Recent simulations have shown that a high-energy proton bunch can excite
strong plasma wakefields and accelerate a bunch of electrons to the energy
frontier in a single stage of acceleration. This scheme could lead to a future
$ep$ collider using the LHC for the proton beam and a compact electron
accelerator of length 170 m, producing electrons of energy up to 100 GeV. The
parameters of such a collider are discussed as well as conceptual layouts
within the CERN accelerator complex. The physics of plasma wakefield
acceleration will also be introduced, with the AWAKE experiment, a proof of
principle demonstration of proton-driven plasma wakefield acceleration, briefly
reviewed, as well as the physics possibilities of such an $ep$ collider.Comment: 6 pages, 2 figures, to appear in the proceedings of the DIS 2014
  Workshop, 28 April - 2 May, Warsaw, Polan

Aimidula, A.

Chattopadhyay, S.

Mandry, S.

Mete, O.

Welsch, C.

Wing, M.

Xia, G.

English

arXiv

Recent simulations have shown that a high-energy proton bunch can excite strong plasma wakefields and accelerate a bunch of electrons to the energy frontier in a single stage of acceleration. This scheme could lead to a future $ep$ collider using the LHC for the proton beam and a compact electron accelerator of length 170 m, producing electrons of energy up to 100 GeV. The parameters of such a collider are discussed as well as conceptual layouts within the CERN accelerator complex. The physics of plasma wakefield acceleration will also be introduced, with the AWAKE experiment, a proof of principle demonstration of proton-driven plasma wakefield acceleration, briefly reviewed, as well as the physics possibilities of such an $ep$ collider.Recent simulations have shown that a high-energy proton bunch can excite strong plasma wakefields and accelerate a bunch of electrons to the energy frontier in a single stage of acceleration. This scheme could lead to a future $ep$ collider using the LHC for the proton beam and a compact electron accelerator of length 170 m, producing electrons of energy up to 100 GeV. The parameters of such a collider are discussed as well as conceptual layouts within the CERN accelerator complex. The physics of plasma wakefield acceleration will also be introduced, with the AWAKE experiment, a proof of principle demonstration of proton-driven plasma wakefield acceleration, briefly reviewed, as well as the physics possibilities of such an $ep$ collider

CERN Document Server

An $ep$ collider based on proton-driven plasma wakefield acceleration

Recent simulations have shown that a high-energy proton bunch can excite strong plasma wakefield and accelerate a bunch of electrons to the energy frontier in a single stage of acceleration This scheme could lead to a future ep collider using the LHC for the proton beam and a compac electron accelerator of length 170 m, producing electrons of energy up to 100 GeV. The parameter of such a collider are discussed as well as conceptual layouts within the CERN accelerato complex. The physics of plasma wakefield acceleration will also be introduced, with the AWAK experiment, a proof of principle demonstration of proton-driven plasma wakefield acceleration briefly reviewed, as well as the physics possibilities of such an ep collider

