ST Accel Research Articles

Erratum: Calculations of spin response functions in rings with Siberian Snakes and spin rotators [Phys. Rev. ST Accel. Beams12, 024001 (2009)

Erratum: Calculations of spin response functions in rings with Siberian Snakes and spin rotators [Phys. Rev. ST Accel. Beams<b>12</b>, 024001 (2009)

Shaping the output pulse of a linear-transformer-driver module

We demonstrate that a wide variety of current-pulse shapes can be generated using a linear-transformer-driver (LTD) module that drives an internal water-insulated transmission line. The shapes are produced by varying the timing and initial charge voltage of each of the module's cavities. The LTD-driven accelerator architecture outlined in [Phys. Rev. ST Accel. Beams 10, 030401 (2007)] provides additional pulse-shaping flexibility by allowing the modules that drive the accelerator to be triggered at different times. The module output pulses would be combined and symmetrized by water-insulated radial-transmission-line impedance transformers [Phys. Rev. ST Accel. Beams 11, 030401 (2008)].

Results of the SINGAP neutral beam accelerator experiment at JAEA

IRFM (CEA Cadarache) and JAEA Naka have entered into a collaboration in order to test a Single Gap, Single Aperture (SINGAP) [H.P.L. de Esch, R.S. Hemsworth, P. Massmann, Updated physics design ITER-SINGAP accelerator, Fusion Eng. Des. 73 (2005) 329.] accelerator at the JAEA Megavolt Test Facility (MTF) at Naka, Japan. Whereas at the CEA testbed the acceleration current was limited to 0.1 A, at JAEA 0.5 A is available. This allows the acceleration of 15 H − beamlets in SINGAP to be tested and a direct comparison between SINGAP and Multi Aperture, Multi Grid (MAMuG) [M. Taniguchi, T. Inoue, N. Umeda, M. Kashiwagi, K. Watanabe, H. Tobari, M. Dairaku, K. Sakamoto, Acceleration of ampere class H − ion beam by MeV accelerator, Rev. Sci. Instrum. 79 (2008) 02C110.] to be made. High voltage conditioning in the SINGAP configuration has been quite slow, with 581 kV in vacuum achieved after 140 h of conditioning. With 0.25 Pa of H 2 gas present in the accelerator 787 kV could be achieved. The conditioning curve for MAMuG is 200 kV higher. SINGAP beam optics appears in agreement with calculation results. A beamlet divergence better than 5 mrad was obtained. SINGAP accelerates electrons to a higher energy than MAMuG. Measurements of the power intercepted on one of the electron dumps have been compared with EAMCC code [G. Fubiani, H.P.L. de Esch, A. Simonin, R.S. Hemsworth, Modeling of secondary emission processes in the negative ion based electrostatic accelerator of the International Thermonuclear Experimental Reactor, Phys. Rev. ST Accel. Beams 11 (2008) 014202.] calculations. Based on the experiments described here, electron production by a SINGAP accelerator scaled up to ITER size was estimated to be too high for comfort.

Dielectric-breakdown tests of water at 6 MV

We have conducted dielectric-breakdown tests on water subject to a single unipolar pulse. The peak voltages used for the tests range from 5.8 to 6.8 MV; the effective pulse widths range from 0.60 to $1.1\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$; and the effective areas tested range from $1.8\ifmmode\times\else\texttimes\fi{}{10}^{5}$ to $3.6\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }{\mathrm{cm}}^{2}$. The tests were conducted on water-insulated coaxial capacitors. The two electrodes of each capacitor have outer and inner radii of 99 and 56 cm, respectively. Results of the tests are consistent with predictions of the water-dielectric-breakdown relation developed in [Phys. Rev. ST Accel. Beams 9, 070401 (2006)].

