emiliano di gennaro - società italiana di fisica[di gennaro et al., apl 93, 164102 (2008)] xcviii...
TRANSCRIPT
Emiliano Di Gennaro
CNR-SPIN and, Dept. of Physics
University of Naples Federico II Italy
Supported by: MIUR
INFN
Regione Campania
Hybrid photonic bandgap accelerating
cavities
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
Acknowledgement:Program FP7-RegPot2010-
1FP7 under MAMA project
Giancarlo Abbate
Antonello AndreoneGianluigi Zito
Priya Rose T.
Giampiero CastaldiVincenzo Galdi
Maria Rosaria Masullo
Dept. of Physics and CNR-SPINUniversity of Naples Federico II
Italy
Waves Group, Dept. of EngineeringUniversity of Sannio Italy
National Institute for Nuclear Physics
Naples Unit Italy
People People involvedinvolved
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
OutlineOutline
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
• RF accelerating cavities requirements
• PBG point defect cavities
• QuasiPeriodic structures
• QPC cavities simulations and measurements
• Conclusions
• 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
NovelNovel cavitiescavities forfor particleparticle accelerationacceleration
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
The usual solution is to use “damping waveguides”
At very high frequency (> 10 GHz) and for many coupled cavities this
solution can be very cumbersome
Frequency spectrumwith
high intensity harmonics
BEAM QUALITY
degrading
fb=fcav
High intensitybunches
of charged particles
HIGH ORDER MODES
are excited, with a spatialdistribution different from
the fundamental one
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
Frequency Selective Surfaces can represent a possible alternative solution!
Electrons
Crystals
Periodic PotentialV(r)
Energy Bands
Photons
Photonic Crystals
Periodic dielectric constant ε(r)
Metacrystals with a periodic
dielectric function ε(r)→
Forbidden frequency ranges appear in
the dispersion function ω(k), calledPhotonic Band Gaps (PBG)
PhotonicPhotonic crystalscrystals ((PCsPCs))
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
PhotonicPhotonic BandgapBandgap AcceleratingAccelerating CavitiesCavities
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 qualityfactor (Q)
Point-defected resonator working in the TM fundamental mode
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
Transmission response of a high Q (~ 5 · 103 @ RT) Copper PBG based cavity
““MonomodalMonomodal”” behaviourbehaviour
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
[Masullo et al., MOTL 93, 2486 (2006)]
QuasicrystalsQuasicrystals (QCs)(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)
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
QPsQPs
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
Quasicrystals are crystals without any translational symmetry
• Growing interest in the geometry of aperiodic patterns
• “Order” not necessarily synonymous with “periodicity”
• Formal definition of “crystal” changed in 1992:
A typical diffraction pattern from a quasicrystal
with 5/10 fold rotational symmetry
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
formulating a suitably inclusive definition, the International Union for Crystallography’s newly-
formed Commission on Aperiodic Crystals defined a crystal to be:
“any solid having an essentially discrete diffraction diagram”
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
Photonic Photonic QuasiCrystalsQuasiCrystals ((QPCsQPCs))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, 161104(R), 2001], [Hase et al., Phys. Rev. B 66, 214205, 2002], [Della Vil la et al., Phys. Rev. Lett. 94, 183903, 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, 081105(R), 2001], [Wang et al., Phys. Rev. B 68, 165106, 2003], [Gauthier and Mnaymneh, Optics Express 13, 1985, 2005], [Kim et al., Appl. Phys. Lett. 86, 031101, 2005], [Feng et al., Phys. Rev. Lett. 94, 247402, 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, 051901, 2006]
TM polarisation
Structural optimisation
procedure that uses a finite
sum of density waves
comparable or larger at low dielectric contrasts
more robust
more isotropic for all contrasts
Band gap Band gap isotropyisotropy
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
r = 1.5 mm
ε’ = 9.2 ε’’ < 10-8 @ 4K
(single crystal sapphire)
h = 6 mm
• large gradient acceleration
• effective suppression
of HOM wakefields
• increased mode confinement
• minor secondary electrons emission
Penrose Dodecagonal Hexagonal
[Masullo et al., MOTL 93, 2486 (2006)]
based on dielectric rods
Operational frequency ~ 17 GHz
QuasiperiodicQuasiperiodic PBG PBG cavitiescavities
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
2D FDTD technique:
radiative properties
3D simulations (using
CST™):
conductive losses @ RT
[Di Gennaro et al., APL 93, 164102 (2008)]SimulationsSimulations……..
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
For reduced-size (R) structures, aperiodic geometries exhibit superior
confinement properties by comparison with periodic ones
Hexagonal
Dodecagonal Penrose
SimulationsSimulations (2)(2)……..
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
E-field distribution in the
tranversal plane
a = 0.75cm, r = 0.3 mm, h = 6 mm)
Open symbols: exp
Closed symbols: sim
[Di Gennaro et al., APL 93, 164102 (2008)]
For larger structures, plate conductive losses are the dominant mechanism of dissipation
And And measurementsmeasurements ……
Penrose
Hexagonal
Dodecagonal
The goal is the development of monomodal compact high Q PBG based
aperiodically ordered cavities operating at high frequency and cryogenic
temperature
SuperconductorSuperconductor--dielectricdielectric PBG PBG cavitiescavities
Q values in the range 106 ÷ 107 can be reached at ~ 10 GHz
Copper
YBa2Cu3O7-δ
Sapphire
Measurements @30 ÷ 40K with high temperature superconducting
thin film plates are in progress
(using a CC cooler)
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
Triangular hybrid point-defected cavity with 5 rows:
Radiation can be further reduced by substitution of peripheral
dielectric rows with metallic cylinders
5 + 0 (all dielectric) 4 + 1 3 + 2
Two-order-of-magnitude step increase in the radiation quality factor
““HybridHybrid”” metallodielectricmetallodielectric PBG PBG cavitiescavities
Radiative quality factor
[Di Gennaro et al., NJP 11 113022 (2009)]
Hex
Pen
Dod
1 20
•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.
““HybridHybrid”” metallometallo--dielectricdielectric PBG PBG cavitiescavities
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
““HybridHybrid”” PBG PBG cavitiescavities measurementsmeasurements
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
4+1 structures
Very good agreement between (2D+3D) simulations and microwave measurements
Penrose
Conclusions Conclusions ……
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
• High Q monomodal PBG based point-defected cavities are very
effective at radiation confinement. Hybrid structures are promisingnew 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 105 ;
• If cavity compactness is a stringent requirement metal-dielectric quasi-periodic configurations outperform the other possible ordered
solutions.
…… and perspectivesand perspectives
• Significant enhancement of quality factor can be achieved in
aperiodic structures. Optimal configuration can be obtained via
genetic algorithm procedure.
XCVIII Congresso Nazionale SIF Napoli, 17-21 Settembre 2012
“Girih” tiles from Medieval Islamic architecture Nearly perfect quasi-crystallinePenrose patterns were produced already in the XV century
[Lu & Steinhardt, Science 315, 1106 (2007)]
Thank you foryour attention !!