Search

Upgrading the SuperKEKB electron-positron collider with polarized electron beams opens a new program of precision physics at a center-of-mass energy of 10.58 GeV. This white paper describes the physics potential of this `Chiral Belle' program. It includes projections for precision measurements of $\sin^2\theta_W$ that can be obtained from independent left-right asymmetry measurements of $e^+e^-$ transitions to pairs of electrons, muons, taus, charm and b-quarks. The $\sin^2\theta_W$ precision obtainable at SuperKEKB will match that of the LEP/SLC world average, but at the centre-of-mass energy of 10.58 GeV. Measurements of the couplings for muons, charm, and $b$-quarks will be substantially improved and the existing $3\sigma$ discrepancy between the SLC $A_{LR}$ and LEP $A_{FB}^b$ measurements will be addressed. Precision measurements of neutral current universality will be more than an order of magnitude more precise than currently available. As the energy scale is well away from the $Z^0$-pole, the precision measurements will have sensitivity to the presence of a parity-violating dark sector gauge boson, $Z_{\rm dark}$. The program also enables the measurement of the anomalous magnetic moment $g-2$ form factor of the $\tau$ to be made at an unprecedented level of precision. A precision of $10^{-5}$ level is accessible with 40~ab$^{-1}$ and with more data it would start to approach the $10^{-6}$ level. This technique would provide the most precise information from the third generation about potential new physics explanations of the muon $g-2$ $4\sigma$ anomaly. Additional $\tau$ and QCD physics programs enabled or enhanced with having polarized electron beams are also discussed in this White Paper. This paper includes a summary of the path forward in R&D and next steps required to implement this upgrade and access its exciting discovery potential., Comment: 74 pages, 56 figures, contribution to Snowmass 2021

Conventional cancer therapies include surgery, radiation therapy, chemotherapy, and, more recently, immunotherapy. These modalities are often combined to improve the therapeutic index. The general concept of radiation therapy is to increase the therapeutic index by creating a physical dose differential between tumors and normal tissues through precision dose targeting, image guidance, and high radiation beams that deliver radiation dose with high conformality, e.g., protons and ions. However, treatment and cure are still limited by normal tissue radiation toxicity, with many patients experiencing acute and long-term side effects. Recently, however, a fundamentally different paradigm for increasing the therapeutic index of radiation therapy has emerged, supported by preclinical research, and based on the FLASH radiation effect. FLASH radiation therapy (FLASH-RT) is an ultra-high dose-rate delivery of a therapeutic radiation dose within a fraction of a second. Experimental studies have shown that normal tissues seem to be universally spared at these high dose rates, whereas tumors are not. The dose delivery conditions are not yet fully characterized. Still, it is currently estimated that large doses of 10 Gy or more delivered in 200 ms or less produce normal tissue sparing effects yet effectively kill tumor cells. There is a great opportunity, but also many technical challenges, for the accelerator community to create the required dose rates with novel and compact accelerators to ensure the safe delivery of FLASH radiation beams., Comment: A Snowmass 2021 White Paper

As the only high-temperature superconducting (HTS) material available as an isotropic, twisted, multifilamentary round wire, Bi-2212 is very promising for expanding the high-field superconducting accelerator magnet toolbox beyond the round-wire, isotropic Nb-Ti and Nb3Sn conductors used by HEP so far. In this paper, we describe the important roles that Bi-2212 might play for future high energy circular colliders including both high energy proton and muon colliders. We describe its present technology status (conductor development, magnet design concepts, prototype magnet status) and then provide a ten-year plan for >15 T accelerator magnets and >25 T solenoid magnets within an integrated strategy to engage industry and the entire US and international scientific enterprise interested in HTS magnet applications., Comment: contribution to Snowmass 2021

While the long-term vision of the advanced accelerator community is aimed at addressing the challenges of future collider technology, it is critical that the community takes advantage of the opportunity to make large societal impact through its near-term applications. In turn, enabling robust applications strengthens the quality, control, and reliability of the underlying accelerator infrastructure. The white paper contributions that are solicited here will summarize the near-term applications ideas presented by the advanced accelerator community, assessing their potential impact, discussing scientific and technical readiness of concepts, and providing a timeline for implementation., Comment: contribution to Snowmass 2021

Future high-power (10 - 20 MW) hadron accelerators offer many unique opportunities for fundamental science and nuclear applications. With the completion of Proton Power Upgrade (PPU) at 2.8 MW [1] and European Spallation Source (ESS) at 5 MW [2], the attention will be focused on the next high-power machine in hadron accelerator community. Charge exchange injection into a synchrotron using diamond stripper foils offers great advantage over direct proton acceleration. However, there are clear limitations associated with foil sublimation above critical beam power density and beam loss due to scattering (~10 rem/hour at 10 MW for SNS)., Comment: white paper

In this White Paper for the Snowmass 2021 Process, we propose the establishment of a magnet Leading-Edge technology And Feasibility-directed Program (LEAF Program) to achieve readiness for a future collider decision on the timescale of the next decade. The LEAF Program would rely on, and be synergetic with, generic R&D efforts presently covered - in the US - by the Magnet Development Program (MDP), the Conductor Procurement and R&D (CPRD) Program and other activities in the Office of HEP supported by Early Career Awards (ECA) or Lab Directed R&D (LDRD) funds. Where possible, ties to synergetic efforts in other Offices of DOE or NSF are highlighted and suggested as wider Collaborative efforts on the National scale. International efforts are also mentioned as potential partners in the LEAF Program. We envision the LEAF Program to concentrate on demonstrating the feasibility of magnets for muon colliders as well as next generation high energy hadron colliders, pursuing, where necessary and warranted by the nature of the application, the transition from R&D models to long models/prototypes. The LEAF Program will naturally drive accelerator-quality and experiment-interface design considerations. LEAF will also concentrate, where necessary, on cost reduction and/or industrialization steps., Comment: Contribution to Snowmass 2021, 19 pages, 5 figures. Corresponding Author: G. Apollinari apollina@fnal.gov

