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
Hybrid of Standing-Wave and Travelling-Wave Structures
Produce short bunches without a magnetic chicane.
Bunching vs. Injection Phase
Peak Current Bunch Form Factor @1THz
EmittanceQ = 500pC
-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.
Full Bunching CaseCharge 500 pC
Energy 21.04 MeV
Xrms, Yrms 1.48, 1.48 mm
Emitx,y 2.1, 2.1 mm.mrad
Trms (T_FWHM),Erms
210 fs (54 fs), 1.3%
Bunch Form Factor (1 THz) 0.18
Emit (t-bg) 2.74 ps
Strong energy modulation by the space charge.
Strong spike.(54 fs, FWHM) Bad around the spike.
Large energy modulation.
“Swan” shape shows strong modulation due to space charge.
3.7 mm.mrad
Bunch shape
Slice emittance
t-E phase space Energy Spectrum
Bunch Form Factor
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.
CCR Experiment at UCLA
a = 250 mm
Fourier Transform
Beam: Q=200pC, st=270fs, E=10MeVDielectric tube: er=3.8 (SiO2), L=1cm
OOPIC SimulationsParameters: 1 THz case Parameters: 1.5 THz
case
Rms beam length 100 μm Rms beam length 50 μm
Rms beam radius 30 μm Rms beam radius 22 μm
Beam total charge Q 1 nC Beam total charge Q 0.5 nC
Fundamental frequency 1 THz Fundamental frequency 1.5 THz
Bunch Form Factor 0.012 Bunch Form Factor 0.085
Outer radius b 115 μm Outer radius b 84.6μm
Inner radius a 77 μm Inner radius a 60.2μm
Peak power 21 MW Peak power 52 MW
Peak long. electric field 294 MV/m Peak long. electric field 619 MV/m
Pulse length 69 ps Pulse length 60 ps
Total CCR energy 1.47 mJ Total CCR energy 1.55 mJ
Scaled to the beam from the hybrid photoinjector
Beam total charge Q 0.5 nC Beam total charge Q 0.5 nC
Fundamental frequency 1 THz Fundamental frequency 1.5 THz
Bunch Form Factor 0.18 Bunch Form Factor 0.042
Peak power 79 MW Peak power 26 MW
Peak long. electric field 570 MV/m Peak long. electric field 310 MV/m
Total CCR energy 5.5 mJ Total CCR energy 1.1 mJ
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.
QUINDI
Flow chart of 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.)
Postprocess on Matlab.
Lienard-Wiechelt potentials
Parallelized with MPI
HDF5
QUINDI Example
G. Andonian et al., ”Observation of coherent terahertz edge radiation from compressed electron beams”, Phys. Rev. ST AB 12, 030701 (2009)
peaks coincide.
CER spectra
CER, coherent edge radiation
CSR, coherent synchrotron radiation
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
Vertical Chicane
QUINDI Example (continued)Polarization of CER + CSR
p-polarization of CER
Far-field radiation intensity distribution of CER + CSR with various polarizer’s angles.
Dots: measured.Solid line: QUINDI.
Color map: measured.Black contour line: QUINDI.
Modest agreement.
G. Andonian et al., ”Observation of coherent terahertz edge radiation from compressed electron beams”, Phys. Rev. ST AB 12, 030701 (2009)
CSR: s-polarizationCER: s- + p-polarization
CER at NEPTUNE
PMQ (Triplet)
PM Dipole (90 deg)
- 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 Spectrum
Polarization property
CER
CER + CSR
Beam (11 MeV)
CER
Other Method
Beam Lorentz factor g 44Rms bunch length 100 mmRms bunch width 200 mmUndulator wavelength 6.9 cmNumber of undulator periods 15Undulator strength K 5.6On-axis radiation wavelength 299 mm (1 THz)
Super-radiant FEL
QUINDI is updating to solve this problem.
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/[email protected]: 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.
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