Upper limit for the accelerating gradient in the collinear wakefield accelerator as a function of the transformer ratio

Abstract

The interrelation between the accelerating gradient and the transformer ratio in the collinear wakefield accelerator has been analyzed. It has been shown that the high transformer ratio and the high efficiency of the energy transfer from the drive bunch to the witness bunch can only be achieved at the expense of the accelerating gradient. Rigorous proof is given that in best cases of meticulously shaped charge density distributions in the drive bunch, the maximum accelerating gradient falls proportionally to the gain in the transformer ratio. Conclusions are verified using several representative examples.

The Dielectric Resonator Wakefield Accelerator

“…Dielectric-lined structures show promise for generating strong accelerating fields arising from relativistic electron bunches (DWA) [1][2][3][4]. Most of the studies on the use of dielectric structures have been carried out for cylindrical collinear configurations, but achieving both high accelerating gradient and elevated transformer ratio in this configuration appears to be impossible [5]. Attention also has been directed to dielectric-lined waveguides having rectangular configuration [6][7][8][9][10][11][12][13].…”

Stability condition for the drive bunch in a collinear wakefield accelerator

“…This can be done by employing the longitudinal wakefield produced by the drive bunch with a special charge distribution. For example, the "door step" electron density distribution proposed in [9] and considered in [12] gives a quasiuniform decelerating wakefield inside the drive bunch. Adding a small quadratic component to a linear ramp in the peak current will add a small linear variation to the decelerating field, enough to keep constant the relative magnitude of the chirp.…”

“…The charge of a witness bunch is much smaller than the charge of a drive bunch. This promising method of particle acceleration attracted many followers (e.g., see [2][3][4][5][6][7][8][9][10][11][12] and references therein) who pursued accelerator designs for a linear collider (e.g., see [13] and reference therein) and a free-electron-laser-based light source [14]. A comprehensive review of the entire field of structure-based wakefield accelerators was recently published in the Reviews of the Accelerator Science and Technology [15].…”

Transformer-ratio optimization in nonlinearly driven hollow plasma channels

“…A high transformer ratio requires a long driver with a carefully chosen current profile [7]. One may use, for example a ramped density bunch [8,9] or a ramped bunch train [10] to control the excited wakefield.…”