Transport and stability of long-pulse relativistic electron beams in UV laser-induced ion channels

Abstract

Results are presented for the first experiments in which long-pulse (0.4–1 μsec), relativistic (0.8 MV) electron beams have been transported in the ion focused regime (IFR) in ion channels formed in low pressure diethylaniline gas by means of KrF excimer laser-induced ionization. These experiments demonstrate that the most efficient (50%–80%) and longest pulse (0.6 μsec) e-beam transport is obtained with laser-induced channels over a very narrow gas pressure range (0.3–1.7 mTorr). Higher than optimal pressures cause excess e-beam-induced ionization and instability of the electron beam. At lower pressures, the laser-induced ion channel density is insufficient for initial e-beam guidance. Transverse oscillations of the electron beam have been measured at a frequency close to that predicted for the ion hose instability. The growth length and wavelength of the transverse oscillations are comparable to the betatron wavelength, further suggesting that these oscillations result from the ion hose instability.

Electron-hose instability in the ion-focused regime

“…At the same time, coherent radiation from intense beams in the IFR has also been the subject of much theoretical [8][9][10][11] and experimental [12] work. These novel applications draw on a large body of work in beam-plasma physics [13][14][15] and extensive application of the IFR in accelerator and radiation research [16,17].Typically the IFR refers to propagation along a narrow plasma channel which is "underdense" (i.e., with charge density much less than that of the beam) and in addition has total plasma charge per unit length less than that of the beam. In this limit, all plasma electrons are ejected radially to large distances.…”

“…At the same time, coherent radiation from intense beams in the IFR has also been the subject of much theoretical [8][9][10][11] and experimental [12] work. These novel applications draw on a large body of work in beam-plasma physics [13][14][15] and extensive application of the IFR in accelerator and radiation research [16,17].…”

Spread-frequency model of the fast beam-ion instability in an electron storage ring

“…When v b 0, Eq. (1) describes the "ion hose" instability of an electron beam focused by an ion channel [12][13][14][15]. In an electron storage ring, where ion effects are a perturbation to the betatron motion in applied magnetic fields, we instead have v b ¿ v e ͑T͒.…”

Suppression of two-stream hose instabilities at wavelengths shorter than the beam’s transverse size

“…b ! c [12,13], the instability wavelength is determined by the beam's bounce frequency in the ion channel, and the phase velocity is nonrelativistic in the laboratory frame. For a typical e-p instability with !…”

“…When a beam of charged particles propagates in a channel of particles with the opposite charge, a transverse dipole (hose) instability may result [1,2]. For a proton beam, this instability has been called the e-p instability [3][4][5][6][7][8], while for an electron beam it has been called the ion hose instability [9][10][11][12][13]. For colliding beams, this instability may give rise to the coherent dipole beambeam effect [14].…”