Turn-by-turn Research Articles

Implementing nonlinear optics from Off-Energy closed orbit at NSLS-II

To characterize the second-order (chromatic sextupole) magnet lattice with high precision, we implemented nonlinear optics from off-energy closed orbit (NOECO) tool based on the linear optics from closed orbit modulation (LOCOM) method, named LOCOM-NOECO. The preliminary numerical study indicates that 1–2% precision can be achieved for the calibration of chromatic sextupoles. This accuracy could potentially help in resolving some long-standing challenges of NSLS-II (e.g., the discrepancy between the designed and measured dynamic apertures) if such high precision can be fulfilled. As an independent crosscheck, we also implemented NOECO based on the independent component analysis (ICA) method using turn-by-turn (TBT) BPM data, named ICA-NOECO. Both ICA-NOECO and LOCOM-NOECO have been successfully applied to identify the pre-dialed random errors of a chromatic sextupole family including five power supplies, and achieved the root mean square (RMS) residual error of 1% and peak error less than 2%. Moreover, to mitigate the chromatic sextupole error effect, we applied the correction and achieved significant improvements in the injection efficiency as well as the dynamic apertures.

Coupled twiss parameters estimation from turn-by-turn data

Linear optics parameters are often estimated using turn-by-turn (TbT) data. In-plane beta functions, which are the most common measurement objectives, can be estimated from the amplitudes or phases of TbT data, providing an overall characterization of the linear lattice. In addition to estimating uncoupled Twiss parameters, TbT data can also be utilized for characterizing coupled linear motion. We investigate several methods for constructing a full normalization matrix at each beam position monitor (BPM). BPMs provide information on beam centroid transverse coordinates, but direct observation of transverse momenta is not available. To estimate momenta, one can use a pair of BPMs or fit data obtained from several BPMs. By using both coordinates and momenta, it is possible to fit the one-turn matrix (or its power) at each BPM, allowing for the computation of coupled Twiss parameters. Another approach involves the minimization of side peak amplitudes in the spectrum of normalized complex coordinates. Similarly, the normalization matrix can be estimated by fitting linear coupled invariants. In this study, we derive and utilize a special form of the normalization matrix, which remains non-singular in the zero coupling limit. Coupled Twiss parameters can be obtained from the normalization matrix. The paper presents the results of applying and comparing these methods to both modeled and measured VEPP-4M TbT data, demonstrating effective estimation of coupled Twiss parameters.

VEPP-4M linear optics correction using orbit response matrices

This paper presents procedures and techniques for correcting the linear optics of the VEPP-4M collider. The accelerator structure investigation is based on the measurement and analysis of orbit response matrices (ORM) and optical functions reconstructed from turn-by-turn (TbT) data. Having no technical description of quadrupole lenses and corrector magnets, we have calibrated their current dependencies of magnetic strengths and fields, respectively. Corresponding to the reference orbit, quadrupole shifts in each plane have been obtained by using the beam-based alignment (BBA) technique. The accelerator optics has been corrected and calibrated at the injection energy of 1.9 GeV. The software combining automated optical functions measurement and correction has been developed and successfully implemented at VEPP-4M.

Enhancing wayfinding and route learning: a human-centred study of the route-defining locations algorithm

ABSTRACT Navigation services play a crucial role in everyday wayfinding. One of their key features is the turn-by-turn guidance, enabling wayfinders to navigate efficiently between locations. However, over-reliance on turn-by-turn guidance can hinder wayfinders' ability to perceive their surroundings and develop spatial awareness, negatively impacting user experience. Previous research has addressed these issues by modifying instructions, user interaction, or both. However, the applicability of these methods beyond specific studies remains unclear. This paper presents a human-centred study by evaluating an algorithm that automatically generates navigation instructions. The instructions are generated by adding route-defining locations to ‘standard’ turn-by-turn instructions to enhance wayfinder's spatial knowledge acquisition, and improve user experience. Route-defining locations, identified using a previously proposed algorithm, serve as anchors for the wayfinder to form a spatial understanding of the environment. The study involved 36 participants divided into two groups: one received ‘standard’ turn-by-turn (TBT) instructions, while the other received instructions that included route-defining locations (RDL). Participants navigated in an unfamiliar virtual environment, and their wayfinding and route learning were compared between the two groups. Results show that RDL instructions led to better wayfinding and route learning performance compared to TBT instructions, suggesting the potential to improve navigation systems and user experiences.

