CyberSec Research

Plasma processing of superconducting radio frequency (SRF) cavities has been an active research effort at Jefferson Lab (JLab) since 2019, aimed at enhancing cavity performance by removing hydrocarbon contaminants and reducing field emission. In this experiment, processing using argon-oxygen and helium-oxygen gas mixtures to find minimum ignition power at different cavity pressure was investigated. Ongoing simulations are contributing to a better understanding of the plasma surface interactions and the fundamental physics behind the process. These simulations, combined with experimental studies, guide the optimization of key parameters such as gas type, RF power, and pressure to ignite plasma using selected higher-order mode (HOM) frequencies. This paper presents experimental data from argon-oxygen and helium-oxygen gas mixture C75 and C100 cavity plasma ignition studies, as well as simulation results for the C100-type cavity based on the COMSOL model previously applied to the C75 cavity.

This document is comprised of a collection of consolidated parameters for the key parts of the muon collider. These consolidated parameters follow on from the October 2024 Preliminary Parameters Report. Attention has been given to a high-level consistent set of baseline parameters throughout all systems of the complex, following a 10 TeV center-of-mass design. Additional details of the designs contributing to this baseline design are featured in the appendix. Likewise, explorative variations from this baseline set can be found in the appendix. The data is collected from a collaborative spreadsheet and transferred to overleaf.

Measurements of the spectral emission properties of an iron-doped Beta-Ga2O3(010) photocathode at 300K reveal the presence of ultracold electron emission with a 6meV mean transverse energy (MTE) in the 3.5-4.4eV photon energy range (282-354nm). This extreme sub-thermal photoemission signal is consistent with direct emission of electrons photoexcited from the Fe dopant states into the low effective mass and positive electron affinity primary conduction band, and it is superimposed on a stronger signal with a larger MTE associated with an (optical)phonon-mediated momentum resonant Franck-Condon (FC) emission process from a thermally populated and negative electron affinity upper conduction band. For photon energies above 4.5eV, a transition from a long to a short transport regime is forced by an absorption depth reduction to below 100nm and both MTE signals exhibit spectral trends consistent with phonon-mediated FC emission if the polaron formation self-energy is included in the initial photoexcited electron thermalization.

Automatic differentiation provides an efficient means of computing derivatives of complex functions with machine precision, thereby enabling differentiable simulation. In this work, we propose the use of the norm of the tangent map, obtained from differentiable tracking of particle trajectories, as a computationally efficient indicator of chaotic behavior in phase space. In many cases, a one-turn or few-turn tangent map is sufficient for this purpose, significantly reducing the computational cost associated with dynamic aperture optimization. As an illustrative application, the proposed indicator is employed in the dynamic aperture optimization of an ALS-U lattice design.

In this paper, we present the Distributed Inter-Strand Coupling Current (DISCC) model. It is a finite element (FE) model based on a homogenization approach enabling efficient and accurate simulation of the transient magnetic response of superconducting Rutherford cables without explicitly representing individual strands. The DISCC model reproduces the inter-strand coupling current dynamics via a novel mixed FE formulation, and can be combined with the Reduced Order Hysteretic Magnetization (ROHM) and Flux (ROHF) models applied at the strand level in order to reproduce the internal strand dynamics: hysteresis, eddy, and inter-filament coupling currents, as well as ohmic effects. We first analyze the performance of the DISCC model alone, as a linear problem. We then extend the analysis to include the internal strand dynamics that make the problem nonlinear. In all cases, the DISCC model offers a massive reduction of the computational time compared to conventional fully detailed FE models while still accounting for all types of loss, magnetization and inductance contributions. Rutherford cables homogenized with the DISCC model can be directly included in FE models of magnet cross-sections for efficient electro-magneto-thermal simulations of their transient response. We present two possible FE formulations for the implementation of the DISCC model, a first one based on the h-phi-formulation, and a second one based on the h-phi-a-formulation, which is well suited for an efficient treatment of the ferromagnetic regions in magnet cross-sections.

