1hg2013 3-6 may 2013 triestetesting with beam in ctf3 - w. farabolini testing with beams in ctf3:...
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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
Testing with beam in CTF3 - W. Farabolini 3HG2013 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
Testing with beam in CTF3 - W. Farabolini 4
Operational models for beam optimization
HG2013 3-6 may 2013 Trieste
For beam focusing:Current in quadrupoles -> beam enveloppe.
For beam trajectory:Current in correctors -> beam position on BPMs
From Quad scan…
… to beam optimization.
Testing with beam in CTF3 - W. Farabolini 5
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).
Testing with beam in CTF3 - W. Farabolini 6
RF production with longer pulses
HG2013 3-6 may 2013 Trieste
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
Testing with beam in CTF3 - W. Farabolini 7
Energy gain measurement
HG2013 3-6 may 2013 Trieste
• 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
Testing with beam in CTF3 - W. Farabolini 8
Energy gain optimization
HG2013 3-6 may 2013 Trieste
• 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
Testing with beam in CTF3 - W. Farabolini 9
Energy gain as function of RF power check
HG2013 3-6 may 2013 Trieste
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
Testing with beam in CTF3 - W. Farabolini 10
Thermal method for RF power measurements
HG2013 3-6 may 2013 Trieste
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
Testing with beam in CTF3 - W. Farabolini 11
Reviewed power and energy spread
HG2013 3-6 may 2013 Trieste
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.
Testing with beam in CTF3 - W. Farabolini 12
Reliable breakdown detection on 2 ACSs
HG2013 3-6 may 2013 Trieste
• 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
Testing with beam in CTF3 - W. Farabolini 13
Test bench for beam diagnosticsRui Pan (PhD student), Electro-0ptical Bunch Profile Measurement at CTF3 IPAC’13 MOPME077.
HG2013 3-6 may 2013 Trieste
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
Testing with beam in CTF3 - W. Farabolini 14
Wake Field Monitors as BPMs
HG2013 3-6 may 2013 Trieste
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
Testing with beam in CTF3 - W. Farabolini 15
Breakdown beam kick studyPhD research of A. Palaia
HG2013 3-6 may 2013 Trieste
• 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
Testing with beam in CTF3 - W. Farabolini 16
Beam observed on MTV0790
HG2013 3-6 may 2013 Trieste
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]
Testing with beam in CTF3 - W. Farabolini 17
Observation of octupolar shapes
HG2013 3-6 may 2013 Trieste
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.
Testing with beam in CTF3 - W. Farabolini 18
Modeling of the octupolar fields
HG2013 3-6 may 2013 Trieste
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
Testing with beam in CTF3 - W. Farabolini 19
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
HG2013 3-6 may 2013 Trieste
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
Testing with beam in CTF3 - W. Farabolini 20
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.
HG2013 3-6 may 2013 Trieste
I would like to thank all of them, CERN staff and collaborators, for their constant effort in running CTF3.
Testing with beam in CTF3 - W. Farabolini 22
Detail of the computations
HG2013 3-6 may 2013 Trieste
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