BeeAR: Augmented Reality Beeline Navigation for Spatial Knowledge Acquisition

Navigation assistance systems have become integral to our daily routines, helping us to find our way through unfamiliar environments. However, their use may come at a price, as empirical evidence suggests a potentially harmful impact of these systems on our spatial abilities, including the acquisition of spatial knowledge. This could be remedied by giving users more freedom and involving them in the decision-making process. Therefore, we present a navigation system that combines augmented reality and Beeline Navigation (BeeAR). Here, the location of the destination is overlaid with a digital landmark and permanently displayed to the user via a visual, translucent AR display (without a map). Since the digital content is integrated into the real world, no mapping between the device and reality is required, potentially lowering the workload. Making one's own decisions along the route is expected to increase engagement with the environment, leading to increased acquisition of spatial knowledge. We compare BeeAR with findings from a previous study comparing Free Choice Navigation (FCN) and Turn-by-Turn (TBT) navigation conducted along the same routes on the outskirts of Vienna, Austria. Although BeeAR and FCN do not provide users with a map, BeeAR users could better retrace the walked route and remembered more points of interest along the route than FCN users. Participants of all three navigation conditions achieved a high configuration similarity between drawn points of interest and their true locations, albeit only one navigation condition included a map.

An exploratory real-world wayfinding experiment: A comparison of drivers’ spatial learning with a paper map vs. turn-by-turn audiovisual route guidance

Turn-by-turn (TBT) route guidance technology installed on mobile phones is very popular among car drivers for wayfinding purposes. Previous studies examined their effect on spatial knowledge predominantly on pedestrians or in virtual environments. Drivers' spatial knowledge was experimentally compared in two random groups: audiovisual route guidance using the TBT navigation feature of the Google Maps app installed on a mobile phone, and a paper map. Participants drove their own vehicles to a predesignated destination in an unfamiliar residential neighborhood. Spatial knowledge tests (orientation, landmark recognition and route recognition) were subsequently administered. The scores of map-assisted drivers were uncorrelated and, on average, higher in orientation (deviation in direction), landmark recognition and route recognition (error percentage). The landmark recognition scores of drivers assisted by TBT route guidance were significantly lower with a very large effect size. The route recognition scores of drivers assisted by route guidance showed strong correlations with orientation and with landmark recognition scores. Results can be attributed to the differences in cognitive effort required to complete the wayfinding task: unlike memorizing a global map survey, passively following TBT audiovisual instructions does not require drivers to actively encode, transform, and continuously monitor their egocentric position in space. Drivers also showed somewhat poorer performance relative to studies with pedestrians which can be explained by the greater mental effort, compared to wandering on foot, involved in wayfinding while safely driving a rapidly moving vehicle. The future implications of the increasing dependence on mobile navigation technologies are further discussed.

Measurement and analysis of fast transient instabilities

Abstract A novel beam diagnostics technique to detect fast beam transient instabilities and glitches has been developed at National Synchrotron Light Source II (NSLS-II). Vertical spikes of beam size and centroid have been observed occasionally and randomly during high current operations. These spikes are believed to be caused by ion instabilities associated with vacuum activity localized in the ring. With the functionality of gated beam position monitor (BPM), the newly developed technique utilizes turn-by-turn (TBT) data to detect beam centroid glitches. Whenever one turn trajectory deviates from a predefined window, a global control event is generated to trigger an online TBT data acquisition. The data acquisition is synchronized for all BPMs around the ring. In the meantime, the bunch-by-bunch (BxB) data, which is acquired from a single dedicated feedback BPM, has also been collected for analyzing possible coupled bunch instabilities (CBI). In addition to CBI caused mainly by ion bursts, other types of fast transient motions, such as, the top-off residual disturbance and fast orbit disturbance, have been captured with the new tool. The sources of the glitches can be approximately localized with the synchronized TBT data from multiple BPMs around the ring.

Refined betatron tune measurements by mixing beam position data

The measurement of the betatron tunes in a circular accelerator is of paramount importance due to their impact on beam dynamics. The resolution of the these measurements, when using turn by turn (TbT) data from beam position monitors (BPMs), is greatly limited by the available number of turns in the signal. Due to decoherence from finite chromaticity and/or amplitude detuning, the transverse betatron oscillations appear to be damped in the TbT signal. On the other hand, an adequate number of samples is needed, if precise and accurate tune measurements are desired. In this paper, a method is presented that allows for very precise tune measurements within a very small number of turns. The theoretical foundation of this method is presented with results from numerical and tracking simulations but also from experimental TbT data which are recorded at electron and proton circular accelerators.

Fast glitch detection of coupled bunch instabilities and orbit motions

During high current operation at NSLS-II storage ring, vertical beam size spikes have been noticed. The spikes are believed due to ion instability associates with vacuum activities localized in the ring. A new tool has been developed using gated BPM turn-by-turn (TBT) data to detect beam centroid glitches. When one turn orbit deviates outside the predefined window, a global event will be generated. This allows synchronized data acquisition of TBT beam positions around the ring. Bunch by bunch data is acquired at the same time to analyze the possible coupled bunch instabilities (CBI). Besides CBI mainly due to ion bursts, fast orbit glitches have been captured with the new tool. Sources of the glitches can be identified.

