124623797
HESYRL 200 MeV linac single bunch energy spectrum measurement
The HESYRL 200-MeV electron linac was completed in December 1987, and has been running well. A careful study of the single-bunch energy spectrum for the linac was done. The measurement shows that the energy spread of the linac is +or-0.4%. The energy spectrum is quite stable and repeatable, and the resolution and accuracy are found to be satisfactory.<<ETX>>
55429266
STUDY OF THE ENERGY CHIRP EFFECTS ON SEEDED FEL SCHEMES AT SDUV-FEL
In this paper, theoretical and simulation study of the energy chirp effects on the HGHG and EEHG schemes are present. It is found that the central wavelength and output bandwidth of EEHG can be nearly immune to the beam energy chirp by properly setting the strengths of the chicanes. Experimental studies for both these two schemes have been carried out at the SDUV-FEL to demonstrate the theoretical predictions.
67837860
Design of a superconducting linac cavity for high-current energy recovery linac operation
The RHIC electron cooler as well as other applications (such as a linac-ring version of eRHIC) requires a very high average current CW electron linac in an energy recovery mode. In this paper we present the design of a 5-cell superconducting linac cavity for velocity of light particles. This cavity will operate at 703.75 MHz with a large beam pipe aperture of 19 cm diameter and ferrite HOM absorbers in the beam pipe, in addition to the conventional HOM couplers for low frequency HOMs. We will report the design of the cavity geometry using the BuildCavity and Superfish codes, loss factor simulations with ABCI, detailed HOM simulations with MAFIA (with and without the ferrite absorbers) and beam breakup simulations using the code TDBBU.
21579776
Mechanical induced beam motion in SRRC storage ring
It has been observed that the mechanical stability of some magnets had an influence on the closed orbit in the storage ring. In this paper, a mechanical shaker at a low vibration level was applied to the quadrupole magnet. The perturbation of the closed orbit was measured. The thermal induced distortion of magnet supporting structure was discussed. The motion of the BPM and quadrupole magnet were measured. Some examples of mechanical induced beam motion are discussed.
18270897
Beam Physics Highlights of the FERMI@ELETTRA Project
The electron beam dynamics in the Fermi Linac has been studied in the framework of the design of a singlepass free electron laser (FEL) based on a seeded harmonic cascade. The wakefields of some accelerating sections represent a challenge for the preservation of a small beam emittance and for achieving a small final energy spread. Various analytical techniques and tracking codes have been employed in order to minimize the quadratic and the cubic energy chirps in the longitudinal phase space, since they may cause a degradation of the fel bandwidth. As for the transverse motion, the beam breakup (BBU) instability has been recognized as the main source of emittance dilution; the simulations show the validity of local and non-local correction methods in order to counteract the typical “banana” shape distortion of the beam caused by the instability.
37693304
Level lifetimes in N=82 isotones from Doppler-shift attenuation method mixed-target measurements.
Lifetimes of the first excited states of the [ital N]=82 isotones [sup 138]Ba, [sup 140]Ce, and [sup 142]Nd have been measured simultaneously with the Doppler-shift attenuation method following inelastic neutron scattering and are found to be in excellent agreement with adopted literature values. In addition, lifetimes of excited states in heavier isotopes of neodymium have been determined. Of special interest are the [ital E]1 transitions for which transition strengths greater than 10[sup [minus]3] W.u. are observed.
26749894
Compensating the electron beam energy spread by the natural transverse gradient of laser undulator in all-optical x-ray light sources.
All-optical ideas provide a potential to dramatically cut off the size and cost of x-ray light sources to the university-laboratory scale, with the combination of the laser-plasma accelerator and the laser undulator. However, the large longitudinal energy spread of the electron beam from laser-plasma accelerator may hinder the way to high brightness of these all-optical light sources. In this paper, the beam energy spread effect is proposed to be significantly compensated by the natural transverse gradient of a laser undulator when properly transverse-dispersing the electron beam. Theoretical analysis and numerical simulations on conventional laser-Compton scattering sources and high-gain all-optical x-ray free-electron lasers with the electron beams from laser-plasma accelerators are presented.
122204593
Measurement of femtosecond electron bunches using a rf zero-phasing method
Bunch lengths as short as 84 fs (rms) have been measured at Jefferson Laboratory using a rf zero-phasing technique. To the best of our knowledge, this is the first accurate measurement of the longitudinal distribution function in this regime. In this paper, an analytical approach for computing the longitudinal distribution function and bunch length is described for arbitrary longitudinal and transverse distributions for the case where the intrinsic energy spread of the bunch is small compared to the correlated energy spread imparted by zero-phasing cavities. The measurement results are presented, which are in excellent agreement with numerical simulations. {copyright} {ital 1998} {ital The American Physical Society}
119222591
Simulation studies on laser pulse stability for Dalian coherent light source
Dalian Coherent Light Source will use a 300 MeV LINAC to produce fully coherent photon pulses in the wavelength range between 150-50 nm by high gain harmonic generation free electron laser (FEL) scheme. To generate stable FEL pulses, a stringent tolerance budget is required for the LINAC output parameters, such as the mean beam energy stability, electron bunch arrival time jitter, peak current variation and the transverse beam position offset. In order to provide guidance for the design of the Dalian Coherent Light Source, in this paper, the sensitivity of FEL pulse energy fluctuation to various error sources of the electron bunch was performed using intensive start-to-end FEL simulations.
109205409
A design and performance analysis tool for superconducting RF systems
Superconducting RF systems are usually operated with continuous RF power or with RF pulse lengths exceeding 1 ms to maximize the overall wall plug power efficiency. Typical examples are CEBAF at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) and the TESLA Test Facility at DESY. The long pulses allow for effective application of feedback to stabilize the accelerating field in presence of microphonics, Lorentz force detuning, and fluctuations of the beam current. In this paper we describe a set of tools to be used with MATLAB and SIMULINK, which allow to analyse the quality of field regulation for a given design. The tools include models for the cavities, the RF power source, the beam, sources of field perturbations, and the RF feedback system. The RF control relevant electrical and mechanical characteristics of the cavity are described in form of time-varying state space models. The power source is modelled as a current generator and includes saturation characteristics and noise. An arbitrary time structure can be imposed on the beam current to reflect a macro-pulse structure and bunch charge fluctuations. For RF feedback several schemes can be selected: Traditional amplitude and phase control as well as I/Q control. The choices for the feedback controller include analog or digital approaches and various choices of frequency response. Feed forward can be added to further suppress repetitive errors. The results of a performance analysis of the CEBAF and the TESLA Linac RF system using these tools are presented.
119232861
Phase-merging enhanced harmonic generation free-electron laser
Together with one of its variants, the recently proposed phase-merging enhanced harmonic generation (PEHG) free-electron laser (FEL) is systematically studied in this paper. Different from a standard high-gain harmonic generation scheme, a transverse gradient undulator is employed to introduce a phase-merging effect into the transversely dispersed electron beam in PEHG. The analytical theory of the phase-merging effect and the physical mechanism behind the phenomenon are presented. Using a representative set of beam parameters, intensive start-to-end simulations for soft x-ray FEL generation are given to illustrate the performance of PEHG. Moreover, some practical issues that may affect the performance of PEHG are also discussed.