1. Fk. Bordry AB/PO Academic Training - 27th March 2003 Technological Challenges for the LHC Power converters for the LHC Frédérick BORDRY AB-PO ? I(A) t 11800 20 min -10 A/sec +10 A/sec 2 min several hours 0.1 A/sec 350 A 1 min 350 A pre-injection (1 min - 1 h) 860 A 500 W 2,2 MW 115 kW

2. Fk. Bordry AB/PO Academic Training - 27th March 2003 What’s special about Powering Superconducting Magnets ? High Current Large Inductance No Resistance Need heavy warm cabling  Need to be near to feed point Difficult and expensive power converter output stage Large Stored Energy, 1 / 2 LI 2  Need to handle carefully! Large Time Constant, L/R  Boost voltages (high voltage only during the ramps)  Difficult control loops Tendency to quench  Need to take special precautions (energy)

3. Fk. Bordry AB/PO Academic Training - 27th March 2003 The beams are controlled by: 1232 SC Main Dipole magnets to bend the beams 392 SC Main Quadrupole magnets to focus the beams 124 SC Quadrupole / Dipole Insertion magnets (in 196 circuits of ~ 6 kA) 6340 SC Corrector magnets (in 1460 circuits 60 to 600A) 112 Warm magnets (in 38 circuits 600 to 900A) SC RF Cavities to accelerate and stabilize the beam –All ~8000 magnets need to be powered in a very controlled and precise manner LHC Large Hadron Collider - What needs powering?

4. Fk. Bordry AB/PO Academic Training - 27th March 2003 LHC : 1232 SC Main Dipole magnets One circuit or several circuits ? Magnet inductance : L = 108 mH L total =1232 * 0.108 = 133 H Ramp: LdI/dt = 1330V Discharge (quench; 120 A/s):  16kV Nominal current 11.8 kA Stored Energy = 9.3 GJ Ultimate current = 13kA Stored Energy = 11.3 GJ L/R  50 hours !!!!

5. Fk. Bordry AB/PO Academic Training - 27th March 2003 Natural segmentation into 8 units as no cryostat in straight sections. Warm cable connections costly in copper, power losses (~30MW) and power converters Total stored electrical energy in LHC main dipoles is ~10.6 GJ. Discharge in 120 seconds means 16 kV! Only 1/8 of the machine needs to be discharged if one magnet quenches No risk of total machine avalanche quench, (false quench detection and provocation) Earthing of the ring in eight galvanically isolated sectors Less risk of build-up of voltages Only two sets of switches for dipoles, one for quads, no timing problems Smaller resonant circuit Eight sub-units give easier installation, testing, commissioning and fault finding for many systems Allows sector-to-sector correction of magnet errors due to different cable, magnet manufacturers, etc..  Need to track from sector to sector Why an Electrical Segmentation of the machine?

6. Fk. Bordry AB/PO Academic Training - 27th March 2003 Tracking between the 8 main dipole converters  ppm Accuracy  B/B nom =  I/I nom =  ppm  B = 9  10 -6 = 1.8 10 -4 T  B/B o = 15  10 -6 Orbit excursion :  X = D x.  B/B o = ~.035  mm  X =.7 mm =>  = 20 ppm  ppm Accuracy  B/B nom =  I/I nom =  ppm  B = 9  10 -6 = 1.8 10 -4 T  B/B o = 15  10 -6 Orbit excursion :  X = D x.  B/B o = ~.035  mm  X =.7 mm =>  = 20 ppm Could be corrected with a pilot run and new cycle => reproducibility 10 ppm reproducibility Orbit excursion :  X = D x.  B/B o = ~ 0.35 mm !!! ”It would be better with 5 ppm” Oliver Brüning Could be corrected with a pilot run and new cycle => reproducibility 10 ppm reproducibility Orbit excursion :  X = D x.  B/B o = ~ 0.35 mm !!! ”It would be better with 5 ppm” Oliver Brüning

7. Fk. Bordry AB/PO Academic Training - 27th March 2003 Power Converter Tolerances for LHC Precision Control

8. Fk. Bordry AB/PO Academic Training - 27th March 2003 LHC Power Converters Number of Converters:  1720 Total Current :1860 kA Steady State Input : 63 MW Peak Input : 86 MW Number of Converters:  1720 Total Current :1860 kA Steady State Input : 63 MW Peak Input : 86 MW LEP % LHC

