AWAKE, the Advanced Proton Driven Plasma Wakefield Accelera9on Experiment at CERN

Transcription

1 AWAKE, the Advanced Proton Driven Plasma Wakefield Accelera9on Experiment at CERN Ulrik Uggerhøj many slides from a presenta0on at PSI by Edda Gschwendtner, CERN

2 Main Driver for PWFA: Linear Collider è Build a High energy collider at TeV range! Linear collider based on RF cavi9es: Accelera9ng field limited to <100 MV/m Several tens of kilometers for future linear colliders For example ILC: 31km long 500 GeV electrons 16 superconduc9ng accelera9ng cavi9es made of pure niobium Gradient of 35 MV/m ILC Linear collider based on plasma wakefield accelera9on: Plasma can sustain up to three orders of magnitude higher gradient à Much shorter linear colliders! 2

3 Main Driver for PWFA research: Linear Collider Aim to reach accelerators in the TeV range! GeV km 3 8 * J.P.Delahaye, E. Adli et al., White Paper input to US Snowmass Process 2013

4 Mo9va9on Cavi9es vs. Plasma ILC Cavity: 35 MV/m 1000 mm Plasma cell: 35 GV/m è 35 MV/mm!! 1 mm (Not to scale!) 4

5 Plasma Wakefield Accelera9on Principle p = 2 k p =1mm cm 3 n p Ez Plasma wave is excited by a rela9vis9c par9cle bunch. Space charge of drive beam displaces plasma electrons. Plasma electrons awracted by plasma ions, and rush back on axis. à decelera9on à accelera9on X, mm 0.7 a) E Z, GeV/m 3 b) n e, cm 3 2 Size of the accelera9ng structure is set by the plasma density: à plasma wavelength λ p =1mm, (for typical plasma density of n p = cm 3 ) à Produce mini cavi9es inside the plasma cell à Gradients at several GV/m c) d) Z, mm Z, mm 0 5

6 What are the invariants? A liwle digression Mo9on perpendicular to an electric field: Recall:

7 Plasma wakefields Transverse focusing forces: Lead to values for realistic parameters:

8 ILC / CLIC Similar situa9ons Blankenbecler, Drell (PRD 36, 277 (1987), Quantum treatment of beamstrahlung: Pulse transforms into a very long narrow string of N charges. Bunch size: μm 3, par9cles Density: Å 3, 0.6 Å 3 (at IP) Density: 0.05 Å 3, of Z = 14 Si crystal

9 Electron Beam Driven PWA Electric fields can accelerate, decelerate, focus, defocus Ez electron beam Test key performance parameters for the witness bunch accelera9on: Gradient Efficiency Energy spread EmiWance è Experimental results show success of PWFA and its research SLAC beam: 42 GeV, 10 Hz, σ x = 10µm, 50 fs 9

10 SLAC FACET: Latest Results High Efficiency accelera9on of an electron beam in a plasma wakefield accelerator M. Litos et al., doi, Nature, 6 Nov 2014, /nature Drive and witness beam: GeV, D and W separated by 160 µm 1.02nC (D), 0.78nC (W) Laser ionized Lithium vapour plasma cell: 36 cm long, Density: cm 3, λ π = 200 µm Result Total efficiency is <29.1%> with a maximum of 50%. Final energy spread of 0.7 % (2% average) Electric field in plasma wake is loaded by presence of trailing bunch Allows efficient energy extrac9on from the plasma wake 10

11 Laser or Electron Beam Driven PWA There is a limit to the energy gain of a witness bunch in the plasma: Δ E witness = R E drive R= 2 N witness /N drive à for N witness << N drive è Δ E witness = 2 E drive è Energy gain of the witness beam can never be higher than 2 9mes the drive beam è Today s electron beams usually < 100 J level. To reach TeV scale with electron driven PWA: also need several stages, but need to have rela9ve 9ming in 10 s of fs range many stages effec9ve gradient reduced because of long sec9ons between accelera9ng elements. Plasma cell Plasma cell Plasma cell Plasma cell Plasma cell Plasma cell Witness beam Drive beam: electron/laser 11

