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A high-power, beam-based, coherently enhanced THz radiation source Yuelin Li, Yin-E Sun, and Kwang-Je Kim Accelerator Systems Division Argonne Accelerator Institute Argonne National Laboratory, Argonne, IL We propose a Smith-Purcell radiation device that can potentially generate high average power THz radiation with very high conversion efficiency. The source is based on a train of short electron bunches from an rf photoemission gun at an energy of a few MeV. Particle tracking simulation and analysis show that with a beam current of 1 mA, it is feasible to generate hundreds of Watts of narrow-band THz radiation at a repetition rate of 1 MHz.

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CLEO 2008, San Jose, May 4-9, Content Power of THz imaging Capability of current available source Our Approach of THz generation –Coherence enhancement –Laser pulse train generation –E-beam generation and dynamics –Smith-Purcell radiation –Putting together Challenges Summary

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CLEO 2008, San Jose, May 4-9, Current sources Broadband, THz TDS, <650 W CW –Gunn diode/Back wave oscillators, <200 mW –THz-wave parametric oscillators, <100 mW –THz gas lasers, <180 mW –QCL, <100 mW –FEL, >20 W, but bulky ~ W, 8 min H. B. Liu et al, Proc. IEEE 95, 1515 (2007). Higher power is needed field application.

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CLEO 2008, San Jose, May 4-9, The matter of coherence Coherent radiation Radiation power from a electron bunch Coherence factor dE/d : electron radiation energy into per spectral frequency N:total number of electrons S(t): electron temporal distribution Incoherent radiation

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CLEO 2008, San Jose, May 4-9, Coherence factor as a function of bunch length Short bunch is the key for high coherent factor! Y.Li and K.-J. Kim, Appl. Phys. Lett. 92, (2008).

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CLEO 2008, San Jose, May 4-9, Degradation of coherence factors in electron bunches The degradation is due to space charge force. Energy from zero to 8 MeV (see later)

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CLEO 2008, San Jose, May 4-9, Effect of the space charge force Q: total charge z, r :longi and trans beam sizes : relativistic factor To solve the problem Higher beam energy, costly on $$$$ Less charge, costly on photons How about bunch train? Reduced space charge but preserved coherence factor.

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CLEO 2008, San Jose, May 4-9, Preserve the coherence factor by bunch trains Coherence factor for a bunch train coh : coherence factor for individual bunched b :bunch spacing, to be set as 2 / N b: Number of bunches

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CLEO 2008, San Jose, May 4-9, Preserve the coherence factor by bunch trains Same coherence factor but narrower band width Coherent factor as a function of frequency for 1-16 bunches

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CLEO 2008, San Jose, May 4-9, Laser pulse train generation Number of pulses= 2 n, n is the number of birefringence crystals (Credit: Cialdi et al., Appl. Phys. 46, 4959 (2007))

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CLEO 2008, San Jose, May 4-9, Rf photoinjector Need high duty factor, kHz to MHz Laser power of 100 W Klystron power: 10 kW Laser Electrons Gun Laser Klystron L/S band gun

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CLEO 2008, San Jose, May 4-9, Simulation for an rf gun: bunch coherent factor Coherence fator at harmonics

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CLEO 2008, San Jose, May 4-9, Smith-Purcell radiation (Credit: Scott Berg, Resonant wavelength Radiation power per electron N g, g : number of grating grooves and grating period. e: evanescent wavelength n: diffraction order S.J. Smith and E. M. Purcell, Phys. Rev. 92, 1069 (1953). P.M. van den Berg, J. Opt. Soc. Am. 63, 1588 (1973).

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CLEO 2008, San Jose, May 4-9, Putting things together: radiation powers at 1 MHz, for 0.5 THz Laser Electrons Gun grating THz total radiation power as a function of the beam center-grating distance with a beam scraper height D in mm measured from the grating surface.

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CLEO 2008, San Jose, May 4-9, Summary Can we make a THz source like this? We showed that with coherence enhancement, a beam based source delivering hundreds of watts of THz power is possible and may be made compact for field application tools.

