Recent high-gradient results,rf testing, places and plans

Steffen Döbert, CLIC Workshop, 17.10.2008

• Test facilities

• High gradient results

• Future testing program

For more detailed high gradient results please see:

The x-band structure design and testing workshop: June 2007

http://indico.cern.ch/conferenceDisplay.py?confId=15112

The High-Gradient workshop, October 2006

http://hg2006.web.cern.ch/HG2006

D FFD

D F D

D F D D F D

D F D

DF DF DF DF DF DF DF DF DF

D F D

F DF D

D FFFDD

D F DD F D

D F DD F D D F DD F D

D F DD F D

DF DF DF DF DF DF DF DF DF DFDF DF DF DF DF DF DF DF DF DF DF DF DF DF DF DF

D F DD F D

F DF DF DF D

Drive Beam Injector

Drive Beam AcceleratorX 2 Delay Loop

X 4 Combiner

Ring

Probe Beam

Injector

4 A - 1.2 s1.5 GHz, 150 MeV

30 A - 140 ns12 GHz, 150 MeV

16 structures - 3 GHz - 7 MV/m

High Power test fasilities at CERN

Two Beam Test stand 12 GHz, 2008

30 GHz Test stand

Rf power production with CTF3

70 MW, 100 ns

200 MW, 140 ns

TBL, 16*160 MW, 140 ns

Klystron Test stand 12 GHz, 200950 MW-150 MW, 500 ns

X-band test facilities at SLAC

• NLCTA: 3 Test Stations: 2x50 MW into SLEDII, 300 MW , 240-400 ns, fully automated conditioning

• Klystron Lab: 2 single Klystron test stands 2x50 MW into SLED II ASTA bunker

X-band Test Facilities at KEK

Single Klystron (50 MW) test stand up and running

NEXTEF: Available from fall 2007, 2x50 MW, 400 ns, 24/7 operation

Reached nominal 30 GHz CLIC values :

150 MV/m 70 ns

Overview of 30 GHz results

Molybdenum shows higher gradient but different slope

HDS performs worse than round brazed structure

New Materials for High-Gradient

Copper has still the best performance at low break down rate

HDS4vg2.6_thick_150degC40vg8_pi/2

Recent 30 GHz results

Structure P (MW)

E (MV/m)

PT1/3/C (wue)

C30vg4.7 20.2 92 7.5

HDS60vg8.0 16.1 61 5.6

HDS60vg5.1 13.3 75 5.5

C40vg7.4_pi/2 19.2 65 6.2

HDS4vg2.6_thick

7.5 67 2.8

All data at 70 ns pulse length and 10-3 breakdown rate

Summary of 30 GHz results

Hybrid damped structures (HDX) at x-band

Frequency scaling

Scaled structures show very similar performance

HDS-type structures show consistently limited performance

A reference structure for CLIC from NLC

Length: 53 cm

Phase advance: 120 deg

Group velocity: 3 %

a/: 0.13

Es/Eacc: 2.2

Pin (65 MV/m):41 MW

Coupler: mode luncher

Preparation: H-brazing,diamond

turning

Tests of old NLC structures at short pulses

T53vg3MC can be used as a first reference for the new CLIC parameters

CLIC goal

Structure P (MW)

E (MV/m)

PT1/3/C (wue)

T53vg3MC (50ns) 118 110 18

T53vg3MC (100ns)

107 105 20

H75vg3 (150 ns) 155 97 27

HDX11vg5 (70 ns)

59 60 9

All data around ~10-6 breakdown rate

Summary of 11 GHz results

Pulse Length Dependence

Conclusions on recent structure tests

Current CLIC design within experimentally demonstrated region

27 wue have been measured (Design used 18)

120 MW input Power for 100 ns into first cell of T53

Hybrid Damped Structures show performance deficit (short phase advance, slots, quadrants and milling)

Copper is still the best material to make accelerating structures (Molybdenum still has some potential, shallow slope seen in previous experiments could be due to iris clamping, slow processing as usual)

Exactly scaled structures seem to perform independent of frequency (therefore 30 GHz test are still meaningful)

Structure manufacturing technology seems to play an important role Damping has to be integrated and tested

Structure Program Philosophy

1. Gradient program (highest priority):Demonstrate a CLIC prototype structure:

(100 MV/m,300ns, 12 GHz, damping)

2. General high gradient R&D (high priority):Find the universal breakdown theory, P/C, phase advance,

materials Try to do that with simple and clear experiments (single cells)

3. Fabrication technology for potential cost savings (high priority):Disks, slots, quadrants, surface treatment, procedures

Start with simple structures and experiments (single cells, DC-spark),

eventually we need to go to full structures

30 GHz break down R&D program in CTF3

- HDS4_vg2.6_thick (iris thickness, phase advance, P/C) Finished !

- NDS4_vg2.5_thick (Effect of slots and quadrants) Installed !

- C30_vg4.7_quad (clear experiment for fab. Tech.)

Decision point, see flow chart !

