Linac4 commissioning strategies (part I, up to 12MeV) G Bellodi (BE-ABP-HSL) , Jim Stovall & L4 beam dynamics group
Timeline
RFQ
MEBT
TANK1
TANK2 + TANK3
01/2011
04/2011
07/2012
01/2013?
Linac4 test stand area
Linac4 tunnel
very important to achieve beam quality : non periodical
lattice, larger beam modulations, important
space charge effects, ‘new’ technology not quite fully
established
not many handles to play with (V vs T)
all PMQs for transverse planes, find correct
matching between tanks and longitudinal RF set
points
Permanent diagnostics: MEBT
TransformersWire scanners
clamp-on steerers
Temporary diagnostics : movable test bench
Emittance meter, spectrometer, 2-3 PUs, 2-3 BCTs, Feschenko, halo monitor
for machine commissioning & to calibrate permanent diagnostics (to be used in operation)
BeamsNominal beam Commissioning full Commissioning
pencil Pulse length 400 ms 50-100ms 50-100msRep rate 2Hz 1Hz 1HzMax beam current 65mA 65mA 1 mA (? tbd)Average beam current (after chopping) 40 mA 40 mA
Tr. beam emittances at RFQ output (RMS norm) 0.25 mm mrad 0.25 mm mrad 0.05 mm mrad
Longitudinal emittances 0.13 deg MeV 0.13 deg MeV 0.18 deg MeV
..& procedures:
1) Transverse plane:
• Steering/orbit correction • Quad tuning • Transverse beam matching
2) Longitudinal plane:
• RF amplitude/phase scans • longitudinal matching
MEBT commissioning path
0 – beam transport, orbit correction, preliminary quad setting
1 – longitudinal plane characterisation, set RF f/A points for buncher cavities
2 – transverse beam matching , quad tuning, halo studies
3 – chopper functionality (time integrated)
4 – chopper functionality (time resolved)
phase 0 – transport & steering
SETUP: low current & pencil beam, chopper plates OFF
AIM: ensure beam transport through MEBT and test bench, measure beam offsets and perform orbit correction, preliminary quad setting
PROCEDURE: Observe beam profiles on wire scanners, beam position signals on BPMs and measure (differential current) transmission at the BCTs. Measure quadrupole response matrix, beam offsets and perform orbit correction.
1 2 3 40
0.2
0.4
0.6
0.8
1
1.2
10mA20mA30mA40mA50mA65mA80mA
# TRAFO
rela
tive
curr
ent
Relative readings of BCTs 1, 2 (MEBT) 3,4 (test stand) for several input currents [bunchers off- no retuning]
Response matrix at WS
-0.6 -0.4 -0.2 0 0.2 0.4 0.6
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
QDA3010 field curves
80%90%100%110%120%
y beam offset at Q [cm]
y at
WS
[m]
Measure beam position at WS while scanning quadrupole field gradients and derive beam offsets inside quads . Correct the orbit with steerers.
phase 1: longitudinalAIM: characterise buncher cavities, set RF phase and amplitude points, measure beam average energy/ energy spread
PROCEDURE: On the spectrometer line (pencil beam, chopper plates OFF) : Find RF phase point: set max voltage on cavity and spectrometer Bfield for 3 MeV (NMR probe). Measure beam displacement on SEM while scanning over phase: beam centered for f=±90o Find RF amplitude point: set phase to 0deg and measure beam displacement on SEM while scanning over voltage values.
