Co-Conveners: Cameron Geddes (LBNL), Mark Hogan (SLAC), Pietro Musumeci (UCLA), Ralph Assmann (DESY)

The Advanced Accelerator program is developing new concepts for particle accelerator, generation, and focusing that could revolutionize the cost paradigm for future accelerators. This is an effort being pursued at laboratories and universities worldwide.

The AAC Topical Group will focus on the concepts that are being developed worldwide, the potential impact that they could have on the accelerator complex and future colliders, the major challenges that need to be addressed, and the development time and cost scales. The group will describe the contributions from and potential impact to the US HEP program in the context of the worldwide effort.

See below for detailed topics being addressed, schedule and plan of work. Please contact the conveners with questions.

For routine communications, we request that you subscribe to the AF6 email list by sending an email to

[email protected]

with a blank subject and with the body of the message consisting of the text:

SUBSCRIBE SNOWMASS-AF-06-AAC firstname lastname

and also encourage you to subscribe to Snowmass general and Frontier area lists available at http://snowmass21.org . The Accelerator, Energy, and Computational frontiers may be of particular interest.

Events will also be posted to the Snowmass Accelerator Frontier Calendar https://snowmass21.org/accelerator/start#meetings_and_calendar to which we ask you to subscribe: https://calendar.google.com/calendar/embed?src=b02unplt6neu8o5h9evtm3bv90%40group.calendar.google.com&ctz=America%2FWhitehorse

Thank you to all the authors for a strong set of papers. A first draft PDF of the complete report is available for your comments in the folder:

https://drive.google.com/drive/folders/1T3dvN43AokoLA41Wq8Ioe6e56fRcQBqr?usp=sharing

Summarizing the rich content in the white papers was challenging and we welcome feedback. This directory is open to all to allow us to keep the report up to date for you. Please do not create additional files in this directory- if you would like to create a copy for your use, please create it elsewhere to avoid confusion. If you find files other than the main PDF, please don’t use them, they will be deleted.

Please enter comments in the google doc at:

https://docs.google.com/document/d/1MXCTfE0cEpHokWTaydKmxqOaMSyQTJTNebTYBsZVPG8/edit

We will have a meeting to discuss feedback on Wednesday July 13th at 0830 Pacific, please see links on the AF06 email list, the AF calendar or contact us for connection details. The aim will be to have a close to final version before the summer study for cross-frontier discussion. Following the Seattle meeting, reports will be finalized in September.

We hope to see you at both AF6 and related sessions at the Seattle meeting, http://seattlesnowmass2021.net/. This will be a very good opportunity to discuss with colleagues and convey the potential of advanced accelerators to advance high energy physics, as well as the need for strong R&D to realize that potential. In addition to AF sessions, sessions with the Energy and Theory frontiers as well as Computational (including accelerator simulations) and Community (including workforce and DEI topics) and others will be important. The Seattle program is on Indico: https://indico.fnal.gov/event/22303/timetable/#20220718

White papers are complete, with due date March 15th and a overview workshop scheduled February 15th (see “Process and Dates” section below. Revisions are still possible. Coordination of input among multiple institutions is encouraged. Groups address several areas, for which information and contacts are listed here. Please contact one of the co-conveners to update or add information on a group, for example linking new documents when available. We invite the formation of additional groups - please email the conveners to discuss and set up a contact listing, or for updates to existing listings.

The format for white papers is requested to follow this template: https://docs.google.com/document/d/16QmNG3a5NkseSk4athsODTOS7ByCu3y-KW3W_h2DKXA/edit?usp=sharing

Plasma and Advanced Structure Accelerators Interest Group (PASAIG)
Coordinators: Eric Esarey (LBNL), John Power (ANL), Vitaly Yakimenko (SLAC), Carl Schroeder (LBNL), Navid Vafaei-Najafabadi (Stony Brook), and Warren Mori (UCLA).
Contact: sign up at https://forms.gle/Th7fTiELbahaQkAM8
Description: The purpose of this interest group is to organize and coordinate community input for the Snowmass process via AF6 (Accelerator Frontier - Advanced Accelerator Concepts) on the topics of plasma-based and advanced structure-based accelerators. This includes accessing the status of current R&D, formulating an R&D strategy that addresses the near, mid and long term plans, reviewing and revisiting the advanced accelerator roadmap, and organizing and coordinating the writing and submission of white papers to Snowmass. This will involve coordination with the Snowmass Frontiers (e.g., Energy Frontier and Theory Frontier) on various topics, such as possible collider options (e.g., gamma-gamma and electron-positron) for very high energies (>10 TeV). White papers falling under this group presently include:

