diamagnetic loops are also presented.
Laser-plasma acceleration has obtained considerable attention in recent years, for its ability to produce quasi-monoenergetic electron beams. A 286TW Ti: Sapphire laser system at CAEP referred as SILEX-1 can provide the experimental conditions for laser-plasma electron acceleration domestically. A preliminary experiment at the SILEX-1 is described in this paper and the results are also discussed.
To improve the configuration of the terminal electrostatic field by modifying the shape of the terminal electrode, a calculation of the surface electrostatic field distributing for several possible shapes was done using Poisson code, and provide the optimum modification constructions.
Beam dynamics design of an RFQ with low energy spread is introduced. The energy spread of the output 14C beam is about 0.6%, which shows the feasibility to use RFQ in the AMS facility instead of tandem accelerators. The RFQ is also compact with low power dissipation. The isotopes 14C, 13C and 12C can be fully separated in the RFQ, so the AMS background could be reduced and the whole system may be simple.
A new axial beam injection system is designed and being constructed at the HIRFL. It consists of 2 GLASSER lenses, 1 dipole, 5 quadrupoles and 3 solenoids. There are two beam line branches for 14.5GHz ECR ion source and 18.5GHz super conducting ECR ion source. Both transverse and longitudinal beam optics are improved in contrast with the old one. The layout, beam optics calculation results and further improved design are given.
In the paper, design of a 2MeV electron linac is introduced, which includes calculation about parameters of the accelerator structure, longitudinal and transverse dynamics. This linac is used for sterilizing anthrax-bacilus in mails. Machine test shows that parameters of the accelerator can satisfy the design target.
Rapid Cycling Synchrotron (RCS) is a key component of the Beijing Spallation Neutron Source (BSNS), and an optimal lattice design is essential for the assessment and the future operation. Based on the comparison of several types of lattice structure, a FODO/Triplet hybrid structure is presented. Two alternative lattices are also given, and the merits and the demerits of each lattice are discussed.
Beijing X-ray free electron laser test facility (BTF) will reside in the BEPCⅡ Linac, which is the best electron linac in China. The BTF will not use the existing DC gun pre-injector, but use photoinjector to obliquely inject beam to the main linac of the BEPCⅡ. At the same time,three accelerator sections will be removed in order to install two magnetic compressors to compress the electron bunch. After the accelerator section A46, the beam is extracted and injected to the undulator through high energy transport line. The BTF will provide the electron beam with the energy of 1.18GeV, the energy spread of 0.15%, and the normalized emittance of less than 2.5mm.mrad.
The heavy ion linac in Lanzhou is designed as a future injector for the Cooling Storage Ring (CSR). In order to keep the total machine within 40 meters, the IH (Interdigital H-type) structure is adopted for its higher acceleration gradient compared with the traditional DTL structure. The designed minimum charge over mass ratio is 1/6, the output energy is 16MeV/u and the beam current is 1A.μA. The RFQ and the first DTL tank will work at 100MHz, and the other DTL tanks will work at the double frequency. The design criteria, main parameters and the detailed beam dynamic design are introduced in this paper.
In order to match the beam from the injection machine SFC of the HIRFL to the main ring of HIRFL-CSR,both beam emittance confining method and beam energy spread reducing method are proposed. The beam preparation principles and calculation results are presented.
BEPCⅡ, the upgrading project of the Beijing Electron-Positron Collider (BEPC), has been designed with a luminosity of 1033cm－2s－1 at the t-charm energy regime. To increase the operating luminosity of the BEPCⅡ, a low momentum compaction factor collision mode has been studied. At the same time, the dynamic aperture of this mode has been calculated since it may not be enough as a result of the sextupole strength increasing. The corresponding luminosity of this mode is calculated through beam-beam simulations.
Several new high brilliance lattices of the HLS storage ring are proposed. The magnetic lattices are designed with the constraints that the positions of all the elements and beamlines in the storage ring are kept unchanged and no new element is used. Small beam emittances can be achieved step by step. In these lattices, all of the straight sections have small vertical beta function, which are suitable for the operation of insertion devices. Tracking study shows that the new lattices have sufficiently large dynamic apertures for injection and storage.
