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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

BEAM DYNAMICS ANALYSIS FOR THE ULTRA-FAST KICKER IN CIRCULAR COOLER RING OF JLEIC

An ultra-fast kicker system consisting of four quarter wavelength resonator based deflecting cavities was developed that simultaneously resonates at 10 subharmonic modes of the 476.3MHz bunch repetition frequency. Thus every 10th bunch in the bunch train will experience a transverse kick while all the other bunches are undisturbed. This fast kicker is being developed for the Energy Recovery Linac (ERL) based electron Circular Cooler Ring (CCR) in the proposed Jefferson Lab Electron Ion Collider (JLEIC, previously MEIC). The electron bunches can be reused 10-30 turns thus the beam current in the ERL can be reduced to 1/10 - 1/30 (150mA - 50mA) of the cooling bunch current (1.5A). In this paper, several methods to synthesize such a kicker waveform and the comparison made by the beam dynamics tracking in Elegant will be discussed.

Huang, Yulu↗
DOE OSTI2018

Experimental Demonstration of Ion Beam Cooling with Pulsed Electron Beam

Cooling ion beams at high energy is presently considered for several ion colliders, in order to achieve high luminosities by enabling a significant reduction of emittance of hadron beams. Electron beam at cooling channel in a few to tens MeV can be accelerated by a RF/SRF linac, and thus using bunched electrons to cool bunched ions. To study such cooling process, the DC electron gun of EC35 cooler at the storage ring CSRm, IMP was modified by pulsing the grid voltage. A 0.07-3.5 micro-second pulse length with a repetition frequency of less than 250 kHz and synchronized with the ion revolution frequency was obtained. The first experimental demonstration of cooling of a coasting and bunched ion beam by a pulsed electron beam was carried out. Data analysis indicates the bunch length shrinkage and the momentum spread reduction of bunched 12C+6 ion beam as evidence of cooling. A longitudinal grouping effect of the coasting ion beam by the electron pulses has also been observed*. In this paper, we will present experimental results and comparison to the simulation modelling, particularly on the bunched electron cooling data after carefully analyzing the beam diagnostic signals.

Zhang, Yuhong↗
DOE OSTI2026

Implementation of a 1550-nm laser system for beam characterization at the Argonne Wakefield Accelerator

Accurately recording an electron bunch’s longitudinal profile is an important diagnostic for wakefield accelerators employing shaped bunches to increase transformer ratios. Electro-optic sampling of terahertz radiation from the bunch is an attractive approach due to its non-destructive nature. In preparation for future characterization experiments, the Argonne Wakefield Accelerator test facility has recently installed a 1550 nm laser system, including the necessary support systems to synchronize with the photoinjector laser system at 81.25 MHz. We report here on the initial installation and synchronization demonstrations.

Ody, Alexander [Argonne, PHY]↗
DOE OSTI2010

Study of an HHG-Seeded Free-Electron Laser for the LBNL Next Generation Light Source

The Next Generation Light Source (NGLS) is a high repetition rate free-electron laser facility proposed by Lawrence Berkeley National Laboratory (LBNL). The proposed facility will provide multiple FEL lines with varying spectral characteristics to satisfy a broad soft X-ray physics programme. At this stage of the project a number of FEL technologies and concepts are being investigated for possible implementation on the facility. In this report we consider a free-electron laser seeded by a Higher Harmonic Generation (HHG) source in which a high power (and consequently relatively low repetition rate) laser pulse is injected into a chamber of inert gas. Through a process of ionisation and recombination coherent higher harmonics of the laser are emitted from the gas and can be injected into an FEL system as a seed field. Further harmonic upconversion can be done within the FEL system to enable temporally coherent FEL output at wavelengths much shorter than, and pulse energies orders of magnitude higher than, the HHG source emission. The harmonic conversion within the FEL works in the following way. The seed field induces an energy modulation within the electron bunch at the start of the modulator. This energy modulation grows within the modulator due to the FEL interaction and starts to convert into a density modulation, or bunching, at the seed wavelength. However, this bunching also has components at higher harmonics which retain the longitudinal coherence of the initial seed. The beam passes through a magnetic chicane, which shears the longitudinal phase space to maximise the bunching at the required harmonic, then a further undulator which is tuned to this harmonic. If this second undulator is short it acts as a further modulator, and because the beam is pre-bunched at the modulator resonance there is a strong coherent burst of radiation which acts to modulate the electron beam energy in much the same way the input laser seed field acted in the first modulator. This second modulator is followed by a second bunching chicane and then a final long radiator tuned to a yet higher harmonic of the laser seed - the final output wavelength. Alternatively, the second undulator can be the radiator itself, in which case only one harmonic conversion from seed wavelength to final output is necessary. We initially consider the case of a 400kW peak power HHG seed source at wavelength 12nm (currently considered the cutoff wavelength for sufficient seed power to dominate shot noise in the electron beam) which is converted in either one or two stages or harmonic conversion to FEL emission at 1nm. We then consider the implications of a factor of ten reduction in seed power to 40kW.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Optical tailoring of xFEL beams

