RF LINAC FOR GAMMA-RAY
COMPTON SOURCES
C. Vaccarezza on behalf of european collaboration
OUTLINE
2
Gamma Ray Compton Sources
 New generation source requirements
 ELI-NP: the European proposal


a S-C-band solution :
the reference WP
 the C-band structures
 the layout
 the lattice error sensitivity

HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
Gamma-Ray Compton sources
3
Thanks to the extremely advanced characteristics:
energy,tunability, mono-chromaticity, collimation, brilliance,
time rapidity, polarizability etc.
the new generation of Compton Sources will play a
critical role for advanced applications in:
Nuclear resonance fluorescence
 Nuclear photonics: (γ-p) (γ-n) reactions
 Medical applications: new medical isotopes production
 Material studies
 Radioactive waste management and isotope identification
 High brilliance Neutron sources

HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
New generation γ-source:
High Phase Space density electron beams vs Lasers
4

Bright
Photon energy

Mono-chromatic
Spectral density

High Spectral Flux

Tunable

Highly Polarized
Bandwith (rms)
# photons/sec within
FWHM bdw.
Linear Polarization
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
1-20 MeV
> 104 ph/sec.eV
<0.3%
0.5÷1.5 109
>95 %
The electron-photon collider approach:
5
The rate of emitted photons is given by:
𝑁𝛾 = 𝐿𝜎𝑇
Laser
where:
𝐿 = 𝑁𝐿 𝑁𝑒 2𝜋 𝜎𝑥 2 + 𝑤0 2 4
e-
leading to:
𝑁𝛾
𝑠𝑒𝑐 −1
= 4.1 ×
𝑈𝐿 𝐽 𝑄 𝑝𝐶 𝑓𝑅𝐹 𝑛𝑅𝐹
108
ℎ𝜈𝐿 𝑒𝑉
𝜎𝑥 2
1
𝜇𝑚 + 𝑤0 2 𝜇𝑚
4
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
𝑐𝜎𝑡 𝛿
1+
4𝜎𝑥
2
Within the desired bandwith:
L. Serafini
6
Δ𝜈𝛾
≅
𝜈𝛾
∆𝛾
4
𝛾𝜗 + 4
𝛾
collimation
system
2
𝜀𝑛
+
𝜎𝑥
4
∆𝜈𝐿
+
𝜈𝐿
2
𝑀2 𝜆𝐿
+
2𝜋𝑤0
N
scattered
 1 .5  N  
+
Laser system
e- beam
A simple model by L. Serafini, V. Petrillo
predicts :
bw
4
2
 ph / sec within    
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
 

𝑎0𝑝 2 3
1 + 𝑎0𝑝 2 2
2
Spectral density SPD: a key parameter
7
For the considered bandwith
∆𝜈𝛾
𝜈𝛾
∶
𝑁𝛾 𝑏𝑤
𝑆𝑃𝐷 𝑝ℎ 𝑠 ∙ 𝑒𝑉

