LHC Power Converters (tracking between sectors)

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

3. Tracking I1 I2 I3 Ability of the converters to follow the reference function (static, dynamics) Iref 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. Tracking : dynamics B Magnet F(s) = 1/(1+Ts) Ts DAC 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) ADC I Iref Power Converter + Circuit T 1/S 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 2 ppm (20mA) 7 ppm (100 mA) No lagging error No overshoot

6. Power Converter Tolerances for LHC 10

7. Tracking between the 8 main dipole converters 5 6 4 3 7 2 8 1 20 ppm Accuracy after calibration DB/Bultimate = DI/Iultimate = 20ppm DB = 9 * 20 10-6 = 1.8 10-4 T DB/Bo = 3.3 10-4 Orbit excursion at injection: dX = Dx . DB/Bo = ~ 0.7 mm 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. Tracking between the dipole and quadrupole converters Tracking between the main quadrupole converters small b beating : no problem (cf. Jorg Wenninger LHCCWG - 17th Meeting on 15-11-2006) 20 ppm Accuracy DB/Bultimate = DI/Iultimate = 20ppm DB = 9 * 20 10-6 = 1.8 10-4 T DB/Bo = 3.3 10-4 Energy error in the machine leads to a tune change : dQ = znat . Dp/po = znat . DB/Bo = 100 * 3.3 10-4 = 0.032 Tuning quadrupoles can correct up to dQ = 0.3 Correction of the effects by LSA – no problems expected.

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. 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. Calibration of main power converters

13. 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. Calibration of high-current [4kA - 13kA ] power converters Courtesy Miguel Cerqueira Bastos

14. 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) Calibration of main power converters

15. 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: Performance Tests : Sector 45 – Summary Courtesy Miguel Cerqueira Bastos

16. Performance Tests : 13kA, 4..7kA converters Sector 45 – Summary • 13kA Converters • Tested RB @ 760A and 8931.91A; RQF @ 8459.81A • Results: * RB stability and noise test was done using DS22 version 8 • 4..7kA Converters • Tested RD4.R4 @ 5520A, RQ5.R4B2 @ 3610A • Results: • Repeatability better than 1 ppm (3 cycles) Courtesy Miguel Cerqueira Bastos

17. 600A Converters Tested RCD.A45B1 @ 550A, RSD2.A45B2 @ 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 RCBYV6 @ 72A Results: Repeatability better than 1 ppm (3 cycles) Performance Tests : 600A, 120A converters Sector 45 – Summary Courtesy Miguel Cerqueira Bastos

18. 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 Performance Tests : 60A converters Sector 45 – Summary Courtesy Miguel Cerqueira Bastos

19. RB, QF & QD: High Precision 22 bits ADCSector 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. 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. RB, QF & QD: High Precision 22 bits ADCSector 45 – Summary

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 Fault @ 9kA 9kA RB OFF => ON @ 5kA - Re-Catch current- Re-take control. => No need to open the discharge switch (up to 2h) => QPS does not trip I.meas 5kA I.ref 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 13 740 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 V_MEAS RQ5.L8B1 I_MEAS RQ5.L8B2 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. 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. RB, QF & QD: High Precision 22 bits ADCSector 45 – Summary