Channeling Experiments at DAFNE BTF for the

Development of a Crystal Undulator for Positrons

“CUP”

S.B. Dabagov, C. Natoli, L. Quintieri

… in collaboration with SPARC, Aarhus, Mainz & Frankfurt teams…

CUP project studies the positron channeling for the development of Crystal

Undulator for Positrons and represents the first step of an ambitious project

that investigates the possibility to create new, powerful sources of high-

frequency monochromatic electromagnetic radiation: crystalline undulatorand -laser, based on crystalline undulator. The physical phenomena to

investigate are essentially two: the spontaneous undulator radiation by

channeling of relativistic positrons and the stimulated emission in

periodically bent crystals (the lasing effect).

Free Electron LaserFree Electron Laser

Self-Amplified-Spontaneous-EmissionSelf-Amplified-Spontaneous-Emission

(No Mirrors - Tunability - Harmonics)(No Mirrors - Tunability - Harmonics)

Channeling Radiation & Coherent Bremsstrahlung

MAMBOMAMBO

+ ChannellingChannelling

FEL project at FEL project at FrascatiFrascati

SSourceource

PPulsedulsed

SelfSelf AAmplifiedmplified

RRadiationadiation

CCoherentoherent

Self-Amplified PulsedSelf-Amplified Pulsed Coherent Radiation SourceCoherent Radiation Source

Channeling: Orientational Effects of Transmission & Radiation

Rev. Mod. Phys. 1974: 1 MeV e- @ Cu crystal

• 1962-63:

Robinson &

Oen: Prediction of anomalous penetrationPiercy &

Lutz: Experimental discovery• 1965:

Lindhard: Theoretical description…..

Andersen

Uggerhoj Classical theoryKagan Quantum theoryKononez

Firsov

Tsyganov

Gibson

Kumakhov

Beloshitsky

Gemmel

Appleton

…..

more than 1000 articles + a number of monographs

Prediction of channeling radiation (ChR)

Experimental confirmation: positron channeling in diamond crystal

USSR-USA collaboration, SLAC 1978

JETP Lett. 1979 (Miroshnichenko, Avakyan, Figut, et al.)

@ Channeling:

e+

Atomic crystal plane

)~(1E

UL

<<< - the Lindhard angle is the critical angle for the channeling

Channeling of Charged Particles

Atomic crystal row (axis)

e-

e-

planar channeling

axial channeling

@ Amorphous:

@ Channeling:

e+

Atomic plane of crystal

@ Channeling Radiation:

)~(1E

UL

<<< - the Lindhard angle is the critical angle for the channeling

cos1)(

||

==fi

- optical frequency Doppler effect 2/30

20-

Powerful radiation source of X-rays and -rays:

•polarized

•Tunable (keV - MeV)

•narrow forwarded

fi

( )1>>

Channeling of Charged Particles & Channeling Radiation

Lindhard:

Continuum model –

continuum atomic plane/axis potential

Channeling: Continuum model

( ) ( )arr

eZZrV

2

21=

screening function of Thomas-Fermi type

( ) 3/22/1

2

2/1

108853. += ZZaa

screening length

( ):ar Molier’s potential( )arii

i=

exp3

1

3112

2/1

2+ C

r

CaLindhard potential

…… Firsov, Doyle-Turner, etc.

( ) ( )+

+= dxxVd

VRS

221

Channeling Radiation…

@ Channeling Radiation:

cos1)(

||

==fi

- optical frequency Doppler effect 2/30

20-

Powerful radiation source of X-rays and -rays:

•polarized

•tunable

•narrow forwarded

fi

( )1>>

Bremsstrahlung & Coherent Bremsstrahlung vs Channeling Radiation

@ amorphous - electron:

•Radiation as sum of independent impacts with atoms

•Effective radius of interaction – aTF

•Coherent radiation length lcoh>>aTF

•Deviations in trajectory less than effective radiation angles:

paTF /

Quantum energy

Nph

Bremsstrahlung & Coherent Bremsstrahlung vs Channeling Radiation

@ interference of consequent radiation events:

phase of radiation wave

Radiation field as interference of radiated waves:

Coherent radiation length can be rather large even for short wavelength

@ crystal:

d

Quantum energy

Nph

Bremsstrahlung & Coherent Bremsstrahlung vs Channeling Radiation

@ crystal:

d

0

channeling

3/22/1Z

B

ChR at definite conditions channeling radiation can be significantly powerful

than bremsstrahlung

B: CB: ChR:

2NZ

NZe

( )2NZ

effcoh NlN /2

( )2ZNeff

ChRChR

lab 022

2

1

2

+

2/1

ChR

ph

dt

dN

2P

- radiation frequency -

- number of photons per unit of time -

- radiation power -

Channeling Radiation vs Thomson Scattering

Constdt

dN

TS

ph

2P

2/32

@ comparison factor:

Laser beam size & mutual orientation

@ strength parameters – crystal & field:

For X-ray frequencies: 100 MeV electrons channeled in 105 μm Si (110) emit ~ 10-3 ph/e-

corresponding to a Photon Flux ~ 108 ph/sec

Channeling Radiation vs Thomson Scattering

ChR – effective source of photons in very wide frequency range:

• in x-ray range – higher than B, CB, and TS

• however, TS provides a higher degree of monochromatization and TS is not

undergone incoherent background, which always takes place at ChR

_The important and novel idea consists in realizing a microundulator, that is a suitable periodically

bent crystal, that allows to achieve much higher energy range for the emitted photons respect to the

conventional free electron laser (up to 100 keV). A crystalline undulator can be realized either

dynamically, using high amplitude transverse acoustic wave, or statically using graded composition of

strained layers. Both methods are easily applicable by means of modern technology.

The theoretical results establish the feasibility of a crystalline undulator, but in order to make the

project to advance it is mandatory to carry out experiments to test the idea and to characterize the

emitted radiation as a function of several parameters.

Bent Crystal as Microundulator & Lasing Effect

Conditions for Microundulating

BTF Facility for Channeling Studies

• BTF as unique European facility to deliver positron beams in the range of the

energy required for CUP

• strong photon peak with energy from 20 keV up to 1,5 MeV should appear

according well accepted channeling and undulator theories for

400-600 MeV positrons

BTF Facility Layout

High background/noise

e+

Crysral

undulator

Piano Finanziario Globale

4610-10188

266-51052009

204-5832008

Totale,k

CostruzioneApparati, k

MaterialiInvent., k

MaterialiConsumo, k

MissioniEstere, k

MissioniInterne, k

ANNI

Appendix

Additional material

Surface scratch technique for field undulating

MAMBOMAMBO

ChannellingChannelling

Experimental scheme

“Channeling” line layout

by Kharkov group

Electron Beam Parameter list

1Rms bunch length @ linac exit (mm)

0.4Rms beam spot size @ linac exit (mm)

0.06Rms incorrelated energy spread (%)

0.2Rms total correlated energy spread (%)

1000Rms longitudinal emittance (deg.keV)

< 1Rms slice norm. emittance (300 μm slice)

< 2Rms normalized transverse emittance @ linac exit

(mm-mrad); includes thermal comp. (0.3)

100Bunch peak current @ linac exit (A) (50% beam

fraction)

5.6Bunch energy @ gun exit (MeV)

1Laser pulse rise time (ps) 10% 90%

10Laser pulse duration, flat top (ps)

33Central RF launch phase (RF deg)

1.13Photocathode spot size (mm, hard edge radius)

0.273Peak solenoid field @ 0.19 m (T)

120Cathode peak field (MV/m)

1-10Repetition rate (Hz)

1.1Bunch charge (nC)

155Electron Beam Energy (MeV)

We have started collaboration with groups from:

Italy, Russia, USA, France, Germany, Switzerland,

Ukraine, Belarus, Armenia

…list will be extended…

Collaboration & Acknowledgements

The Scientific Case in the 10 nm 1 nm range:High Peak Brightness ( > 1030 ) Ultra-short (< 100 fs) radiation pulses are of

great interest in various areas

• molecular physics (vibrational modes, bond breaking and formation at

=10-1 nm)

• physics of the clusters (phase transitions at =10-1 nm,)

• surface and interfaces (real time dynamics and phase transitions, =10-

1 nm)

• time resolved chemical reactions (metastable and transition states,

magnetic scattering, confined systems, =10-1 nm)

Channeling Radiation

eV100

keVforward 200max22

0

EEx x 22 22laslas (1-cos (1-cos ))

• Produzioni di impulsi X :

101099 fotoni/s fotoni/s, durata 3 ps, monocromaticimonocromatici

tunabili nel range 20 keV - 1 MeV20 keV - 1 MeV.

Raggiungimento di 10101111 fotoni/s fotoni/s con spot focali

all’interazione di 5 5 μμmm.

• Studi di tecniche di mammografia (e angiografia

coronarica) con X monocromatici.

• Studi di single molecule protein cristallography.

NX T fN

eNh

coll2 = 2 109 / 11

Accelerazione a plasmaAccelerazione a plasma di pacchetti di elettroni ( di pacchetti di elettroni (25 pC25 pC) da) da

100 MeV a 130 MeV100 MeV a 130 MeV con spread energetico < 5%, emitt. con spread energetico < 5%, emitt.

< 1 < 1 μμm, con laser non guidato (5 mm acc. length).m, con laser non guidato (5 mm acc. length).

Accelerazione con laser guidato (Accelerazione con laser guidato (5 cm5 cm) fino a 400 MeV,) fino a 400 MeV,

gradienti > 5 GV/mgradienti > 5 GV/m..

p 50 μm

p 30 100 μmnnpnp

p

2