Physics - Accelerator Physics Publications (50)


Physics - Accelerator Physics Publications

Precise beam based measurement and correction of magnetic optics is essential for the successful operation of accelerators. The LOCO algorithm is a proven and reliable tool, which in some situations can be improved by using a broader class of experimental data. The standard data sets for LOCO include the closed orbit responses to dipole corrector variation, dispersion, and betatron tunes. Read More

We consider the process of cooling of a heavy particle beam in a co-moving electron beam of low temperature guided by a solenoidal magnetic field. This paper summarizes the main results of theoretical studies of this process conducted by the author during a period of several years. The main result of these studies is a conclusion that magnetization of the electron beam can provide the possibility of drastic enhancement of the cooling rate of a heavy particle beam with achieving equilibrium temperatures that are much lower than the transverse temperatures of the electron beam. Read More

Electron injection in an evolving ellipsoid bubble for laser wakefield acceleration is investigated by 2.5D PIC (Particle-In-Cell) simulation. Generally speaking, the self-injection electrons come from the position near the transverse radius in the bubble acceleration. Read More

The analysis of beamstrahlung radiation, emitted from a beam of charged particles due to the electromagnetic interaction with a second beam of charged particles, provides a diagnostic tool that can be used to monitor beam-beam collisions in a $e^{+}e^{-}$ storage ring. In this paper we show that the beamstrahlung time profile is related to the timing of the collisions and the length of the beams, and how its measurement can be used to monitor and optimize collisions at the interaction point of the SuperKEKB collider. To measure the time dependence of beamstrahlung, we describe a method based on nonlinear frequency mixing in a nonlinear crystal of beamstrahlung radiation with photons from a pulsed laser. Read More

A detailed thermal analysis of a Niobium (Nb) based superconducting radio frequency (SRF) cavity in a liquid helium bath is presented, taking into account the temperature and magnetic field dependence of the surface resistance and thermal conductivity in the superconducting state of the starting Nb material with different impurity levels. The drop in SRF cavity quality factor (Q_0) in the high acceleration gradient regime (before ultimate breakdown of the SRF cavity) is studied in details. It is argued that the high field Q_0-drop in SRF cavity is considerably influenced by the material parameters such as electrical conductivity, and thermal diffusivity. Read More

The article considers an opportunity of pulsed acceleration of the proton beam in a spiral wave guide. The radial focus of the proton beam in the accelerator is carried out by means of the magnetic field of ten Tesla, generated by a superconducting solenoid. Read More

This letter reports the successful use of feedback from a spin polarization measurement to the revolution frequency of a 0.97 GeV/$c$ bunched and polarized deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control both the precession rate ($\approx 121$ kHz) and the phase of the horizontal polarization component. Real time synchronization with a radio frequency (rf) solenoid made possible the rotation of the polarization out of the horizontal plane, yielding a demonstration of the feedback method to manipulate the polarization. Read More

The laser-plasma accelerator has attracted great interest for constituting an alternative in the production of the relativistic electron beams of high peak current. But the generated electron beam has poor monochrome and emittance, which make it difficult to produce high brightness radiation. Here we propose a compact flexible laser undulator based on ponderomotive force to constitute a millimeter-sized synchrotron radiation source of X-ray. Read More

Instruments to visualize transient structural changes of inhomogeneous materials on the nanometer scale with atomic spatial and temporal resolution are demanded to advance materials science, bioscience, and fusion sciences. One such technique is femtosecond electron microdiffraction, in which a short pulse of electrons with femtosecond-scale duration is focused into a micron-scale spot and used to obtain diffraction images to resolve ultrafast structural dynamics over localized crystalline domain. In this letter, we report the experimental demonstration of time-resolved mega-electron-volt electron microdiffraction which achieves a 5 {\mu}m root-mean-square (rms) beam size on the sample and a 100 fs rms temporal resolution. Read More