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CLEO 2008, San Jose, May 4-9, References B. Ferguson and X.C. Zhang, Nature Materials 1, 26 (2002). K. Kawase, J. Shikata, K. Imai, and H. Ito, Appl. Phys. Lett. 78, 2819 (2001). See, for example, D. Abbott and X.-C Zhang, Proc. IEEE 95, 1509 (2007) and the references therein. G.L. Carr, M.C. Martin, W.R. McKinney, K. Jordan, G.R. Neil, and G.P. Williams, Nature 420, 153 (2002). S.V. Miginsky, N.A. Vinokurov, D.A. Kayran, B.A. Knyazev, E.I. Kolobanov, V.V. Kotenkov, V.V. Kubarev, G.N. Kulipanov, A.V. Kuzmin, A.S. Lakhtychkin, A.N. Matveenko, L.E. Medvedev, L.A. Mironenko, A.D. Oreshkov, V.K. Ovchar, V.M. Popik, T.V. Salikova, S.S. Serednyakov, A.N. Skrinsky, O.A. Shevchenko, M.A. Scheglov, Proc of 2007 Asian Patical Accelerator Conference, Indore, India. J.S. Nodvick and D.S. Saxon, Phys. Rev. 96, 180 (1954). Y.K. Batygin, Phys. Plasmas 8, 3103 (2001). B.J. Siwick, J.R. Dwyer, R.E. Jordan, R.J.D. Miller, J. Appl. Phys. 92, 1643 (2002). A.M. Michalik and J.E. Sipe, J. Appl. Phys. 99, (2006). Y.Li and K.-J. Kim, Appl. Phys. Lett. 92, (2008). S.E. Korbly, A.S. Kesar, J.R. Sirigiri, and R.J. Temkin, Phys. Rev. Lett. 94, (2005). M. Arbel, A. Abramovich, A. L. Eichenbaum, A. Gover, H. Kleinman, Y. Pinhasi, and I. M. Yakover, Phys. Rev. Lett. 86, 2561 (2001), and references therein. S.J. Smith and E. M. Purcell, Phys. Rev. 92, 1069 (1953). P.M. van den Berg, J. Opt. Soc. Am. 63, 1588 (1973). H.L. Andrews and C.A. Brau, Phys. Rev. ST AB 7, (2004). M. Boscolo, M. Ferrario,I. Boscolo, F. Castelli, and S. Cialdi, Nucl. Instr. and Meth. Phys. Res. A 577(3), 409 (2007). J.G. Neumann, P.G. O'Shea, D. Demske, W.S. Graves, B. Sheehy, H. Loos and G.L. Carr, Nucl. Instr. Meth. Phys. Res. A 507, 498 (2003). B. Dromey, M. Zepf, M. Landreman, K. O'Keeffe, T. Robinson, and S. M. Hooker, Appl. Opt. 46, 5142 (2007). D.H. Dowell, F.K. King, R.E. Kirby, J. F. Schmerge, and J.M. Smedley, Phys. Rev. ST-AB 9, (2006). T. Srinivasan-Rao, I. Ben-Zvi, J. Smedley, X.J. Wang, M. Woodle, Proc. PAC 97, 2790 (1998). F. Röser, J. Rothhard, B. Ortac, A. Liem, O. Schmidt, T. Schreiber, J. Limpert, and A. Tünnermann, Opt. Lett. 30, 2754 (2005). P. Dupriez, C. Finot, A. Malinowski, J.K. Sahu, J. Nilsson, D.J. Richardson, K.G. Wilcox, H.D. Foreman, and A.C. Tropper, Opt. Express 14, 9611 (2006). D.N. Papadopoulos, Y. Zaouter, M. Hanna, F. Druon, E. Mottay, E. Cormier, and P. Georges, Opt. Lett. 32, 2520 (2007) D.H. Dowell, J.W. Lewellen, D. Nguyen, and R. Rimmer, Nucl. Instrum. Meth. Phys. Research A 557, 61 (2006). A. Todd, Nucl. Instrum. Meth. Phys. Research A 557, 36 (2006). M. Cornacchia, S. Di Mitri, and G. Penco, and A.A. Zholents, Phys. Rev. ST-AB 9, (2006), and reference therein.

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