Halo coupling and cleaning by a space charge resonance in high intensity beams

Abstract

We show that the difference resonance driven by the space charge pseudo-octupole of high intensity beams not only couples the beam core emittances; it can also lead to emittance exchange in the beam halo, which is of relevance for beam loss in high intensity accelerators. With reference to linear accelerators the ''main resonance'' k z =k x;y ¼ 1 (corresponding to the Montague resonance 2Q x À 2Q y ¼ 0 in circular accelerators) may lead to such a coupling and transfer of halo between planes. Coupling of transverse halo into the longitudinal plane-or vice versa-can occur even if the core (rms) emittances are exactly or nearly equal. This halo argument justifies additional caution in linac design including consideration of avoiding an equipartitioned design. At the same time, however, this mechanism may also qualify as an active dynamical halo cleaning scheme by coupling a halo from the longitudinal plane into the transverse plane, where local scraping is accessible. We present semianalytical emittance coupling rates and show that previously developed linac stability charts for the core can be extended-using the longitudinal to transverse halo emittance ratio-to indicate additional regions where halo coupling could be of importance.

Active Plasma Lensing for Relativistic Laser-Plasma-Accelerated Electron Beams

“…To compare to the radially-symmetric triplet configuration, we follow the optimized configuration ±(2f, −f, f ) of Ref. [36], where each quadrupole is separated by distance s = f 0 , with f 0 the single-element focal length at the specific design energy [300 MeV in Fig. 1(b)].…”

“…1(b), based on a state-of-the-art ∂B φ /∂r=500 T/m [21]. The focal length for a radially-symmetric solenoid lens [36] is F = f = (2m 0 γc/e) 2 /(B 2 L) [black curve in Fig. 1(b) for B=2 T and L=20 cm].…”

Compact LWFA-Based Extreme Ultraviolet Free Electron Laser: design constraints

“…In order to deliver the LWFA electron beam to an FEL undulator a dedicated beam transport has to be designed to provide: capture of electrons from the LWFA source [19]; effective transport of the electron beam with preservation of its quality; possible manipulation with the electron bunch in the longitudinal phase-space [20] and, finally, matching of the electron beam to the undulator [21]. Moreover, a combination of the significant initial transverse divergence and the large energy spread of LWFA electrons leads to an intrinsic growth of the normalized transverse beam emittance in a drift space after the laser plasma interaction area [22].…”

Design, fabrication, and beam commissioning of a continuous-wave four-rod rf quadrupole

“…Since the beam was transported through the cavity in the linac only once, these experiences occur also only one times. Thus the coupling between transverse and longitudinal planes has a weak effect on the rms emittance growth [18].…”