Preservation of Beam Emittance in the Presence of Ion Motion in Future High-Energy Plasma-Wakefield-Based Colliders

Gholizadeh, R.; Katsouleas, T.; Muggli, P.; Huang, Chengkun; Mori, W. B.

doi:10.1103/physrevlett.104.155001

Cited by 31 publications

(28 citation statements)

References 16 publications

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“…The color bar on (a) indicates n e =n e0 the ratio of the local plasma electron density to the unperturbed plasma density (value of À1). Several techniques have already been proposed to mitigate the ion motion or minimize the emittance growth [10,11]. In this paper, we investigate the possibility of using plasma ions with a nonzero temperature, to counter the strong force imposed on them by the dense electron bunches.…”

Section: Fig 1 (A)mentioning

confidence: 99%

Effect of temperature on ion motion in future plasma wakefield accelerators

Gholizadeh

Katsouleas

Huang

et al. 2011

Phys. Rev. ST Accel. Beams

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We study the effect of plasma temperature on ion motion in a plasma wakefield accelerator with parameters typical of a future high-energy accelerator. We show that the collapse of the plasma ions caused by the extremely high fields of ultradense electron bunches can be prevented only by a very high plasma ion temperature. DOI: 10.1103/PhysRevSTAB.14.021303 PACS numbers: 52.40. Mj, 52.75.Di, 29.27.Àa Plasmas are capable of sustaining extremely high amplitude electric fields that can be used to accelerate particles to high energies, in distances orders of magnitude shorter than in conventional accelerators. In fact, in a recent experiment at the SLAC National Accelerator Laboratory, the energy of 42 GeV trailing electrons was doubled in only 85 cm of lithium plasma [1].In a beam driven plasma-based particle accelerator or plasma wakefield accelerator (PWFA) [2], a high-density relativistic drive electron bunch expels the plasma electrons off its path [ Fig. 1(a)] [1]. In order to reach large accelerating fields, the electron bunch must be short, and the plasma density such that the wavelength of the relativistic plasma wave pe is on the order of the bunch length z :pe ¼ 2c=! pe $ z . The plasma angular frequency in a plasma with electron density n e is ! pe ¼ ð2n e e 2 =m e Þ 1=2 . When the beam density n b is larger than the plasma density (n b > n e ), all the plasma electrons are displaced on a time scale given by the electron plasma frequency ( e $ 2 ! pe ) to a distance on the order of the bunch neutralization radius: r e $ ðn b =n e Þ 1=2 r , where r is the bunch radius. Typically, the ions respond and move on a much longer time scale given by the ion plasma frequency. Therefore the ions (usually assumed cold, T i ¼ 0) can be considered immobile and the ion column density uniform [ Fig. 2(a)] since the wake generation and particle acceleration processes are over after a time $ e . Gauss' law dictates that the uniformly distributed ions create a transverse electric field that increases linearly with radius r: E r ¼ 2n i er [n i ¼ n e for the neutral plasma, Fig. 2(b)], which focuses a following witness bunch. This field also pulls back to the axis the expelled plasma electrons that sustain the accelerating structure [ Fig. 1(a)]. The intense longitudinal component of the wakefield accelerates the witness bunch when injected at the proper position behind the drive bunch [ Fig. 1(b)]. Energy is therefore transferred from the drive bunch to the witness bunch through the plasma wake.The ion column also acts as a focusing channel that prevents the two bunches from expanding because of their finite transverse emittances thus allowing for acceleration over long distances ($ 1 m) [1]. In the case of a uniform column density with linear focusing force [Figs. 2(a) and 2(b)], the emittance of the witness bunch is preserved upon propagation and acceleration [4]. However, in the case of an ultradense (drive or witness) electron bunch with n b ) n e , the electric field of the bunch is so intense that the cold ions ar...

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Section: Fig 1 (A)mentioning

confidence: 99%

Effect of temperature on ion motion in future plasma wakefield accelerators

Gholizadeh

Katsouleas

Huang

et al. 2011

Phys. Rev. ST Accel. Beams

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“…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.…”

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confidence: 99%

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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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“…A strategy to mitigate emittance growth based on the use of an adiabatic matching section at the entrance of the PA stage was described in Ref. [17]. Here we propose to longitudinally tailor the transverse bunch profile (and phase space) in such a way that, even though ion motion is enabled and the transverse wake is perturbed, the bunch transverse distribution at each longitudinal location is an equilibrium solution (i.e., the bunch properties do not evolve), and so the bunch remains matched at all times.…”

Section: Equilibrium Bunch Distributions Enabling Ion Motion Withomentioning

confidence: 99%

“…[17], the emittance growth problem was addressed by considering an adiabatic matching section, located at the entrance of the PA, consisting of a short plasma section with a decreasing ion mass to allow for the beam to remain matched to the focusing wakefield.…”

Section: Introductionmentioning

confidence: 99%

Emittance preservation in plasma-based accelerators with ion motion

Benedetti

Schroeder

Esarey

et al. 2017

Phys. Rev. Accel. Beams

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In a plasma-accelerator-based linear collider, the density of matched, low-emittance, high-energy particle bunches required for collider applications can be orders of magnitude above the background ion density, leading to ion motion, perturbation of the focusing fields, and, hence, to beam emittance growth. By analyzing the response of the background ions to an ultrahigh density beam, analytical expressions, valid for nonrelativistic ion motion, are derived for the transverse wakefield and for the final (i.e., after saturation) bunch emittance. Analytical results are validated against numerical modeling. Initial beam distributions are derived that are equilibrium solutions, which require head-to-tail bunch shaping, enabling emittance preservation with ion motion.

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Preservation of Beam Emittance in the Presence of Ion Motion in Future High-Energy Plasma-Wakefield-Based Colliders

Cited by 31 publications

References 16 publications

Effect of temperature on ion motion in future plasma wakefield accelerators

Effect of temperature on ion motion in future plasma wakefield accelerators

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

Emittance preservation in plasma-based accelerators with ion motion

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