Wing, M

Xia, G

Mete, O

Aimidula, A

Welsch, C

Chattopadhyay, S

Mandry, S

University of Liverpool Repository

An ep collider based on proton-driven plasmawakefield accelerationMatthew WING∗†UCLE-mail: m.wing@ucl.ac.ukG. Xia, O. MeteUniversity of Manchester, Cockcroft InstituteA. Aimidula, C. WelschUniversity of Liverpool and Cockcroft InstituteS. ChattopadhyayUniversity of Lancaster, University of Liverpool, University of Manchester and CockcroftInstituteS. MandryMax Planck Institute for Physics, Munich and UCLRecent simulations have shown that a high-energy proton bunch can excite strong plasma wake-fields and accelerate a bunch of electrons to the energy frontier in a single stage of acceleration.This scheme could lead to a future ep collider using the LHC for the proton beam and a compactelectron accelerator of length 170 m, producing electrons of energy up to 100 GeV. The parame-ters of such a collider are discussed as well as conceptual layouts within the CERN acceleratorcomplex. The physics of plasma wakefield acceleration will also be introduced, with the AWAKEexperiment, a proof of principle demonstration of proton-driven plasma wakefield acceleration,briefly reviewed, as well as the physics possibilities of such an ep collider.XXII. International Workshop on Deep-Inelastic Scattering and Related Subjects,28 April - 2 May 2014Warsaw, Poland∗Speaker.†Also affiliated with DESY, Hamburg.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/arXiv:1407.1989v1  [physics.acc-ph]  8 Jul 2014Plasma wakefield collider Matthew WING1. IntroductionA high (TeV-scale) energy electron–proton collider would complement the proton–protonphysics programme at the LHC and the planned electron–positron physics programme at the ILC.The rich physics programme of the Large Hadron–Electron Collider (LHeC) is given in detailelsewhere [1], with only a brief discussion given here. The cross section for Higgs production atLHeC is similar to that at the ILC and so with sufficiently high luminosity (1034 cm−2 s−1), precisemeasurements of in particular the triple-gauge boson couplings can be made. Measurements ofinclusive deep inelastic scattering at these high scales should allow a full flavour decomposition ofthe parton densities in the proton and eliminate assumptions currently used as well as significantlyreducing the uncertainty on their determination, often a limiting factor in the search for exoticphysics at the LHC. As well as considering the highest energy scales, the property of saturationat the very lowest Bjorken x values will be probed. At low x, the nuclear structure is very poorlyknown and so an eA physics programme will investigate an unmeasured region for x < 0.01.In order to investigate such a wide-ranging physics programme of precision and potentialdiscovery, the LHeC would use the 7 TeV proton beam from the LHC and requires a new electronaccelerator with energies of about 60 GeV, giving a centre-of-mass energy of 1.3 TeV. To achievesuch an electron energy, the favoured solution, based on conventional acceleration using radiofrequency cavities, is a 9 km long “racetrack" complex. Such a large accelerator is needed due to thelimitation in the maximum accelerating gradient to about 100 MV m−1 due to the onset of ionisationof the metal cavities. Given this size, it is sensible to look at alternative technologies which couldsignificantly reduce the length of the electron accelerator. In these proceedings, such a technology,based on proton-driven plasma wakefield acceleration, is described. Plasma wakefield accelerationis a scheme originally proposed at the end of the 1970s [2] and is, in principle, applicable to alluses of accelerators and not just the LHeC. The use of proton-driven plasma wakefield accelerationhas applications in general to the acceleration of particles to high energies [3] and so could alsolead to a future e+e− machine of much reduced size.2. Proton-driven plasma wakefield accelerationPlasma wakefields occur when a drive beam, a laser pulse or particle beam, enters a plasmaand disturbs the free electrons. In the case of a proton beam, the free electrons are attracted to theproton bunch, accelerate towards it, overshoot, are attracted back by the region of high positivecharge density formed by the stationary ions, and hence form an oscillating system which createslarge electric fields with an accelerating gradient in the direction of the incoming beam. In the caseof a laser pulse or an electron bunch as the driver, accelerating gradients of up to 100 GV m−1 havebeen observed [4].Given the limitations of the initial energies of the laser pulse or electron beam, multiple accel-eration stages would be required in order to accelerate electrons to the scales required for energyfrontier machines. As current proton beams have up to O(100) kJ of energy, the beam can propagatefor long distances in a plasma and so act as a powerful driver of plasma wakefields. Simulationsdemonstrated that electrons could be accelerated from 10 GeV to 500 GeV in about 300 m of plasmausing a proton beam of 1 TeV [5], with a maximum accelerating gradient of 3 GV