Tanaji Sen
Fermilab, Accelerator Physics Center, Department Member
- Accelerator physicistedit
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... 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
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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... 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.
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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... 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.
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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... 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.
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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... 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.
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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... 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.
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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... 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...
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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... 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 deteriorate beam life time, a compensation scheme with current carrying wires has been proposed. Two long-range beam-beam compensators were... 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.
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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 Superconducting Test Accelerator test facility. Partial compression of a 40MeV bunch and its acceleration to higher energies before full compression offers... 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. 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... 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 ...
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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... 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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We discuss the generation of parametric X-rays (PXR) in the photoinjector at the new FAST facility at Fermilab. Detailed calculations of the intensity spectrum, energy and angular widths and spectral brilliance with a diamond crystal are... more
We discuss the generation of parametric X-rays (PXR) in the photoinjector at the new FAST facility at Fermilab. Detailed calculations of the intensity spectrum, energy and angular widths and spectral brilliance with a diamond crystal are presented. We also report on expected results with PXR generated while the beam is channeling. The low emittance electron beam makes this facility a promising source for creating brilliant X-rays.
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Long-range as well as head-on beam-beam effects are expected to limit the LHC performance with design parameters. They are are also important consideration for the LHC upgrades. To mitigate long-range effects, current carrying wires... more
Long-range as well as head-on beam-beam effects are expected to limit the LHC performance with design parameters. They are are also important consideration for the LHC upgrades. To mitigate long-range effects, current carrying wires parallel to the beam were proposed. Two such wires are installed in RHIC where they allow studying the effect of strong long-range beam-beam effects, as well
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We study channeling radiation from electron beams with energies under 100 MeV. We introduce a phenomenological model of dechanneling, correct nonradiative transition rates from thermal scattering, and discuss in detail the population... more
We study channeling radiation from electron beams with energies under 100 MeV. We introduce a phenomenological model of dechanneling, correct nonradiative 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.
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We present semi-analytical methods for calculating the electromagnetic field in dipole and quadrupole stripline kickers with curved plates of infinitesimal thickness. Two different methods are used to solve Laplace's equation by... more
We present semi-analytical methods for calculating the electromagnetic field in dipole and quadrupole stripline kickers with curved plates of infinitesimal thickness. Two different methods are used to solve Laplace's equation by reducing it either to a single or to two coupled matrix equations; they are shown to yield equivalent results. Approximate analytic solutions for the lowest order fields (dipole or quadrupole) are presented and their useful range of validity are shown. The kickers plates define a set of coupled transmission lines and the characteristic impedances of modes relevant to each configuration are calculated. The solutions are compared with those obtained from a finite element solver and found to be in good agreement. Mode matching to an external impedance determines the kicker geometry and this is discussed for both kicker types. We show that a heuristic scaling law can be used to determine the dependence of the characteristic impedance on plate thickness. The ...
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We discuss the generation of parametric X-rays in the new photoinjector at the FAST (Fermilab Accelerator Science and Technology) facility in Fermilab. These experiments will be conducted in addition to channeling X-ray radiation... more
We discuss the generation of parametric X-rays in the new photoinjector at the FAST (Fermilab Accelerator Science and Technology) facility in Fermilab. These experiments will be conducted in addition to channeling X-ray radiation experiments. The low emittance electron beam makes this facility a promising source for creating brilliant X-rays. We discuss the theoretical model and present detailed calculations of the intensity spectrum, energy and angular widths and spectral brilliance under different conditions. Furthermore, we report on expected results with parametric X-rays generated while under channeling conditions.
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This report summarizes studies of long-range collisions and their compensation by current carrying wires for the Tevatron Run-II, which were performed during a two-week stay at Fermilab, February 22 to March 8, 2004. The weak-strong code... more
This report summarizes studies of long-range collisions and their compensation by current carrying wires for the Tevatron Run-II, which were performed during a two-week stay at Fermilab, February 22 to March 8, 2004. The weak-strong code WSDIFF was significantly extended to simulate the actual long-range encounters at the Tevatron for different antiproton bunches in the train at injection and in collision. Tune footprints and diffusive apertures simulated by this code are presented for various cases, differing in the bunch position, the energy, the number of long-range and head-on collisions, the presence of additional compensating wires and the momentum deviation. It is confirmed that the solution of 4 wires for injection, previously found by B. Erdelyi, raises the dynamic aperture, by about 1.0-1.5σ. For both injection and collision an ideal compensation of the 6 or 3 closest long-range encounters was modeled, by removing these collisions altogether. At collision, an improvement i...
