Demonstration of passive plasma lensing of a laser wakefield accelerated electron bunch

Abstract

We report on the first demonstration of passive all-optical plasma lensing using a two-stage setup. An intense femtosecond laser accelerates electrons in a laser wakefield accelerator (LWFA) to 100 MeV over millimeter length scales. By adding a second gas target behind the initial LWFA stage we introduce a robust and independently tunable plasma lens. We observe a density dependent reduction of the LWFA electron beam divergence from an initial value of 2.3 mrad, down to 1.4 mrad (rms), when the plasma lens is in operation. Such a plasma lens provides a simple and compact approach for divergence reduction well matched to the mm-scale length of the LWFA accelerator. The focusing forces are provided solely by the plasma and driven by the bunch itself only, making this a highly useful and conceptually new approach to electron beam focusing. Possible applications of this lens are not limited to laser plasma accelerators. Since no active driver is needed the passive plasma lens is also suited for high repetition rate focusing of electron bunches. Its understanding is also required for modeling the evolution of the driving particle bunch in particle driven wake field acceleration.

Flexible x-ray source with tunable polarization and orbital angular momentum from Hermite-Gaussian laser modes driven plasma channel wakefield

“…The attenuation of off-axis results is caused by the exponential term in Eq. (7). For a wide laser pulse, this decrement is slight.…”

“…(18), and the blue solid lines are numerical results obtained for a cylindrically symmetric electron beam with a spot size of σ b ¼ 4.0 by solving the transverse momentum equation with the electric field in Eq. (7). The normalized emittance of the electron beam is 0.0047.…”

“…The total size of the facility using an LPA and magnetic undulator will be, in a general case, dictated not by the size of the accelerator, but by the size of the electron optics (conventionally several meters for magnetic quadrupole lenses) and the undulator (conventionally several tens of meters or more). It has recently been experimentally demonstrated that electron optics can, in principle, also be replaced by plasma technology [6][7][8], leaving the undulator as the only major factor defining the size of the facility. Several ideas for undulators with periods on the order of millimeter or below (often referred to as microundulators) have been proposed, including electrostatic [9,10], crystalline [11][12][13], microwave [14], plasma [15], nano-wire [16] and laserbased [17][18][19][20][21][22][23][24][25].…”

Fundamentals and Applications of Hybrid LWFA-PWFA

“…Experimentally, plasma beam dumps via collective deceleration [13]-a signature of energy transfer from driver beam to plasma and as such a first step in the direction of hybrid LWFA-PWFA-has been observed in a setup with two gas jets [14]. Passive plasma lensing has also been shown experimentally in a similar setup [15]. This is important, because one of the drawbacks of LWFA-generated electron bunches (in fact, of any plasma wakefield-accelerated electron bunch) is the typically large divergence with which they leave the plasma stage.…”

Laser-Driven Electron Lensing in Silicon Microstructures

“…Active plasma lenses have focusing gradients exceeding 3 kT/m [12], while plasma wakefield lensing has focusing strengths on the order of 1 MT/m [13,14]. Plasma wakefield lensing fits naturally with plasma-based accelerators [15], and provides more than sufficient focusing strength. However, integration of plasma lenses with photonic accelerators would require generation of stable plasmas on-chip that are compatible with the accelerator nanofabrication processes.…”