Simultaneous correction of high order geometrical driving terms with octupoles in synchrotron light sources
Not Available
36 MATERIALS SCIENCE↗
Engineering topics
Shaftan, Timur
Publications and source records attributed to Shaftan, Timur.
Accurate prediction of mega-electron-volt electron beam properties from UED using machine learning
To harness the full potential of the ultrafast electron diffraction (UED) and microscopy (UEM), we must know accurately the electron beam properties, such as emittance, energy spread, spatial-pointing jitter, and shot-to-shot energy fluctuation. Owing to the inherent fluctuations in UED/UEM instruments, obtaining such detailed knowledge requires real-time characterization of the beam properties for each electron bunch. While diagnostics of these properties exist, they are often invasive, and many of them cannot operate at a high repetition rate. Here, we present a technique to overcome such limitations. Employing a machine learning (ML) strategy, we can accurately predict electron beam properties for every shot using only parameters that are easily recorded at high repetition rate by the detector while the experiments are ongoing, by training a model on a small set of fully diagnosed bunches. Applying ML as real-time noninvasive diagnostics could enable some new capabilities, e.g., online optimization of the long-term stability and fine single-shot quality of the electron beam, filtering the events and making online corrections of the data for time-resolved UED, otherwise impossible. This opens the possibility of fully realizing the potential of high repetition rate UED and UEM for life science and condensed matter physics applications.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Numerical simulation of NSLS-II fast orbit feedback system
We discuss recent work on the construction of a numerical simulation of the fast orbit feedback system at NSLS-II. The simulation operates in the time domain and also includes the spatial domain, i.e. all beam position monitors (BPMs) and correctors. It can accept inputs of the real beam orbit and the measured orbit response matrix. It can also add errors to every stage of the calculation. We present methods to verify the simulation results by comparing the simulation results with experimental data collected at NSLS-II. The results are in very good agreement. The effects of errors from BPMs and correctors, as well as the amplitude of excitation, on the feedback performance, are also explored. This simulation can be used to predict the behavior and performance of the system for a future upgrade.
36 MATERIALS SCIENCE↗
Toward monochromated sub-nanometer UEM and femtosecond UED
A preliminary design of a mega-electron-volt (MeV) monochromator with 10 –5 energy spread for ultrafast electron diffraction (UED) and ultrafast electron microscopy (UEM) is presented. Such a narrow energy spread is advantageous in both the single shot mode, where the momentum resolution in diffraction is improved, and the accumulation mode, where shot-to-shot energy jitter is reduced. In the single-shot mode, we numerically optimized the monochromator efficiency up to 13% achieving 1.3 million electrons per pulse. In the accumulation mode, to mitigate the efficiency degradation caused by the shot-to-shot energy jitter, an optimized gun phase yields only a mild reduction of the single-shot efficiency, therefore the number of accumulated electrons nearly proportional to the repetition rate. Inspired by the recent work of Qi et al. (Phys Rev Lett 124:134803, 2020), a novel concept of applying reverse bending magnets to adjust the energy-dependent path length difference has been successfully realized in designing a MeV monochromator to achieve the minimum energy-dependent path length difference between cathode and sample. Thanks to the achromat design, the pulse length of the electron bunches and the energy-dependent timing jitter can be greatly reduced to the 10 fs level. The introduction of such a monochromator provides a major step forward, towards constructing a UEM with sub-nm resolution and a UED with ten-femtosecond temporal resolution. The one-to-one mapping between the electron beam parameter and the diffraction peak broadening enables a real-time nondestructive diagnosis of the beam energy spread and divergence. The tunable electric–magnetic monochromator allows the scanning of the electron beam energy with a 10 –5 precision, enabling online energy matching for the UEM, on-momentum flux maximizing for the UED and real-time energy measuring for energy-loss spectroscopy. A combination of the monochromator and a downstream chicane enables “two-color” double pulses with femtosecond duration and the tunable delay in the range of 10 to 160 fs, which can potentially provide an unprecedented femtosecond time resolution for time resolved UED.
36 MATERIALS SCIENCE↗
Recent improvements in beam orbit feedback at NSLS-II
This paper discusses improvements made to the fast orbit feedback (FOFB) system at NSLS-II in 2019. We first characterized the system by measuring the transfer function and the closed-loop gain of the system. We also constructed a model to predict the performance, which was based on physical behaviors. After finding and fixing the sources of the latency, we improved the closed-loop gain’s bandwidth from 250 Hz to 400 Hz in the horizontal plane and 250 Hz to 300 Hz in the vertical plane. As a result, the orbit beam instability improved by 30% and 10% in the horizontal and vertical planes, respectively.
