emiliano di gennaro - società italiana di fisica[di gennaro et al., apl 93, 164102 (2008)] xcviii...

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


OutlineOutline


• 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


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


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))


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


Transmission response of a high Q (~ 5 · 103 @ RT) Copper PBG based cavity

““MonomodalMonomodal”” behaviourbehaviour


[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)


QPsQPs


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


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”

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


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


2D FDTD technique:

radiative properties

3D simulations (using

CST™):

conductive losses @ RT

[Di Gennaro et al., APL 93, 164102 (2008)]SimulationsSimulations……..


For reduced-size (R) structures, aperiodic geometries exhibit superior

confinement properties by comparison with periodic ones

Hexagonal

Dodecagonal Penrose

SimulationsSimulations (2)(2)……..


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)


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


““HybridHybrid”” PBG PBG cavitiescavities measurementsmeasurements


4+1 structures

Very good agreement between (2D+3D) simulations and microwave measurements

Penrose

Conclusions Conclusions ……


• 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.


“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 !!

emiliano di gennaro - società italiana di fisica[di gennaro et al., apl 93, 164102 (2008)] xcviii...

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