1. Beam driven plasma acceleration, contact Spencer Gessner
2. Laser driven plasma acceleration, contact Carl Schroeder. Draft for viewing at https://www.overleaf.com/read/fskzcjsmbjxf, contact for edits.
3. Structure based acceleration, conatact Chunguang Jing
4. Physics case and demonstrators, contact Stepan Bulanov. Draft for viewing at https://docs.google.com/presentation/d/1UYkmMyr7R09CCIBTAE6GHws3PbDMHIZa/edit?usp=sharing&ouid=111956190322834801330&rtpof=true&sd=true, contact for edits.
5. AWAKE proton beam driven plasma colliders, contact Patric Muggli
6. Summary paper in AF4 format integrating the above with driver, BDS and other collider elements

https://aacseminarseries.lbl.gov/pasaig

Beam delivery and manipulation
Coordinators: Spencer Gessner (SLAC)
Contact: [email protected]
Description: The Beam Delivery System (BDS) is a critical component of a high-energy linear collider. It transports the beam from the accelerator and brings it to a focus at the Interaction Point. The BDS system includes diagnostic sections for measuring the beam energy, emittance, and polarization, as well as collimators for machine protection. The length of the BDS system increases with collision energy. Higher collision energies also require higher luminosities, and this is a significant constraint on the design of BDS systems for energy-frontier machines. Here, we compare the design of BDS systems based on traditional quadrupole magnets and novel plasma lenses, with the goal of producing a compact system that scales to the 10-TeV regime and provides excellent luminosity per input power.

https://www.overleaf.com/9328336798cjgzkytxddts

Laser-driven structures
Coordinators: Joel England (SLAC)
Contact: [email protected]
Description: Particle acceleration in microstructures driven by ultrafast solid state lasers is a rapidly evolving area of advanced accelerator research, leading to a variety of concepts based on planar-symmetric dielectric gratings, hollow core fibers, photonic crystals, and plasmonic meta-surfaces. This approach leverages well-established industrial fabrication capabilities and the commercial availability of tabletop lasers to reduce cost, with demonstrated axial accelerating fields in the GV/m range. Wide-ranging international efforts have significantly improved understanding of gradient limits, structure design, particle focusing and transport, staging, and development of compatible low-emittance electron sources. With a near-term focus on low-current MeV-scale applications for compact scientific and medical instruments, as well as novel diagnostics capabilities, structure-based laser-driven accelerators have several key benefits that warrant consideration for future high-energy physics machines, including low beamstrahlung energy loss, modest power requirements, stability, and readiness of supporting technologies.

Nanomaterials based Nanoplasmonic Accelerator and Wiggler
Coordinators:Aakash Sahai (U. Colorado Denver)
Contact: [email protected]
Description: Alternate multi TeV/m gradient concepts although originally envisioned many decades ago using bulk modes in crystals have remained unrealizable. This un-realizability using crystals arises from the disruptive collisional effects such as energy loss, emittance degradation and severe filamentation of the beam which can be overcome using nanomaterials. With the recent opening up of the possibility of attosecond x-ray pulses of high intensities, a scheme of driving Carbon nanotubes with these x-ray pulses has been proposed and is being investigated. While the development of x-ray pulses may be expected over the next decade or so, a new scheme utilizes the sub-micron charged particle beam such as the electron beams currently being commissioned at FACET-II for the excitation of nanoscale plasmonic modes in nanomaterials to access tens of TV per meter acceleration and focusing gradients. Realization of ultrahigh gradients of tens of TV per meter fields using collective modes in nanomaterials may be promising for HEP as well as in a wide range of areas of research that utilize beams of high-energy particles or photons. A draft of the white paper is available for viewing by the community (authors are being sent a individual email for editing, and others are welcome to contact the lead above): https://olucdenver-my.sharepoint.com/:f:/g/personal/aakash_sahai_ucdenver_edu/EktgN3eFyCtEpbRlAZc0NdkByTejlIqgn_ZEcBgXpRuBGg?e=1td4nm

Near term applications
Coordinators: Jeroen van Tilborg (LBNL), Claudio Emma (SLAC)
Contact: Jeroen van Tilborg (LBNL) [email protected], Claudio Emma (SLAC) [email protected]
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, while also developing the technology towards future ollider requirements, through near-term applications. 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.

