Klystron based 375 Ge V ee Linear collider

Klystron based 375 Ge. V e+e- Linear collider. Evaluation. I. Syratchev for the CLIC study and NC & HG community. CLIC Workshop 2013, CERN

The scope of this evaluation is to revisit the klystron based Linear Collider (denoted as CLIC’k hereafter) but now at 375 Ge. V cm. The former developments within NLC/GLC project combined with recent progress in the high gradient acceleration demonstrated within the CLIC project, have a potential to make such an approach attractive enough for the low energy machine. This exercise is not an optimisation study! 1. The possible candidates for accelerating structure were identified earlier (A. Grudiev et. al. ). 2. The RF Pulse Compressor and RF distribution network were critically analysed in an attempt to improve cost/performance issues following the adopted CLIC’k RF unit layout. 3. The klystron and modulator performances were kept close to the demonstrated ones (even reduced where possible). CLIC Workshop 2013, CERN

NLC/GLC X-Band Linac Baseline RF Unit (2004) (One of ~2000 at 500 Ge. V cms, one of ~4000 at 1 Te. V cms) CLIC Workshop 2013, CERN

Dualmoded SLED II efficiency issue Model x 3. 1(3. 44) The gain through the dual-moded SLED-II for a compression ratio of 4 was approximately 3. 1 out of an ideal lossless gain of 3. 44. The round-trip amplitude efficiency is 0. 912. CLIC Workshop 2013, CERN

Designing the linac Klystron peak power for the fixed layout: 2 x Kl(PPM)+PC -> 6 x structures Scaled (244 ns) 12 GHz DM SLED II performance XL 5 klystron measured CLIC_G _502 _1 _2 RF transport efficiency 0. 9 is included 50 Hz Case CLIC_G CLIC_502 #1 #2 Gradient, MV/m 100 80 67 57 Length, m 0. 23 0. 48 P peak, MW 61. 3 74. 2 84 76 Efficiency, % 28. 5 39. 6 41. 9 49. 5 F. Merit [a. u. ] 3. 81 3. 3 2. 79 3. 41 Used input: Klystron efficiency 0. 55 (measured). Modulator efficiency 0. 7 (expected) CLIC Workshop 2013, CERN

2 x Kl(PPM)+PC -> 6 x structures CLIC_G _502 _1 2 x Kl(PPM)+PC -> 8 x structures _2 RF transport efficiency 0. 9 is included 50 Hz CLIC Workshop 2013, CERN

Klystron pulse length evaluation 2 x Kl(PPM)+PC -> 8 x CLIC_G structures PC 50 Hz Including rise/fall time contribution CLIC Workshop 2013, CERN Fixed (0. 7) M. efficiency

CLIC’k RF unit components table x 2 Klystron: PPM or SC? focusing 59 MW, 1. 95 sec 460 k. V, 234 A (µK=0. 75) Efficiency 0. 55 Single output Modulator: 1 per 2 klystrons 460 KV 0. 47 k. A 2. 0 sec flat top Efficiency 0. 76 DM Pulse Compressor : Tout: 244 ns Power gain: 4. 64 Pout: 490 MW x 8 CLIC G accelerating structure: Length: 0. 23 m Pin: 61. 3 MW G Loaded: 100 MV/m CLIC Workshop 2013, CERN 375 Ge. V CLIC’k (general): 1. 2. 3. 4. 5. 6. Energy overhead: 10% Linac filling factor: 1. 2 Number of klystrons: 4. 484 k. K Number of structures: 17. 936 k. S Active length/single linac: 2. 242 km Length/single linac: 2. 7 km

x 8 distribution RF network. Revisited CLIC Workshop 2013, CERN

x 8 RF distribution system NLC/GLC C. Nantista ISG-10 SLAC June 17, 2003 This layout is bulky and complicated enough. It certainly cannot be directly used for the CLIC’k, where the module length is about 2 m long / 8 structures. TE 01 Mode converter 1 ->3 channels RF power head (~0. 6 m long) TE 01 Structure #1 Power divider Load hybrid CLIC Workshop 2013, CERN Load Structure #2

Inline (tap-off) x 8 distribution RF network #2 TE 01 tap-off extractor by S. Kazakov Coupling also can be manipulated with irises TE 01 line, 32 mm 1/4 1/3 1/2 1/1 Common vacuum network 490 MW The use of TE 01 line and tap-off extractors will provide high peak RF power capability, low RF losses (0. 4%) and high vacuum conductivity. The line length is ~1. 8 m. All tap-off extractors have the same design and will not require tight fabrication tolerances (~20 µm). Such a line can be easily adopted to any layout (# structures) CLIC Workshop 2013, CERN