We present a muon capture front-end scheme for muon based applications. In this Front-End design, a proton bunch strikes a target and creates secondary pions that drift into a capture channel, decaying into muons. A series of rf cavities forms the resulting muon beams into a series of bunches of differerent energies, aligns the bunches to equal central energies, and initiates ionization cooling. Read More

Existence of different types of interference in the spectrum of radiation emitted by a doubly hard scattered electron is demonstrated. The spectrum develops oscillations in two regions: the hard, where the oscillations depend on the electron Lorentz factor, and the soft, where the oscillations depend on the electron scattering angles. This interference pattern owes to the presence of jetlike radiation configurations, formed by a piecewise-rectilinearly moving electron and the accompanying photon. Read More

We present an overview of the performance of the Neutralized Drift Compression Experiment-II (NDCX-II) accelerator at Berkeley Lab, and report on recent target experiments on beam driven melting and transmission ion energy loss measurements with nanosecond and millimeter-scale ion beam pulses and thin tin foils. Bunches with around 10^11 ions, 1-mm radius, and 2-30 ns FWHM duration have been created with corresponding fluences in the range of 0.1 to 0. Read More

In this talk, I introduce the proposed next superconducting radio-frequency (SRF) technologies that will make it possible to achieve much higher accelerating electric field than the present SRF technologies. Audiences are assumed to be non-experts. We start from a brief review of basics of SRF, history of the high gradient technologies and the layered structure behind it. Read More

We propose a new scheme for high gain harmonic generation free electron lasers (HGHG FELs), which is seeded by a pair of intersecting laser beams to interact with an electron beam in a modulator undulator located in a dispersive section. The interference of the laser beams gives rise to a two-dimensional modulation in the energy-time phase space because of a strong correlation between the electron energy and the position in the direction of dispersion. This eventually forms pseudo energy bands in the electron beam, which results in efficient harmonic generation in HGHG FELs in a similar manner to the well-known scheme using the echo effects, with the requirement on the energy modulation being much more relaxed. Read More

The temporal resolution of sub-relativistic ultrafast electron diffraction (UED) is generally limited by RF phase jitter of the radio frequency lenses that are used to compress the electron pulses. We theoretically show how to circumvent this limitation by using a combination of several radio frequency (RF) compression cavities. We show that if powered by the same RF source and with a proper choice of RF field strengths, RF phases and distances between the cavities the combined jitter due to the cavities at the compression point is cancelled. Read More

We have been developing optical resonant cavities for laser-Compton scattering experiment at the Accelerator Test Facility in KEK. The main subject of the R&D is to increase laser pulse energy by coherently accumulating the pulses in an optical resonant cavity. We report previous results, current status and future prospects, including a new idea of an optical resonant cavity. Read More

Two standing-wave single-cell choke-mode damped structures with different choke dimensions which worked at 11.424 GHz were designed, manufactured and tuned by accelerator group in Tsinghua University. High power test was carried out to study choke-mode structure's properties in high gradient and related breakdown phenomenon. Read More

Dielectric lined waveguides are under extensive study as accelerating structures that can be excited by electron beams. Rectangular dielectric structures are used both in proof of principle experiments for new accelerating schemes and for studying the electronic properties of the structure loading material. Analysis of Cherenkov radiation generated by high current relativistic electron bunch passing through a rectangular waveguide with transversal isotropic dielectric loading has been carried out. Read More

In this paper, a new type magnet is proposed and processed to uniform the transverse beam profile. Compeared to the octupole, the new type magnet can prove a similar octupole magnet field in the middle, but the rise rate declines quickly in the edge. So that, a same uniform beam is got with less particles loss. Read More

The particle motion equation in the Radio Frequency (RF) quadrupole is derived. The motion equation shows that the general transform matrix of RF quadrupole with length less than or equal to 0.5b*l (b is the relativistic velocity of particles and l is wavelength of radio frequency electromagnetic field) can describe the particle motion in arbitrary long RF quadrupole. Read More