Plasma-based accelerators are beginning to employ relativistic beams with unprecedented charge and ultrashort durations. These dense driver beams can drive wakes even in high-density plasmas ($\gtrsim10^{19}$ cm$^{-3}$), where betatron radiation becomes increasingly important and begins to affect the dynamics of the accelerated beam. In this Letter, we show that betatron cooling leads to a strong, structuring of the phase space of the beam. This gives rise to bunched, ring-like structures with positive radial position and momentum gradients, \emph{i.e.}, population inversion of the amplitude of oscillation. We derive the characteristic timescales for this process analytically and confirm our predictions with multi-dimensional Particle-in-Cell simulations. The radiation-dominated regime of beam dynamics fundamentally alters the acceleration process and produces self-structured beams capable of triggering coherent betatron emission in ion channels.

Fiber optic pulsed polarimetry is a LIDAR-like fiber sensing technique that uses a backscatter enhanced single mode backscatter-tailored optical fiber(BTOF) to measure the distributed B fields on all Magnetic Fusion Energy devices. The BTOF has a series of wavelength resonant reflection fiber Bragg gratings written uniformly along its length. The fiber's Verdet constant determines the strength of the Faraday effect which effectuates the measurement of local B along the fiber placed intimately next to or within a magnetized plasma volume. A robust measurement of the field distribution along the fiber is obtained at high rep rates, 5 MHz, high spatial resolution(1-10cm), high B field accuracy(<1%) and temporal response (ns). Multipathing in the BTOF produces 3rd order reflections that contaminate the LIDAR signal. Algorithms are given for calculating the level of contamination for uniform and flat reflection designs, in particular and any reflection series in general. The contamination is bracketed giving confidence in designing and implementing a BTOF. Applications include magnetic fusion devices, rail guns, high temperature superconducting magnets and magnetized target fusion research.

PIP-II is a superconducting linac that is in the initial acceleration chain for the Fermilab accelerator complex. The RF system consists of a warm front-end with an RFQ and buncher cavities along with 25 superconducting cryo-modules comprised of cavities with five different acceleration \(\beta\). The LLRF system for the linac has to provide field and resonance control for a total of 125 RF cavities. Various components of the LLRF system have been tested with and without beam at the PIP-II test stands. The LLRF system design is derived from the LCLS-II project with its self-excited loop architecture used in the majority of the cryo-modules. The PIP-II beam loading at 2 mA is much higher than the LCLS-II linac. The control system architecture is analyzed and evaluated for the operational limits of feedback gains and their ability to meet the project regulation requirements for cavity field amplitude and phase regulation.

This book begins with the basic accelerator knowledge required to understand the latter chapters. This is followed by topics from Fermilab accelerator specifics to general accelerator physics concepts. These chapters are accompanied by descriptions of the instrumentation and utilities required to operate a high-energy physics laboratory. Last, we discuss the role of operators in safety at the lab.

Dispersive shock waves (DSWs) are expanding nonlinear wave trains that arise when dispersion regularizes a steepening front, a phenomenon observed in fluids, plasmas, optics, and superfluids. Here we report the first experimental observation of DSWs in an intense electron beam, using the University of Maryland Electron Ring (UMER). A localized induction-cell perturbation produced a negative density pulse that evolved into a leading soliton-like peak followed by an expanding train of oscillations. The leading peak satisfied soliton scaling laws for width^2 vs inverse amplitude and velocity vs amplitude, while the total wave-train width increased linearly with time, consistent with Korteweg--de Vries (KdV) predictions. Successive peaks showed decreasing amplitude and velocity toward the trailing edge, in agreement with dispersive shock ordering. These results demonstrate that intense charged particle beams provide a new laboratory platform for studying dispersive hydrodynamics, extending nonlinear wave physics into the high-intensity beam regime.

The study investigated transparent on-chip structures with a rectangular profile and triangular profiles with grating ridge base angles of $\alpha = 36^\circ$, $30^\circ$, and $20^\circ$. Each triangular structure had both left- and right-handed profile orientations. For all variants, a modified version with a reflective gold coating was additionally considered. The maximum energy gains and accelerating gradients were determined and quantified for all structure classes: transparent and reflective (with both rectangular and triangular profiles).