(
SPD  1 . 67  10 U L Q f RF n RF
8

 2
) 4


 
 2


2



 n 

 
 x
 4 x
2
4
2
 w0


2𝜋ℎ𝜋∆𝜈𝛾
  
 L 2
L
1 
2


4  2 2
a0 p




2w
3 
0


M L
2
 z c  t
2
2
2
4 x  w0
2
2

fRF = repetition rate
UL = Laser pulse energy (J) h = laser photon energy=2.4 eV
nRF = bunches per RF pulse Q = el. bunch charge (pC) f = collision angle
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
x = e beam focal rms spot size in mm w0 = laser focal spot size in mm
Analytical model vs. classical/quantum
simulation
8
Number of
photons
CAIN (quantum
MonteCarlo)
Run by I.Chaichovska
and A. Variola
TSST (classical)
Developed by
P. Tomassini
bandwidth
Comp_Cross (quantum
semianalytical)
Developed by V.Petrillo
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
V. Petrillo
ELI-NP: a new generation γ-ray source
9
Photon energy
Spectral Density
Bandwidth (rms)
# photons per shot within FWHM bdw.
# photons/sec within FWHM bdw.
Source rms size
Source rms divergence
Peak Brilliance (Nph/sec.mm2mrad2.0.1%)
Radiation pulse length (rms, psec)
Linear Polarization
Macro rep. rate
# of pulses per macropulse
Pulse-to-pulse separation
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
1-20 MeV
> 104 ph/sec.eV
0.3%
1.0-4.0.105
2.0-8.0.108
10 - 30 µm
25-250 µrad
1022 - 1024
0.7-1.5
> 99 %
100 Hz
31
16 nsec
ELI-NP: the F-I-UK European proposal
10
European Collaboration for
the proposal of the gammaray source:
Italy: INFN,Sapienza
France: IN2P3, Univ. Paris Sud
UK: ASTeC/STFC
~ 80 collaborators elaborating the
CDR/TDR
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
ELI-NP requirements:
11
State of the
art
+
Compact
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
S-band
Photoinjector
=
+
C-band linac
A r.t. RF linac vs pulsed laser source
12
Electron beam parameter at IP
Energy (MeV)
Bunch charge (pC) 
Bunch length (µm)
εn_x,y (mm-mrad)
 spread (%)
Bunch Energy
Focal spot size (µm)
# bunches in the train
Bunch separation (nsec)
energy variation along the train
Energy jitter shot-to-shot
Emittance dilution due to beam
breakup
Time arrival jitter (psec)
Pointing jitter (m)
180-750
25-400
100-400
0.2-0.6
0.04-0.1
15-30
31
16
0.1 %
0.1 %
< 10%
< 0.5
1
Yb:Yag
Collision Laser
Pulse energy (J)
Low
High Energy
Energy
Interaction
Interaction
0.2
0.5
Wavelength (eV)
2.4
2.4
FWHM pulse length (ps)
2-4
2-4
Repetition Rate (Hz)
100
100
1.2
1.2
> 25
> 25
0.05 %
0.05 %
1
1
< 1 psec
< 1 psec
1%
1%
M2
Focal spot size w0 (µm)
Bandwidth (rms)
Pointing Stability (µrad)
Sinchronization to an ext.
clock
Pulse energy stability
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
The hybrid scheme for the Linac:
 Operation criteria:
 Long bunch at cathode for high phase
space density :
Q/n2 >103 pC/(µrad)2
 Short exit bunch (280 µm) for low
energy spread (~0.05%)
 Advantages:
 Moderate risk (state of art RF gun, reduced
multibunch operation problems respect to higher
frequencies, low compression factor<3)
 Economic
 Compact (the use of the C-band booster meets
the requirements on the available space)
 Possibility to use SPARC as test stand
WPref from the photoinjector (Tstep tracking)
14
Egun=120 MV/m
E(S1)=E(S2)=21 MV/m
Q=250 pC
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
C. Ronsivalle
C-band structures
15
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
D. Alesini
Central cells
16
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
Mitigation of multibunch effect with
damped structure
17
D. Alesini
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
The machine layout
18
ELI-NP
infrastructure
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
N. Bliss
Linac & Transfer lines
19
Low energy
High Energy
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
SB-Transverse beam size and
distribution (Elegant tracking)
20
Low energy
High energy
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
WPref_SB-energy spread & current
21
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
Wake on Δx=500 µm
22
M. Migliorati
Wake res Q 11000
Wake res Q 100
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
Wake on Δx=500 µm
23
SB
Wake res Q 100
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
Lattice error sensitivity:
Error
value
RFCW
12
QUAD
28
DIP
4
Δx
Δy
ΔV
ΔΦ
Δk
Δ
80 µm
80 µm
300 kV
1°
5x10-4 fs
1x10-3 fs
X
X
X
X
-
X
X
X
X
X
X
The Latin Hypercube:

138 Variables (12*4+28*3+4*3)


-1.0
Δu/u
1.0
100 machine runnings
• The applied Δx,y affects all the elements at
the same time like a real machine
• Δx and Δy are applied together
• For each sample machine an Elegant input
lattice is written with the corresponding errors
• The sample machine is runned
• The all results are read and plotted
Ex. 10 machines Δu/u distribution:
ΔV= ± 300 kV
27
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
ΔΦ= 1°
Δx= ± 80 m
28
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
Δk/kmax= ± 5.0E-4
ΔB/Bmax= ± 1.0E-3
29
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
All the contributions applied
30
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013
Conclusions
31

A C-band RF linac has been presented based on
the requirements of the new generation gamma-ray
source in the framework of the ELI-NP project:
 The
key parameters have been described together with
the main aspects of the proposed solution
 A lattice sensitivity study has been presented that even
if not exhaustive anyway shows acceptable probability
margin for the linac routine operation.
HBEB 2013, San Juan Mar, Puerto Rico |March 25-28, 2013