klystron based 375 gev e+e- linear collider. evaluation

CLIC Workshop 2013, CERN

Klystron based 375 GeV e+e- Linear collider. Evaluation.

I. Syratchev for the CLIC study and NC & HG community.


The scope of this evaluation is to revisit the klystron based Linear Collider (denoted as CLIC’k hereafter) but now at 375 GeV 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.

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) .

This exercise is not an optimisation study!


NLC/GLC X-Band Linac Baseline RF Unit (2004)(One of ~2000 at 500 GeV cms, one of ~4000 at 1 TeV cms)


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.

Model x 3.1(3.44)

Dualmoded SLED II efficiency issue


Scaled (244 ns) 12 GHz DM SLED II performance

CLIC_G _502 _1 _2

XL5 klystron measured

Klystron peak power for the fixed layout: 2 x Kl(PPM)+PC -> 6 x structures

RF transport efficiency 0.9 is included

Used input: Klystron efficiency 0.55 (measured). Modulator efficiency 0.7 (expected)

Case CLIC_G CLIC_502 #1 #2

Gradient, MV/m 100 80 67 57

Length, m 0.23 0.23 0.48 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

50 Hz

Designing the linac


2 x Kl(PPM)+PC -> 6 x structures 2 x Kl(PPM)+PC -> 8 x structures

CLIC_G _502 _1 _2

RF transport efficiency 0.9 is included

50 Hz


Fixed (0.7) M. efficiencyIncluding rise/fall time contribution

2 x Kl(PPM)+PC -> 8 x CLIC_G structures

Klystron pulse length evaluation

50 Hz

PC


x 2 Klystron:PPM or SC? focusing59 MW, 1.95 sec460 kV, 234 A (µK=0.75)Efficiency 0.55Single output

Modulator:1 per 2 klystrons460 KV0.47 kA 2.0 sec flat top Efficiency 0.76

DM Pulse Compressor : Tout: 244 ns Power gain: 4.64Pout: 490 MW

x 8 CLIC G accelerating structure:Length: 0.23 mPin: 61.3 MWG Loaded: 100 MV/m

CLIC’k RF unit components table

375 GeV CLIC’k (general):

1. Energy overhead: 10%2. Linac filling factor: 1.23. Number of klystrons: 4.484 kK4. Number of structures: 17.936 kS5. Active length/single linac: 2.242 km6. Length/single linac: 2.7 km


x 8 distribution RF network. Revisited


C. Nantista ISG-10 SLAC June 17, 2003 x8 RF distribution system NLC/GLC

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.

Mode converter

Power divider

hybrid

Load

Load

Structure #1

Structure #2

TE01TE011->3 channels RF

power head (~0.6 m long)


Inline (tap-off) x 8 distribution RF network #2

TE01 tap-off extractor by S. Kazakov

1/4 1/3 1/2 1/1

TE01 line, 32 mm Common vacuum network

The use of TE01 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)

490 MW

Coupling also can be manipulated with irises


SLED II Pulse compressor. Revisited


Super hybrid

#1

#1Input taper x2

#2

#2

Output taper x2

#3

#3

~29 m, 17.08 cm

Dualmoded SLED II detailsS. Tantawi et. al.

http://accelconf.web.cern.ch/accelconf/l04/TALKS/FR202_TALK.PDF


Mode launcher

Alternative#1. One channel design.

Such a pulse compressor is under construction at KEK 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.

Compared to DM SLED II, OC SLED is 8% less efficient. High RF power capability is the biggest issue. Another design of the mode launcher may solve this problem

E surf = 180 MV/m at 490 MW

E surf = 90 MV/m at 490 MW

490 MW

30 MW/channel


Alternative#2. SLED, (single cavity) design.

1

2

V1

V2

PhM

AM

To structuresBOC, Q0=2x105

Cavity is about 30 cm in

Load

Modulator rise time

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 m3 of vacuum volume and 40 000 m2 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.

C-band BOC,Q0 =2.04x105

Courtesy PSI


~17.7 m, 16.3 cm

2-pack solid state modulator

59 MW1.95 s

PPM klystrons

118 MW1.95 s

492 MW244 ns

2 m, 1.83 active

x 8 accelerating structures, 100 MV/m loaded gradient

CLIC’k RF unit layout

TE01 900 bend

TE01 transfer line (? m) Inline RF distribution network

Common vacuum network

460 kV, 2 s flat top

x 4.64

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.

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.


X-band klystrons.