SLED II Pulse compressor. Revisited CLIC Workshop 2013, CERN

#1 Dualmoded SLED II details S. Tantawi et. al. #2 ~29 m, 17. 08 cm #3 #1 Input taper x 2 #2 Super hybrid Output taper x 2 #3 CLIC Workshop 2013, CERN http: //accelconf. web. cern. ch/accelconf/l 04/TALKS/FR 202_TALK. PDF

Alternative#1. One channel design. Mode launcher E surf = 180 MV/m at 490 MW E surf = 90 MV/m at 490 MW 30 MW/channel CLIC Workshop 2013, CERN 490 MW Ø Such a pulse compressor is under construction at KEK Ø Potentially, the factor >2 cost reduction compared to DM SLED II can be anticipated – one channel and much less sophisticated RF network. Indirect savings will come from halving the number of pipes needed to be installed in a tunnel. Ø Compared to DM SLED II, OC SLED is 8% less efficient. Ø High RF power capability is the biggest issue. Another design of the mode launcher may solve this problem

Alternative#2. SLED, (single cavity) design. Ph. M V 1 1 V 2 2 AM Load BOC, Q 0=2 x 105 Cavity is about 30 cm in To structures Modulator rise time C-band BOC, Q 0 =2. 04 x 105 Courtesy PSI CLIC Workshop 2013, CERN SLED pulse compressor with ‘flat top’ is ~25% less efficient then SLED II. Thus, its implementation will require 25% more klystrons (1120) and a similar increase in the average power (+ 13. 75 MW). The layout should also be changed from 8 to 6 structures per RF unit. However, this will allow the removal of ~80 km of SLED II pipes (1600 m 3 of vacuum volume and 40 000 m 2 of copper surface). One must not forget the cost/consumption of the vacuum pumps (6 pumps/ PC), active tuners and electronics, as well as big savings in the tunnel integration.

CLIC’k RF unit layout The alternative PC schemes certainly must be considered (especially for the low energy machine), but for our evaluation, we will keep DM SLED II as a base line option, as its performance was confirmed through the high RF power testing. 2 -pack solid state modulator 460 k. V, 2 s flat top PPM klystrons 59 MW 1. 95 s 118 MW 1. 95 s TE 01 transfer line (? m) x 4. 64 TE 01 900 bend ~17. 7 m, 16. 3 cm Inline RF distribution network Common vacuum network 492 MW 244 ns x 8 accelerating structures, 100 MV/m loaded gradient 2 m, 1. 83 active Compared to NLC, the energy gain per unit in CLIC’k case is 26% lower (need more klystrons per meter), but the unit active length is ~ 2 time shorter. CLIC Workshop 2013, CERN

X-band klystrons. CLIC Workshop 2013, CERN

KMD and X-Band Overview, January 5, 2011 Erik Jongewaard Klystron XL 4 series X-band klystrons (industrialized) design Klystron XL 5 series 18 tubes built to date (not counting rebuilds) 5 tubes have been fabricated at SLAC (1. 5 are in operation). The first tube is ordered from industry (CPI) CLIC Workshop 2013, CERN Efficiency 32. 5% performance CLIC’k target CLIC’k klystron: 59 MW 418 k. V, 324 A (µK=1. 2) Efficiency 0. 436 CLIC’k klystron: 59 MW 404 k. V, 308 A (µK=1. 2) Efficiency 0. 474

X-band klystrons#2 PPM Klystron. PPM (KEK) and XC (SLAC) series performance design s XP 3 -4 • Integral pole piece drift tunnel for reduced transverse field • Increased coupler iris radii • Air cooled • 75 MW at 1. 62 μs pulse length, 120 Hz • 1. 3% beam interception (very good) XP 3 -3 CLIC’k klystron: 59 MW, 2 sec 460 k. V, 234 A (µK=0. 75) Efficiency 0. 55 Single output (a la XL) CLIC Workshop 2013, CERN CLIC’k target “Safe” area (120 Hz) MW The PPM technology for the high peak RF power klystrons has not matured yet. The new klystrons in the pipeline have not been built at SLAC at this time. However, the achieved results can assure that CLIC’k klystron development is a feasible task.

