Physical Review Special Topics-accelerators and Beams最新文献

{"title":"Laser-triggered proton acceleration from hydrogenated low-density targets","authors":"A. V. Brantov, E. Obraztsova, A. Chuvilin, E. Obraztsova, a.V. Yu Bychenkov","doi":"10.1103/PHYSREVACCELBEAMS.20.061301","DOIUrl":"https://doi.org/10.1103/PHYSREVACCELBEAMS.20.061301","url":null,"abstract":"","PeriodicalId":20072,"journal":{"name":"Physical Review Special Topics-accelerators and Beams","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2017-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90728602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influence of the injected beam parameters on the capture efficiency of an electron cyclotron resonance based charge breeder","authors":"A. Galatà, D. Mascali, G. Torrisi, L. Neri, L. Celona, J. Angot","doi":"10.1103/PHYSREVACCELBEAMS.20.063401","DOIUrl":"https://doi.org/10.1103/PHYSREVACCELBEAMS.20.063401","url":null,"abstract":"Electron cyclotron resonance ion sources based charge breeders (ECR-CB) are fundamental devices for Isotope Separation On Line (ISOL) facilities aiming at postaccelerating radioactive ion beams (RIBs). Presently, low intensity RIBs do not allow a conventional tuning of the ECR-CB: as a consequence, it has to be set with a stable 1+ pilot beam first, switching then to the radioactive one without changing any parameter; this procedure is usually called “blind tuning.” Besides having different masses, pilot and radioactive beams can also differ in terms of the rms transverse emittance erms and/or longitudinal energy spread ΔE, so the choice of a given pilot beam can determine the overall performances of the final breeding stage. This paper shows a numerical study of how the capture efficiency of the PHOENIX charge breeder is affected by the aforementioned beam paramaters: the analysis reveals the two-step nature of the process, highlighting the role of the injection optics and the plasma capture capability in the overall performances of this device. The simulations predict highest efficiency for erms<5π  mm mrad and ΔE<5  eV in a optimum energy range between 2 and 6 eV, thus giving important information on the possibility of blindly tuning an ECR-CB. No isotopical effects were observed, while it clearly came out the necessity to improve the 1+ beam characteristics with a rf beam cooler prior to the injection into an ECR-CB.","PeriodicalId":20072,"journal":{"name":"Physical Review Special Topics-accelerators and Beams","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2017-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90798571","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Transverse coupled-bunch instability thresholds in the presence of a harmonic-cavity-flattened rf potential","authors":"F. Cullinan, R. Nagaoka, G. Skripka, P. Tavares","doi":"10.1103/PHYSREVACCELBEAMS.19.124401","DOIUrl":"https://doi.org/10.1103/PHYSREVACCELBEAMS.19.124401","url":null,"abstract":"A small vacuum chamber aperture is a present trend in the design of future synchrotron light sources. This leads to a large resistive-wall impedance that can drive coupled-bunch instabilities. Another trend is the use of passively driven cavities at a harmonic of the main radio frequency to lengthen the electron bunches in order to increase the Touschek lifetime and reduce emittance blowup due to intrabeam scattering. In some cases, the harmonic cavities may be tuned to fulfill the flat potential condition. With this condition met, it has been predicted in simulation that the threshold current for coupled-bunch resistive-wall instabilities is much higher than with no bunch lengthening at all. In this paper, the features of a bunch in the flat potential that would contribute toward this stabilization are identified and discussed. The threshold currents for these instabilities are estimated for the MAX IV 3 GeV storage ring at different values of chromaticity using macroparticle simulations in the time domain and, within the limits of the existing theory, frequency domain calculations. By comparing the results from these two methods and analyzing the spectra of the dominant head-tail modes, the impact of each of the distinguishing features of a bunch in the flat potential can be explained and quantified in terms of the change in threshold current. It is found that, above a certain chromaticity, the threshold current is determined by the radial structure of the zeroth-order head-tail mode. This happens at a lower chromaticity if the bunch length is longer. (Less)","PeriodicalId":20072,"journal":{"name":"Physical Review Special Topics-accelerators and Beams","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2016-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83871506","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Extreme regimes of femtosecond photoemission from a copper cathode in a dc electron gun","authors":"P. Pasmans, Van Vugt, van Jp Lieshout, G. Brussaard, O. J. Luiten","doi":"10.1103/PHYSREVACCELBEAMS.19.103403","DOIUrl":"https://doi.org/10.1103/PHYSREVACCELBEAMS.19.103403","url":null,"abstract":"The femtosecond