Erratum: Full spin flipping in the presence of full Siberian Snake [Phys. Rev. ST Accel. Beams11, 091001 (2008)

Erratum: Full spin flipping in the presence of full Siberian Snake [Phys. Rev. ST Accel. Beams<b>11</b>, 091001 (2008)

Emittance growth due to static and radiative space charge forces in an electron bunch compressor

Evolution of short intense electron bunches passing through bunch-compressing beam lines is studied using the UAL (Unified Accelerator Libraries) string space charge formulation [R. Talman, Phys. Rev. ST Accel. Beams 7, 100701 (2004); N. Malitsky and R. Talman, in Proceedings of the 9th European Particle Accelerator Conference, Lucerne, 2004 (EPS-AG, Lucerne, 2004); R. Talman, Accelerator X-Ray Sources (Wiley-VCH, Weinheim, 2006), Chap. 13]. Three major configurations are studied, with the first most important and studied in greatest detail (because actual experimental results are available and the same results have been simulated with other codes): (i) Experimental bunch compression results were obtained at CTF-II, the CERN test facility for the ``Compact Linear Collider'' using electrons of about 40 MeV. Previous simulations of these results have been performed (using TraFiC4* [A. Kabel et al., Nucl. Instrum. Methods Phys. Res., Sect. A 455, 185 (2000)] and ELEGANT [M. Borland, Argonne National Laboratory Report No. LS-287, 2000]). All three simulations are in fair agreement with the data except that the UAL simulation predicts a substantial dependence of horizontal emittance ${ϵ}_{x}$ on beam width (as controlled by the lattice ${\ensuremath{\beta}}_{x}$ function) at the compressor location. This is consistent with the experimental observations, but inconsistent with other simulations. Excellent agreement concerning dependence of bunch energy loss on bunch length and magnetic field strength [L. Groening et al., in Proceedings of the Particle Accelerator Conference, Chicago, IL, 2001 (IEEE, New York, 2001), http://groening.home.cern/groening/csr_00.htm] confirms our understanding of the role played by coherent synchrotron radiation (CSR). (ii) A controlled comparison is made between the predictions of the UAL code and those of CSRTrack [M. Dohlus and T. Limberg, in Proceedings of the 2004 FEL Conference, pp. 18\char21{}21, MOCOS05, available at http://www.JACoW.org], a code with similar capabilities. For this comparison an appropriately new, 50 MeV, ``standard chicane'' is introduced. Unlike CSRTrack (which neglects vertical forces) the present simulation shows substantial growth of vertical emittance. But ``turning off'' vertical forces in the UAL code (to match the CSRTrack treatment) brings the two codes into excellent agreement. (iii) Results are also obtained for 5 GeV electrons passing through a previously introduced ``standard chicane'' [Coherent Synchrotron Radiation, CSR Workshop, Berlin 2002, http://www.desy.de/csr] [of the sort needed for linear colliders and free electron lasers (FEL's) currently under design or construction]. Relatively little emittance growth is predicted for typical bunch parameters at such high electron energy. Results are obtained for both round beams and ribbon beams (like those actually needed in practice). Little or no excess emittance growth is found for ribbon bunches compared to round bunches of the same charge and bunch width. The UAL string space charge formulation (like TraFic4 and CSRTrack) avoids the regularization step (subtracting the free-space space charge force) which is required (to remove divergence) in some methods. Also, by avoiding the need to calculate a retarded-time, four-dimensional field history, the computation time needed for realistic bunch evolution calculations is modest. Some theories of bunch dilution, because they ascribe emittance growth entirely to CSR, break down at low energy. In the present treatment, as well as CSR, all free-space Coulomb and magnetic space charge forces (but not image forces), and also the centrifugal space charge force (CSCF) are included. Charge-dependent beam steering due to CSCF, as observed recently by Beutner et al. [B. Beutner et al., in Proceedings of FEL Conference, BESSY, Berlin, Germany, 2006, MOPPH009], is also investigated.

