Advanced Photon Source Storage Ring Research Articles

Application of a machine learning based algorithm to online optimization of the nonlinear beam dynamics of the Argonne Advanced Photon Source

A machine learning-based optimization algorithm, the multigeneration Gaussian process optimizer, is used to optimize the nonlinear beam dynamics of the Advanced Photon Source storage ring. The dynamic aperture (DA) and the local momentum aperture (LMA) are first optimized separately with sextupole knobs. Solutions found with these optimizations are used to seed the initial population of seeds in two-objective optimizations that simultaneously optimize the DA and LMA, which lead to a distribution of solutions with different DA and LMA performances, from which a setting suitable for operation can be selected.

Fabrication and Testing of 10-Pole Short-Period Nb3Sn Superconducting Undulator Magnets

NbTi superconducting undulators (SCUs) are currently reliably operating at the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). These devices have significantly enhanced x-ray flux and brightness at the high energy spectrum. As NbTi SCU technology is close to its full potential, further performance enhancement requires using different superconducting materials. Nb3Sn is a promising candidate to achieve that goal. Recently the APS has started developing a Nb3Sn superconducting undulator compatible with the APS storage ring. The completed device is planned to be installed in the APS storage ring. To develop the Nb3Sn SCU technology, a series of short SCU models has been previously fabricated and successfully tested. In this study, the design has been further optimized to address previously unresolved problems. Several 10-pole, 4.5-period models were fabricated and tested. All of the fabricated models have reached the maximum operating current; however, one of the model, MM4, has failed right after reaching the maximum design current. The details of quench and training performances are presented.

Development and operating experience of a 1.2-m long helical superconducting undulator at the Argonne Advanced Photon Source

Development of superconducting undulators (SCUs) continues at the Advanced Photon Source (APS). Several planar SCUs were designed and built, and two of them are currently in operation at the APS. In January 2018 a new helical SCU (HSCU) was installed on the storage ring at the APS. It has a 1.2 m-long magnet with bifilar winding that generates on its axis a single harmonic of about 6 keV x-rays. The magnet is housed in the newly designed compact cryostat equipped with four cryocoolers. The HSCU was extensively tested prior to its installation on the APS storage ring, and it demonstrated cryogenic and magnetic performance in accordance with the design specifications. The HSCU was rapidly and successfully commissioned, and in February 2018 it was transferred to user operations. Its performance as an x-ray radiation source has been studied and spectral characteristics confirmed. The HSCU is currently used to support unique scientific program at the APS.

Thermal Analysis of a Helical Superconducting Undulator Cryostat

A novel cryocooler-cooled helical superconducting undulator (HSCU) was built and installed in the Advanced Photon Source (APS) storage ring and has been in operation since January 2018. The new cryostat for the HSCU is a major improvement of the cryogenic system used for the existing APS planar superconducting undulators. In both systems, superconducting magnets are cooled independently from the beam chamber by liquid helium (LHe) passing through a channel in the magnet/mold assembly. The original planar undulator cryostat consists of three thermal circuits: the outer shield circuit to cool both the warm part of the magnet current leads and the outer shield, the beam chamber cooling circuit to cool the beam chamber and the inner shield, and the magnet cooling circuit to cool the magnets and the LHe tank. On the other hand, the new system consists of only two thermal circuits: the thermal shield circuit to cool the beam chamber, the shield, and the warm part of the magnet leads; and the magnet cooling circuit to cool the LHe tank and the magnet/mold assembly. An finite element analysis-based thermal model of the new HSCU cryostat was developed while the cryogenic performance of the HSCU was measured in a series of standalone tests as well as after installation in the storage ring. This paper presents a thermal analysis of the new HSCU cryostat and, in particular, a comparison of calculated and measured temperatures as well as the excess cooling capacity of the new cryostat in static and dynamic (beam-induced heating) modes.

Thermal Model of a Quench in Superconducting Undulators

Currently there are two 1.1 m long planar superconducting undulators (SCUs) in operation in the Advanced Photon Source storage ring. Their NbTi magnets are cooled with liquid Helium (LHe) penetrating through a channel in the magnet coil formers. In this scheme, the latent heat of LHe provides an effective energy buffer that allows the magnet to return to normal operation within minutes. An FEA-based dynamic thermal model of the SCU is being developed to analyze the behavior of the SCU cryogenic systems during a quench. In this paper, preliminary results of these FEA-based calculations and a comparison with the current operation of SCUs are presented.

A second-generation superconducting undulator cryostat for the APS

A second-generation cryocooler-based cryostat has been designed and built to support a new helically wound superconducting undulator (SCU) magnet for the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). The design represents an evolution of existing SCU cryostats currently in operation in the APS storage ring. Value engineering and lessons learned have resulted in a smaller, cheaper, and simpler cryostat design compatible with existing planar magnets as well as the new helically wound device. We describe heat load and quench response results, design and operational details, and the “build-to-spec” procurement strategy.

