Presentation on theme: "Vulcan Front End OPCPA System"— Presentation transcript:
1 Vulcan Front End OPCPA System Rutherford Appleton LaboratoryPump LaserStage 1 - BBOStage 3 - LBOStage 2 - BBO
2 OPCPA Test BandwidthRutherford Appleton LaboratoryBandwidth ~ nmTheoretical bandwidth for this system is > 250 nm 1053 nmIn previous tests (limited by bandwidth of optics) we demonstrated ~ 50 nmActually require just 16 nmSo far first 2 stages tested (unsaturated gain of 106)Need the 3rd stage for saturation and stability
3 Amplification in Vulcan PW SchemeRutherford Appleton LaboratoryRutherford Appleton LaboratoryOscillator5 nJ 100fs TiSaAdaptive mirror3 ex NOVA 208 amplifiers(650J ; 208 mm)X 8Stretch2 x 2 pass ;4.8 ns; 16 nm3 - stage OPCPA2 x BBO + LBOAmplification in Vulcan(85J ; 150 mm P & Si)X 450Expansion to 600 mm(19 m VSF)Compression to 500fs(1480 l/mm)Pre-amp. pump200 mJ 10 HzX 3.107Focusing on target(F3.2 OAP)Existing BuildingNew Target Area
4 The Vulcan PW Facility Computer Schematic - 2000 Rutherford Appleton LaboratoryComputer SchematicVulcan PW FacilityEnergy on target 500JPulse duration 500 fsecIntensity on target 1021 Wcm-2
5 Single electron motion Rutherford Appleton LaboratoryA single electron in the laser field exhibits a figure of eight motion due to the vxB term in the Lorentz forceF = -e(E+vxB)Twice every laser cycle, electrons are accelerated in the direction of kThe kinetic energy the electron acquires is roughly proportional to the ponderomotive potentialEkBAt 1021 Wcm-2, kT 10 MeV.
6 Self-modulated wakefield, classical wakefield and beatwave accelerators studies on the VULCAN PW facilityRutherford Appleton LaboratoryRutherford Appleton LaboratoryWave breaking of self-modulated laser wakefield demonstrated using 100 TW Vulcan facility - large energy spread.Improved electron beam quality expected with conventional laser wakefield - long focal length optics.CPA beatwave schemes also possible and will be investigated on the PW facility
7 Accelerated electrons observed at energies up to 120 MeV Rutherford Appleton LaboratoryRutherford Appleton LaboratoryIn the self modulated wakefield, stimulated Raman scatter arises from noise - generating an electron plasma wave and a down-shifted electromagnetic wave. This em wave ‘beats’ with the incident laser pulse, and the increased intensity in the beat-wave pattern enhances the plasma wave. Gradients of 1 GeV/cm have been measured. Eventually, the plasma wave breaks, generating a wide energy spread shown here.In the classical wakefield, the laser intensity and plasma density are reduced below the threshold for stimulated Raman scatter. In this case, the ponderomotive force expels electrons from the focus, but space charge requires that they returnMIK Santala et al. Phys. Rev. Lett, 86, 1227 (2001)after the laser pulse has passed. This sets up a large amplitude (GeV/cm) oscillating longitudinal electric field that can accelerate low emittance electron bunches - provided the plasma wakefield is quasi - 1 dimensional - requires PW -class lasers with long focal lengths optics.
8 Beat-wave accelerators Rutherford Appleton LaboratoryBeatwave accelerators were the first to be studied in the 1980’sTwo laser pulses of different frequencies are focused into a plasma gas. At a resonant density, the ponderomotive force of the induced beat pattern amplifies small density fluctuations arising from noise - and a large amplitude longitudinal electric field is set up.Nd glass operating at 1mm is better than CO2 (10.6mm) as higher plasma densities are required - hence larger electric fields.However, if the laser pulse duration is too long, the modulation instability limits the amplitude of the plasma waves that can be generated.With chirped pulse, picosecond laser pulses, a beat-wave pattern can be induced by spectral shaping the laser pulse. The pulse duration is sufficiently short to amplify the plasma waves before the modulational instability can grow to disrupt the process.The VULCAN PW laser will be used to study this beat-wave accelerator process.
9 Astra laser hallRutherford Appleton LaboratoryAstra is extremely compact, driving physics at up to 1019Wcm-2 at 10Hz with “table top” scaleBeam expanderThe “engine” for Astra’s high energy output is the 5J frequency doubled Nd:YAG pump laserPulse pickerTiSa rod, 16mm apertureThe final amplifier will be upgraded next year to enable full energy to be delivered to TA2
10 Astra high intensity target area Rutherford Appleton LaboratoryTarget chamberVacuum pulse compressor