Precision experiments, such as the search for electric dipole moments of charged particles using storage rings, demand for an understanding of the spin dynamics with unprecedented accuracy. The ultimate aim is to measure the electric dipole moments with a sensitivity up to 15 orders in magnitude better than the magnetic dipole moment of the stored particles. This formidable task requires an understanding of the background to the signal of the electric dipole from rotations of the spins in the spurious magnetic fields of a storage ring. Read More

Integrable optics is an innovation in particle accelerator design that provides strong nonlinear focusing while avoiding parametric resonances. One promising application of integrable optics is to overcome the traditional limits on accelerator intensity imposed by betatron tune-spread and collective instabilities. The efficacy of high-intensity integrable accelerators will be undergo comprehensive testing over the next several years at the Fermilab Integrable Optics Test Accelerator (IOTA) and the University of Maryland Electron Ring (UMER). Read More

Integrable optics is an innovation in particle accelerator design that potentially enables a greater betatron tune spread and damps collective instabilities. An integrable rapid-cycling synchrotron (RCS) would be an effective replacement for the Fermilab Booster, as part of a plan to reach multi-MW beam power at 120 GeV for the Fermilab high-energy neutrino program. We provide an example integrable lattice with features of a modern RCS - dispersion-free drifts, low momentum compaction factor, superperiodicity, chromaticity correction, bounded beta functions, and separate-function magnets. Read More

Entangled photon pairs-discrete light quanta that exhibit non-classical correlations-play a central role in quantum information and quantum communication technologies. It is a natural demand from technological applications on the intensity of the entangled photon pairs, such that sufficient signal strength can be achieved. Here we propose approaches based on klystron tubes that could potentially achieve stable amplification of the entangled photon pairs generated by spontaneous parametric down conversion (SPDC) and entanglement transfer. Read More


Recent work at Fermilab in collaboration with the Advanced Photon Source and members of other national labs, designed an experiment to study the relationship between the RF repetition rate and the average current per RF pulse. While existing models anticipate a direct relationship between these two parameters we observed an inverse relationship. We believe this is a result of damage to the barium coating on the cathode surface caused by a change in back-bombardment power that is unaccounted for in the existing theories. Read More

We propose a method based on the slice energy spread modulation to generate strong subpicoseond density bunching in high-intensity relativistic electron beams. A laser pulse with periodic intensity envelope is used to modulate the slice energy spread of the electron beam, which can then be converted into density modulation after a dispersive section. It is found that the double-horn slice energy distribution of the electron beam induced by the laser modulation is very effective to increase the density bunching. Read More

The free electron laser (FEL), as the new generation light source, is an attractive tool in scientific frontier research, because of its advantages of full coherence, ultra-short pulse and controllable polarization. Generally, the soft X-ray FEL facilities require a precise measurement of polarization and X-ray energy spectrum. In this paper, based on the soft X-ray FEL user facility under construction at Shanghai, a numerical model in the framework of Geant4 was developed for simulating electron time of flight (e-TOF) based polarimeter and spectrometer. Read More

Channeling properties and radiation spectra are studied on the grounds of numerical simulations for the 855 MeV electrons in a periodically bent diamond crystal. The bent crystalline profiles are shown to enhance the re-channeling of the projectiles and to produce distinct lines in the radiation spectra. The results obtained are analyzed and contrasted to the properties of the planar channeling and of the channeling in uniformly bent crystals. Read More

We analyze the stimulated (emission/absorption) interaction of an electron quantum wavepacket with coherent radiation, using perturbation theory and numerical solution of Schrodinger equation. The analysis applies to a wide class of free electron radiative interaction schemes, and exemplified for Smith-Purcell radiation. Though QED theory and experiments indicate that spontaneous emission of radiation by a free electron is independent of its dimensions, we show that wavepacket dimensions do affect the stimulated radiative interaction in a certain range. Read More