There is an inherent flexibility unique to free electron lasers (FELs) that lends well to experimental approaches normally too difficult for other light sources to accomplish. This includes the ability to optically shape the electron bunch prior to final its acceleration for the final FEL process. Optical pulse shaping of the electron bunch can enable both femtosecond and attosecond level FEL pulse control. Pulse shaping is currently implemented, not optically but mechanically, in LCLS-I with an adjustable foil slit that physically spoils the momentum phase of the electron bunch. This selectively suppresses the downstream FEL process of spoiled electrons. Such a mechanical spoiling method fails for both the soft x-ray regime as well as the high repetition rates that are planned in LCLS-II. Our proposed optical spoiling method circumvents this limitation by making use of the existing ultrafast laser beam that is typically used for adjusting the energy spread for the initial electron bunch. Using Fourier domain shaping we can nearly arbitrarily shape the laser pulses to affect the electron bunch. This can selectively spoil electrons within each bunch. Here we demonstrate the viability of this approach with a programmable acousto-optic dispersive filter. This method is not only well suited for LCLS-II but also has several advantages over mechanical spoiling, including lack of radiation concerns, experiment specific FEL pulse shapes, and real-time adjustment for applications that require high duty-cycle variation such as lock-in amplification of small signals.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Longitudinal Beam Parameter Tolerances of NSLS-II

Similar to the transverse phase space, the beam parameters in the longitudinal phase space must also be monitored and controlled. In the longitudinal phase space the fundamental parameters are: bunch arrival time(or the corresponding RF phase), average momentum, bunch length, and momentum spread. These parameters are usually perturbed by the various noises in a real machine. The noises could excite longitudinal bunch motion, seen by the users as timing jitter, intensity and wavelength variation, and transverse position shift et al. The longitudinal oscillations also cause longitudinal emittance growth, therefore lengthen the bunch and increase the momentum spread, and eventually decrease the brightness. As a rule of thumb for the tolerances, either transverse or longitudinal, the perturbation caused by the noises should not result in a decrease of brightness by more than 10%. The users are concerned about the longitudinal beam parameters in several ways. First the timing jitter affects the timing-dependent experiments. Even though a photo-diode detection system is usually used to to determine the arrival time, the bandwidth is only about 1 kHz. The users from this category ask for a timing jitter tolerance to be 5% of the RMS bunch length over the frequency range from 500 Hz to 50 kHz. This corresponds to a phase error of Δφ = 1.6 mr or 0.1° for a 10 ps bunch with a 500 MHz rf system.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

MEBT Chopper System: System Design Document (SDD)

The Medium Energy Beam Transport (MEBT) chopper removes unwanted beam bunches by deflecting them to a target from a bunched beam transported through the MEBT from RFQ to the Drift-Tube Linac (DTL) entrance. The unchopped bunches propagate through the MEBT to DTL, while the deflected bunches are deposited on a target downstream of chopper. The chopper system consists of a deflecting structure, where the beam-deflecting fields are created, and a pulse generator (pulser) that feeds this structure with voltage pulses having the required time pattern. Ideally, the system should turn deflection on and off in the time interval between the bunches to prevent partially chopped / deflected bunches. This usually requires traveling slow-wave chopper structures where the field propagates with the same velocity as the beam, as illustrated in Fig. 1.