A development effort to improve the performance of superconducting radio-frequency half-wave resonators (SRF HWRs) is underway at the Facility for Rare Isotope Beams (FRIB), where 220 such resonators are in operation. Our goal was to achieve an intrinsic quality factor (Q0) of >= 2E10 at an accelerating gradient (Ea) of 12 MV/m. FRIB production resonators were prepared with buffered chemical polishing (BCP). First trials on electropolishing (EP) and post-EP low temperature baking (LTB) of FRIB HWRs allowed us to reach higher gradient (15 MV/m, limited by quench) with a higher quality factor at high gradient, but Q0 was still below our goal. Trapped magnetic flux during the Dewar test was found to be a source of Q0 reduction. Three strategies were used to reduce the trapped flux: (i) adding a local magnetic shield (LMGS) to supplement the ``global'' magnetic shield around the Dewar for reduction of the ambient magnetic field; (ii) performing a ``uniform cool-down'' (UC) to reduce the thermoelectric currents; and (iii) using a compensation coil to further reduce the ambient field with active field cancellation (AFC). The LMGS improved the Q0, but not enough to reach our goal. With UC and AFC, we exceeded our goal, reaching Q0 = 2.8E10 at Ea = 12 MV/m.

The current Timing System at Fermilab has been around for 40 years and currently relies on 7 CAMAC crates and over 100 CAMAC cards to produce the Tevatron Clock (TCLK). Thanks to the ingenuity of those before us, this has allowed Fermilab the flexibility to change the timing and Events for its accelerator as beamlines and projects have changed over the years. With the advent of the Proton Improvement Plan-II (PIP-II), the Timing System at Fermilab is being reimagined into a single chassis with even greater flexibility and functionality for decades to come while tackling the ever-challenging task of maintaining backwards compatibility.

The PIP-II linac is an international collaboration project with in kind contributions of key subsystems from multiple countries including India (DAE). In the research and development phase of the project, the LLRF and resonance control systems were jointly developed by BARC and Fermilab and were delivered to Fermilab for testing and validation. Initial testing of the LLRF system was carried out using Fermilabs analog cavity emulator. Following successful emulator testing, the LLRF system was deployed at STC on a PIP-II 325 MHz SSR2 cavity. The cavity was operated in both SEL and GDR modes at a gradient of 5 MV/m. The results of the testing are presented here.

Flying-focus wakefields, which can propagate with a tunable velocity along the optical axis, are promising solutions to electron dephasing in laser-wakefield accelerators. This is accomplished by a combination of spatio-temporal couplings and focusing with an axiparabola, a specialized optical element which produces a quasi-Bessel beam. If implemented, dephasingless acceleration would allow for a hitherto unachievable mixture of high acceleration gradients and long acceleration lengths. Here, we conduct an in-depth study of the structure and behavior of such a flying-focus wakefield, through a combination of direct imaging and simulations. We show the stability of the wakefield structures, explore how the wakefield evolves with changes of density, study the effects of ionization on the wakefield structure with a variety of gases, and analyze the importance of the focusing position. These insights shed light onto this novel wakefield regime and bring understanding that is important to the realization of dephasingless acceleration.

Particle accelerators play a pivotal role in advancing scientific research, yet optimizing beamline configurations to maximize particle transmission remains a labor-intensive task requiring expert intervention. In this work, we introduce RLABC (Reinforcement Learning for Accelerator Beamline Control), a Python-based library that reframes beamline optimization as a reinforcement learning (RL) problem. Leveraging the Elegant simulation framework, RLABC automates the creation of an RL environment from standard lattice and element input files, enabling sequential tuning of magnets to minimize particle losses. We define a comprehensive state representation capturing beam statistics, actions for adjusting magnet parameters, and a reward function focused on transmission efficiency. Employing the Deep Deterministic Policy Gradient (DDPG) algorithm, we demonstrate RLABC's efficacy on two beamlines, achieving transmission rates of 94% and 91%, comparable to expert manual optimizations. This approach bridges accelerator physics and machine learning, offering a versatile tool for physicists and RL researchers alike to streamline beamline tuning.

The Self-Excited Loop (SEL) architecture, used in some continuous-wave (CW) superconducting linacs, relies on a positive feedback mechanism that requires carefully defined operating limits to ensure stable operation. These limits are typically derived from amplifier calibration, which characterizes the relationship between forward power and DAC drive. However, amplifier non-linearity often prevents a simple linear fit of this characteristic, introducing errors that can compromise stability. To address this, we present a modified calibration procedure that incorporates amplifier non-linearity into the SEL framework. The approach is validated with test data from a 32 kW solid-state amplifier (SSA) and a cavity emulator developed for the Fermilab PIP-II linac.

Landau damping is a key mechanism to preserve the stability of particle beams under the influence of various collective forces that would otherwise spoil its quality through beam instabilities. We describe its root cause as well as ways to control it in order to design and operate particle accelerators.