photoemission yield from a copper cathode and the emittance of the created electron beams has been studied in a 12 MeV/m, 100 keV dc electron gun over a wide range of laser fluence, from the linear photoemission regime until the onset of image charge limitations and cathode damaging. The measured photoemission curves can be described well with available theory which includes the Schottky effect, second-order photoemission, and image charge limitation. The second-order photoemission can be explained by thermally assisted one-photon photoemission (1PPE) and by above-threshold two-photon photoemission (2PPE). Measurements with a fresh cathode suggest that the 2PPE process is dominant. The beam emittance has been measured for the entire range of initial surface charge densities as well. The emittance measurements of space-charge dominated beams can be described well by an envelope equation with generalized perveance. The dc gun produces 0.1 pC bunches with 25 nm rms normalized emittance, corresponding to a normalized brightness usually associated with rf photoguns. In this experimental study the limits of femtosecond photoemission from a copper cathode have been explored and analyzed in great detail, resulting in improved understanding of the underlying mechanisms.","PeriodicalId":20072,"journal":{"name":"Physical Review Special Topics-accelerators and Beams","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2016-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81775383","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"TMCI threshold with space charge and different wake fields","authors":"V. Balbekov","doi":"10.1103/PhysRevSTAB.20.034401","DOIUrl":"https://doi.org/10.1103/PhysRevSTAB.20.034401","url":null,"abstract":"Transverse mode coupling instability of a bunch with space charge and wake field is considered within the frameworks of the boxcar model. Eigenfunctions of the bunch without wake are used as a basis for the solution of the equations with the wake field included. A dispersion equation for constant wake is presented in the form of an infinite continued fraction and also as the recursive relation with an arbitrary number of the basis functions. Realistic wake fields are considered as well including resistive wall, square, and oscillating wakes. It is shown that the TMCI threshold of the negative wake grows up in absolute value when the SC tune shift increases. Threshold of positive wake goes down at the increasing SC tune shift. The explanation is developed by an analysis of the bunch spectrum.","PeriodicalId":20072,"journal":{"name":"Physical Review Special Topics-accelerators and Beams","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2016-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80115560","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Focusing effects in laser-electron Thomson scattering","authors":"C. Harvey, M. Marklund, A. Holkundkar","doi":"10.1103/PhysRevAccelBeams.19.094701","DOIUrl":"https://doi.org/10.1103/PhysRevAccelBeams.19.094701","url":null,"abstract":"We study the effects of laser pulse focusing on the spectral properties of Thomson scattered radiation. Modeling the laser as a paraxial beam we find that, in all but the most extreme cases of focusing, the temporal envelope has a much bigger effect on the spectrum than the focusing itself. For the case of ultrashort pulses, where the paraxial model is no longer valid, we adopt a subcycle vector beam description of the field. It is found that the emission harmonics are blue shifted and broaden out in frequency space as the pulse becomes shorter. Additionally the carrier envelope phase becomes important, resulting in an angular asymmetry in the spectrum. We then use the same model to study the effects of focusing beyond the limit where the paraxial expansion is valid. It is found that fields focussed to subwavelength spot sizes produce spectra that are qualitatively similar to those from subcycle pulses due to the shortening of the pulse with focusing. Finally, we study high-intensity fields and find that, in general, the focusing makes negligible difference to the spectra in the regime of radiation reaction.","PeriodicalId":20072,"journal":{"name":"Physical Review Special Topics-accelerators and Beams","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2016-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84382430","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Studies of Beam Induced Electron Cloud Resonances in Dipole Magnetic Fields","authors":"J. Calvey, W. Hartung, J. Makita, M. Venturini","doi":"10.1103/PhysRevAccelBeams.19.074401","DOIUrl":"https://doi.org/10.1103/PhysRevAccelBeams.19.074401","url":null,"abstract":"The buildup of low energy electrons in an accelerator, known as electron cloud, can be severely detrimental to machine performance. Under certain beam conditions, the beam can become resonant with the cloud dynamics, accelerating the buildup of electrons. This paper will examine two such effects: multipacting resonances, in which the cloud development time is resonant with the bunch spacing, and cyclotron resonances, in