Three categories have been recognized as core content to this whitepaper:
(1) Light source applications based on electron beams driven by plasma wakefields (both beam- and laser-driven) and dielectric structures. This includes XUV, X-ray, and gamma emission from betatron emission, free-electron lasing, Compton/Thomson scattering, and through other particle-matter interaction mechanisms.
(2) Medical applications of particle beams produced at advanced accelerators, such as few-MeV and high-energy electron beams, protons, and ions.
(3) Fundamental discovery science targeting particle physics and astro-phenomena accessible with moderate energy (substantially below TeV) advanced accelerators A draft of the white paper is available for viewing by the community (authors are being sent a individual email for editing, and others are welcome to contact the leads above): https://www.overleaf.com/read/jrtfpjfzgdxp

Test Facilities
Coordinators: John Power (ANL), Vitaly Yakimenko (SLAC)
Contact: [email protected], [email protected]
Description: The whitepaper will summarize plans of five beam test facilities, supported by GARD in support of SC mission. The facilities provide access to a suite of complementary and diverse capabilities for a broad community of scientists representing universities, industry and National laboratories to advance accelerator technologies for the next generation of SC research facilities, basic research in accelerator and beam physics, and education and training for future scientists and engineers. An effort to re-examine priorities and update roadmaps for Advanced Concepts and identifying needs for demonstration and beam test facilities will be attempted. Partnership with universities will be discussed for training of the next generation of leaders in accelerator physics, developing the workforce with skills to build and operate the next generation of SC research facilities that requires specialized facilities suitable for hands-on training. A draft of the white paper is available for viewing by the community (authors are being sent a individual email for editing, and others are welcome to contact the leads above): https://www.overleaf.com/9468336955tdwxxqqqctbm

Laser drivers
Coordinators:Leily Kiani (LLNL), Tong Zhou (LBNL)
Contact: [email protected], [email protected]
Description: Highly efficient ultrafast lasers at average powers significantly beyond the state of the art are needed as drivers for many accelerator technologies under consideration to advance the energy frontier. For example, achieving the long-term goal of an laser-plasma based collider and near-term goals in advancing HEP applications will require ultrafast lasers with kHz repetition rates at Joules of energy per pulse, with long-term goals requiring tens or hundreds of such lasers. Technologies are under development to combine the capabilities of today’s Hz-class lasers which meet per-pulse energy needs, and mJ-class lasers which meet multi-kHz repetition rate needs, to create efficient multi-kHz lasers at and above Joule pulse energies for HEP applications.” A draft of the white paper is available for viewing by the community (authors are being sent a individual email for editing, and others are welcome to contact the leads above): https://docs.google.com/document/d/1VkcCj5TpEcKMEDGvjGZfWx1674aXONoNf-1D5Euythk/edit?usp=sharing

Particle Sources
Coordinators: Matthias Fuchs (U. Nebraska Lincoln)
Contact: [email protected]
Description: Experimental and theoretical development of particle injectors for the generation of high-brightness beams are important for future accelerators. Topics include novel methods to generate particle beams with increased efficiency, peak and average brightness, methods that will allow the manipulation of their 6D phase space distribution and novel diagnostics. This includes particle injectors that can generate beams with sufficient brightness for future particle colliders and for near term applications. It also includes sources with sufficiently high quality to avoid the need for a damping ring or at least to mitigate damping needs. Topics include spin-polarized sources (e.g. from polarized gases) and methods to rapidly capture and accelerate secondary particles, such as positrons and muons. High-fidelity phase-space manipulation methods including during injection, during acceleration and post initial acceleration, such as compact cooling in plasma undulators, etc and high resolution diagnostics are also of interest.

1. Electron sources - Matthias Fuchs. Draft available at: https://www.overleaf.com/register?project_name=Snowmass_AF6_ParticleSources&user_first_name=mfuchs
2. Polarized positrons - Pietro Musumeci

Channeling Acceleration in Crystals and Nanostructures and Studies of Solid Plasmas
Coordinators: S.Corde, V.Shiltsev, T.Tajima

1. To clarify the process, questions, and invite additional community input, AF6 conveners held a public townhall meeting. on August 17th from 8-10 AM Pacific Daylight Time as listed on the calendar. It consisted of a brief presentation by the conveners outlining the process, discussion of the LOIs in progress, and open discussion of coordination among the community. The slides including record of discussions are available: https://drive.google.com/file/d/125JmTLad0_TsBppF3Wq_Psa_x2P8rv-P/view?usp=sharing

2- LOIs are 2 page informal documents due August 31, 2020. The LOIs essentially serve as the first line to collect input from the community. Surveying the status of the field, the path to collider concepts, discussing large collaboration efforts, and pitching completely new ideas are all encouraged at this point as LOI content. Due to the international nature of high energy physics, international submissions are especially encouraged. Please refer to http://snowmass21.org/loi for information on how to submit. These documents will inform the AF6 conveners and community and will allow better organization of the work in the months ahead.

