AWAKE Phase III preparation Assoc. Prof. Erik Adli Dep. of Physics, University of Oslo, Norway AWAKE Physics and Experiments Board CERN,

Outline What is AWAKE Phase III (P3)? Preliminary list of topics to be addressed When? Schedule Next steps; how to organize the work

What is P3? What do we want to demonstrate? I)Demonstrate scalability of the AWAKE concept – injection into SMI wake (seed section plus acceleration section) – scalable length plasma sources – sustain gradient in SMI wake over long distance II)Demonstrate quality electron bunch acceleration – generate optimum electron bunch to be accelerated – preserve beam quality To me looks like we aim for two different, though related, goals : Underlying reason to push SMI concept: practically not feasible to compress SPS, LHC bunches. Must therefore rely on SMI for proton drivers based on the CERN accelerator complex. Softer goal: convince conventional accelerator community of usefulness of plasma.

Early sketch of what we talk about

What about space? What are the ultimate space limitations at the current location?

AWAKE Time Line AWAKE approved in August st Phase: First proton and laser beam in nd Phase: first electron beam in Physics program for 3 – 4 years Proton and laser beam- line Experimental area Electron source and beam-line Studies, design FabricationInstallation Commissioning Installation Modification, Civil Engineering and installation Study, Design, Procurement, Component preparation Study, Design, Procurement, Component preparation Data taking Continue data taking after LS2 Phase 1 Phase 2 Long Shutdown 2 24 months First possibility for P3 full experiments: at earliest P3 not funded. Need to provide a proposal to CERN (~ mid-2017 ?)

Main topics to be addressed Parameter choice. Based on a first application ? Further understanding of SMI Understand ideal injection electron bunch parameters Electron injector development Plasma source development Diagnostics One possible way of organizing the topics that need to be studied : Mainly technology development Mainly numerical studies I probably have forgotten many things...

Numerical and theoretical studies Experimental studies (existing, upcoming facilities) Hardware development Target date for completi on TOPIC SubtopicBINP 1/1/2019 SubsubtopicMPP (Muggli), 1/1/2019 First attempt to structure studies and work that needs to be done :

Parameter choice Applications or road maps not part of P3 study, however, we need to define what we mean by good beam quality and high gradient. To me, it makes sense to ne inspired by potential applications to define requirement on the electron application. We know e- e+ collider parameters are extremely challenging (10 nm emittances), and we can not get nowhere near them in the first rounds of experiments. eP collider application proposed : A. Caldwell and M.Wing,‘VHEeP:Averyhighenergyelectron–proton collider based on proton-driven plasma wakefield acceleration’, PoS (DIS2015) 240. Possible parameters are well studied in design conventional technology : LHeC Study Group, CERN-OPEN Proposed ILC-style linac : 140 GeV, 20 MV/m

Parameters LHeC ebeam Luminosity does not depend strongly on electron emittances : 50 um norm. for LHeC versus 20 nm norm. for CLIC Our target? Some overall parameters to aim for in P3 “target parameters” : Gradient : much larger than conventional: ~1 GV/m Emittance preservation: preserve gun (~ 1 um)? or ~ 10 um OK? Or “as good as possible?” Energy spread: 1% ? Charge, peak current: LHeC few 10e9? (Peak current depends on acceleration process) Phase III parameters: indicated by potential applications, but also constrained by acceleration process – come back to parameters later.

Numerical and theoretical studies Experimental studies (existing, upcoming facilities) Hardware development Target date for completion Target parameters for P3 demonstration 31/12/2016 Suggest level of beam quality preservation for P3 31/12/2016 Suggest accelerating gradient for P3 31/12/2016 All names and numbers in these tables are of course preliminary :

Further understanding of the SMI evolution Plasma density profile Maximum wakefield amplitude Key questions: optimum seed time, gap length, steps, tolerances on uniformity K.V.Lotov, arXiv: , "Physics of beam self-modulation in plasma wakefield accelerators”

Numerical and theoretical studies Experimental studies (existing, upcoming facilities) Hardware development Target date for completi on Further understanding of PB SMI maintain significant gradient : can a self- consistent equilibrium for SMI be reached over long distances? With one step? N steps? Gradient? optimum or necessary length to seed (one SMI growth length?) optimum gap length between the two plasma sources (p+, wakefield in gap and plasma transitions) further study of growth of transverse instabilities (example hosing) in the proton beam (asymmetric beam, 3D studies) optimum plasma densities for the two sources tolerances on longitudinal and transverse plasma density uniformity for SMI