43 PARTICLE ACCELERATORS↗
NASA NTRS2004

Steps in Solution Growth: Revised Gibbs-Thomson Law, Turbulence and Morphological Stability

Two groups of new phenomena revealed by AFM and high resolution optical interferometry on crystal faces growing from solutions will be discussed. 1. Spacing between strongly polygonized spiral steps with low less than 10(exp -2) kink density on lysozyme and K- biphtalate do not follow the Burton-cabrera-Frank theory. The critical length of the yet immobile first Short step segment adjacent to a pinning defect (dislocation, stacking fault) is many times longer than that following from the step free energy. The low-kink density steps are typical of many growth conditions and materials, including low temperature gas phase epitaxy and MBE. 2. The step bunching pattern on the approx. 1 cm long { 110) KDP face growing from the turbulent solution flow (Re (triple bonds) 10(exp 4), solution flow rate approx. 1 m/s) suggests that the step bunch height does not increase infinitely as the bunch path on the crystal face rises, as is usually observed on large KDP crystals. The mechanism controlling the maximal bunch width and height is based on the drag of the solution depleted by the step bunch down thc solution stream. It includes splitting, coagulation and interlacing of bunches

Chernov, A. A.↗
DOE OSTI2011

Operational results from the LHC luminosity monitors

The luminosity monitors for the high luminosity regions in the LHC have been operating to monitor and optimize the luminosity since 2009. The device is a gas ionization chamber inside the neutral particle absorber 140 m from the interaction point and monitors showers produced by high energy neutral particles from the collisions. It has the ability to resolve the bunch-by-bunch luminosity as well as to survive the extreme level of radiation in the nominal LHC operation. We present operational results of the device during proton and lead ion operations in 2010 and make comparisons with measurements of experiments. The Large Hadron Collider (LHC) at CERN can accelerate proton and lead ion beams to 7 TeV and 547 TeV and produce collisions of these particles. Luminosity measures performance of the LHC and is particularly important for experiments in high luminosity interaction points (IPs), ATLAS (IP1) and CMS (IP5). To monitor and optimize the luminosities of these IPs, BRAN (Beam RAte Neutral) detectors [1, 2] have been installed and operating since the beginning of the 2009 operation [3]. A neutral particle absorber (TAN) protects the D2 separation dipole from high energy forward neutral particles produced in the collisions [4]. These neutral particles produce electromagnetic and hadronic showers inside the TAN and their energy flux is proportional to the collision rate and hence to the luminosity. The BRAN detector is an Argon gas ionization chamber installed inside the TANs on both sides of the IP1 and IP5 and monitors the relative changes in the luminosity by detecting the ionization due to these showers. When the number of collisions per bunch crossing (multiplicity) is small, the shower rate inside the TAN is also proportional to the luminosity. Hence, the detector is designed to operate by measuring either the shower rate (counting mode for low and intermediate luminosities) or the average shower flux (pulse height mode for high luminosities). The detector is also designed (1) to survive the extreme level of radiation ({approx}1 GGy in the nominal condition), (2) to resolve the shower from each bunch crossing (40 MHz in the nominal condition) and measure the bunch-by-bunch luminosities, and (3) to have four independent square shaped channels, each occupying a quadrant, making the detector sensitive to the crossing angle [1, 2]. During the proton operation in 2010, the beam energy was 3.5 TeV and the multiplicity did not exceed four. Because the counting mode is still effective in such a condition [5], the BRAN were operated in the counting mode in 2010. This paper presents operational results of the BRANs during the operation in 2010 (mainly the proton operation) and makes comparisons with measurements of the experiments. The luminosity optimization is discussed in detail in [6] and so this paper focuses on measurements during the normal operation.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Effects of e-beam parameters on coherent electron cooling

Coherent Electron Cooling (CeC) requires detailed control of the phase between the hadron an the FEL-amplified wave packet. This phase depends on local electron beam parameters such as the energy spread and the peak current. In this paper, we examine the effects of local density variations on the cooling rates for CeC. Coherent Electron Cooling (CeC) [1] is a new concept in intense, high energy hadron beamcooling, in which the Debye screened charge perturbation calculated in [2] is used to seed a high-gain free electron laser (FEL). Using delays to give the perturbing hadron an energy-dependent longitudinal displacement relative to its frequencymodulated charge perturbation, the hadron receives an energy-dependent kick which reduces its energy variation from the design energy. The equations of motion in [1] assume that the electron bunch is the same physical size as the hadron bunch, and has a homogeneous charge density across the entire bunch. In practice, the electron bunches will be much shorter than the hadron bunch, and this local spacial inhomogeneity in the charge distribution will alter the gain length of the FEL, resulting in both a change in the amplification of the initial signal and a phase shift. In this paper we consider these inhomogeneity effects, determining cooling equations for bunched beam CeC consistent with these effects and determining thresholds for the cooling parameters.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Beam Tilt Due to Transverse Wakefields for DAFNE, SuperB, KEKB and SuperKEKB