After a summary of relevant comments and recommendations from various reports over the last ten years, this paper examines the modeling needs in accelerator physics, from the modeling of single beams and individual accelerator elements, to the realization of virtual twins that replicate all the complexity to model a particle accelerator complex as accurately as possible. We then discuss cutting-edge and emerging computing opportunities, such as advanced algorithms, AI/ML and quantum computing, computational needs in hardware, software performance, portability and scalability, and needs for scalable I/O and in-situ analysis. Considerations of reliability, long-term sustainability, user support and training are considered next, before discussing the benefits of ecosystems with integrated workflows based on standardized input and output, and with integrated frameworks and data repositories developed as a community. Last, we highlight how the community can work more collaboratively and efficiently through the development of consortia and centers, and via collaboration with industry., Comment: contribution to Snowmass 2021

The discovery of the Higgs boson at Large Hadron Collider (LHC) of CERN in July 2012 raised new opportunities for large-scale accelerators. The Higgs boson is the heart of the Standard Model (SM) and is at the center of many biggest mysteries.In September 2012, Chinese scientists proposed a 240 GeV Circular Electron Positron Collider (CEPC) as a Higgs Factory, having two large detectors for Higgs studies and other topical researches. The 100 km tunnel of CEPC could also host a Super proton proton Collider (SppC) to reach energies well beyond the LHC. CEPC Conceptual Design Report (CDR) has been released in Nov. 2018, and in this CEPC Accelerator White Paper to Snowmass21 AF3, CEPC Technical Design Report (TDR) status with optimized design and key technology R and D progresses have been reported. The energy range, luminosity, upgrade and staging potentials, power consumption, cost, readiness assessment, timelines, construction and operation plans, etc. are covered., Comment: 48 pages,34 figures

Following the PIP-II 800 MeV Linac, Fermilab will need an accelerator that extends from that linac to the MI injection energy of ~8 GeV, completing the modernization of the Fermilab high-intensity accelerator complex. This will maximize the beam available for neutrino production for the long baseline DUNE experiment to greater than 2.5 MW and enable a next generation of intensity frontier experiments. In this white paper, we propose an 8 GeV Linac for that purpose. The Linac consists of an extension of the PIP-II Linac to ~2 GeV using PIP-II 650 MHz SRF cryomodules, followed by a 2 -->8.0 GeV Linac composed of 1300 MHz SRF cryomodules, based upon the LCLS-II cryomodules developed at Fermilab. The 8 GeV Linac will incorporate recent improvements in SRF technology. The research needed to implement this Linac is described., Comment: contribution to Snowmass 2021

Particle accelerators for high energy physics will generate TeV-scale particle beams in large, multi-Km size machines colliding high brightness beams at the interaction point [1-4]. The high luminosity in such machines is achieved by producing very small asymmetric beam size at the interaction point, with short durations to minimize beam-beam effects. Tuning energy, timing and position of the beam for optimal performance will require high-precision controls of amplitude and phase of high-frequency electromagnetic fields and real-time processing of complex algorithms. The stability of the colliding beams has a large impact on the collider's effective luminosity. Therefore, the technology readiness level of diagnostic and control systems will be a major consideration in the collider design. The technical requirements of such systems depend on the specifics of beam parameters, such as transverse and longitudinal dimensions, charge/pulse and beam pulse format, which are driven by the accelerating technology of choice. While feedback systems with single bunch position monitor resolution below 50 nm and latency <300 ns have been demonstrated in beam test facilities, many advanced collider concepts make use of higher repetition rates, brighter beams and higher accelerating frequencies, and will require better performance, up to 1-2 order of magnitude, demanding aggressive R&D to be able to deliver and maintain the targeted luminosity., Comment: contribution to Snowmass 2021

Plasmonic modes offer the potential to achieve PetaVolts per meter fields, that would transform the current paradigm in collider development in addition to non-collider searches in fundamental physics. PetaVolts per meter plasmonics relies on collective oscillations of the free electron Fermi gas inherent in the conduction band of materials that have a suitable combination of constituent atoms and ionic lattice structure. As the conduction band free electron density, at equilibrium, can be as high as $\rm 10^{24}cm^{-3}$, electromagnetic fields of the order of $\rm 0.1 \sqrt{\rm n_0(10^{24}cm^{-3})} ~ PVm^{-1}$ can be sustained by plasmonic modes. Engineered materials not only allow highly tunable material properties but quite critically make it possible to overcome disruptive instabilities that dominate the interactions in bulk media. Due to rapid shielding by the free electron Fermi gas, dielectric effects are strongly suppressed. Because the ionic lattice, the corresponding electronic energy bands and the free electron gas are governed by quantum mechanical effects, comparisons with plasmas are merely notional. Based on this framework, it is critical to address various challenges that underlie PetaVolts per meter plasmonics including stable excitation of plasmonic modes while accounting for their effects on the ionic lattice and the electronic energy band structure over femtosecond timescales. We summarize the ongoing theoretical and experimental efforts as well as map out strategies for the future. Extreme plasmonic fields can shape the future by not only bringing tens of TeV to multi-PeV center-of-mass-energies within reach but also by opening novel pathways in non-collider HEP. In view of this promise, we invite the scientific community to help realize the immense potential of PV/m plasmonics and call for significant expansion of the US and international R\&D program., Comment: contribution to Snowmass 2021

