energy up-grading of the sparc photo-injector, with a c-band rf system

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 GROUPD. 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, FranceM. Bougeard, B. Carré, D. Garzella, M. Labat, G. Lambert, H. Merdji, P. Salières, O. Tchebakoff, CEA Saclay, DSM/DRECAM, France.

SPARC electron beam main parameters nominal achieved

Electron beam energy (MeV) 150 150

Bunch charge (nC) 1 0.3

Bunch rep.rate (Hz) 10 10

Cathode RF peak field (MV/m) 120 120

Laser pulse duration (ps) – gaussian profile 10 6-8

Bunch peak current (A) 100 40

rms norm. transv. Emittance (mm-mrad) < 2 2

rms bunch length at linac exit (mm) 1 ≈ 1

rms beam spot size at linac exit (mm) 1 ≈ 0.7

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

‘X-ray Science at the Femto to Attosecond Frontier’UCLA, May 18-20, 2009

10 dB

d.c.

d.c.

TW CG 2p/3

9 MWd.c.

d.c.

RF GUN

P.S

60 MW 60 MW0.8

m

sec 0.8

m

sec

P.S

20 MW

3

m

sec

C

2128C P.S.Att

K45 MW

4.5

m

sec

d.c.

A250 W

P.S.

SLED

K2128C

Fastphase-shifter

d.c.

Att

250 W

130MW0.8

m

sec

2856 MHz RFIN

40 MW

beam out

20 MW3

m

sec

Att P.S

2 MW

RF Defl

Switch

d.c.

Load

d.c.

ATT

3 dB

3 dB

5 dB

360°

360°

TW CG 2p/3 TW CG 2p/3

LASER BEAM

SSA

TWT

CIRC.


SPARC RF LAYOUTSPARC RF LAYOUT

KLYSTRON GALLERY

MOD 1MOD 2

ACCELERATORHALL


cad view

Linac commissioning results .. so far …

beam parameters

Max bunch charge limited to 300 pC due, mainly, to poor cathodesurface 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%

emittance measurements Typical rms value ≈ 2 μm @ 250 pC


Kly. Mod. HV stability ≤ 0.1 %RF Phase jitter ≤ 70 fsec … with feedback ….

Experiments underway and present results ….

SASE experiment SASE experiment

VELOCITY BUNCHING experiment VELOCITY BUNCHING experiment

Coherent radiation at 500 nm have been observed with amplification factor ≈ 10 6

rms Smif mif 500

-35.243·10

480 490 500 510 520

wavelength (nm)

Pow

er S

pect

rum

(a.u

.)Single shot spectra at the end of the undulator linePulse energy measured at the undulator intersections


Measured RMS bunch length of a 300 pC beamvs the phase of the first accelerating structure

BUNCHLENGTH

psec

PHASE SHIFT

compression factor ≈ 14Ipeak ≈ 120 A

over-compression

SPARC photos


ONDULATOR SECTION

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

(*): Italian Minister for Education, University & Research(*): Italian Minister for Education, University & Research


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 surpluson the total energy (≈ 240 vs 200 MeV)

… 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



GUNACC. STRUCTURE

KlystronN°1

S-BAND Station 2856 MHz – 45 MW

C-bandStation

C-bandENERGY

COMPRESSOR

C-band acc. structures35 MV/mE ≈ 105 MeVE ≈ 240 MeV

Up-graded layout

ACC. STRUCTURE

HIGH GRADIENT SECTION ≈ 120 MeV

ACC. STRUCTURE

KlystronN°2

ENERGY COMPRESSOR

S-BAND Station 2856 MHz – 45 MW

5712 MHz50 MW/2.5µs

ΔE ≈ + 70÷80 MeV


40 MW 40 MW

90 MW/0.5µs

9 MW

≈120 MW/0.8µs

≈ 50 MW ≈ 50 MW


KLYSTRON Manufactured by … Toshiba Electron Tubes & Devices Co., Ltd (TETD)

TOSHIBA 37202

.. contacts are in course with TETD …..

… delivery time 8÷9 months a.r.o.

double output klystronwith waveguide re-combiner

Frequency (MHz) 5712

Peak outpu Power (MW) 50

RF Gain (dB) ≥ 50

Efficiency (%) ≥ 40

RF pulse width @ 3 dB (μsec) 2.5

Rep. Rate (Hz) 60

Beam voltage/current (kV/A) 350/310

Kly main specs.



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.


HV PULSED MODULATOR

30005300

3510

K

T

20001200

2900

3 dB

SLED

ACCELERATOR HALL

MID-GALLERY

KLYSTRON-GALLERY

6 m

3 m

3 m

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.


HV PULSED MODULATOR

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 (‰) ≤ ± 1

Pulse rise/fall time (µsec) ≤ 50/100

Pulse to Pulse time jitter (nsec) ≤ ± 2.5

Pulse width time jitter (nsec) ≤ ± 5

≤ 1300 mm≤ 4000 mm

≤ 2500 mmKLY

MOD

Main Modulator Specs

Size constraints


SCANDINOVA MODULATOR

NICHICON MODULATOR

1400 mm

1000 mmcourtesy T. Shintake

Full Solid State system

Standard design with PFN & Thy …..but very compact because immersed in oil

HV PULSED MODULATOR


3 m.

3 m.

SPARC buildingmid-gallery

winch or pulley system


RF Pulse Compressor and Waveguide system

Spring8 C-band power distribution system, courtesy T. Shintake

SLEDTE038 modePout ≈ 200 MWTp = 0.5 µsec- exponential pulse -


Manufactured by Mitsubishi

Waveguide system

The WR187 rectangularWaveguide is the standard used bySpring8.

Components and accessories areavailable from the industry

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 oflonger 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.

.. 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

·tf /(2Q) [Np] 0.56 0.56 ----

ZAV (M/m) ≈ 53 to 60 ≈ 80 scales as f1/2

vg/c = L /(ctf) ≈ 0.02 to 0.006 ≈ 0.017 ----

(°) - G. Loew & R. Talman, SLAC-PUB 3221,

center cell

S-band SLAC-type section

iris-dia 2a = 22.066 mmcell-dia 2b = 82.272 mm

all cellsiris-dia 2a = 11.033 mmcell-dia 2b = 41.136 mm

C-band CI section

(*), Nevertheless, precise RF design and code simulations are necessary.An R&D activity is in progressat LNF to desing and build a TW section to be tested at high power.


For a CI -TW structure °°

(°°) . J. Le Duff, LAL/RT/84-01

MWMeV PeZLPU 0

21

0 912 //


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


STEPS TOWARD THE ACHIEVEMENT OF C-BAND ACCELERATING SECTIONS

Contact Industry (Mitsubishi)

RFQ of 2 C-band, TW, CI, 1.5 m. sections.

Design a 20÷30 cell prototype

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



LNF vacuum furnace

0.8 m high800°C10-6 mbar

S-band section to be replaced with 2 C-band structures

C-band station layout

Time ScheduleX

X

50 MW5712 MHzklystron 30 MW

2.5 μsec

90 MW0.5 μsec

40 MW 40 MW

Waveguide losses ≈ 0.03 dB/m ≈ 10%

≈ 37÷38 MV/m

≈ 110 MeV

2009 2010 2011 2012

MOD

KLY

Waveguides & SLED

Accel. sections

Power & beam test


Conclusions & Outlook

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 5.712 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.


energy up-grading of the sparc photo-injector, with a c-band rf system

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