9. Fk. Bordry AB/PO Academic Training - 27th March 2003 LEP versus LHC for Power Converters LEP 200 (up to 110 GeV) Number of converters  900 Installed Power = 130 MW (80 MW for the magnets and 50 MW for RF cavities) Total output current = 115 kA Main dipole current = 4500A Main quadrupole current = 420 A LHC (up to 7.7 TeV) Number of converters  1720 Installed Power = 86 MW (40MW for cryogenics) (70 MW for the magnets and 16 MW for RF cavities) Flat top at 7.7 TeV :  50 MW Total output current = 1’860 kA Main dipole current = 13’000A Main quadrupole current = 13’000 A

10. Fk. Bordry AB/PO Academic Training - 27th March 2003

11. Fk. Bordry AB/PO Academic Training - 27th March 2003 Performances : -High current with high precision (accuracy, reproducibility, stability, resolution) and large dynamics -current range (for 1-quadrant converter: from 1% to 100%) - a lot of 4-quadrant converters (energy from magnets) - tracking :  Need to track from sector to sector - voltage ripple and perturbation rejection The Challenges : Installation (LEP infrastructure) and Operation: - volume ( a lot of converter shall be back-to-back) - weight (difficult access) => modular approach - radiation for [±60A,±8V] converters - losses extraction : high efficiency, water cooling - EMC : very close to the others equipment ; system approach

12. Fk. Bordry AB/PO Academic Training - 27th March 2003 UA23 (Ex-LEP Klystron gallery) Now used to house the majority of machine equipment such as power converters, magnet protection, injection, extraction, RF generators, etc. Very Low Radiation Dose No Access during “Beam-On” Access with full power on Very Low Radiation Dose No Access during “Beam-On” Access with full power on

13. Fk. Bordry AB/PO Academic Training - 27th March 2003 V olume, back-to-back, losses, weight,... No Access during “Beam-On” Access restricted without beam New Enlargement (RR) for Machine Power Converters around ATLAS and CMS Constraints :

14. Fk. Bordry AB/PO Academic Training - 27th March 2003 Radiation Dose 1 Gy/year under dipoles No Access during “Beam-On” Access restricted without beam : Low power Main Arc Tunnel Orbit Corrector PCs 4*[60A,8V]  752 converters Orbit Corrector PCs 4*[60A,8V]  752 converters High reliability : MTBF : 80 ’000 h 1 converter breakdown every 4 days One campaign every 2 or 3 months

15. Fk. Bordry AB/PO Academic Training - 27th March 2003 General approach Minimise the number of converter types Separate out the subsystems that are desirable/acceptable by industry. Place development and production contracts. Design and build prototypes of remaining subsystems. Place production contracts. Assume system integration responsibility Integration and test at CERN before installation

16. Fk. Bordry AB/PO Academic Training - 27th March 2003 Special Development Converter topologies : –High current (13kA) and high power (2.5 MW) 2-quadrant converters (main dipoles) –Switch-mode converters (soft-commutation 20 to 100 kHz) Parallel subconverters 4-quadrant converters (energy management) High precision current transducer (DCCT) Current calibration system High precision ADC (>20 bits ;  ) Control loops : –robust digital loop (RST) –Inner triplet powering (nested converters => decoupling)

17. Fk. Bordry AB/PO Academic Training - 27th March 2003 +15 o -15 o 3 Phase 50 Hz Supply Good Symmetry Freewheel circuit - Used for booster of Main Bend and large warm magnets - Heavy and large - Voltage bandwidth < 70Hz - Well proven - Inversion possible Two Quadrant Phase Controlled Rectifiers for high current SC magnets: Power Converter Topologies

18. Fk. Bordry AB/PO Academic Training - 27th March 2003 [13kA,±190 V] Few ppm Main dipole power converter 11 m Dev. I(A) t 11800 20 min -10 A/sec +10 A/sec 2 min several hours 0.1 A/sec 350 A 1 min 350 A pre-injection (1 min - 1 h) 860 A 500 W 2,2 MW 115 kW

19. Fk. Bordry AB/PO Academic Training - 27th March 2003 Power Diode and Thyristor or SCR (Silicon-Controlled Rectifier ) Link to frequency of the electrical network 50 Hz (60 Hz) High frequency => high performances (ripple, bandwidth, perturbation rejection,...) small magnetic (volume, weight) From mercury arc rectifier, grid-controlled vacuum-tube rectifier, inignitron,…. High frequency power semiconductors : MosFet, IGBTs, GTOs, MCTs,….

