CNR-SPIN and, Dept. of Physics University of Naples Federico II Italy

Transcription

1 Hybrid photonic bandgap accelerating cavities Emiliano Di Gennaro CNR-SPIN and, Dept. of Physics University of Naples Federico II Italy Supported by: MIUR INFN Regione Campania Acknowledgement: Program FP7-RegPot2010-1FP7 under MAMA project

2 People involved Giancarlo Abbate Antonello Andreone Gianluigi Zito Priya Rose T. Dept. of Physics and CNR-SPIN University of Naples Federico II Italy Giampiero Castaldi Vincenzo Galdi Waves Group, Dept. of Engineering University of Sannio Italy Maria Rosaria Masullo National Institute for Nuclear Physics Naples Unit Italy

3 Outline RF accelerating cavities requirements PBG point defect cavities QuasiPeriodic structures QPC cavities simulations and measurements Conclusions

4 Novel cavities for particle acceleration Cavities operate usually in the fundamental mode, BUT it is not the only one allowed (HOM, higher order modes) High intensity beam by wake field effect sustains unwanted HOM, producing beam instability Secondary electrons emission are more likely in metallic structures, which may give rise to rf breakdown

5 High intensity bunches of charged particles Frequency spectrum with high intensity harmonics f b =f cav HIGH ORDER MODES are excited, with a spatial distribution different from the fundamental one The usual solution is to use damping waveguides BEAM QUALITY degrading At very high frequency (> 10 GHz) and for many coupled cavities this solution can be very cumbersome Frequency Selective Surfaces can represent a possible alternative solution!

6 Photonic crystals (PCs) Metacrystals with a periodic dielectric function ε(r) Forbidden frequency ranges appear in the dispersion functionω(k), called Photonic Band Gaps (PBG) Electrons Photons Crystals Photonic Crystals Periodic Potential V(r) Periodic dielectric constant ε(r) Energy Bands

7 Photonic Bandgap Accelerating Cavities Point-defected resonator working in the TM fundamental mode PROS: intrinsic monomodal behavior can be easily scaled to work at high frequencies CONS: complex realisation (if metallic or superconducting based cavities) radiative limitations to the quality factor (Q)

8 Monomodal behaviour [Masullo et al., MOTL 93, 2486 (2006)] Transmission response of a high Q (~ 5 10 RT) Copper PBG based cavity

9 Quasicrystals (QCs) November 1984: A metallic phase with long-range order and no translational symmetry discovered [Shechtman et al. PRL 53, 1951, 1984], [Levine and Steinhardt, PRL 53, 2477, 1984] Al-Mn alloys exhibiting 10-fold rotational symmetries ( quasicrystals ) Many other examples of aperiodic metallic phase found in nature (e.g., Al-Cu-Fe, Al-Pd-Mn, Al-Li-Cu)

10 QPs Growing interest in the geometry of aperiodic patterns Order not necessarily synonymous with periodicity Formal definition of crystal changed in 1992: formulating a suitably inclusive definition, the International Union for Crystallography s newlyformed Commission on Aperiodic Crystals defined a crystal to be: any solid having an essentially discrete diffraction diagram A typical diffraction pattern from a quasicrystal with 5/10 fold rotational symmetry Quasicrystals are crystals without any translational symmetry

