1. Energy up-grading of the SPARC photo-injector, with a C-band RF system
R. Boni on behalf of the SPARC group
Workshop on “ X-ray Science at the Femtosecond to Attosecond Frontier “
UCLA, May 18-20, 2009
SPARC GROUP
D. Alesini, M. Bellaveglia, R. Boni, M. Boscolo, M. Castellano, E. Chiadroni, A. Clozza, L. Cultrera, G. Di Pirro, A. Drago, A. Esposito, M.Ferrario, L. Ficcadenti, D. Filippetto, V. Fusco, A. Gallo,
G. Gatti, A. Ghigo, B. Marchetti, A. Marinelli, A. Marcelli, M. Migliorati, A. Mostacci, E. Pace, L. Palumbo, L. Pellegrino, R. Ricci, U. Rotundo, C. Sanelli, F. Sgamma, B. Spataro, S. Tomassini,
C. Vaccarezza, M. Vescovi, C. Vicario, INFN-LNF, Frascati, RM, Italy.
F. Ciocci, G. Dattoli, M. Del Franco, A. Dipace, A. Doria, G. P. Gallerano, L. Giannessi, E. Giovenale, G. L. Orlandi, S. Pagnutti, A. Petralia, M. Quattromini, C. Ronsivalle, E. Sabia,
I. Spassovsky, V. Surrenti, ENEA C.R. Frascati, RM, Italy.
A. Bacci, I. Boscolo, F.Broggi, F. Castelli, S. Cialdi, C. De Martinis, D. Giove, C. Maroli, V. Petrillo, A.R. Rossi, L. Serafini, INFN-Mi, Milano, Italy.
M. Mattioli, M. Petrarca, M. Serluca, INFN-Roma I, Roma, Italy.
L. Catani, A. Cianchi, INFN-Roma II, RM, Italy.
J. Rosenzweig, UCLA, Los Angeles, CA, USA.
M. E. Couprie, SOLEIL, Gif-sur-Yvette, France
M. Bougeard, B. Carré, D. Garzella, M. Labat, G. Lambert, H. Merdji, P. Salières, O. Tchebakoff, CEA Saclay, DSM/DRECAM, France.

2. SPARC is a Free-Electron-Laser operating at 500 nm, driven
by a high brightness photo-injector at a beam energy of 150 MeV.
SPARC employs a RF-gun, illuminated by Ti-Sa laser beam pulses,
and 3 S-band, TW, CG, 2p/3, accelerating structures.
The undulator line consists of six, 2m. long, PM, variable gap sections.
SASE and SEEDED FEL experiments in the visible and UV light are underway
SPARC is a test facility for the VUV/soft X-rays FEL project SPARX
SPARC electron beam main parameters
nominal
achieved
Electron beam energy (MeV)
150
Bunch charge (nC) 1
0.3
Bunch rep.rate (Hz) 10
Cathode RF peak field (MV/m)
120
Laser pulse duration (ps) – gaussian profile
6-8
Bunch peak current (A)
100 40
rms norm. transv. Emittance (mm-mrad)
< 2 2
rms bunch length at linac exit (mm)
≈ 1
rms beam spot size at linac exit (mm)
≈ 0.7
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

3. SPARC RF LAYOUT SSA TWT CIRC. LASER BEAM
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

4. cad view KLYSTRON GALLERY MOD 2 MOD 1 ACCELERATOR HALL
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

5. Linac commissioning results .. so far …
Max bunch charge limited to 300 pC due, mainly, to poor cathode
surface quality despite of careful laser cleaning and smooth RF conditioning.
Rough cathode surface …. Slice emittance limited to 1μm
Bunch length 6 ÷ 8 psec (FWHM)
Peak current ≈ 40 A
Beam stable and reproducible
Energy spread ≈ 0.1%
Energy stability ≈ 0.1%
beam parameters
emittance measurements
Typical rms value ≈ 2 μm @ 250 pC
Kly. Mod. HV stability ≤ 0.1 %
RF Phase jitter ≤ 70 fsec … with feedback ….
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

6. Experiments underway and present results ….
SASE experiment
Coherent radiation at 500 nm have been observed with amplification factor ≈ 10 6
Pulse energy measured at the undulator intersections
Single shot spectra at the end of the undulator line
VELOCITY BUNCHING experiment
BUNCH
LENGTH
psec
Measured RMS bunch length of a 300 pC beam
vs the phase of the first accelerating structure
compression factor ≈ 14
Ipeak ≈ 120 A
over-compression
PHASE SHIFT
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