Ion acceleration with ultra-thin foils using elliptically polarized laser pulses

We present theoretical considerations on the process of ion acceleration with ultra-thin foils irradiated by elliptically polarized, highly intense laser pulses. Very recently the radiation pressure acceleration regime was predicted where mono-energetic ion bunches can be produced with high efficiencies (Klimo et al 2008 Phys. Rev. ST Accel. Beams 11 031301; Robinson et al 2008 New J. Phys. 10 013021). We have studied the process by means of 1D particle-in-cell (PIC) simulations and analytical models and have considered effects of areal mass density of the target and laser ellipticity on the ion acceleration process. For certain target densities and laser parameters the optimum target thickness has been extracted. Peaked ion spectra are found for ellipticity beyond a threshold value of about 0.7. Here, we highlight the drastic difference between linear and circular polarization by movie animations.

Full spin flipping in the presence of full Siberian Snake

This paper proposes a new design of spin flipper for high-energy accelerators to obtain full spin flip with the spin tune staying at half integer. The traditional technique of using a single rf spin rotator with a fixed spin rotation axis and an oscillating spin rotation, either an rf dipole or solenoid, as spin flipper to achieve full spin flip in the presence of a full Siberian snake has been demonstrated [B. B. Blinov et al., Phys. Rev. Lett. 81, 2906 (1998); B. B. Blinov et al., Phys. Rev. Lett. 88, 014801 (2001); V. S. Morozov et al., Phys. Rev. ST Accel. Beams 7, 024002 (2004); R. A. Phelps, AIP Conf. Proc. 338, 361 (1994); Ya. S. Derbenev et al., Part. Accel. 8, 115 (1978)]. However, this technique requires one to change the snake configuration to move the spin tune away from half integer which is not practical for an operational high-energy polarized proton collider such as RHIC where beam and polarization lifetime are sensitive to small changes. Based on the conceptual designs to use rf dipoles to achieve full spin flip with the spin tune at half integer [T. Roser, BNL Report No. BNL-52453, 1994; R. A. Phelps, BNL Report No. BNL-52453, 1994], this paper presents a compact design of a spin flipper for a high-energy accelerator. The theory of the new spin flipper technique and numerical simulations are also presented.

Erratum: Ultrahigh brightness electron beams by plasma-based injectors for driving all-optical free-electron lasers [Phys. Rev. ST Accel. Beams11, 070703 (2008)

Received 22 August 2008DOI:https://doi.org/10.1103/PhysRevSTAB.11.099902This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Publisher’s Note: High intensity ion beams in rf undulator linac [Phys. Rev. ST Accel. Beams11, 074201 (2008)

Publisher’s Note: High intensity ion beams in rf undulator linac [Phys. Rev. ST Accel. Beams<b>11</b>, 074201 (2008)

Production of ultrashort FEL XUV pulses via a reverse undulator taper

We adapt the “reverse taper” scheme presented by Saldin et al. (Phys. Rev. ST Accel. Beams 9 (2006) 050702) for attosecond pulse production to the XUV/soft-X-ray regime. We find that GW-level pulses of a few femtosecond duration or shorter can be produced using electron beams of quite moderate parameters and undulators of 20-m length or shorter. The output pulse is significantly shifted in wavelength relative to the main background which permits a further increase in contrast ratio via simple monochromatization. Moreover, the output pulse has a natural wavelength chirp that allows further temporal compression, if wanted. Both positive and negative chirps can be produced depending upon the sign of the undulator taper.

Reply to “Comment on `Uniformization of the transverse beam profile by means of nonlinear focusing method’”

In order to clarify the difference of outcomes between our recent work [Y. Yuri et al., Phys. Rev. ST Accel. Beams 10, 104001 (2007)] and the work done by Los Alamos National Laboratory in the 1990s outlined in the Comment [R. E. Shafer, Phys. Rev. ST Accel. Beams 11, 039001 (2008)], we briefly summarize the former progress of the research and development on beam uniformization by means of the nonlinear focusing method, and insist on the newness of our recent publication in this Reply.

