Emittance measurements of trapped electrons from a plasma wakefield accelerator

Kirby, Neil; Berry, M.; Blumenfeld, I.; Decker, F.J.; Hogan, Mark; Ischebeck, R.; Iverson, R.; Siemann, R.H.; Walz, D.; Clayton, C. E.; Huang, Chengkun; Joshi, C.; Lü, Wei; Mori, W. B.; Zhou, Miaomiao; Katsouleas, T.; Muggli, P.; Öz, E.

doi:10.1109/pac.2007.4440075

Cited by 2 publications

(7 citation statements)

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“…For [39]. The trapped electron bunches appeared with rms x sizes near the system resolution [36]. Thus, as γ increases so does the upper Similarly, the theoretical model shows there is a minimum scale for N,x ; a combination of this scale with the measured upper limit for N,x /I t results in a lower limit for I t .…”

Section: Transverse Emittance and Peak Currentmentioning

confidence: 86%

“…The lowest emittances determined by this method extended below 1 µm. Note, the trapped electrons appeared with transverse sizes near the camera resolution [36].…”

Section: Trapped Electron Divergencementioning

confidence: 97%

“…5, the spatial resolution of A1 is important. Two terms account for the resolution limit of the system: the resolution of the camera and the resolution limit from multiple Coulomb scattering in the various elements traversed by the electrons from the plasma to A1 [36]. Camera resolution is measured by imaging a back illuminated 5 µm pinhole that is located 2.5 m from the camera, just as in the experiment.…”

Section: Large Dipole Energy Spectrometermentioning

confidence: 99%

“…As will be shown later, ionization of helium in the buffer gas is an important effect to consider in this propagation; however, the first step in the analysis is to consider just the focusing forces from the lithium ions [36]. While exiting the plasma, the electrons traverse a roll-off in lithium density which creates a roll-off in the focusing forces of the plasma.…”

Section: Trapped Electron Divergencementioning

confidence: 99%

“…So far the propagation has only included the focusing forces of the Gaussian density roll-off in lithium ions, ignoring the effects of helium ionization [36]. Under this assumed propagation model, the trapped electrons appear to achieve emittances better than 1 µm with transverse sizes that are matched to the plasma.…”

Section: Trapped Electron Divergencementioning

confidence: 99%

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Properties of Trapped Electron Bunches in a Plasma Wakefield Accelerator

Kirby¹

2009

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Plasma-based accelerators use the propagation of a drive bunch through plasma to create large electric fields. Recent plasma wakefield accelerator (PWFA) experiments, carried out at the Stanford Linear Accelerator Center (SLAC), successfully doubled the energy for some of the 42 GeV drive bunch electrons in less than a meter; this feat would have required 3 km in the SLAC linac. This dissertation covers one phenomenon associated with the PWFA, electron trapping. Recently it was shown that PWFAs, operated in the nonlinear bubble regime, can trap electrons that are released by ionization inside the plasma wake and accelerate them to high energies. These trapped electrons occupy and can degrade the accelerating portion of the plasma wake, so it is important to understand their origins and how to remove them. Here, the onset of electron trapping is connected to the drive bunch properties.Additionally, the trapped electron bunches are observed with normalized transverse emittance divided by peak current, N,x /I t , below the level of 0.2 µm/kA. A theoretical model of the trapped electron emittance, developed here, indicates that the emittance scales inversely with the square root of the plasma density in the nonlinear "bubble" regime of the PWFA. This model and simulations indicate that the observed values of N,x /I t result from multi-GeV trapped electron bunches with emittances of a few µm and multi-kA peak currents. These properties make the trapped electrons a possible particle source for next generation light sources.This dissertation is organized as follows. The first chapter is an overview of the PWFA, which includes a review of the accelerating and focusing fields and a survey of the remaining issues for a plasma-based particle collider. Then, the second chapter examines the physics of electron trapping in the PWFA. The third chapter uses theory and simulations to analyze the properties of the trapped electron bunches. Chapters vi four and five present the experimental diagnostics and measurements for the trapped electrons. Next, the sixth chapter introduces suggestions for future trapped electron experiments. Then, Chapter seven contains the conclusions. In addition, there is an appendix chapter that covers a topic which is extraneous to electron trapping, but relevant to the PWFA. This chapter explores the feasibility of one idea for the production of a hollow channel plasma, which if produced could solve some of the remaining issues for a plasma-based collider.vii Acknowledgement