7. SPARC photos ONDULATOR SECTION
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

8. SPARC energy up-grading
There are funds available from the MIUR* to increase the energy of SPARC.
Increasing the SPARC beam energy is required for lasing at UV wavelengths
and to improve the Seeding experiment
We could replace the 3rd low-gradient 15 MV/m S-band section with
a high-gradient unit powered with sledded pulses,
.. or …
with 2 C-band structures that allow to gain ≈20 % energy surplus
on the total energy (≈ 240 vs 200 MeV)
(*): Italian Minister for Education, University & Research
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

9. We decided to adopt a C-band system.
… SPARC energy up-grading ….
We decided to adopt a C-band system.
This choice, as well as more beam energy,
allows to gain experience with a rather novel high power RF technology.
The C-band, also, helps in producing shorter bunches.
MAIN COMPONENTS of the C-BAND RF STATION
a) Klystron
b) Pulsed Modulator
c) Pulse Compressor (SLED)
d) RF Power transmission system (waveguides)
e) Accelerating Structures
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

10. ΔE ≈ + 70÷80 MeV Up-graded layout … SPARC energy up-grading ….
C-band
ENERGY
COMPRESSOR
S-BAND Station
2856 MHz – 45 MW
Klystron
N°1
C-band
Station
90 MW/0.5µs
5712 MHz
50 MW/2.5µs
9 MW
40 MW
40 MW
ACC. STRUCTURE
HIGH GRADIENT SECTION ≈ 120 MeV
Klystron
N°2
ENERGY
COMPRESSOR
S-BAND Station
2856 MHz – 45 MW
ACC. STRUCTURE
GUN
C-band acc. structures
35 MV/m
E ≈ 105 MeV
≈ 50 MW
≈ 50 MW
E ≈ 240 MeV
Up-graded layout
≈120 MW/0.8µs
ΔE ≈ + 70÷80 MeV
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

11. … Toshiba Electron Tubes & Devices Co., Ltd (TETD)
… SPARC energy up-grading ….
KLYSTRON
Manufactured by
… Toshiba Electron Tubes & Devices Co., Ltd (TETD)
Kly main specs.
TOSHIBA 37202
Frequency (MHz)
5712
Peak outpu Power (MW) 50
RF Gain (dB)
≥ 50
Efficiency (%)
≥ 40
RF pulse 3 dB (μsec)
2.5
Rep. Rate (Hz) 60
Beam voltage/current (kV/A)
350/310
double output klystron
with waveguide re-combiner
.. contacts are in course with TETD …..
… delivery time ÷9 months a.r.o.
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

12. A few companies can develope the HV power supply.
… SPARC energy up-grading ….
HV PULSED MODULATOR
A few companies can develope the HV power supply.
LNF is in contact with:
a) SCANDINOVA (Sweden)
b) PPT (Germany)
c) GloryMV (China)
All the above companies are available to respond to a call for tender.
d) the JP company Nichicon (the Spring8 modulator manufacturer ) however, seems not willing to provide a unit outside of Japan.
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

13. HV PULSED MODULATOR
INSTALLATION
We could install the power-station in the accelerator hall, but are concerned
about the possible e.m.noise and spikes that could disturb LLRF and diagnostics ...
So we decided to put the unit in the mid-gallery even though there is limited space.
6 m
3 m
3 m
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

14. ≤ 1300 mm ≤ 4000 mm ≤ 2500 mm KLY MOD Main Modulator Specs
HV PULSED MODULATOR
≤ 1300 mm
≤ 4000 mm
≤ 2500 mm
KLY
MOD
Main Modulator Specs
Mod. Peak Power (MW)
130
Mod. Average Power (kW)
5.2
Voltage range (kV)
0÷370
Current range (A)
0÷250
Pulse rep.rate (Hz)
0÷10
Top Pulse length (µsec)
≥ 2.5
Top flatness (‰)
≤ ± 1
Amplitude stability (‰)
Pulse rise/fall time (µsec)
≤ 50/100
Pulse to Pulse time jitter (nsec)
≤ ± 2.5
Pulse width time jitter (nsec)
≤ ± 5
Size constraints
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

15. SCANDINOVA MODULATOR NICHICON MODULATOR Full Solid State system
HV PULSED MODULATOR
1400 mm
SCANDINOVA MODULATOR
Full Solid State system
NICHICON MODULATOR
Standard design with PFN & Thy …..
but very compact because immersed in oil
1000 mm
courtesy T. Shintake
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

16. SPARC building mid-gallery winch or pulley system 3 m. 3 m.
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

17. RF Pulse Compressor and Waveguide system
Spring8 C-band power distribution system,
courtesy T. Shintake
SLED
TE038 mode
Pout ≈ 200 MW
Tp = 0.5 µsec
- exponential pulse -
Waveguide system
The WR187 rectangular
Waveguide is the standard used by
Spring8.
Components and accessories are
available from the industry
Manufactured by Mitsubishi
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

