Showing papers in "Physical Review Special Topics-accelerators and Beams in 2005"
TL;DR: In this article, a multimode $X$-band rf pulse compression system suitable for a TeV-scale electron-positron linear collider such as the Next Linear Collider (NLC).
Abstract: We present a multimode $X$-band rf pulse compression system suitable for a TeV-scale electron-positron linear collider such as the Next Linear Collider (NLC). The NLC main linac operating frequency is 11.424 GHz. A single NLC rf unit is required to produce 400 ns pulses with 475 MW of peak power. Each rf unit should power approximately 5 m of accelerator structures. The rf unit design consists of two 75 MW klystrons and a dual-moded resonant-delay-line pulse compression system that produces a flat output pulse. The pulse compression system components are all overmoded, and most components are designed to operate with two modes. This approach allows high-power-handling capability while maintaining a compact, inexpensive system. We detail the design of this system and present experimental cold test results. We describe the design and performance of various components. The high-power testing of the system is verified using four 50 MW solenoid-focused klystrons run off a common 400 kV solid-state modulator. The system has produced 400 ns rf pulses of greater than 500 MW. We present the layout of our system, which includes a dual-moded transmission waveguide system and a dual-moded resonant line (SLED-II) pulse compression system. We also present data on the processing and operation of this system, which has set high-power records in coherent and phase controlled pulsed rf.
199 citations
TL;DR: In this paper, a dc photo-emission electron gun was used to accelerate a high brightness, high average current photoinjector under development at Cornell University, and the optimized injector was simulated to deliver beam of very high quality (e.g., a rms normalized emittance of 0.1 mm mrad for 0.5 nC, and 0.7 mm mdr for 1 nC bunches).
Abstract: We have conducted a multiobjective computational optimization of a high brightness, high average current photoinjector under development at Cornell University. This injector employs a dc photoemission electron gun. Using evolutionary algorithms combined with parallel computing resources, the multivariate parameter space of the photoinjector was explored for optimal values. This powerful computational tool allows an extensive study of complex and nonlinear systems such as the space-charge dominated regions of an accelerator, and has broad areas of potential application to accelerator physics and engineering problems. In the present case, the optimized injector is simulated to deliver beam of very high quality (e.g., a rms normalized emittance of 0.1 mm mrad for 0.1 nC, and 0.7 mm mrad for 1 nC bunches). The field strengths of the active elements of the injector are moderate and technically practical. The relevance of these results to various novel linac-based accelerator proposals is pointed out.
167 citations
TL;DR: In this paper, a focusing system using permanent magnet quadrupoles (PMQs) is reported, which achieves a field gradient of 560 T/m, the highest ever reported in a magnetic optics system, and is tuned by adjusting the position of the three magnets along the beamline axis.
Abstract: Next generation advanced-accelerators such as the plasma wake-field accelerator, and beamradiation interaction scenarios such as inverse-Compton scattering (ICS), depend on the achieving of ultra-small spot sizes in high current beams. Modern injectors and compressors enable the production of high-brightness beams having needed short bunch lengths and small emittances. Along with these beam properties comes the need to produce tighter foci, using stronger, shorter focal length optics. An approach to creating such strong focusing-systems using high field, small-bore permanent-magnet quadrupoles (PMQs) is reported here. A final focus system employing three PMQs, each composed of 16 neodymium iron boride sectors in a Halbach geometry has been installed in the PLEIADES ICS experiment. The field gradient in these PMQs is 560 T/m, the highest ever reported in a magnetic optics system. As the magnets are of a fixed field-strength, the focusing system is tuned by adjusting the position of the three magnets along the beamline axis, in analogy to familiar camera optics. This paper discusses the details of the focusing system, simulation, design, fabrication and experimental procedure in creating ultra-small beams at PLEIADES.
120 citations
TL;DR: In this paper, an energy modulation of electrons via interaction with a laser pulse in a wiggler magnet is used for a significant increase of the electron peak current prior to entering a long self-amplified spontaneous emission (SASE) free electron laser undulator.
Abstract: We describe a technique by which an energy modulation of electrons via interaction with a laser pulse in a wiggler magnet is used for a significant increase of the electron peak current prior to entering a long self-amplified spontaneous emission (SASE) free electron laser undulator. This results in a reduction of the gain length for the SASE process and a modification of the structure of the output x-ray radiation. It also temporally links the output x-ray pulse to the initial laser pulse, thus providing an opportunity for accurate synchronization between the laser pump pulse and x-ray probe pulse for pump-probe experiments.