m−1.2Plasma wakefield collider Matthew WING3. The AWAKE experiment at CERNThe Advanced Wakefield (AWAKE) collaboration was formed to perform a proof-of-principleexperiment at CERN, showing that protons can drive strong plasma wakefields and that these can beused to accelerate electrons, in an initial phase, up to the GeV-scale in under 10 m [6]. The AWAKEexperiment will use the SPS beam with an energy of 400 GeV to drive the wakefields, however, instrong contrast to the concept of proton-driven plasma wakefield acceleration [5], where the beamlength considered was σz = 100 µm, the length of the SPS proton bunch is 12 cm. Given thestrength of the wakefield generated is proportional to 1/σ2z , the strength of the wakefield for theSPS beam is potentially very low. This is overcome by relying on the self-modulation instability(SMI) [8] in which transverse fields in the plasma split the long proton bunch into micro-bunches,spaced at the plasma wavelength. These higher densities act constructively to create wakefieldswith an accelerating gradient of about 1 GV/m. Witness electrons will be injected behind the protonbunch and a fraction of the electrons (up to 10% of the bunch) will be accelerated from about16 MeV to about 2 GeV in 6 m of plasma.!!!Plasma !!!!!!!!!!           7-10m, 1015 cm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igure 1: Baseline design of the AWAKE experiment: The proton bunch extracted from the SPS is injectedwith the ionising laser pulse (1). The laser pulse and the proton bunch travel together through the metalvapor cell. The co-propagating ionisation front shown in (2) provides the seeding of the SMI. Growth ofthe SMI and the resulting self-modulation of the proton bunch occurs over the first 3− 5 m of plasma (3).The modulated bunch resonantly drives wakefields over the remaining length of plasma (4). The laser pulseis dumped (5) and the proton bunch radial modulation is measured using electro-optical sampling (EOS)diagnostics (6) and optical transition radiation diagnostics (7). An RF-gun driven by a laser pulse derivedfrom the ionizing laser produces a witness electron bunch (8). The electron bunch can be side-injectedinto the wakefield after the SMI has saturated (9). Downstream of the plasma, the electron bunch energyspectrum is measured using a broad acceptance magnetic spectrometer (10).The AWAKE experiment will be housed in the CNGS facility at CERN. The general layout ofthe experiment is shown in Fig. 1. The proton beam propagates through a 10 m long plasma cell,excites the wakefield and becomes modulated by this wakefield. The short laser pulse propagatescollinearly with the proton beam and serves the dual function of creating the plasma and seedingthe SMI. The electron bunch enters the plasma cell parallel to the proton beam with an initial offsetof about 1 cm and is merged into the wakefield several metres downstream as soon as the proton3Plasma wakefield collider Matthew WINGFigure 2: A schematic of a possible ep collider using the CERN accelerator complex and the SPS protonbeam to drive plasma wakefield acceleration. Electrons would be accelerated in the wakefields and collidewith protons in the LHC.beam is modulated by the SMI. A configuration in which the electron beam is collinear with theproton beam is now considered the default mode of running and although a beam of lower energyand larger energy spread is expected, this mode will have a higher capture efficiency. Modulationof the proton beam radius is measured by electro-optical sampling (EOS) and optical and coherenttransition radiation (OTR/CTR) diagnostics. The accelerated electron beam is characterised with amagnetic spectrometer.4. An ep collider: design and issuesAssuming that the AWAKE experiment will demonstrate proton-driven plasma wakefield ac-celeration and that simulations correctly describe the physics of the process, application of theaccelerator technology can be considered for a future ep collider. Aiming for similar energies tothose proposed for the LHeC, a schematic of a possible ep collider is shown in Fig. 2. The SPSproton beam is used to drive the wakefield and accelerate a trailing electron bunch to 100 GeV in170 m of plasma. These electrons then collide with the LHC proton beam, creating an ep modewhich runs parasitically with the LHC proton–proton collisions. The basic sub-systems of theep collider are: the transfer and matching of protons to the plasma section; the electron source;the plasma section; the beam delivery and final focus; and the beam dump and/or recycling. Asthis scheme utilises existing CERN infrastructure, there is the prospect of realising a high energy,cost-effective collider.Although on the face of it this concept is very attractive, with a centre-of-mass energy of√s = 1.67 TeV achieved with the a relatively short new electron beam line, there are a number ofissues and challenges to be overcome in order to make this realisable [3].Phase slippage (or dephasing) occurs because there are particles travelling at different veloc-ities and is a limiting factor of proton-driven plasma wakefield acceleration. For a velocity