Klystron XL4 seriesX-band klystrons (industrialized)

Efficiency 32.5%

18 tu

bes b

uilt

to d

ate

(not

cou

nting

rebu

ilds)

design

performance

CLIC’k klystron:59 MW418 kV, 324 A (µK=1.2)Efficiency 0.436

Klystron XL5 series

CLIC’k klystron:59 MW404 kV, 308 A (µK=1.2)Efficiency 0.474

KMD and X-Band Overview, January 5, 2011 Erik Jongewaard

CLIC’k target

5 tubes have been fabricated at SLAC (1.5 are in operation). The first tube is ordered from industry (CPI)


X-band klystrons#2PPM Klystron. PPM (KEK) and XC (SLAC) series

designXP3-4• 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)

performance

XP3-3CLIC’k target

s

MWCLIC’k klystron:59 MW, 2 sec460 kV, 234 A (µK=0.75)Efficiency 0.55Single output (a la XL)

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.

“Safe” area (120 Hz)


PPM, KEK 1994

…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….

PPM focusing vs. Superconducting Solenoids

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.


8 A/cm2

Production yield

High production rate

The most common failures are associated withthe windows and failures are likely related to an end of lifecathode. The average age of online klystronsin the gallery is over 50,000 high voltage. The 12 Month Average MTBF now averages about 90,000 hours.

SLAC S-band 5045 tube (>800 tubes statistics). 65 MW x 3.5 µs x 41 kW

Low production rate

Life time issues#1

…All tubes eventually fail, at which point they must be repaired or scrapped…But 44 of them run over 100000 hours!

cathodewindow and leaks Gaussian fit:

µ=56000=13000

Includes ‘learning curve’


Life time issues#2

SLAC 5045

XL5 projection

“…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 acompilation of measured data taken within the past 30 years...”

Direct scaling for the XL5 life time gives 27 000 hours.However, the existing (much improved) RF window design of XL5, can decrease probability of failure. We will consider next, that CLIC’k klystron life time can be as high as 35 000 hours.

CLIC’k klystron life time projection

µ=7.3=1.0

M.V. Fazio, proceedings IPAC2011, Spain

~4000 hours


Modulator


1.7 x 1.15 m2 footprint

DFM2, concept

500 kV, 0.5 kA, 1600 ns

1.8 x 2.9 m2 footprint.

Top view

SLAC (2-pack)KEK(2-pack)

CLIC’k Modulator:2-pack460 KV0.47 kA 2.0 sec flat top Efficiency 0.76

These ‘compact’ modulators were developed back in 2004, but have never been build or tested to their full specs.

State of art


Power supply for 2 x modulator

2.5 m 1.5 m

4.0 m

DFM2

Modulator & Space reservation issuesBecause 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 DFM2 modulator can be fitted. More studies (which should include space reservation for all the other systems) will be needed to prove such a concept.


Discussion 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.

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.


MBK 16 MBK 64

<50 kV>5 MW>60%PPM focusing

50 MW

Sami Tantawi promised to demonstrate X-band MBK 16 in operation this year!

…collaborative research towards transformational RF source technology at SLAC

Choice of the Material (SLAC data); >factor x1.5 in gradient?

hard CuAg

soft Cu

75 100 125 150 175 200 22510 -7

10 -6

10 -5

10 -4

10 -3

10 -2

10 -1

10 0

Gradient [M V /m ]

Brea

kdow

nPr

obab

ility

[1/p

ulse

/met

er]

a0.105 , t2.0 mm , Ag150ns 1st1a0.105 , t2.0 mm , Clamped 2150 ns a0.105 , t2.0 mm , 150 nsa0.105 , t2.0 mm , Ag150ns

hard CuAg, initial

soft Cu

hard Cu

We should invest and are investing into the efforts to make the high gradient even higher and power production more efficient.

S. Tantawi presentation


Klystrons: Toshiba development for PSIFrom 50 Hz 2.5 s to 100 Hz 3 s with heat recovering system (HRS)

Toshiba E37202 60 Hz 2.5 s

Delivered in May 2011

Toshiba E37210 100 Hz 3.0 sDelivered in December 2011

Toshiba E37212 100 Hz 3.0 s with adapted to HRSSAT in April 2013

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)

R. Zennaro presentation GREEN TECHNOLOGY

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.


HG2013 International Workshop onBreakdown Science andHigh Gradient Technology

ICTP, Adriatico Guesthouse, Kastler Lecture HallTrieste, Italy3-6 June 2013

HG2012 at KEK

https://indico.cern.ch/conferenceDisplay.py?ovw=True&confId=208932

http://indico.cern.ch/conferenceDisplay.py?confId=231116

Now in our seventh year. Focus steadily expanding to include broad high-gradient, normal-conducting RF community.

klystron based 375 gev e+e- linear collider. evaluation

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