20. Fk. Bordry AB/PO Academic Training - 27th March 2003 Low speed High speed Large Filtering Light Filtering

21. Fk. Bordry AB/PO Academic Training - 27th March 2003 Voltage loop: bandwidth few kHz AC 50 Hz AC 20 - 100 kHz DC Fast power semiconductors (IGBT) Semiconductor losses : soft commutation HF transformer and output filter : ferrite light weight, reduced volume (HF transformers and filters) good power factor (0.95) high bandwidth and good response time Soft commutation gives low losses and low electrical noise small residual current ripple at output light weight, reduced volume (HF transformers and filters) good power factor (0.95) high bandwidth and good response time Soft commutation gives low losses and low electrical noise small residual current ripple at output Switch-Mode Power Converters + - + - Passive high-current output stage HF soft-commutation inverter on low current input side

22. Fk. Bordry AB/PO Academic Training - 27th March 2003 OutputModule Inverter Module Input Module Reactive network + - HF soft-commutation inverter on low current input side Passive high-current output stage Sub-converter 3.25 kA, 18V or 2kA, 8V Inverter : 20 - 50 kHz 30 - 70 KVA Since they are natural current sources, and can be easily paralleled to make up very high currents

23. Fk. Bordry AB/PO Academic Training - 27th March 2003 Current sources in parallel 13 kA, 16V 3.25 kA, 16 V n + 1 subconverters : redundancy, reliability repairability ease of handling underground versatility (6.5kA, 9.75kA, 13kA, 21 kA) n + 1 subconverters : redundancy, reliability repairability ease of handling underground versatility (6.5kA, 9.75kA, 13kA, 21 kA)

24. Fk. Bordry AB/PO Academic Training - 27th March 2003 Loop

25. Fk. Bordry AB/PO Academic Training - 27th March 2003 Line-commutated thyristor-controlled converter SCR semiconductor Switch Mode Converter IGBT semiconductor [14kA,16V] converter Volume : 25 m 3 Weight : 8 tons Ripple : ~ 200 mV Voltage bandwidth : 40 Hz [16kA,16V] converter Volume : 6 m 3 Weight : 1.2 tons Ripple : ~ 10 mV Voltage bandwidth : 1000 Hz Dev.

26. Fk. Bordry AB/PO Academic Training - 27th March 2003 I measured V I Iref B  + Reg. F(s) - Vref VV G(s) Current loop Voltage loop

27. Fk. Bordry AB/PO Academic Training - 27th March 2003 1- Fast internal current sourceF CL B ~ 8 kHz 2- Global voltage loopF CL B ~ 700 Hz 3- High precision current loop (DCCT)F CL B ~ 0.1 - 1 Hz Control loops

28. Fk. Bordry AB/PO Academic Training - 27th March 2003 Digital current loop : RST algorithm Frequency Divider T1/S yref(k) k.Ts ADC Power Part y(t) DAC Anti aliasing filter  k Digital Filter R Ts Over sampling Digital controller Tracking and Regulation with independent objectives Tracking Regulation

29. Fk. Bordry AB/PO Academic Training - 27th March 2003 0 20 40 60 80 012345678 0 1 2 3 4 Current offset in Milliamps Current offset in ppm of 20 kA Time in Seconds I 0 = 1019.9 Amps Reference Measured Current in Amps 500.0 500.1 500.2 0123456 0 5 10 Current offset in ppm of 20 kA Time in Seconds  1ppm Reference Measured

30. Fk. Bordry AB/PO Academic Training - 27th March 2003 String 2 Powering area

31. Fk. Bordry AB/PO Academic Training - 27th March 2003 Power cycle, 13A.s -1, ±600A Reception 270 mm

32. Fk. Bordry AB/PO Academic Training - 27th March 2003 Start of the ramp (from 200 A to 225 A) dI/dt = 50 A/s Iref ADC 10 ms No lagging error !