Plasma-based accelerators have made remarkable progress over the last two decades. Their unique characteristics make them tools that can revolutionize fields of science and applications. AWAKE takes advantage of the availability of high-energy, relativistic proton bunches to drive large amplitude wakefields ($\sim$GV/m) in a single plasma over distances sufficient to produce hundreds of GeV to TeV electron bunches., Comment: contribution to Snowmass 2021

The Cornell-BNL FFAG-ERL Test Accelerator (C$\beta$) will comprise the first ever Energy Recovery Linac (ERL) based on a Fixed Field Alternating Gradient (FFAG) lattice. In particular, we plan to use a Non Scaling FFAG (NS-FFAG) lattice that is very compact and thus space- and cost- effective, enabling multiple passes of the electron beam in a single recirculation beam line, using the superconducting RF (SRF) linac multiple times. The FFAG-ERL moves the cost optimized linac and recirculation lattice to a dramatically better optimum. The prime accelerator science motivation for C$\beta$ is proving that the FFAG-ERL concept works. This is an important milestone for the Brookhaven National Laboratory (BNL) plans to build a major Nuclear Physics facility, eRHIC, based on producing 21 GeV electron beams to collide with the RHIC ion beams. A consequence of the C$\beta$ work would be the availability of significantly better, cost-effective, compact CW high-brightness electron beams for a plethora of scientific investigations and applications, such as X-ray sources, dark-matter and dark-energy searches, and industrial high-power Free-Electron Laser (FEL) applications. C$\beta$ brings together the resources and expertise of a large DOE National Laboratory, BNL, and a leading research university, Cornell. C$\beta$ will be built in an existing building at Cornell, for the most part using components that have been developed under previous R&D programs, including a fully commissioned world-leading photoemission electron injector, a large SRF accelerator module, and a high-power beam stop. The only elements that require design and construction from scratch is the FFAG magnet transport lattice. This white paper describes a project that promises to propel high-power, high-brightness electron beam science and applications to an exciting new level., Comment: White paper dated December 16, 2014. 16 pages, 8 figures

We criticize the thesis exposed the paper 'Seeded quantum FEL at 478 keV' AIP Conf. Proc. 'Light at Extreme Intensities,' 1462 173-176 (2012), which presents the possibility of producing gamma rays at 478 KeV by means of a seeded quantum FEL driven by an electron beam at 125 MeV, current I=40 A, interacting with an infrared laser. We show that, in the case analyzed, the FEL Pierce parameter has a value two orders of magnitude less than what claimed in the paper in question, overturning the conclusions of the analysis.

Toward the goal of maximizing the impact of computer modeling on the design of future particle accelerators and the development of new accelerator techniques & technologies, this white paper presents the rationale for: (a) strengthening and expanding programmatic activities in accelerator modeling science within the Department of Energy (DOE) Office of High Energy Physics (HEP) and (b) increasing the community-wide coordination and integration of code development., Comment: 4 pages, 0 figures, originally presented at the US Department of Energy workshop: Community Summer Study

Very intense neutrino beams and large neutrino detectors will be needed in order to enable the discovery of CP violation in the leptonic sector. We propose to use the proton linac of the European Spallation Source currently under construction in Lund, Sweden to deliver, in parallel with the spallation neutron production, a very intense, cost effective and high performance neutrino beam. The baseline program for the European Spallation Source linac is that it will be fully operational at 5 MW average power by 2022, producing 2 GeV 2.86 ms long proton pulses at a rate of 14 Hz. Our proposal is to upgrade the linac to 10 MW average power and 28 Hz, producing 14 pulses/s for neutron production and 14 pulses/s for neutrino production. Furthermore, because of the high current required in the pulsed neutrino horn, the length of the pulses used for neutrino production needs to be compressed to a few $\mu$s with the aid of an accumulator ring. A long baseline experiment using this Super Beam and a megaton underground Water Cherenkov detector located in existing mines 300-600 km from Lund will make it possible to discover leptonic CP violation at 5 $\sigma$ significance level in up to 50% of the leptonic Dirac CP-violating phase range. This experiment could also determine the neutrino mass hierarchy at a significance level of more than 3 $\sigma$ if this issue will not already have been settled by other experiments by then. The mass hierarchy performance could be increased by combining the neutrino beam results with those obtained from atmospheric neutrinos detected by the same large volume detector. This detector will also be used to measure the proton lifetime, detect cosmological neutrinos and neutrinos from supernova explosions. Results on the sensitivity to leptonic CP violation and the neutrino mass hierarchy are presented., Comment: 28 pages

A staged approach towards muon based facilities for Intensity and Energy Frontier science, building upon existing and proposed facilities at Fermilab, is presented. At each stage, a facility exploring new physics also provides an R&D platform to validate the technology needed for subsequent stages. The envisioned program begins with nuSTORM, a sensitive sterile neutrino search which also provides precision neutrino cross-section measurements while developing the technology of using and cooling muons. A staged Neutrino Factory based upon Project X, sending beams towards the Sanford Underground Research Facility (SURF), which will house the LBNE detector, could follow for detailed exploration of neutrino properties at the Intensity Frontier, while also establishing the technology of using intense bunched muon beams. The complex could then evolve towards Muon Colliders, starting at 126 GeV with measurements of the Higgs resonance to sub-MeV precision, and continuing to multi-TeV colliders for the exploration of physics beyond the Standard Model at the Energy Frontier. An Appendix addresses specific questions raised by the Lepton Colliders subgroup of the CSS2013 Frontier Capabilities Study Group., Comment: 56 pp. Submission to "Snowmass" Community Summer Study 2013

We show that the numerical code used in the above mentioned paper does not take into account the multiple scattering effects of electromagnetic field properly and is therefore incorrect., Comment: 2pages,submitted to NIM B

The claim in ref.1 [M. Conte et al: "Stern-Gerlach Force on a Precessing Magnetic Moment", Proceedings of PAC07 (http://cern.ch/AccelConf/p07/PAPER/THPAS105.pdf)] that the Stern-Gerlach force on a charged particle with a magnetic moment causes a change in longitudinal momentum proportional to gamma-squared when it traverses a specially configured localized electromagnetic field, contradicts the prediction based on the established interaction Lagrangian. It is shown that extending the calculation in ref. 1 to include the entire spin motion eliminates the gamma-squared term and thus the inconsistency.