The goal of the first phase of the AWAKE \cite{AWAKE1,AWAKE2} experiment at CERN is to measure the self-modulation \cite{SMI} of the $\sigma_z = 12\,\rm{cm}$ long SPS proton bunch into microbunches after traversing $10\,\rm{m}$ of plasma with a plasma density of $n_{pe}=7\times10^{14}\,\rm{electrons/cm}^3$. The two screen measurement setup \cite{Turner2016} is a proton beam diagnostic that can indirectly prove the successful development of the self-modulation of the proton beam by imaging protons that got defocused by the transverse plasma wakefields after passing through the plasma, at two locations downstream the end of the plasma. This article describes the design and realization of the two screen measurement setup integrated in the AWAKE experiment. Read More

Affiliations: 1Fermilab, 2Fermilab, 3Fermilab, 4Fermilab, 5Fermilab, 6Fermilab

The transfer line for beam extraction from the Recycler ring to P1 line provides a way to deliver 8 GeV kinetic energy protons from the Booster to the Delivery ring, via the Recycler, using existing beam transport lines, and without the need for new civil construction. It was designed in 2012. The kicker magnets at RR520 and the lambertson magnet at RR522 in the RR were installed in 2014 Summer Shutdown, the elements of RR to P1 Stub (permanent quads, trim quads, correctors, BPMs, the toroid at 703 and vertical bending dipole at V703 (ADCW) were installed in 2015 Summer Shutdown. Read More

In this paper, we extend several time reversible numerical integrators to solve the Lorentz force equations from second order accuracy to higher order accuracy for relativistic charged particle tracking in electromagnetic fields. A fourth order algorithm is given explicitly and tested with numerical examples. Such high order numerical integrators can significantly save the computational cost by using a larger step size in comparison to the second order integrators. Read More

We present a new concept for a multi-stage Zeeman decelerator that is optimized particularly for applications in molecular beam scattering experiments. The decelerator consists of a series of alternating hexapoles and solenoids, that effectively decouple the transverse focusing and longitudinal deceleration properties of the decelerator. It can be operated in a deceleration and acceleration mode, as well as in a hybrid mode that makes it possible to guide a particle beam through the decelerator at constant speed. Read More

There's presently a growing demand for cw high current proton and deuteron linear accelerators based on superconducting technology to better support various fields of science. Up to now, high order modes (HOMs) studies induced by ion beams with current higher than 10 mA and even 100 mA accelerated by low beta non-elliptical Superconducting rf (SRF) cavities are very few. Peking University has recently designed and fabricated a beta=0. Read More

The manuscript describes several monochromatization schemes starting from A.~Renieri \cite{ref:Renieri} proposal for head-on collisions based on correlation between particles transverse position and energy deviation. We briefly explain initial proposal and expand it for crossing angle collisions. Read More

Electron cloud can lead to a fast instability in intense proton and positron beams in circular accelerators. In the Fermilab Recycler the electron cloud is confined within its combined function magnets. We show that the field of combined function magnets traps the electron cloud, present the results of analytical estimates of trapping, and compare them to numerical simulations of electron cloud formation. Read More


An electron cloud instability might limit the intensity in the Fermilab Recycler after the PIP-II upgrade. A multibunch instability typically develops in the horizontal plane within a hundred turns and, in certain conditions, leads to beam loss. Recent studies have indicated that the instability is caused by an electron cloud, trapped in the Recycler index dipole magnets. Read More

Comparing with conventional accelerator, laser plasma accelerator can generate high energy ions in a greatly reduced scale due to its TV/m acceleration gradient. A compact laser plasma accelerator (CLAPA) has been built at Institute of Heavy Ion physics in Peking University, based on which application researches like biological irradiation, astrophysics simulation etc. will be carried on. Read More

The Schr\"odinger equation is solved for the wave function of an electron moving in a superposition of external constant and uniform electric and magnetic fields at an arbitrary angle between the field directions. The changing of the potential barrier under influence of the magnetic field parallel to the metal surface is shown. Read More

