lhc bpm system: status, measurement reliability and outlook for 2011
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Eva Calvo (BE-BI)7 December 2010 1
LHC BPM system: status, measurement
reliability and outlook for 2011
Thanks to all the LHC-BPM team
Eva Calvo (BE-BI)7 December 2010 2/18
Content
Performance• System availability• Closed orbit modes• Resolution• Stability
Intensity dependence
Temperature dependence
Future measurements/checks
Conclusions
Eva Calvo (BE-BI)7 December 2010 3/18
System availability
Complex distributed system with good reliability Just a few hours down during the year. FEC reboots are rare.
Currently (17th Nov), only 3% of channels disabled on OFC(71 out of 2152).
None of these channels are ‘dead’:Non-physical offsetsToo noisy measurements
Number quite constant during 2010
97 % OK!
Eva Calvo (BE-BI)7 December 2010 4/18
3 % missing channels
Most of them are strip line monitors (BPMS/SA/SE) Beam directivity smaller than sensitivity of electronics (~20 dB vs 35dB). With Ibeam>2e10 p/bunch, B1 bunches can trigger B2 channels and vice versa.
(LHC BPM front-end electronics auto-triggered, no timing signals in tunnel). During 2011 commission Synchronous orbit mode (bunch mask) will reduce
this problem.
75% correspond to BPMs close to the IR Long coaxial cables (deported electronics) Coupled noise and/or ground loops
Cable adapters will be installed this XMAS stop Expect to reduce RMS noise in many channels
Eva Calvo (BE-BI)7 December 2010 5/18
LHC BPM closed-orbit modes #1
Present: • Asynchronous closed-orbit:
– Position signal from all bunches (from the auto-triggered front-end cards) enters digital IIR filter. (Filter time constant can be configured).
– Output of the filter is read-out, calibrated and transmitted at 25Hz– Recovered by the OFSU from where YASP gets it (typically at 1Hz)
Starting 2011:
• Synchronous orbit:- Only bunches from selected slots averaged (225 turns)- Initially the mask allows one or all bunches.- It requires the phase adjustment of each channel in the DAB module.
Output from both modes read-out, calibrated and transmitted at 25Hz to OFSU system (YASP update 1Hz) – choice of mode
Eva Calvo (BE-BI)7 December 2010 6/18
Resolution
Resolution of LHC BPM system in closed-orbit mode is ~5um.
Data from Timber, Fill 1455, during stable beams (3h).
Eva Calvo (BE-BI)7 December 2010 7/18
Stability
Data from Timber, Fill 1455, during stable beams (3h).
Comparison between the LHC BPM v.s. diode-BPM
Courtesy of R. Steinhagen and M. Gasior.
Orbit @ BPMC.8L4.B1
Eva Calvo (BE-BI)7 December 2010 8/18
Temperature issue #1
Long term stability limited by ambient temperature dependence Systematic offset in the position measurement Average value: 2.2 ADC bins/deg C (ARC BPM = ~50 um/deg C). ∆Temp in 24h varies from day to day but can be up to 6⁰C.
12:00 13:00 14:00 15:00 16:00 17:00-1020
-1010
-1000
-990
-980
-970
-960
Local Time (2010-04-12)
H P
ositio
n o
n B
PM
SW
.1R
8 (
um
)
12:00 13:00 14:00 15:00 16:00 17:0027.5
28
28.5
29
Local Time (2010-04-12)
Cra
te t
em
pera
ture
(deg.
C)
Eva Calvo (BE-BI)7 December 2010 9/18
Temperature issues #3
An expert application was developed: Simulates using calibration signals a centered beam VME fan trays speed is then reduced (reduce air-cooling). Linear fit is applied to the data of each channel. (Gradient values). Low-level server corrects ADC data by applying the gradients found with
temperature difference .