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This report summarizes studies of long-range collisions and their compensation by current carrying wires for the Tevatron Run-II, which were performed during a two-week stay at Fermilab, February 22 to March 8, 2004. The weak-strong code... more
This report summarizes studies of long-range collisions and their compensation by current carrying wires for the Tevatron Run-II, which were performed during a two-week stay at Fermilab, February 22 to March 8, 2004. The weak-strong code WSDIFF was significantly extended to simulate the actual long-range encounters at the Tevatron for different antiproton bunches in the train at injection and in collision. Tune footprints and diffusive apertures simulated by this code are presented for various cases, differing in the bunch position, the energy, the number of long-range and head-on collisions, the presence of additional compensating wires and the momentum deviation. It is confirmed that the solution of 4 wires for injection, previously found by B. Erdelyi, raises the dynamic aperture, by about 1.0-1.5σ. For both injection and collision an ideal compensation of the 6 or 3 closest long-range encounters was modeled, by removing these collisions altogether. At collision, an improvement i...
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A photocathode, immersed in solenoidal magnetic field, can produce canonical-angular-momentum (CAM) dominated or “magnetized” electron beams. Such beams have an application in electron cooling of hadron beams and can also be uncoupled to... more
A photocathode, immersed in solenoidal magnetic field, can produce canonical-angular-momentum (CAM) dominated or “magnetized” electron beams. Such beams have an application in electron cooling of hadron beams and can also be uncoupled to yield asymmetric-emittance (“flat”) beams. In the present paper we explore the possibilities of the flat beam generation at Fermilab’s Accelerator Science and Technology (FAST) facility. We present optimization of the beam flatness and four-dimensional transverse emittance and investigate the mapping and its limitations of the produced eigen-emittances to conventional emittances using a skew-quadrupole channel. Possible application of flat beams at the FAST facility are also discussed. INTRODUCTION A charged particle with mass m and charge q moving in axially symmetric EM-field has a constant of motion associated with its canonical angular momentum (CAM). This statement is also known as Busch’s theorem and conventionally the integral of motion is wr...
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We examine the stability of intense flat bunches in barrier buckets used in the Fermilab Recycler. We consider some common stationary distributions and show that they would be unstable against rigid dipole oscillations. We discuss the... more
We examine the stability of intense flat bunches in barrier buckets used in the Fermilab Recycler. We consider some common stationary distributions and show that they would be unstable against rigid dipole oscillations. We discuss the measurements which identify stable distributions. We also report on experimental studies on the impact of creating a local extremum of the incoherent frequency within the rf bucket. We considered two typical stationary distributions and found they were not adequate descriptions of the Recycler bunches. From the measured line density distribution we find (a) the tanh function is a good fit to the line density, and (b) the coherent frequency of the rigid dipole mode for this distribution is within the incoherent spread at nominal intensities. Stability diagrams when the beam couples to space charge and external impedances will be discussed elsewhere. Our initial experimental investigations indicate that longitudinal stability in the Recycler is, consiste...
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We investigate the dynamics of longitudinally flat bunches created with a second harmonic cavity in a high energy collider. We study Landau damping in a second harmonic cavity with analytical and numerical methods. The latter include... more
We investigate the dynamics of longitudinally flat bunches created with a second harmonic cavity in a high energy collider. We study Landau damping in a second harmonic cavity with analytical and numerical methods. The latter include particle tracking and evolution of the phase space density. The results are interpreted in the context of possible application to the LHC.
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We discuss the generation of parametric X-rays in the photoinjector at the new FAST facility at Fermilab. Detailed calculations of the intensity spectrum, energy and angular widths and spectral brilliance with a diamond crystal are... more
We discuss the generation of parametric X-rays in the photoinjector at the new FAST facility at Fermilab. Detailed calculations of the intensity spectrum, energy and angular widths and spectral brilliance with a diamond crystal are presented. We also report on expected results with PXR generated while the beam is channeling. A new goniometer with several ports could allow the simultaneous detection of PXR at multiple energies. The low emittance electron beam makes this facility a promising source for creating brilliant PXR emission.
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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... 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 channeling spectrum including background from bremsstrahlung and the use of a Compton scatterer during higher bunch charge operation.
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Transverse beam echoes can be excited with a single dipole kick followed by a single quadrupole kick. They have been used to measure diffusion in hadron beams and have other diagnostic capabilities. Here we develop theories of the... more
Transverse beam echoes can be excited with a single dipole kick followed by a single quadrupole kick. They have been used to measure diffusion in hadron beams and have other diagnostic capabilities. Here we develop theories of the transverse echo nonlinear in both the dipole and quadrupole kick strengths. The theories predict the maximum echo amplitudes and the optimum strength parameters. We find that the echo amplitude increases with smaller beam emittance and the asymptotic echo amplitude can exceed half the initial dipole kick amplitude. We show that multiple echoes can be observed provided the dipole kick is large enough. The spectrum of the echo pulse can be used to determine the nonlinear detuning parameter with small amplitude dipole kicks. Simulations are performed to check the theoretical predictions. In the useful ranges of dipole and quadrupole strengths, they are shown to be in reasonable agreement.
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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... 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 beam intensity. This study shows that echoes can be used to measure diffusion much more quickly than present methods and possibly be useful to a variety of hadron synchrotrons. * tsen@fnal.gov 1