11

12 Photonic QuasiCrystals (QPCs) 2-D arrays of cylindrical rods placed at the vertices (or at the tile centers) of aperiodic tilings 5-fold [Kaliteevski et al., J. Mod. Opt. 47, 1771, 2000], [Bayndir et al., Phys. Rev. B 63, (R), 2001], [Hase et al., Phys. Rev. B 66, , 2002], [Della Villa et al., Phys. Rev. Lett. 94, , 2005; Optics Express 14, 14021, 2006] 8-fold [Chan et al., Phys. Rev. Lett. 80, 956, 1998], [Jin et al., Appl. Phys. Lett. 75, 1848, 1999], [Romero-Vivas et al., Optics Express 13, 826, 2005] 12-fold [Zoorob et al., Nature 404, 740, 2000], [Jin et al., Phys. Rev. B 61, 10762, 2000], [Zhang et al., Phys. Rev. B 63, (R), 2001], [Wang et al., Phys. Rev. B 68, , 2003], [Gauthier and Mnaymneh, Optics Express 13, 1985, 2005], [Kim et al., Appl. Phys. Lett. 86, , 2005], [Feng et al., Phys. Rev. Lett. 94, , 2005] 3-D structures (stereo- and holographic lithography, laser writing ) [W. Man et al., Nature 436, 993, 2005], [Ledermann et al., Nature Mat. 5, 942, 2006], [Wang et al., Appl. Phys. Lett. 88, , 2006]

13 Band gap isotropy TM polarisation Structural optimisation procedure that uses a finite sum of density waves comparable or larger at low dielectric contrasts more isotropic for all contrasts more robust

14 Quasiperiodic PBG cavities based on dielectric rods r = 1.5 mm h = 6 mm ε = 9.2 ε < 4K (single crystal sapphire) Penrose Dodecagonal Hexagonal large gradient acceleration effective suppression of HOM wakefields increased mode confinement minor secondary electrons emission [Masullo et al., MOTL 93, 2486 (2006)] Operational frequency ~ 17 GHz

15 Simulations. [Di Gennaro et al., APL 93, (2008)] 2D FDTD technique: radiative properties 3D simulations (using CST ): conductive RT For reduced-size (R) structures, aperiodic geometries exhibit superior confinement properties by comparison with periodic ones

16 Simulations (2). Hexagonal E-field distribution in the tranversal plane Dodecagonal Penrose

17 And measurements [Di Gennaro et al., APL 93, (2008)] a = 0.75cm, r = 0.3 mm, h = 6 mm) Dodecagonal Hexagonal Penrose Open symbols: exp Closed symbols: sim For larger structures, plate conductive losses are the dominant mechanism of dissipation

18 Superconductor-dielectric dielectric PBG cavities Copper YBa 2 Cu 3 O 7-δ Sapphire 40K with high temperature superconducting thin film plates are in progress (using a CC cooler) The goal is the development of monomodal compact high Q PBG based aperiodically ordered cavities operating at high frequency and cryogenic temperature Q values in the range can be reached at ~ 10 GHz

19 Hybrid metallodielectric PBG cavities Radiation can be further reduced by substitution of peripheral dielectric rows with metallic cylinders Triangular hybrid point-defected cavity with 5 rows: [Di Gennaro et al., NJP (2009)] (all dielectric) Radiative quality factor Two-order-of-magnitude step increase in the radiation quality factor

20 Hybrid metallo-dielectric PBG cavities Hex Pen Dod Increasing the number of metallic rings levels the performance of the hybrid cavities Hybrid structures with one or two metallic rings outperform the fully-dielectric and fully-metallic ones.

21 Hybrid PBG cavities measurements 4+1 structures Penrose Very good agreement between (2D+3D) simulations and microwave measurements

22 Conclusions High Q monomodal PBG based point-defected cavities are very effective at radiation confinement. Hybrid structures are promising new tools for particle acceleration (MOTL 2006, APL 2008, NJP 2010) Superconducting vertical confinement is needed to achieve accelerating cavities with overall quality factor greater than 10 5 ; If cavity compactness is a stringent requirement metal-dielectric quasi-periodic configurations outperform the other possible ordered solutions. and perspectives Significant enhancement of quality factor can be achieved in aperiodic structures. Optimal configuration can be obtained via genetic algorithm procedure.

23 Thank you for your attention!! Girih tiles from Medieval Islamic architecture Nearly perfect quasi-crystalline Penrose patterns were produced already in the XV century [Lu & Steinhardt, Science 315, 1106 (2007)]