Circular mode beams are beams with non-zero angular momentum and strong inter-plane coupling. This coupling can be achieved in linear accelerators (linacs) through magnetization of electrons or ions at the source. Depending on the magnetization strength, the intrinsic eigenmode emittance ratio can be large, which produces intrinsic flatness. This flatness can either be converted to real space flatness or can be maintained as round coupled beam through the system. In this paper, we discuss rotation invariant designs that allow circular modes to be transported through the lattice while accelerating the beam and maintaining its circularity. We demonstrate that with rotation invariant designs the circularity of the mode can be preserved as round beam while maintaining intrinsic flatness to be converted to flat beam for high brightness or injected into a ring.

In circular particle accelerators, storage rings, or colliders, mitigating beam losses is critical to ensuring optimal performance, particularly for rings that include superconducting magnets. A thorough understanding of beam-halo dynamics is essential for this purpose. This paper presents recent results for the measurement of the nonlinear diffusion process of the beam halo at the CERN Large Hadron Collider (LHC). The novel approach used in this paper is based on the analytical framework of the Nekhoroshev theorem, which provides a functional form for the diffusion coefficient. By monitoring the beam loss signal during controlled movements of the collimator jaws, we determine the beam losses at equilibrium for various amplitudes and analyze the beam-halo distribution. Post-processing of these measurements provides the nonlinear diffusion coefficient, which is found to be in excellent agreement with the theoretical assumptions. Measurements from an experiment investigating the effectiveness of beam-beam compensation using beam-beam compensation wires also provide a direct assessment of the compensation's effectiveness on beam-tail diffusion.

A recent experiment showed that a Cherenkov radiation spectrum from thin radiators possessing frequency dispersion could transform into quasi-monochromatic spectral lines. Simulations based on the standard Geant4 toolkit could not correctly describe the experimental results because Geant4 uses the traditional Frank-Tamm theory developed for an ideal (infinitely thick) radiator. Because of that, our endeavors in this paper are to present a new way of utilizing Cherenkov radiation using new Gneat4 models, while the paper should be used as a helping text to understand the Cherenkov process in Geant4 and what one can expect out of new models. Now, one can analyze quasi-monochromatic Cherenkov spectral lines using Geant4, which is a significant milestone for investigating the possibilities of this technique., Comment: 11 pages, 6 figures, 1 table

The muon collider has the potential to be a powerful tool for the exploration of frontiers in particle physics. In order to reach high luminosity, the 6D emittance of the muon beam needs to be reduced by several orders of magnitude. The cooling process for a muon collider involves two parts; initial six-dimensional cooling and final transverse cooling. This paper focuses on the former and proposes a conceptual design of the rectilinear cooling channel with additional dipole magnets. In this paper, we first introduce a general method for designing the rectilinear cooling channel. Subsequently, we apply this method to develop two rectilinear cooling channels before and after a bunch merging system. Furthermore, we investigate the impact on cooling performance by employing $\pi$-mode RF cavities and considering the effect of errors in the magnetic and RF fields.

Seeded Free Electron Lasers (FELs) demonstrate a good performance and are successfully used in different user experiments in extreme ultraviolet and soft X-ray regimes. In this paper a simple modification of the seeding scenario is proposed relying on generation of two closely spaced bunches with very different properties: a low-current seeding bunch, and a high-current bunch that amplifies coherent radiation, produced by the seeding bunch. This approach eliminates different limitations and mitigates some harmful effects in the standard scenario. In particular, one can generate very high harmonic numbers with a moderate laser power in a simple high-gain harmonic generation (HGHG) scheme. Alternatively, in case of moderate harmonic numbers, one can strongly reduce the required laser power thus simplifying design of high repetition rate seeded FELs. An influence of beam dynamics effects (like nonlinearities of the longitudinal phase space of electron beams, coherent synchrotron radiation, longitudinal space charge, geometrical wakefields, microbunching instabilities etc.) on properties of output radiation (spectrum broadening, pedestals, stability) can be to a large extent reduced in the proposed scheme. In this paper we illustrate the operation of the two-bunch seeding scheme in HGHG configuration with realistic start-to-end simulations for the soft X-ray user facility FLASH. We show that nearly Fourier-limited multi-gigawatt pulses can be generated at 4 nm using the present compact design of the undulator system. With several thousand pulses per second this can be a unique source for photon science.

The upcoming Proton Improvement Plan-II (PIP-II), designated for enhancements to the Fermilab accelerator complex, features a new 800 MeV superconducting linac and a Beam Transfer Line (BTL) to transport the beam to the existing Booster synchrotron. To mitigate the space charge tune shift associated with a high intensity accumulated beam, the low emittance linac beam is used to paint the ring phase space both transversely and longitudinally. To prevent losses caused by particles injected outside the rf separatrix while painting longitudinal phase space, the momentum spread of the incoming beam should not exceed 2.1 x 10^-4. Detailed simulations showed that due to space charge, the rms momentum spread increases to 4 x 10^-4 while it is transported in the BTL --about twice the allowable limit. In this paper, we outline a mitigation strategy involving a debuncher cavity. We discuss location, operating frequency, and gap voltage under both nominal and perturbed beam conditions, specifically accounting for momentum jitter. The impact of cavity misalignments is also assessed. The paper concludes by recommending an optimized configuration., Comment: IPAC'24 - 15th International Particle Accelerator Conference

