1 Permanent address: LPP JINR, Dubna 141980 Russia Abstract ν′y Under certain circumstances such ... more 1 Permanent address: LPP JINR, Dubna 141980 Russia Abstract ν′y Under certain circumstances such as large chromatic tune modulation, bunch length comparable with the betafunction, crossing at an angle or finite dispersion at the interaction points the beam-beam interaction can be a source of the synchro-betatron coupling. In the present report the effect of these factors on the p-bar stability in the Tevatron Run II configuration is considered. ν′x
In the framework of the CARE HHH European Network, we have developed a web-based dynamic accelera... more In the framework of the CARE HHH European Network, we have developed a web-based dynamic acceleratorphysics code repository. We describe the design, structure and contents of this repository, illustrate its usage, and discuss our future plans, with emphasis on code benchmarking.
The dynamic aperture at collision energy is determined primarily by the nonlinear fields of the I... more The dynamic aperture at collision energy is determined primarily by the nonlinear fields of the IR quadrupoles but is also influenced by the beam-beam interactions. We revisit the choice of the crossing angle that maximizes the dynamic aperture with an accurate modeling of the longrange interactions and use of the present values of the IR quadrupole field harmonics. A separate but related issue we address is the amplitude growth of particles in the beam halo due to the long-range interactions. 85 LHC99 Beam-beam Workshop brought to you by CORE View metadata, citation and similar papers at core.ac.uk
We discuss simulations and experiments on creating micro-bunch beams for generating narrow band T... more We discuss simulations and experiments on creating micro-bunch beams for generating narrow band THz radiation at the Fermilab Accelerator Science and Technology (FAST) facility. The low-energy electron beamline at FAST consists of a photoinjector-based RF gun, two L-band superconducting accelerating cavities, a chicane, and a beam dump. The electron bunches are lengthened with cavity phases set off-crest for better longitudinal separation and then micro-bunched with a slit-mask installed in the chicane. We carried out the experiments with 30 MeV electron beams and detected signals of the micro-bunching using a skew quadrupole magnet in the chicane. In this paper, the details of micro-bunch beam production, the detection of micro-bunching and comparison with simulations are described.
The Integrable Optics Test Accelerator (IOTA) ring is a new Fermilab facility dedicated to beam p... more The Integrable Optics Test Accelerator (IOTA) ring is a new Fermilab facility dedicated to beam physics experiments, currently operating with 150 MeV electrons. Space charge effects are expected to be significant when it operates with 2.5 MeV protons. In this contribution, we present results of a suite of validation tests of PyORBIT, a PICstyle space charge code. Single particle dynamics of quasiintegrable optics using an octupole string in IOTA is compared with MADX, and shown to be in good agreement. Requirements for the convergence of space charge computations are systematically established and when possible, tests involving space charge are compared with theoretical predictions.
X-rays have widespread applications in science. Developing compact and high-quality X-ray sources... more X-rays have widespread applications in science. Developing compact and high-quality X-ray sources, easy to disseminate, has been an on going challenge. Our group has explored the possible use of channeling radiation driven by a 50 MeV low-emittance electron beam to produce narrowband hard X-rays (photon energy from 40 keV to 140 keV). In this contribution we present the simulated X-ray spectrum including the background bremsstrahlung contribution, and optimization of the relevant electron-beam parameters required to maximize the X-ray brilliance. The results of experiments carried out at Fermilab's FAST facility – which include a 50 MeV superconducting linac and a high-brightness photoinjector – are also discussed. The average brilliance in our experiment is expected to be about one order of magnitude higher than that in previous experiments.
The Integrable Optics Test Accelerator (IOTA) at Fermilab is a small machine dedicated to a broad... more The Integrable Optics Test Accelerator (IOTA) at Fermilab is a small machine dedicated to a broad frontier accelerator physics program. An important aspect of this program is to investigate the potential benefits of the resonance free tune spread achievable with integrable optics to store and accelerate high intensity proton beams for which space charge is significant. In this context, a good understanding of proton beam emittance growth and particle loss mechanisms is essential. Assuming nominal design parameters, simulations show that for a bunched beam, the bulk of emittance growth takes place immediately following injection, typically within tens of turns. We attempt to account for this growth using a simplified RMS mismatch theory; some of its limitations and possible improvements are briefly discussed. We then compare theoretical predictions to simulations performed using the PIC code pyORBIT. Further exploring ways to mitigate emittance growth and reduce particle loss, we compare two beam matching strategies: (1) matching at the injection point (2) matching at the center of the nonlinear (octupole) insertion region where β x = β y. To observe how nonlinearity affects emittance growth and whether it dominates growth due to mismatch, we track two different distributions. Finally, we explore the potential of using octupoles in a quasi-integrable configuration to mitigate growth using a variety of initial distributions both at reduced and full intensities.
The low-energy section of the photoinjector-based electron linear accelerator at the Fermilab Acc... more The low-energy section of the photoinjector-based electron linear accelerator at the Fermilab Accelerator Science & Technology (FAST) facility was recently commissioned to an energy of 50 MeV. This linear accelerator relies primarily upon pulsed SRF acceleration and an optional bunch compressor to produce a stable beam within a large operational regime in terms of bunch charge, total average charge, bunch length, and beam energy. Various instrumentation was used to characterize fundamental properties of the electron beam including the intensity, stability, emittance, and bunch length. While much of this instrumentation was commissioned in a 20 MeV running period prior, some (including a new Martin- Puplett interferometer) was in development or pending installation at that time. All instrumentation has since been recommissioned over the wide operational range of beam energies up to 50 MeV, intensities up to 4 nC/pulse, and bunch structures from ~1 ps to more than 50 ps in length.
