Overview of CLIC main linac accelerating structure design

21/10/2010A.Grudiev (CERN)

C L I CC L I C

CLIC-ACE, 16 Jan. 2008Alexej Grudiev, Structure optimization.

RF design constraints for CLIC

Beam dynamics (BD) constraints based on the simulation of the main linac, BDS and beam-beam collision at the IP:

• N – bunch population depends on <a>/λ, Δa/<a> because of short-range wakes

• Ns – bunch separation depends on the long-range dipole wake suppression

RF breakdown and pulsed surface heating (PSH) constraints:

• ΔTmax(Hsurfmax, tp) < 56 K (accelerating structure life time

issues)

• Esurfmax < 250 MV/m

• Pin/Cin·(tp)1/3 < 18 MW/mm · ns1/3

• (Sc = Re{S} + Im{S}/6)·(tp)1/3 < 4 MW/mm2 · (200 ns)1/3

RF constraints: data analysis 1RF design name f [GHz]

dphi [deg] vg1 [%]

1 DDS1 11.424 120 11.72 T53VG5R 11.424 120 53 T53VG3MC 11.424 120 3.34 H90VG3 11.424 150 35 H60VG3 11.424 150 2.86 H60VG3R18 11.424 150 3.37 H60VG3R17 11.424 150 3.68 H75VG4R18 11.424 150 49 H60VG4R17 11.424 150 4.510 HDX11-Cu 11.424 60 5.111 CLIC-X-band 11.424 120 1.112 T18VG2.6-In 11.424 120 2.613 T18VG2.6-Out 11.424 120 1.0314 T18VG2.6-Rev 11.424 120 1.0315 T26VG3-In 11.424 120 3.316 T26VG3-Out 11.424 120 1.6517 TD18_KEK_In 11.424 120 2.418 TD18_KEK_Out 11.424 120 0.919 SW20A3p75 11.424 180 020 SW1A5p65T4p6 11.424 180 021 SW1A3p75T2p6 11.424 180 022 SW1A3p75T1p66 11.424 180 023 2pi/3 29.985 120 4.724 pi/2 29.985 90 7.425 HDS60-In 29.985 60 826 HDS60-Out 29.985 60 5.127 HDS60-Rev 29.985 60 5.128 HDS4Th 29.985 150 2.629 HDS4Th 29.985 150 2.630 PETS9mm 29.985 120 39.8

constBDR

tE pa 530

High power test results has been scaled to tp=200 nsBDR=1e-6 bpp/m using power scaling lower

based on the fitting the data

3

RF constraints: data analysis 2Data has been scaled to tp=200 ns BDR=1e-6 bpp/m

6/ImRe SS cS4

In TD18, all quantities are close to T18 at the same average gradient, except for the pulsed surface heating temperature rise which is factor 5 higher in the last cell.

0 2 4 6 8 10 12 14 16 180

50

100

150

200

250

iris number

P [

MW

] (b

lack

), E

s (

gre

en),

Ea (

red

) [M

V/m

],

T

[K

] (b

lue)

, S

c*50

[MW

/mm

2 ] (m

agen

ta)

30.6

49.4

157

234

3.3

4.5

79

120

56.8

33.8

Pinload = 56.8 MW, P

outload = 33.8 MW

Eff = 0.0 % tr = 0.0 ns, t

f = 0.0 ns, t

p = 100.0 ns

0 2 4 6 8 10 12 14 16 180

50

100

150

200

250

iris number

P [

MW

] (b

lack

), E

s (

gre

en),

Ea (

red

) [M

V/m

],

T

[K

] (b

lue)

, S

c*50

[MW

/mm

2 ] (m

agen

ta)

8.1 12.5

148

232

2.7

4.4

76

126

53.0

37.4

Pinload = 53.0 MW, P

outload = 37.4 MW

Eff = 0.0 % tr = 0.0 ns, t

f = 0.0 ns, t

p = 100.0 ns

1st generation of CLIC X-band test structure prototypes T18/TD18Parameters at tp=100 ns, <Ea>=100 MV/mT18_vg2.6_disk: TD18_vg2.4_disk:

Very strong tapering inspired by the idea of having constant P/C along the structure

High surface fields

5

2007

0 5 10 15 200

50

100

150

200

250

iris number

P [

MW

] (b

lack

), E

s (

gre

en),

Ea (

red

) [M

V/m

],

T

[K

] (b

lue)

, S

c*50

[MW

/mm

2 ] (m

agen

ta)

26.8 25.1

183193

3.5

3.0

94102

44.4

20.6

Pinload = 44.4 MW, P

outload = 20.6 MW

Eff = 0.0 % tr = 0.0 ns, t

f = 0.0 ns, t

p = 100.0 ns

0 4 8 12 16 20 24240

50

100

150

200

250

iris number

P [

MW

] (b

lack

), E

s (

gre

en),

Ea (

red

) [M

V/m

],

T

[K

] (b

lue)

, S

c*50

[MW

/mm

2 ] (m

agen

ta)

7.5 8.4

176

205

3.03.2

90

108

41.1

23.4

Pinload = 41.1 MW, P

outload = 23.4 MW

Eff = 0.0 % tr = 0.0 ns, t

f = 0.0 ns, t

p = 100.0 ns

In TD24, all quantities are lower than in TD18 at the same average gradient. In particular pulsed surface heating temperature rise reduced by factor 2.

2nd generation of CLIC X-band test structure prototypes T24/TD24Parameters at tp=100 ns, <Ea>=100 MV/mT24_vg1.8_disk: TD24_vg1.8_disk:

Weaker tapering (quasi const gradient) together with smaller aperture (11% instead of 12.8%) reduce surface fields significantly compared to T18/TD18.

6

2007

From RF design to a piece of Copper

IWLC2010 Walter Wuensch 19 October 2010

Scaling to CLIC conditions: Scaled from lowest measured BDR to BDR=4*10-7 and =180 ns (CLIC flat-top is 170 ns), using standard E295/BDR =const. Correction to compensate for beam loading not included – expected to be less than about 7%.

T18 by KEK/SLAC at SLAC #1

T18 by KEK/SLACat KEK

T18 by CERNat SLAC

TD18 by KEK/SLACat SLAC

TD18 by KEK/SLACat KEK

unloaded gradient [MV/m]

Synthesis of accelerating structure test results scaled to CLIC breakdown rate

T24 by KEK/SLACat SLAC

1400

3900

550

Total testing time [hr]

1300

3200

200

T18 by KEK/SLACat SLAC #2

280

60 70 80 90 100 110

HOM damping

HOM damping

Comparison at tp=252 ns, BDR=1e-6 bpp/m

0 2 4 6 8 10 12 14 16 180

50

100

150

200

250

iris number

P [

MW

] (b

lack

), E

s (

gre

en),

Ea (

red

) [M

V/m

],

T

[K

] (b

lue)

, S

c*50

[MW

/mm

2 ] (m

agen

ta)

T18--KEK, tp=252 ns, BDR = 1e-5 bpp/m, <E

a> = 101 MV/m,

13.120.3

149

235

2.7

4.5

76

127

54.1

38.2

Pinload = 54.1 MW, P

outload = 38.2 MW

Eff = 0.0 % tr = 0.0 ns, t

f = 0.0 ns, t

p = 252.0 ns

P/C*tp^(1/3) = 13.4 [MW/mm*ns^(1/3)] P/C*tp^(1/3) = 10.6 [MW/mm*ns^(1/3)]

T18: <Ea> = 101 MW/m TD18: <Ea> = 86.6 MW/m

In TD18, all quantities are lower than in T18 measured at the same tp and BDR, except for the pulsed surface heating temperature rise which is factor 3 higher ???