Beam position monitor gate functionality implementation and applications

We introduce a novel technique to implement gate functionality for the beam position monitors (BPM) at the National Synchrotron Light Source II (NSLS-II). The functionality, now implemented in FPGA, allows us to acquire two separated bunch-trains’ synchronized turn-by-turn (TBT) data simultaneously with the NSLS-II in-house developed BPM system. The gated position resolution is improved about 3 times by narrowing the sampling width. Experimentally we demonstrated that the machine lattice could be transparently characterized with the gated TBT data of a short diagnostic bunch-train Cheng et al., 2017; Li et al., 2017. Other applications, for example, precisely characterizing storage ring impedance/wake-field through recording the beam positions of two separated bunch trains has been experimentally demonstrated.•Gated BPM signal processing improves the position resolution.•Transparent lattice measurement using the gate function with diagnostic bunches.•Collective effect study with simultaneous position measurement from two gates.

Improving the precision of linear optics measurements based on turn-by-turn beam position monitor data after a pulsed excitation in lepton storage rings

Beam optics control is of critical importance for machine performance and protection. Nowadays, turn-by-turn (TbT) beam position monitor (BPM) data are increasingly exploited as they allow for fast and simultaneous measurement of various optics quantities. Nevertheless, so far the best documented uncertainty of measured $\ensuremath{\beta}$-functions is of about 10\mbox{\textperthousand} rms. In this paper we compare the $\ensuremath{\beta}$-functions of the ESRF storage ring measured from two different TbT techniques---the N-BPM and the Amplitude methods---with the ones inferred from a measurement of the orbit response matrix (ORM). We show how to improve the precision of TbT techniques by refining the Fourier transform of TbT data with properly chosen excitation amplitude. The precision of the N-BPM method is further improved by refining the phase advance measurement. This represents a step forward compared to standard TbT measurements. First experimental results showing the precision of $\ensuremath{\beta}$-functions pushed down to 4\mbox{\textperthousand} both in TbT and ORM techniques are reported and commented.

Techniques for transparent lattice measurement and correction

A novel method has been successfully demonstrated at NSLS-II to characterize the lattice parameters with gated BPM turn-by-turn (TbT) capability. This method can be used at high current operation. Conventional lattice characterization and tuning are carried out at low current in dedicated machine studies which include beam-based measurement/correction of orbit, tune, dispersion, beta-beat, phase advance, coupling etc. At the NSLS-II storage ring, we observed lattice drifting during beam accumulation in user operation. Coupling and lifetime change while insertion device (ID) gaps are moved. With the new method, dynamical lattice correction is possible to achieve reliable and productive operations. A bunch-by-bunch feedback system excites a small fraction (∼1%) of bunches and gated BPMs are aligned to see those bunch motions. The gated TbT position data are used to characterize the lattice hence correction can be applied. As there are ∼1% of total charges disturbed for a short period of time (several ms), this method is transparent to general user operation. We demonstrated the effectiveness of these tools during high current user operation.

A method for simultaneous linear optics and coupling correction for storage rings with turn-by-turn beam position monitor data

We propose a method to simultaneously correct linear optics errors and linear coupling for storage rings using turn-by-turn (TbT) beam position monitor (BPM) data. The independent component analysis (ICA) method is used to isolate the betatron normal modes from the measured TbT BPM data. The betatron amplitudes and phase advances of the projections of the normal modes on the horizontal and vertical planes are then extracted, which, combined with dispersion measurement, are used to fit the lattice model. The fitting results are used for lattice correction. The method has been successfully demonstrated on the NSLS-II storage ring.

Determination of linear optics functions from turn-by-turn data

A method for evaluation of coupled optics functions, detection of strong perturbing elements, determination of BPM calibration errors and tilts using turn-by-turn (TBT) data is presented as well as the new version of the Hamiltonian perturbation theory of betatron oscillations the method is based upon. An example of application of the considered method to the Tevatron is given.

Preliminary application of turn-by-turn data analysis to the SSRF storage ring

There is growing interest in utilizing the beam position monitor turn-by-turn (TBT) data to debug accelerators. TBT data can be used to determine the linear optics, coupled optics and nonlinear behaviors of the storage ring lattice. This is not only a useful complement to other methods of determining the linear optics such as LOCO, but also provides a possibility to uncover more hidden phenomena. In this paper, a preliminary application of a β function measurement to the SSRF storage ring is presented.