Procedure has reduced the problem. However: The fan speed reduction allows for calibration in small dynamic range
(5 - 6°C) Error non-negligible if temperature too far from the measured points
(non-linear behaviour)
Eva Calvo (BE-BI)7 December 2010 10/18
Temperature issues #4
Eva Calvo (BE-BI)7 December 2010 11/18
Temperature issues #5 BP
M.3
3R8.
B2
Eva Calvo (BE-BI)7 December 2010 12/18
Temperature issues #6
In order to attenuate further the temperature drifts:
Add to LHC sequencer standard BPM calibration Remove long term accumulated temperature variations. (“Reset
effect”). Procedure is “safe” – Several checks assure that it will not introduce
“bad calibration factors”. Long term, plans to implement “temperature regulated racks”.
First prototype received beginning of next year. Complete replacement during long shutdown (2012? / 2013?).
Eva Calvo (BE-BI)7 December 2010 13/18
Intensity dependence #2
MD on 28th of May - Beam 2 scraping with collimators (point 7) Calibrating beam position versus bunch intensity.
Switching between high and low gain every 10s.
Optimum switch point 5e10p/bunch.
Drift on the orbit due to intensity <40um.
0 1 2 3 4 5 6 7 8 9 10
x 1010
-100
-80
-60
-40
-20
0
20
40
60
80
100
Po
siti
on
V (
t) -
Po
siti
on
V (
t 0) (u
m)
Intensity(p/bunch)
BPM arc mean (high sens)BPM arc mean (low sens)
Eva Calvo (BE-BI)7 December 2010 14/18
Intensity dependence #4
0 2 4 6 8 10 12
x 1010
-1600
-1400
-1200
-1000
-800
-600
-400
-200
0
200
Mea
n(P
osi
tio
n(t
) -
Po
siti
on
(t0))
(u
m)
Intensity(p/bunch)
Average BPM arc type monitors
mean(PosV) low sensmean(PosH) low sensmean(PosV) high sens.mean(PosH) high sens.
One test with complete scraping per sensibility mode.
No optimal switch point ! Switching @4e10, the
maximum drift was ~300um.
MD on 8th of June - Beam 1 scraping with collimators (point 7) Calibrating beam position versus bunch intensity.
Eva Calvo (BE-BI)7 December 2010 15/18
Intensity issues
The Front-end cards for Beam 1 and Beam 2 are identical. B1 behavior was caused by a small impedance mismatch at the input of the
intensity module. Solving this issue would require :
Replacing the intensity card by termination card. (Possibly this shutdown). Producing new cards with better impedance matching (Long term).
→ Decision to be taken!
Eva Calvo (BE-BI)7 December 2010 16/18
3 main lines of defence against BPM errors and faults
Pre-checks without beams using the in-build calibration unit Test the electronics (not the cabling neither the monitors). Eliminates dead BPMs, detects noisy or misbehaving channels. Removes electronic offsets Provides the electronic sensibility of each channel.
Pre-checks with Pilot and Intermediate beams Forced slow COD-driven betatron oscillation with rotating phase Idea: “Every non-moving position reading indicates a dead BPM” Test the complete acquisition chain (including monitors and cabling). Tests also calibration factors.
Continuous data quality monitoring through Orbit Feedback Detect spikes, steps and BPMs that are under verge of failing
→ Done
→ Needs integration
→ Done
Eva Calvo (BE-BI)7 December 2010 17/18
Conclusions
The global performance of the system is very good.
In 2011: Synchronous orbit implementation will solve double trigger issue. Long cable adapters will reduce the RMS noise. BPM calibration procedure in the sequencer will reduce the temperature
induced offsets.
To decide if this Xmas shutdown the intensity modules should be removed.
A temperature regulated racks prototype will be evaluated. (Future operational installation during the long shutdown).
Thank you !