0 2 4 6 8 10 12 14 16 180

50

100

150

200

250

iris number

P [

MW

] (b

lack

), E

s (

gre

en),

Ea (

red

) [M

V/m

],

T

[K

] (b

lue)

, S

c*50

[MW

/mm

2 ] (m

agen

ta)

TD18--KEK, tp = 252 ns, BDR = 1e-6 bpp/m, <Ea. = 86.6 MV/m

36.5

59.0

136

202

2.5

3.3

68

104

42.6

25.4

Pinload = 42.6 MW, P

outload = 25.4 MW

Eff = 0.0 % tr = 0.0 ns, t

f = 0.0 ns, t

p = 252.0 ns

9

Comparing last cell at tp=252 ns, BDR=1e-6 bpp/mT18: <Ea> = 101 MW/m, Ea = 127 MV/m TD18: <Ea> = 86.6 MW/m; Ea = 104 MV/m

10

0 5 10 15 200

50

100

150

200

250

iris number

P [

MW

] (b

lack

), E

s (

gre

en),

Ea (

red

) [M

V/m

],

T

[K

] (b

lue)

, S

c*50

[MW

/mm

2 ] (m

agen

ta)

21.1 19.0

184194

3.7

3.1

94102

40.5

18.7

Pinload = 40.5 MW, P

outload = 18.7 MW

Eff = 0.0 % tr = 0.0 ns, t

f = 0.0 ns, t

p = 100.0 ns

Near term plans

0 2 4 6 8 10 12 14 16 180

50

100

150

200

250

iris number

P [

MW

] (b

lack

), E

s (

gre

en),

Ea (

red

) [M

V/m

],

T

[K

] (b

lue)

, S

c*50

[MW

/mm

2 ] (m

agen

ta)

30.6

49.4

157

234

3.3

4.5

79

120

56.8

33.8

Pinload = 56.8 MW, P

outload = 33.8 MW

Eff = 0.0 % tr = 0.0 ns, t

f = 0.0 ns, t

p = 100.0 ns

TD18_vg2.4_disk:

0 5 10 15 200

50

100

150

200

250

iris number

P [M

W] (

blac

k), E

s (g

reen

), E

a (red

) [M

V/m

],

T [K

] (bl

ue),

Sc*5

0 [M

W/m

m2 ] (

mag

enta

)26.8 25.1

183193

3.5

3.0

94102

44.4

20.6

Pinload = 44.4 MW, Pout

load = 20.6 MW

Eff = 0.0 % tr = 0.0 ns, tf = 0.0 ns, tp = 100.0 ns

TD24_vg1.8_disk:At 11.424 GHz testing of T24/TD24 should come this year.

Very interesting because TD24 has 2 times lower PSH ΔT than TD18

0 5 10 15 200

50

100

150

200

250

iris number

P [M

W] (

blac

k), E

s (g

reen

), E

a (red

) [M

V/m

],

T [K

] (bl

ue),

Sc*5

0 [M

W/m

m2 ] (

mag

enta

)

27.7 26.9

184193

3.7

3.1

94102

40.7

18.6

Pinload = 40.7 MW, P

outload = 18.6 MW

Eff = 0.0 % tr = 0.0 ns, t

f = 0.0 ns, t

p = 100.0 nsAt 11.994 GHz testing of

T24/TD24/TD24_R05 are planed for the next year.

TD24 TD24_R05 provides further reduction of PSH ΔT by 1/3

TD24_vg1.8_disk TD24_vg1.8_R05:

11

Geometry difference between TD24_vg1.8_disk TD24_vg1.8_R05

12

Design of the HOM Damping Load

Tip size 1x1 mmTip length 20 mm or 30 mmBase size 5.6 x 5 or 5.5 mmBase length 10 mmWaveguide width awd = 10.1 mm or 11 mm50.00 60.00 70.00 80.00 90.00 100.00 110.00

sdw [mm]

3000.00

3500.00

4000.00

4500.00

5000.00

5500.00

6000.00

Y1

Ansoft Corporation f0_45_adw11mmXY Plot 1

Curve Info

Q(1)Setup1 : LastAdaptive

Q(1)1Imported

thick line: awg = 11mm, thin line: awg = 10.1 mm

Will be used for CLIC module prototype and for a structure prototype for high power testing with damping load inside (TD24_vg1.8_R05_SiC)

