Canada

The Transverse Feedback system at the Canadian Light Source can identify, categorize, and mitigate against periodic instabilities that arise in the storage ring beam. By quickly opening and closing the feedback loop, previously mitigated instabilities will be allowed to grow briefly before being damped by the system. The resulting growth in the beam oscillation amplitude curve can be analyzed to determine growth/damp rates and modes of the coupled bunch oscillations. Grow/damp curves will be collected and analyzed for various storage ring beam properties, including beam profile density, beam energy, machine chromaticity, injection instability, insertion device gap width, or bunch fill patterns. These results will be used to characterize the known instability growth rates, and search for unknown instability modes that may cause stability problems in the future. The instability analysis in the CLS will also impact the design of future insertion devices that might be added for new beamlines and the design of the CLS2 ring which is being planned.

CAP Virtual Congress 2021

Analyzing Growth/Damp curves in the Canadian Light Source storage ring

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The Canadian Light Source (CLS) is considering a linear accelerator (LINAC) upgrade. As a result, the radio frequency (RF) structure in the downstream Energy Compression System (ECS) needs to be redesigned. In this paper, we describe the design process followed to determine the geometry of the RF structure cells and coupler. Wakefield simulation results are also presented. The wakefields and input RF fields are applied to beam dynamics simulations.

Energy Compression System Radio Frequency Design at the Canadian Light Source

A key feature of third-generation light sources is their small vertical opening angle, which is difficult to measure experimentally. To reconstruct the vertical phase space, one can scan the beam’s position using X-ray synchrotron radiation (XSR) and a pinhole camera. The XSR diagnostic beamline, operational in the wavelength region of $\lambda$= 0.05 - 0.15 nm, in Canadian Light Source (CLS) is qualified to measure the beam position with X-ray radiation. Using the corrector magnets in CLS lattice made of 12 identical double-bend achromats (DBA) cells, vertical iterations of 100 $\mu$m can be executed parallel to the beam's original orbit. The outcomes of this experiment are: 1) the vertical beam positions that are monitored by BPMs on both sides of the X-ray’s source point, 2) the X-ray image of the beam that is projected through the pinhole and converted to visible light to be captured on the CCD camera. The bumps were simulated using Matlab Middle Layer (MML) for Accelerator control systems to get an insight of the source point's position in the XSR's bending magnet. The simulation shows the position of the source point depends on which corrector sets are chosen. To make a truly parallel bump in the DBA sector and to be able to calculate the source point's actual position, critical in reconstructing the vertical phase space, a particular set of correctors should be chosen.

Vertical phase space measurement at Canadian Light Source

The Canadian Light Source (CLS) synchrotron uses four fast kicker magnets to inject electrons into the storage ring from a 2.9 GeV booster ring. The injection occurs over several turns of the stored beam, which is also perturbed by the injection kickers. The resultant oscillations of the stored beam can negatively affect the quality of beamline experiments, so it is desirable to implement an injection scheme which does not disturb the stored beam. Injection schemes of this type allow for transparent injection and are very desirable for the planned top-up operations of the CLS storage ring. Many alternative injection techniques have been presented in recent years and we have examined several of these techniques as they apply to the CLS storage ring. Pulsed multipole magnets and a non-linear kicker are the most viable alternatives for integration with the current ring. Non-linear kicker designs are also being considered for the proposed CLS 2.0 and studying this injection method in the limitations of the current machine provides additional insight to guide the work on the new machine. Simulation with the accelerator code ELEGANT shows the viability of the non-linear kicker design as developed at BESSY, MAX IV and SOLEIL (other synchrotron facilities) for transparent injection at the CLS.

Design and Simulation of Transparent Injection Upgrade for the CLS Storage Ring

Perturbation theory for gravitating quantum systems tends to fail at very late times (a type of perturbative breakdown known as secular growth). We argue that gravity is best treated as a medium/environment in such situations, where reliable late-time predictions can be made using tools borrowed from quantum optics. To show how this works, we study the explicit example of a qubit hovering just outside the event horizon of a Schwarzschild black hole (coupled to a real scalar field) and reliably extract the late-time behaviour for the qubit state. At very late times, the so-called Unruh-DeWitt detector is shown to asymptote to a thermal state at the Hawking temperature.