Eva Calvo (BE-BI)7 December 2010 18/18
Intensity issues
Spare slides
Eva Calvo (BE-BI)7 December 2010 19/18
Interventions
Almost no calls from the CCC Typical interventions:
3 VME crate P.S. replaced 1 VME CPU replaced. 16 DAB cards replaced (11 in the same campaign in April, only 1 after then). -> youth errors 5 WBTN replaced 1 BYPMD crate replaced 2 inverted polarities 5 bad contacts at the flange level 2 defects inside the cryostat 1 time power disjunctors trip on the tunnel
Eva Calvo (BE-BI)7 December 2010 20/18
Performance
The resolution of the BPM system in bunch by bunch basis is <100 um
RMS from the Orbit Feedback GUI
Eva Calvo (BE-BI)7 December 2010 21/18
Eva Calvo (BE-BI)7 December 2010 22/18
LHC BPM closed-orbit modes #1
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16-1.5
-1
-0.5
0
0.5
1
-1.00
-0.90
-0.80
-0.70
-0.60
-0.50
-0.40
-0.30
-0.20
-0.10
0.00
0.10
Comparison between Synchronous and IIR orbit in the cfv-sx4-bpmb1la (1/12/2010)
IIR filterSync. orbitDifference
BPM channel
Hor
. Pos
ition
(mm
)
Diff
eren
ce(u
m)
Eva Calvo (BE-BI)7 December 2010 23/18
Slot 1 Slot 2 Slot 3 … Slot 3564
Turn i+1 0.211 0.198 0.203 … 0.221
Turn i+2 0.225 0.185 0.194 … 0.205
… … … … … …
Turn i+N 0.208 0.175 0.184 … 0.182
∑ Sum 1/NTOTAL = sync. orbit
LHC BPM orbit modes
Sum 3564/N3564Sum 1/N1 Sum 2/N2 Sum 3/N3 = bunch sync. orbit (vector)
…
The mask will allow only the bunches in the first slot to be averaged.
Eva Calvo (BE-BI)7 December 2010 24/18
BPM calibration
H plane
V plane
Checks in offset, spread, and number of bad acquisitions
Eva Calvo (BE-BI)7 December 2010 25/18
LHC BPM orbit modes
IIR time constant effect
Eva Calvo (BE-BI)7 December 2010 26/18
Intensity dependence #3
600 700 800 900 1000-1
-0.5
0
0.5
1
BPM index
Max
. dri
ft (
) (m
m)
Low sensitivity
600 700 800 900 1000-1
-0.5
0
0.5
1
BPM index
Max
. dri
ft (
) (m
m)
High sensitivity
0 10 20 30-1
-0.5
0
0.5
1Histogram for the low sens. curves
histogram hits
Max
. dri
ft (
mm
)
mean()=55um()=68um
0 10 20 30-1
-0.5
0
0.5
1Histogram for the high sens. curves
histogram hits
Max
. dri
ft (
mm
) mean()=32um()=138um
Eva Calvo (BE-BI)7 December 2010 27/18
Intensity issues
0 100 200 300 400 500-1
-0.5
0
0.5
1
BPM index
Max
. dri
ft (
mm
)
Low sensitivity, Vertical positions
0 5 10 15 20 25-1
-0.5
0
0.5
1Histogram for Low sensitivity
Histogram hits
Max
. dri
ft (
mm
) mean()=55um()=55um
0 100 200 300 400 500-20
-10
0
10
20
BPM index
Max
. dri
ft (
mm
)
High sensitivity, Vertical positions
0 50 100 150 200 250 300-15
-10
-5
0
5
10
15Histogram for High sensitivity
Histogram hits
Max
. dri
ft (
mm
)
mean()=701umsigma()=3.2mm!
Eva Calvo (BE-BI)7 December 2010 28/18
Intensity dependence
Linearity error as function of beam intensity qualified for each installed card .
Eva Calvo (BE-BI)7 December 2010 29/18
Temperature issue #2
Temperature variation (over 24h) for each BPM (12 April 2010)Depending on the day, we observe different drifts in different points.(This would limit our accuracy if we do not calibrate the system often enough)
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