Thermal analysis of superconducting undulator cryomodules

A cryocooler-cooled superconducting undulator (SCU0) has been operating in the Advanced Photon Source (APS) storage ring since January of 2013. Based on lessons learned from the construction and operation of SCU0, a second superconducting undulator (SCU1) has been built and cold tested stand-alone. An excess cooling capacity measurement and static heat load analysis show a large improvement of cryogenic performance of SCU1 compared with SCU0. ANSYS-based thermal analysis of these cryomodules incorporating all the cooling circuits was completed. Comparisons between measured and calculated temperatures at the three operating conditions of the cryomodule (static, beam heat only, beam heat and magnet current) will be presented.

Test Results of a Planar Superconducting Undulator for the Advanced Photon Source

The first superconducting planar undulator (SCU0) at the Advanced Photon Source (APS) has been built with the goal of providing the APS users with higher photon fluxes at higher photon energies. The undulator magnetic structure is wound with NbTi superconducting wire. The magnet is indirectly cooled by liquid helium circulating in a closed circuit. The cooling of the helium circuit, the current leads, and the thermal shields are provided by four cryocoolers. After a rigorous stand-alone cold test the undulator has been installed into the APS storage ring. The results of the SCU0 cold test are presented in this paper.

Realization of a locally-round beam in an ultimate storage ring using solenoids

“Ultimate" storage rings (USRs), with electron emittance smaller than 100 pm-rad and on the scale of the diffraction limit for hard X-rays in both transverse planes, have the potential to deliver photons with much higher brightness and higher transverse coherence than that projected for the rings currently operational or under construction. Worldwide efforts have been made to design and to build light sources based on USRs. How to obtain a round beam, i.e., a beam with equivalent transverse emittances, is an important topic in USR studies. In this paper, we show that a locally-round beam can be achieved by using a pair of solenoid and anti-solenoid with a circularly polarized undulator located in between. Theoretical analysis and application of this novel method, particularly to one of the Beijing Advanced Photon Source storage ring design having natural emittance of 75 pm·rad, are presented.

Development of a superconducting undulator for the APS

As the western hemisphere's premier x-ray synchrotron radiation source, the Advanced Photon Source (APS) continues to advance the state of the art in insertion device technology in order to maintain record high brightness, especially in the hard x-ray wavelength region. Due to the unique bunch pattern used for normal APS operations and its ultimate capabilities, the APS has chosen superconducting technology for its future hard x-ray undulator sources. In the last several years, the APS in collaboration with the Budker Institute of Nuclear Physics has being developing the technology for planar, small-period superconducting undulators (SCUs). These developments include the design and construction of several prototypes and the construction of the necessary mechanical, vacuum, and cryogenic infrastructure at the APS site. Several prototypes of the SCU magnetic structure have been built and tested. The first SCU is assembled and will be installed in the APS storage ring at the end of 2012. Expected SCU performance in terms of x-ray brightness should noticeably exceed that of existing APS undulators. Immediately after commissioning, the SCU will be used at APS Sector 6 as the radiation source for high-energy x-ray studies.

Mechanical design and fabrication of a two-blade stripline for the Advanced Photon Source storage ring

The storage ring tune measurement system at the Advanced Photon Source (APS) consists of signal pickup and beam excitation drive striplines. Striplines currently installed in the APS storage ring are of a four-blade (inner conductor) design that serves as a beam diagnostic tool and for transverse and longitudinal tune measurements. A new two-blade stripline was designed for the transverse feedback system and to be used for horizontal beam excitation. In this paper, we discuss its mechanical design, assembly procedure, and construction.

Picosecond time-resolved laser pump/X-ray probe experiments using a gated single-photon-counting area detector

The recent developments in X-ray detectors have opened new possibilities in the area of time-resolved pump/probe X-ray experiments; this article presents the novel use of a PILATUS detector to achieve X-ray pulse duration limited time-resolution at the Advanced Photon Source (APS), USA. The capability of the gated PILATUS detector to selectively detect the signal from a given X-ray pulse in 24 bunch mode at the APS storage ring is demonstrated. A test experiment performed on polycrystalline organic thin films of alpha-perylene illustrates the possibility of reaching an X-ray pulse duration limited time-resolution of 60 ps using the gated PILATUS detector. This is the first demonstration of X-ray pulse duration limited data recorded using an area detector without the use of a mechanical chopper array at the beamline.

Transient bunch compression using pulsed phase modulation in high-energy electron storage rings

A method for producing short electron bunches in an electron storage ring using pulsed phase modulation has been demonstrated. A simple theoretical model was validated using the particle tracking code elegant, and the bunch compression process was observed experimentally in the Advanced Photon Source storage ring using a visible light streak camera. Compression to 54% of the initial bunch length was achieved.