SiC properties from M.Luong, 1999

13

Will be used for CLIC module prototype and for a structure prototype for high power testing with damped compact coupler (TD26_vg1.8_R05_CC)

Design of the damped compact coupler

14

Beyond CLIC_G• Next step in rf design will be a structure with a degree of tapering lower than TD18 (41%) and TD24 (8%)• For example, ~ 20-25 %• It will probably have bigger average aperture if CLIC main beam bunch charge can be increased accordingly.• A detailed optimization of the parameters and rf design will be done soon

0 5 10 15 200

50

100

150

200

250

iris number

TD18 vg2.4 disk

29.147.0

155

226

3.2

4.4

79

120

57.5

34.3

41%

0 5 10 15 20 250

50

100

150

200

250

iris number

TD24 vg1.7 disk

24.621.7

183193

3.3

2.9

94102

44.4

20.6

8%

15

Quadrants/halves familyHALVES

Here T18_vg2.6_quad design is used. It has no slots.

QUADs with SLOTST18_vg2.6_quad design is used but rounded 4 slots of 0.2 mm are introduced.

16

Symmetrical disk design

It has a number of pros and cons:+ higher Q― higher cost― requires axial alignment ― tuning is more difficult and it is not implement―

The structure is in the production

17

Alternative damping designs1. DDS type is underdevelopment at 12 GHz by Cockcroft Institute and

Manchester University (R. Jones, A. D’Elia, V. Khan).2. Choke-mode type is under development in collaboration with

Tsinghua University (J. Shi)1. Minimum gap acceptable from the point of view rf breakdowns

to be determined using CD10_choke with different gaps: 1mm, 2mm, etc.

2. Damping design of the full structure is under way aiming at full structure prototype high power test

18

The choke mode cavity and radial choke

19

Damping simulation with Gdfidl/HFSS

(Model in HFSS)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 210

-1

100

101

102

103

Wy /

[V

/pC

/m/m

m]

s / m

gap 1mm

gap 1.5mmgap 2mm

0 10 20 30 40 50 60 70 80 90-10

0

10

20

30

40

Z y / k

/m

/mm

f / GHz

gap 1mm

gap 1.5mmgap 2mm

Gap 1mm 2mm Good damping forfirst dipole

Mode reflected by the choke, to be studied…

E field, fundamental mode

E field of a dipole mode that is reflected by the choke Impedance and wakefield simulated in Gdfidl 20

Design of CD-10-Choke

• CD10-Choke for demonstration– RF Design for Gap 1mm, 1.5mm, 2mm– Mechanical Design finished for 1mm-gap– Qualification disks and bonding test

• To the production pipeline and High Power testing

21

• Limited number of cells (N=24) in a structure (poor sampling of a Gaussian) means truncation of Gaussian leading to re-coherence of the wake (t=1/Δfmin)

• Re-coherence of the wake is suppressed by moderate damping: Coupling out the HOMs using a waveguide like structure i.e. manifolds running parallel to the accelerating cells

• Interleaving neighboring structure frequencies improves wake suppression

• Gaussian distribution of cell parameters is chosen in this (CLIC_DDS) structure which causes Wakefield to decay in nearly Gaussian fashion for short time scale (few nsec)

Damped Detuned Structure

• This is a similar technique to that experimentally verified and successful employed for the NLC/JLC program

• Potential benefits include, reduced pulse temperature heating (In principle true but not for CLIC_DDS_A: pulse heating is greater than CLIC_G), ability to optimally locate loads, built-in beam and structure diagnostic (provides cell to cell alignment) via HOM radiation. Provides a fall-back solution too!

24

Disk cross-section.

Parameter Value

a (mm) 3.8523

b (mm) 11.0031

t (mm) 3.8884

ε 1.0203

g (mm) 4.3316

CLIC_DDS_A: Regular disk #1 Section profile and Parameters Table

Parameters table.L

= t +

g

t

a

b

t/2

ε*t/2

Ellipse

25

CLIC_DDS_A: E-Field profile along the structure

Thank you