When a beam bunch traverses a transverse impedance, the bunch head generates a transverse wakefield that kicks the bunch tail, generating a betatron motion of the tail relative to the head. In a storage ring, in a steady state, this kick to the bunch tail produces a transverse closed orbit (e.g. in the y-direction) of the bunch tail relative to the bunch head, which means the beam now has a y-z tilt. Such beam tilt due to transverse wakefields may cause a loss of luminosity in storage ring colliders or loss of brightness in light sources. In this paper, we present a preliminary study of the beam tilt effect for the colliders DAFNE, SuperB, KEKB and SuperKEKB.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Upgrade of the Drive LINAC for the AWA Facility Dielectric Two-Beam Accelerator

We report on the design of a seven-cell, standing-wave, 1.3-GHz rf cavity and the associated beam dynamics studies for the upgrade of the drive beamline LINAC at the Argonne Wakefield Accelerator (AWA) facility. The LINAC design is a compromise between single-bunch operation (100 nC {at} 75 MeV) and minimization of the energy droop along the bunch train during bunch-train operation. The 1.3-GHz drive bunch-train target parameters are 75 MeV, 10-20-ns macropulse duration, and 16 x 60 nC microbunches; this is equivalent to a macropulse current and beam power of 80 A and 6 GW, respectively. Each LINAC structure accelerates approximately 1000 nC in 10 ns by a voltage of 11 MV at an rf power of 10 MW. Due to the short bunch-train duration desired ({approx}10 ns) and the existing frequency (1.3 GHz), compensation of the energy droop along the bunch train is difficult to accomplish by means of the two standard techniques: time-domain or frequency-domain beam loading compensation. Therefore, to minimize the energy droop, our design is based on a large stored energy rf cavity. In this paper, we present our rf cavity optimization method, detailed rf cavity design, and beam dynamics studies of the drive beamline.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2012

Design for a Longitudinal Density Monitor for the LHC

Synchrotron radiation is currently used on the LHC for beam imaging and for monitoring the proton population in the 3 microsecond abort gap. In addition to these existing detectors, a study has been initiated to provide longitudinal density profiles of the LHC beams with a high dynamic range and a 50ps time resolution. This would allow for the precise measurement both of the bunch shape and the number of particles in the bunch tail or drifting into ghost bunches. A solution is proposed based on counting synchrotron light photons with two fast avalanche photo-diodes (APD) operated in Geiger mode. One is free-running but heavily attenuated and can be used to measure the core of the bunch. The other is much more sensitive, for measurement of the bunch tails, but must be gated off during the passage of the bunch to prevent the detector from being swamped. An algorithm is then applied to combine the two measurements and correct for the detector dead-time, afterpulsing and pile-up effects. Initial results from laboratory testing of this system are described here.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Studies of eRHIC coherent instabilities

In the presence of an effective coherent electron cooling, the rms ion bunch length in eRHIC will be kept at 8.3 cm for 250 GeV protons, which is much shorter than the current RHIC 45 cm rms bunch length. Together with the increased bunch intensity and total bunch number, coherent instabilities could be a potential limitation for achieving desired machine performance. In this study, we use the tracking code TRANFT to find thresholds and growth rates for single bunch and coupled bunch instabilities with linear chromaticity and amplitude dependent tune shift taken into account. Based on the simulation results, requirements of machine parameters such as rf voltage, linear chromaticity, and tune dependence of betatron amplitude are specified to suppress these instabilities.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Z-Slicer: A Scheme for Shaping the Electron Beam Profile in a Linac

A train of short bunches ( 100 fs) are at a premium at accelerator facilities and their applications include terahertz (THz) generation, short bunch diagnostics, advanced accelerator R&D, etc. In this work we report on the design and simulation of an experiment involving a 20 MeV electron beam, that will be intercepted by a set of metallic slits inside a bunch compressor. After the mask, some electrons are scattered while other pass through unaffected. After exiting the bunch compressor, those electrons that were not affected by the slits will appear as short electron bunches. The key advantage of our scheme is its simplicity, tunability and low cost. The scheme does not require any additional hardware such as lasers, undulator, or transverse deflecting cavity. The tuning variable is only the RF-chirp. The detection of the bunching requires just a skew quad in the chicane and a transverse screen downstream.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