120 citations
TL;DR: In this paper, a formulation for the characterization of superradiant and stimulated-superradiant radiative emission from bunched electron beams is presented, where the radiation is characterized in terms of power and spectral power per radiation mode.
Abstract: A formulation for the characterization of superradiant and stimulated-superradiant radiative emission from bunched electron beams is presented. The radiation is characterized in terms of power and spectral power per radiation mode, which provide a measure of the useful spatially coherent radiation power and spectral power emitted by a radiation source. When the bunched electron beam emits superradiantly, these parameters scale like the square of the number of electrons, orders of magnitude more than spontaneous emission. The formulation applies to emission from single bunches, a finite number of bunches in a macropulse, or periodic bunching. It can be employed on any kind of $e$-beam radiation scheme. Specific analytic expressions are derived for coherent synchrotron radiation and prebunched free-electron laser, providing a basis for comparing and understanding their connection.
110 citations
TL;DR: In this paper, it was shown that the Smith-Purcell free-electron laser cannot operate at the point of maximum gain at an intermediate energy, called the Bragg condition, when the group velocity of the evanescent wave vanishes and both the gain and the attenuation due to resistive losses in the grating diverge.
Abstract: It has previously been shown that the electron beam in a Smith-Purcell free-electron laser interacts with a synchronous evanescent wave. At high electron energy, the group velocity of this wave is positive and the device operates on a convective instability, in the manner of a traveling-wave tube. For operation as an oscillator, the gain must exceed the losses in the external feedback system. At low electron energy, the group velocity of the synchronous evanescent wave is negative and the device operates on an absolute instability, like a backward-wave oscillator, and no external feedback is required. For oscillation to occur, the current must exceed the so-called start current. At an intermediate energy, called the Bragg condition, the group velocity ${v}_{g}$ of the evanescent wave vanishes and both the gain and the attenuation due to resistive losses in the grating diverge. It is shown that near the Bragg condition the gain depends on ${v}_{g}^{\ensuremath{-}1/3}$, while the attenuation depends on ${v}_{g}^{\ensuremath{-}1}$. Since the attenuation increases faster than the gain near the Bragg condition, the Smith-Purcell free-electron laser cannot operate at the point of maximum gain. The effects of resistive losses become increasingly important as Smith-Purcell free-electron lasers move to shorter wavelengths.
110 citations
TL;DR: In this article, the peak brightness of head-on collisions is derived for femto-cond laser systems and found to scale quadratically with the normalized energy, inversely with the electron beam duration, and the square of its normalized emittance.
Abstract: No monochromatic ($\ensuremath{\Delta}{\ensuremath{\omega}}_{x}/{\ensuremath{\omega}}_{x}l1%$), high peak brightness [$g{10}^{20}\text{ }\mathrm{photons}/(\mathrm{m}{\mathrm{m}}^{2}\ifmmode\times\else\texttimes\fi{}{\mathrm{mrad}}^{2}\ifmmode\times\else\texttimes\fi{}\mathrm{s}\ifmmode\times\else\texttimes\fi{}0.1%\text{ }\mathrm{bandwidth})$], tunable light sources currently exist above 100 keV. Important applications that would benefit from such new hard x-ray and $\ensuremath{\gamma}$-ray sources include the following: nuclear resonance fluorescence spectroscopy and isotopic imaging, time-resolved positron annihilation spectroscopy, and MeV flash radiography. In this paper, the peak brightness of Compton scattering light sources is derived for head-on collisions and found to scale quadratically with the normalized energy, $\ensuremath{\gamma}$; inversely with the electron beam duration, $\ensuremath{\Delta}\ensuremath{\tau}$, and the square of its normalized emittance, $\ensuremath{\epsilon}$; and linearly with the bunch charge, $e{N}_{e}$, and the number of photons in the laser pulse, ${N}_{\ensuremath{\gamma}}\mathrm{\text{:}}\text{ }{\stackrel{^}{B}}_{x}\ensuremath{\propto}{\ensuremath{\gamma}}^{2}{N}_{e}{N}_{\ensuremath{\gamma}}/{\ensuremath{\epsilon}}^{2}\ensuremath{\Delta}\ensuremath{\tau}$. This ${\ensuremath{\gamma}}^{2}$ scaling shows