Hot qubits on the horizon

First-semester physics labs typically aim to confirm and mirror relationships explored in the lectures. Often using computer-interfaced equipment to measure physical variables, students investigate relationships with time or other variables. We took our move to online delivery in the pandemic as an opportunity to re-think physics labs. We report here a suite of remotely delivered labs developed to introduce scientific attitudes and skills. Emphasized attitudes were collaboration, creativity, perseverance, decision making, communication, and innovation. Skills such as moving from question to hypothesis, spreadsheet basics, linearization, and introductory statistics leveraged simple experiments (time to roll down a ramp, period of a pendulum) into hands-on introductions to scientific tools and ways of thinking. We abandoned the lab manual model, instead requiring students to create plans and communicate their work. Experiment plans included details on the objective/hypothesis, equipment used, experimental setup, detailed procedure of data acquisition, and specifics of data analysis. Sharing created plans occurred before data acquisition. Choosing not to rely on each student having a particular device, we explored kinematics using basic household items, and analysis utilized university-provided Microsoft Excel. Focusing on physics-specific nomenclature (such as uncertainty) gave way to adopting standardized statistical ideas like t-prime comparisons. We believe these labs emphasize attitudes and skills that are more valued across the scientific disciplines than those typically developed in traditional introductory physics labs.

Home-Based Labs to Develop Broadly Applicable Scientific Skills and Attitudes

The observed gender gap in physics testing is a problem which plagues physics education. Many studies in universities across North America show that female students consistently perform worse than male students on written examinations and concept inventories, though the size of this performance gap varies from study to study. In some cases, this gender gap in performance has been linked to more negative perceptions and lower confidence in physics among female students. The goal of our study was to determine if there is a gender gap in perceived confidence and interest in physics at the introductory level. 
An online survey was distributed to the three streams of introductory physics students at McMaster University which had students answer a range of questions about their undergraduate degree, background, comfort, confidence, and other metrics. We asked students to rate their interest and preparedness in physics before and after taking their introductory course. Upon analysis of these results, a clear gender gap was observed in key areas such as perceived confidence within the course, and the student's level of interest in physics. Female students consistently reported lower perceptions of preparedness and interest in the course relative to their male counterparts. However, when analyzing the change in interest and confidence, the gender gap greatly varied dependant on the introductory stream. An online survey will also be distributed to upper year physics students to probe whether the confidence and interest gap extends throughout undergraduate degrees, or whether the gap narrows as students get accustomed to the university environment. Lower confidence in first year could negatively impact the performance of female physics students at McMaster and could contribute to a lack of gender diversity in upper year physics programs.  
The affirmation of the student gender gap in confidence within introductory physics courses at a large Canadian institution is a troubling but crucial step in creating a welcoming and inclusive physics education environment for all students.

Investigating the Gender Gap in Introductory Physics Courses

We present our simple and cost-efficient setup for real-time monitoring of substrate thickness in plasma etching/deposition processes. Thin film interference occurs as light from the plasma passes through the substrate material, by observing the cycles of peaks and troughs in the intensity, the rate of etching/deposition was obtained.

