Ion-channel Laser Research Articles

Far-field constant-gradient laser accelerator of electrons in an ion channel

We predict that electrons in an ion channel can gain ultra-relativistic energies by simultaneously interacting with a laser pulse and, counter-intuitively, with a decelerating electric field. The crucial role of the decelerating field is to maintain high-amplitude betatron oscillations, thereby enabling constant rate energy flow to the electrons via the inverse ion channel laser mechanism. Multiple harmonics of the betatron motion can be employed. Injecting electrons into a decelerating phase of a laser wakefield accelerator is one practical implementation of the scheme.

Ion-channel laser growth rate and beam quality requirements

In this paper, we determine the growth rate of the exponential radiation amplification in the ion-channel laser, where a relativistic electron beam wiggles in a focusing ion channel that can be created in a wakefield accelerator. For the first time the radiation diffraction, which can limit the amplification, is taken into account. The electron beam quality requirements to obtain this amplification are also presented. It is shown that both the beam energy and wiggler parameter spreads should be limited. Two-dimensional and three-dimensional particle-in-cell simulations of the self-consistent ion-channel laser confirm our theoretical predictions.

Study of the beam tolerance for plasma based ion channel lasers

In this work we use the one-dimensional free electron laser (FEL) model to define necessary parameters of an electron beam to produce self amplified spontaneous emission (SASE) in an ion channel laser (ICL) undulator. Limits and constraints on beam parameters are given, based on theoretical argument and numerical simulations results using the Architect hybrid code.

Resonant excitation of betatron oscillations

Resonant excitation of betatron oscillations is a proposed mechanism for creating large amplitude, sinusoidal electron oscillations by overlaying a standard magnetic undulator and the radial electric fields of an ion channel to effectively create a very high strength undulator. By satisfying a resonance condition between the undulator and betatron periods, large transverse wiggling amplitudes are possible at short periods of oscillation. This skirts the existing limitations of magnetic undulators whose effective strength is constrained by the limits on high peak field values in a short (∼cm) period. Additionally, such motion can be achieved with on axis beam injection and greater operational amplitude and polarization tunability than offered in other incarnations of the plasma wiggler. This technique provides a path to applications that demand high K, tunable, bright x-ray or gamma ray radiation such as high flux polarized positron production and a practical realization of the ion channel laser.

The ion channel free-electron laser with varying betatron amplitude

The ion-channel laser (ICL) is an ultra-compact version of the free-electron laser (FEL), with the undulator replaced by an ion channel. Previous studies of the ICL assumed transverse momentum amplitudes which were unrealistically small for experiments. Here we show that this restriction can be removed by correctly taking into account the dependence of the resonance between oscillations and emitted field on the betatron amplitude, which must be treated as variable. The ICL model with this essential addition is described using the well-known formalism for the FEL. Analysis of the resulting scaled equations shows a realistic prospect of building a compact ICL source for fundamental wavelengths down to UV, and harmonics potentially extending to x-rays. The gain parameter ρ can attain values as high as 0.03, which permits driving an ICL with electron bunches with realistic emittance.

Kinetic description of a wiggler-pumped ion-channel free-electron laser by applying the Einstein coefficient technique

AbstractA kinetic theory is used to investigate the theory of a free-electron laser with a helical wiggler and an ion channel based on the Einstein coefficient method. The laser gain in the low-gain regime is obtained for the case of a cold tenuous relativistic electron beam, where the beam plasma frequency is much less than the radiation frequency, propagating in this configuration. The resulting gain equation is analyzed numerically over a wide range of system parameters.

Chaos in an ion-channel free-electron laser with realistic helical wiggler

Chaotic behavior of an electron motion in a free-electron laser with realistic helical wiggler and ion-channel guiding is studied using Poincaré surface-of-section maps. The effects of a realistic electron beam density on chaotic electron dynamics are investigated by considering an electron beam with Gaussian density profile in radial distance. The effects of self-fields on chaotic electron dynamics are investigated for different Gaussian beam parameters, and the results are compared with those of uniform electron beam. It is shown that the electron chaotic behavior can be controlled by changing the Gaussian beam parameter. Also, the chaotic behavior can be controlled by increasing the ion-channel and/or the electron beam densities.

Linear theory of magnetized ion-channel free-electron laser

A theory of wiggler pumped ion-channel free-electron laser (WPIC-FEL) and an axial magnetic field is presented. The motion of a relativistic electron is analyzed in the field configuration consisting of a helical wiggler magnetic field, a uniform axial magnetic field, and an electrostatic electric field produced by an ion-channel. An equation for the function Φ, which determines the rate of change of axial velocity with energy, is derived. Numerical calculations are made to illustrate the effects of two electron beam guiding devices on the trajectories. By means of linear fluid theory, the sixth-degree polynomial dispersion equation for electromagnetic and space-charge waves is derived. The dependence of growth rate-frequency curves on the ion-channel frequency and axial magnetic field is studied numerically.

