1HG2013 3-6 may 2013 TriesteTesting with beam in CTF3 - W. Farabolini Testing with beams in CTF3: breakdown kick and advanced diagnostics.

Testing with beam in CTF3 - W. Farabolini 1HG2013 3-6 may 2013 Trieste

Testing with beams in CTF3: breakdown kick and advanced diagnostics

Testing with beam in CTF3 - W. Farabolini 2

Contents

• Two Beam test stand equipments and tools• Beam used for structures RF diagnostics• Energy gain / spread measurement and optimization• RF power measurements• BD detection• Test bench for beam diagnostics• Wake Field Monitors study• Beam kicks study• Beam shape distortion and multipolar field modeling• Conclusion

HG2013 3-6 may 2013 Trieste


Drive beam(24 Amps)

Probe beam(1 Amp)

QuadrupolesDipoles

BPMs PMTs

Correctors

Screens

Variable phase shifters& On/Off mechanisms

RF couplers

Water thermal probes and flow meters

Ion analyzerFCU

Wake Field Monitors

Spectrometer lines

The Two Beam Test Stand

Franck Peauger - IRFUGermana Riddone


Operational models for beam optimization


For beam focusing:Current in quadrupoles -> beam enveloppe.

For beam trajectory:Current in correctors -> beam position on BPMs

From Quad scan…

… to beam optimization.


Tuning frequency validation of the structures

HG2013 3-6 may 2013 Trieste 5

LO = 11994.2 - 10 MHz LO = 11994.2 - 1 MHz LO = 11994.2 MHz

LO = 11994.2 + 1 MHz LO = 11994.2 + 2 MHz LO = 11994.2 + 10 MHz

• RF output generated by a short beam pulse (3 ns: 5 bunches) is down-mixed with a local reference oscillator -> structure resonant frequency .

• Nominal tuning: 11.9942 GHz checked (accuracy < 1 MHz).


RF production with longer pulses


Pulse 150 ns LO = 11894.2 MHz Pulse 194 ns LO = 11994.2 MHz

Extracted Faraday cup acts as a button pick-up

• RF output frequency forced by the probe beam pulse frequency RF output rising time = ACS filling time (65 ns)RF output rising time + sustain time = pulse lengthRF output falling time = ACS filling time (65 ns)

• Delays between the (RF couplers , Faraday cup, BPMs, PMTs, WFMs) -> instrumentation calibration


Energy gain measurement


• Accelerated /non-accelerated beam -> dipole strength to be adapted • Califes beam energy fluctuation +/- 2 MeV , period around 150 s

(temperature oscillations ?)• Sinusoidal function fit -> valid at least during 30 minutes

Accurate measurement of the energy gain despite CALIFES beam energy fluctuations.

Double pulsing method for energy gain lower than 30 MeV


Energy gain optimization


• Inter-structures phase shifter position set for no acceleration whatever Drive Beam / Califes phase.

• This phase is then shifted by 180 deg -> accelerating crest.

RF power control

• PETS On/Off mechanism • Timing between drive beam pulse and probe beam pulse.• 2 phase shifters (RF/ probe beam phase and inter-structures phase)

Drive beam and probe beam detected by PMT

Structures phase in opposition


Energy gain as function of RF power check


Phase scan

Power fluctuations

Energy gain lower than the nominal one -> uncertainties in the calibration of the RF chains ?

• Califes / Drive beam phase scanned over 360 deg of 12 GHz


Thermal method for RF power measurements


Water cooling circuit

Finite differences thermal model of structure and cooling circuit.

• Inlet/outlet water temperature difference -> mean RF power deposited• 10 % discrepancy factor found (power overvalued by the RF couplers)

0.02 oC


Reviewed power and energy spread


Structures performances much closer to the nominal

Energy spread maximal at the zero crossing due the phase extension of the bunch on the 12 GHz period -> bunch length measurement method.


Reliable breakdown detection on 2 ACSs


• Two criteria used: Reflected Power and Missing Energy

Miss = Enerin – Enerout x attenuation

• Data are post processed with adaptative thresholds.Thresholds = mean + 3.72 s

[ PGauss(X>3.72s) = 10-4]

• Compromise between Detection prob. and False Alarm prob.

• A BD sometime triggers the other structure BD.

• Reflected power and Missing energy are data logged for each RF pulse• Faraday cup and Photomultiplier tube activity also used to confirm BD


Test bench for beam diagnosticsRui Pan (PhD student), Electro-0ptical Bunch Profile Measurement at CTF3 IPAC’13 MOPME077.


Inside CLEX optical tables for laser beam injection

F. Cullinan (PhD student), J. Towner A Prototype Cavity Beam Position Monitor for the CLIC Main Beam, IBIC'12 MOPA18

Sophie Mallows(PhD student), A fiber Based BLM System Research and Development at CERN, HB2012 THO3C05

Position and beam charge linearity


Wake Field Monitors as BPMs


0.12 mm

• Two types of WFM installed on the structures : (HOMs: 18 GHz and 24 GHz). • Resolution already better than 20 mm.• First successful results: realignment of the ACSs tank.• Robustness with nominal 12 GHz RF power (42 MW) still under investigation

F. Peauger - IRFU

18 GHz on diodes

24 GHz on log

detectors

WFM signals without 12 GHz RF power

WFM signals with RF power

WFM signals from a PB pulse


Breakdown beam kick studyPhD research of A. Palaia


• Average measured kick to the beam orbit : 29 +/- 14 keV• Kicks angle measured not isotropic, not clear why

cavity BPM CA.BPM0745V

0.68 mm0.75 mm

Screen MTV 790

w/o BD With BD


Beam observed on MTV0790


Hor

. Pos

ition

[mm

]

Vert. Pos.