18. C-band accelerating structures
Spring8 adopts 3p/4, CG, TW, 1.8 m. units, with symmetrical in-out coupling RF slots.
The 3p/4 mode allows to have more space to insert the SiC HOM damper disks because of
longer RF cells (≈ 20 mm).
SPARC operates in single bunch mode.
We intend to use 2p/3, TW, 1.5 m. sections with NO HOM dampers,
scaled by the SLAC-type models.
The last choice is between CG and CI sections.
CG structures were conceived at SLAC, before the invention of the SLED, to offset
the RF voltage drop along the sections due to the RF losses
They consist of a series of RF cells with smooth decrease, along the longitudinal axis
of iris and outer diameter sizes.
However, in CG’s, the gradient along the section, due to the exponential profile of a SLED pulse,
is no longer constant and the effective field seen by the particles increases with z.
CI structures, with regular RF-cell size, would be easier to fabricate and, therefore, cheaper.
With CI units, the SLED-pulse exponential decay is, at least in part, compensated.
Also, with a single bunch, the B.B.U., that can happen in CI’s (due to their geometrical homogeneity)
does not take place.
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

19. Scaling the SLAC-type model (*)
.. C-band accelerating structures ….
Scaling the SLAC-type model (*)
S-band (SLAC-type)
CI C-band
note
F (MHz)
2856
5712
scales (°) as f
tf (μsec)
0.8
0.3
scales as f-3/2
QAV
13,000
9,500
scales as f-1/2
t = w·tf /(2Q) [Np]
0.56
----
ZAV (MW/m)
≈ 53 to 60
≈ 80
scales as f1/2
vg/c = L /(ctf)
≈ 0.02 to 0.006
≈ 0.017
(*), Nevertheless, precise RF design and code simulations are necessary.
An R&D activity is in progress
at LNF to desing and build a TW section to be tested at high power.
(°) - G. Loew & R. Talman, SLAC-PUB 3221,
S-band SLAC-type section
center cell
iris-dia 2a = mm
cell-dia 2b = mm
C-band CI section
all cells
iris-dia 2a = mm
cell-dia 2b = mm
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

20. .. C-band accelerating structures ….
For a CI -TW structure °°
(°°) . J. Le Duff, LAL/RT/84-01
Therefore, we think to use a CI section for the following reasons:
1) it is easier to fabricate; thus, it is cheaper.
2) with a Sledded pulse, the field profile along the section is
more or less constant and there are no field enhancements
in the last cells that could cause discharges.
3) Since SPARC operates in single bunch mode, the geometrical
homogeneity of the section should not cause BBU.
4) On the other hand, it must be said that, in order to have the best
advantage from a CI section, the SLED parameters (i.e the β factor)
should be optimized. P
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

21. .. C-band accelerating structures ….
STEPS TOWARD THE ACHIEVEMENT OF C-BAND ACCELERATING SECTIONS
u Contact Industry (Mitsubishi)
u RFQ of 2 C-band, TW, CI, 1.5 m. sections.
u Design a 20÷30 cell prototype
u Design the coupler (with e.m. symmetry)
Construction and bench-characterization
of the prototype.
Brazing the model in our vacuum furnace.
High power RF test of the model at LNF
Construction and brazing of two
1.5 m structures at local firms
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

22. S-band section to be replaced with 2 C-band structures
LNF vacuum furnace
0.8 m high
800°C
10-6 mbar
S-band section to be replaced
with 2 C-band structures
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

23. X X C-band station layout Time Schedule 50 MW 5712 MHz klystron
0.5 μsec
50 MW
5712 MHz
klystron
C-band station layout X
30 MW
2.5 μsec
Waveguide losses ≈ 0.03 dB/m ≈ 10% X
40 MW
40 MW
≈ 37÷38 MV/m
≈ 110 MeV
2009
2010
2011
2012
MOD
KLY
Waveguides & SLED
Accel. sections
Power & beam test
Time Schedule
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009

24. Conclusions & Outlook w
The SPARC energy up-grading to > 200 MeV will be made with a C-band system.
An R&D program to develop the C-band sections at LNF is about to start.
We aim to realize two GHz, TW, CI, 2p/3, 1.5 m. accel. Structures.
A call for tender will be issued after summer to purchase the power modulator
The klystron is supplied by a sole company. The order will be made in autumn 2009.
‘X-ray Science at the Femto to Attosecond Frontier’
UCLA, May 18-20, 2009