An overview is given of the physics issues relevant to the plasma wakefield accelerator, the plasma beat-wave accelerator, the laser wakefield accelerator, including the self-modulated regime, and wakefield accelerators driven by multiple electron or laser pulses. Basic properties of linear and nonlinear plasma waves are discussed, as well as the trapping and acceleration of electrons in the plasma wave. Formulas are presented for the accelerating field and the energy gain in the various accelerator configurations. The propagation of the drive electron or laser beams is discussed, including limitations imposed by key instabilities and methods for optically guiding laser pulses. Recent experimental results are summarized.

Overview of plasma-based accelerator concepts

Discrete Solitons in Optics

By L I Sedov London: Cleaver-Hume Press Ltd Pp xvi + 363 Price 105s This is really two separate books within the same pair of covers First of all Chapters 1-3, some 145 pages, are devoted to the discussion of similarity and dimensional, methods and their application to a variety of problems in mechanics and fluid mechanics

http://iopscience.iop.org/article/10.1088/0031-9112/11/6/008/pdf

Similarity and Dimensional Methods in Mechanics

To develop plasma wakefield acceleration into a compact and affordable replacement for conventional accelerators, beams of charged particles must be accelerated at high efficiency in a high electric field; here this is demonstrated for a bunch of charged electrons ‘surfing’ on a previously excited plasma wave. Particle colliders that operate at the high-energy frontier using electric fields generated by radio waves are approaching the limits of feasibility in terms of size and cost, but there are other acceleration techniques that could make less expensive and more compact devices. The plasma wakefield accelerator, in which an electron bunch is accelerated by making it 'surf' on a plasma wave excited by another electron bunch, promises an energy gain in the gigaelectron-volt regime over just a few centimetres — an energy gain that requires hundreds of metres using traditional accelerators. Previously, this technique had only been used to accelerate a very small number of electrons at a time. Now, researchers working at FACET, the Facility for Advanced Accelerator Experimental Tests at SLAC National Accelerator Laboratory, USA, have achieved acceleration of about half a billion electrons at once with an unprecedented efficiency for a plasma accelerator. This achievement could be a milestone in the development of affordable and compact accelerators for applications ranging from high energy physics to medical and industrial applications. High-efficiency acceleration of charged particle beams at high gradients of energy gain per unit length is necessary to achieve an affordable and compact high-energy collider. The plasma wakefield accelerator is one concept1,2,3 being developed for this purpose. In plasma wakefield acceleration, a charge-density wake with high accelerating fields is driven by the passage of an ultra-relativistic bunch of charged particles (the drive bunch) through a plasma4,5,6. If a second bunch of relativistic electrons (the trailing bunch) with sufficient charge follows in the wake of the drive bunch at an appropriate distance, it can be efficiently accelerated to high energy. Previous experiments using just a single 42-gigaelectronvolt drive bunch have accelerated electrons with a continuous energy spectrum and a maximum energy of up to 85 gigaelectronvolts from the tail of the same bunch in less than a metre of plasma7. However, the total charge of these accelerated electrons was insufficient to extract a substantial amount of energy from the wake. Here we report high-efficiency acceleration of a discrete trailing bunch of electrons that contains sufficient charge to extract a substantial amount of energy from the high-gradient, nonlinear plasma wakefield accelerator. Specifically, we show the acceleration of about 74 picocoulombs of charge contained in the core of the trailing bunch in an accelerating gradient of about 4.4 gigavolts per metre. These core particles gain about 1.6 gigaelectronvolts of energy per particle, with a final energy spread as low as 0.7 per cent (2.0 per cent on average), and an energy-transfer efficiency from the wake to the bunch that can exceed 30 per cent (17.7 per cent on average). This acceleration of a distinct bunch of electrons containing a substantial charge and having a small energy spread with both a high accelerating gradient and a high energy-transfer efficiency represents a milestone in the development of plasma wakefield acceleration into a compact and affordable accelerator technology.

High-efficiency acceleration of an electron beam in a plasma wakefield accelerator

High‐energy accelerators have been physicists’ main tools for exploring the building blocks of matter for more than 60 years. During this time the particle energy has increased exponentially as a result of a combination of improvements in existing machines and the invention of new acceleration techniques. Historically, whenever a given type of accelerator has reached the limit of its performance, an innovative idea for particle manipulation, storage, cooling or acceleration has made possible experiments at ever higher energies. The tremendous increase in the energy of accelerators has not, however, been without an increase in capital costs. The cancellation of the Superconducting Super Collider makes timely an examination of possible alternative concepts for investigating some of the same physics.

Advanced accelerator concepts

/pdf/a-plasma-wake-field-accelerator-3mwbntc9x7.pdf

A plasma wake field accelerator

https://www.slac.stanford.edu/pubs/slacpubs/2250/slac-pub-2498.pdf

Beam emittance growth caused by transverse deflecting fields in a linear accelerator

We report the results of observations of a new regime of ion instabilities at the Advanced Light Source (ALS). With artificially increased pressure and gaps in the bunch train large enough to avoid multiturn ion trapping, we observed a factor of 2{endash}3 increase in the vertical beam size along with coherent beam oscillations which increased along the bunch train. The observations are qualitatively consistent with the {open_quotes}fast beam-ion instability{close_quotes} [T.O. Raubenheimer and F. Zimmermann, Phys.Rev.E {bold 52}, 5487 (1995); G.V. Stupakov {ital et al.,} Phys.Rev.E {bold 52}, 5499 (1995)], which can arise even when the ions are not trapped over multiple beam passages. This effect may be important for many future accelerators. {copyright} {ital 1997} {ital The American Physical Society}

/pdf/first-observations-of-a-fast-beam-ion-instability-uei7cw18pw.pdf

First observations of a 'Fast Beam-Ion Instability'

In recent years, electron storage ring designers have become aware of the problems caused by the interaction of short, high current bunches with their environment. Important effects are: (1) energy loss can cause local overheating of chamber components; (2) additional rf power is required due to overall energy loss; (3) the increased energy spread requires increased aperture; (4) destructive instabilities could occur. Anomalous bunch lengthening and energy spread, the spectroscopy of longitudinal modes and the shift of synchronous phase were simultaneously measured in order to study the dynamics of the interaction. From the data obtained at SPEAR II one is led to a model of coupling impedance which should be useful in the design of any electron ring.

/pdf/bunch-lengthening-and-related-effects-in-spear-ii-38b3fb9x35.pdf

Bunch Lengthening and Related Effects in SPEAR II

The nonlinear dynamics of transverse particle oscillations in the Fermilab Tevatron is studied experimentally and compared with prediction. Accurate measurements of various phase-space features are obtained. A theoretically expected metastable state of the accelerator, with particles captured on nonlinear resonance islands, is demonstrated experimentally, and stability of the state is investigated.

Alex Chao

Papers

A plasma wake field accelerator

Beam emittance growth caused by transverse deflecting fields in a linear accelerator

First observations of a 'Fast Beam-Ion Instability'

Bunch Lengthening and Related Effects in SPEAR II

Experimental investigation of nonlinear dynamics in the Fermilab Tevatron.