Low Level RF (LLRF) control systems of linear accelerators (LINACs) are typically implemented with heterodyne based architectures, which have complex analog RF mixers for up and down conversion. The Gen 3 Radio Frequency System-on-Chip (RFSoC) device from AMD Xilinx integrates data converters with maximum RF frequency of 6~GHz. This enables direct RF sampling of C-band LLRF signal typically operated at 5.712 GHz without any analogue mixers, which can significantly simplify the system architecture. The data converters sample RF signals in higher order Nyquist zones and then up or down convert digitally by the integrated data path in RFSoC. The closed-loop feedback control firmware implemented in FPGA integrated in RFSoC can process the base-band signal from the ADC data path and calculate the updated phase and amplitude to be up-mixed by the DAC data path. We have developed a C-band LLRF control RFSoC platform with direct RF sampling, which targets Cool Copper Collider (C3) and other C or S band LINAC research and development projects. In this paper, the architecture of the platform will be described. We have optimized the configuration of the data converter and characterized performance of them with RF pulses. The test results for some of the key performance parameters for the LLRF platform with our custom solid-state amplifier, such as phase and amplitude stability, will be discussed in this paper.

In this paper, three specific scenarios of a novel accelerator light source mechanism called steady-state micro-bunching (SSMB) have been studied, i.e., longitudinal weak focusing, longitudinal strong focusing and generalized longitudinal strong focusing (GLSF). Presently, GLSF is the most promising among them in realizing high-power short-wavelength coherent radiation with a mild requirement on the modulation laser power. Its essence is to exploit the ultrasmall natural vertical emittance in a planar electron storage ring for efficient microbunching formation, like a partial transverse-longitudinal emittance exchange at the optical laser wavelength range. By invoking such a scheme, the laser modulator of an SSMB storage ring can work in a continuous wave or high duty cycle mode, thus allowing a high filling factor of microbunched electron beam in the storage ring and high average output radiation power. The backbone of it is the precision transverse-longitudinal phase space coupling dynamics, which is analyzed in depth in this paper. Based on the investigation, an example parameters set of a GLSF SSMB storage ring which can deliver 1 kW-average-power EUV light is presented. The presented work here, like the analysis on theoretical minimum emittances, transverse-longitudinal coupling dynamics, derivation of bunching factor and modulation strengths, is expected to be useful not only for the development of SSMB, but also future accelerator light sources in general which demand more and more precise electron beam phase space manipulations., Comment: 67 pages, 16 figures, 2 tables

Coherent synchrotron radiations (CSR) emitted by a high-brightness electron beam during transport in a bending magnet is a double-edged sword in electron accelerators. While CSR contributes to a stronger radiation field than the incoherent radiation, it simultaneously leads to degradation of the electron beam quality. Specifically, CSR effects manifest in increases of the beam energy spread and the projected emittance, and amplification of the microbunching instability. This paper presents analytical formulas for the CSR-induced microbunching instability gain and for the induced emittance growth in an arbitrary achromatic four-bend chicane with inclusion of both the steady-state and transient CSR effects. The analytical formulas are compared and show good agreement with Vlasov calculations and particle tracking simulations. The obtained analytical formulas are then applied to evaluate the CSR effects in the design of a general achromatic four-bend bunch compressor chicane, providing a quick estimate on the microbunching gain and the induced emittance growth. From the widely adopted symmetric C-shape chicane to a non-symmetric S-shape chicane, our analytical formulas offer insight into the evolution of the microbunching gain and the emittance growth with the variations of design parameters. In comparison to particle tracking simulations currently employed for CSR effect analyses, the analytical formulas presented in this paper significantly reduce the evaluation time, enabling systematic study of parametric dependencies with inclusion of CSR effects within specified design parameter ranges., Comment: 31 pages, 7 figures

Coherent electron cooling is a novel method to cool dense hadron beams on timescales of a few hours. This method uses a copropagating beam of electrons to pick up the density fluctuations within the hadron beam in one straight section and then provide corrective energy kicks to the hadrons in a downstream straight, cooling the beam. Microbunched electron cooling is an extension of this idea which induces a microbunching instability in the electron beam as it travels between the two straights, amplifying the signal. However, initial noise in the electron bunch will also be amplified, providing random kicks to the hadrons downstream which tend to increase their emittance. In this paper, we develop an analytic estimate of the effect of the electron noise and benchmark it against simulations. We also discuss how this effect has impacted the cooler design., Comment: 12 pages, 10 figures; paper updated to include additional discussion of diffusion in near-saturated regime and impact on cooler design

High peak and average power free-electron lasers (FELs) in the terahertz region (THz) require small diameter, low-emittance, and high voltage electron beams. This paper presents two 1.5-2 MV, 100-200 A, thermionic cathode electron source approaches for compact megawatt range peak power, multi-kilowatt average power, high repetition rate, THz FELs. The preferred beam generation system includes grading electrodes and is quite compact compared to the other standard diode gun approaches. Both provide highly compressed beams at the waist having low values of normalized rms emittance. In particular, the new injector approach with grading electrodes, operating at a body voltage of 1.5-2 MV and 100 A, has a normalized rms emittance of roughly 10 mm-mrad at the beam waist. Power supply switching considerations are considered in the paper as well as considerations for very high-voltage multi-stage depressed collectors for device efficiency enhancement. Based on these designs, we provide performance estimates for FELs operating in the THz spectral region.

