Search Results (13 total)

We propose a novel gamma source suitable for generating a polarized positron beam for the next generation of electron-positron colliders, such as the International Linear Collider (ILC), and the Compact Linear Collider (CLIC). This 30-MeV polarized gamma source is based on Compton scattering inside a picosecond CO₂ laser cavity generated from electron bunches produced by a 4-GeV linac. We identified and experimentally verified the optimum conditions for obtaining at least one gamma photon per electron. After multiplication at several consecutive interaction points, the circularly polarized gamma rays are stopped on a target, thereby creating copious numbers of polarized positrons. We address the practicality of having an intracavity Compton-polarized positron source as the injector for these new colliders.

A free relativistic electron in an electromagnetic field is a pure case of a light-matter interaction. In the laboratory environment, this interaction can be realized by colliding laser pulses with electron beams produced from particle accelerators. The process of single photon absorption and reemission by the electron, so-called linear Thomson scattering, results in radiation that is Doppler shifted into the x-ray and γ-ray regions. At elevated laser intensity, nonlinear effects should come into play when the transverse motion of the electrons induced by the laser beam is relativistic. In the present experiment, we achieved this condition and characterized the second harmonic of Thomson x-ray scattering using the counterpropagation of a 60 MeV electron beam and a subterawatt CO₂ laser beam.

Presented are details of the staged electron laser acceleration (STELLA) experiment, which demonstrated high-trapping efficiency and narrow energy spread in a staged laser-driven accelerator. Trapping efficiencies of up to 80% and energy spreads down to 0.36% (1σ) were demonstrated. The experiment validated an approach that may be suitable for the basic design of a laser-driven accelerator system. In this approach, a laser-driven modulator together with a chicane creates a train of microbunches spaced apart by the laser wavelength. These microbunches are sent into a second laser-driven accelerator designed to efficiently trap the microbunches in the ponderomotive potential well of the laser electric field while maintaining a narrow energy spread. The STELLA scientific apparatus and procedures are described in detail. In-depth comparisons between the data and model are given including the predicted energy spectrum, energy-phase plot, and microbunch length profile. Data and model comparisons as a function of the phase delay between the microbunches and the accelerating wave are presented. The model is exercised to reveal how the high-trapping efficiency process evolves during the acceleration process.

Laser-driven electron accelerators (laser linacs) offer the potential for enabling much more economical and compact devices. However, the development of practical and efficient laser linacs requires accelerating a large ensemble of electrons together (“trapping”) while keeping their energy spread small. This has never been realized before for any laser acceleration system. We present here the first demonstration of high-trapping efficiency and narrow energy spread via laser acceleration. Trapping efficiencies of up to 80% and energy spreads down to 0.36% (1σ) were demonstrated.

We propose using an optical parametric amplifier, with a ∼12   μm wavelength, for optical-stochastic cooling of ⁷⁹Au ions in the Relativistic Heavy Ion Collider. While the bandwidth of this amplifier is comparable to that of a Ti:sapphire laser, it has a higher average output power. Its wavelength is longer than that of the laser amplifiers previously considered for such an application. This longer wavelength permits a longer undulator period and higher magnetic field, thereby generating a larger signal from the pickup undulator and ensuring a more efficient interaction in the kicker undulator, both being essential elements in cooling moderately relativistic ions. The transition to a longer wavelength also relaxes the requirements for stability of the path length during ion-beam transport between pickup and kicker undulators.

We describe our studies of the generation of plasma wake fields by a relativistic electron bunch and of phasing between the longitudinal and transverse fields in the wake. The leading edge of the electron bunch excites a high-amplitude plasma wake inside the overdense plasma column, and the acceleration and focusing wake fields are probed by the bunch tail. By monitoring the dependence of the acceleration upon the plasma’s density, we approached the beam-matching condition and achieved an energy gain of 0.6 MeV over the 17 mm plasma length, corresponding to an average acceleration gradient of 35  MeV/m. Wake-induced modulation in energy and angular divergence of the electron bunch are mapped within a wide range of plasma density. We confirm a theoretical prediction about the phase offset between the accelerating and focusing components of plasma wake.

Detailed experimental results of staging two laser-driven, relativistic electron accelerators are presented. During the experiment called STELLA (staged electron laser acceleration), an inverse free-electron laser (IFEL) is used to modulate the electron energy, thereby, causing ∼3 fs microbunches to form separated by the laser wavelength at 10.6 μm (equivalent to a 35 fs period). A second IFEL accelerates the electrons depending upon the phase of the microbunches entering the second IFEL with respect to the laser beam driving the second IFEL. The data presented includes electron energy spectra as a function of the phase delay and laser power driving the first IFEL. Also shown is a comparison with the computer model, which includes space charge and misalignment effects.

Staging of two laser-driven, relativistic electron accelerators has been demonstrated for the first time in a proof-of-principle experiment, whereby two distinct and serial laser accelerators acted on an electron beam in a coherently cumulative manner. Output from a CO₂ laser was split into two beams to drive two inverse free electron lasers (IFEL) separated by 2.3 m. The first IFEL served to bunch the electrons into ∼3 fs microbunches, which were rephased with the laser wave in the second IFEL. This represents a crucial step towards the development of practical laser-driven electron accelerators.

7.6×10⁶ x-ray photons per 3.5 ps pulse are detected within a 1.8–2.3 Å spectral window during a proof-of-principle laser synchrotron source experiment. A 600 MW CO₂ laser interacted in a head-on collision with a 60 MeV, 140 A, 3.5 ps electron beam. Both beams were focused to a σ  =  32 μm spot. Our next plan is to demonstrate 10¹⁰ x-ray photons per pulse using a CO₂ laser of ∼1 TW peak power.

Response is made to Y. I. Salamin's preceding Comment [Phys. Rev. ST Accel. Beams 3, 059001 (2000)]. We confirm the areas of applicability of the original and Salamin's general solutions and discuss new applications of the developed formalism.

Three dimensional test particle simulations are applied to optimization of the plasma-channeled laser wakefield accelerator (LWFA) operating in a weakly nonlinear regime. Electron beam energy spread, emittance, and luminosity depend upon the proportion of the electron bunch size to the plasma wavelength. This proportion tends to improve with the laser wavelength increase. We simulate a prospective two-stage ∼1GeV LWFA with controlled energy spread and emittance. The input parameters correspond to realistic capabilities of the BNL Accelerator Test Facility that features a picosecond-terawatt CO₂ laser and a high-brightness electron gun.

The exact solution of the classical nonlinear equation of motion for a relativistic electron in the field of two electromagnetic (EM) waves is obtained. For the particular case of the linearly polarized standing EM wave in the planar optical cavity, intensity of the nonlinear Compton scattering, the time of flight, and the momentum variation after the relativistic electron passes along the cavity axis are calculated in weak and strong field limits. These effects depend on the initial phase of the EM wave at the electron entrance into the cavity and can be used for producing, diagnostics, and acceleration of relativistic electron (positron) microbunches.

A 580-MW peak power, radially polarized CO₂ laser beam (λ=10.6 μm) focused by an axicon accelerated 40-MeV electrons by ≤3.7 MeV over a 12-cm interaction length (31 MeV/m), using the inverse Cherenkov effect in which a gas is used to slow the light wave. This represents the first direct observation of acceleration using this effect and demonstrates the effectiveness of the radially-polarized-axicon-focused geometry. The observed energy gain agrees with model predictions.