1. (tracking between sectors)
Session 4 - Beam Plans for Accelerator Systems
LHC Power Converters
(tracking between sectors)
LHC Powering in 8 sectors
Tracking between sectors
LHC power converter performance
HW commissioning: first results
LHC beam commissioning phases % PO
Tracking issues were presented:
11th Chamonix workshop - 18th January 2001
LHCCWG - 17th Meeting - 15th November 2006
LTC 67th  Meeting - 6th December 2006

2. LHC Powering in 8 Sectors
Powering Sector
8 * [154 dipoles] not in series
Sector 1 5
DC Power feed 3
Octant
DC Power 2 4 6 8 7
LHC
27 km Circumference
Powering Subsectors:
cryostats in matching section
long arc cryostats
triplet cryostats
Powering Subsectors allow progressive Hardware Commissioning

3. Iref I1 I2 I3 Static part is covered by the static definition :
Tracking
Ability of the converters to follow the reference function
(static, dynamics)
Iref I1 I2 I3
Static part is covered by the static definition :
accuracy, reproducibility
Tracking error
between I1 and I2
Dynamic part comes from :
- timing error or jitter
- lagging error in the regulation
11th Chamonix workshop - 18th January 2001

4. B I Iref Magnet T 1/S R Dynamics : Tracking : dynamics DAC
F(s) = 1/(1+Ts)
# I => B : time constant (T : vacuum chamber, beam screen…)
must be known and could be corrected by control system
Measurement campaign : test benches and String 2 (field measurement)
Iref I
DAC Ts
Power Converter +
Circuit T
1/S Ts
ADC
presentation by
L. Bottura in the 14th LHCCWG meeting
Magnet reproducibility 10-4
Digital controller R
Dynamics :
- Measurement and command must be synchronised : timing (1ms)
- Lagging error :
# Iref => I : regulation loop are designed with no lagging error
independent of the load time constant
11th Chamonix workshop - 18th January 2001

5. Regulation loop: no lagging error
7 ppm (100 mA)
2 ppm (20mA)
No lagging error
No overshoot

6. Power Converter Tolerances for LHC10

7. 20 ppm Accuracy after calibration DB/Bultimate = DI/Iultimate = 20ppm
Tracking between the 8 main dipole converters
20 ppm Accuracy after calibration
DB/Bultimate = DI/Iultimate = 20ppm
DB = 9 * = T
DB/Bo =
Orbit excursion at injection:
dX = Dx . DB/Bo = ~ 0.7 mm 3 8 7 2 4 5 1 6
Could be corrected with a pilot run
and new cycle => reproducibility
10 ppm reproducibility
Orbit excursion :
dX = Dx . DB/Bo = ~ 0.35 mm
”It would be better with 5 ppm”
Oliver Brüning (X < 180 m)
11th Chamonix workshop - 18th January 2001

8. Power Converter Tolerances for LHC

9. small b beating : no problem
Tracking between the dipole and quadrupole converters
20 ppm Accuracy
DB/Bultimate = DI/Iultimate = 20ppm
DB = 9 * = T
DB/Bo =
Energy error in the machine leads to a tune change :
dQ = znat . Dp/po = znat . DB/Bo = 100 * = 0.032
Tuning quadrupoles can correct up to dQ = 0.3
Correction of the effects by LSA – no problems expected.
Tracking between the main quadrupole converters
small b beating : no problem
(cf. Jorg Wenninger LHCCWG - 17th Meeting on )

10. Tracking Tests RB-RQF-RQD (sector 7-8)
Test Method:
I Channel A swapped
Regulation with I Channel B
RB, RQD, RQF synchronized ramp
Courtesy Dave Nisbet

11. Tracking between the three main circuits of sector 78
2ppm

12. Calibration of main power converters
The power converter output current accuracy and reproducibility is determined by the DCCT, ADC and DAC. To ensure correct performance, these components have to be calibrated before installation and then maintained over the life of the accelerator.
For that purpose a calibration infra structure
which allows automatic on-site calibration of
the power converter has been developed.
Calibrations will be launched from the CERN
Control Centre at periodic intervals.
The infra structure is based on a extremely
accurate current reference, developed
at CERN, which is injected in the DCCTs
calibration winding, simulating a primary
current.