PPM focusing vs. Superconducting Solenoids 1994 PPM, KEK …A superconducting focusing solenoid system for an X band klystron has been developed. The system consists of a conduction cooled superconducting solenoid, a GM refrigerator and high Tc material current leads. The system cools down to the operation temperature of about 4 K by 4 days just by turning on the refrigerator…. In the past 2 decades, the SC technology has progressed a lot. It is worth revising the use of SC (cryogen-free) solenoids for the klystrons again. If cost effective, such an approach will bring benefits for the technology as a whole. CLIC Workshop 2013, CERN

SLAC S-band 5045 tube (>800 tubes statistics). 65 MW x 3. 5 µs x 41 k. W 8 A/cm 2 Life time issues#1 Includes ‘learning curve’ Production yield High production rate cathode window and leaks Low production rate Gaussian fit: µ=56000 =13000 …All tubes eventually fail, at which point they must be repaired or scrapped… But 44 of them run over 100000 hours! The most common failures are associated with the windows and failures are likely related to an end of life cathode. The average of online klystrons in the gallery is over 50, 000 high voltage. The 12 Month Average MTBF now averages about 90, 000 hours. CLIC Workshop 2013, CERN

Life time issues#2 M. V. Fazio, proceedings IPAC 2011, Spain SLAC 5045 XL 5 projection ~4000 hours “…For any mature, well-designed tube the primary mode of failure is cathode end-of-life, a result of barium depletion…Figure is based on a compilation of measured data taken within the past 30 years. . . ” Direct scaling for the XL 5 life time gives 27 000 hours. However, the existing (much improved) RF window design of XL 5, can decrease probability of failure. We will consider next, that CLIC’k klystron life time can be as high as 35 000 hours. CLIC Workshop 2013, CERN CLIC’k klystron life time projection µ=7. 3 =1. 0

Modulator CLIC Workshop 2013, CERN

State of art SLAC (2 -pack) KEK(2 -pack) 1. 8 x 2. 9 m 2 footprint. CLIC’k Modulator: 2 -pack 460 KV 0. 47 k. A 2. 0 sec flat top Efficiency 0. 76 Top view 500 k. V, 0. 5 k. A, 1600 ns 1. 7 x 1. 15 m 2 footprint DFM 2, concept CLIC Workshop 2013, CERN These ‘compact’ modulators were developed back in 2004, but have never been build or tested to their full specs.

Modulator & Space reservation issues Because of the high accelerating gradient and thus the need for high RF power density (245 MW/m), there is a very severe demand on space reservation (~ 1 klystron/m) in the service tunnel to insure a high enough technical gradient. As a first approximation, the DFM 2 modulator can be fitted. More studies (which should include space reservation for all the other systems) will be needed to prove such a concept. 2. 5 m 1. 5 m Power supply for 2 x modulator DFM 2 4. 0 m CLIC Workshop 2013, CERN

Discussion Ø The X-band high power production technology is matured enough and most likely does not need extensive R&D, but certainly cost/efficiency optimisation and wider industrialization efforts are needed. Ø In collaboration with other labs and industries, experts from CERN can participate in the following activities: 1. Design and fabrication of SC solenoid for X(L)-band klystrons. 2. Fabrication and testing of compact 2 x Pack modulator. 3. RF network and pulse compressor evaluation. High gradient technology is now gaining momentum. Technical and economical improvements in RF power production, distribution and particle acceleration will bring benefits to the community. CLIC Workshop 2013, CERN

S. Tantawi presentation …collaborative research towards transformational RF source technology at SLAC <50 k. V >5 MW >60% PPM focusing MBK 16 50 MW MBK 64 Sami Tantawi promised to demonstrate X-band MBK 16 in operation this year! Choice of the Material (SLAC data); >factor x 1. 5 in gradient? hard Cu. Ag soft Cu hard Cu CLIC Workshop 2013, CERN hard Cu. Ag, initial We should invest and are investing into the efforts to make the high gradient even higher and power production more efficient.

GREEN TECHNOLOGY R. Zennaro presentation Klystrons: Toshiba development for PSI From 50 Hz 2. 5 s to 100 Hz 3 s with heat recovering system (HRS) Toshiba E 37202 60 Hz 2. 5 s Delivered in May 2011 Toshiba E 37210 100 Hz 3. 0 s Delivered in December 2011 Toshiba E 37212 100 Hz 3. 0 s with adapted to HRS SAT in April 2013 ü Can we convert RF power (loads) and klystron’s spent beam energy directly into electricity in an efficient way? This could be the topic for the coming “…High gradient technology” Workshop. The klystron collector cooling water is at 80 °C (separate circuit) the body at 30 °C. The 80 °C water is used to heat PSI buildings (up to 9000 MWh/year) CLIC Workshop 2013, CERN

HG 2012 at KEK HG 2013 International Workshop on Breakdown Science and High Gradient Technology ICTP, Adriatico Guesthouse, Kastler Lecture Hall Trieste, Italy 3 -6 June 2013 https: //indico. cern. ch/conference. Display. py? ovw =True&conf. Id=208932 Now in our seventh year. Focus steadily expanding to include broad high-gradient, normal-conducting RF community. http: //indico. cern. ch/conference. Display. py? conf. Id=231116 CLIC Workshop 2013, CERN