Possibility of THz Light Generation by using SW/TW Hybrid Photoinjector

1. Possibility of THz Light Generation by using SW/TW Hybrid Photoinjector 11/16-19, 2009, HBEB, MauiAtsushi Fukasawa, James Rosenzweig, David Schiller, UCLA, Los Angeles, CA, USA

2. Hybrid of Standing-Wave and Travelling-Wave Structures Produce short bunches without a magnetic chicane.

3. Bunchingvs. Injection Phase Peak Current Bunch Form Factor @1THz Q = 500pC Emittance • The peak current reaches as high as 2.3 kA. • The bunch form factor at 1 THz is 0.43. • The emttance will get worse by increasing bunching force.

4. Full Bunching Case Strong spike.(54 fs, FWHM) Bad around the spike. 3.7 mm.mrad Slice emittance Bunch shape t-E phase space Energy Spectrum Large energy modulation. Bunch Form Factor “Swan” shape shows strong modulation due to space charge. Strong energy modulation by the space charge.

5. Coherent Cherenkov Radiation • The mode whose vph = vb will be excited well. • b-a is most important to determine the resonant frequency. • The energy of the beam does not matter.

6. CCR Experiment at UCLA Beam: Q=200pC, st=270fs, E=10MeV Dielectric tube: er=3.8 (SiO2), L=1cm Fourier Transform a = 250 mm

7. OOPIC Simulations

8. Scaled to the beam from the hybrid photoinjector

9. Coherent Edge Radiation • The edge radiation is produced at the interface of the dipole field: the entrance and the exit. • The property of the edge radiation is similar to that of the transition radiation; the radial polarization and the hollow distribution.

10. QUINDI QUINDI is a first principles beam diagnostics simulator which calculates the radiative spectrum from a relativistic electron bunch passing through a magnetic array. (From QUINDI’s home page.) Parallelized with MPI Lienard-Wiechelt potentials HDF5 Flow chart of QUINDI Postprocess on Matlab.

11. QUINDI Example peaks coincide. Coherent THz Edge Radiation • Measured at BNL ATF. • Used vertical four-bend magnet array. • (f = 20o and r = 1.2 m, • or B = 1.7kGauss at 61 MeV) • Bunch length = 100 – 150 fs. • Initial distribution for QUINDI input: UCLA PARMELA and Elegant CER spectra Vertical Chicane CSR, coherent synchrotron radiation CER, coherent edge radiation G. Andonianet al., ”Observation of coherent terahertz edge radiation from compressed electron beams”, Phys. Rev. ST AB 12, 030701 (2009)

12. QUINDI Example (continued) Color map: measured.Black contour line: QUINDI. Polarization of CER + CSR Dots: measured.Solid line: QUINDI. p-polarization of CER Far-field radiation intensity distribution of CER + CSR with various polarizer’s angles. CSR: s-polarization CER: s- + p-polarization Modest agreement. G. Andonianet al., ”Observation of coherent terahertz edge radiation from compressed electron beams”, Phys. Rev. ST AB 12, 030701 (2009)

13. CER at NEPTUNE PM Dipole (90 deg) CER CER Spectrum PMQ (Triplet) Beam (11 MeV) Polarization property CER • 90-deg bending (r = 4 cm) enables to watch the radiation mainly from CER. • CER signal was as large as Cherenkov radiation at the beam dump. • Radial polarization, which is characteristic to CER was observed. CER + CSR

14. Other Method Super-radiant FEL QUINDI is updating to solve this problem.

15. Summary • SW/TW hybrid photoinjector can produce the high brightness beam. • Q = 500 pC, ex=2.1 mm.mrad, trms = 210 fs, bunch form factor @1THz = 0.18. • Coherent Cherenkov radiation was simulated. (Scaled from OOPIC results) • @1THz: P = 79 MW (5.1mJ), Ez = 570 MV/m • @1.5THz: P = 26 MW (1.1mJ), Ez=360MV/m • Coherent edge radiation was being investigated from the experiment and simulation. • - QUINDI is being developed. • Demonstrated at BNL ATF, and being commenced at Neptune, UCLA. - Super-radiant FEL will be simulated on QUINDI.