Plasma wakefield acceleration experiments at FACET

Hogan, Mark; Raubenheimer, T.O.; Seryi, Andrei; Muggli, P.; Katsouleas, T.; Huang, Chengkun; Lü, Wei; An, Weiming; Marsh, K. A.; Mori, W. B.; Clayton, C. E.; Joshi, C.

doi:10.1088/1367-2630/12/5/055030

Cited by 121 publications

(125 citation statements)

References 40 publications

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“…Simulation results are given in In the figure on the left, the field is less than the ionization threshold and there is no ionization. The middle figure is for positron bunch parameters similar to those planned for FACET [11], i.e., z ¼ 20 m, r ¼ 10 m, N ¼ 1:8 Â 10 10 corresponding to a maximum field gradient of $47 GV=m. In this case, some ionization can occur.…”

Section: A Ionization Of Hydrogen Gasmentioning

confidence: 99%

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Hollow plasma channel for positron plasma wakefield acceleration

Kimura

Milchberg

Muggli

et al. 2011

Phys. Rev. ST Accel. Beams

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Plasma wakefield acceleration (PWFA) has demonstrated the ability to produce very high gradients to accelerate electrons and positrons. In PWFA, a drive bunch of charged particles passes through a uniform plasma, thereby generating a wakefield that accelerates a witness bunch traveling behind the drive bunch. This process works well for electrons, but much less so for positrons due to the positive charge attracting rather than repealing the plasma electrons, which leads to reduced acceleration gradient, halo formation, and emittance growth. This problem can be alleviated by having the positron beam travel through a hollow plasma channel. Presented are modeling results for producing 10-100 cm long hollow plasma channels suitable for positron PWFA. These channels are created utilizing laser-induced gas breakdown in hydrogen gas. The results show that hollow channels with plasma densities of order 10 16 cm À3 and inner channel radii of order 20 m are possible using currently available terawatt-level lasers. At these densities and radii, preliminary positron PWFA modeling indicates that longitudinal electric fields on axis can exceed 3 GV=m.

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Section: A Ionization Of Hydrogen Gasmentioning

confidence: 99%

“…Nonetheless, a high n e is desirable because multi-GeV=m energy gains are then possible [1,11]. Positron bunch lengths <100 m are feasible [11]; hence, a channel wall density of 6 Â 10 16 cm À3 , corresponding to p slightly longer than 100 m, was selected as the target value for our modeling effort. Then based upon the aforementioned c=!…”

Section: Introductionmentioning

confidence: 99%

Hollow plasma channel for positron plasma wakefield acceleration

Kimura

Milchberg

Muggli

et al. 2011

Phys. Rev. ST Accel. Beams

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“…The longitudinal field within the beam region is E z =E 0 ≃ ffiffiffiffiffiffiffiffiffiffiffi I b =I A p [17,18], where I b is the beam current and I A ≃ 17 kA is the Alfvén current. Hence, ϵ ≃ − ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2I b =ðI A γ 0 Þ p , and Facility for Advanced Accelerator Experimental Tests (FACET) experimental parameters [19,20], for instance, yieldε ≈ 0.007. This indicates that hosing stops well before energy depletion in typical PWFA scenarios and possibly justifies why hosing was not detected in previous experiments [2,5].…”

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confidence: 99%

Mitigation of the Hose Instability in Plasma-Wakefield Accelerators

et al. 2017

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Current models predict the hose instability to crucially limit the applicability of plasma-wakefield accelerators. By developing an analytical model which incorporates the evolution of the hose instability over long propagation distances, this work demonstrates that the inherent drive-beam energy loss, along with an initial beam-energy spread, detunes the betatron oscillations of beam electrons and thereby mitigates the instability. It is also shown that tapered plasma profiles can strongly reduce initial hosing seeds. Hence, we demonstrate that the propagation of a drive beam can be stabilized over long propagation distances, paving the way for the acceleration of high-quality electron beams in plasma-wakefield accelerators. We find excellent agreement between our models and particle-in-cell simulations. DOI: 10.1103/PhysRevLett.118.174801 Plasma-based accelerators can provide accelerating fields in excess of 10 GV=m [1,2]. As a result, these devices can potentially contribute to a future generation of more compact particle accelerators and radiation sources. Plasma-wakefield accelerators (PWFAs) [3,4] employ charged particle beams as drivers of large-amplitude plasma waves. Significant experimental results [2,5] were obtained in the blowout regime, in which a particle beam with a charge density greater than the ambient plasma density expels all plasma electrons within its vicinity, thereby generating a copropagating ion channel with linear electron focusing and extreme accelerating fields [6].Identified by Whittum et al. in the early 1990s [7], the hose instability (HI) remains a long-standing challenge for PWFAs. Hosing is seeded by initial transverse asymmetries of the beam or plasma phase-space distributions. According to current models, the beam-centroid displacement is amplified exponentially during propagation in the plasma [7][8][9][10][11], ultimately leading to a beam breakup. The most recent description for the coupled evolution of the ionchannel centroid X c ðξ; tÞ and the beam centroid X b ðξ; tÞ in the blowout regime is given by [11]with the time t and the comoving coordinate ξ ¼ ct − z, where z is the longitudinal coordinate and c is the speed of light. The plasma wave number is denoted by k p ¼ ω p =c, and the betatron frequency by ω β ¼ ω p = ffiffiffiffiffi 2γ p , with the Lorentz factor γ, where ω p ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 4πn 0 e 2 =m p is the plasma frequency with the ambient plasma density n 0 , the elementary charge e, and the electron rest mass m. The coefficients c ψ ðξÞ and c r ðξÞ account for the relativistic motion of electrons in the blowout sheath and for a ξ dependence of the blowout radius and the beam current [11]. According to Eq. (1), a beam-centroid displacement X b leads to a displacement of the ion-channel centroid X c along the beam. The displacement X c couples back to the temporal evolution of X b according to Eq. (2). The case where c ψ ¼ c r ¼ 1 recovers the seminal hosing model [7]. This limit, which accounts for a linear resp...

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“…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].…”

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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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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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Plasma wakefield acceleration experiments at FACET

Cited by 121 publications

References 40 publications

Hollow plasma channel for positron plasma wakefield acceleration

Hollow plasma channel for positron plasma wakefield acceleration

Mitigation of the Hose Instability in Plasma-Wakefield Accelerators

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

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