Understand ideal injection electron bunch parameters Earlier discussed high level target parameters for application Injection parameters : optimal in terms of preserving beam quality during acceleration, preferably compatible with target parameters. Depends on physics of SMI A few parameters to consider is the electron bunch : energy spread acceleration efficiency emittance preservation How the beam loads the wake decides the performance in terms of the above. Optimal bunch length, peak current and eventual shaping is currently under study. Short bunches (small fraction of p ) V.K.Berglyd Olsen et al.,ProceedingsofIPAC2015

Effect of non-uniform plasma on beam quality Measured temporal variation in current Helicon design (from last PEB) Different sources may have different possibilities for gradients, ramps. Examples from Rb sources : Unwanted plasma density variations (longitudinal, radial, temporal) may affect beam quality Desired plasmas density shaping may be helpful (transverse matching easier, gradients for SMI evolution= Both unwanted effects (tolerances) and desired effects on beam quality need to be further explored

Numerical and theoretical studies Experimental studies (existing, upcoming facilities) Hardware development Target date for completi on Ideal injection electron bunch parameters Understanding of beam loading in the SMIS wake; field flattening versus energy extraction Understand electron bunch emittance growth factors in the SMI wake Study combination of parameters -bunch length -peak current -initial energy -spot size and emittance that will optimize acceleration with respect to target parameters Injection tolerances. Longitudinal (timing), transverse Electron beam instability studies (related to tolerances) Shaping of plasma density for optimal acceleration; longitudinal, transverse spatial, ramps, gradients Tolerances on plasma density, longitudinal, transverse spatial, ramps, gradients

Injector technology: RF gun Optimum injector parameters not yet ready: result of studies (prev topic). However, clear that bunch length must be small fraction of p and peak current high (~ kA?). Optimal injection energy is to be studied, Can the current RF gun reach these parameters? Bunch compressor may be needed? Will such a beamline fit? What about X-band injectors? “Ultimate RF- injectors”? Steffen to elaborate. “Example preliminary injection parameters”:  z ~ 40 um, I peak ~ 1 kA, E0 ~ 100 MeV Current AWAKE gun (PHIN) parameters: From K. Pepitone, S. Doebert Preliminary studies for a witness bunch injector done at SLAC, for FACET-II (Glen White)

Injector technology: LWFA Generation of a ~ 100 MeV electron beam from LWFA well proven. According to scaling laws, a ~100 MW electron beam requires about ~ 40 MW laser power, and a plsams density of ~ Example: W. Leemans, 1 GeV in 3 cm, 40 TW laser (2006). Few % energy spread reported. 30 pC, few um bunch length (?) LWFA experimental scaling. S. Mangles, CAS on PWFA. Some comparison with RF gun + Interesting experiment in itself + very short bunches possible (few um) - poor Shot-to-shot stability still an issue in LWFA -Experiment in experiment: eventual large shot- to-shot jitter may make analysis challenging (cannot measure before and after proton driven plasma simultaneously)? +/- Cost with respect to RF gun option? +/- Size of 40 TW Ti:Sa with respect to RF gun?

Other injection mechanisms Ionization injection: see Erdem’s talk. Used as main injector for P3? -Negative points : as for LWFA, but stronger? -Demonstration may be less convincing if we cannot compare parameters before plasmas with parameters after plasma Should also investigate trapping of Rb electrons. Dark current a huge problem at SLAC experiments (PEB talk on this?)

Numerical and theoretical studies Experimental studies (existing, upcoming facilities) Hardware development Target date for completi on Electron injector RF gun Study parameters of available RF gun technology Development of RF gun with optimal parameters Development of beamline, including compressor and injection into proton beam line LWFA injector Study parameters of existing LWFA Development of LWFA with optimal parameters Development of LWFA setup, including injector into the proton beam line

Plasma source development * Rubidium source : + expected to perform up to AWAKE spec + excellent uniformity (temperature) shown - requires laser ionization, costly, limited to m - ramps makes on-axis injection challenging * Helicon source : + does not need laser ionization - uniformity (spatial, temporal) needs work - relatively complex (expensive) * Discharge cell : + does not need laser ionization + cheap - uniformity needs work - needs window * Resonance Enhanced Multi-Photon Ionization scheme Helicon source tests The higher energy, the more appeal has a PWFA application. With ~1 GeV/m, ~100 m long plasma source needed for an “LHeC application”. Other considerations: Possibility to include steps and/or gradients (how much flexibility will depend on results of numerical studies) Does the source need to be continuous? What is the “cost” of staging several sources (pbeam and ebeam remains on- axis)

