Free-electron lasers driven by laser plasma accelerators

Abstract

Abstract. Laser-plasma accelerators (LPAs) have the potential to drive compact free-electron lasers (FELs). Even with LPA energy spreads typically at the percent level, the e-beam brightness can be excellent, due to the low normalized emittance (<0.5 μm) and high peak current (multi-kA) resulting from the ultra-short e-beam duration (few fs). It is critical, however, that in order to mitigate the effect of percent-level energy spread, one has to actively manipulate the phase-space distribution of the e-beam. We provide an overview of the methods proposed by the various LPA FEL research groups. At the BELLA Center at LBNL, we are pursuing the use of a chicane for longitudinal e-beam decompression (therefore greatly reducing the slice energy spread), in combination with short-scale-length e-beam transportation with an active plasma lens and a strong-focusing 4-m-long undulator. We present ELEGANT & GENESIS simulations on the transport and FEL gain, showing strong enhancement in output power over the incoherent background, and present estimates of the 3D gain length for deviations from the expected e-beam properties (varying e-beam lengths and emittances). To highlight the role of collective effects, we also present ELEGANT & GENESIS simulation results.

Comparative study of active plasma lenses in high-quality electron accelerator transport lines

“…2 of Ref. 15. Following 15 cm of drift, the beam propagated through an APL with a radius of R APL ¼ 500 lm and a length of L APL ¼ 1.5 cm.…”

“…; 8 > > > > > > > > > < > > > > > > > > > : (15) where in the derivation, it was assumed that ðk 0 =k p Þ 2 ðk p L APL Þ ( 1 (thin lens approximation). The emittance growth at focus due to wake effects is…”

“…17, the theoretical degradation is compared with modeling results obtained with the 2D-cylindrical particle-in-cell (PIC) code INF&RNO (using the quasi-static modality). 45,46 The following parameters, relevant to the LPA FEL application, 15 were used: L APL ¼ 2.9 cm, R APL ¼ 500 lm, h 0 ¼ 1 mrad, 250 MeV energy, n0 ¼ 0.49 lm, L b ¼ 2 lm, I b ¼ 4.5 kA (30 pC), I APL ¼ 750 A, and L drift ¼ 9.3 cm (thus r r ¼ 93 lm and beam density n b0 ¼ 1.7 Â 10 15 cm -3 ). One can observe in Fig.…”

“…Laser plasma accelerators (LPAs) 1 have produced MeV to multi-GeV electron beams in mm-to-cm scale plasma structures. [2][3][4][5][6][7][8][9] The LPA community is pursuing applications such as ultra-fast electron beam pump-probe studies, 10 compact light sources including coherent X-rays [11][12][13][14][15] and incoherent MeV photons, [16][17][18][19] and high-energy particle colliders. 20,21 For these applications, collimation and focusing of electron beams over short, cm-scale distances is important.…”

Optimization of low aspect ratio, iron dominated dipole magnets

“…These theoretical and computational methods were brought to bear on the design of an electromagnetic chicane for an LPA experiment currently being implemented at the LBNL BELLA Laboratory. This experiment aims to demonstrate the generation of coherently enhanced x-ray radiation from an LPA driven free electron laser (FEL) [22]. In order to achieve the required slice energy spread, the LPA electron beam must be stretched by a dispersive element, e.g., a chicane.…”