1. The HiLumi LHC Design Study is included in the High Luminosity LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404. Powering schemes for inner triplet and matching section Power converters for HL-LHC WP 6b : Warm powering Jean-Paul Burnet, CERN TE-EPC

2. 2 Content List of circuits Circuit layout Ramp down Squeeze process HL-LHC TC – 30 April 2015

3. 3 List of circuits Layout of the Inner Triplet Layout of the Matching section 43 circuits per IP side. In total, 172 power converters HL-LHC TC – 30 April 2015

4. 4 List of power converters List of power converters needed with the last magnet parameters: The total current to be delivered for the new inner triplet and matching section is 600kA with 172 power converters. The total current of the Present inner triplet and matching section is 232kA with 112 power converters. The present LHC machine has a total current delivered by the power converters of 1.8MA and it will reach 2.2MA with HL-LHC. HL-LHC TC – 30 April 2015

5. 5 LHC power converters The LHC was build with 5 families of switch-mode power converters. Main Quadrupoles: 13kA/18VAtlas Toroid: 20.5kA/18VIndividual Quadrupoles: 6kA/8V 4-quadrant for correctors : ±600A/±10V4-quadrant for correctors : ±120A/±10V4-quadrant for correctors : ±60A/±10V Same family HL-LHC TC – 30 April 2015

6. 6 Circuit layout parameters The circuit layout need to be chosen based on the impact on 3 parameters:  Beam optic flexibility(number of Converter)Individual powering for full flexibility  Tune shift(inductance of the circuit)Stability in current  Squeeze time(time constant of the circuit) turnaround, fb -1 production and ramp down HL-LHC TC – 30 April 2015

7. 7 Present Inner triplet The present layout is quite complex with nested circuits. It requires decoupling matrix to get a good control of each circuit. The operation of such system is complex and need experts especially in case of fault when it is difficult to identify the cause of the fault. HL-LHC TC – 30 April 2015

8. 8 Baseline for the Inner triplet The new layout allows the full flexibility for beam optics. Each circuit has a single trim power converter. The goal is to ease the operation and diagnostic to improve the availability of the machine. Extra-cost: +1 power converter, +2 current leads, +2 SClink cables. HL-LHC TC – 30 April 2015

9. 9 Alternative layout for the Inner triplet HL-LHC C&S Review #1 – March 2015 The new layout allows the full flexibility for beam optics and reduce the tune shift. More complex but still feasible. Cheaper due to less SClink, and power converters. Higher inductance (255mH) to reduce current ripple (tune shift). Q1 Q2a Q2b Q3 PC1 17.4 kA PC2 ±2.0 kAPC3 ±0.2 kAPC4 ±2.0 kA Q1-Q2-Q3: -slightly smaller tune shift than Q1-Q2a Q2b-Q3 for current control regime -best compensation voltage control regime => best scheme (for beam dynamics) HL-LHC TC – 30 April 2015

10. 10 Inner triplet ramp down The current of inner triplet doesn’t move a lot during the squeeze process. The only concern is for the ramp down. Circuits with Sclink and 20m of DC water cooled cables. Minimum ramp down time = 5* time constant Present LHC ramp down = 1200s If we stay with 1-quadrant power converter, we have a big issue with the ramp down. Ramp down will be 1.5-3H. Precycle from present 1H to 3-4H. Only solution = 2-quadrant power converters. Not in the baseline of WP6b. Impact on size, cost and manpower. HL-LHC TC – 30 April 2015

11. 11 Inner triplet ramp down Circuits without SClink and 100m of DC water cooled cables. (present LHC solution). With the present baseline, we are back on the LHC ramp down of 1200s. The alternative scheme will double the ramp down time. +100% ramp down time +50% precycle time HL-LHC TC – 30 April 2015

12. 12 Q4 Q4 has a very low inductance 2.9mH. The time constant is very small. The current ripple will be much high than the Inner triplet. Big issue for current stability even with two aperture in series. Sensible to grid perturbation. Test done today on test stand 13kA: R = 0.836mOhms, L = 5mH (warn magnet) Ripple 50Hz = 16mA HL-LHC TC – 30 April 2015

13. 13 D1 D2 in series D1 and D2 with SClink has a time constant which allows a ramp down in 1200s. D1 and D2 in series with Sclink will increase the ramp down time of LHC. D1 and D2 in series without Sclink is fine with the LHC ramp down. HL-LHC TC – 30 April 2015

14. 14 All D1 D2 in series for one IP side  All D1 and D2 can be put in series in the surface building (with Sclink). Major impact on the ramp down time of LHC.  All D1 and D2 can be put in series with DC cables inside the parallel gallery (Gallery version). Cable length 400m. Cable size 6000mm 2 (normally rated for 36kA). Choice based on cost of one 13kA power converter versus cost of the cables. HL-LHC TC – 30 April 2015