STEPS: i) Calibrate buncher1 – bunchers 2, 3 off ii) Calibrate buncher2 – buncher1 at nominal, buncher3 off iii) Calibrate buncher3 – bunchers 1, 2 at nominal
f=±90deg no energy gain
f=0, 180deg max energy deviation
-110 -105 -100 -95 -90 -85 -80 -75 -70
-10
-5
0
5
10
-30-20-100102030
f(x) = 2.64167901234569 x + 237.687255555557
f(x) = 0.541359382716049 x + 48.0841844444445
buncher1 phase
phase [deg]
dx [m
m]
dE [k
eV]
30 40 50 60 70 80 90 100 110 120 130
-10
-5
0
5
10
f(x) = 0.1923703 x − 16.0894821666667
buncher1 voltage
cavity voltage [kV]
dx [m
m]
-110 -105 -100 -95 -90 -85 -80 -75 -70
-10
-5
0
5
10
f(x) = 0.567542654320988 x + 50.1604733333333
buncher 2 phase
phase [deg]
dx [m
m]
40 50 60 70 80 90 100 110 120 130
-10-505
1015
f(x) = 0.216712583333333 x − 15.0703918055556
buncher2 voltage
voltage [kV]
dx [m
m]
-110 -105 -100 -95 -90 -85 -80 -75 -70
-10
-5
0
5
10
f(x) = 0.739115119395712 x + 66.5503484758772
buncher3 phase
phase [deg]
dx [m
m] 40 60 80 100 120 140 160 180 200
-20-15-10
-505
10
f(x) = 0.201630555555556 x − 31.4925188888889
buncher3 voltage
voltage [kV]
dx [m
m]
Sensitivity: 0.5mm per deg offset, 0.2mm for 1kV offset/ ok for SEM grid resolution
Crosscheck with TOF measurement of average beam energy BPMs phase calibration
TOF measurement
PUs at s=4318, 5148, 6275 mm (from start of chopper line)
Case1 : df=2deg, dL=0 Case2 : df=1deg dL=0.3mm
PUs 3 MeV 12 MeV
Case1 Case2 Case1 Case2
1-2 3.50 keV 2.57 keV 23.8 keV 14.1 keV2-3 2.58 1.90 17.5 10.41-3 1.48 1.09 10.1 6
Sensitivity:
~ok for case2 and 1‰ sensitivity requirement
Beam debunching vs current
0 10 20 30 40 50 60 70 80 900
20406080
100120140160 PU1
no focusingfocusingbuncher 1 onbuncher 1+2
current [mA]
RMS
phas
e sp
read
[deg
]
0 10 20 30 40 50 60 70 80 900
50
100
150
200
PU2
no focusingfocusingbuncher 1 onbuncher 1+2
current [mA]
RMS
phas
e sp
read
[deg
]
0 10 20 30 40 50 60 70 80 900
50
100
150
200
250
PU3
no focusingfocusingbuncher 1 onbuncher 1+2
current [mA]
RMS
phas
e sp
read
[deg
]
AIM: characterise longitudinal plane, find matching point to DTL (full current beam, chopper plates OFF ) Feshenko monitor calibration (bkgnd subtraction of detached e-)
PROCEDURE:Measure bunch profiles with Feschenko monitor while varying buncher settings.3-points emittance measurement with low intensity beam?
0.600000000000001 1.1 1.610
15
20
25
30
35
40
45
50 buncher 1buncher 2buncher 3
fraction of buncher voltage
RMS
phas
e sp
read
[deg
]
-120-100 -80 -60 -40 -20 0 20 40 60 80
100120
0
500
1000
1500
2000
2500
3000
3500
MEBT buncher1 on Feshenko
90%100%110%
phase [deg]
Freq
uenc
y
s=35,30,26 deg
Longitudinal matching with Feshenko
Gaussian fitted RMS spread vs buncher settings 1 deg phase resolution
phase 2 – transverse beam matching
SETUP: full current beam, chopper plates OFF
AIM: establish transverse matching conditions, find initial Twiss parameters, quad tuning
PROCEDURE:Quadrupole gradients scan technique with measurement of beam profiles at WS, transmission on BCTs and emittances on scanner
STEPS:
i) RFQ to MEBT : 1st FODO (L4L.QDA3010, L4L.QFA3030,L4L.QDA3050,L4L.QFA3070)
ii) MEBT central quads
iii) MEBT to DTL : last FODO (L4L.QDD3170, L4L.QFD3180,L4L.QDA3200,L4L.QDA3220)
RFQ to MEBT quad gradient scan (±20%)
Nice signature for quad2, not so clear for other quads Clear peak signature, can tune to
few % level if we can resolve 1% in differential beam current with BCT
Beam measured on MEBT diagnostics: WS and BCTFairly ideal simulation case, no mismatch, no errors; only one quad gradient varied at any one time (others assumed at nominal settings)
