P. San Miguel Clavería ( presented by S. Corde)

Gamma-ray radiation in beam-plasma interaction as a diagnostics for emittancegrowth in PWFA and for beamfilamentationinstabilities P. San Miguel Clavería (presented by S. Corde) Sep 16, 2019, EAAC 2019

Part I – E-300 experiment: Energydoubling of narrowenergy spread witnessbunchwhilepreservingemittancewith a high pump-to-witnessenergytransferefficiency in a plasma wakefieldaccelerator • Introduction to PWFA. • Betatron radiation and emittancepreservation. Part II – E-305 experiment: Beamfilamentation and bright gamma-ray bursts • Electromagneticfilamentationinstabilities for particlebeams in plasmas • Exponentialgrowth of gamma-ray production. Experiments to startearly 2020 at the FACET-II facility

Part I: PWFA Introduction • From linear theory:(z = longitudinal direction, x,y = transverse direction) • Plasma density wave. • Wake amplitude is maximized for Plasma acc. gradient ≫ RF cavity acc. gradient (blow-out regime: ) 1

Part I: PWFA Introduction • From linear theory:(z = longitudinal direction, x,y = transverse direction) • Plasma density wave. • Wake amplitude is maximized for Plasma acc. gradient ≫ RF cavity acc. gradient (blow-out regime: ) « 9 GeVenergy gain in a beam-driven plasma wakefieldaccelerator », M Litoset al 2016 Plasma Phys. Control. Fusion 58 034017 Next milestone: Beam Quality 1

PWFA Introduction: Beamemittance Collective variables Beam parameters • Beam radius . • Beam divergence . () • Geometrical emittance: (Tracespace area occupied by the particles) • Normalized emittance: 2

PWFA Introduction: Beamemittance Collective variables Beam parameters • Beam radius . • Beam divergence . () • Geometrical emittance: (Tracespace area occupied by the particles) • Normalized emittance: Linear transverse fields Blow-out regime () . • Beam envelope oscillations at • Beam matching, . • Trace-space ellipse rotation at (unless matched). • is conserved for monoenergetic beams 2

PWFA Introduction: Beamemittance If the beam is not matched and is not monoenergetic… Chromaticity spread is one of the main contributions to the emittance growth in PWFA experiments 3

PWFA Introduction: Beamemittance If the beam is not matched and is not monoenergetic… Chromaticity spread is one of the main contributions to the emittance growth in PWFA experiments Solution: beam matching Matched beam Mismatched beam QuickPIC simulations 3

PWFA Introduction: Beamemittance If the beam is not matched and is not monoenergetic… Chromaticity spread is one of the main contributions to the emittance growth in PWFA experiments Solution: beam matching Matched beam Mismatched beam QuickPIC simulations Can we experimentally measure beam matching? 3

Betatron radiation and emittancepreservation. Radiated energy per betatron period [S. Corde, 2013, Femtosecond X-rays from Laser-Plasma Accelerators,Rev. Mod. Phys. 85, 1 (2013) arXiv:1301.5066. ] E-300 experiment Mismatched propagation Increase in radiated energy QuickPIC Simulations with FACET II beam parameters + radiation post-processing: Liénard-Wiechert potentials with synchrotron approximation 4

Betatron radiation and emittancepreservation. Plasma density profile Beam parameters at trailing waist n/n0 Drive-trailing separation Focal plane separation E-300 experiment z (cm) Scan for different trailing (and drive) focal plane position Trailing focal plane position Trailing focal plane position 5

Betatron radiation and emittancepreservation. Plasma density profile Beam parameters at trailing waist Trailing radiation n/n0 Drive-trailing separation Focal plane separation E-300 experiment z (cm) Scan for different trailing (and driving) focal plane position 5

Betatron radiation and emittancepreservation. Plasma density profile Beam parameters at trailing waist Trailing radiation Drive bunch also emits betatron radition n/n0 Drive-trailing separation Focal plane separation E-300 experiment z (cm) Scan for different trailing (and driving) focal plane position 5

Betatron radiation and emittancepreservation. Beam parameters at trailing waist Trailing radiation Drive-trailing separation Focal plane separation E-300 experiment Drive + trailing radiation Different drive-trailing matching conditions blurs out the correlation between emittance growth and radiated energy. • Solutions: • Spectral/angular information. • Statistical subtraction of drive-only radiation. 6

Betatron radiation and emittancepreservation. Radiation spectra Beam parameters at trailing waist Drive-trailing separation Focal plane separation E-300 experiment Angular distributions 400 300 • Betatron angular profiles very different between the matched trailing beam and the drive beam • Drive angular distribution: different x-y focal plane position makes cross-shaped betatron angular profiles. 300 200 (a.u.) (a.u.) 200 100 100 0 0 7

Part II: BeamFilamentationInstabilities • Transverse beam stability: • If the beam is focused towards a stable equilibrium: stable plasma-wave excitation. • If the beam undergoes transverse instabilities. Plasma return current flows inside the relativistic e- beam. FACET 10 GeV Electron Bunch Evolution during propagation over 1.5 mm of Al (1.8.1023 cm-3 ) Two inter-penetrating e- flows. E-305 experiment Large variety of EM-modes can develop from noise Weibel (CFI), Oblique, Two-stream They break up the beam. Which mode has the fastest growth rate? What is the amplitude of those modes? How do they affect the beam? 8

Part II: BeamFilamentationInstabilities and ɣ-ray generation. Gamma rays in solids Once filamentation instability has developed, beam electrons experience large electromagnetic fields, bending their trajectories, and leading to synchrotron-type gamma-ray emission. Full PIC (CALDER) simulations to model filamentation process and ɣ-ray generation. 3D Calder PIC Simulation E-305 experiment 9

Part II: BeamFilamentationInstabilities and ɣ-ray generation. Gamma rays in solids Once filamentation instability has developed, beam electrons experience large electromagnetic fields, bending their trajectories, and leading to synchrotron-type gamma-ray emission. Peak bunch density is varied keeping bunch charge and emittance constant. Full PIC (CALDER) simulations to model filamentation process and ɣ-ray generation. 3D Calder PIC Simulation E-305 experiment Conversion efficiency 2D Calder PIC Simulation with 10 GeV FACET beam 9

Summary & Conclusions PART I: Betatron radiation and emittance preservation (E-300) • Integrated betatron radiated signal can be used to assess emittance growth due to chromaticity spread in a PWFA accelerator. • Challenge: retrieve betatron radiation emitted by the trailing beam from the drive+trailing radiation PART II: Gamma-ray production during filamentation instabilities (E-305) • Gamma-ray production during beam filamentation instabilities in a beam-solid interaction can provide information about the evolution of the instability. 10

Summary & Conclusions E-300 and E-305 Collaboration: Ecole Polytechnique/LOA: P. San Miguel Claveria, O. Kononenko, G. Raj and S. CordeUCLA: C. Zhang, N. Zan, H. Fujji, K. A. Marsh, W. B. Morri, and C. Joshi SLAC: D. Storey, B. O'Shea, M. Hogan, F. Fiuza and V. Yakimenko CU Boulder: K. Huntstone, M. LitosStonybrook U: N. Vafaei-Najafabadi U. Oslo: E. Adli Tsinghua U.: W. Lu CEA: X. Davoine and L. GremilletMPIK: M. Tamburini and C. H. Keitel Thank you for your attention 11

P. San Miguel Clavería ( presented by S. Corde)