KE opportunity: Compact radiation source based on a laser-plasma wakefield accelerator

Transcription

1 KE opportunity: Compact radiation source based on a laser-plasma wakefield accelerator Dino Jaroszynski University of Strathclyde dino@phys.strath.ac.uk

2 Outline of talk Large and small accelerators + high power lasers Laser driven wakes Ultra-short bunch electron production using wakefield accelerators The Advanced Laser Plasma High-energy Accelerators towards X-rays (Alpha-X) project Synchrotron, free-electron laser and betatron sources Conclusion

3 Synchrotrons and light sources: tools for scientists and industrialists Synchrotron size and cost determined by accelerator technology Diamond DESY undulator undulator synchrotron

4 Wakefield accelerator UCLA: Tajima + Dawson 1979 The ponderomotive force is given by the gradient of the light pressure The electrons are pushed out of high intensity regions by the ponderomotive force Phase velocity gives 2 2 e de 2 d 2 ( 2 ) Wake behind optical pulse travels and laser group velocity vg ω = c 1 ω Fpond 2 p 2 0 = P Fpond = = mc a λp 4mω dz dz γ φ = ω0 ω p 3-D plasma wave Critical density for 800 nm: cm

5 Particles accelerated by electrostatic fields of plasma waves Accelerators: Surf a 10 s cm long microwave conventional technology δ n ω δn n δn γ = γ = = 2 p 0 p c p 2 φ 2 2 n p ω p np np np 2 Surf a 10 s μm long plasma wave laser-plasma technology

6 Wakefield acceleration λ p 2 p 2 Dephasing length: = where the phase velocity gives L d λ γ φ π ω0 γ φ = ω p

7 ALPHA-X UK consortium: Injectors (conventional and all-optical) Laser-plasma wake-field acceleration Plasma capillaries Free-electron laser (FEL) Beam transport systems Diagnostics 6.5 MeV photo-injector 1.2 J 30 fs 800 nm wakefield accelerator beam transport plasma filled capillary GeV beam transport γ = period undulator FEL or synchrotron source IR to VUV SASE or SACSE optical selfinjection λ u λ = γ 2γ = ( 1 a u ) 2 7 laser λ = 100 μm 2 nm Advanced Laser-Plasma High-energy Accelerators towards X-rays consortium

8 ALPHA-X project Strathclyde: Riju Issac, Gregory Vieux, Enrico Brunetti, Bernhard Ersfeld, Albert Reitsma, Ranaul Islam, David Clark, Tom McCanny, Seth Brussaard, Jinhai Sun, Jordan Gallacher, Richard Shanks, Maria Pia Anania, Sijia Chen, Silvia Cipiccia, John Farmer, Xue Yang Lancaster U., Cockcroft Institute / STFC - ASTeC, STFC RAL CLF, U. St. Andrews, U. Dundee, U. Abertay-Dundee, Imperial College IST Lisbon, U. Paris-Sud - LPGP, Pulsar Physics, UTA, CAS, LBNL FSU Jena, U. Stellenbosch, U. Oxford, LAL, U. Twente, TUE, Supported by University of Strathclyde, RCUK, EPSRC, E.U. Laserlab and EuroLEAP

9 TOPS laser: Hz λ = 800 nm LASER IN 30 fs PLASMA ACCELERATOR ALPHA-X beam line at Strathclyde ELECTRON ENERGY SPECTROMETER UNDULATOR BENDING MAGNET RADIATION SPECTROMETER m

10 Modelling of Laser Wakefield Acceleration Strathclyde laser pulse envelope electrostatic wakefield bunch density energy density of wakefield z-vgt (units of λp) laser pulse envelope dynamics: ponderomotive wakefield excitation, electron bunch acceleration, phase slippage, beam loading

11 ALPHA-X all-optical injection experiments on ASTRA 800 nm mj 40 fs F/16 mirror Wcm -2 in 25 mm spot a 0 ~ n e ~ 2 x cm -3 n δ n c p γ = 2 = 175 n n p p Imperial/RAL/Strathclyde S. Mangles et al. Nature 2004 τ ~ 5 10 fs I ~ 5 ka δγ γ 3% Few fs duration electron bunch

12 LBNL - Oxford campaign (ALPHA-X) team: GeV beams from capillary W. Leemans, S. Hooker, (Nature Physics 2006) Oxford & Berkeley Pre-formed plasma channels Spence & Hooker (PRE 2001)

13 1 GeV beams Oxford & Berkeley Acceleration to 1 GeV in 33 mm long pre-formed plasma channels 5% shot-to-shot fluctuations in mean energy E = 0.48 GeV±6% and an r.m.s. spread <5%. 12TW (73fs) - 18TW (40fs) 50 pc 30 pc W. Leemans, S.Hooker, (Nature Physics 2006) E = (0.50 +/-0.02) GeV ΔE = 5.6% r.m.s Δθ = 2.0 mrad r.m.s. Q = 50 pc Laser ~ 1 J n δ n c p γ max = 2 = 1750 n n p p