A comparison between electron orbits for both an axial magnetic field and an ion-channel guiding in a FEL with an electromagnetic wave wiggler

AbstractThe operation of a free-electron laser (FEL) with electromagnetic wave wiggler in the presence of an ion-channel guiding as well as an axial guide magnetic field is considered and compared. Theoretical studies of electron trajectories and dispersion relations in a combined ion electrostatic field as well as large-amplitude backward-propagating electromagnetic waves are analyzed. The large-amplitude wave acts like a magnetostatic wiggler in a FEL. The results of a numerical study are presented and discussed. It is shown that in the wiggler pumped ion-channel free-electron laser (WPIC-FEL), electron orbits and dispersion relation are time-dependent, and over time, electron orbits while oscillating bear a periodic motion.

Boundary effect analysis of electromagnetic mode in the beam-ion channel

Considering the disturbance of the plasma electrons at the beam-ion channel boundary, the eigen-equation of TM mode has been derived. On the basis of comparing the electromagnetic characteristics of the beam-ion channel with a traditional medium waveguide for the condition of a step-boundary defined in this paper, the numerical simulation results show that by changing the plasma frequency one can control the electromagnetic working mode in ion channel. Analyzing the influence of the disturbed charge boundary and the step-boundary on electromagnetic mode in the beam-ion channel, one can find that the cut-off frequency of the beam-ion channel have increased in the low frequency range effectively (ωωp， ωp is the plasma frequency) and some new electromagnetic modes appear in the high frequency range (ω>ωp) with the disturbed charge boundary. These findings can provide an important theoretical basis for the design of the ion channel electronics cyclotron maser (ICECM) and the ion channel laser (ICL).

Self-fields in an Ion-channel Free-electron Laser

A theory of self-fields in a free-electron laser with a helical wiggler and ion-channel guiding is presented. The effects of self-electric and magnetic fields on electron trajectories are investigated. It is shown that, under the Budker condition, there is one group of orbits (group I) for which the wiggler-induced self-magnetic field is negative and acts as a diamagnetic correction to the wiggler magnetic field. The function Φ that determines the rate of change of axial velocity with energy in the presence of the self-fields is derived and studied numerically.

X-ray generation in an ion channel

X-ray generation by relativistic electrons in an ion channel is studied. The emission process is analyzed in the regime of high harmonic generation when the plasma wiggler strength is large. Like for the conventional free electron laser, the synchrotron-like broadband spectrum is generated in this regime. An asymptotic expression for the radiation spectrum of the spontaneous emission is derived. The radiation spectrum emitted from an axisymmetric monoenergetic electron beam is analyzed. The stimulated emission in the ion channel is studied and the gain of the ion-channel synchrotron-radiation laser is calculated. It is shown that the use of laser-produced ion channels leads to a much higher power of x-ray radiation than the one in a self-generated channel. In addition, the mean photon energy, the number of emitted photons and the brilliance of the photon beam increase dramatically. Three-dimensional particle-in-cell simulations of a 25-GeV electron bunch propagating in a laser-produced ion channel are made. Several GeV γ-quants are produced in a good agreement with the analytical results.

Synchrotron radiation from electron beams in plasma-focusing channels.

Spontaneous radiation emitted from relativistic electrons undergoing betatron motion in a plasma-focusing channel is analyzed, and applications to plasma wake-field accelerator experiments and to the ion-channel laser (ICL) are discussed. Important similarities and differences between a free electron laser (FEL) and an ICL are delineated. It is shown that the frequency of spontaneous radiation is a strong function of the betatron strength parameter a(beta), which plays a role similar to that of the wiggler strength parameter in a conventional FEL. For a(beta) > or approximately 1, radiation is emitted in numerous harmonics. Furthermore, a(beta) is proportional to the amplitude of the betatron orbit, which varies for every electron in the beam. The radiation spectrum emitted from an electron beam is calculated by averaging the single-electron spectrum over the electron distribution. This leads to a frequency broadening of the radiation spectrum, which places serious limits on the possibility of realizing an ICL.