that for low normalized emittance electron beams (1 nC, $1\text{ }\text{ }\mathrm{mm}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{mrad}$, $l1\text{ }\text{ }\mathrm{ps}$, $g100\text{ }\text{ }\mathrm{MeV}$), and tabletop laser systems ($1--10\text{ }\mathrm{J}$, 5 ps) the x-ray peak brightness can exceed ${10}^{23}\text{ }\mathrm{photons}/(\mathrm{m}{\mathrm{m}}^{2}\ifmmode\times\else\texttimes\fi{}{\mathrm{mrad}}^{2}\ifmmode\times\else\texttimes\fi{}\mathrm{s}\ifmmode\times\else\texttimes\fi{}0.1%\text{ }\mathrm{bandwidth})$ near $\ensuremath{\hbar}{\ensuremath{\omega}}_{x}=1\text{ }\mathrm{MeV}$; this is confirmed by three-dimensional codes that have been benchmarked against Compton scattering experiments performed at Lawrence Livermore National Laboratory. The interaction geometry under consideration is head-on collisions, where the x-ray flash duration is shown to be equal to that of the electron bunch, and which produce the highest peak brightness for compressed electron beams. Important nonlinear effects, including spectral broadening, are also taken into account in our analysis; they show that there is an optimum laser pulse duration in this geometry, of the order of a few picoseconds, in sharp contrast with the initial approach to laser-driven Compton scattering sources where femtosecond laser systems were thought to be mandatory. The analytical expression for the peak on-axis brightness derived here is a powerful tool to efficiently explore the 12-dimensional parameter space corresponding to the phase spaces of both the electron and incident laser beams and to determine optimum conditions for producing high-brightness x rays.
93 citations
TL;DR: In this article, a series of experiments designed to measure the flashover strength of various azimuthally symmetric $45\ifmmode^\circ\else\text degree\fi{}$ vacuum-insulator configurations was conducted.
Abstract: We have conducted a series of experiments designed to measure the flashover strength of various azimuthally symmetric $45\ifmmode^\circ\else\textdegree\fi{}$ vacuum-insulator configurations. The principal objective of the experiments was to identify a configuration with a flashover strength greater than that of the standard design, which consists of a $45\ifmmode^\circ\else\textdegree\fi{}$ polymethyl-methacrylate (PMMA) insulator between flat electrodes. The thickness $d$ and circumference $C$ of the insulators tested were held constant at 4.318 and 95.74 cm, respectively. The peak voltage applied to the insulators ranged from 0.8 to 2.2 MV. The rise time of the voltage pulse was 40--60 ns; the effective pulse width [as defined in Phys. Rev. ST Accel. Beams 7, 070401 (2004)] was on the order of 10 ns. Experiments conducted with flat aluminum electrodes demonstrate that the flashover strength of a crosslinked polystyrene (Rexolite) insulator is $(18\ifmmode\pm\else\textpm\fi{}7)%$ higher than that of PMMA. Experiments conducted with a Rexolite insulator and an anode plug, i.e., an extension of the anode into the insulator, demonstrate that a plug can increase the flashover strength by an additional $(44\ifmmode\pm\else\textpm\fi{}11)%$. The results are consistent with the Anderson model of anode-initiated flashover, and confirm previous measurements. It appears that a Rexolite insulator with an anode plug can, in principle, increase the peak electromagnetic power that can be transmitted across a vacuum interface by a factor of $[(1.18)(1.44){]}^{2}=2.9$ over that which can be achieved with the standard design.
90 citations
TL;DR: In this paper, a self-amplified spontaneous emission (SSE) was used for the generation of a single attosecond X-ray pulse in a free electron laser.
Abstract: We describe a technique for the generation of a solitary attosecond X-ray pulse in a free electron laser (FEL), via a process of self-amplified spontaneous emission. In this method, electrons experience an energy modulation upon interacting with laser pulses having a duration of a few cycles within single-period wiggler magnets. Two consecutive modulation sections, followed by compression in a dispersive section, are used to obtain a single, sub-femtosecond spike in the electron peak current. This region of the electron beam experiences an enhanced growth rate for FEL amplification. After propagation through a long undulator,this current spike emits a {approx}250 attosecond X-ray pulse whose intensity dominates the X-ray emission from the rest of the electron bunch.
