key: cord-0664940-oos9r9yk
authors: Power, John; Clarke, Christine; Downer, Michael; Esarey, Eric; Geddes, Cameron; Hogan, Mark J.; Hoffstaetter, Georg Heinz; Jing, Chunguang; Nagaitsev, Sergei; Palmer, Mark; Piot, Philippe; Schroeder, Carl; Umstadter, Donald; Vafaei-Najafabadi, Navid; Valishev, Alexander; Willingale, Louise; Yakimenko, Vitaly
title: Beam Test Facilities for R&D in Accelerator Science and Technologies
date: 2022-03-21
journal: nan
DOI: nan
sha: 9ee194c8b888f6392fc63f64d19acccb973a5e9d
doc_id: 664940
cord_uid: oos9r9yk

This is the Snowmass Whitepaper on Beam Test Facilities for R&D in Accelerator Science and Technologies and it is submitted to two topical groups in the Accelerator Frontier: AF1 and AF6.

4 record-setting transformer ratios, the first demonstration of optical stochastic cooling, ion acceleration, etc. In addition to HEP milestones, multiple spin offs from the beam test facilities have impacted mid-term applications, such as BES light-sources, with its role in the development of the RF photoinjector, demonstration of SASE FEL, etc. as well as near-term spinoffs impacting societal applications in the medical, security, and industrial fields with the development of compact accelerators.

Upgrades to US beam test facilities will require significant investment by USDOE-HEP to ensure the US GARD program remains internationally competitive. In turn, upgraded beam test facilities are needed to enable DOE-HEP to build a cutting-edge program in the energy and intensity frontiers. For example, the European Strategy for Particle Physics has committed considerable funds to accelerator R&D in Europe. All USDOE GARD beam test facilities have near-term upgrades underway and have developed proposals for mid-term upgrades to continue progress on the previously developed roadmaps and support from DOE-HEP is needed to realize these plans.

In the long-term, several options are under consideration ranging from a greenfield beam test facility to re-using the infrastructure of next-generation facilities such as ILC, CLIC, FNAL site linac, C3. . . etc with Advanced Acceleration technology. Once again, long-term plans require serious study and support. In the long term, the US community is exploring a possible greenfield beam test facility to enable a large-scale demo of the application to AAC and possibly support medium-energy research in elementary particle physics. [4] . These programs support fundamental accelerator research and development of accelerator technology and methods to increase beam brightness, accelerating gradient, average power, etc., to dramatically improve the cost effectiveness and performance of accelerators [1] . These programs are the key to creating accelerator User Facilities in the mid-and far-term for discovery science (particle physics, neutron sources, light sources, etc.) and to create near-term, low-cost, compact accelerator technology for future societal applications in the medical, security, and industrial fields. US beam test facilities are crucial components for advancing accelerator science and technology (S&T).

The mission of the beam test facilities are to provide the experimental test beds where fundamental accelerator research can be explored and advanced accelerator technology can be developed and undergo integration testing. While limited R&D can be done in User Facilities dedicated to non-accelerator science (e.g. LHC), typically these facilities have a dedicated user base that cannot tolerate interruption. Their limited beam availability is used for near-term accelerator technology to improve operations. These facilities are ill-suited for exploring and developing advanced accelerator science. This is where beam test facilities, dedicated to accelerator science, play an essential role. In addition to the S&T mission, beam test facilities are where a large number of future scientists and engineers needed by the accelerator community are educated and trained [5, 6] . At the highest level, the mission of the facilities can be broken down as:

1. Providing experimental test beds to carry out basic research in advanced accelerators and beam physics.

2. Developing the S&T needed to enable the next generation of energy-frontier and intensityfrontier science facilities and societal accelerator applications.

3. Educating and training future scientists and engineers.

The above mission is carried out at several beam test facilities located both domestically, at US National Laboratories and Universities and international facilities in Europe and Asia, are used to perform research critical to advancing accelerator science and technology (S&T). In this section, a list of major beam test facilities that possess one or more of the following capabilities is presented: (O(100) MeV energy drive beams, O(10) Petawatt drive lasers, O(1) Gigawatt RF power sources, high-quality charged particle sources (low emittance electron beams and positron beams), advanced beam manipulation systems (e.g. nonlinear integrable optics, optical stochastic cooling, emittance exchange) and emerging capabilities to demonstrate AI/ML. Each facility description is accompanied by an overview of its research program. Note, this list is not exhaustive as it leaves out many university-scale beam test facilities due to space limitations. We note that universitybased beam test facilities are vital to accelerator research since this is where many ideas are first developed before being tested on a larger scale. 