12 Proton beams carry much higher energy: 19kJ for 3E11 protons at 400 GeV/c. Proton Beam Driven PWA Drives wakefields over much longer plasma length, only 1 plasma stage needed. Simula9ons show that it is possible to gain 600 GeV in a single passage through a 450 m long plasma using a 1 TeV p+ bunch driver of 10e11 protons and an rms bunch length of 100 µm. A. Caldwell, K. Lotov, Physics of Plasma, 18, (2011) Plasma cell Witness beam Drive beam: protons Protons are posi9vely charged. They don t blow out the plasma electrons, they suck them in. The general accelera9on mechanism is similar. 12

13 Beam Driven Wakefield Accelera9on: Landscape Facility AWAKE SLAC FACET DESY Zeuthen DESY FLASH Forward Brookhaven ATF Where CERN, Geneva, Switzerland SLAC, Stanford, USA PITZ, DESY, Zeuthen, Germany DESY, Hamburg, Germany BNL, Brookhaven, USA Drive (D) beam 400 GeV protons 20 GeV electrons and positrons 20 MeV electron beam X ray FEL type electron beam 1 GeV 60 MeV electrons Witness (W) beam Start End Goal Externally injected electron beam (PHIN 15 MeV) Two bunch formed with mask (e /e + and e e + bunches) No witness (W) beam, only D beam from RF gun. D + W in FEL bunch. Or independent W bunch (LWFA). Several bunches, D+W formed with mask Sept 2016 Use for future high energy e /e+ collider. Study Self Modula9on Instability (SMI). Accelerate externally injected electrons. Demonstrate scalability of accelera9on scheme. Accelera9on of witness bunch with high quality and efficiency Accelera9on of positrons FACET II proposal for 2018 opera9on 2015 ~2017 Study Self Modula9on Instability (SMI) On going Applica9on (mostly) for x ray FEL Energy doubling of Flash beam energy Upgrade stage: use 2 GeV FEL D beam Study quasi nonlinear PWFA regime. Study PWFA driven by mul9ple bunches Visualisa9on with op9cal techniques 13

14 AWAKE at CERN AWAKE in CNGS Facility (CERN Neutrinos to Gran Sasso) CNGS physics program finished in 2012 CNGS approved for 5 years: Expect ~8 tau neutrinos, 4 published so far Running underground facility Desired beam parameters è adequate site for AWAKE CERN produce muon neutrinos 732km measure tau neutrinos Gran Sasso 14

15 CERN SPS Proton Beam SMI Instability Ez Drive beam for AWAKE: 400 GeV/c SPS proton beam SPS longitudinal beam size (σ z = 12 cm) is much longer than plasma wavelength (λ = 1mm) è AWAKE Experiment is based on self modula9on instability Modulate long bunch to produce a series of micro bunches in a plasma with a spacing of plasma wavelength λ p. à Strong self modula9on effect of proton beam due to transverse wakefield in plasma à Starts from any perturba9on and grows exponen9ally un9l fully modulated and saturated. è Immediate use of CERN SPS beam 15

16 AWAKE Advanced Proton Driven Plasma Wakefield Accelera9on Experiment Final Goal: Design high quality & high energy electron accelerator based on acquired knowledge. Proof of Principle Accelerator R&D experiment at CERN First proton driven wakefield experiment worldwide Study the Self Modula9on Instability Demonstra9on of high gradient accelera9on of electrons Approved in 2013 First beam expected in 2016 AWAKE Collabora9on: 16 Ins9tutes world wide Spokesperson: Allen Caldwell, MPI Munich Deputy Spokesperson: MaWhew Wing, UCL Physics and Experiment Coordinator: Patric Muggli, MPI Munich Simula9on Coordinator: Konstan9n Lotov, BINP Technical Coordinator and CERN AWAKE Project Leader: Edda Gschwendtner, CERN Deputy: Chiara Bracco, CERN Vancouver Glasgow Manchester London Lisbon Oslo Hamburg, Greifswald Dusseldorf Munich CERN Novosibirsk 16