- HDS11_vg2 (clear P/C experiment without other changes)

- HDS4_vg2.6_thick_clean (compares cleaning with previous)

- NDS4_vg3.6_thin (iris thickness in comparison with NDS4_thick)

- C30_vg2.6 (P/C)

- C30_vg8.2 (P/C)

- C30_vg4.7_sb (speed bump)

- C30_vg2_TM02 (vg)

- HDS 11 copper/molybdenum (for better statistics)

New list of planned experiments ordered by priority and reality

30 GHz flow chart

C30_vg2_TM02

HDS4_vg2.6_thick (negative test result)

HDS11_vg2

HDS4_vg2.6_thick_clean

NDS4_vg2.5_thick (under test)

NDS4_vg3.6_thin

Quads or slot are a problem

Quads or slot are not a problem

P/C ok

C30_vg2.6

C30_vg8.2

C30_vg4.7_sb

New ideas if needed

2008

2007

Input for x-bandC30_vg4.7_quad

11 GHz CLIC structure program

11.4 GHz:

- TD18_vg2.4_quad (CERN, VDL, Japanese industry) [2x] (test of P/C, damping, quadrant technology)

- T28_vg2.9 (done by SLAC) (conservative approach)

- T18_vg2.4_disk (SLAC,KEK) [4x] {1 CERN, 2 SLAC/KEK (test 1 at SLAC and 1 at KEK), 1 KEK}

(test of P/C in conservative technology, technology comparison)

Decision point, see flow chart

- T18_vg2.4_quad (CERN) (test of P/C, quadrant technology)

- TD18_vg2.4_disk (CERN, KEK) [2x] (mainly test of damping)

- TD28_vg2.9 (CERN) (back up test of damping if others are not successful)

New list of planned experiments

11 GHz flow chart

TD18_vg2.4 geometry OK

2008

TD18_vg2.4geometry not OK

Disks OKQuads OK+Damp

2009

CLIC prototype disks dampedCLIC prototype TD28 like

CLIC prototype quads damped

Go towards more extreme structures

2010

Input from break down R&D

TD18_vg2.4_quadT28_vg2.9T18_vg2.4_disk

TD28_vg2.9

(T18_vg2.4_quad)

TD18_vg2.4_disk

?

DampingNot OK

TD24vg1.7

TD24vg1.7

Aug

Oct Nov Dec

CTF3 30 GHz

NLCTA

Station 1 11.4 GHz

Pi/2 HDS4_vg2.6_thickheat treated

NEXTEF 11.4 GHz

Sept

Jul

Current structure testing program

HDX11 Cularge grains

C30_vg4.7_quad

NLCTA

Station 2 11.4 GHz

2007

NDS4_vg2.6_thick

T53vg3MC

H60vg3S18 ?

Old Clic vg1.1 ?

Apr-Jun Jul-Sep Oct-Dec

CTF3 30 GHz

NLCTA

Station 1 11.4 GHz

C30_vg2.6

NEXTEF11.4 GHz

Jan-Mar

Current structure testing program

C30_vg8.2

C30_vg2_TM02

NLCTA

Station 2 11.4 GHz

2008

C10vg2.9 [2x]

C10vg0.7 [2x]

C10vg2.2_thick [2x]

T18_vg2.4_disk [1]

TD18_vg2.4

T18_vg2.4_disk [2] TD18_vg2.4_qua

d

PETS 11.4 GHz

HDS11_vg2

TD18_vg2.4_quad

T28_vg2.9

C10vg1.3 [2x]

CLEX 12GHz

T18_vg2.4_disk

PETS 12 GHz

Shut down

Shut down

T18_vg2.4_disk [4]

T18_vg2.4_disk [3]

TD18_vg2.4 TD28vg3

Parameters along the structures

TD18_vg2.4 is more extreme in maximum surface field, pulsed heating and lowest group velocity

Parameters of new structure TD24vg1.7

Structure TD24vg1.7

Frequency: f [GHz] 12

Average iris radius/wavelength: <a>/λ

0.11

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

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

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

24, 229

Bunch separation: Ns [rf cycles] 6

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

Bunch population: N 3.72×109

Number of bunches in a train: Nb 312

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

Pulse length: τp [ns] 240.8

Input power: Pin [MW] 63.8

Pin/CtPp

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

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

Max. temperature rise: ΔTmax [K] 53

Efficiency: η [%] 27.7

Figure of merit: ηLb× /N [a.u.] 9.1

Structure Nick-Names

Type No of cells vg (start) special feature

HDS 11 8.3 thick

Constant Imp 30 2.4 thin

Tapered 5 3.6 quad

TDamped clean

Old names New names

- CLIC vg3/1 quadrants damped TD18_vg2.4_quad

- T26vg3MC T28_vg2.9

- CLIC vg3/1 disks undamped T18_vg2.4_disk

- CLIC vg3/1 quadrants undamped T18_vg2.4_quad

- CLIC vg3/1 disks damped TD18_vg2.4_disk

- T26vg3MC disks damped TD28_vg2.9

Scattered Dark Spots

Areas of DiscolorationPatchy breakdown areas along sides of irises

High Current Region

Input Coupler

Iris

Post mortem inspection of HDX11cu

Comparison of 11.4 GHz results

P/C*tp^1/3 [Wu3]

0

5

10

15

20

25

30

2 3 4 5 6

a1 [mm]

P/C

*tp

^1/3

[W

u3