Optical Emission Interferometry for Monitoring of Plasma Processes

Sea spray icing is created by wind/wave-induced spray in harsh arctic and antarctic environments. It is reported that sea spray icing causes hazardous conditions and operational problems for vessels and offshore structures. Nuclear Magnetic Resonance (NMR) is a powerful tool that can provide information about local environment, diffusion, and structure of a sample containing NMR-sensitive nuclei. NMR studies of sea ice are well-known for investigating seawater brine properties and structure. However, typical NMR instruments are big, expensive, and they cannot be moved outside a scientific laboratory. Also, seaspray icing hasn’t been studied with NMR until very recently (Wilbur et al, JMR, 2020). This study was focused on how to measure freezing of a sea-water spray with a portable, unilateral NMR instrument consisting of a handheld 3-magnet array.
For our instrument, the 1H NMR signal was generated approx. 1 cm away from the magnet surface, in the presence of a constant 250 G/cm magnetic field gradient. The pulse sequence used in this study was a combination of the Hahn and CPMG sequences (the CPMG echoes could be either added to increase the SNR, or used for obtaining T2 information). An optimum quality factor for a desired slice thickness was chosen to increase the sensitive volume. Additionally, we explored 1D-imaging with a unilateral NMR by performing Fourier Transform of the echoes acquired in the presence of the constant gradient.
The following parameters of NMR signal from freezing seawater accumulating on a cold surface inside the sensitive volume were measured and analyzed: signal intensity (proportional to the brine concentration), T2 relaxation, and diffusion for a range of temperatures (from-6oCto-14oC) and for two different surface orientations (horizontal and vertical). Results showed differences in signal intensity caused by ice growth rates at different temperatures. The diffusion was highly dependent on temperatures and surface orientations. This study shows that portable NMR devices can be useful for studies of seawater freezing, and freezing in general.

Studies of seawater spray icing phenomena with unilateral NMR

Introductory physics courses are required at McMaster for students in a pure physics stream, engineering stream, or life sciences stream. The background preparation of these students, as well as their attitudes towards the course, can vary greatly. There lies huge importance in identifying topics and aspects of introductory physics courses that students enjoy and find challenging as a key method to improving their overall understanding and experience. Additionally, with the recent switch to fully online teaching methods, the way in which students approach their lecture content and participate in classroom activities has also changed. Examining the online lecture attendance in comparison to in-person lectures is a useful way to see what aspects of an online model are beneficial to carry forward once on-campus classes return.  

In this study, a survey was distributed to students in three streams of introductory physics courses, with an open-ended question to identify what they enjoy and find most challenging in physics. Students were able to answer with specific topics covered in the course or general aspects of physics (problem-solving, math, etc.). Interestingly, students enjoyed real-life applications of physics the most, while finding the math and problem-solving aspects of the course most challenging. Kinematics was the most liked topic, while the most challenging topic varied depending on the choice of stream. A similar survey will be distributed to students after they complete a second introductory physics course, allowing this question to be assessed again, as well as their comfort with mathematics, and the topics they deem most relevant to their field of study.  By examining these additional questions, we hope to clarify why students from different science disciplines prefer specific topics, and whether students continue to struggle with the same topics as they progress into upper-year physics courses.

These results can be used as a tool in identifying areas of introductory physics courses that should be improved to help with students' overall understanding and experience.

Students’ Preferences and Participation in Introductory Physics Courses in an Online Environment

The DC gas discharge is a non-thermal laboratory plasma that is initiated by an applied electric field. It serves as a useful apparatus for studying fundamental phenomena in plasma physics and has found several applications in materials science and engineering. In contrast to thermally ionized plasma, the distribution function of a gas discharge deviates from Maxwellian at low pressures. It is affected by a high-energy tail due to accelerated electrons and is truncated by inelastic collisions. To have a good understanding of particle kinetics within the plasma, measurements of the distribution function are important. Fortunately, this is made possible with the Langmuir probe diagnostic. In addition to measurement of the distribution function, Langmuir probes can also directly measure several important plasma properties including the electron temperature and plasma density. Furthermore, spatially separated probes can measure gradients in potential that can be used to infer an electric field. To investigate properties of gas discharges and to evaluate the design and implementation of a Langmuir probe diagnostic, an array of several probes was designed and inserted into an intermediate pressure DC gas discharge. Before the Langmuir probe experiments, measurements of the discharge were performed including obtaining IV characteristics and determining breakdown voltages for several gases. Images of the discharges were recorded using a USB camera and emission spectra were obtained using a visible light spectrometer. Langmuir probe measurements were then taken of the electric field in the cathode region and IV characteristics were obtained to determine plasma properties: both by a graphical method and by the calculation of the electron energy distribution function (EEDF) from the second derivative.

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