• Beam kicks during acceleration observed, especially when beam is passing off-axis through the 12 GHz structures.

• Beam shape can also be distorted

Horizontal beam kick during scan in horizontal positions within the ACSs

Non-accelerated (left) and accelerated (right) beam shapes observed on the straight line screen, 4.75 m downstream the ACS

accelerated

non accelerated

[mm]


Observation of octupolar shapes


Without RF power

At zero-crossing (rising RF power

side), 25 MW

At zero-crossing (falling RF power

side)

On crests (accelerating or

decelerating)

• Used of a non-focused beam to fully observe beam shape distortion -> full structure aperture covered (4.7 mm bore diameter).

• The octupolar beam shape changes from positive to negative at the RF crest phases.


Modeling of the octupolar fields


A. Grudiev

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35-10

0

10on crest

{E

acc

(0)

} [V

/m]

@ 1

V

r = 2 mm

r = 1 mmr = 0

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35-10

0

10

{E

acc

(1)

} [V

/m2 ]

@ 1

V

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35-1

0

1x 10

4

{E

acc

(2)

} [V

/m3 ]

@ 1

V

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35-2

0

2x 10

6

{E

acc

(3)

} [V

/m4 ]

@ 1

V

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35-2

0

2x 10

9

{E

acc

(4)

} [V

/m5 ]

@ 1

V

z [m]

Comparison b(4) @Vx=1VLF: 0.17 +3.23i [mTm/m2]PW: 0.22 +3.22i [mTm/m2]

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

z [m]

Oct

upol

ar k

ick

in [

T/m

3 ] @

1V

90o off crest

F(4)x /ec

j4/w*Eacc(4)

Dipolar field

Quadrupolar field

Sextupolar field

Octupolar field

Panofsky-Wenzel (PW) theorem

Lorenz Force (LF)or


sjnr

ns

n ebnunuerrp )(1)( )sin()cos(),,(

-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

x [mm]

y [m

m]

Vz = 0 MeV

Consequences


for Vz = 22.8 MV; Pin = 46.5 MWTD24_vg1p8

f [GHz] 11.994

Vz(x=0) [MV] 22.8 +0i

Vx [MV] 0

b(2) [mTm/m] 0 - 15i

b(3) [Tm/m2 ] 0

b(4) [kTm/m3] -4.6 +73.4i

ΔVy@Δx=2mm/structure Δx after 5m for 180 MeV beam

18 V

176000 V ~5 mm

A. Grudiev

-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

Beam spots in the structure Beam spots on the screen-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

x [mm]

y [m

m]

Vz = 0.5 MeV

-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

x [mm]

y [m

m]

Vz = 1 MeV

-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

x [mm]

y [m

m]

Vz = 1.5 MeV

-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

x [mm]

y [m

m]

Vz = 2 MeV

-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

x [mm]

y [m

m]

Vz = 2.5 MeV

-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

x [mm]

y [m

m]

Vz = 3 MeV

-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

x [mm]

y [m

m]

Vz = 3.5 MeV

-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

x [mm]

y [m

m]

Vz = 4 MeV

-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

x [mm]

y [m

m]

Vz = 4.5 MeV

-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

x [mm]

y [m

m]

Vz = 5 MeV

-4 -3 -2 -1 0 1 2 3 4

x 10-3

-4

-3

-2

-1

0

1

2

3

4x 10

-3

x [mm]

y [m

m]

Vz = 6 MeV


Conclusion• A facility with a well controlled beam and a full

set of diagnostics is an important tool for testing RF structures.

• In addition it attracts many users and PhD students who develop innovative diagnostics.

• But of course it requires significant resources for operation and maintenance.


I would like to thank all of them, CERN staff and collaborators, for their constant effort in running CTF3.



Detail of the computations


Ln

rnn

L

kickzkick

L

cvz

kickzkickcvkickzkick

zcj

kick

zcj

kick

dzFnunurc

rp

dzHuZEc

edz

v

Frp

HuZEeBvEeF

eHHeEE

z

z

0

)(1)(

0

0

0

0

)sin()cos(1

),(

),(

;

)(1)(

0

)sin()cos(),(

1:where

~for;),,(),(

naccr

nn

r

tjL

acc

Vnununrje

rp

ru

ru

eEzrEdzje

rp

n

nnacc

n

innnaccacc

Lnacc

nacc

L

accacc

zcj

zacc

nrVerVrV

dzzEVdzzrErV

ezrEzrE

)cos(),(

)(;),,(),(

),,(),,(

)()(

0

)()(

0

Accelerating gradient:

Accelerating voltage:

Multipole expansion in vacuum only:

Panofsky-Wenzel (PW) theorem:

Gives an expression for multipolar RF kicks:

Lorenz Force (LF):Gives an expression for kick directly from the RF EM fields:

Which can be decomposed into multipoles:

Equating the RF and magnetic kicks, RF kick strength can be expressed in magnetic units:

]/[1

]/[1

1

0

)(

0

)()()(

1)()()(

nL

nacc

Lnnn

nnacc

nn

mTmVnj

dzFec

dzBb

mTEnj

Fec

B

A. Grudiev

1HG2013 3-6 may 2013 TriesteTesting with beam in CTF3 - W. Farabolini Testing with beams in CTF3: breakdown kick and advanced diagnostics.

Documents

tools beam

beam trajectory

beam optimization hg2013

beam califes phase

drive beam pulse

short beam pulse

amps probe beam

farabolini3 drive beam