INEXPENSIVE ELECTRON BEAM OPTICS FOR ULTRAFAST ELECTRON MICROSCOPY
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Quantum aspects of charged-particle beam optics
The classical treatments have been successful in designing numerous charged-particle devices. It is natural to develop a quantum prescription, since all systems are fundamentally quantum mechanical in nature. The quantum theory leads to new insights accompanied with wavelength-dependent contributions. The action of a magnetic quadrupole is derived from the Dirac equation.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Stability of aerosol droplets in Bessel beam optical traps under constant and pulsed external forces
We report on the dynamics of aerosol droplets in optical traps under the influence of additional constant and pulsed external forces. Experimental results are compared with simulations of the three-dimensional droplet dynamics for two types of optical traps, the counter-propagating Bessel beam (CPBB) trap and the quadruple Bessel beam (QBB) trap. Under the influence of a constant gas flow (constant external force), the QBB trap is found to be more stable compared with the CPBB trap. By contrast, under pulsed laser excitation with laser pulse durations of nanoseconds (pulsed external force), the type of trap is of minor importance for the droplet stability. It typically needs pulsed laser forces that are several orders of magnitude higher than the optical forces to induce escape of the droplet from the trap. If the droplet strongly absorbs the pulsed laser light, these escape forces can be strongly reduced. The lower stability of absorbing droplets is a result of secondary thermal processes that cause droplet escape.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Communication: Global minimum search of Ag{sub 10}{sup +} with molecular beam optical spectroscopy
The present study is focused on the optical properties of the Ag{sub 10}{sup +} cluster in the photon energy range ℏω = 1.9–4.4 eV. Absorption spectra are recorded by longitudinal molecular beam depletion spectroscopy and compared to optical response calculations using time-dependent density functional theory. Several cluster isomers obtained by the new pool-based parallel implementation of the Birmingham Cluster Genetic Algorithm, coupled with density functional theory, are used in excited state calculations. The experimental observations, together with additional simulations of ion mobilities for the several geometries found within this work using different models, clearly identify the ground state isomer of Ag{sub 10}{sup +} to be composed of two orthogonal interpenetrating pentagonal bipyramids, having overall D{sub 2d} symmetry.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Effects of a 4.3T superconducting wiggler on the electron beam optics and dynamics at NSLS-II
A superconducting wiggler (SCW) with a peak field of 4.3 T has recently been installed at NSLS-II. The wiggler generates a high-flux X-ray beam with a photon energy range from 20 keV to 200 keV for the High Energy Engineering X-ray Scattering beamline. This device induces significant distortions in the electron beam orbit and optics. Here, we have corrected these adverse effects using feed-forward tables. The effects of the SCW on the electron beam emittance, energy spread, and bunch length were calculated and measured. The beam-induced heating of the cryogenic vacuum chamber was also studied. Finally, the superconducting wiggler has been commissioned for user operations.
36 MATERIALS SCIENCE↗
Analytic Nonlinear Methods for Beam Optics
In recent years there have been major advances in the computation and use of high-order maps for the design, optimization and operation of beamlines. We will describe five practical examples for both linear and circular colliders. From least to most complex these examples will be: use of similarity transformations (FFTB design, SLC diagnosis); statistical maps (SSC smear and tune-shift); aberrations (SLC upgrade); resonance basis and nPB tracking (PEP-II design); and kick factorization (possibly LHC).
43 PARTICLE ACCELERATORS↗
Beam optics and the pp2pp experiment at RHIC
The newly installed forward detector system at the STAR experiment at RHIC measures small angle elastic and inelastic scattering of polarized protons on polarized protons. The detector system makes use of a pair of Roman Pot (RP) detectors, instrumented with silicon detectors, and located on either side of the STAR intersection region downstream of the DX and D0 dipoles and quadrupole triplets. The parallel to point optics is designed so that scattering angles are determined from position measurements at the RP's with small error. The RP setup allows measurement of position and angle for a subset of the scattered protons. With this position/angle correlations at the RP's can be compared with optics model predictions to get a measure of the accuracy of the quadrupole triplet current settings. The current in each quadrupole in the triplets is comprised of sums and differences of up to six power supplies and an overall 1% error in the triplet field strengths results in a 4% error in four-momentum transfer squared. This technique is also useful to check the polarity of the skew elements located in each quadrupole triplet. Results of the analysis will be presented.