33. Fk. Bordry AB/PO Academic Training - 27th March 2003 [13kA,18V] converter 1mH inductance ; 0.8 m  resistance (  = 1.5 s) dI/dt = 200 A/s [13kA,18V] converter 1mH inductance ; 0.8 m  resistance (  = 1.5 s) dI/dt = 200 A/s 25 ppm 1 A 10 ppm Ramp from 200 A to 13000A

34. Fk. Bordry AB/PO Academic Training - 27th March 2003 Integration, system with protection, circuit Getting the current into the cold Current source Power Converter 13kA, 10V flat top, ± 180V boost Time Constant = 23000 seconds (6 hours 23 minutes) 2x Energy extraction systems. Maximum rate of discharge = 120A/sec. Cryo feedboxes, Current leads,… Cold cryostat : magnets, bus bars, diodes,… 13kA Karl Hubert Mess

35. Fk. Bordry AB/PO Academic Training - 27th March 2003

36. Fk. Bordry AB/PO Academic Training - 27th March 2003 Four Point Feed of LHC Courtesy of P.Proudlock

37. Fk. Bordry AB/PO Academic Training - 27th March 2003 One Sector (1/8) of the LHC Machine Cryostat containing 154 Main Dipoles Nominal Current = 11.8kA (For 7 TeV) Ultimate Current = 13kA (For 9 Tesla) 23x3x2=138 magnets in the arc 16 magnets in the two dispersion suppressors 154 magnets in total Ltotal = 0.108 H x 154  16.6 H (LHC sector  1.2GJ at 11.8kA, 1.4 GJ at 13kA!) (HERA ~ 480 MJ) (Tevatron ~ 300 MJ) Charging voltage= 16.6 Hx10A/sec= ±166V (2.2 MW )  0 mins Time Constant = 23000 seconds (6 hours 23 minutes)

38. Fk. Bordry AB/PO Academic Training - 27th March 2003 LHC power converters A- Elementary module [3.25 kA, 18V], [2kA,8V] : (~120) (~700) Switch Mode Converter (25-40 kHz, soft commutation) Modular approach : 4.0 kA (28), 6.0 kA (160), 8.0 kA (8), 13 kA (24) Redundancy; small volume and weight B- Unipolar and Bipolar converters 600A [± 600 A,± 10 V] : (~ 328); [600 A,10 V] : (~ 70) [± 600 A,± 40 V] : (~ 40) Energy dissipation SMPC : soft commutation ; 50-100 kHz C- Bipolar converter [±60 A, ± 8 V] and [±120A,±10V] (~760) (~300) SMPC : soft commutation SMPC : soft commutation High reliability, radiation resistance (tunnel installation) D- High voltage power converter [13 kA, ±180 V] (8) High power SCR converter and Topology studies Ramp (up and down) : [13 kA, ± 180 V] Flat bottom and flat top : [13 kA, 18 V] SCR converter : [13 kA, ± 180 V] with Active filter : ±600A,±12V

39. Fk. Bordry AB/PO Academic Training - 27th March 2003 DCCT Performance Requirements

40. Fk. Bordry AB/PO Academic Training - 27th March 2003 Class1 DCCTs (13kA) - Highest performance - state of the art - Separate Head and electronics chassis 19” rack mounting. - Fitted with Calibration Windings - Temperature-controlled environment in the Accelerator. - Full testing and calibration at CERN on the 20kA Test Bed. - Highest performance - state of the art - Separate Head and electronics chassis 19” rack mounting. - Fitted with Calibration Windings - Temperature-controlled environment in the Accelerator. - Full testing and calibration at CERN on the 20kA Test Bed.

41. Fk. Bordry AB/PO Academic Training - 27th March 2003 4kA to 8kA DCCTs 600A DCCTs 120A DCCTs

42. Fk. Bordry AB/PO Academic Training - 27th March 2003 Main Dipole Current Cycle I t 11500 A 20 min -10 A/sec (~20 mins) +10 A/sec (~25 mins) 3-5 mins several hours (~24 hrs) 0.1 A/sec 350 A 1 min 350 A pre-injection (0-1 hr) 740 A 500 W 2.2 MW 115 kW Injection Plateau Acceleration Coast Dump Beam

43. Fk. Bordry AB/PO Academic Training - 27th March 2003 One Sector (1/8) of the LHC Machine Total inductance = 16.6H. Total stored energy = 1.2GJ Current source Power Converter 13kA, 10V flat top, ± 180V boost Time Constant = 23000 seconds (6 hours 23 minutes) EVEN POINTS 2x Energy extraction systems. Maximum rate of discharge = 120A/sec. ODD POINTS Cryostat containing 154 Main Dipoles 13kA