which the cyclotron period of electrons in a magnetic field is a multiple of bunch spacing. Both resonances have been studied directly in dipole fields using retarding field analyzers installed in the Cornell Electron Storage Ring (CESR). These measurements are supported by both analytical models and computer simulations.","PeriodicalId":20072,"journal":{"name":"Physical Review Special Topics-accelerators and Beams","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2016-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81845728","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Linearization of the longitudinal phase space without higher harmonic field","authors":"B. Zeitler, K. Floettmann, F. Grüner","doi":"10.1103/PHYSREVSTAB.18.120102","DOIUrl":"https://doi.org/10.1103/PHYSREVSTAB.18.120102","url":null,"abstract":"Alternative technique for linearizing the longitudinal phase space of an electron bunch formed via photoemission in an rf gun.","PeriodicalId":20072,"journal":{"name":"Physical Review Special Topics-accelerators and Beams","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83084496","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New supersonic gas jet target for low energy nuclear reaction studies","authors":"F. Favela, L. Acosta, E. Andrade, V. Araujo, A. Huerta, Ó. D. Lucio, G. Murillo, M. E. Ortiz, R. Policroniades, P. S. Rita, A. Varela, E. Chávez","doi":"10.1103/PHYSREVSTAB.18.123502","DOIUrl":"https://doi.org/10.1103/PHYSREVSTAB.18.123502","url":null,"abstract":"","PeriodicalId":20072,"journal":{"name":"Physical Review Special Topics-accelerators and Beams","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81696854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dipole fringe field thin map for compact synchrotrons","authors":"K. Hwang, S. Y. Lee","doi":"10.1103/PHYSREVSTAB.18.122401","DOIUrl":"https://doi.org/10.1103/PHYSREVSTAB.18.122401","url":null,"abstract":"The fringe field of dipole magnets can be mportant in charged-particle beam dynamics [1,2]. For example, the edge angle effect on the vertical focusing has been parametrized by the fringe field integral introduced [1] and measured [3]. The nonlinear beam dynamics of the fringe field has also been included up to a sextupolelike potential in Ref. [2]. The fringe field effect is particularly important for compact accelerators that have a small bending radius. Applications of compact storage rings include the Inverse Compton Light Source (see, e.g., [4]), proton therapy synchrotrons, etc. The fringe field of dipole magnets typically extends to the range of the vertical magnet gap. The range of the fringe field is usually minimized to avoid magnetic field coupling due to limited available space in compact storage rings. As the range of the fringe field is reduced, parts of the fringe field effects may be minimized and others amplified. In particular, higher-order nonlinearity can become important. Often overlooked, an important feature of the dipole fringe field effect is the closed orbit deviation from the design orbit. This change of the closed orbit arises from the fact that the fringe field introduces continuously varying curvature, while the design orbit is defined by constant curvature starting from the hard edge dipole boundary. Although this fact is naive and simple, its effect can be large for compact storage rings and thus should not be disregarded. If not considered, it can cause significant misalignment errors for all other accelerator elements. As the fringe field extent decreases, the closed orbit deviation will also decrease. However, higher-order nonlinearity would increase. It is important to understand how these effects rely on the fringe field extent. Recently, the fringe field effects on nonlinear dynamics for compact rings and large emittance beams have been considered in Refs. [5,6]. The numerical method was used to extract the Taylor map or Lie map out of the 3D field data [7,8]. However, there is still a demand for an analytic expression of the fringe field map, particularly when the 3D field data are not available at the design stage. Because of its complex nonlinear effects, it is often hard to uncover the underlying physics based on simulation results alone. In addition, a good understanding of the dipole fringe field map can benefit not only storage ring design but also dipole magnet design. Theoretical studies on the influence of dipole fringe fields have been carried out by many researchers from the early 1960s through the early 1970s [9–14]. Although some earlier studies derived mapping equations up to third order of phase space variables, they often led to complicated expressions with too many integration parameters. This paper is intended to provide a simpler physics picture of fringe field effects. The Lie algebraic method is useful to study the fringe field effect [15]; e.g., the Methodical Accelerator Design ver.10 ","PeriodicalId":20072,"journal":{"name":"Physical Review Special Topics-accelerators and Beams","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78143082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}