17 AWAKE Experimental Program Understand the physics of self modula9on instability processes in plasma. Probe the accelera9ng wakefields with externally injected electrons. Laser SPS protons RF gun p e SMI 10m Accelera9on Proton diagnos9cs BTV,OTR, CTR e spectrometer Laser dump Proton beam dump Plasma cell à Rb vapour source Proton beam à drives the plasma wakefield + undergoes self modula9on instability. à LHC type proton beam, 400 GeV/c, 3E11 protons/bunch, 400ps long Laser beam: à ionizes the plasma + seeds the self modula9on instability of the proton beam. à 4.5TW laser, 100fs Diagnos9cs à BTVs, OTR, CTR Electron source and beam à Witness beam to surf on the wakefield and get accelerated à 16 MeV/c, 1.29 electrons/ bunch, 4ps long Electron spectrometer system 17

18 AWAKE Experimental Facility SPS protons Laser RF gun p e SMI 10m Accelera9on Proton diagnos9cs BTV,OTR, CTR e spectrometer Laser dump Proton beam dump electron source, klystron laser room proton beam protons plasma cell diagnos9cs AWAKE experiment 18

19 Planning Proton beam line Experimental area Installa9on Study, Design, Procurement, Component prepara9on Modifica9on, Civil Engineering and installa9on Study, Design, Procurement, Component prepara9on Commissioning Data taking Phase 1 LS2 18 months Data taking Electron source and beam line Studies, design Fabrica9on Installa9on Commissio ning Phase 2 AWAKE was approved in August st Phase: First proton and laser beam in nd Phase: first electron beam in Physics program for 3 4 years Run scenario Nominal Number of run periods/year 4 Length of run period 2 weeks Total number of beam shots/year (100% efficiency) Total number of protons/year Ini9al experimental program p 3 4 years 19

20 Summary AWAKE is proof of principle accelerator R&D experiment currently being built at CERN. First proton driven wakefield accelera9on experiment The experiment opens a pathway towards plasma based TeV lepton collider. 400 GeV SPS proton beam as drive beam MeV electrons as witness beam 2 TW laser beam for plasma ioniza9on and seeding of the SMI AWAKE program Study the physics of self modula9on instability as a func9on of plasma and proton beam parameters (1 st Phase, 2016) Probe the longitudinal accelera9ng wakefields with externally injected electrons (2 nd Phase, ) Develop long scalable and uniform plasma cells, produc9on of shorter electron and proton bunches (2020) 20

21 1. Drive Beam: CERN Accelerator Scheme In 2011: protons to LHC protons to CERN s Non LHC Experiments and Test Facili9es LHC: 7 TeV SPS: 400/450 GeV CNGS BOOSTER: 1.4 GeV PS: 24 GeV 21

22 2a. Plasma Source: Different Types Metal Vapor Source (Li, Cs, Rb) à SLAC experiments Very uniform, very well known Ioniza9on with laser. Scaling to long lengths? Discharge plasma source Simple, scalable Uniformity? Density? Helicon source Scalable, density recently achieved. Uniformity? 22

23 2a. Plasma Source: Rubidium Vapor Source Density adjustable from cm 3 10 m long, 4 cm diameter Plasma formed by field ioniza9on of Rb Ioniza9on poten9al Φ Rb = 4.177eV above intensity threshold (I ioniz = 1.7 x W/cm 2 ) 100% is ionized. Plasma density = vapor density System is oil heated: 150 to 200 C à keep temperature uniformity à Keep density uniformity Required: Δn/n = ΔT/T

24 4. Witness Beam: Beam Characteris9cs à Op9mal electron energy is MeV Electron energy = wakefield phase velocity at self modula9on stage. à Electron bunch length: Should be small to be in phase with high field region. à Electron beam should have small enough size and angular divergence to fit into high capture efficiency region. à Electron beam intensity: get good signal in diagnos9cs! Electron beam Baseline Range for upgrade phase Momentum 16 MeV/c MeV Electrons/bunch (bunch charge) 1.25 E E9 Bunch charge 0.2 nc nc Bunch length σ z =4ps (1.2mm) ps Bunch size at focus σ * x,y = 250 µm mm Normalized emiwance (r.m.s.) 2 mm mrad mm mrad Rela9ve energy spread Δp/p = 0.5% <0.5% 24