The Accelerator Test Facility (ATF) at Brookhaven National Laboratory serves the US DOE Accelerator Stewardship program and develops advanced acceleration methods for leptons and ions as well as high-energy photon sources. The ATF provides access to three classes of experimental facilities: a long-wave infrared high-power laser at 9.2 µm, a high-brightness linac-driven 75-MeV electron beam, and near-IR laser sources. This combination of capabilities enables programs on particle and photon source development, wakefield acceleration, inverse Compton scattering, and laser-driven plasma ion acceleration.

FIG. 1. Overview of the ATF facility. User experiments can be configured to utilize the near-IR laser beams, long-wave IR beam, and electron beam singly or in any combination.

The Argonne Wakefield Accelerator (AWA) Facility [7] is dedicated to the investigation of Structure Wakefield Acceleration (SFWA) including both collinear wakefield acceleration (CWA) and short-pulse two-beam acceleration (TBA). The AWA facility (Fig. 2) consists of three accelerators: the Drive Photoinjector (producing up to 70-MeV high-charge electrons), the Main Photoinjector (which forms 15-MeV electron bunches), and a few MeV cathode test-stand. AWA research focuses on underlying beam-dynamics challenges (e.g., production of bright-and highcharge-beams), beam manipulation (e.g., beam-current shaping) and beam control (e.g., mitigation of the BBU instability), and the development of advanced accelerating structures (e.g., dielectric waveguides, planar structures, metamaterials, rapid filling metallic structures, etc.) for efficient, high-peak-power RF generation and high-gradient acceleration. AWA has demonstrated unprecedented beam-transformer ratios (> 5) in both SWFA and Plasma Wakefield Accelerator (PWFA) setups. Likewise, it has generated GW-scale peak-power RF-pulses and demonstrated staging in a TBA configuration in the pursuit of a linear collider. AWA develops these technologies for other applications (FELs and compact accelerators) and synergistically supports other advanced-accelerator concepts. 

The BELLA Center at LBNL has been performing research on laser-plasma accelerators (LPAs) for over two decades. The main research objectives are the development of LPA modules at the 10 GeV level and the staging (coupling) of LPA modules, which are two essential R&D components for a future plasma-based linear collider. The current laser systems at the BELLA Center include the BELLA Petawatt (PW) laser and two independent 100 Terawatt (TW) laser systems. Upgrades are underway to the BELLA PW beamline to allow the delivery of two synchronized pulses, with independent compressors, on target, enabling staging, and a short focal length capability, enabling experiments at ultrahigh intensity (Fig. 3) . The BELLA Center is also pursuing a new facility, kBELLA, consisting of a 1 kHz, few J, 30 fs, high average power laser for the demonstration of a high rep-rate, precision LPA and subsequent applications. The BELLA Center functions as a collaborative research center and is part of LaserNetUS [8] . This is optimal for gas target wakefield acceleration experiments. 

Advancing accelerator science and technology (S&T) is the subject of great international interest as the international community seeks to develop the next generation of energy-frontier and intensity-frontier user facilities. This section provides a brief overview of beam test facilities around the world.

The European landscape currently maintains a large portfolio of Advanced and Novel Accel- In addition to the current ANA facilities, the European community has recently committed to the commissioning of a new large-scale accelerator project called EuPRAXIA. In its first implementation phase, the EuPRAXIA consortium will construct a PWFA facility, 479 named

EuPRAXIA@SPARC-LAB at the LNF-INFN [11] . In its second phase, EuPRAXIA consortium will build a LWFA facility at a site to be chosen within the next 2 years between several options in Europe. This major commitment by the European accelerator community will have a high impact on the future of accelerator technology.

The Asian accelerator landscape includes a variety of facilities to study the four ANA categories Machine Learning [14] .

In Table I , we list the main thrusts of the US ANA program as carried out by the ANA facilities at the national laboratories: advanced acceleration concepts, particle source development, beam physics, and diagnostics and beam control. Note that this list is not exclusive of all accelerator S&T conducted at the US ANA facilities.

ANA beam test facilities have been instrumental in advancing accelerator S&T throughout their history. In this section, we present short summaries of these advances in two subsections (i) progress made since the previous Snowmass process and (ii) spinoffs from the DOE GARD beam test facilities.