13. Calibration of high-current [4kA - 13kA ] power converters
The reference current can
be switched between several
DCCTs’ windings through a
current switching matrix.
The power converter can be
calibrated by reading the
values of the ADCs while
injecting this reference
current in the DCCT winding.
The system is connected to
the CERN Control Centre through
the World FIP, allowing the calibrations to be
remotely triggered and fully automated. The measured error values resulting from the calibrations are uploaded to a database to be used by the converter controller when generating a primary current.
Courtesy Miguel Cerqueira Bastos

14. Calibration of main power converters
On-site calibration of 13kA power converters (x8 in the UAs)
All the precision components for the main converters, as well as the calibration devices are installed in temperature controlled racks in order to minimize output drifts caused by ambient temperature variations. The racks also provide for EMC protection and are powered by redundant UPS.
Identical installation for the inner triplets converters (x8 in pt 1,2,5,8)

15. Performance Tests : Sector 45 – Summary
Test Method multi kA: secondary current of the internal DCCT back to back with the CERN Current Calibrator
Test Method 600A, 120A: reference DCCT at the output of the converter
FGCs powered for more than a week before the test
Measurement uncertainties:
Measurement uncertainties (estimations)
600A
13kA
4..7kA
120A
Offset (stability run)
± 0.5
Gain (stability run)
± 2
± 5
Noise Hz (pk-pk)
± 0.3
Accuracy (gain + offset)
± 0.2
Asymmetry (pos-neg gain)
± 0.1
Courtesy Miguel Cerqueira Bastos

16. Performance Tests : 13kA, 4..7kA converters Sector 45 – Summary
Tested 760A and A; A
Results:
* RB stability and noise test was done using DS22 version 8
4..7kA Converters
Tested 5520A, 3610A
Repeatability better than 1 ppm (3 cycles)
Reference limits (ppm)
1 year
accuracy: 50
1/2h
stability: 3
HC tests
1 month
accuracy
stability 2h
Noise p-p
( Hz)
Results
≤1.3
≤0.4
≤0.5
≤1.1(max 1.7)
Reference limits (ppm)
1 year
accuracy: 70
1/2h
stability: 5
HC tests
5 months
accuracy
stability 1h
Noise p-p
( Hz)
Results
≤12.5 ≤1 ≤2
≤5.4 (max 8)
Courtesy Miguel Cerqueira Bastos

17. Performance Tests : 600A, 120A converters Sector 45 – Summary
Tested 550A, 550A
Results:
* RCD more noisy at the beginning of stability test, then decreases 2 times
Both converters tested at zero. Noise p-p avg of 14ppm p-p (bear in mind that in sector 7-8 we saw 40ppm p-p of noise at zero).
120A Converters
Tested 72A
Repeatability better than 1 ppm (3 cycles)
Reference limits (ppm)
1 year
accuracy: 200
1/2h
stability: 10
HC tests
6 months
accuracy
stability 1h
Noise p-p
( Hz)
Results
≤10
≤1.7*
≤6 (max 8.2)
Reference limits (ppm)
1 year
accuracy: 1000
1/2h
stability: 50
HC tests
6 months
accuracy
stability 1h
Noise p-p
( Hz)
Results
≤10 ≤2 ≤3
≤6 (max 10)
Courtesy Miguel Cerqueira Bastos

18. Performance Tests : 60A converters Sector 45 – Summary
Calibration campaigns
60A Converters – first two point measurement completed for sector 4-5
Time span between the two calibration campaigns is 8 months
The temperature difference between the two calibration campaigns is smaller than 1.6ºC for all locations in the arc
Results (LHC spec for 1 year accuracy is 1000 ppm):
Offsets drifts for DCCTs and ADCs are 1 ppm ±3ppm
More drift in Vref POS because Vref POS is made from Vref NEG
Note that most of the time the converters are OFF so the results have to be interpreted carefully
Average error (ppm)
Std dev (ppm)
FGC Vref POS
-9.2
2.8
FGC Vref NEG
-6.4
DCCT Gain POS
-4.7
6.7
DCCT Gain NEG
-4.8
7.1
ADC Gain POS
+8.9
5.5
ADC Gain NEG
+9.1
4.9
Courtesy Miguel Cerqueira Bastos

19. RB, QF & QD: High Precision 22 bits ADC Sector 45 – Summary
Problems found - 22 tones
When ramping the RB converter from 350A to 1kA, two spikes were detected in the measurement of the loop tracking error. These spikes were as big as 20ppm p-p.
An FFT of the measurements at the point where the spikes ocurred showed a noise peak in both measuring channels, but at different frequencies. Further testing showed that these peaks moved in frequency according to the value of the current, although in a very limited range (few Amps).
After investigating the problem, it was found that it was caused by the ADCs in the RB converter. The RB converter uses two 22 bit Delta Sigma ADCs to convert the output from the DCCTs.
Measurements in the lab reproduced these spikes at the same DC input levels as found in the RB.
820A
900A