36 MATERIALS SCIENCE↗
A novel nondestructive diagnostic method for mega-electron-volt ultrafast electron diffraction
Abstract A real-time, nondestructive, Bragg-diffracted electron beam energy, energy-spread and spatial-pointing jitter monitor is experimentally verified by encoding the electron beam energy and spatial-pointing jitter information into the mega-electron-volt ultrafast electron diffraction pattern. The shot-to-shot fluctuation of the diffraction pattern is then decomposed to two basic modes, i.e., the distance between the Bragg peaks as well as its variation (radial mode) and the overall lateral shift of the whole pattern (drift mode). Since these two modes are completely decoupled, the Bragg-diffraction method can simultaneously measure the shot-to-shot energy fluctuation from the radial mode with 2·10 −4 precision and spatial-pointing jitter from the drift mode having wide measurement span covering energy jitter range from 10 −4 to 10 −1 . The key advantage of this method is that it allows us to extract the electron beam energy spread concurrently with the ongoing experiment and enables online optimization of the electron beam especially for future high charge single-shot ultrafast electron diffraction (UED) and ultrafast electron microscopy (UEM) experiments. Furthermore, real-time energy measurement enables the filtering process to remove off-energy shots, improving the resolution of time-resolved UED. As a result, this method can be applied to the entire UED user community, beyond the traditional electron beam diagnostics of accelerators used by accelerator physicists.
43 PARTICLE ACCELERATORS↗
NSLS-II FOFB Performance Improvement in 2019
APS-U declared that they have achieved 700 Hz to 1kHz fast orbit feedback (FOFB) closeloop bandwidth in their two-section test setup. Before this, most light sources have been running FOFB with 100-200Hz bandwidth. Table 1 shows the information of bandwidths and sampling rates of various Synchrotron facilities.
36 MATERIALS SCIENCE↗
Towards coherent X-ray free-electron lasers
Increased bandwidth and fluctuations are difficulties on the path towards generating intense fully coherent X-ray free-electron laser output. A recent experiment at FERMI Trieste observed that these problems can be overcome by an approach called echo-enabled harmonic generation.
43 PARTICLE ACCELERATORS↗
Study of Fluctuations in Undulator Radiation in the IOTA Ring at Fermilab
We study turn-by-turn fluctuations in the number of emitted photons in an undulator, installed in the IOTA electron storage ring at Fermilab with an InGaAs PIN photodiode and an integrating circuit. Our study was motivated by the previous experiment *. We propose a theoretical model for the experimental data from * and in our own experiment we attempted to verify the model in an independent and more systematic way. Moreover, these fluctuations are an interesting subject for a study by itself, since they act as a seed for SASE in FELs. We improve the precision of the measurements from * by subtracting the average signal amplitude using a comb filter with a one-turn IOTA delay, and by using a special algorithm for noise subtraction. We obtain a reasonable agreement between our theoretical model and experiment. Along with repeating the experiment from *, which was performed at a constant beam current, we also collect data for fluctuations in undulator light at different beam current values. Lastly, in our experiment we were able to see the transition from Poisson statistics to Super-Poisson statistics for undulator light, whereas in * only the latter statistics was observed.
43 PARTICLE ACCELERATORS↗
Experimental Study of a Single Electron in a Storage Ring via Undulator Radiation
A single electron orbiting around a ring and emitting single quanta at the rate of about one event per hundred turns could produce a wealth of information about physical processes in large traps (i.e. storage rings) for charged particles. It should be noted that Paul and Penning traps in the 1980s led to the Nobel prize for studying state and motion of single quantum particles, and just recently the Penning trap technique has enabled the measurement of a single proton magnetic moment with an unprecedented precision of 10 decimal places. The information from the storage ring traps could also be used for characterization of a quantum system as well as the "trap" itself, i.e. measuring properties of the storage ring lattice and electron interaction with the laser fields. Although, the interest in single electron quantum processes today is mostly academic in nature, the diagnostics and methodology developed for single electron radiation studies could find subsequent applications in a variety of applied disciplines in quantum technology, including quantum communications and quantum computing.