Numerical and theoretical studies Experimental studies (existing, upcoming facilities) Hardware development Target date for completion Plasma source development Rubidium source Verify performance during P1-P2 Study laser propagation in vapour, and other potential limitations for max. length Helicon source Discharge source Resonance Enhanced Multi-Photon Ionization scheme

Diagnostics development Electron beam key measurements: Energy spectrum – upgraded spectrometer (energy? 1 – 100 GeV?, resolution ~0.1 % ?) Strong enough dipole, enough space? Emittance – pepper pot? Butterfly for very low emittance? (< 1 um? Or ok with ~10 um?) Betatron radiation from electron beam in plasma? Pyro / bunch length measurements? Is there need to keep P1-P2 electron diagnostics after 1 st stage? Proton beam measurements: Similar to current setup? May want to keep P1-P2 proton equipment after 1 st stage, and add second set for P3? What we need to measure to demonstrate success.

List of “nice to have” developments Positron sources, positron acceleration. ( HEP applications: pP collisions, ep collisions? ) -Steffen Doebert Your favorite experiment here Not needed for a minimal P3. A P4?

Numerical and theoretical studies Experimental studies (existing, upcoming facilities) Hardware development Target date for completion Diagnostics Electron beam Upgraded energy spectrometer Emittance measurements Pyro / bunch length? Betatron radiation? Proton beam “Second set” of OTRs? Second streak camera?

Phase III time line? Proton and laser beam- line Experimental area Electron source and beam-line Studies, design FabricationInstallation Commissioning Installation Modification, Civil Engineering and installation Study, Design, Procurement, Component preparation Study, Design, Procurement, Component preparation Data taking Continue data taking after LS2 Phase 1 Phase 2 Long Shutdown 2 24 months Some open questions ? Do we want to demonstrate all the sub- goals with the same installation? -Already a great result: beam quality preservation in SMI Rb source? -When to downselect (RF/PWFA, source..) Do we need more time for P1-P2? When do we install new source(s)? I)Demonstrate scalability of the AWAKE concept – injection into SMI wake (seed section plus acceleration section) – scalable length plasma sources – sustain gradient in SMI wake over long distance II)Demonstrate quality electron bunch acceleration – generate optimum electron bunch to be accelerated – preserve beam quality Two sub goals :

Further steps How to ensure we cover all topics that needs to be addressed? – Some topics obviously already have persons working on them Present all topics that needs work in Lisbon, with more technical details Further outreach/recruitment at IPAC Follow up meetings? Something like : – “Plenary” update each coll. meeting – “Plenaries” in between? Many topics are disjoint; better smaller meetings Some form of table of topics is good, at least for our internal book keeping. Could also share table with collaboration / future collaborators Before Lisbon: need to discuss (with Mgt Board?) topics,procedures and deadlines in more detail

Main topics to be addressed Parameter choice. Based on a first application ? Further understanding of SMI Understand ideal injection electron bunch parameters Electron injector development Plasma source development Diagnostics One possible way of organizing the topics that need to be studied : Mainly technology development Mainly numerical studies

More stuff

Two-bunch PWFA vs AWAKE ~kJ proton bunches.  z >> p, low peak current (~100A), rely on SMI for large fields. AWAKE: proton driven PWFA in self-modulated regime : FACET: e- driven PWFA mainly in the blow-out regime : FACET : ~J e- bunches.  z ~ p, high peak current (~10kA), blow-out

Beam loading and efficiency, linear regime A beam “placed” inside an existing wake can add energy (field) to the wake, or extract energy (field) from the wake. The latter is called beam loading. If all the energy is transferred from the wake to the witness bunch, 100% energy efficiency, it is called full beam loading. In the linear regime, beam loading in calculated simply by superposition of the fields from the driver wake and the fields from the witness beam. Constant accelerating field, flattened field, along the witness bunch gives zero energy spread. In the linear regime, there are important trade- offs between charge, energy spread, energy efficiency and gradient. We will not discuss the details here.

Non-linear regime Can not be described by field superposition in the blow-out regime. Non-linear theory shows that an ideal-shaped witness bunch can perfectly flatten the field and a bunch can be accelerated without added energy spread. Charge ratio drive to witness may be a few. High charge witness acceleration possible. High efficiencies of energy transfer from drive bunch to witness bunch shown in PIC simulations, up to 90%. M. Tzoufras et al. Phys. Rev. Lett (simulations)

Linear regime : Blow out regime :