Comment on “Uniformization of the transverse beam profile by means of nonlinear focusing method”

This Comment presents unpublished and published work done by Los Alamos National Laboratory (LANL) in the period 1990 to 1999 using the nonlinear focusing method outlined in the recent publication by Yuri et al. [Phys. Rev. ST Accel. Beams 10, 104001 (2007)]. The LANL work included theory, design, modeling, and testing of nonlinear focusing beam ``expanders'' for use with high energy proton beams, including the proposed 1.7-GeV, 100-mA cw proton Accelerator for the Production of Tritium (APT). For several reasons listed in the text, the APT nonlinear focusing beam expander design was replaced with a high-frequency beam raster system.

Adiabatic thermal equilibrium theory for periodically focused axisymmetric intense beam propagation

An adiabatic equilibrium theory is presented for an intense, axisymmetric charged-particle beam propagating through a periodic solenoidal focusing field. The thermal beam distribution function is constructed based on the approximate and exact invariants of motion, i.e., a scaled transverse Hamiltonian and the angular momentum. The approximation of the scaled transverse Hamiltonian as an invariant of motion is validated analytically for highly emittance-dominated beams and highly space-charge-dominated beams, and numerically tested to be valid for cases in between with moderate vacuum phase advances (σv&amp;lt;90°). The beam root-mean-square (rms) envelope equation is derived, and the self-consistent nonuniform density profile is determined. Other statistical properties such as flow velocity, temperature, total emittance and rms thermal emittance, equation of state, and Debye length are discussed. Numerical examples are presented, illustrating the effects of the beam perveance, emittance, and rotation on the beam envelope and density distribution. Good agreement is found between theory and a recent high-intensity beam experiment performed at the University of Maryland Electron Ring [S. Bernal, B. Quinn, M. Reiser, and P. G. O’Shea, Phys. Rev. ST Accel. Beams 5, 064202 (2002)].

Erratum: Beam emittance measurement with laser wire scanners in the International Linear Collider beam delivery system [Phys. Rev. ST Accel. Beams10, 112801 (2007)

Accurate measurement of the beam phase-space is essential for the next generation of electron accelerators. A scheme for beam optics optimization and beam matrix reconstruction algorithms for the diagnostics section of the beam delivery system of the International Linear Collider based on laser-wire beam profile monitors are discussed. Possible modes of operation of the laser-wire system together with their corresponding performance are presented. Based on these results, prospects for reconstructing the ILC beam emittance from representative laser-wire beam size measurements are evaluated.

Erratum: Self-consistent time dependent two dimensional and three dimensional space charge distributions with linear force [Phys. Rev. ST Accel. Beams6, 094202 (2003)

Received 7 January 2008DOI:https://doi.org/10.1103/PhysRevSTAB.11.019901This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Study of the biased-disc effect using Langmuir-probes inserted in the hot region of the electron cyclotron resonance ion source (ECRIS) plasma

The plasma potential and its distribution play an important role in the highly-charged ion production and it is an important parameter of the electron cyclotron resonance (ECR) plasma. Emitting probes have been successfully used to determine plasma potential distributions in many plasma machines. In the framework of the ATOMKI–ECRIS plasma diagnostics research project, plasma-induced emitting probe was developed. It was proved that in certain conditions such probes could be reliably used without being damaged and without disturbing the plasma. Important observations were made related to the biased-disc effect. In favor of establishing the method of emitting probe usage in ECR plasma, dedicated experiments were performed at the NIRS–Kei2 all permanent compact ECR ion source. Based on the experiences gained after the NIRS experiments, the ATOMKI plasma-induced probe measurements could be interpreted. It was shown that biasing the Disc electrode negatively with respect to the source potential, the plasma potential measured on the resonant zone decreased, while the well-known ion beam current increase was obtained. This result proves the previous assumption [K.E. Stiebing, O. Hohn, S. Runkel, L. Schmidt, H. Schmidt-Böcking, V. Mironov, G. Shirkov, Phys. Rev. ST Accel. Beams 2 (1999) 123501], that the biased-disc changes the plasma potential distribution creating favorable conditions for ion beam extraction.

