A relativistic electron beam propagating through an unmagnetized, underdense plasma exhibits a transverse instability due to the coupling of the beam centroid to plasma electrons at the "ion-channel" edge. The transverse wake field corresponding to this "electron-hose" effect is calculated in the "frozen-field" approximation for a low-current, cylindrical beam in a radially infinite plasma. The asymptotic growth of beam-centroid oscillations is computed, and the growth length is found to be very rapid, indeed much less than the betatron period of the beam. Results for a radially finite plasma and for a slab beam are noted. Damping and saturation mechanisms are discussed.PACS numbers: 52.40. Mj, 29.15.Dt, 52.50.Gj In recent years, the demands of the TeV-energy electron-positron collider [l] have spurred considerable interest in the transport of intense relativistic electron beams in the "ion-focused regime" (IFR). Proposed applications include the plasma lens [2], the continuous plasma focus [3,4], the plasma emittance damper [5], and plasma wake-field acceleration [6,7]. 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. However, for many novel applications, the plasma may initially extend to large radii, or a broad plasma may be created by beam and secondary ionization. In this Letter, we show that propagation in such a regime suffers from a previously unrecognized hose instability, similar in character to the "transverse two-stream" instabilities [18,19] (e.g., the "ion-hose" instability [15]). This instability results from the electrostatic coupling of transverse beam displacements to plasma electrons at the boundary between the ion channel and the surrounding quasineutral plasma, beyond the beam volume. We show that the growth length for the "electron-hose" instability is so short that IFR transport in this regime is problematic at best.To compute this growth length, we consider first equilibrium propagation of a relativistic electron beam in a uniform, unmagnetized, preionized plasma of density rie, and infinite radial extent. We assume unperturbed beam charge density of the form pboir,s)'= -enij(s)H(a -r), where H is the step function, -^ is the electron charge, rib is the beam density on axis, a is the beam radius ( Fig. 1), s-t -zic is the retarded time, t is time, z is axial displacement, and c is the speed of light. As the beam head propagates through the plasma, it expels plasma electrons from the beam volume on the sho...

The authors have validated a GEANT4 simulated IAEA-compliant phase space of the TrueBeam linac for the 6 MV beam obtained using a high accuracy geometry implementation from CAD. These files are publicly available and can be used for further research.

No abstract

The hollow plasma channel is analyzed as an accelerating structure. The excitation of the channel by an ultrarelativistic beam is analyzed. Coupling to the fundamental and all higher-order azimuthal modes of the excited electromagnetic fields is derived. Implications of this work for plasma-based accelerators, including beam loading and beam breakup, are discussed. Small initial transverse displacements of the beam are shown to couple to deflecting modes in the channel. The asymptotic growth rate of the resultant beam breakup instability is analyzed and a method for reducing the growth is proposed.[S0031-9007(99)08413-6] PACS numbers: 52.75. Di, 41.75.Lx, 52.35.Py, 52.40.Mj The reach of high-energy physics is limited by its instruments, accelerators, and passive conducting structures attaining large accelerating fields by resonant excitation [1]. In conventional accelerators, the size of these accelerating fields is limited by breakdown. For two decades, plasma-based accelerators [2] have been investigated as a means of overcoming this breakdown constraint. Two schemes of plasma excitation have been the focus of much of the work: the laser wakefield accelerator and the plasma wakefield accelerator. In the laser wakefield accelerator, a short intense laser pulse excites a plasma wave through radiation pressure (the ponderomotive force). In the plasma wakefield accelerator, the plasma wave is excited by the self-fields of an intense relativistic particle beam.For the laser wakefield accelerator one of the most severe limitations is the weakening of the laser pulse intensity due to diffraction. To overcome this limitation, the use of a preformed plasma channel to provide optical guiding has been proposed [3,4]. A parabolic profile was first studied [3], and subsequently a hollow plasma channel [4,5]. In a hollow plasma channel, the transverse profile of the driver is decoupled from the transverse profile of the accelerating mode. Therefore, for a relativistic driver, the accelerating gradient is uniform and the focusing fields are linear [4]. In addition, the accelerating mode of the hollow plasma channel is fully electromagnetic, unlike the electrostatic fields excited in a homogeneous plasma. These properties make it well suited as a structure for both particle beam wakefield accelerators as well as laser driven wakefield accelerators.Preformed channel creation is currently being explored experimentally [6-9]. Since the original demonstration of the guiding of a low intensity laser in a plasma channel by Milchberg and co-workers [6], several groups are examining methods of channel formation [6-9] and the guiding of high intensity lasers [6][7][8]. Methods of forming a plasma channel include inverse bremsstrahlung heating of the plasma by a precursor laser pulse resulting in hydrodynamic expansion and channel formation [6] and ionization of a preformed capillary tube [7].In this Letter, we characterize an externally formed hollow plasma channel as an accelerating structure, independent of the structure excitatio...