43 PARTICLE ACCELERATORS↗
A compact tunable quadrupole lens for brighter and sharper ultra-fast electron diffraction imaging
In this article, we report our proof-of-principle design and experimental commissioning of a broadly tunable and low-cost transverse focusing lens system for MeV-energy electron beams. The lens system based on electromagnetic (EM) quadrupoles has been built as a part of the existing instrument for ultra-fast electron diffraction (UED) experiments at the Accelerator Test Facility II (ATF-II) at Brookhaven National Laboratory (BNL). We experimentally demonstrated the independent control of the size and divergence of the beam with the charge ranging from 1 to 13 pC. The charge density and divergence of the beam at the sample are the most important factors determining the quality of the Bragg-diffraction image (BDI). By applying the Robust Conjugate Directional Search (RCDS) algorithm for online optimization of the quadrupoles, the transverse beam size can be kept constant down to 75 µm from 1 to 13 pC. The charge density is nearly two orders of magnitude higher than the previously achieved value using a conventional solenoid. Using the BDI method we were able to extract the divergence of the beam in real-time and apply it to the emittance measurement for the first time. Our results agree well with simulations and with the traditional quadrupole scan method. The real-time divergence measurement opens the possibility of online optimization of the beam divergence (< 0.2 mrad) at the sample with the increased beam charge. This optimization is crucial for the future development of single-shot ultra-fast electron microscope (UEM). Finally, we demonstrated BDI with significant improvement, up to 3 times higher peak intensity and 2 times sharper Bragg-diffraction peaks at 13 pC. The charge is now limited by the laser power and increasing charge may improve the quality of BDI further. The capability we demonstrated here provides us with opportunities for new sciences using near-parallel, bright and ultrafast electron beams for single-shot imaging, to directly visualize the dynamics of defects and nanostructured materials, or even record molecular movie, which are impossible using present electron-beam technologies.
43 PARTICLE ACCELERATORS↗
Complex Bend II
We present a new optics solution for the Complex Bend, which offers to substantially reduce the device length by removing the dipole poles. The bending is now realized by shifting the quadrupole poles along the horizontal axis. The ring optics can be stable if a specific condition on the relationship between the shifts of focusing and defocusing poles is satisfied. This condition is described in Section 2 of this Tech note. Section 1 describes general analysis of beam transport in a shifted quadrupole. Section 3 presents a set of parameters for such a ring, assuming that a single cell of the Complex Bend consists of 2 Combined Function dipoles. Section 4 describes more realistic model of a single cell constructed with two quadrupoles shifted off their reference trajectory. Section 5 is dedicated to calculations of synchrotron radiation from Complex Bend poles. Throughout this preprint we will call the QF-D-B-D-QD-D-B-D version as Complex Bend I (CBI) and the QF-D-QD-D version as Complex Bend II (CBII).
36 MATERIALS SCIENCE↗
Maximum Current of the NSLS-II Linac
The maximum current of the NSLS-II linac is an important operational parameter for determining the safety envelope of the acceleration. In this document we establish the maximum current of the NSLS-II linac. First we establish the maximum current that can be emitted by the gun and the parameters that limit this. Then we show that beam loading in the linac further limits the current available at the exit of the linac. Beam loading also determines the energy spectrum of the beam at the end of the linac. Once the maximum current at the exit of the linac is established, we transport this beam through the linac to booster transport line using the designed optics which will match the beam from the linac into the booster. This will determine the maximum current that can be delivered to the booster accelerator from the linac.
36 MATERIALS SCIENCE↗
Specifications on the RF ramp for the NSLS-II Booster
Detailed specifications for the booster RF ramp and discuss its relation to the dipole PS current waveform.
36 MATERIALS SCIENCE↗
ParameterizationBR2
In the following we detail the ramp parameterization procedure. The purpose of this procedure is in reduction of the data volume loaded into PSC. The same approach will be implemented in HLA “Booster Ramp Generator”.
42 ENGINEERING↗
Parameters and Tolerances for the Booster Dipole Power Supplies
In this technical note we discuss the parameters and tolerances for the booster dipole power supplies. We first discuss the requirements on the current ramp profile for the cases of energy ramps at 1 and 2 Hz. Then we determine the voltage waveforms that correspond to these current ramps. Using the booster magnet lattice and the actual power supply circuit layouts we then calculate the orbit distortion and tune spread caused by the magnetic field amplitude errors in the combined-function dipole magnets at the time of injection and extraction and establish the requirements on the value of the magnetic field amplitude errors at these points along the ramp. We then conclude the note by translating these requirements into the amplitude and time tolerances for the dipole power supplies.
42 ENGINEERING↗
Merging Dog-leg for Including the Second Gun in the NSLS-II Linear Accelerator
The low-energy part of the NSLS-II linear accelerator begins with the 100-keV gun, which is the key component for the injector performance. The gun electronics determine the generated bunch patterns, emittance, energy spread and charge transport efficiency in the low-energy part of the injector. We proposed to include a second gun to the NSLS-II linac. This upgrade will: a) increase reliability of the NSLS-II accelerator complex and, b) enable more efficient operations in generating complex bunch patterns. The latter is critical since for supporting complex bunch patterns the same gun must be able to switch robustly between single- and multi-bunch modes within the time interval between the top-off cycles. Including the 2nd gun, operating exclusively in the single-bunch mode, would greatly simplify switching between the modes as well as reduce beam charge losses. We designed the NSLS-II linac tunnel so there is a small extra room for the second gun that we proposed to introduce into the main linac via a short dog-leg. To minimize the additional space the dog-leg must be very short and parameters of the dog-leg optical components must stay within reasonable field and gradient values.
43 PARTICLE ACCELERATORS↗