Storage-ring-based, ultrashort positron beam source

We propose a scheme to generate high-flux, short-burst γ-ray radiation and its application for generating ultrashort positron beams. The intense γ-ray bursts are generated from short laser pulses scattering off high-energy electron beams in a storage ring. The γ-ray bursts are then used to irradiate thin metal targets to generate the positron beams via pair production. Using the example of the Advanced Photon Source storage ring, more than 107positrons∕s in 1ps pulses at energies of a few MeV can be generated.

A fast mechanical shutter for submicrosecond time-resolved synchrotron experiments

A new high-speed high-repetition-rate X-ray beam shutter for time-resolved photocrystallography at synchrotron sources has been developed and tested. The new design is based on a commercially existing DC servomotor and a frequency-lock control capable linear amplifier. Accurate speed control combined with an air bearing results in extremely low jitter in the motor rotation. Measured jitter at rotation speeds of 12000 to 30000 r min-1 is less than 2 ns at a 6sigma confidence level. The chopper disc is interchangeable, allowing maximum flexibility. The chopper disc currently installed has 45 radial slots which allows synchronization from the 12th to the 20th subfrequencies of the orbit frequency of the Advanced Photon Source storage ring, corresponding to X-ray pulse frequencies of 13.6 to 22.6 kHz. At 30000 r min-1 the opening time window with a 350 microm slot size is 2.11 micros, and correspondingly less with smaller openings, which may be compared with the 3.68 micros orbit time of the Advanced Photon Source. The shutter provides high accuracy and efficient use of X-rays at a modest cost.

X-ray photoelectron spectroscopy and secondary electron yield analysis of Al and Cu samples exposed to an accelerator environment

It is well known that exposure to an accelerator environment can cause “conditioning” of the vacuum chamber surfaces. In order to understand the manner in which the surface structure might influence the production of gases and electrons in the accelerator, such surfaces should be studied both before and after exposure to accelerator conditions. Numerous studies have been performed on representative materials prior to being inserted into an accelerator, but very little has been done on materials that have “lived” in the accelerator for extended periods. In the present work, we mounted Al and Cu coupons at different positions in a section of the Advanced Photon Source storage ring and removed them following exposures ranging from 6 to 18 months. X-ray photoelectron spectroscopy (XPS) of the surface was performed before and after exposure. Changes were observed that depended on the location and whether the coupon was facing the chamber interior or chamber wall. These results will be presented and compared to XPS and secondary electron yield data obtained from laboratory measurements meant to simulate the accelerator conditions.

A synchronized rotating crystal x-ray beam chopper

A new x-ray beam chopper has been designed and tested at the Advanced Photon Source. This beam chopper uses the diffractive properties of a rotating crystal to produce transmission window times as short as about 10 ns from a single diffracting face for 10 keV radiation. Precision control of the crystal rotation allows phase locking with the orbital frequency of the synchrotron storage ring; hence, the transmission of short x-ray pulses, corresponding to the 50 ps full width at half maximum charge bunch length, is possible with any fill pattern presently used at the Advanced Photon Source storage ring.

A rudimentary electron energy analyzer for accelerator diagnostics

We have constructed a compact, planar retarding field analyzer for the diagnostics of low-energy, background electrons in a high-energy particle accelerator. Bench measurements of the analyzer have been made to characterize it, and the results are reasonable in light of models of this type of analyzer. Comparisons to results obtained using a beam-position monitor (BPM) show the advantages of this analyzer for electron diagnostics. Sample results from analyzers installed at the Advanced Photon Source storage ring at Argonne National Laboratory and the Proton Storage Ring at Los Alamos National Laboratory show how the analyzers can be used for studying the intensity, energy, and time structure of electrons in an accelerator environment.

A new high-speed beam chopper for time-resolved X-ray studies

A new high-speed X-ray beam chopper, which can be phase locked to the temporal structure of the Advanced Photon Source (APS) storage ring, has been developed and tested. The open window time of the chopper is 2450 ns, which corresponds to approximately 67% of the revolution time of the APS storage ring. By phase locking the rotation of the beam chopper to the storage-ring orbital frequency, any portion of the storage-ring fill pattern can be positioned within the beam-chopper transmission-time window.

Digital closed orbit feedback system for the Advanced Photon Source storage ring

Closed orbit feedback for the Advanced Photon Source (APS) storage ring employs unified global and local feedback systems for stabilization of particle and photon beams based on digital signal processing. Hardware and software aspects of the system will be described. In particular, we will discuss global and local orbit feedback algorithms, PID (proportional, integral, and derivative) control algorithm, application of digital signal processing to compensate for vacuum chamber eddy current effects, resolution of the interaction between global and local systems through decoupling, self-correction of the local bump closure error, user interface through the APS control system, and system performance in the frequency and time domains. The system hardware, including the digital signal processor (DSPs), is distributed in 20 VME crates around the ring, and the entire feedback system runs synchronously at 4-kHz sampling frequency in order to achieve a correction bandwidth exceeding 100 Hz. The required data sharing between the global and local feedback systems is facilitated via the use of fiber-optically networked reflective memories.