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.

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

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

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

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

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

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

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

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

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

… 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 width @ 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 8÷9 months a.r.o. ‘X-ray Science at the Femto to Attosecond Frontier’ UCLA, May 18-20, 2009

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

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

≤ 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

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

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

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

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

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 = 22.066 mm cell-dia 2b = 82.272 mm C-band CI section all cells iris-dia 2a = 11.033 mm cell-dia 2b = 41.136 mm ‘X-ray Science at the Femto to Attosecond Frontier’ UCLA, May 18-20, 2009

.. 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

.. 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

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

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

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