The use of non-invasive sensors & systems to measure particle beam characteristics is a crucial part of modern accelerator control systems due to their ability to return real time passive measurements without impacting the beam quality. Simulations, which can predict these sensors' behaviour and performance under anticipated accelerator conditions, are valuable tools to ensure confidence in the sensors' functionality prior to a physical bench test. This paper details the design, testing, and results of two sensor models developed using CST Studio Suite software. One model is an elliptical, large-aperture beam position monitor (BPM) for which vertical & horizontal position signal linearity was analyzed. The second model is an AC current transformer (ACCT) beam current monitor (BCM), which was used to search for potential fault cases within the BCM and beam pipe flange gaps. Fermilab Proton Improvement Plan II (PIP-II) accelerator beam conditions were applied, and special focus is given to the discovery of linearity variations within the BPM as well as the use of frequency domain techniques in the BCM fault case analyses., Comment: 5 pages, 9 figures. To be submitted to the Journal of Instrumentation

In nuclear and atomic physics experiments, charged ion beams often need to be guided from the ion production to the experimental site. In the PUMA experiment, an ion source beamline was developed, which can be operated with up to \SI{5}{\kilo\electronvolt} beam energy at a base pressure of $10^{-9}$\,mbar or better. In this paper, a low-energy pulsed drift tube for beam energy modification, a hybrid einzel lens assembly for beam focusing and steering and an iris shutter assembly for separating beamline sections with different vacuum requirements are described with their design principles and performances., Comment: 22 pages, 13 figures

Magnetized beams beam with significant canonical angular momentum are critical to electron cooling of hadron beams such as contemplated in next-generation hadron and electron-ion colliders. The transport of magnetized electron beams over long distances in a locally non-axisymmetric external field is challenging. An alternative is to transform the beam into an uncoupled "flat beam", transport the produced "flat" beam over a long distance, and reintroduce the cross-plane coupling to "re-magnetize" the beam. In this paper, we demonstrate via numerical simulation and laboratory experiments such a cascaded-transformation approach., Comment: Submitted to Proceedings of AAC 2024 Workshop

Understanding and predicting complex dynamics in accelerators is necessary for their successful operation. A grand challenge in accelerator physics is to develop predictive virtual accelerators that mitigate design cost and schedule risk. Data-driven techniques greatly appeal to generating virtual accelerators due to their limited dimensionality compared with first-principle simulation, yet require significant up-front investment and lack interpretability in the context of governing equations. This paper uses an alternative, interpretable, data-driven technique called Sparse Identification of Nonlinear Dynamics (SINDy) developed by University of Washington researchers to study nonlinear beam centroid dynamics excited by realistic beam injection. We propose evolution equations based solely on data analysis and intuition of the underlying lattice structure, without recourse to an underlying first-principles centroid model nor the actual lattice forcing functions. We do this to mimic an application environment where analytic models are inadequate or where detailed lattice forcing functions are unknown. In the context of the accurate centroid model, we report and interpret SINDy's beam evolution equations learned from the training data and show favorable prediction results. We compare with an alternative machine learning model used on the same training data and contrast its prediction ability, computational expense, and interpretability with SINDy's results.

Flat beams are preferred in high-intensity accelerators and high-energy colliders due to one of the transverse plane emittances being much smaller than the other, which enhances luminosity and beam brightness. However, flat beams are not desirable at low energies due to space charge forces which are significantly enhanced in one plane. The same is true, although to a lesser degree, for non-symmetric elliptical beams. To mitigate this effect and enable flat beams at higher energies, circular mode beam optics can be used. In this paper, we show that circular mode beams offer better control of space charge effects at lower energies and can be transformed into flat beams at higher energies.

In this paper we present a novel scheme for the controlled generation of of tunable narrowband gamma-ray radiation by ultra-relativistic positron beams inside acoustically driven periodically bent crystals. A novel acoustic crystalline undulator is presented, in which excitation of a silicon single crystal along the (100) planar direction by a piezoelectric transducer periodically modulates the crystal lattice in the [100] axial direction. An ultra-relativistic positron beam is directed diagonally into the crystal and propagates along the (110) planes. The lattice modulation forces the positrons to follow periodic trajectories,resulting in the emission of undulator radiation in the MeV range. A computational methodology for the design and development of such acoustically based light sources is presented together with the results of simulations demonstrating the favourable properties of the proposed technology. The longitudinal acoustic strains induced in the crystal by high-frequency piezoelectric elements are calculated by finite element simulations. The resulting bending profiles of the deformed crystal planes are used as geometrical conditions in the relativistic molecular dynamics simulations that calculate the positron trajectories and the spectral distribution of the emitted radiation. The results show a strong enhancement of the emitted radiation within a narrow spectral band defined by the bending period, demonstrating the feasibility and potential of the proposed technology., Comment: 32 pages, 11 figures, submitted to Phys. Rev. - Accel. Beams

Space charge has been a limiting factor for low energy accelerators inducing emittance growth and tune spread. Tune shift and tune spread parameters are important for avoiding resonances, which limit intensity of the beam. Circular modes are round beams with intrinsic flatness that are generated through strong coupling, where intrinsic flatness can be transformed to real space flatness through decoupling. It is understood that flat beams increase beam quality parameters, such as beam brightness and collision luminosity, due to one of the planes' emittance being much smaller than in the other plane, and since both luminosity and beam brightness depend inversely on the beam emittances. We show that circular mode beams manifest smaller space charge tune spread compared to uncorrelated round beams, which allows better control of beam quality. Minimized tune spread allows more flexible operating points on the tune map.