The primary goal of the US DOE GARD program is to carry out accelerator- [16] . In this subsection, we present selected S&T highlights of progress made on the subpanel recommendations in which the GARD beam test facilities were crucial. Examples of milestones accomplished covered here will include progress in both the intensity and energy frontiers. Intensity-Frontier accelerator science saw the first demonstration of Optical Stochastic Cooling [17] . Energy-Frontier linear collider accelerator science delivered multi-GeV/m accelerating gradients and multi-GeV energy gain in plasma accelerators using beam-drivers at FACET [18] and laser-drivers at BELLA [19] , multi-GeV/m positron acceleration at FACET [20] , staging of two plasma accelerator modules at BELLA [21] , demonstration of controlled injection in a plasma wakefield accelerator [22] , record setting transformer ratios at AWA in both structures [23] and plasmas [24] , pioneering work at ATF on shock wave monoenergetic ion acceleration [25] , nonlinear effects in inverse Compton scattering (red shift, higher harmonics) [26] , highgain high-harmonic generation FEL [27] , fundamental research of electron acceleration in dielectric waveguides (e.g., using 3D woodpile structures [28] ), fundamental research on nonlinear Thomson scattering [29] , and novel methods for controlled optical injection of electrons into wakefields [30] .

The development of community-driven research roadmaps was major organizational success for the GARD program. Roadmaps have been published for all GARD thrusts except the Accelerator and Beam Physics Roadmap [31] thrust area which was delayed by COVID but is expected to be published shortly. These roadmaps enable pressing challenges to be more easily identified and addressed to move the field forward and insured a list of prioritized milestones that were aligned to the most compelling HEP science. The GARD beam test facilities play crucial roles in the following roadmaps. (i) In 2016, US DOE published the Advanced Accelerator Roadmap [6] that laid out a series of research plans and goals that would provide the foundation for a technical design report of a multi-TeV linear collider. Significant progress along the AAC roadmap has been made at the GARD beam test facilities over the last 5 years and they remain critical for pursuing the continued advancements.

A secondary, yet vital goal, is to apply this long-term, general R&D carried out at the ANA facilities to generate spinoff technologies to benefit other applications in science, medicine and industry. Not only does this help validate the accelerator S&T underway but also to benefit other accelerator applications (e.g. light sources, and neutron sources, etc.). Note that these spinoffs often come many years down the road, sometimes decades later. Sometimes they come from Universities, sometimes from National Laboratories, sometimes from Industry, or a combination of two or three stakeholders. A partial list of some of these spinoff technologies is given in Table II . Table III . Similarly, the capabilities of the university-based facilities are summarized in Table IV . Capabilities with high-quality beam parameters and diagnostic tools are essential to support research into new beam generation, acceleration, and transport techniques with the potential to mitigate technical risks of upcoming projects and to reduce the cost of future accelerator facilities.

In order to continue progress in accelerator science and technology, for instance progress along the AAC Roadmap, major upgrades to the facilities are required. beams [33] [34] [35] . While the facility is currently capable of producing a 5 TW CO 2 pulse, only about half of that is delivered to users due to limitations of the air transport system. An upgrade to a vacuum transport system as well as the development of nonlinear pulse compression (NLPC) [36] technique is expected to allow the delivery of ¿10 TW pulses over the next several years with pulse lengths as short as hundreds of femtoseconds. The facility is also pursuing an active R&D program on optical pumping of CO 2 molecules as well as other technologies that make efficient use of the CO 2 gain profile and enable the delivery of high-repetition rate, high-average power, reliable LWIR pulses. The ATF plans also envision several thrusts for upgrading the linac-driven e-beam, including beam energy and pulse compression. Together with the expanded near IR capabilities, which encompasses the integration and the delivery of a compressed (≤ 100 fs), terawatt-class Ti:Sapphire laser pulse to the IP, simultaneous experiments using the LWIR laser, e-beam, and the Ti:Sapphire enable the research and development of next generation of particle and photon sources.

A proposal to impliment a major upgrade of the Argonne Wakefield Accelerator (AWA) to the AWA-HE (HIGH ENERGY) Facility is under development . In several years, after completing 21 the 500-MeV demonstrator, the AWA will become limited in its ability to continue advancing the SWFA Roadmap. Our vision is to continue to advance the Roadmaps by enacting a phased upgrade of the AWA facility so that by the end of the decade the SWFA method will be ready to present an SWFA CDR for a 3-TeV e+e-linear collider. Bunker expansion.

