Generation of intense THz pulses using ultra-short, high-brightness electron bunches Jom Luiten 8 Oct 2009 John Adams accelerator institute 1
Coherence & Quantum Technology (CQT) Willem Op ‘t Root – PhD student Technical support: Peter Smorenburg – PhD student Bas van der Geer – Pulsar Physics (GPT) Eddy Rietman Ad Kemper Marieke de Loos – Pulsar Physics (GPT) Harry van Doorn Marnix van der Wiel – former group leader NL Foundation for Fundamental Research on Matter 8 Oct 2009 John Adams accelerator institute 2
Outline Part I: RF photogun • technology • ultra-short bunches 8 Oct 2009 John Adams accelerator institute 3
Outline Part I: RF photogun Part II: THz generation • technology • free-space CTR THz • ultra-short bunches • THz plasmons on a wire 8 Oct 2009 John Adams accelerator institute 4
Part I: RF photogun 8 Oct 2009 John Adams accelerator institute 5
RF photoguns: the brightest pulsed electron sources... • U = 3-5 MeV • Q = 0.1-1 nC I = 0.1-1 kA • τ ≤ 1 ps • ε n ≤ 1 mm·mrad Injector X-FEL... SLAC, DESY, ... 8 Oct 2009 John Adams accelerator institute 6
RF photoguns: the brightest pulsed electron sources... • U = 3-5 MeV • Q = 0.1-1 nC I = 0.1-1 kA • τ ≤ 1 ps • ε n ≤ 1 mm·mrad ...injector LWA... TU/e, Strathclyde, EuroLeap... 8 Oct 2009 John Adams accelerator institute 7
RF photoguns: the brightest pulsed electron sources... • U = 3-5 MeV • Q = 0.1-1 nC I = 0.1-1 kA • τ ≤ 1 ps • ε n ≤ 1 mm·mrad ...ultrafast electron diffraction... TU/e, UCLA, BNL, ... 200 nm Ti foil, Musumeci et al., UCLA 8 Oct 2009 John Adams accelerator institute 8
RF photoguns: the brightest pulsed electron sources... • U = 3-5 MeV • Q = 0.1-1 nC I = 0.1-1 kA • τ ≤ 1 ps • ε n ≤ 1 mm·mrad ... intense THz pulses. 8 Oct 2009 John Adams accelerator institute 9
RF photoguns: the brightest pulsed electron sources... Pulsed laser photoemission... λ /2 3 GHz ( λ =10 cm) resonant cavity 8 Oct 2009 John Adams accelerator institute 10
RF photoguns: the brightest pulsed electron sources... ...and RF acceleration. RF field strength ~100 MV/m, limited by vacuum breakdown λ /2 3 GHz ( λ =10 cm) resonant cavity 8 Oct 2009 John Adams accelerator institute 11
RF photoguns: the brightest pulsed electron sources... ...and RF acceleration. RF field strength ~100 MV/m, limited by vacuum breakdown λ /2 3 GHz ( λ =10 cm) resonant cavity 8 Oct 2009 John Adams accelerator institute 12
RF photoguns: the brightest pulsed electron sources... ...and RF acceleration. RF field strength ~100 MV/m, limited by vacuum breakdown λ /2 3 GHz ( λ =10 cm) resonant cavity 8 Oct 2009 John Adams accelerator institute 13
RF photoguns: the brightest pulsed electron sources... ATF-BNL-UCLA 1.6 cell photogun 8 Oct 2009 John Adams accelerator institute 14
TU/e approach: Emittance growth due to non-linear acceleration fields: • full cylindrical symmetry single-diamond turning • no tuning plungers • on-axis RF coupling Emittance growth due to space-charge fields: • space-charge blow-out at cathode • ideally: ellipsoidal bunches • 100 fs photoemission of 100 pC in 100 MV/m 8 Oct 2009 John Adams accelerator institute 15
Laser Shaped fs laser pulse... intensity y x 1 mm surface charge density distribution: ( ) σ = σ − 2 ( ) 1 r r R 0 Luiten et al., PRL 93 , 094802 (2004) 8 Oct 2009 John Adams accelerator institute 16
...evolution into uniform ellipsoid . → linear & reversible Coulomb expansion 1 mm Luiten et al., PRL 93 , 094802 (2004) 8 Oct 2009 John Adams accelerator institute 17
2nd generation TU/e gun: • Elliptical irises – Highest field strength on cathode; • Cavity parts are clamped, not braized – Easily replaced; • Copper cavity inside stainless vacuum can. 8 Oct 2009 John Adams accelerator institute 18
2nd generation TU/e gun: Elliptical irises: Highest field strength on cathode 40 30 R [mm] 20 10 0 100 50 Ez [MV/m] 0 -50 -100 0 10 20 30 40 50 60 70 80 90 100 z [mm] GPT 8 Oct 2009 John Adams accelerator institute 19
2nd generation TU/e gun: Clamped construction: cavity parts cathode plate first (half) cell second cell 8 Oct 2009 John Adams accelerator institute 20
2nd generation TU/e gun: Clamped construction: cavity parts single-diamond turning 8 Oct 2009 John Adams accelerator institute 21
2nd generation TU/e gun: Clamped construction: assembled cavity parts 8 Oct 2009 John Adams accelerator institute 22