MEBT to DTL classic quad gradient scan (±20%) Measurements on test bench installed after Tank1
Fairly ideal simulation case, no mismatch, no errors; only one quad gradient varied at any one time
Good if already close to the solution…
0.700000000000001 1.22.500E-07
3.000E-07
3.500E-07
4.000E-07
4.500E-07
5.000E-07
RMS x emittance
q8q9q10q11
gradient ratio
emitt
ance
[m ra
d]
0.700000000000001 1.22.000E-072.500E-073.000E-073.500E-074.000E-074.500E-075.000E-07
RMS y emittance
q8q9q10q11
gradient ratio
emitt
ance
[m ra
d]
0.700000000000001 1.21.00E-03
1.50E-03
2.00E-03
2.50E-03
3.00E-03
3.50E-03
RMS x size
q8q9q10q11
gradient ratio
size
[m]
0.700000000000001 1.27.50E-04
8.50E-04
9.50E-04
1.05E-03
1.15E-03
1.25E-03
RMS y size
q8q9q10q11
gradient ratio
size
[m]
No clear signature with available diagnostics resolution [ 0.1mm mrad / 0.5mm]…
MEBT to DTL random quad gradient scan (±20%)
0.750000000000001 1.250.00E+00
2.00E-07
4.00E-07
6.00E-07
8.00E-07
1.00E-06
1.20E-06
q8, rms x emitt
gradient ratio
emitt
ance
[m ra
d]
0.750000000000001 1.250.00E+002.00E-074.00E-076.00E-078.00E-071.00E-061.20E-06
q9, rms x emitt
gradient ratio
emitt
ance
[m ra
d]
0.750000000000001 1.250.00E+00
2.00E-07
4.00E-07
6.00E-07
8.00E-07
1.00E-06
1.20E-06
q10, rms x emitt
gradient ratio
emitt
ance
[m ra
d]
0.750000000000001 1.250.00E+00
2.00E-07
4.00E-07
6.00E-07
8.00E-07
1.00E-06
1.20E-06
q11, rms x emitt
gradient ratio
emitt
ance
[m ra
d]
Apart from Q10, no clean single knob for tuning, but rather flat signal
Beam measured on test bench installed after Tank1no mismatch, no errors
All quads randomly varied at the same time
Multi-variables approach (offline/online?)
0.0015 0.002 0.0025 0.003 0.0035 0.004 0.00450
0.0005
0.001
0.0015
0.002
0.0025
x size
y siz
e
0.0015 0.002 0.0025 0.003 0.0035 0.004 0.00450.00E+00
2.00E-07
4.00E-07
6.00E-07
8.00E-07
1.00E-06
1.20E-06
x size
emitt
x R
MS
Build a statistical database of cases. Cut in multivariable space to reduce data sample and plot data projectionsExample: e RMS (x,y) < 0.4 mm mrad & T> 95%
0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 More0
1
2
3
4
5
6
7
8
q9
Gradient factor
Freq
uenc
y
Mean ≈1 , s≈10%
0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 More0
1
2
3
4
5
6
7
8
q8
gradient factor
freq
uenc
y
Automated transverse beam matching? (a` la SNS/JPARC )
WSWS Bench/WS?
High level software application to:•Compare measured and model predicted beam sizes in the MEBT for a variety ofMEBT magnet settings•Solve for MEBT entrance Twiss parameters to best match measured wire profiles under a variety of quad settings•Uses solver + online model packages with live machine data input.
phase 3 – chopper functionality (time ∫)SETUP: low current beam, chopper ON DC
AIM: measure individual elements’effect on beam deflection
PROCEDURE: measure beam centroid deflection on MEBT WS near dump & residual transmission on TRAFOs.
X - Y Y-Y’
W/o optical deflection enhancement
with optical deflection enhancement
phase 4 – chopper functionality (time resolved)
SETUP: MEBT+ test bench, full current beam, chopper ON AC
AIM: test time resolved chopper functionality
PROCEDURE: measure intensity of partially chopped beam with Masaki’s detector, chopping efficiency, rise/fall times with beam
Not completely chopped bunch
Transmitted bunch
mm scale, <2ns resolution
DTL commissioning• Transverse commissioning should be easier, if we get the initial conditions right! (all intertank PMQs)
• Set RF point by scanning in phase/amplitude and looking for best match with simulated characteristic curves. Measure output average phase and energy
SteererP.U.
EMQ
SteererP.U.
Steerer , P.U.
