Canada

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.

CAP Virtual Congress 2021

Energy Compression System Radio Frequency Design at the Canadian Light Source

radiofrequency particle accelerator

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A relativistic theory of gravity like general relativity produces phenomena differing fundamentally from Newton’s theory. An example, analogous to electromagnetic induction, is gravitomagnetism, or the dragging of inertial frames by mass-energy currents. These effects have recently been confirmed by classical observations. Here we show, for the first time, that they can be observed by a quantum detector. We study the response function of Unruh De-Witt detectors placed in a slowly rotating shell. We show that the response function picks up the presence of rotation even though the spacetime inside the shell is flat and the detector is locally inertial. The detector can distinguish between the static situation when the shell is nonrotating and the stationary case when the shell rotates and the dragging of inertial frames, i.e., gravitomagnetic effects, arise. Moreover, it can do so when the detector is switched on for a finite time interval within which a light signal cannot travel to the shell and back to convey the presence of rotation.

Quantum Detection of Inertial Frame Dragging

We derive Loop Quantum Gravity corrections to the Raychaudhuri equation in the interior of a Schwarzschild black hole and near the classical singularity for several schemes of quantization. We show that the resulting effective equation implies defocusing of geodesics due to the appearance of repulsive terms. This prevents the formation of conjugate points, renders the singularity theorems inapplicable, and leads to the resolution of the singularity for this spacetime.

Effective Raychaudhuri equation and black hole singularity resolution

We study the response of a static Unruh-DeWitt detector outside an exotic compact object (ECO) with a variety of (partially) reflective boundary conditions in 3+1 dimensions. The horizonless ECO, whose boundary is extremely close to the would-be event horizon, acts as a black hole mimicker. We find that the response rate is notably distinct from the black hole case, even when the ECO boundary is perfectly absorbing. For a (partially) reflective ECO boundary, we find resonance structures in the response rate that depend on the different locations of the ECO boundary and those of the detector. We provide a detailed analysis in connection with the ECO's vacuum mode structure and transfer function.

Unruh-DeWitt Detector Differentiation of Black Holes and Exotic Compact Objects

The mass and spin properties of black hole binaries inferred from their gravitational-wave signatures reveal important clues about how these binaries form. For instance, stellar-mass black holes that evolved together from the same binary star will have spins that are preferentially aligned with their orbital angular momentum. Alternatively, if the black holes formed separately from each other and later became gravitationally bound, then there is no such preference for having aligned spins. Furthermore, it is known that the presence of misaligned spins induces a general relativistic precession of the orbital plane, imprinting unique structure onto the gravitational-wave signal. The fidelity with which gravitational-wave detectors can measure off-axis spins, or equivalently, precession, will therefore have important implications for the use of gravitational waves to study binary black hole formation channels. I will summarize a new study that examines how well the A+/AdV+ detector network will measure off-axis spin components, and report preliminary results comparing spin resolution between the fourth and fifth LIGO-Virgo observing runs using simulated detector noise and multiple sets of simulated signals distributed over the mass-spin parameter space.

Prospects for measuring off-axis spins of binary black hole sources with A+/AdV+

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

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.

Next from CAP Virtual Congress 2021

Quantum Detection of Inertial Frame Dragging

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Resources in Introductory Physics: Multiple Modes of Engagement and Feedback

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