14 Wakefield undulator experiment Electron and optical spectra Strathclyde, Jena & Stellenbosch Jena: JETI laser H-P Schlenvoigt,.. D.A. Jaroszynski: Nature Physics 2008

15 ALPHA-X: Measured electron and radiation spectra σγ/γ=2% Jena: JETI laser N ph ~300,000 photons Q = MeV ϕ = 2 mrad δλ/λ = 55 nm (FWHM) Visible: B = 6.5x10 16 ph/sec/mrad²/mm²/0.1%bw ( ) Strathclyde, Jena & Stellenbosch δγ / γ < 0.5 δλ / λ ( ϑ γ ) 1/ N measured u 1/2 H-P Schlenvoigt,.. D.A. Jaroszynski: Nature Physics 2008 Sets an upper limit to total energy spread ( 1%) and emittance (1 π mm mrad)

16 Photon Flux [Photons/0.1% BW] Predicted Synchrotron radiation and SASE FEL for Strathclyde undulator 3x x x SASE FEL matched beam SASE FEL Photon Flux [Photons/0.1% BW] Peak Brilliance: 2.97 x photons/sec/mrad²/mm²/0.1%b.w. 1.5x x x synchrotron radiation Photon flux into 200 μrad Photon energy [ev] σ γ /γ = 0.1% I pk ε n N = 200 u τ e < 10 fs = 12 ka = 1 πmm mrad Synchrotron: Photon energy [ev] Peak Brilliance B = 3 x ph./sec/mrad 2 /mm 2 /0.1% b.w. for 10 Hz Average brilliance B = 2.5 x With laser improvements: 1 khz: rep rate: average brilliance B >10 13 FEL: B >10 6 times higher

17 Predicted SASE FEL Power growth E = 1 GeV Q = 100 pc 6.3 x coherent photons per pulse I pk = 30 ka ε n = 1 π mm mrad δγ/γ = 0.1% β = 0.5 m ρ = E ph = 422 ev B pk = 6 x phot/sec/mm 2 /mrad 2 /0.1% BW

18 Synchrotron radiation from an ion channel wiggler: betatron radiation Wiggler motion electron deflection angle a~(p x /p z ) is much larger than the angular spread of the radiation ϑ=(1/γ) γ >> a u >> 1 Ω=1/γ deflection angle a u /γ Only when k & p point in the same direction do we get a radiation contribution. Spectrum rich in harmonics peaking at crit 8 2 Radiation rate W γ therefore only emission at dephasing length h 3a 3 u Ld

19 X-ray generation in a plasma wake Strong radial forces cause synchrotron or betatron oscillations of electron beam Restoring force given by Gauss law: Oscillation at the betatron frequency: 1 F = m r 2 ω = b 2 ωp ω p 2γ e Emitted synchrotron radiation viewed in the lab frame h harmonic number h crit - maximum intensity at harmonic Undulator/wiggler deflection parameter 2 2 hλβ au 2 hπ c au 2 λh = 1 ( ) 1 ( ) γeϕ = γ 3/2 + + eϕ 2γe 2 ωpγe 2 h crit a 3a 8 3 u = γ k r = u e β e 2γ e π r e λ p

20 Betatron radiation: simulations for capillary a = γ k r = u e β e 2γ e π r e λ p n crit 3a 8 3 u Ω few mrad and 10 9 x-ray photons

21 Where do we stand with plasmawakefield accelerator based sources brilliance of a wakefield based incoherent radiation source figure from

22 Synchrotron, betatron and FEL radiation peak brilliance λ u ε n τ e Q I I(k) ~ I 0 (k)(n+n(n-1)f(k)) = 1.5 cm = 1 π mm mrad = 10 fs = pc = 25 ka betatron source FEL = spontaneous emission x 10 7 ALPHA-X ideal 1GeV bunch δγ/γ < 1% FEL: Brilliance 5 7 orders of magnitude larger

23 The Scottish Centre for the Application of Plasma based Accelerators: SCAPA A SUPA initiative to develop and apply ultracompact accelerators and radiation sources

24 Conclusions Laser driven plasma waves are a useful way of accelerating charged particles and producing a compact radiation source: times smaller than conventional sources Some very good properties: sub 10 fs electron bunches potentially shorter (< 1 fs?) and high peak current (up to 35 ka?), ε n < 1 π mm mrad, δγ/γ < 1%?. Slice values important for FEL - potentially 10 times better. Wide energy range, wide wavelength range: THz x-ray Good candidate for FEL coherence & tuneability Betatron radiation towards fs duration gamma rays Still in R&D stage need a few years to show potential Challenges: rep rate, stability, energy spread and emittance, higher charge and shorter bunch length, beam transport Synchronised with laser can combine radiation, particles (electrons, protons, ions), intrinsic synchronisation Compact light source for every university or 5 th Generation light source?

25 FIN Thank you