INFN Frascati contributions to CTF3-002:

Monitors and Kickers forDrive Beam Phase Feed-forward

F.Marcellini, D.Alesini, A.Ghigo

CLIC working meeting 3th November 2011

In the two beam acceleration scheme is important to synchronize precisely the Main Beam with respect to the RF power produced by the Drive Beam.Timing errors lead to energy variations in the Main Linac and would have an impact on the collider performance (luminosity reduction).

Control of the drive beam phase errors within about 0.1° (23fs @ 12GHz). Feedback and/or feed-forward systems needed.

Phase error control

Overall CLIC layout and the placement of the detectors (green cylinders) in the turnarounds.

Phase monitor main requirementsResolution of the order of 20 fs. Very low coupling impedance due to the high beam current. Rejection, by means of proper designed filters, of RF noise and weak fields in

the beam pipe that otherwise could affect the measurements.Detection is done at 12 GHz.tf monitor ≈ 10ns=2Q/ω →Q ≈380, BW ≈30MHz.

Pick-up designA prototype could be tested in the CTF3 and installed in the chicane region,

before the Delay Loop, where the vacuum pipe diameter is 40mm. At 12 GHz, 6 modes can propagate in a Ø=40mm pipe, A smaller pipe cross section would be useful to reduce the no. of modes.Reducing the pipe diameter at Ø=23mm, only 2 modes have a cut-off

frequency lower than 12 Ghz.

DRIVE BEAM LINAC

CLEXCLIC Experimental Area

DELAY LOOP

COMBINERRING

10 m

4 A – 1.2 ms150 Mev

32 A – 140 ns150 Mev

Phase monitorKicker

Drive Beam phase measurement and correction in CLIC turn around

Feed-forward experiment in CLIC Test Facility CTF3

RF noise RF noise

reflectedreflected

12 GHznotch filter

12 Ghznotch filter

Beam signal pick-up

Beam induced signal

beam

Beam induced field in the volume between the notch filters.

12 GHz component of beam generated field after the first filter could be reflected back by the second filter and detected again.

Unless the distance between the filters is chosen to define a volume resonating at 12 GHz. The pick-up is positioned in correspondence of zero crossing standing wave field. RF noise has to be filtered at both the pick-up sides.

12 GHz resonating volume

How the pick-up works

11.50 12.00 12.50Freq [GHz]

0.00

0.05

0.10

mag

(S(W

aveP

ort1

,Wav

ePor

t1))

Ansoft Corporation HFSSDesign3XY Plot 2 delta='10.85mm'

The beam induced signal is coupled out of the beam pipe through a rectangular slot in a double ridged waveguideThe thickness of the slot defines the coupling levelThe ridged waveguide has a transition to 50 Ω coaxial where a commercial vacuum feedthrough (MSSI part #853872) is placed

Transition design

Reflection coefficient at the input port

d

Cut view of the waveguide pick-ups

Pick-up design

11.80 11.85 11.90 11.95 12.00 12.05 12.10 12.15 12.20Freq [GHz]

-0.008

-0.007

-0.006

-0.005

-0.004

-0.003

-0.002

-0.001

0.000

dB(S

(Wav

ePor

t5,W

aveP

ort5

))

Ansoft Corporation tm01finalXY Plot 1Setup1 : Sw eep1

TM01Resonating volume tuning @12 GHz

Notch for the TM01 Notch for the TE11No coupling with the waveguide

TE11Resonating volume tuning @12 GHz

11.70 11.80 11.90 12.00 12.10 12.20 12.30Freq [GHz]

-0.000010

-0.000009

-0.000008

-0.000007

-0.000006

-0.000005

-0.000004

-0.000003

-0.000002

-0.000001

0.000000

dB(S

(Wav

ePor

t1,W

aveP

ort1

))

Ansoft Corporation te11finalXY Plot 1dB(S(WavePort1,WavePort1))

Setup1 : Sw eep1

Pick-up elettromagnetic design

CTF3 phase pick-up prototype

Beam pipe F=23mm

Tuned pick-up Q=41fres=fRF=12 [GHz]

Detuned pick-up to decrease the voltage Q=42fres=≠fRF=12.22 [GHz]

Waveguides designed to increase coupling and decrease Q -> faster rise time

11.80 11.90 12.00 12.10 12.20 12.30 12.40 12.50Freq [GHz]

-90.00

-70.00

-50.00

-30.00

-20.00

dB(S

(6,5

))

XY Plot 5

ANSOFT

Setup1 : Sweep1

notch frequency

fres=monitor resonance

Qb=2.33e-9 [C] (bunch charge)fRF=12 [GHz]Bunch separation: 1/fRF

I=28 [A]Vout=710 V 0 100 200 300 400 500

-800

-600

-400

-200

0

200

400

600

800

bunch #

Vou

t [V]

0 100 200 300 400 500-40

-30

-20

-10

0

10

20

30

40

bunch #

Vou

t [V]

Qb=2.33e-9 [C] (bunch charge)fRF=12[GHz]Bunch separation: 1/fRF

I=28 [A]Vout=28 V

Tuned version fres=12 GHz

Detuned version fres=12.2 GHz

Time response signal, in bunch number, of the monitor precisely tuned at the bunch frequency

same pick-up with the notch filter with slightly different distance that gives the detuned

The response time is approximately 50 bunches on 2100 bunches of the train

Phase jump (π/6)

Rejection of RF noise and beam generated wake fields, in the detection frequency range, is done by notch filters.The notch filter is realized as a bump in the beam pipe. The dimensions of this bump are chosen to reject the 12GHz frequency component of the noise.

Transmission response of stop-band filter for the TM01 mode

S21[dB]

Installation of the monitor prototype is foreseen before the CTF3 Delay Loop. The pipe radius has been reduced down to 11.5 mm, to limit to only 2 modes (TE11 and TM01) propagation at 12 GHz.

1

4

3

2

V1+V2+V3+V4≠ 0, TM01

= 0 , TE11

This property can be used as a primary mean to reject TE11

Rejection of RF noise and wakefield

TE11 TM01

Pick-up mechanical design

Stripline lenght=0.4m Vin = 3. 9 kV 1mrad @ 150MeV

Stripline lenght=1.0m Vin = 1.35kV 1mrad @ 150MeV

Vin

-Vin

Phase-forward system kicker

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00Freq [GHz]

0.00

0.02

0.04

0.06

0.08

0.09

mag

(S(1

,1))

full_struct1000mmXY Plot 1 ANSOFTmag(S(1,...Stripline lenght = 1m Reflection coefficient from stripline input port

0 0.5 1 1.5 2 2.5 3 3.50

5

10

15

20

25

30

35

Longitudinal coupling impedanceZ [Ω]

f [GHZ]

The striplines ends are tapered in order to reduce the beam coupling impedance and to have good 50 W matching to the amplifiers

Simulations of the kickerwith stripline 80 cm long + 2x10 cm tapers

Proposed layout of the CTF3 line

CURRENT PROPOSEDSX+Q 84 41.7 QuadDift 16 17.1 BPIQ 41.7 41.7 Quad

BPI 17.1 120 KICKER

Q + Corr 64.8 20 TaperVPI 23.6 6.7 Drift

247.2 247.2 cm

Kicker mechanical design

Lstrip=960mm

LTOT=1100mm

Strip-line Internal Diameter=40mm

WP CTF3-002 INFN Contribution