energetic electron
Recently Published Documents


TOTAL DOCUMENTS

750
(FIVE YEARS 185)

H-INDEX

46
(FIVE YEARS 5)

2022 ◽  
Vol 5 (1) ◽  
Author(s):  
Jie Zhao ◽  
Yan-Ting Hu ◽  
Yu Lu ◽  
Hao Zhang ◽  
Li-Xiang Hu ◽  
...  

AbstractGeneration of energetic electron-positron pairs using multi-petawatt (PW) lasers has recently attracted increasing interest. However, some previous laser-driven positron beams have severe limitations in terms of energy spread, beam duration, density, and collimation. Here we propose a scheme for the generation of dense ultra-short quasi-monoenergetic positron bunches by colliding a twisted laser pulse with a Gaussian laser pulse. In this scheme, abundant γ-photons are first generated via nonlinear Compton scattering and positrons are subsequently generated during the head-on collision of γ-photons with the Gaussian laser pulse. Due to the unique structure of the twisted laser pulse, the positrons are confined by the radial electric fields and experience phase-locked-acceleration by the longitudinal electric field. Three-dimensional simulations demonstrate the generation of dense sub-femtosecond quasi-monoenergetic GeV positron bunches with tens of picocoulomb (pC) charge and extremely high brilliance above 1014 s−1 mm−2 mrad−2 eV−1, making them promising for applications in laboratory physics and high energy physics.


2021 ◽  
Vol 11 (22) ◽  
pp. 10768
Author(s):  
Ye Chen ◽  
Frank Brinker ◽  
Winfried Decking ◽  
Matthias Scholz ◽  
Lutz Winkelmann

Sub-ångström working regime refers to a working state of free-electron lasers which allows the generation of hard X-rays at a photon wavelength of 1 ångström and below, that is, a photon energy of 12.5 keV and above. It is demonstrated that the accelerators of the European X-ray Free-Electron Laser can provide highly energetic electron beams of up to 17.5 GeV. Along with long variable-gap undulators, the facility offers superior conditions for exploring self-amplified spontaneous emission (SASE) in the sub-ångström regime. However, the overall FEL performance relies quantitatively on achievable electron beam qualities through a kilometers-long accelerator beamline. Low-emittance electron beam production and the associated start-to-end beam physics thus becomes a prerequisite to dig in the potentials of SASE performance towards higher photon energies. In this article, we present the obtained results on electron beam qualities produced with different accelerating gradients of 40 MV/m–56 MV/m at the cathode, as well as the final beam qualities in front of the undulators via start-to-end simulations considering realistic conditions. SASE studies in the sub-ångström regime, using optimized electron beams, are carried out at varied energy levels according to the present state of the facility, that is, a pulsed mode operating with a 10 Hz-repetition 0.65 ms-long bunch train energized to 14 GeV and 17.5 GeV. Millijoule-level SASE intensity is obtained at a photon energy of 25 keV at 14 GeV electron beam energy using a gain length of about 7 m. At 17.5 GeV, half-millijoule lasing is achieved at 40 keV. Lasing at up to 50 keV is demonstrated with pulse energies in the range of a few hundreds and tens of microjoules with existing undulators and currently achievable electron beam qualities.


Author(s):  
Sheng Hui Fu ◽  
Li Cheng Tian ◽  
Zhen- Feng Ding

Abstract Thus far, effects of secondary γ-electrons emitted from accelerator grids of gridded ion sources on ionization in discharge chambers have not been studied. The presence and induced processes of such secondary electrons in a microwave electron cyclotron resonance gridded ion source are confirmed by the consistent explanations of: (1) the observed jump of ion beam current (Ib) in case of a low-density plasma appearing at the chamber’s radial center due to the microwave skin effect; (2) the evolution of glow images recorded from the end-view of the ion source during the jump of Ib; (3) the over-large jump step of Ib with the increasing microwave power; (4) the pattern appearing on the temperature sticker exposed to the discharge operated in the regime where the arrayed energetic-electron beamlets are injected into the discharge chamber; (5) the measured step-increment in the voltage drop across the screen grid sheath. A positive feedback loop composed of involved processes are established to elucidate the underlying mechanism. Energetic γ-electrons from the accelerator grid and warm δ-electrons from the opposite antenna do not produce direct excitation and ionization, but they enhance the electrical confinement of cold electrons by elevating the voltage drop across the sheaths at the antenna and screen grid, thus leading to the jump of Ib. The energetic γ-electrons-based model can be also modified to explain abnormal results observed in the other gridded ion sources. Energetic γ-electrons from accelerator grids should be taken into account in understanding gridded ion sources.


Sign in / Sign up

Export Citation Format

Share Document