Step 1 is to expand the AWA bunker length so that it occupies all available space in its current building. Energy upgrade.

Step 2 is to add more RF stations and accelerating structures to increase the energy from 65 to 150

MeV. This will enable GV/m class acceleration gradients and a 3-GeV demonstrator.

Upgrades are underway to the BELLA PW laser beamline (operating at 1 Hz) to allow the delivery of two synchronized pulses on target, enabling staging at the few GeV level, and a short focal length capability, enabling experiments at ultrahigh intensity (e.g., laser ion acceleration).

The BELLA Center is also pursuing a new facility, kBELLA, consisting of a 1 kHz, few J, 30 fs, high average power laser for the demonstration of a high rep-rate, precision LPA and subsequent

applications. This will function as a user facility with the kHz, GeV class electron beams and the intrinsically synchronized photon pulses being available for a wide variety of experiments in the basic and applied sciences. One possible candidate laser technology for kBELLA is coherent combining of fiber lasers, which holds promise for providing high average power at high efficiency.

To this end, the BELLA Center has a very active R&D program on coherent combining (in both time and space, as well as spectrally) of fiber lasers in collaboration with University of Michigan and LLNL. Furthermore, fiber lasers have the potential to provide high average power and high efficiency at 10 kHz and beyond, which is needed for a future LPA-based collider. The development of highaverage power, high efficiency lasers is delineated as an important R&D topic on the Advanced Accelerator Roadmap.

In the coming years, the IOTA ring will be upgraded with a proton injector and an electron lens/cooler [37] . The research with protons and electrons will focus on nonlinear beam optics studies [38] , investigation of space-charge effects [39] , realization of Electron Lens with its broad research program [37] , continuation of the OSC program [40] , and photon science opportunities [41] .

A significant required upgrade to the FAST facility is the addition of a laser system to enable [2] US Department of Energy (DOE), Office of Science, . URL https://www.energy.gov/science/ leadership.

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Physics briefing book

Advanced accelerator development strategy report: DOE advanced accelerator concepts research roadmap workshop

AWAKE readiness for the study of the seeded self-modulation of a 400 GeV proton bunch

Eupraxia@ sparc lab design study towards a compact fel facility at lnf. Nuclear Instruments and Methods in

Radiofrequency accelerator R&D strategy report: Doe hep general accelerator R&D RF research roadmap workshop

Accelerator and beam physics research goals and opportunities

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Accelerating discovery: A strategic plan for accelerator r&d in the u.s

Update on p5 gard subpanel recommendations

First Results of the IOTA Ring Research at Fermilab

Highefficiency acceleration of an electron beam in a plasma wakefield accelerator

Petawatt laser guiding and electron beam acceleration to 8 gev in a laser-heated capillary discharge waveguide

Multi-gigaelectronvolt acceleration of positrons in a self-loaded plasma wakefield

Multistage coupling of independent laser-plasma accelerators

Generation and acceleration of electron bunches from a plasma photocathode

Observation of high transformer ratio of shaped bunch generated by an emittance-exchange beam line

Single shot characterization of high transformer ratio wakefields in nonlinear plasma acceleration

Monoenergetic proton beams accelerated by a radiation pressure driven shock

Observation of the second harmonic in thomson scattering from relativistic electrons

First lasing of a high-gain harmonic generation free-electron laser experiment

Experimental characterization of electronbeam-driven wakefield modes in a dielectric-woodpile cartesian symmetric structure

Attosecond electron bunch measurement with coherent nonlinear thomson scattering

Electron trapping from interactions between laser-driven relativistic plasma waves

Accelerator and beam physics research goals and opportunities

Report of the accelerator test facility science planning workshop

Extending laser plasma accelerators into the mid-ir spectral domain with a next-generation ultra-fast co2 laser

Ultra-low emittance beam generation using two-color ionization injection in laser-plasma accelerators

Laser Acceleration of Electrons, Protons, and Ions III; and Medical Applications of Laser-Generated Beams of Particles III

Laser-driven shock acceleration of monoenergetic ion beams

Post-compression of long-wave infrared 2 picosecond sub-terawatt pulses in bulk materials

Beam physics research with the IOTA electron lens

Quasi-integrable nonlinear optics experiment at iota

Rapidly converging chaos indicator for studying dynamic aperture in a storage ring with space charge

The design of optical stochastic cooling for IOTA

Measurements of undulator radiation power noise and comparison with ab initio calculations