Directions for CLIC structures: Lower energy machines and

overview of damping alternatives

A. Grudiev18/04/2012

HG2012, KEK Tsukuba

Outline• 3 TeV and lower enegry CLIC structures

– Structure tapering– Single feed coupler– 500 GeV structure– Intermediate energy structure

• Overview of the damping alternatives– DDS– Choke mode damping

Motivations 3 TeV CLIC structure1. The CLIC_G structure has been designed in 2008. We have learned a lot

since then but the structure is not tested yet and we cannot say for sure if it satisfied CLIC requirements or not.

2. All what we learned so far indicate that CLIC_G is on the edge. We need a reliable test results in order to see where is(are) the weak point(s) of CLIC_G, then we can try to improve it.

3. Moreover, CLIC parameters are frozen since 2008. There is no need in a design of a new structure with different parameters (length, aperture, gradient, etc.).

4. In summary, there is no strong motivation on the new RF design, nevertheless, several new structure prototypes are being designed along two lines:

a. improve high gradient performance for the same bunch charge by tuning the structure tapering

b. simplification of the associated RF network by introducing compact couplers with single feed (CCSF)

Maximum average gradient versus tapering

0 5 10 150

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T18-vg2p6-disk

8.1 12.5

148

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53.037.4

tp = 100.0 ns

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394 BKDs within 0~250hrs193 BKDs within 250~500hrs298 BKDs within 500~750hrs57 BKDs within 750~900hrs74 BKDs within 900~1000hrs34 BKDs within 1000~1200hrs24 BKDs within 1200~1400hrs

T18_SLAC#1• If we forget for the moment about the hot cell #7, the BDR is higher in the last cell, where field quantities are higher.•N.B., in T24, the BDR distribution is more flat but there are also other differences• What is the optimum tapering ?

0 4 8 12 16 20 24240

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7.5 8.4

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41.1

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Pinload = 41.1 MW, Pout

load = 23.4 MW Eff = 0.0 % tr = 0.0 ns, tf = 0.0 ns, tp = 100.0 ns

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T24_KEKT24_vg1.8_disk

T18_vg2.6_disk

Const unloaded versus const loaded gradient ?

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33.048.2

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268

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26.4

Pinload = 60.7 MW, Pout

load = 10.3 MW Eff = 26.1 % tr = 31.0 ns, tf = 62.4 ns, tp = 240.4 ns

CLIC-O

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load = 9.8 MW Eff = 27.9 % tr = 22.4 ns, tf = 62.6 ns, tp = 240.5 ns

CLIC-G

We will try to answer this question in the dedicated test in ‘dog-leg’ area in CTF3 (2013)

See more on the different tapering design at LCWS2011, Granada:http://ilcagenda.linearcollider.org/contributionDisplay.py?contribId=80&sessionId=19&confId=5134

Alternative layout of CLIC SAS based on compact coupler with single feed (CCSF)

AS1 AS2

Hybrid

Load

Load

Load

Advantages:• No splitters (HOMagic-T)• 3 loads per SAS instead of 5• less waveguides• group delay difference between two AS can be adjusted to 0• more space for input/output waveguide connection to the AS

Baseline layoutAlternative layout:• Input and Output kicks are compensated independently within one SAS = AS1 – AS2

Image courtesy of A. Samoshkin

Compact coupler with single feed, geometry

b

idw

idw

ipw

idw

Beam dynamics colleagues are working on to give their OK for using it for CLIC.

See more on the single feed coupler design at LCWS2011, Granada:http://ilcagenda.linearcollider.org/contributionDisplay.py?contribId=80&sessionId=19&confId=5134

500 GeV CLIC structure: CLIC_502Case 3TeV

nominal500 GeV 1st stage

Structure CLIC_G CLIC_502

Average accelerating gradient: <Ea> [MV/m] 100 80

rf phase advance: ∆φ[o] 120 150

Average iris radius/wavelength: <a>/λ 0.11 0.145

Input/Output iris radii: a1,2 [mm] 3.15, 2.35 3.97, 3.28

Input/Output iris thickness: d1,2 [mm] 1.67, 1.00 2.08, 1.67

Group velocity: vg(1,2)/c [%] 1.66, 0.83 1.88, 1.13

N. of reg. cells, str. length: Nc, l [mm] 24, 229 19, 229

Bunch separation: Ns [rf cycles] 6 6

Luminosity per bunch X-ing: Lb× [m-2] 1.22×1034 0.57×1034

Bunch population: N 3.72×109 6.8×109

Number of bunches in a train: Nb 312 354

Filling time, rise time: τf , τr [ns] 62.9, 22.4 50.3, 15.3

Pulse length: τp [ns] 240.8 242.1

Input power: Pin [MW] 63.8 74.2

Pin/CtPp

1/3[MW/mm ns1/3] 18 17

Max. surface field: Esurfmax [MV/m] 245 250

Max. temperature rise: ΔTmax [K] 53 56

Efficiency: η [%] 27.7 39.6

Figure of merit: ηLb× /N [a.u.] 9.1 3.3

Preliminary design is done in 2008

RF design of CLIC_502 prototype using ACE3P

Work of Kyrre Sjøbæk , CERN/Oslo University

Transverse wake in the CLIC_G 1st cell benchmark

Optimization of the surface fields in the cells

Work in progress

Intermediate energy CLIC (1.5 TeV?)