Beam–beam dynamics in an electron–ion collider with detector-integrated dipole

To maximize luminosity in a collider, low- β quadrupoles need to be installed as close as possible to the interaction point (IP), where beams are focussed to small spot sizes. In an asymmetric collider such as an asymmetric B-factory [An Asymmetric B Factory Based on PEP: Conceptual Design Report, SLAC-0372 [1]; KEKB B-Factory Design Report, KEK Report 95-7 [2]] or an electron–ion collider [Hera—A Proposal for a Large Electron Proton Colliding Beam Facility at DESY, DESY HERA 81-10 [3]; M. Farkhondeh, V. Ptitsyn (Eds.), eRHIC Zeroth Order Design Report, BNL Note C-A/AP/142; L. Merminga, Y. Derbenev, ELIC: an electron-light ion collider at CEBAF, ICFA Beam Dynamics Newsletter No. 30, 2003, p. 22; J.B. Dainton, M. Klein, P. Newman, E. Perez, F. Willeke, Deep Inelastic Electron–Nucleon Scattering at the LHC, DESY 06-006, and Cockcroft-06-04], beams of different energy are brought into collision at the IP. The energy difference requires separate focusing systems for the two beams. Placing regular separator dipoles between the IP and the focussing system either reduces the available space for the detector and therefore the detector acceptance or forces the low- β quads to be placed further away from the IP, resulting in reduced luminosity. Combining the separation and focusing functions of the innermost elements by using off-center quadrupoles and/or additional dipole coils on superconducting low- β quadrupoles ameliorates the problem somewhat. However, even in this case the separation occurs rather far away from the interaction point, leading to a large width of the synchrotron radiation fan generated by the deflection of the lower-energy electron or positron beam. To overcome these limitations in the eRHIC design, we have proposed integration of dipole coils in the (superconducting) detector solenoid [C. Montag, et al., Interaction region design for the electron–ion collider eRHIC, in: Proceedings of the PAC 2005, 2005], a concept that had originally been proposed for the Linear Collider detector solenoid [B. Parker, A. Seryi, Phys. Rev. ST Accel. Beams 8 (2005) 041001]. This results in a curved trajectory of the lower-energy electron beam across the interaction point, and therefore in a considerable transverse offset of the head and tail of the long ion bunches with respect to the (short) electron bunches. This paper examines beam dynamics issues arising from the collision of a long high-energy ion beam with a lower-energy electron beam on a trajectory curved by the detector-integrated dipole.

Erratum: Three-dimensional quasistatic model for high brightness beam dynamics simulation [Phys. Rev. ST Accel. Beams9, 044204 (2006)

Erratum: Three-dimensional quasistatic model for high brightness beam dynamics simulation [Phys. Rev. ST Accel. Beams<b>9</b>, 044204 (2006)

Maps for electron cloud density in Large Hadron Collider dipoles

The generation of a quasistationary electron cloud inside the beam pipe through beam-induced multipacting processes has become an area of intensive study. The analyses performed so far have been based on heavy computer simulations taking into account photoelectron production, secondary emission, electron dynamics, and space charge effects, providing a detailed description of the electroncloud evolution. Iriso and Peggs [U. Iriso and S. Peggs, Phys. Rev. ST Accel. Beams 8, 024403 (2005)] have shown that, for the typical parameters of RHIC, the bunch-to-bunch evolution of the average electron-cloud density at a point can be represented by a cubic map. Simulations based on this map formalism are orders of magnitude faster compared to those based on standard particle tracking codes. In this communication we show that the map formalism is also applicable to the case of the Large Hadron Collider (LHC), and that, in particular, it reproduces the average electron-cloud densities computed using a reference code to within 15% for general LHC bunch filling patterns. We also illustrate the dependence of the polynomial map coefficients on the physical parameters affecting the electron cloud (secondary emission yield, bunch charge, bunch spacing, etc.).