Particle-in-cell simulations of tunneling ionization effects in plasma-based accelerators

Bruhwiler, David L.; Dimitrov, Dimitre; Cary, John R.; Esarey, E.; Leemans, Wim; Giacone, Rodolfo

doi:10.1063/1.1566027

Cited by 107 publications

(89 citation statements)

References 27 publications

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“…the ADK formalism [22]. We use 16 particles per cell for each simulated species, and electrons from the creation of Rb + , Rb 2+ and Ar + are tracked separately.…”

Section: Slac-pub-15919mentioning

confidence: 99%

“…If σ * r is small enough, the combined action of the beam's radial field E r and the wakefield E z can ionize Rb + to Rb 2+ . The threshold electric field (defined here as 10% ionization level) needed to produce Rb 2+ (IP= 27.3 eV) is calculated using the ADK theory [22] as 53 GV/m. Taking σ * r of 3 µm, we can estimate the maximum E r at the peak of the bi-Gaussian beam to be E max r = 17.3GV/m(N/10 10 )(10µm/σ * r )(30µm/σ z ) = 56 GV/m.…”

Section: Slac-pub-15919mentioning

confidence: 99%

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Beam Loading by Distributed Injection of Electrons in a Plasma Wakefield Accelerator

Vafaei-Najafabadi

Clayton

et al. 2014

Phys. Rev. Lett.

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We show through experiments and supporting simulations that propagation of a highly relativistic and dense electron bunch through a plasma can lead to distributed injection of electrons, which depletes the accelerating field; i.e. beam loads the wake. The source of the injected electrons is ionization of the second electron of rubidium (Rb II) within the wake. This injection of excess charge is large enough to severely beam load the wake, and thereby reduce the transformer ratio T . The reduction of the average T with increasing beam loading is quantified for the first time by measuring the ratio of peak energy gain and loss of electrons while changing the beam emittance. Simulations show that beam loading by RbII electrons contributes to the reduction of the peak accelerating field from its weakly loaded value of 43 GV/m to strongly loaded value of 26 GV/m.The FACET facility [1] at the SLAC National Accelerator Laboratory is presently being used for basic research on the Plasma Wakefield Accelerator (PWFA). In this concept, a short, dense electron bunch [2] is used to generate a high gradient accelerating field in plasma that accelerates a second trailing beam to high energies [3]. Two critical physics issues that affect the energy gain and the emittance of the accelerated beam are beam head erosion [4] and ion motion [5]. The severity of both effects can be mitigated by using a plasma containing a heavier ion species such as rubidium (Rb), rather than the previously used lithium [6,7]. In this Letter, we show that the maximum accelerating gradient that a wake can support is determined not by the plasma density as expected [8], but by the onset of electron injection due to further ionization of rubidium ions. This injected charge extracts energy from the wake in a process known as beam loading and thereby reduces the maximum energy gained by the electrons. Other heavier ions that are potential candidates [9] for mitigating the aforementioned issues may have a similar limitation on the maximum achievable acceleration gradient.The onset of electron injection in the wake leads to a reduction in the important figure of merit for a PWFA known as the transformer ratio T = E + /E − [10]. Here, E − and E + are the peak decelerating and accelerating fields that act upon the beam electrons, respectively. In this experiment, injected electrons are generated via the further ionization of Rb + by the beam electrons' self field or induced wakefield. These "Rb II electrons", observed as excess charge exiting the plasma, are born within the wake [11][12][13][14] as Rb + is ionized to Rb 2+ at the tightly pinched regions of the initially mismatched drive bunch as it executes envelope oscillations [15] in the plasma. Since different slices of the beam lose energy at a different rate due to the wakefield, betatron oscillations of these beam slices quickly become out of phase resulting in continuous injection of the Rb II electrons. This unwanted beam loading results in a reduced average transformer ratio T . Simulations confirm t...

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“…the ADK formalism [22]. We use 16 particles per cell for each simulated species, and electrons from the creation of Rb + , Rb 2+ and Ar + are tracked separately.…”

Section: Slac-pub-15919mentioning

confidence: 99%

Section: Slac-pub-15919mentioning

confidence: 99%

Beam Loading by Distributed Injection of Electrons in a Plasma Wakefield Accelerator

Vafaei-Najafabadi

Clayton

et al. 2014

Phys. Rev. Lett.

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“…Previous experiments [8][9][10][11]16,17] ionized the lithium vapor with an excimer laser operating at 193 nm and controlled the plasma density with the laser energy [19]. In the experiments described here, the neutral lithium vapor is fully ionized by the large radial electric field of the compressed electron bunches [12,13] and the plasma density is then equal to the lithium vapor density. Field-ionized plasma production is advantageous in that there are no timing, lifetime, or alignment issues normally associated with plasmas in this density-length range.…”

mentioning

confidence: 99%

“…When the electron bunch enters the lithium vapor, the electric field of the leading portion of the bunch ionizes the valence electron of each lithium atom in its vicinity leaving fully ionized neutral plasma for the remainder of the bunch [12,13]. The plasma electrons are then expelled from the beam volume and return one-half plasma period later.…”