20. RB, QF & QD: High Precision 22 bits ADC Sector 45 – Summary
Problems found - DS22 tones
When measuring a previous version of the ADC, it was seen that these tones were much smaller. They were hidden in the system’s noise floor.
A test was carried out in the RB converter using a previous version of the ADC and no perturbation was detected in the current due to idle tones.
AB-PO is analysing the differences between the tunnel version of the ADC and the previous one and at the same time investigating the relation between the dither and the amplitude of the tones. This is necessary to understand the mechanisms that increase the tones above the noise floor.

21. Powering Group of Circuits
138 circuits powered
Use of machine optics functions (LSA)

22. RB: [Fault => Unexpected successful] test
“Re-catch” current
Earth Fault Detected
=> RB Trip in 9kA
9kA
RB OFF => 5kA
- Re-Catch current - Re-take control.
=> No need to open the discharge switch
(up to 2h)
=> QPS does not trip
I.meas
I.ref
5kA
PO In Action
PO specialists mobilized
=> Problem diagnosed as a weak component Not a TRUE earth flt
=> Make the repair on LIVE circuit (5kA circulating)
Converter off 1h30
Load Time constant sec (4 hours).
Time 9kA => 0A > 7hours
Courtesy Yves Thurel

23. Squeeze tests

24. Squeeze tests (PSQ) : Q4 and Q5
Sector 7-8
RQ4.L8B2 is close to limit
New optic function much improved (15min squeeze)
All systems performed as calculated
With LHC Software Application
LSA: generation of table (I,t) => dI/dt >> between points
MQM control touchy during ramp down with 1-Quadrant converter
=> Good Performance even if the limits are closed
RQ5.L8B2 I_MEAS
RQ5.L8B1 I_MEAS
RQ5.L8B2 V_MEAS
RQ5.L8B1 V_MEAS
RQ4.L8B2 I_MEAS
RQ4.L8B2 V_MEAS
RQ4.L8B1 I_MEAS
RQ4.L8B1 V_MEAS
Close to Limits 0V
Courtesy Dave Nisbet

25. Inner Triplet Commissioning
Complex system with interleaved circuits
Was never tested on superconductive loads (nossa terra incognita)
Crucial for machine operation
Will require time before reaching required performance
(high precision on high complex system)
(mainly during hardware commissioning but also during beam ramps)

26. Conclusion
LHC Power converters are tested before beam commissioning
Intensive tests of the LHC power converters:
Parts (power source, DCCT, FGC, ADC,…)
Complete power converters (current source) in surface test halls (performance and 24h heat run)
Short-circuit tests in the underground final location
(24h endurance test: 16h at ultimate and 8h nominal)
Hardware commissioning:
Compatibility with QPS, PIC,… and high precision per sector
Ramp and squeeze functions; tracking tests; Powering Group of Circuits
Long run tests (8h to 24h)
EMC with injection kickers and with dump kickers
a lot of early failure (“défaut de jeunesse”) has been and will be solved (initial MTBF will be crucial at the start of LHC operation)

27. Conclusion LHC beam commissioning phases % Power Converters
LHC Power Converters performance will be measured and improved mainly without dedicated beam time but PC experts should be very close to beam operation.
Periodic calibration would be required.
A2.4 Offsets between different sectors (Interleaved)
A4.12 Tracking errors: measurements and corrections
A8.2 Ramp single beam;  ring 1
A8.3 Post Ramp analysis
A8.4 Beam at Intermediate Intensity
A9.2 Measure & correct linear optics, verify reproducibility cycle - cycle
A9.6 Pre squeeze optics checks

28. The end

29. RB, QF & QD: High Precision 22 bits ADC Sector 45 – Summary
Problems found - DS22 tones
Measurements in the lab reproduced these spikes at the same DC input levels as found in the RB. The first analysis suggested that these could be idle tones from the Delta Sigma modulator.
A Delta Sigma ADC consists of a Delta Sigma modulator and a low pass filter. The output of the modulator is a one-bit stream at a bit rate much higher than the maximum frequency of the signals being read. The average level of the bit stream represents the input signal level. The high DC gain of the loop will ensure excellent accuracy.
When a Delta Sigma modulator is supplied with a DC input signal, the quantizer output is likely to exhibit a periodic or cyclic behavior. Such a periodic output pattern generates noise components which are known as idle tones or pattern noise.