of thewakefield which is the velocity of the proton driver, γp and a velocity of the accelerating electrons,4Plasma wakefield collider Matthew WINGγe, the value of γe can soon be greater than γp and so the electrons overrun the wakefield and hencedephase. The distance of the plasma accelerating section is therefore limited and for the SPS beamthis is 170 m; for the LHC beam as the driver, due to the higher energy, it is about 4 km with elec-trons accelerated to 1 TeV. Such a scheme where the LHC is the drive beam can be used for ane+e− linear collider with collisions at the TeV energy scale.The proton beam will at some point become too spread and will not be able to drive a strongwakefield. A way to compensate for this is to use external quadrupole magnets which will providetransverse focusing of the beam. Additionally, the wakefields themselves have a focusing compo-nent and this may be enough to guide the proton beam. Also given the highly relativistic nature ofthe proton beams, variations of the momentum spread will not be significant over the lengths beingconsidered.The witness electrons can scatter off the plasma ions or electrons. To assess this effect indetail, a model is being developed using a plasma simulation code and GEANT.At AWAKE, the witness bunch will be electrons, but a similar controlled acceleration ofpositrons is necessary for a future linear collider, but also preferable at an ep collider where thepossibility to change between an electron and positron beam allows the electroweak sector to beprobed. Recent simulations have shown that a bunch of positrons can also be continuously accel-erated to the TeV scale in a ∼ 1 km long plasma [9].The luminosity of an ep machine is given byLep =Pe Np γp4pi Ee εNp β ∗p,where Ee is the electron beam energy, Np is the number of particles in the proton bunch, εNp is thenormalised emittance of the proton beam, γp is the Lorentz factor and β ∗p is the beta function of theproton beam at the interaction point. The electron beam power, Pe, is given byPe = Ne Ee nb frep ,where Ne is the number of particles in the electron bunch, nb is the number of bunches in the linacpulse and frep is the repetition rate of the linac. Using the LHC beam parameters, Np = 1.15×1011,γp = 7460, β ∗p = 0.1 m, εNp = 3.5µm, and assuming electron beam parameters, Ne = 1.15×1010,Ee = 100 GeV, nb = 288 and frep = 15, gives a luminosity of,Lep = 1×1030 cm−2 s−1. This lumi-nosity value is significantly below that of conventional LHeC designs and so raises the question asto whether this can be increased, by e.g. increasing the repetition rate or decreasing the size of theelectron beam at the interaction point. Alternatively, physics at high energy, but lower luminosityshould be considered. As plasma wakefield acceleration has clearly demonstrated high accelerat-ing gradients, there are prospects for a future ep of e+e− collider at the high energy frontier, butpossibly with reduced luminosity than can be achieved with RF acceleration. Brief studies havestarted [10] considering the physics that could be investigated at such colliders, such as classicali-sation in electroweak and gravity, and should be further pursued.5. SummaryThe concept of proton-driven plasma wakefield acceleration and its application to a futureep facility has been presented. A proof-of-principle experiment, AWAKE, will start taking data5Plasma wakefield collider Matthew WINGin 2016 to demonstrate proton-driven plasma wakefield acceleration for the first time. Based onsuch a scheme, simulations show that the current CERN accelerator complex could be used togenerate a 100 GeV electron beam in about 170 m and along with the LHC proton beam have epcollisions at a centre-of-mass energy of 1.67 TeV. Many challenges remain before such a collidercould be realised, such as high luminosity and the acceleration of positrons, but further studies andthe results of the AWAKE experiment will help to address these challenges.References[1] P. Newman and A. Statso, Nature Phys. 9 (2013) 448;LHeC Study Group, J.L. Abelleira Fernandez et al., J. Phys. G 39 (2012) 075001.[2] T. Tajima and J.M. Dawson, Phys. Rev. Lett. 43 (1979) 267.[3] G. Xia et al., Nucl. Instrum. Meth. A 740 (2014) 173.[4] W.P. Leemans et al., Nature Phys. 2 (2006) 696;I. Blumenfeld et al., Nature 445 (2007) 741.[5] A. Caldwell et al., Nature Phys. 5 (2009) 363.[6] AWAKE Collaboration, R. Assmann et al., accepted by Plasma Phys. Control. Fusion,[arXiv:1401.4823];AWAKE Collaboration, Design Report, CERN-SPSC-2013-013.[7] A. Caldwell and K. Lotov, Phys. Plasmas 18 (2011) 103101.[8] N. Kumar, A. Pukhov and K. Lotov, Phys. Rev. Lett. 104 (2010) 255003.[9] L. Yi et al., Sci. Rep. 4 (2014) 4171.[10] J. Bartels et al., Particle Physics at High Energies but Low Luminosities, Contribution to EuropeanStrategy for Particle Physics, Krakow, 10–12 September, 2012.6

An ep collider based on proton-driven plasma wakefield acceleration

An $ep$ collider based on proton-driven plasma wakefield acceleration

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An $ep$ collider based on proton-driven plasma wakefield acceleration