Observation of Enhanced Transformer Ratio in Collinear Wakefield Acceleration

A new scheme for a dielectric wakefield accelerator is proposed that employs a cylindrical multizone dielectric structure configured as two concentric dielectric tubes with outer and inner vacuum channels for drive and accelerated bunches. Analytical and numerical studies have been carried out for such coaxial dielectric-loaded structures (CDS) for high-gradient acceleration. An analytical theory of wakefield excitation by particle bunches in a multizone CDS has been formulated. Numerical calculations are presented for an example of a CDS using dielectric tubes with dielectric permittivity 5.7, having external diameters of 2.121 and 0.179 mm with inner diameters of 2.095 and 0.1 mm. An annular 5 GeV, 6 nC electron bunch with rms length of 0.035 mm energizes a wakefield on the structure axis having an accelerating gradient of $600 MeV=m with a transformer ratio $8:1. The period of the accelerating field is $0:33 mm. If the width of the drive bunch channel is decreased, it is possible to obtain an accelerating gradient of >1 GeV=m while keeping the transformer ratio approximately the same. Full numerical simulations using a particle-in-cell code have confirmed results of the linear theory and furthermore have shown the important influence of the quenching wave that restricts the region of the wakefield to within several periods following the drive bunch. Numerical simulations for another example have shown nearly stable transport of drive and accelerated bunches through the CDS, using a short train of drive bunches.

Section: Excitation Of a Two-channel Coaxial Structure By A Bunchmentioning

confidence: 99%

Coaxial two-channel high-gradient dielectric wakefield accelerator

Sotnikov

Marshall

Hirshfield

2009

“…[3] and we only recap the main results here. (Note, the analysis we present is for a dielectric wakefield accelerator but the conclusion can be generalized to metallic structures and linear plasma wakefield accelerators.)…”

Section: Introductionmentioning

confidence: 99%

“…R is peaked near z ¼ =4, while dropping off towards 1 for bunch lengths on either side of =4. To understand how z effects the transformer ratio enhancement (R n :R nÀ1 ) numerical simulations were performed for the previous experiment [3] [13.625 GHz dielectric-loaded accelerating (DLA) structure, ¼ 2 mm]. Figure 3(a) shows that there is no significant increase for the transformer ratio after the second drive bunch.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Increasing the transformer ratio at the Argonne wakefield accelerator

Jing

Power

Conde

et al. 2011

Self Cite

The transformer ratio is defined as the ratio of the maximum energy gain of the witness bunch to the maximum energy loss experienced by the drive bunch (or a bunch within a multidrive bunch train). This plays an important role in the collinear wakefield acceleration scheme. A high transformer ratio is desirable since it leads to a higher overall efficiency under similar conditions (e.g. the same beam loading, the same structure, etc.). One technique to enhance the transformer ratio beyond the ordinary limit of 2 is to use a ramped bunch train. The first experimental demonstration observed a transformer ratio only marginally above 2 due to the mismatch between the drive microbunch length and the frequency of the accelerating structure [C. Jing, A. Kanareykin, J. Power, M. Conde, Z. Yusof, P. Schoessow, and W. Gai, Phys. Rev. Lett. 98, 144801 (2007)]. Recently, we revisited this experiment with an optimized microbunch length using a UV laser stacking technique at the Argonne Wakefield Accelerator facility and measured a transformer ratio of 3.4. Measurements and data analysis from these experiments are presented in detail.

“…To date, cylindrically symmetric DLW's have been extensively studied both theoretically [10,[16][17][18] and experimentally [19][20][21][22]. Since the angular divergence of the beam also increases during focusing it is hard to maintain a low transverse size of the beam over a long propagation distance.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional analysis of wakefields generated by flat electron beams in planar dielectric-loaded structures

Mihalcea

Piot

Stoltz

2012

An electron bunch passing through a dielectric-lined waveguide generates Č erenkov radiation that can result in a high-peak axial electric field suitable for acceleration of a subsequent bunch. Axial fields beyond gigavolt-per-meter are attainable in structures with sub-mm sizes depending on the achievement of suitable electron bunch parameters. A promising configuration consists of using a planar dielectric structure driven by flat electron bunches. In this paper we present a three-dimensional analysis of wakefields produced by flat beams in planar dielectric structures thereby extending the work of Tremaine, Rosenzweig, and Schoessow, Phys. Rev. E 56, 7204 (1997)] on the topic. We especially provide closed-form expressions for the normal frequencies and field amplitudes of the excited modes and benchmark these analytical results with finite-difference time-domain particle-in-cell numerical simulations. Finally, we implement a semianalytical algorithm into a popular particle-tracking program thereby enabling start-to-end high-fidelity modeling of linear accelerators based on dielectric-lined planar waveguides.