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| TUPME048 | Injection of a LWFA Electron Bunch in a PWFA Driven by a Self-modulated-proton-bunch | 1470 |
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| The AWAKE experiment recently approved at CERN will study the acceleration of an externally injected electron bunch in a plasma wakefield accelerator (PWFA) driven by a self-modulated proton bunch. We study the possibility of injecting a bunch created by a laser-driven plasma wakefield accelerator (LWFA). We consider a first plasma source used for self-modulation of the drive bunch and a gas discharge source for acceleration of the collinearly injected bunch. The LWFA produces an electron bunch very short when compared to the PWFA wavelength and with relatively large current, possibly allowing for loading of the wakefields. Short length and high current lead to a small final energy spread. Co-linear injection preserves the incoming bunch quality and insures trapping and acceleration of the whole bunch. The energy of the LWFA electron bunch can easily exceed the trapping energy and can be produced over only a few millimeters gas-jet plasma driven by a laser of relatively modest power by today’s standards. We explore the parameter space suitable for this injection scheme that is more compact, simpler to implement and more suitable for injection in the mm-size accelerator structure. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME048 | |
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| TUPME049 | Hosing Suppression in the Self-modulated Wakefield Accelerator | 1473 |
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Funding: FCT-Portugal contract no EXPL/FIS-PLA/0834/1012; European Research Council contract no ERC-2010-AdG Grant 267841; by DOE contract no DE-SC0008491, DE-SC0008316, and DE-FG02- 92-ER40727. The proton driven plasma wakefield accelerator (PDPWFA) uses short LHC proton (p+) bunches (shorter than the plasma wavelength) as drivers for strongly non-linear plasma waves. Simulations showed that the PDPWFA could be used to accelerate electrons to 600 GeVs in 600 m long plasmas*. Currently available p+ bunches are much longer than the plasma wavelength, being ideal to excite intese wakefields through the self-modulation instability (SMI). An experiment is being prepared at CERN to demonstrate SMI of p+ bunches. In addition, lepton SMI experiments are also being prepared at SLAC, DESY-PITZ and RAL. The hosing instability (HI) is a competing instability that may lead to beam breakup, and needs to be controlled over the long propagation distances required for SMI growth and saturation. In this work we show that the HI can be suppressed after SMI saturation in the linear wakefield excitation regime. SMI saturation before beam-break up can be achieved by seeding SMI, and as long as the initial bunch centroid displacements are within the initial bunch transverse size. The HI suppression occurs via a plasma analogue of the BNS damping in conventional accelerators. * A. Caldwell et al, Nat. Physics Nat. Phys. 5, 363 (2009). |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME049 | |
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| TUPME050 | Electron Bunch Self-modulation in Long Plasmas at SLAC FACET | 1476 |
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Funding: This work performed in part under DOE Contract DE-AC02-76SF00515. We study the physics of self-modulation instability (SMI) of long, when compared to the wake wavelength, electron and positron bunches in pre-formed plasmas at SLAC-FACET. Self-modulation is the result of the action of focusing/defocusing transverse wakefields on the bunch radius. Self-modulation leads to observables such as overall defocusing of the bunch, periodic modulation of the bunch radius at the wake period and multi-GeV energy gain/loss by drive bunch particles. Defocusing is observed from OTR images, radial self-modulation from CTR spectra and interferometric traces and energy gain/loss from energy spectra with sub-GeV resolution. The plasma density is varied by changing the vapor density ionized by a laser/axicon system. The bunch length, radius and charge can also be varied. The SMI can be seeded using a notch collimator system. Numerical simulations indicate that seeding the SMI mitigates the hose instability. Hose instability can also be seeded, for example by using the RF deflecting cavity to impart a tilt to the incoming bunch axis. The overall experimental plan as well as the latest experimental results obtained with electron bunches will be presented. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME050 | |
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| TUPME076 | Numerical modeling of the E-209 self-modulation experiment at SLAC - FACET | 1531 |
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| The E-209 experiment currently running at SLAC- FACET used a long electron bunch (∼ 5 times the plasma wavelength) to drive plasma wakefields through the self- modulation instability. In this work we present and analyze numerical simulation results performed with the particle-in- cell (PIC) code OSIRIS. The results show that SMI saturates after 5cm of propagation in the plasma and that the maxi- mum acceleration wakefields, 15 − 20GV/m, are sustained over a 1m long plasma. Electron bunch energy loss of 4GeV was observed in the simulations. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME076 | |
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| TUPME077 | The Challenge of Interfacing the Primary Beam Lines for the AWAKE Project at CERN | 1534 |