3- An Advanced Accelerator Snowmass Workshop organized around the LOIs and the Advanced Accelerator Development Strategy was held starting September 23-24, 2020 starting at 0800 Pacific as listed in the calendar and on Indico at https://indico.fnal.gov/event/45651/. At this workshop discussed the submitted LOIs and identify additional material needed to prepare for Snowmass.

4- All the Frontiers participated in a general Snowmass Community workshop October 5-8, 2020 where the connections between the various Snowmass frontiers were explored. https://indico.fnal.gov/event/44870/

5- Contributed paper (white paper) interest groups were formed and are listed above, based on the LOI discussion (for example, merging similar LOI submissions) to generate a compelling and coherent vision for our field and its impact on High Energy Physics. Please contact the groups listed above for participation, or contact the conveners to have a new group listed.

6- A review and discussion workshop will be held February 15th, 0900-1300 Pacific time. The goal is to engage the AF6 community, make everyone aware of the papers in progress, and invite contributions by those not yet involved either to white papers in progress or new papers if desired. https://indico.fnal.gov/event/52963/

7- The contributed papers (white papers) were submitted by March 15, 2022, and will provide the input for the main Snowmass workshop which will be held in July 2022. Submit papers at: https://snowmass21.org/submissions/start and indicate submission to AF06.

8 - A group summary will be prepared covering all of the input and will be discussed at the Snowmass Workshop in July 2022. Drafts for input are available at: https://snowmass21.org/accelerator/start, and AF06 specific content is in the section above on this page

9- We will have a meeting to discuss feedback on Wednesday July 13th at 0830 Pacific, please see links on the AF06 email list, the AF calendar or contact us for connection details. The aim will be to have a close to final version before the summer study for cross-frontier discussion.

10 - The Snowmass summer study will be July 17-27 in Seattle

11- Following the Seattle meeting, reports will be finalized in Septembe

The frontier will focus on the high gradient schemes that are being developed, the new physics capabilities that could be enabled, the major challenges that need to be addressed to enable physics machines using these new concepts, and the development time and cost scales. The path from current results towards achieving beam parameters required for applications, particularly high energy physics (HEP) colliders at the TeV scale. Ultimately, future colliders for High Energy Physics also require development of particle beam generation, diagnosis and manipulation methods which advanced accelerator concepts can also contribute to. We will also include consideration of intermediate applications, such as compact radiation sources, which will develop these technologies along the path to a potential future collider.

Letters of intent are encouraged to address the following accelerator areas, which will also serve as organizing themes:

1. PWFA - particle beam driven Plasma WakeField Acceleration
2. LWFA - Laser driven plasma WakeField Acceleration
3. Proton-driven plasma accelerators
4. Crystal / nanostructure accelerators
5. High frequency metal and dielectric structures
6. Dielectric laser-driven accelerators
7. High efficiency lasers and drivers
8. Injection, beam cooling, manipulation and focusing elements relevant to other accelerators
9. Creation and use of novel beam regimes to enhance luminosity
10. Hybrids of methods

Within each accelerator area, we will address topics including

1. System concepts, luminosity, and beam dynamics for colliders
2. Polarized positron production and transport
3. Intermediate applications such as compact photon sources: FELs, Gamma-ray sources
4. Controlled particle injection to produce beams that are: stable and reproducible, lower in energy spread and emittance, and higher in charge meeting collider requirements.
5. Efficient transfer of the driver energy to the particle beam, including drive pulse manipulation/guiding.
6. Staging, or combining multiple elements to reach high beam energy for HEP applications, and also has applications to beam disposal (deceleration) for radiation sources.
7. Diagnostic techniques suited to resolve unprecedented beam parameters
8. Compact beam manipulation techniques needed alongside accelerator structures. These include compact radiation cooling, focusing, and beam phase space exchanges.

Here is the list of submitted LOIs to this topic. First index before “/” corresponds to the primary frontier used for the submission.