U.S. Particle Accelerator School

Particle Driven Wakefield Accelerators course

Sponsoring University:

University of Texas, Austin


Particle Driven Wakefield Accelerators


James Rosenzweig, UCLA and Mike Litos, SLAC

Purpose and Audience
This course will introduce the physics associated with one of the most promising new accelerations techniques for enabling compact next generation accelerators through obtaining ultra-high gradients (i.e. > GV/m) — particle beam driven wakefields. It is suitable for upper division undergraduate students or graduate students with an interest in an emerging multi-disciplinary field. The course is also appropriate for physicists or engineers working in accelerator-related fields who wish to familiarize themselves with advanced accelerator concepts.

Courses in upper division electromagnetism and classical mechanics, as well as an introduction to beam physics.

It is the responsibility of the student to ensure that he or she meets the course prerequisites or has equivalent experience.

This course is aimed to provide the fundamentals needed to understand wakefield acceleration mechanisms, as well as some of the computational and experimental tools needed to explore the physical phenomena involved. It should give an introduction to the field, permitting the student to be conversant in the research literature describing the state-of-the-art, as well as a foundation for entering into this exciting new field.

Instructional Method
This course includes a series of lectures in the morning and in the afternoon, followed by computational laboratory sessions on related subject matter. Problem sets, to be completed outside of scheduled class time, will be assigned in the lecture sessions. There will be an open-book final exam at the conclusion of the course. 

Course Content
The course will begin with a review of the effects limiting the accelerating gradient in current accelerators, in the context of applications to energy frontier colliders and next generation free-electron lasers. Noting the demand for scaling the accelerator electromagnetic wavelength to the mm-level or below in order to achieve GV/m fields, we introduce a new mechanism for producing the needed power: wakefields. We first examine purely electromagnetic wakefields in metallic and dielectric structures, developing the formalism for their analysis, including the Panofsky-Wenzel theorem, the Fundamental Theorem of beam loading, and transformer ratio enhancement. Beam acceleration and transverse instability are discussed. We then explore advanced dielectric wakefield accelerator designs having slab symmetry, photonic confinement, and electromagnetic focusing properties. The use of dielectric wakefield accelerators  (DWA) as very high power mm-wave to THz sources is analyzed. Very high field nonlinear effects in dielectrics, and breakdown phenomena, are discussed.

Charged particle wakefields above a few GV/m field are permitted in ionized matter, or plasma. We introduce the linear theory of plasma wakefield acceleration (PWFA), in which the waves have an electrostatic nature. We analyze acceleration and focusing in the linear regime, as well as plasma compensation of beam self- and beam-beam- effects. The formation of beam equilibria such as Bennett pinches is discussed, along with related issues of emittance growth.  The limitations of the application of the linear regime being noted, we proceed to discuss the nonlinear “blowout” regime, in which emittance dilution in all phase planes is mitigated. We examine nonlinear plasma response in 1D and in 3D, identifying new phenomena such as accelerating wave steepening and linear ion focusing. Scaling laws governing the nonlinear regime of PWFA are developed. Issues such as beam-ion collisions and ion collapse are examined. Betatron motion and its attendant radiative processes are discussed. Problems such ion motion and hosing instability are analyzed. Injection of background electrons or through laser-controlled ionization, for production of extreme low emittance beams, are discussed. The potential use of positron and proton drivers for plasma wakefields is introduced. 

The experimental state-of-the-art, including advanced methods developed specifically for PWFA and DWA experiments, is reviewed. Potential applications in particle physics and light source development, such as: electron-positron colliders, compact FELs, adiabatic plasma lenses, betatron radiation, space-radiation simulation, and quasi-nonlinear resonance are discussed. Powerful computing tools will be used to aid in understanding and visualizing wakefield concepts.

Reading Requirements
(To be provided by the USPAS)  "Fundamentals of Beam Physics II: Collective and Radiative Effects" by James Rosenzweig and Agostino Marinelli. Additional materials and lecture notes will be provided by the instructors.

Suggested Reading 
- James Rosenzweig, " Fundamentals of Beam Physics ", (Oxford Univ. Press 2003).
- J. D. LawsonThe Physics of Charged-Particle Beams”, (Oxford Univ. Press 1988).
- Andrey Seryi, " Unifying Physics of Accelerators, Lasers and Plasma ", CRC Press (2015).
- F. Chen, “Introduction to Plasma Physics” (Springer, 2012).

Credit Requirements
Students will be evaluated based on the homework and computer assignments (70% of final grade) and the final exam (30% of final grade).

Credit is only earned when this one-week half course is taken with a second one-week half course and both are successfuly completed thereby earning 3 credit hours.

UT Austin course number & course title on transcript: PHY 396T (69875): ADV TOPICS IN ACCELERATOR PHYSICS
Indiana University course number and title on transcript:
Physics 671, Advanced Topics in Accelerator Physics
Michigan State University course number: PHY 963
MIT course number: 8.790 "Accelerator Physics"