Electropolishing process and cathodes have undergone modification and optimization for both low- and high-beta 650 MHz five-cell niobium cavities for PIP-II. Cavities treated with these modified electropolishing conditions exhibited smooth surfaces and good performance in baseline tests. Nonetheless, due to administrative constraints on project cavities, maximum gradient performance testing was not conducted. This paper presents a study conducted on a single-cell 650 MHz cavity utilizing the optimized electropolishing conditions, highlighting the maximum performance attained for this specific cavity. The cavity tested at 2 K in a vertical cryostat reached a superior accelerating field gradient of 53.3 MV/m at Q0 of 1.6x1010, which is the highest gradient attained for this type of large-sized cavities., Comment: 32nd Linear Accelerator Conference (LINAC 2024)

In this paper we present detailed simulations with asymmetric initial beam settings in the context of the proposed Future Circular Collider e+e- (FCC-ee) using the Xsuite framework. We compare simulated equilibrium bunch sizes and luminosities against an already existing analytical model, which shows remarkably good agreement for realistic small perturbations. We investigate the longitudinal top-up injection, the currently preferred injection scheme for the FCC-ee, using self-consistent simulations featuring beam-beam collisions with beamstrahlung and the injection process, for the first time. We present and assess the sensitivity and required precision of the nominal beam parameters in a potential real-life operation by providing first estimates of the tolerances in the initial asymmetry of several machine parameters, with respect to the 3D flip-flop mechanism, obtained from parameter scan simulations., Comment: 12 pages, 15 figures

The Beam Dump Facility (BDF) is a planned fixed-target installation in CERN's North Area, set to start operating in 2031. A proton beam of 400 GeV/c will be delivered in 1 s pulses of 4e13 protons every 7.2 s, amounting to 4e19 protons on target (PoT) per year, with an average thermal power deposition of 305 kW. The experiment requires high-Z and high-density materials and involves challenging thermomechanical conditions; hence, a water-cooled refractory metal core is proposed. To prevent corrosion and erosion, the target materials - tungsten and a molybdenum-based alloy, TZM-, are clad with a tantalum alloy using hot isostatic pressing. To verify the reliability of the target design and manufacturing process, a reduced-scale prototype target was manufactured and irradiated with 2.4e16 PoT in 2018. This paper presents the findings of the post-irradiation examination (PIE) conducted 2.5 years later. The PIE consisted of non-destructive and destructive activities, including film imaging, microscopy, metrology, ultrasonic testing, microstructural analysis, and mechanical and thermal characterization. No irradiation effects resulting from thermal stresses, such as geometrical changes or cracks in the cladding, were observed, and it was determined that the bonding between the core and cladding materials was robust. Moreover, no changes were detected in the microstructures or mechanical properties of the bulk materials. In conclusion, the robustness of the target baseline design and manufacturing process was confirmed, validating its suitability for operating under the desired conditions. Nonetheless, the observed brittleness of sintered tungsten indicates a potential area for improvement to enhance the lifetime of the BDF target. Overall, the examinations provided valuable insights into the performance of the prototype and indicated potential refinements for the future BDF target complex.

IJCLab has been leading the development and deployment of low-$\beta$ Superconducting Radio Frequency (SRF) cavities for proton and heavy ion accelerators. We are launching an electron accelerator project for sustainable Energy Recovery Linac (iSAS/PERLE) with state-of-the-art SRF cavities at 800~MHz. Our proposal includes advanced heat treatment of such cavities to reach an excellent quality factor of $3\times 10^{10}$ at $22$~MV/m. In this paper, we overview the status of this activity., Comment: Contribution to LCWS2024 proceedings

During operation, the radio-frequency quadrupole (RFQ) of the LINAC4 at CERN is exposed to high electric fields, which can lead to vacuum breakdown. It is also subject to beam loss, which can cause surface modification, including blistering, which can result in reduced electric field holding and an increased breakdown rate. First, experiments to study the high-voltage conditioning process and electrical breakdown statistics have been conducted using pulsed high voltage DC systems in order to identify materials with high electric field handling capability and robustness to low-energy irradiation. In this paper, we discuss the results obtained for the different materials tested. To complement these, an investigation of their metallurgical properties using advanced microscopic techniques was done to observe and characterize the different materials and to compare results before and after irradiation and breakdown testing.

This work studies the suitability of a set of different materials for manufacturing of more efficient and durable Radio-Frequency Quadrupole (RFQ) structures compared to that currently used in many linear particle accelerators, traditionally made out of copper. RFQs are susceptible to vacuum breakdowns caused by the exposure to high electric fields, resulting in surface degradation. Additionally, a further limitation of present-day copper RFQs is surface blistering under hydrogen ion beam exposure, due to beam halo losses. Irradiation is associated with a further reduction of the breakdown field strength of the metal surface thereby affecting the overall efficiency of the RFQ. The investigated materials, Cu-OFE, CuCr1Zr, CuBe2, Ti6Al4V, SS316LN, Nb and Ta, were submitted to low-energy (45 keV) H$^-$ irradiation and tested in a direct-current (DC) system with pulsed high voltage. For comparison, the maximum surface electric field was measured for both irradiated and pristine (non irradiated) surfaces of the same material. The effects of irradiation on the surface of the materials, before and after being submitted to high electric fields, were studied with the help of microscopic imaging and chemical analysis. Blistering caused by H$^-$ irradiation has been observed in all copper and copper alloy materials. Despite reductions in breakdown field strength post-irradiation, no indications were found that the blisters on the surface have a direct cause in triggering breakdowns during high electric field tests. SS316LN, Ti6Al4V, CuBe2 and CuCr1Zr showed maximum surface electric fields higher than copper, making these promising candidate materials for future RFQs manufacturing. This paper focuses on the results with CuCr1Zr, CuBe2, SS316LN and Ta, complementing and expanding previous work exploring Cu-OFE, Nb and Ti6Al4V.

