Electromagnetic instability of the ion-focused regime

Abstract

A relativistic electron beam propagating through a wide plasma channel in the ion-focused regime exhibits an electromagnetic instability coupled to the ‘‘betatron’’ motion, with peak growth rate near a resonant angular frequency ω∼2γ2ωβ, where γ is the Lorentz factor for the beam, and ωβ is the angular frequency of transverse oscillations. An eikonal formalism is derived analogous to that for the free-electron laser and the dispersion relation is determined. Constraints due to energy spread and other sources of detuning are noted. Analytic scaling laws are compared to the results of numerical simulation for a practical example corresponding to a microwave amplifier. Constraints due to competing instabilities are noted and the extension to short wavelengths is discussed.

Laser based synchrotron radiation

“…In this interaction regime, as the intense and femtosecond laser propagates in the underdense plasma (fully ionized helium gas), the ponderomotive force pushes plasma electrons away from the high intensity regions, leaving an ion channel almost free of background electrons in the wake of the laser. [7][8][9] As the relativistic electrons propagate in the ion channel (Fig. 1), they experience a radial restoring force due to the transverse electrostatic field generated by the space charge separation with the ions.…”

Production of a keV X-Ray Beam from Synchrotron Radiation in Relativistic Laser-Plasma Interaction

“…A particularly efficient mechanism for wakefield generation occurs in the parameter regime corresponding to ultrashort laser pulses ( 30 fs), called the forced laser wakefield regime, which has been studied experimentally [11] as well as with 3D particle-in-cell (PIC) simulations [11,12]. In this regime the wake has an electron-density depression right behind the laser pulse, leading to the formation of an ion column [13][14][15]. This charge displacement results in a strong radial electrostatic field.…”

Microsynchrotron

“…De ce fait, les électrons relativistes soumis à cette force de rappel vont effectuer un mouvement oscillatoire (oscillations « bétatron ») dans le plasma [19][20][21][22], ce qui va produire, comme dans un synchrotron, un faisceau de rayonnement X collimaté et polychromatique. La période des oscillations étant plus faible dans le plasma (quelques centaines de microns) que dans un synchrotron (quelques centimètres), il n'est pas nécessaire d'avoir des faisceaux d'électrons aussi énergétiques dans le cas de l'onduleur plasma.…”