82 citations
TL;DR: Velocity bunching has been recently proposed as a tool for compressing electron beam pulses in modern high brightness photoinjector sources as discussed by the authors, which can be naturally considered as an extension of the emittance compensation process at moderate energies.
Abstract: Velocity bunching has been recently proposed as a tool for compressing electron beam pulses in modern high brightness photoinjector sources. This tool is familiar from earlier schemes implemented for bunching dc electron sources, but presents peculiar challenges when applied to high current, low emittance beams from photoinjectors. The main difficulty foreseen is control of emittance oscillations in the beam in this scheme, which can be naturally considered as an extension of the emittance compensation process at moderate energies. This paper presents two scenarios in which velocity bunching, combined with emittance control, is to play a role in nascent projects. The first is termed ballistic bunching, where the changing of relative particle velocities and positions occur in distinct regions, a short high gradient linac, and a drift length. This scenario is discussed in the context of the proposed ORION photoinjector. Simulations are used to explore the relationship between the degree of bunching, and the emittance compensation process. Experimental measurements performed at the UCLA Neptune Laboratory of the surprisingly robust bunching process, as well as accompanying deleterious transverse effects, are presented. An unanticipated mechanism for emittance growth in bends for highly momentum chirped beam was identified and studied in these experiments. The second scenario may be designated as phase space rotation, and corresponds closely to the recent proposal of Ferrario and Serafini. Its implementation for the compression of the electron beam pulse length in the PLEIADES inverse Compton scattering (ICS) experiment at LLNL is discussed. It is shown in simulations that optimum compression may be obtained by manipulation of the phases in low gradient traveling wave accelerator sections. Measurements of the bunching and emittance control achieved in such an implementation at PLEIADES, as well as aspects of the use of velocity-bunched beam directly in ICS experiments, are presented.
80 citations
TL;DR: In this paper, the authors proposed a two-level economical conservative scheme for electromagnetic field calculations in three dimensions, which does not have dispersion in the longitudinal direction and is staircase-free (second order convergent).
Abstract: The Yee finite-difference time domain method (FDTD) is commonly used in wake field and particle-in-cell simulations. However, in accelerator modeling the high energy particles can travel in vacuum faster than their own radiation. This effect is commonly referred to as numerical Cherenkov radiation and is a consequence of numerical grid dispersion. Several numerical approaches are proposed to reduce the dispersion for all angles and for a given frequency range, that justifies itself for domains big in all three directions. On the contrary, in accelerator modeling the transverse dimensions and transverse beam velocity are small, but it is extremely important to eliminate the dispersion error in the well-defined direction of the beam motion for all frequencies. In this paper we propose a new two-level economical conservative scheme for electromagnetic field calculations in three dimensions. The scheme does not have dispersion in the longitudinal direction and is staircase-free (second order convergent). Unlike the FDTD method, it is based on a ``transversal-electric/transversal-magnetic'' (TE/TM)-like splitting of the field components in time. The scheme assures energy and charge conservation. Additionally, the usage of damping terms allows suppressing high frequency noise generated due to the transverse dispersion and the current fluctuations. The dispersion relation of the damping scheme is analyzed. As numerical examples show, the new scheme is much more accurate on the long-time scale than the conventional FDTD approach.
TL;DR: In this paper, a special magnetic channel designed such that higher momentum corresponds to a longer path length, and therefore larger ionization energy loss, provides the desired emittance exchange in a homogeneous absorber without special edge shaping.
Abstract: The fast reduction of the six-dimensional phase space of muon beams is an essential requirement for muon colliders and also of great importance for neutrino factories based on accelerated muon beams. Ionization cooling, where all momentum components are degraded by an energy absorbing material and only the longitudinal momentum is restored by rf cavities, provides a means to quickly reduce transverse beam sizes. However, the beam energy spread cannot be reduced by this method unless the longitudinal emittance can be transformed or exchanged into the transverse emittance. Emittance exchange plans until now have been accomplished by using magnets to disperse the beam along the face of a wedge-shaped absorber such that higher momentum particles pass through thicker parts of the absorber and thus suffer larger ionization energy loss. In the scheme advocated in this paper, a special magnetic channel designed such that higher momentum corresponds to a longer path length, and therefore larger ionization energy loss, provides the desired emittance exchange in a homogeneous absorber without special edge shaping. Normal-conducting rf cavities imbedded in the magnetic field regenerate the energy lost in the absorber. One very attractive example of a cooling channel based on this principle uses a series of high-gradient rf cavities filled with dense hydrogen gas, where the cavities are in a magnetic channel composed of a solenoidal field with superimposed helical transverse dipole and quadrupole fields. In this scheme, the energy loss, the rf energy regeneration, the emittance exchange, and the transverse cooling happen simultaneously. The theory of this helical channel is described in some detail to support the analytical prediction of almost a factor of ${10}^{6}$ reduction in six-dimensional phase space volume in a channel about 56 m long. Equations describing the particle beam dynamics are derived and beam stability conditions are explored. Equations describing six-dimensional cooling in this channel are also derived, including explicit expressions for cooling decrements and equilibrium emittances.
