Generation of angular-momentum-dominated electron beams from a photoinjector

Phys. Rev. ST Accel. Beams

Sun

Kim

2006

Self Cite

The generation of a flat electron beam directly from a photoinjector is an attractive alternative to the electron damping ring as envisioned for linear colliders. It also has potential applications to light sources such as the generation of ultra-short x-ray pulses or Smith-Purcell free electron lasers. In this Letter, we report on the experimental generation of a flat-beam with a measured transverse emittance ratio of 100 ± 20.2 for a bunch charge of ∼ 0.5 nC; the smaller measured normalized root-mean-square emittance is ∼ 0.4 µm and is limited by the resolution of our experimental setup. The experimental data, obtained at the Fermilab/NICADD Photoinjector Laboratory, are compared with numerical simulations and the expected scaling laws. 41.75.Fr Flat electron beams, e.g. beams with large transverse emittance ratios, have been proposed in the context of linear colliders and some novel electron-beambased light sources. In the case of a linear e + /e − collider, a flat beam at the interaction point reduces the luminosity disruption caused by beamsstrahlung [1]. In the case of light sources, such as the LUX project proposed at LBL [2], a flat beam with a smaller emittance of 0.3 µm and emittance ratio of 50 is needed to produce x-ray pulses that can be compressed to the order of femtoseconds via standard x-ray pulse compression techniques [3]. Another type of light source recently drawing attention is based on self-amplification of Smith-Purcell radiation [4]. Given one or two planar metal gratings, a flat beam could enhance the interaction between the electrons and metal grating surface, thus reducing the gain length associated with the Smith-Purcell free-electronlaser mechanism [5,6,7].In the proposed International Linear Collider (ILC) the needed flat-beam parameters (emittance ratio of 300) are foreseen to be achieved via radiation cooling in a damping ring [8]. Although the required transverse emittances for the ILC have been demonstrated at the ATF damping ring of KEK [9], ILC puts stringent requirements on the damping ring design, and the cost of the damping ring is a significant portion of the total collider cost. Therefore alternative ways of producing flat beams directly from an electron source have been explored by several groups [10]. In conjunction with the invention of a linear transformation capable of transforming an incoming flat beam into an angular-momentum-dominated (or "magnetized") beam [11], a scheme which inverses this * Electronic address: piot@fnal.gov † Electronic address: yinesun@uchicago.edu; now at Argonne National Laboratory.transformation was proposed to generate a flat beam directly out of a photoinjector [12]. The method consists of generating an magnetized beam by immersing the photocathode in an axial magnetic field. After acceleration, the beam is transformed into a flat beam using three skew quadrupoles [13]. This has been verified experimentally [14,15,16,17], and transverse emittance ratios of 40-50 were reported. Theoretical analysis of the conversion of a magnetized cyl...

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confidence: 54%

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confidence: 98%

Photoinjector generation of a flat electron beam with transverse emittance ratio of 100

Phys. Rev. ST Accel. Beams

Sun

Kim

2006

Self Cite

“…The downstream beamline includes quadrupoles, steering dipole magnets, and diagnostics stations. A skew-quadrupole channel can be set up as a round-to-flat-beam transformer (RFBT) to convert an incoming angular-momentum-dominated beam into a flat beam with high transverse emittance ratio [13,14]. The beamline also incorporates a four-bend magnetic bunch compressor (BC1) which, consists of four 0.2-m rectangular dipoles (B1, B2, B3, B4) with respective bending angles of (+,-,-,+) 18 • .…”

Section: Accelerator Beamline Overviewmentioning

confidence: 99%

Beam dynamics performances and applications of a low-energy electron-beam magnetic bunch compressor

Prokop

Nuclear Instruments and Methods in Physics Research Section A:

Carlsten

et al. 2013

Self Cite

Many front-end applications of electron linear accelerators rely on the production of temporally-compressed bunches. The shortening of electron bunches is often realized with magnetic bunch compressors located in high-energy sections of accelerators. Magnetic compression is subject to collective effects including space charge and self interaction via coherent synchrotron radiation. In this paper we explore the application of magnetic compression to low-energy (∼ 40 MeV), high-charge (nC) electron bunches with low normalized transverse emittances (< 5 µm).

“…Flat beams can be produced in photoinjectors by using a roundto-flat beam transformation [36,37]. In such a scheme, a beam with large angular momentum is produced in a photoinjector [38]. Upon removal of the angular momentum by applying a torque with a set of skew quadrupole, the beam has its transverse emittance repartitioned with a tunable transverse emittances ratio [39].…”

Section: Two-dimensional Limitmentioning

confidence: 99%

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

Mihalcea

Phys. Rev. ST Accel. Beams

Stoltz

2012

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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.