43 PARTICLE ACCELERATORS↗
First measurement of traverse beam optics for the Fermilab Muon Campus using a magnet scanning technique
In the following years the Fermilab Muon Campus will deliver highly polarized muon beams to the storage ring of the Muon g-2 Experiment. The transmission fraction of the storage ring has been shown to depend strongly on the transverse optics of the injected beam. Unfortunately, the current diagnostics in the Muon Campus allow only measurement of the beam configuration space which limits how well propagation can be predicted. This work demonstrates an experimental technique based on a conventional magnet scan to obtain the Twiss parameters at a point, using only beam profiles such that installation of new equipment is not required. A proof-of-principle experiment is presented which shows that this new method is applicable to the Muon Campus, offering a viable approach to optimization of injection in the Muon g-2 Experiment.
43 PARTICLE ACCELERATORS↗
Nonlinear integrable optics beam dynamics experiment and diagnostics
All present circular particle accelerators are built around linear focusing optics. Un-avoidable nonlinear elements appear in accelerators, such as magnetic aberrations and space-charge effects, which are typically corrected using nonlinear magnets. However, these added nonlinearities degrade particle beam stability, and in most cases, the system becomes non-integrable. The Integrable Optics Test Accelerator (IOTA), at Fermi National Accelerator Laboratory (Fermilab), is a test bed to study beam dynamics in integrable lattices for both electron and proton beams, independently. This work presents experimental results of the nonlinear electron beam dynamics behavior in IOTA using an elliptical nonlinear magnet. The elliptical nonlinear magnet allows for a large betatron tune spread, allowing for a stable high-intensity beam. In a future experimental run, minimally invasive beam instrumentation is needed to study time-dependent collective instabilities, and halo formation in space-chargedominated proton beams. Traditional profile monitors are too destructive to the beam or just measure one dimension of the beam. A gas sheet can be injected perpendicular to theproton beam at an angle. By doing so, a two-dimensional, turn-by-turn, transverse profile measurement can be made, which will preserve the integrity of the beam. The developmentand progress of a gas sheet beam profile monitor will also be presented.
43 PARTICLE ACCELERATORS↗
Beam Optics Measurements at the Fermilab Linac
The Fermilab Linac delivers 400 MeV H- beam to the rest of the accelerator complex. The Linac will be replaced by a SRF Linac that doubles the output energy as part of the Proton Improvement Plan-II (PIP-II) project. For successful PIP-II commissioning and operation, a comprehensive suite of longitudinal and transverse measurements are planned to fully characterize the beam dynamics. In the 400 MeV Linac, we used prototype programs to demonstrate the viability of these workflows. Here we present the results of these measurements of longitudinal and transverse optics.
Chen, Erin [Fermilab]↗
Compact Simultaneous-beam Optical Strain Measurement System, Phase 5
Recent advances on the laser speckle strain measurement system under development at NASA Lewis Research Center have resulted in a compact, easy-to-use measurement package having many performance improvements over previous systems. NASA has developed this high performance optical strain measurement system for high temperature material testing applications. The system is based on I. Yamaguchi's two-beam speckle-shift strain measurement theory, and uses a new optical design that allows simultaneous recording of laser speckle patterns. This design greatly improves system response over previous implementations of the two-beam speckle-shift technique. The degree of immunity to transient rigid body motions is no longer dependent on the data transfer rate. The system automatically calculates surface strains at a frequency of about 5 Hz using a high speed digital signal processor in a personal computer. This system is fully automated, and can be operated remotely. This report describes the designs and methods used by the system, and shows low temperature strain test results obtained from small diameter tungsten-rhenium and palladium-chrome wires.