This paper proposes an alternative implementation of the MENT algorithm, an exact maximum-entropy algorithm used to infer a phase space distribution from its projections. A key step in the MENT algorithm is to compute the distribution's projections via numerical integration. In this approach, the run time scales quickly with the phase space dimension and measurement resolution. The proposed MENT implementation computes the projections via particle sampling, rather than numerical integration, eliminating the dependence on the measurement resolution. Furthermore, with the appropriate sampling algorithm, the particle-based approach scales to $N$-dimensions without computer memory limitations. Using synthetic data, we demonstrate MENT convergence in four dimensions using a grid-based sampling method and in six dimensions using Markov Chain Monte Carlo (MCMC) sampling., Comment: 7 pages, 2 figures, comments welcome

In this paper, we introduce two complementary approaches for the accurate prediction of AC losses in large-scale low-temperature superconducting (LTS) magnets. These methods account for the temperature rise within the LTS coil and its impact on AC losses. The first approach is multi-scale and relies on the coupling between a macroscopic homogenized model of the LTS coil and a mesoscopic model of a single conductor for loss prediction. The second approach is semi-analytical and is based on analytical approximations for the hysteresis losses, which are validated against a single filament model. The second approach offers a faster computation suitable for initial design considerations, while the multi-scale method is shown to provide more accurate results. We apply both methods to the prediction of AC losses generated in the LTS coil inside the IBA S2C2 synchrocyclotron during its ramp-up procedure. Additionally, we discuss the convergence properties of the multi-scale approach and demonstrate the good agreement between the numerical results and experimental data., Comment: This work has been submitted to the IEEE for possible publication

The commissioning and operation of future large-scale scientific experiments will challenge current tuning and control methods. Reinforcement learning (RL) algorithms are a promising solution thanks to their capability of autonomously tackling a control problem based on a task parameterized by a reward function. The conventionally utilized machine learning (ML) libraries are not intended for microsecond latency applications, as they mostly optimize for throughput performance. On the other hand, most of the programmable logic implementations are meant for computation acceleration, not being intended to work in a real-time environment. To overcome these limitations of current implementations, RL needs to be deployed on-the-edge, i.e. on to the device gathering the training data. In this paper we present the design and deployment of an experience accumulator system in a particle accelerator. In this system deep-RL algorithms run using hardware acceleration and act within a few microseconds, enabling the use of RL for control of ultra-fast phenomena. The training is performed offline to reduce the number of operations carried out on the acceleration hardware. The proposed architecture was tested in real experimental conditions at the Karlsruhe research accelerator (KARA), serving also as a synchrotron light source, where the system was used to control induced horizontal betatron oscillations in real-time. The results showed a performance comparable to the commercial feedback system available at the accelerator, proving the viability and potential of this approach. Due to the self-learning and reconfiguration capability of this implementation, its seamless application to other control problems is possible. Applications range from particle accelerators to large-scale research and industrial facilities.

Wakefield acceleration methods are known due to some their advantages. The main of them is the high accelerating gradient up to several teravolts per meter. In the paper another important advantage is concluded to the possibility of using a wakefield accelerator as a source of electrons by means of obtaining self injected bunches and their accelera-tion. The result is the simulation of the process of plasma wakefield excitation by a laser pulse with an energy of tens of mJ and a power of 1-2 TW for obtaining the promising electron source. Homogeneous and Gaussian plasma profiles were investigated and compared to increase the energy of the self-injected bunches. The laser parameters were taken that corresponded to the parameters of the laser setup in the Institute of Plasma Electronics and New Methods of Acceleration of the National Scientific Center "Kharkiv Institute of Physics and Technology". Based on the results of the simulation, the possibility of obtaining relativistic self-injected bunches that can be used for further laser acceler-ation experiments, including dielectric laser acceleration, was demonstrated., Comment: 6 pages, 10 figures, 5 tables

In this paper, we propose the Reduced Order Hysteretic Magnetization (ROHM) model to describe the magnetization and instantaneous power loss of composite superconductors subject to time-varying magnetic fields. Once the parameters of the ROHM model are fixed based on reference simulations, it allows to directly compute the macroscopic response of composite superconductors without the need to solve the detailed current density distribution. It can then be used as part of a homogenization method in large-scale superconducting models to significantly reduce the computational effort compared to detailed simulations. In this contribution, we focus on the case of a strand with twisted superconducting filaments subject to a time-varying transverse magnetic field. We propose two levels of ROHM models: (i) a rate-independent model that reproduces hysteresis in the filaments, and (ii) a rate-dependent model that generalizes the first level by also reproducing dynamic effects due to coupling and eddy currents. We describe the implementation and inclusion of these models in a finite element framework, discuss how to deduce the model parameters, and finally demonstrate the capabilities of the approach in terms of accuracy and efficiency over a wide range of excitation frequencies and amplitudes., Comment: Updated preprint (improved figures and added explanations), 20 pages, 28 figures

New developments in accelerator physics have broadened the set of available techniques for manipulating charged-particle beams. Adiabatic trapping and transport of beam in resonance islands has been studied and successfully implemented at the CERN Proton Synchrotron to perform multiturn extraction. Bent crystals have been successfully installed in the CERN Large Hadron Collider, improving the cleaning performance of the collimation system, and at the CERN Super Proton Synchrotron for reducing losses at the extraction septum in the case of slow extraction. In this paper, we discuss the potential of the combined use of resonance islands and bent crystals to devise a novel technique to perform slow extraction in circular hadron accelerators. The proposed approach is promising, particularly for applications with high-intensity beams, as it could dramatically reduce the losses on the extraction devices.

It is a truth universally acknowledged, that space charge effects in ultrarelativistic electron storage rings are irrelevant due to the steep inverse dependence of their strength on the Lorentz factor. Yet, with the push towards the diffraction limit, the state-of-the-art light sources are approaching the point where their emittance becomes so small that the space charge force can no longer be ignored. In this paper, we demonstrate how space charge effects affect the injection dynamics, dynamical aperture, and collective beam stability on the example of 4th generation light sources PETRA IV and SOLEIL II.