A 100MeV high intensity cyclotron was designed to provide more than 200μA proton beam, and will provide pulse beam. The injection system has two considerations, which correspond to the 1# and 2# injection lines. The 1# line is designed to solve the DC beam injection using the neutralization with H-beam. For a high neutralization, the transverse focusing elements are all magnetic ones. The purpose of the 2# line is to provide pulse beam with certain intensity. It's difficult to build neutralization for the pulse beam, so the transverse focusing elements are all static electronic. The proper design for the structure of the two injection lines makes operation easy. Using computer program, including space charge effect calculations, we matched the injection optics for different neutralization degrees. The emphases of the calculations are getting 40° phase acceptance. The results calculated from the ion source to 15 turns acceleration show that the injection system designed for the 100MeV cyclotron can control the beam envelope efficiently and reduce the beam loss. The central region with the high RF phase acceptance makes the 100MeV machine have the ability of accelerating high intensity H－ beam.
Shanghai Synchrotron Radiation Facility (SSRF) is a low emittance third-generation synchrotron radiation light source under construction.The lattice performance of SSRF storage ring has been optimized. The lattice conducts an emittance of 3.9nm.rad at 3.5GeV, 432m in circumference, two types of straight sections in length and enough adjusting flexibility of beta function and dispersion function at straight section. Tracking studies show that this lattice has large enough dynamic apertures and energy acceptance even with multipole field errors of magnets.
The HIRFL (Heavy Ion Research Facility at Lanzhou) is a cyclotron complex. Its injector is a cector focusing cyclotron with K=69. Since the HIRFL started the operation in 1989, two bigger items of improvements have been finished, the species and intensity of the accelerated particles are increased obviously. But due to the lower extraction efficiency of the SFC, on one hand, a lot of beam lost, and on other hand, outgas from the surface of the electrostatic deflector is serious because of beam hitting. Even sometimes the vacuum press is destroyed. In the paper a new physical design is made to get an extraction system of the SFC with a higher efficiency.
The BEPCⅡ injector linac upgrade aims at having higher beam energy with smaller beam emittance and energy spread to meet the colliding luminosity upgrade by two orders of magnitudes higher. It is a great challenge to various systems and the beam physics for this injector linac. This paper describes the constructions of the new electron gun, the new positron source, the new RF power supply, the new phasing system and the upgraded beam instrumentation, which are immediately affected on the beam performance. The beam physics with high current and small emittance and energy spread are systematically studied. The preliminary beam commissioning results and the further machine improvement plans are presented.
With the advent of the chirped-pulse-amplification technology, one is able to obtain the ultrashort laser pulses with a focused intensity over 1018W/cm2 and with a duration less than 100fs. Such laser pulses can accelerate electrons to relativistic energy directly. More importantly, they can drive large-amplitude plasma waves, so called the laser wakefields, which can accelerate electrons to the energy of hundreds of MeV in mm-length. In this paper, we introduce briefly various schemes of the laser wakefield accelerators, the recent progress, and the remaining challenges.
In this paper a general procedure to determine linear collider parameters is given. As an example,a parameter list is proposed for ILC with very low bunch charge. The main aim of this paper is to demonstrate the beam parameter relations with the constraints from the interaction point and damping ring. It is suggested that the energy of the damping ring should be 7GeV instead of 5GeV if a 17km damping ring is to be used. However, if 6km damping ring (which is preferable) is adopted, 5GeV damping ring energy is reasonable.
China Institute of Atomic Energy (CIAE) has got the approval to build the BRIF, Beijing Radioactive Ion-beam Facility. At present, the basic design has been finished. In this paper, it is focusing to discuss the design of the main accelerator of the BRIF, 100MeV high intensity cyclotron. It includes the design strategy, design feature, the general design and the main technical specification, the brief design results of the crucial equipment (ion source, axial injection, central region, magnet, RF system, vacuum system, extraction, diagnosis system, control system, etc.)
The project of the CIAE Heavy Ion Nuclear Physics Researcher Facilities has been proposed. It is composed of a super-conducting linac with 9 cryostatus and 36 QWR cavities, which can boost the energy of heavy ion up to 18MeV/q following the existing HI-13 tandem. A new low energy heavy ion linac composed of an on-line ECR ion source, a four rods RFQ and an IH-DTL linac was also designed to accept the RNB directly from the ISOL bypassing the existing HI-13 tandem and inject the beam into the superconducting linac.
After upgrade of the Hefei light source, the optics parameters of electron storage ring were adjusted and measured. Both the kicker and the RF system were reconstructed completely, and were commissioned well. The SVD algorithm is used for the global closed orbit feedback. Two methods were used to suppress the transverse coupled bunch instability. So a 300mA beam intensity is achieved.
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