EMQ,BCT,Profile
(SEM)
DTL1 DTL2 DTL3
Permanent diagnostics
-50 -40 -30 -20 -10 0 10 20 30 40 50
-60
-50
-40
-30
-20
-10
0
10
20
30
Tank1
110%108%106%104%102%100%98%96%94%92%
Df in (deg)
Df
ou
t (d
eg
)
-50 -40 -30 -20 -10 0 10 20 30 40 508
8.5
9
9.5
10
10.5
11
11.5
12
12.5
Tank1
92%94%96%98%100%102%104%106%108%110%
( )Df in deg
ener
gy (M
eV)
A=108%, 3 points at Dphi=15deg, 0 , 15 deg
input jitter 0.1% dp/p, RF errors, output jitter (measurement error)=0.5deg, 0.05% dp/p Gauss. (1‰ dE/E)
0.5%-0.5deg 1%-1deg
-15 0.55 deg 13keV 1.13deg 15keV
0 0.4deg 4keV 0.44deg 13keV
15 0.45deg 3keV 0.5deg 13keV
DTL commissioning: RF curves
DTL tank1 acceptance studies
-30 -20 -10 0 10 20 30
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
tank1 acceptance
( )Df in deg
()
DE
MeV
Input beam
cut at 10.5MeV output energy
Can be further developed to obtain alternative calculation of longitudinal profiles and/or emittance by measuring beam losses (BCTs, BLMs?)
Tank2, Tank3 Jim’s talk
Software applications desiderata Service applications:
o elogbooko logger
Device specific applications: o Wire scanner o Emittance meter o Beam losses o Feshenko, halo monitor
General purpose tools: o scope applicationo f(t)o histograms o (1-D,2-D?) scan applicationo correlator application
Online model: o automated longitudinal f/A scans and signature matcho comparison of measured and model predicted beam sizes for a variety of
settings, iterative optimisation match to solve for Twiss parameters o orbit correction through steering
basic
complex
Reserve slides
0 10 20 30 40 50 60 70 80 900
50
100
150
200
250
tank2 off
1rms5rms
current (mA)
phas
e sp
read
(deg
)
0 10 20 30 40 50 60 70 80 900
10
20
30
40
50
60
70
80
tank3 off
1rms5rms
current (mA)
phas
e sp
read
(deg
)
TOF for DTL tank2, tank3? Phase spread at the exit of tank2
Phase spread at the exit of tank3
LengthsDTL tanks:4.2m,7.6m,7.4mCCDTL: 2.6-3.3mPIMS modules: 1.3-1.5m (2modules at least for 1‰dE/E)
0 1000 2000 3000 4000 5000 6000 7000 80000
20
40
60
80
100
120
140
160
180
TOF, dphi=1deg, dL=0.3mm
12 MeV
30 MeV
50 MeV
100 MeV
distance bw PUs (mm)
de
lta
E (
ke
V)
-50 -40 -30 -20 -10 0 10 20 30 40 50
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
Tank2
92%94%96%98%100%102%104%106%108%110%
( )Df in deg
(
)D
fo
ut
de
g
-50 -40 -30 -20 -10 0 10 20 30 40 5010
15
20
25
30
35
Tank2
92%94%96%98%100%102%104%106%108%110%
( )Df in deg
Ener
gy (M
eV)
A=103%, 3 points at Dphi=15deg, 0 , 15 deg input jitter 0.025% dp/p, 1deg, RF errors, output jitter (measurement error)=0.5deg, 0.05% dp/p Guass (1‰ dE/E)
0.5%-0.5deg 1%-1deg
-15 0.33 deg 11.5keV 0.55deg 37.2keV0 0.46deg 8keV 0.83deg 34keV
15 0.85deg 8.6keV 1.7deg 34keV
30keV resolution for at least 1.5m distance b/w PUs
-50 -40 -30 -20 -10 0 10 20 30 40 50
-140
-120
-100
-80
-60
-40
-20
0
tank3
92%94%96%98%100%102%104%106%108%110%
( )Df in deg
(
)D
fout
deg
-50 -40 -30 -20 -10 0 10 20 30 40 5035
37
39
41
43
45
47
49
51
53
Tank3
92%94%96%98%100%102%104%106%108%110%
( )Df in deg
Ener
gy (M
eV)
A=104%, 3 points at Dphi=15deg, 0 , 15 deg
input jitter 0.023% dp/p, 0.5deg, RF errors, output jitter (measurement error)=0.5deg, 0.05% dp/p Gauss (1‰ dE/E)
0.5%-0.5deg 1%-1deg
-15 0.76 deg 15.8keV 1.5deg 54.4keV
0 0.46deg 8keV 0.56deg 54.7keV
15 0.85deg 8.6keV 0.48deg 51.5keV
50keV resolution for at least ~2m distance b/w PUs