We propose a method for the detection of a dynamical Casimir effect. Assuming that the Casimir photons are being generated in an electromagnetic cavity with a vibrating wall (dynamical Casimir effect), we consider electrons passing through the cavity to be interacting with the intracavity field. We show that the dynamical Casimir effect can be observed via the measurement of the change in the average or in the variance of the electron kinetic energy. Read More

We have performed Joule power loss calculations for a flat dechirper. We have considered the configurations of the beam on-axis between the two plates---for chirp control---and for the beam especially close to one plate---for use as a fast kicker. Our calculations use a surface impedance approach, one that is valid when corrugation parameters are small compared to aperture (the perturbative parameter regime). Read More

In this paper, we propose an optimized field/circuit coupling approach for the simulation of magnetothermal transients in superconducting magnets. The approach improves the convergence of the iterative coupling scheme between a magnetothermal partial differential model and an electrical lumped-element circuit. Such a multi-physics, multi-rate and multi-scale problem requires a consistent formulation and a dedicated framework to tackle the challenging transient effects occurring at both circuit and magnet level during normal operation and in case of faults. Read More

This paper presents a model based on Deep Learning algorithms of LSTM and GRU for facilitating an anomaly detection in Large Hadron Collider superconducting magnets. We used high resolution data available in Post Mortem database to train a set of models and chose the best possible set of their hyper-parameters. Using Deep Learning approach allowed to examine a vast body of data and extract the fragments which require further experts examination and are regarded as anomalies. Read More

In the framework of the earlier derived dispersion equation, we study induced Smith Purcell (SP) radiation of relativistic electron beam in the absence of a resonator. We offer a new method for calculation of coefficients for partial amplitudes in the case of rectangular grating. Using this method we calculate the growth rate of the SPFEL with a rectangular grating. Read More

Multiple Electrostatic Quadrupole Array Linear Accelerators (MEQALACs) provide an opportunity to realize compact radio-frequency (RF) accelerator structures that can deliver very high beam currents. MEQALACs have been previously realized with acceleration gap distances and beam aperture sizes of the order of centimeters. Through advances in Micro-Electro-Mechanical Systems (MEMS) fabrication, MEQALACs can now be scaled down to the sub-millimeter regime and batch processed on wafer substrates. Read More

For the grating, which has depth of grooves as a small parameter, the dispersion equation of the Smith-Purcell instability was obtained. It was found that the condition of the Thompson or the Raman regimes of excitation does not depend on beam current but depends on the height of the beam above grating surface. The growth rate of instability in both cases is proportional to the square root of the electron beam current. Read More

A Hollow Electron Lens (HEL) has been proposed in order to improve performance of halo control and collimation in the Large Hadron Collider in view of its High Luminosity upgrade (HL-LHC). The concept is based on a beam of electrons that travels around the protons for a few meters. The electron beam is produced by a cathode and then guided by a strong magnetic field generated by a set of superconducting solenoids. Read More

The resonance frequency of the system is found and the linear gain is derived for the odd harmonics of this frequency. Averaging of the gain is carried out over the initial distribution of electrons in a transverse cross section of the beam. Estimates are obtained of the maximum lasing frequency and of the gain at this frequency Read More

After more than a century of debate, there remains continuing discomfort over what is the correct expression for the electromagnetic momentum in a dielectric medium. This is the so-called the Minkowski-Abraham controversy. We show that there is indeed a consistent picture for the electromagnetic momentum associated with waves in a dielectric, but one must start with the fields E and B, not D and H as fundamental objects. Read More

Superconducting linacs are capable of producing intense, stable, high-quality electron beams that have found widespread applications in science and industry. The 9-cell 1.3-GHz superconducting standing-wave accelerating RF cavity originally developed for $e^+/e^-$ linear-collider applications [B. Read More