• For the staged approach there will be a set of parameters to be optimized at an intermediate energy ~1.5 TeV taking into account cost and performance of CLIC.

• As a consequence, there probably will be a new accelerating structure for the CLIC main linac to be designed in the near future.

• This work is just taking shape in the CLIC staged approach working group lead by Daniel Schulte

Outline• 3 TeV and lower enegry CLIC structures

– Structure tapering– Single feed coupler– 500 GeV structure– Intermediate energy structure

• Overview of the damping alternatives– CLIC DDS– Choke mode damped CLIC_G– Comparison to waveguide damped CLIC_G

R.M. Jones, DDS Workshop, January 11th, 2012 12 12

CLIC DDS

Roger M. JonesCockcroft Institute and

The University of ManchesterR.M. Jones, DDS Workshop, January 11th, 2012

Choke mode damped CLIC structureJiaru Shi, Hao Zha (Tsinghua University)

Enormous progress in wakefield suppression from radial choke to

See

mor

e in

Jiar

u’s t

alk

Courtesy of Jiaru Shi and Hao Zha

CLIC_Main Linacs Multi-bunch wake effect in various damping schemes

Vasim Khan07.03.2012

CLIC RF structure group meeting, CERN

Vasim Khan CLIC RF structure group meeting, CERN 07.03.2011 15/17

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Direct effect Direct and indirect effect

In CLIC_G

Vasim Khan CLIC RF structure group meeting, CERN 07.03.2011 16/17

TD26_vg1.8_discR05_CC: GdfidL simulations with PML

Envelope wake

A=

a=Kick on multiple bunches

Vasim Khan CLIC RF structure group meeting, CERN 07.03.2011 17/17

Amplification factors

Envelope wake

Wake

Envelope wake

Wake

Envelope wake

Wake

Kick on only first trailing bunch

Vasim Khan CLIC RF structure group meeting, CERN 07.03.2011 18/17

Choke Mode

TD26_discR05_CC

Courtesy of Jiaru Shi

Alternative designs preliminary results

nb311={Fc,Frms,Fworst}={357.924, 31.6057, 1094.08}

Wake (with phase information)

nb311={Fc,Frms,Fworst}={1515.58, 151.144, 6480.98}Envelope Wake

8 x DDS_CircularStructure Wake (with phase information)

Fc Frms Fw

DDS_A 1.29 x 1024 1.25 x 1027 1.32 x 1028

8 x DDS_A 3.4 x 105 2.8 x 107 7.5 x 108

8 x DDS (Circular cells)

6573 5 x 106 1.55 x 108

CERN and Uni. Manchester + C.I. collaboration

Comparison damping scheme alternative

Structure CLIC_G_WDS CLIC_G_CDS 8 x DDS* (Circular cells)

Average accelerating gradient: <Ea> [MV/m] 100 100 100

rf phase advance: ∆φ[o] 120 120 120

Average iris radius/wavelength: <a>/λ 0.11 0.11 0.126

Input/Output iris radii: a1,2 [mm] 3.15, 2.35 3.15, 2.35 4.0, 2.3

Input/Output iris thickness: d1,2 [mm] 1.67, 1.00 1.67, 1.00 4.0, 0.7

Group velocity: vg(1,2)/c [%] 1.66, 0.83 1.38, 0.73 2.06, 1.07

Bunch separation: Ns [rf cycles] 6 6 8

Bunch population x number of bunches: N x Nb 3.72×109 x 312 3.72×109 x 312 4.2×109 x 312

Input power: Pin [MW] 63.8 67.8 73

Max. surface field: Esurfmax [MV/m] 245 246 320

Max. temperature rise: ΔTmax [K] 53 23 72

Efficiency: η [%] 27.7 24.5 23

Fc 1.06 80 6573

Frms 6 15 5 x 106

Fw 26 1300 1.55 x 108

Summary and Outlook Several new structure prototypes are under consideration which have a potential of improving CLIC_G performance or/and cost 500 GeV structure prototype RF design is under way Both new high-gradient test results for CLIC_G and possible reconsideration of CLIC parameters can significantly change motivations and the boundary conditions for the CLIC accelerating structure design. Alternative damping structures show promising results but more work still to be done to arrive to a complete solution satisfying CLIC requirements