15. 15 Pre-squeeze and Squeeze Objective: Analyse pre-squeeze and squeeze optics file provided by Massimo Giovannozzi to estimate the time required for each circuit: https://indico.cern.ch/event/342270/optics file https://indico.cern.ch/event/342270/ Identify the slowest circuit Repeat for different types of power converter topology (1-quadrant, 2-quadrant) Method: Simplistic first approach using linear interpolation between the 278 points resulting in one continuous squeeze function. No parabolic acceleration/deceleration so results will not be precise but will give an idea of the time needed for the squeeze. Allows comparison between different converter topologies. HL-LHC TC – 30 April 2015

16. 16 Pre-squeeze and Squeeze http://project-cclibs.web.cern.ch/project-cclibs/cclibs/cctest/results/html/tests/HL_LHC/ Current versus step process 278 steps for pre-squeeze ( β * from 6 to 0.44), 69 steps for squeeze ( β * from 0.44 to 0.1) HL-LHC TC – 30 April 2015

17. 17 Simulation Squeeze times IR2 : Total time: 215.983 IR4 : Total time: 69.691 IR1/5 : Total time: 825.683 IR6 : Total time: 14.070 IR8 : Total time: 81.242 IR8_3m : Total time: 175.908 IR5 (IR1 is the same) dominates the squeeze time. Ignoring acceleration/deceleration and intermediate stopping points Magnets involved from IT to Q13 β * from 6 to 0.15 With SClink HL-LHC TC – 30 April 2015

18. 18 Simulation Squeeze times at IR5 IR5 : Iq4.l5b1: 1.943 IR5 : Iq4.r5b1: 14.666 IR5 : Iq5.r5b1: 91.888 IR5 : Iq5.l5b2: 216.857 IR5 : Iq5.r5b2: 500.330 IR5 : Total time: 825.683 Within IR5, it is the Iq5 circuits that are the slowest. HL-LHC TC – 30 April 2015

19. 19 IR5 times with 2-quandrant q5 converters If the q5 converters are 2-quadrant, the time is reduced: IR5-q5-2Q : Iq4.l5b1: 16.450 IR5-q5-2Q : Iq4.r5b1: 22.428 IR5-q5-2Q : Iq4.l5b2: 6.142 IR5-q5-2Q : Iq6.l5b1: 5.849 IR5-q5-2Q : Iq6.r5b1: 16.400 IR5-q5-2Q : Iq6.l5b2: 58.631 IR5-q5-2Q : Iq6.r5b2: 149.010 IR5-q5-2Q : Total time: 274.911 Now the Iq6 converters are the slowest. HL-LHC TC – 30 April 2015

20. 20 IR5 times with 2-quandrant q5 & q6 converters IR5-q56-2Q : Iq4.l5b1: 17.197 IR5-q56-2Q : Iq4.r5b1: 32.389 IR5-q56-2Q : Iq4.l5b2: 14.466 IR5-q56-2Q : Iq5.r5b1: 4.473 IR5-q56-2Q : Iq5.l5b2: 0.342 IR5-q56-2Q : Iq5.r5b2: 3.386 IR5-q56-2Q : Iq9.r5b2: 1.423 IR5-q56-2Q : Iq10.r5b1: 3.758 IR5-q56-2Q : Iq10.l5b2: 14.059 IR5-q56-2Q : Total time: 91.493 If both Iq5 and Iq6 converters are 2-quadrant, the time is reduced unnecessarily because IR2 will take more than 200 s. HL-LHC TC – 30 April 2015

21. 21 Alternative to 2-quadrant converters One solution to improve the ramp down of the current is to add diodes in series with the power converter. The power converter can apply 0V to 8V to the magnets, but with additional diodes in series the voltage applied to the magnets change to -1V to 7V Vmagnet = Vpc-Vdiode Advantage: Faster ramp down Drawback: additional losses to be dissipated in water Pdis= Vdiode * Imagnet 3kW / diode HL-LHC TC – 30 April 2015

22. 22 I5 squeeze times with 2 series diodes IR5-q56-1V : Iq4.l5b1: 15.683 IR5-q56-1V : Iq4.r5b1: 20.122 IR5-q56-1V : Iq5.r5b1: 58.627 IR5-q56-1V : Iq5.l5b2: 29.382 IR5-q56-1V : Iq5.r5b2: 84.767 IR5-q56-1V : Total time: 208.581 If both Iq5 and Iq6 converters have two diodes in series (1V offset) then the time is reduced by a further 100 seconds and is now less than IR2. HL-LHC TC – 30 April 2015

23. 23 Summary Not enough resistance in circuit with SClink to ramp down as today. Only solution with SClink is 2-quadrant converters for IT. Not included in WP6b, R&D needed. Alternative solution with DC cables eases the ramp down time to stay within the present time. Q4 inductance is a major concern. Need integration work to define all parameters of the circuits. HL-LHC TC – 30 April 2015