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| The Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) at CERN foresees the simultaneous operation of a proton, a laser and an electron beam. The first stage of the experiment will consist in proving the self-modulation, in the plasma, of a long proton bunch into micro-bunches. The success of this experiment requires an almost perfect concentricity of the proton and laser beams, over the full length of the plasma cell. The complexity of integrating the laser into the proton beam line and fulfilling the strict requirements in terms of pointing precision of the proton beam at the plasma cell are described. The second stage of the experiment foresees also the injection of electron bunches to probe the accelerating wakefields driven by the proton beam. Studies were performed to evaluate the possibility of injecting the electron beam parallel and with an offset to the proton beam axis. This option would imply that protons and electrons will have to share the last few meters of a common beam line. Issues and possible solutions for this case are presented. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME077 | |
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| TUPME078 | Electron Injection Studies for the AWAKE Experiment at CERN | 1537 |
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| The AWAKE experiment recently approved at CERN will use the self-modulation instability (SMI) of long (12 cm), relativistic (400 GeV/c) proton bunches in dense plasmas to drive wakefields with accelerating gradients at the GV/m level. These accelerating gradients will be probed by externally injected electrons. In order to preserve the plasma uniformity required for the SMI the first experiments will use on-axis injection of a low energy 10-20 MeV electron beam collinearly with the proton beam. In this article we describe the physics of electron injection into the proton driven SMI wakefields. Requirements on the injected electron beam are determined and the final accelerated beam parameters are obtained via numerical simulations. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME078 | |
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| TUPME051 | Self-Injection by Trapping of Plasma Electrons Oscillating in Rising Density Gradient at Vacuum-Plasma Interface | 1479 |
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Funding: DE-SC0010012, NSF-PHY-0936278 We model the trapping of plasma electrons within the density structures excited by a propagating energy source in a rising plasma density gradient. Rising density gradient leads to spatially contiguous coupled up-chirped plasmons (d{ω2pe(x)}/{dx}>0). Therefore phase mixing between plasmons can lead to trapping until the plasmon field is high enough such that e- trajectories returning towards a longer wavelength see a trapping potential. Rising plasma density gradients are ubiquitous for confining the plasma within sources at the vacuum-plasma interfaces. Therefore trapping of plasma-e- in a rising ramp is important for acceleration diagnostics and to understand the energy dissipation from the excited plasmon train [1]. Down-ramp in density [2][3] has been used for plasma-e- trapping within the first bucket behind the driver. Here, in rising density gradient the trapping does not occur in the first plasmon bucket but in subsequent plasmon buckets behind the driver. Trapping reduces the Hamiltonian of each bucket where e- are trapped, so it is a wakefield-decay probe. Preliminary computational results for beam and laser-driven wakefield are shown. 1.Sahai, A. A. et.al.,Proc of IPAC2013, MOPAC10, Oct2013 2.Suk, H. et.al.,Phys. Rev.Lett. 86 2001 10.1103/PhysRevLett.86.1011 3.Dawson, J, Phys Rev 113 1959 10.1103/PhysRev.113.383 |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME051 | |
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| TUPME073 | A Novel Laser Ionized Rb Plasma Source for Plasma Wakefield Accelerators | 1522 |
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Funding: AWAKE collaboration A proton driven plasma wakefield accelerator* is to be conducted at CERN by the AWAKE collaboration. Externally injected electrons are accelerated in a large gradient (~GeV/m) wakefield. The large gradient is achieved by resonant formation of the wakefield by a train of micro-bunches. Transverse modulation of a long (~12 cm) proton bunch by the self modulation instability** creates these plasma wavelength size (~1 mm) micro-bunches. This resonant mechanism brings a strict requirement on the plasma density uniformity, namely % 0.2, in order for the injected electron bunch to remain in the accelerating and focusing phase of the wakefields. We describe the plasma source*** that satisfies this requirement during the beam plasma interaction. Rb vapor with ~1015 cm-3 density is confined in a 10 m long 4 cm diameter, stainless-steel tube which is heated to ~200 Co by an oil heat exchanger. The access to the source during interaction is provided by custom built fast valves. The vapor is fully tunnel ionized (first e-) by a laser forming a 2 mm diameter plasma channel. * http://awake.web.cern.ch/awake/ ** http://link.aps.org/doi/10.1103/PhysRevLett.104.255003 *** http://dx.doi.org/10.1016/j.nima.2013.10.093 |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME073 | |
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| TUPME074 | First Experiences with the PITZ Plasma Cell for Electron Beam Self-modulation Studies | 1525 |
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| The self-modulation of long particle beams in a plasma has recently gained interest in light of the ongoing preparation for the plasma wakefield acceleration experiment of the AWAKE collaboration at CERN. Instrumental to the experiment is the self-modulation of a proton beam to generate bunches short enough for producing high acceleration fields. As electron bunches are easier to handle and the underlying physics is identical, it is judicious to first gain insight into the experimental conditions of the self-modulation of long particle beams in plasma by using electron bunches before progressing to the experiment with proton bunches. The experimental demonstration of self-modulation of an electron bunch is in preparation at the Photo Injector Test facility at DESY, location Zeuthen (PITZ). In this contribution the fabrication and first experimental tests towards a Lithium plasma cell are highlighted. The distinctive feature of this plasma cell is the addition of side ports for insertion of the ionization laser beam and for diagnostics purposes. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME074 | |
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