TL;DR: In this paper, the authors measured the effects of high magnetic fields on the operating conditions of 805 MHz accelerating cavities, and discovered that the maximum accelerating gradient drops as a function of the axial magnetic field.
Abstract: We have measured the effects of high (0--4.5 T) magnetic fields on the operating conditions of 805 MHz accelerating cavities, and discovered that the maximum accelerating gradient drops as a function of the axial magnetic field. While the maximum gradient of any cavity is governed by a number of factors including conditioning, surface topology and materials, we argue that $\mathbf{J}\ifmmode\times\else\texttimes\fi{}\mathbf{B}$ forces within the emitters are the mechanism for enhanced breakdown in magnetic fields. The pattern of emitters changes over time and we show an example of a bright emitter which disappears during a breakdown event. We also present unique measurements of the distribution of enhancement factors, $\ensuremath{\beta}$, of secondary emitters produced in breakdown events during conditioning. We believe these secondary emitters can also be breakdown triggers, and the secondary emitter spectrum helps to determine the maximum operating field.
TL;DR: In this article, a simulation of the generation of Smith-Purcell (SP) radiation at microwave frequencies is performed using the two-dimensional particle-in-cell code MAGIC.
Abstract: A simulation of the generation of Smith-Purcell (SP) radiation at microwave frequencies is performed using the two-dimensional particle-in-cell code MAGIC. The simulation supposes that a continuous, thin (but infinitely wide), monoenergetic electron beam passes over a diffraction grating, while a strong axial magnetic field constrains the electrons to essentially one-dimensional motion. The code computes the time-dependent electric and magnetic fields by solving the Maxwell equations using a finite element approach. We find that the passage of the beam excites an evanescent electromagnetic wave in the proximity of the grating, which in turn leads to bunching of the initially continuous electron beam. The frequency and wave number of the bunching are determined, and found to be close to those proposed by Brau and co-workers in recent work. This frequency is below the threshold for SP radiation. However, the bunching is sufficiently strong that higher harmonics are clearly visible in the beam current. These harmonic frequencies correspond to allowed SP radiation, and we see strong emission of such radiation at the appropriate angles in our simulation, again in agreement with Brau's predictions. We also find that at the ends of the grating, some of the evanescent wave is diffracted away from the surface, and radiation below the threshold occurs. In addition, we observe a second evanescent wave at the same frequency, but with a different wave number. The existence of this wave is also predicted by the theory, although its presence in our simulation is unexpected. Numerical estimates of the growth of the evanescent wave are also in reasonable agreement with the predictions, although the precise form of the dependence of the gain on beam current remains hard to establish.
TL;DR: The Tevatron in Collider Run II (2001-present) is operating with 6 times more bunches, many times higher beam intensities and luminosities than in Run I (1992-1995) as discussed by the authors.
Abstract: The Tevatron in Collider Run II (2001-present) is operating with 6 times more bunches, many times higher beam intensities and luminosities than in Run I (1992-1995). Electromagnetic long-range and head-on interactions of high intensity proton and antiproton beams have been significant sources of beam loss and lifetime limitations. We present observations of the beam-beam phenomena in the Tevatron and results of relevant beam studies. We analyze the data and various methods employed in operations, predict the performance for planned luminosity upgrades, and discuss ways to improve it.
TL;DR: In this article, the most desirable characteristics of thermionic-cathode and photocathode rf guns were combined for high-voltage electron microscopy, precision electron-beam welding, and long-wavelength (THz) radiation generation.