We study the measurement of transverse diffusion through beam echoes. We revisit earlier observat... more We study the measurement of transverse diffusion through beam echoes. We revisit earlier observations of echoes in RHIC and apply an updated theoretical model to these measurements. We consider three possible models for the diffusion coefficient and show that only one is consistent with measured echo amplitudes and pulse widths. This model allows us to parameterize the diffusion coefficients as functions of bunch charge. We demonstrate that echoes can be used to measure diffusion much quicker than present methods and could be useful to a variety of hadron synchrotrons.
This paper presents expected THz radiation spectra emitted by micro-bunched electron beams produc... more This paper presents expected THz radiation spectra emitted by micro-bunched electron beams produced using a slit-mask placed within a magnetic chicane in the FAST (Fermilab Accelerator Science and Technology) electron injector at Fermilab. Our purpose is to generate tunable narrow-band THz radiation with a simple scheme in a conventional photo-injector. Using the slit-mask in the chicane, we create a longitudinally micro-bunched beam after the chicane by transversely slicing an energy chirped electron bunch at a location with horizontal dispersion. In this paper, we discuss the theory related to the micro-bunched beam structure, the beam optics, the simulation results of the micro-bunched beam and the bunching factors. Energy radiated at THz frequencies from two sources: coherent transition radiation and from a wiggler is calculated and compared. We also discuss the results of a simple method to observe the micro-bunching on a transverse screen monitor using a skew quadrupole placed...
We study channeling radiation from electron beams with energies under 100 MeV. We introduce a phe... more We study channeling radiation from electron beams with energies under 100 MeV. We introduce a phenomenological model of dechanneling, correct non-radiative transition rates from thermal scattering, and discuss in detail the population dynamics in low order bound states. These are used to revisit the X-ray properties measured at the ELBE facility in Forschungszentrum Dresden-Rosenstock (FZDR), extract parameters for dechanneling states, and obtain satisfactory agreement with measured photon yields. The importance of rechanneling phenomena in thick crystals is emphasized. The model is then used to calculate the expected X-ray energies, linewidths and brilliance for forthcoming channeling radiation experiments at Fermilab's ASTA photoinjector.
In order to avoid the effects of long-range beam-beam interactions which produce beam blow-up and... more In order to avoid the effects of long-range beam-beam interactions which produce beam blow-up and deteriorate beam life time, a compensation scheme with current carrying wires has been proposed. Two long-range beam-beam compensators were installed in RHIC rings in 2006. The effects of the compensators have been experimentally investigated. An indication was observed that the compensators are beneficial to beam life time in measurements performed in RHIC during 2009. In this paper, we report the effects of wire compensator on beam loss and emittance for proton-proton beams at collision energy.
Simulations of beam-beam phenomena in the Tevatron and RHIC as well for the LHC are reviewed. The... more Simulations of beam-beam phenomena in the Tevatron and RHIC as well for the LHC are reviewed. The emphasis is on simulations that can be closely connected to observations. I.
Bunch compression through two chicanes will be explored in Fermilab’s new Advanced Superconductin... more Bunch compression through two chicanes will be explored in Fermilab’s new Advanced Superconducting Test Accelerator test facility. Partial compression of a 40MeV bunch and its acceleration to higher energies before full compression offers advantages in maximization of peak current and minimization of bunch length. Additional effects due to coherent synchrotron radiation (CSR) quickly become apparent at these energies and introduce nonlinearities in the longitudinal phase space that are less than optimal for acceleration to high energies. We show that two-stage compression offers several advantages in this area if the bunch is initially partially compressed to weaken the propagation of CSR distortions incurred in the first bunch compressor BC1. This results in a higher peak current that we could obtain if we sought full compression through the first chicane.
The Supper Proton-Proton Collider is a next-generation hadron collider that is now being designed... more The Supper Proton-Proton Collider is a next-generation hadron collider that is now being designed. A baseline design aims for a peak luminosity of about 1*10^35 cm^-2 s^-1. The focus of this article is the effect of beam-beam interactions which are expected to strongly influence stability in the beams. We start with a discussion of a scheme to generate the crossing angles at the interaction points while also correcting the dispersion thus created. The optics constraints on the achievable \b{eta}* were studied. Weak-strong simulations were performed to study single particle dynamics via tune footprints, frequency map analysis and dynamic aperture calculations. The long-range interactions with the smallest separations are shown to determine the dynamic aperture. Empirical scaling laws for the dependence of the dynamic aperture on the transverse separations and on the number of long-range interactions are found. A tune scan shows several alternative working points with slightly better ...
The photoinjector at the new Fermilab FAST facility will accelerate electron beams to about 50 Ge... more The photoinjector at the new Fermilab FAST facility will accelerate electron beams to about 50 GeV. After initial beam commissioning, channeling radiation experiments to generate hard X-rays will be performed. In the initial stage, low bunch charge beams will be used to keep the photon count rate low and avoid pile up in the detector. We report here on the optics solutions, the expected channaling spectrum including background from bremmstrahlung and the use of a Compton scatterer for higher bunch charge operation.
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Papers by Tanaji Sen