2nd generation TU/e gun: Clamped construction: cavity inside stainless steel vacuum can 8 Oct 2009 John Adams accelerator institute 23
2nd generation TU/e gun: Assembled gun: Solenoid around cavity 8 Oct 2009 John Adams accelerator institute 24
2nd generation TU/e gun: Entire setup: gun & beamline 8 Oct 2009 John Adams accelerator institute 25
2nd generation TU/e gun: RF characterization: resonances f 0 =2.9980 GHz π -mode f 0 =2.9918 GHz 0-mode 8 Oct 2009 John Adams accelerator institute 26
2nd generation TU/e gun: RF characterization: on axis field profile 1 Superfish ♦ measured 0,8 E/Emax 0,6 0,4 0,2 0 0 20 40 60 80 100 z (mm) 8 Oct 2009 John Adams accelerator institute 27
2nd generation TU/e gun: RF characterization: on axis field profile 1 Superfish ♦ measured 0,8 --- Superfish E/Emax 0,6 radius ±5 μ m 0,4 0,2 0 0 20 40 60 80 100 z (mm) 8 Oct 2009 John Adams accelerator institute 28
2nd generation TU/e gun: High power RF commissioning: • 80 MV/m at cathode (after one month of training) • Still occasional breakdown • 3 MeV electrons • QE ≈ 3·10 -5 → bunch charge Q max ≈ 300 pC Conclusion: clamping is OK! 8 Oct 2009 John Adams accelerator institute 29
Emittance measurement: Quadrupole scan: 8 Oct 2009 John Adams accelerator institute 30
Emittance measurement: Quadrupole scan: 8 Oct 2009 John Adams accelerator institute 31
Emittance measurement: Quadrupole scan: 8 Oct 2009 John Adams accelerator institute 32
Emittance measurement: Quadrupole scan: Q = 5 pC ε n = 0.40(5) mm·mrad 8 Oct 2009 John Adams accelerator institute 33
Emittance GPT simulation: Quadrupole scan: Q = 5 pC, 10 6 particles Phase-space at focal point 1.0 500 0.5 400 stdx [micron] px [keV/c] 300 0.0 200 -0.5 ε n = 0.6 mm·mrad 100 -1.0 0.2 0.3 0.4 0.5 0.6 0.7 -1.0 -0.5 0.0 0.5 1.0 80000 fx [m] x [mm] GPT GPT 60000 Rms: 0.15 mm Count Peak fit: 0.10 mm 40000 • very good agreement 20000 • still space-charge dominated 1.7 % 1.7 % 0 -1.0 -0.5 0.0 0.5 1.0 8 Oct 2009 John Adams accelerator institute 34 x [mm] GPT
Emittance measurement: Quadrupole scan: Q = 70 pC ε n = 1. 0(1) mm·mrad 8 Oct 2009 John Adams accelerator institute 35
Bunch length measurement: Coherent Transition Radiation (CTR) 8 Oct 2009 John Adams accelerator institute 36
Bunch length measurement: Coherent Transition Radiation (CTR) Q = 70 pC τ bunch < 2 ps 8 Oct 2009 John Adams accelerator institute 37
Arrival time jitter: Coherent Transition Radiation (CTR) 20 fs jitter RF phase 8 Oct 2009 John Adams accelerator institute 38
Performance TU/e gun: • charge Q = 70 pC; peak current 35-140 A • measured bunch length τ < 2 ps; • at gun exit τ < 0.5 ps (GPT); • arrival time jitter < 20 fs; • normalized emittance ε n = 1 mm·mrad. LCLS injector (Akre et al., PRSTAB 11, 030703, 2008) • normalized emittance: ε n = 1 mm·mrad • peak current: 100 A ( 1 nC / 10 ps ) 8 Oct 2009 John Adams accelerator institute 39
Part II: THz generation 8 Oct 2009 John Adams accelerator institute 40
THz radiation "THz gap" Electronics Photonics, optics Frequency 8 Oct 2009 John Adams accelerator institute 41
THz radiation Many materials transparent: “T-rays” Medical applications: skin cancer diagnostics Security: body scan Science: charge carriers dynamics, molecular physics, imaging of biological tissues, ... 8 Oct 2009 John Adams accelerator institute 42
Single-cycle THz pulses generated by Coherent Transition Radiation (CTR) Goal: E THz = 10-100 MV/m ~ 1 ps BW > 1 THz 8 Oct 2009 John Adams accelerator institute 43
Single-cycle THz pulses generated by Coherent Transition Radiation (CTR) 8 Oct 2009 John Adams accelerator institute 44
Single-cycle THz pulses generated by Coherent Transition Radiation (CTR) • ~0.1 eV per electron • Coherent addition → ~N 2 → many μ J per bunch • bunch length 1 ps → > 1 THz bandwidth 8 Oct 2009 John Adams accelerator institute 45
Single-cycle THz pulses generated by Coherent Transition Radiation (CTR) 8 Oct 2009 John Adams accelerator institute 46
Single-cycle THz pulses CTR : radially polarized CCD A CCD B Expected signal 8 Oct 2009 John Adams accelerator institute 47
Single-cycle THz pulses generated by Coherent Transition Radiation (CTR) polarizer CCD A 8 Oct 2009 John Adams accelerator institute 48
Single-cycle THz pulses generated by Coherent Transition Radiation (CTR) polarizer CCD B 8 Oct 2009 John Adams accelerator institute 49
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