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confidence: 99%

Multi-GeV Energy Gain in a Plasma-Wakefield Accelerator

et al. 2005

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3module. A 28.5 GeV electron beam with 1:8 10 10 electrons is compressed to 20 m longitudinally and focused to a transverse spot size of 10 m at the entrance of a 10 cm long column of lithium vapor with density 2:8 10 17 atoms=cm 3 . The electron bunch fully ionizes the lithium vapor to create a plasma and then expels the plasma electrons. These electrons return one-half plasma period later driving a large amplitude plasma wake that in turn accelerates particles in the back of the bunch by more than 2.7 GeV.Plasmas have extraordinary potential for advancing the energy frontier in high-energy physics due to the large focusing and accelerating fields that are generated.Beam-plasma interactions have demonstrated focusing gradients of MT=m [1] while laser plasma interactions have demonstrated GeV=cm accelerating gradients [2 -7] over distances of a few mm. Beam-driven plasmawakefield accelerators (PWFA) have recently demonstrated acceleration and focusing of both electrons [8,9] and positrons [10,11] in meter scale plasmas.The experiment described in this Letter uses an ultrarelativistic electron bunch to simultaneously create a plasma in lithium vapor and drive a large amplitude plasma wave. When the electron bunch enters the lithium vapor, the electric field of the leading portion of the bunch ionizes the valence electron of each lithium atom in its vicinity leaving fully ionized neutral plasma for the remainder of the bunch [12,13]. The plasma electrons are then expelled from the beam volume and return one-half plasma period later. The returning plasma electrons form density concentrations on axis behind the bunch leading to a large accelerating field for the particles in the back of the bunch.In linear plasma theory [14] the wakefield amplitude increases as N= 2 z , provided the plasma density is increased such that k p z 2 p where N is the number of electrons in the bunch, z is the bunch length, and k p ! p =c is the inverse of the plasma collisionless skin depth. The nonlinear or blowout regime is reached when the electron bunch density n b N= 2 3=2 z 2 r is greater than the plasma density n p and the beam radius satisfies r c=! p . In the blowout regime, for bunch lengths on the order of the plasma wavelength, the plasma electrons are expelled from the beam volume to a radius r c 2 N= 2 3=2 z n p q leaving behind a pure ion column. This experiment is in a regime in which the electron bunch radius, bunch length, ion channel radius, and plasma wavelength are all on the same order. Although the experiments described here are on the edge of the blowout regime, numerical simulations indicate the N= 2 z increase in plasma-wakefield amplitude can still be realized [15]. Verification of the dramatic increase in accelerating gradient predicted for short bunches is a critical milestone for the application of plasma-wakefield accelerators to future high-energy accelerators and colliders.A single 28.5 GeV bunch of 1:8 10 10 electrons from the Stanford Linear Accelerator Center (SLAC) linac enters the Final Focus Test B...

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“…There are also a few use carbon dioxide or oxygen as the injection gas, but only oxygen atoms contribute to the injections 17,19 . In order to see the different ionization thresholds for the inner shell of a few such elements, we use the widely accepted ADK model [32][33][34] . According to this model, the ionization probabilities for different elements under different laser field amplitudes are shown in Fig.…”

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confidence: 99%

High quality electron beam acceleration by ionization injection in laser wakefields with mid-infrared dual-color lasers

et al. 2016

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For the laser wakefield acceleration, suppression of beam energy spread while keeping sufficient charge is one of the key challenges. In order to achieve this, we propose bichromatic laser ionization injection with combined laser wavelengths of 2.4µm and 0.8µm for wakefield excitation and for triggering electron injection via field ionization, respectively. A laser pulse at 2.4µm wavelength enables one to drive an intense acceleration structure with relatively low laser power. To further reduce the requirement of laser power, we also propose to use carbon dioxide as the working gas medium, where carbon acts as the injection element. Our full three dimensional particle-in-cell simulations show that electron beams at the GeV energy level with both low energy spreads (around one percent) and high charges (several tens of picocoulomb) can be obtained by this scheme with laser parameters achievable in the near future.PACS numbers: 52.65. Rr, 41.75.Jv, 52.38.Kd, 41.85.Ar Ever since its invention, the laser wakefield accelerator (LWFA) has been considered as one of the most promising candidates of the next generation of accelerators 1 . Compared with conventional radio-frequency accelerators, a laser wakefield accelerator has the advantage of several orders higher acceleration gradient, meanwhile currently it has the drawbacks of relatively poor beam qualities. Great progresses has been made over the past years 2-7 . Nevertheless, to further improve the beam quality including the charge, peak energy, energy spread, and emittance is still one of the top priorities in the community in order to make the LWFA suitable for applications.There are mainly two ways of improving the output beam quality. One is improving the beam phase space distribution during the acceleration processes 8 , and the other is improving the injection processes at the very beginning of the acceleration 9-11 . Among the variety of injection schemes, the ionization-induced injection is found to be simple and effective [12][13][14][15][16][17][18][19][20] . By using different variations of this mechanism, electron beams with low emittances down to the nano-meter level [21][22][23] , or low energy spreads down to a few percent [24][25][26] were produced. Recently, a new ionization injection variation utilizing the beating of bichromatic lasers to produce subpercent energy spread is proposed 27 . In this scheme, the driver is a femtosecond laser pulse with two frequency components ω 1,2 , and the laser peak electric field amplitude evolves due to the dispersion difference of the two frequency components. The evolution length period of the electric field amplitude is The laser is square-wave-like bichromatic with wavelengths of 2.4 µm and 0.8 µm, and the ionization object is C 4+ . The solid line shows the ionization probability after one laser cycle when the combined electric field takes the form of E 10 cos(ωt) + 1 3 cos(3ωt) , and the dash-dot line shows that when it takes the form of E 10 sin(ωt) + 1 3 sin(3ωt) .which is typically in hundred microm...

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Particle-in-cell simulations of tunneling ionization effects in plasma-based accelerators

Cited by 107 publications

References 27 publications

Beam Loading by Distributed Injection of Electrons in a Plasma Wakefield Accelerator

Beam Loading by Distributed Injection of Electrons in a Plasma Wakefield Accelerator

Multi-GeV Energy Gain in a Plasma-Wakefield Accelerator

High quality electron beam acceleration by ionization injection in laser wakefields with mid-infrared dual-color lasers

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