Abstract: We present a novel method of combining the most desirable characteristics of thermionic-cathode and photocathode rf guns, using a field-emission cathode and multiple rf frequencies. Simulations indicate that extremely low-emittance beams (on the order of 2 nm normalized emittance) at moderate beam currents (1 mA) and beam energies of $\ensuremath{\sim}2\text{ }\text{ }\mathrm{MeV}$ can be obtained using this technique. The resulting gun design promises to be useful as a driver source for a number of applications, including high-voltage electron microscopy, precision electron-beam welding, and long-wavelength (THz) radiation generation; we include performance calculations for the electron microscopy and precision welding applications.
TL;DR: In this paper, the use of sextupole magnets to correct nonlinearities in the longitudinal phase space transformation of a relativistic beam of charged particles in a dispersionless translating section, or dogleg, was examined.
Abstract: 1098-4402= We examine the use of sextupole magnets to correct nonlinearities in the longitudinal phase space transformation of a relativistic beam of charged particles in a dispersionless translating section, or dogleg Through heuristic analytical arguments and examples derived from recent experimental efforts, augmented by simulations using the particle tracking codes PARMELA and ELEGANT, sextupole corrections are found to be effective in optimizing the use of such structures for beam compression or for shaping the current profile of the beam, by manipulation of the second-order longitudinal dispersion Recent experimental evidence of the use of sextupoles to manipulate second-order horizontal and longitudinal dispersion of the beam is presented The theoretical and experimental results indicate that these manipulations can be used to create an electron bunch with a current profile having a long ramp followed by a sharp cutoff, which is optimal for driving large-amplitude wake fields in a plasma wake field accelerator
TL;DR: In this paper, the Smith-Purcell (SP) radiation was computed in three dimensions, including the effects of finite grating length and superradiance due to periodic electron bunching at an arbitrary frequency.
Abstract: Smith-Purcell (SP) radiation is emitted when an electron passes close to the surface of a metallic grating. The radiation becomes coherent (fluence proportional to the square of the number of electrons) when the electrons are in bunches whose dimensions are smaller than the wavelength of the radiation. This has been observed in experiments in which the electrons are prebunched by an rf linac. The enhancement of the spectral intensity is accompanied by large changes in the angular and spectral distribution of the radiation when the electrons appear in periodic bunches. This is called superradiance. Recently, superradiant SP radiation has been observed from a so-called Smith-Purcell free-electron laser (SP-FEL) in which the electrons are bunched by the lasing process. As in other slow-wave structures, the electron beam in a SP-FEL interacts with an evanescent wave for which the phase velocity matches the electron velocity and amplifies it. The frequency of this wave lies below the range of SP radiation and the wave is not radiated except from the ends of the grating. However, the bunching of the electrons by the interaction with the evanescent wave enhances the ordinary Smith-Purcell radiation and changes the angular and spectral distribution due to superradiant effects. In this article, we introduce a new method for computing the SP radiation in three dimensions, including the effects of finite grating length and superradiance due to periodic electron bunching at an arbitrary frequency. We show that the SP radiation develops spectrally and angularly narrow peaks at the harmonics of the bunching frequency. In rf linacs, where the bunches are widely spaced, several closely spaced harmonics lie under the spectral envelope of the emission from a single electron. In a SP-FEL the harmonics are widely spaced and the SP radiation appears in narrow cones at the SP angles corresponding to the harmonics of the bunching frequency. Finally, we calculate the angular spectral fluence radiated by an electron passing over a lamellar grating of finite length, examine its coherent enhancement in SP-FELs and rf linacs, and compare the results with numerical simulations and available experimental data.
TL;DR: In this article, the authors present detailed simulations and analysis of Zholents's concept for using deflecting cavities in a synchrotron light source storage ring for the purpose of producing short x-ray pulses.
Abstract: We present detailed simulations and analysis of Zholents’s [A. Zholents, P. Heimann, M. Zolotorev, and J. Byrd, Nucl. Instrum. Methods Phys. Res., Sect. A 425, 385 (1999).] concept for using deflecting cavities in a synchrotron light source storage ring for the purpose of producing short x-ray pulses. In particular, we look at the optimization and performance of such a system for the Advanced Photon Source. We find the concept is practical and that x-ray pulse durations of about 1.5 ps FWHM should be achievable with more than 15% of the original intensity retained. Issues covered include lattice design, emittance degradation, lifetime, photon beam modeling, errors, and optimum choice of rf parameters.