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Section: Transverse Emittance and Peak Currentmentioning

confidence: 86%

“…The lowest emittances determined by this method extended below 1 µm. Note, the trapped electrons appeared with transverse sizes near the camera resolution [36].…”

Section: Trapped Electron Divergencementioning

confidence: 97%

Section: Large Dipole Energy Spectrometermentioning

confidence: 99%

Section: Trapped Electron Divergencementioning

confidence: 99%

Section: Trapped Electron Divergencementioning

confidence: 99%

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Properties of Trapped Electron Bunches in a Plasma Wakefield Accelerator

Kirby¹

2009

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Emittance and Current of Electrons Trapped in a Plasma Wakefield Accelerator

Kirby¹,

Blumenfeld²,

Clayton³

et al. 2009

AIP Conference Proceedings

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Abstract. In recent experiments plasma electrons became trapped in a plasma wakefield accelerator (PWFA). The transverse size of these trapped electrons on a downstream diagnostic yields an upper limit measurement of transverse normalized emittance divided by peak current, ε N,x /I. The lowest upper limit for ε N,x /I measured in the experiment is 1.3 · 10 −10 m/A.Keywords: Electron, Trapping, Plasma Wakefield Accelerator PACS: 52.35. Py, 52.40.Mj, 41.75.Lx In this experiment, ultrarelativistic electron drive bunches field ionized neutral vapor, creating a plasma [1] and expelling the plasma electrons from the bunch axis. The ions then pulled the plasma electrons back to the bunch axis with a time scale set by the inverse of the plasma frequency, ω p = n p e 2 /(mε 0 ), where n p , e, m, and ε 0 are the plasma density, the electron charge magnitude, the electron mass, and the permittivity of free space. The resulting plasma wake could accelerate some plasma electrons from rest to relativistic energies before they slipped out of the wake, trapping bunches of electrons. This process can produce electron bunches with small emittance and high peak current. Direct measurements of the trapped electron emittance and peak current were not possible; however, the ratio of these quantities is experimentally accessible. This paper presents a measurement of transverse emittance divided by peak current.This experiment took place in the Final Focus Test Beam facility, located at the end of the Stanford Linear Accelerator Center linac. Let the quantities x and y represent the transverse coordinates and z denotes the longitudinal coordinate. Electron drive bunches of 3 nC and 42 GeV with normalized emittances of ε N,x = 60 µm and ε N,y = 7 µm, transverse sizes of 10 µm, and longitudinal bunch lengths of tens of µm entered a heat-pipe oven [2]. This heat-pipe oven confined lithium vapors of density, n p , equal to 2.7 · 10 23 m −3 with a helium buffer gas. The lithium density was uniform in the middle of the oven, had a full width at half max (fwhm) length of 85 cm, and had Gaussian roll-offs at its up and downstream edges:, where z − z 0 denotes the distance from the edge of the uniform region and σ L = 3.97 cm. Figure 1 displays the partial pressures of the two gas species in the heat-pipe oven. Beryllium windows of thickness 50 and 75 µm were located up and downstream of

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Emittance measurements of trapped electrons from a plasma wakefield accelerator

Cited by 2 publications

References 9 publications

Properties of Trapped Electron Bunches in a Plasma Wakefield Accelerator

Properties of Trapped Electron Bunches in a Plasma Wakefield Accelerator

Emittance and Current of Electrons Trapped in a Plasma Wakefield Accelerator

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