A Study of Resonant Excitation of Longitudinal HOMs in the Cryomodules of LCLS-II

The Linac Coherent Light Source (LCLS) at SLAC, the world’s first hard X-ray FEL, is being upgraded to the LCLS-II. The major new feature will be the installation of 35 cryomodules (CMs) of TESLA-type, superconducting accelerating structures, to allow for high rep-rate operation. It is envisioned that eventually the LCLS-II will be able to deliver 300 pC, 1 kA pulses of beam at a rate of 1 MHz. At a cavity temperature of 2 K, any heat generated (even on the level of a few watts) is expensive to remove. In the last linac of LCLS-II, L3—where the peak current is highest—the power radiated by the bunches in the CMs is estimated at 13.8 W (charge 300 pC option, rep rate 1 MHz). But this calculation ignores resonances that can be excited between the bunch frequency and higher order mode (HOM) frequencies in the CMs, which in principle can greatly increase this number. In the present work we calculate the multi-bunch wakefields excited in a CM of LCLS-II, in order to estimate the probability of the beam losing a given amount of power. Along theway, we find some interesting properties of the resonant interaction. In detail, we begin this report by finding the wakes experienced by bunches far back in the bunch train. Then we present a complementary approach that calculates the field amplitude excited in steady-state by a train of bunches, and show that the two approaches agree. Next we obtain the properties of the 450 longitudinal HOMs that cover the range 3–5 GHz in the CMs of LCLS-II, where we include the effects of the inter-CM ceramic dampers. At the end we apply our method using these modes.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Space Charge Effects in Low Energy Magnetized Electron Beams

Magnetized electron cooling of the ion beam is one of the major approaches towards obtaining the required high luminosity in the proposed Electron-Ion Collider (EIC). To increase the cooling efficiency, a bunched electron beam with a high bunch charge and high repetition rate is required. However, these features can combine to enhance the collective interactions, such as the space charge effect. A magnetized electron beam was successfully generated at the Thomas Jefferson National Accelerator Facility (JLab) using a compact, 300 kV DC high voltage photo-gun with an inverted insulator geometry and bi-alkali antimonide photocathode. The beam magnetization was characterized using a modest diagnostic beamline to measure beam sizes, rotation angles, and normalized transverse emittance as a function of magnetic field at the photocathode, laser spot size, and gun high-voltage. Simultaneously, simulations were performed using the A Space Charge Tracking Algorithm (ASTRA) and General Particle Tracer (GPT) programs. Further, sustained high average current magnetized beam up to 28 mA was demonstrated, and the photocathode lifetime for different magnetized electron beam currents was investigated. In the second part of the project, the space charge effect in low-energy magnetized electron beams was studied and compared with GPT simulations. The high bunch charge studies showed evidence of space charge current limitations starting at 0.3 nC and limited the maximum delivered bunch charge to 0.7 nC. To reach the high bunch charge goal of a few nC, the existing DC photo-gun design was modified using CST Studio Suite’s electromagnetic field solver, and a way to cancel the beam deflection exerted by the non-symmetric nature of the inverted insulator photo-gun geometry was discovered. This thesis presents a detailed description of the generation, characterization, and simulation of high current, high bunch charge magnetized electron beams at JLab, as well as the modified photo-gun design. Together with measurements and simulations, the purpose of this thesis is to provide a solid background on the theoretical aspects and the experimental challenges associated with magnetized electron beams for accelerator applications.

Wijethunga, W M Sajini↗
DOE OSTI2023

Nanopatterned electron beams for temporal coherence and deterministic phase control of x-ray free-electron lasers

A method includes accelerating an electron bunch along a direction of propagation to a relativistic energy and partitioning the electron bunch by transmitting the electron bunch through a grating at the relativistic energy. The grating includes a plurality of alternating narrow portions and wide portions. The narrow portions have a first thickness in a direction substantially parallel to the direction of propagation of the electron bunch, and the wide portions have a second thickness in the direction substantially parallel to the direction of propagation of the electron bunch. The second thickness is greater than the first thickness. The method also includes generating a pulse of light using the partitioned electron bunch.

Graves, William↗