TL;DR: In this article, an asymmetric solenoid lens concept for transforming the circular beam from a high-perveance electron gun to a planar configuration was described, and the first experimental demonstration of this lens was performed at Los Alamos National Laboratory.
Abstract: Currently ongoing at Los Alamos National Laboratory is a program to develop high-power, planar 100--300 GHz traveling-wave tubes. A necessary part of this effort is a sheet electron beam source. Previously, we have described a novel asymmetric solenoid lens concept for transforming the circular beam from a high-perveance electron gun to a planar configuration. The lens is a standard electromagnetic solenoid with elliptical, instead of circular, pole apertures. The elliptical pole openings result in asymmetric focusing, which in turn forms an elliptical sheet beam suitable for our planar structures. Here we report the first experimental demonstration of this lens.
TL;DR: In this article, the authors derived completely integrated formulas for emittance growth times due to intrabeam scattering for charged particle beams in the high energy limit, including the effect of lattice parameters that vary around the accelerator ring.
Abstract: We derive completely integrated formulas for emittance growth times due to intrabeam scattering for charged particle beams in the high energy limit, including the effect of lattice parameters that vary around the accelerator ring. Using accelerator lattices for the prototype damping ring called the Accelerator Test Facility at KEK and those for two proposed International Linear Collider damping rings, we compare our results with other calculations.
TL;DR: In this paper, the symmetric elliptic integral (SILI) was used to express the small-angle multiple intrabeam scattering (IBS) growth rate for a smooth-lattice approximation.
Abstract: Small-angle multiple intrabeam scattering (IBS) emittance growth rates are normally expressed through integrals, which require a numeric evaluation at various locations of the accelerator lattice. In this paper, I demonstrate that the IBS growth rates can be presented in closed-form expressions with the help of the so-called symmetric elliptic integral. This integral can be evaluated numerically by a very efficient recursive method by employing the duplication theorem. Several examples of IBS rates for a smooth-lattice approximation, equal transverse temperatures and plasma temperature relaxation are given.
TL;DR: In this paper, independent component analysis (ICA) is applied to analyze the beam motion in a rapid-cycling booster synchrotron at the Fermilab in order to decompose sampled signals into its underlying source signals.
Abstract: Autocorrelation is applied to analyze sets of finite-sampling data such as the turn-by-turn beam position monitor (BPM) data in an accelerator. This method of data analysis, called the independent component analysis (ICA), is shown to be a powerful beam diagnosis tool for being able to decompose sampled signals into its underlying source signals. We find that the ICA has an advantage over the principle component analysis (PCA) used in the model-independent analysis (MIA) in isolating independent modes. The tolerance of the ICA method to noise in the BPM system is systematically studied. The ICA is applied to analyze the complicated beam motion in a rapid-cycling booster synchrotron at the Fermilab. Difficulties and limitations of the ICA method are also discussed.
TL;DR: In this paper, an ionization cooling ring with realistic three-dimensional fields was used for neutrino factory or muon collider designs. The performance of the ring compared favorably with the linear cooling channel used in the second U.S. Neutrino Factory Study.
Abstract: Practical ionization cooling rings could lead to lower cost or improved performance in neutrino factory or muon collider designs. The ring modeled here uses realistic three-dimensional fields. The performance of the ring compares favorably with the linear cooling channel used in the second U.S. Neutrino Factory Study. The normalized 6D emittance of an ideal ring is decreased by a factor of approximately 240, compared with a factor of only 15 for the linear channel. We also examine such real-world effects as windows on the absorbers and rf cavities and leaving empty lattice cells for injection and extraction. For realistic conditions the ring decreases the normalized 6D emittance by a factor of 49.
TL;DR: In this paper, a detailed analytical study of plasma wakefield generation in a wide parabolic plasma channel is reported, where a perturbative technique involving orders of the incident laser beam and the effects of inhomogeneity of the plasma density is used to obtain explicit electric as well as magnetic wakefields.
Abstract: 1098-4402= A detailed analytical study of plasma wakefield generation in a wide parabolic plasma channel is reported. A perturbative technique involving orders of the incident laser beam and the effects of inhomogeneity of the plasma density is used to obtain explicit electric as well as magnetic wakefields. The axial and transverse forces acting on a test electron due to the wakefields have been evaluated.