Electromagnetic wave pumped ion-channel free electron laser

Theoretical study of electromagnetic wave pumped ion-channel free-electron laser (EPIC-FEL) is presented. The physical mechanism responsible for the generation of coherent radiation in the EPIC-FEL is described and the fundamental role of the ponderomotive wave in bunching and trapping the beam is emphasized. The dispersion relation of the EPIC-FEL has been obtained and growth rates are calculated for different parameters. It shows that EPIC-FEL has a very bright future.

Propagation of short electron pulses in underdense plasmas.

Dense relativistic electron beams traversing a plasma, in what is known as the underdense, or ion focusing, regime experience a strong, linear transverse restoring force. This force arises from the nearly immobile ions which form a channel of uncompensated positive charge when the plasma electrons are ejected in response to the introduction of the beam charge. This phenomenon can be used for focusing the electron beam to very high densities over long propagation distances. Several schemes have been proposed, including the nonlinear plasma wake-field accelerator, the adiabatic plasma lens, and the ion-channel laser, whose viability is based on this focusing effect for very short pulse, high current electron beams propagating in plasma. In this paper we examine, analytically and numerically, the self-consistent requirements on plasma density, beam current, length, and transverse emittance which must be satisfied in order for ion-channel formation and near equilibrium beam propagation to exist over the majority of the length of the electron beam. The dynamics of the beam-plasma system are modeled by a simultaneous solution of the plasma electron cold-fluid equations, and the Maxwell-Vlasov equation governing the beam's thermal equilibrium. The effects of introducing a strong axial magnetic field on the plasma response and beam equilibria are examined. In addition to developing criteria for self-consistent equilibrium focusing, a time-dependent analysis where the beam particles are treated as mobile particles in cells is developed in order to study the dynamical approach of this equilibrium. Inherently time-dependent phenomena, such as matching of the beam into the plasma and adiabatic lenses, are then examined with this method.

One-particle theory of Ion-Channel Laser

Following the work of Chen and Dawson (1991) on Ion-Channel Laser (ICL), we study the amplification mechanism of the ICL by using the one-particle model proposed by them, and methods of secular perturbation theory. We calculate the conditions for resonance in the wave-particle interaction, and estimate the gain expected. The resonant Electro-Magnetic wave frequency appears to depend strongly on the amplitudes of oscillations of the beam particles. This may significantly reduce the amplification, and limit the use of ICL to relatively low frequencies, up to Infra-Red, where high output power (/spl sim/GW) is achievable. Analytical results are confirmed by numerical simulations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of ion-channel laser using the Madey's theorem

Ion-Channel Laser (ICL) is a new form of laser, which can produce tunable coherent radiation with frequencies ranging from microwaves to soft X-rays. In this paper, the ICL with slab geometry in the low gain is studied. Using the Madey's theorem, the gain formula of the ICL is derived. The result shows that the Madey's theorem is a valuable guide in research with new types of FEL's.

Ion-channel laser.

A relativistic electron beam propagating through a plasma in the ion-focused regime exhibits an electromagnetic instability with peak growth rate near a resonant frequency {omega}{similar to}2{gamma}{sup 2}{omega}{sub {beta}}. Growth is enhanced by optical guiding in the ion channel, which acts as a dielectric waveguide, with fiber parameter {ital V}{similar to}1({ital I}/{ital I}{sub {ital A}}){sup 1/2}. A 1D theory for a laser making use of this instability is formulated, scaling laws are derived, and numerical examples are given. Possible experimental evidence is noted.

On the amplification mechanism of the ion-channel laser

The amplification mechanism of the ion-channel laser (ICL) in the low-gain regime is studied. In this concept, a relativistic electron beam is injected into a plasma whose density is comparable to or lower than the beam's density. The head of the electron beam pushes out the plasma electrons, leaving an ion channel. The ion-focusing force causes the electrons to oscillate (betatron oscillations) about the axis and plays a role similar to the magnetic field in a cyclotron autoresonance maser (CARM). Radiation can be produced with wave frequencies from microwaves to X-rays depending on the beam energy and plasma density: omega approximately 2 gamma /sup 3/2/ omega /sub pe/, where gamma is the Lorentz factor of the beam and omega /sub pe/ is the plasma frequency. Transverse (relativistic) bunching and axial (conventional) bunching are the amplification mechanisms in ICLs; only the latter effect operates in free-electron lasers. The competition of these two bunching mechanisms depends on beam velocity nu /sub 0z/; their dependences on nu /sub 0z/ cancel for the cyclotron autoresonance masers. A linear theory is developed to study the physical mechanisms, and a PIC (particle-in-cell) simulation code is used to verify the theory. The mechanism is examined as a possible explanation for experimentally observed millimeter radiation from relativistic electron beams interacting with plasmas. >