Lant, Christian T.↗
Continuous Deflection of Laser Beams
Optical beam deflection method based on polarization change of acoustically deflected light as compared to incident beam
POLARIZATION CHARACTERISTICS↗
Beam Optics Studies for Larger Beampipe Diameters for the LAMP-PSR
The proposed beampipe diameter increase of the PSR beamlines for the LAMP PSR upgrade is expected decrease beam loss due to tuning errors and misalignment. However, a larger beampipe diameter would require increasing the pole-to-pole gap height within all magnets in the PSR (dipole gap, quadrupole bore, etc.). This would in turn affect the extent and profile of the fringe fields at the ends of the magnets, altering the effective length of the magnets and thus the magnetic optics. In this work, we used the simulation code MAD-X to model the PSR lattice for different beampipe diameters. The results of these simulations will be later used to benchmark particle simulations using the code pyORBIT. The MAD-X simulations are described, and the simulation results are discussed in this technote.
43 PARTICLE ACCELERATORS↗
Geometry Effects on Multipole Components and Beam Optics in High-Velocity Multi-Spoke Cavities
Velocity-of-light, multi-spoke cavities are being proposed to accelerate electrons in a compact light-source. There are strict requirements on the beam quality which require that the linac have only small non-uniformities in the accelerating field. Beam dynamics simulations have uncovered varying levels of focusing and defocusing in the proposed cavities, which is dependent on the geometry of the spoke in the vicinity of the beam path. Here we present results for the influence different spoke geometries have on the multipole components of the accelerating field and how these components, in turn, impact the simulated beam properties.
43 PARTICLE ACCELERATORS↗
X-ray Spectrometry in the Era of Aberration-Corrected Electron Optical Beam Lines
Abstract Aberration correction in the analytical transmission electron microscope is most closely associated with improvements in high-resolution imaging. In this paper, the combination of that technology with new system designs, which optimize both electron optics and x-ray detection, is shown to provide more than a tenfold increase in performance over the last 25 years.
Zaluzec, Nestor J. (ORCID:0000000248573487)↗
PERLE – BEAM OPTICS DESIGN
PERLE (Powerful ERL for Experiments) [1] is a novel ERL test facility, initially proposed to validate design choices for a 60 GeV ERL needed for a future extension of the LHC towards a hadron-electron collider, the LHeC [2]. Its main goal is to test the limits of a high current, CW, multi-pass operation with superconducting cavities at 802 MHz (and perhaps exploring other frequencies of interest). PERLE optics features Flexible Momentum Compaction (FMC) lattice architecture for six vertically stacked return arcs and a high current, 5 MeV photo-injector. With only one pair of 4-cavity cryomodules, 400 MeV beam energy can be reached in three re-circulation passes, with beam currents in excess of 15 mA. This unique quality beam is intended to perform a number of experiments in different fields reaching from uncharted tests of accelerator components via elastic ep scattering to laser-Compton backscattering for photon physics [3]. Following the experiment, the CW beam is decelerated in three consecutive passes back to the injection energy, transferring virtually stored energy back to the RF.
Bogacz, S.↗
Surface registration using a multi-beam optical probe and backscatter reflectometer
We introduce a technique for locating the position and orientation of an object surrounding a compound optical probe. The probe allows for simultaneous measurement of 150 points of laser velocimetry, and prior to a dynamic experiment it is important to know the initial position of the surface. Using an optical switch and a Luna OBR rangefinder, we measure the surface distance at hundreds of locations. These measurements are then combined with a dimensional inspection of the object and analysis routines to report the orientation and location of the inner surface relative to the probe. In addition, we present a technique to simultaneously measure the beam paths using a reference hemispherical surface and a number of distance measurements.
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