TL;DR: Recently, resonance driving terms were successfully measured in the CERN SPS and the BNL RHIC from the Fourier spectrum of beam position monitor (BPM) data, and a new analysis has been derived to extract truly local observables from BPM data as discussed by the authors.
Abstract: Recently, resonance driving terms were successfully measured in the CERN SPS and the BNL RHIC from the Fourier spectrum of beam position monitor (BPM) data. Based on these measurements a new analysis has been derived to extract truly local observables from BPM data. These local observables are called local resonance terms since they share some similarities with the global resonance terms. In this paper we derive these local terms analytically and present experimental measurements of sextupolar global and local resonance terms in RHIC. Nondestructive measurements of these terms using ac dipoles are also presented.
TL;DR: In this paper, the formulation of superradiant and stimulated-superradiant (ST-SR) radiative emission processes in prebunched electron-beam coherent radiation sources was derived.
Abstract: In a companion article (part I, Ref. [1]), the formulation of superradiant (SR) and stimulated-superradiant (ST-SR) radiative emission processes in prebunched electron-beam coherent radiation sources was derived. Special attention was given to the understanding and comparison between the prebunched beam (PB-FEL) [2 ‐14] and the coherent synchrotron radiation (CSR) radiation sources [15]. The main results of the formulation are general expressions for the characteristic optical parameters of radiation emitted by the two different coherent emission processes of SR and ST-SR emission. Choosing to characterize the optical radiation in terms of discrete transverse (free space or waveguide) radiation modes, the coherence optical properties of SR and ST-SR emission are described in terms of the spectral energy emission per mode. The generic expressions of these parameters for any e-beam radiation scheme are � dW q d!
TL;DR: In this paper, the photonic band gap (PBG) resonators and traveling-wave accelerator structures were designed and tested at Ku-band (17.140 GHz) and 11 GHz, respectively.
Abstract: We present the detailed description of the successful design and cold test of photonic band gap (PBG) resonators and traveling-wave accelerator structures. Those tests provided the essential basis for later hot test demonstration of the first PBG accelerator structure at 17.140 GHz [E. I. Smirnova, A. S. Kesar, I. Mastovsky, M. A. Shapiro, and R. J. Temkin, Phys. Rev. Lett., 95, 074801 (2005).]. The advantage of PBG resonators is that they were built to support only the main, ${\mathrm{TM}}_{01}$-like, accelerator mode while not confining the higher-order modes (HOM) or wakefields. The design of the PBG resonators was based on a triangular lattice of rods, with a missing rod at the center. Following theoretical analysis, the rod radius divided by the rod spacing was held to a value of about 0.15 to avoid supporting HOM. For a single-cell test the PBG structure was fabricated in X-band (11 GHz) and brazed. The mode spectrum and $Q$ factor ($Q=5\text{ }000$) agreed well with theory. Excellent HOM suppression was evident from the cold test. A six-cell copper PBG accelerator traveling-wave structure with reduced long-range wakefields was designed and was built by electroforming at Ku-band (17.140 GHz). The structure was tuned by etching the rods. Cold test of the structure yielded excellent agreement with the theoretical design. Successful results of the hot test of the structure demonstrating the acceleration of the electron beam were published in E. I. Smirnova, A. S. Kesar, I. Mastovsky, M. A. Shapiro, and R. J. Temkin, Phys. Rev. Lett., 95, 074801 (2005).
TL;DR: In this paper, the adiabaticity of the ramping process of an ac dipole as a function of the different parameters involved is studied. But the authors focus on the acceleration of the dipole.
Abstract: ac dipoles in accelerators are used to excite coherent betatron oscillations at a drive frequency close to the tune. If the excitation amplitude is slowly increased to the desired value and slowly decreased back to zero there is no significant emittance growth. The aim of this article is to study the adiabaticity of the ramping process of an ac dipole as a function of the different parameters involved.
TL;DR: In this paper, the energy modulation of 1.7-GeV electrons by femtosecond laser pulses was studied at the BESSY II ''femtoslicing'' source, a facility commissioned in 2004 for the purpose of producing sub-100 fs x-ray pulses.
Abstract: The energy modulation of 1.7-GeV electrons by femtosecond laser pulses was studied at the BESSY II ``femtoslicing'' source, a facility commissioned in 2004 for the purpose of producing sub-100 fs x-ray pulses. As a test case for future seeded free-electron lasers, the laser-electron interaction was investigated as function of various laser and electron beam parameters using different experimental methods.