The implementation of hysteresis in the FIDEL model and implications for the

LHC operation

P. HagenNovember 2010

2

Hysteresis in the FiDeL model

o The FiDeL description of the magnets assume / require that a specific pre-cycle has been followed

o The reason being that the hysteresis depend upon the magnet history

o There are 3 components in the FiDeL model which contribute to hysteresis:

o PEN - current penetration in the cable filamentso DCMAG - persistent currents in SC magnetso RESMAG – residual magnetisation of materials

o PEN is only used in MQM and MQY to model exponential behavior @ low B

o DCMAG depends upon the sign of the dI/dt (ramp up or down). We do not know the exact conditions (Δt, ΔI) causing a switch of branch

o RESMAG depends upon the history (previous cycle)

3

Example of TF with RESMAG hysteresis

o The curves a, b, c, d correspond to different pre-cycles (Imin and Imax)

o The person implementing FiDeL for a magnet must decide upon which curve (or something in-between) based upon how the magnet is used

o Example MQWA, pre-cycle constrained by power supply + magnet only ramp-up (dI/dt > 0) so we only use that specific branch

0 20 40 60 80 100 120 140 160 180 200-100

0100200300400500600700

MQW 10 ap 1 a

b

c

d

Current (A)

TF (u

nits

)

4

Extending the FiDeL model to 4 quadrants!

-0.00002-0.000010.000000.000010.000020.000030.000040.000050.000060.000070.00008

-150 -100 -50 0 50 100 150TF

[T m

/ A

]

Current [A]

o In FiDeL we basically model one quadrant (1 or 4)

o The sign of the current is not given by FiDeL but by the powering scheme

o The width of the hysteresis depends on the previous Imin and Imax

I > 0I < 0

Imin < 0

Imin < 0

I < 0 I > 0Imin > 0

Imin > 0123 4

5

LHC magnets and hysteresisMagnet Known hysteresis |I| range (A) |I| max FiDeL hyst comp dI/dt change sign? op. with hyst? Hysteresis related issues in op CatMB 3 and 5 units @ 760 A 757-6000 12850 RESMAG, DCMAG No No AMBRB 6 units @ 400 A 395-3068 6400 DCMAG No No AMBRC 8 units @ 300 A 283-2204, 384-2992 6100 DCMAG No No AMBRS 16 units @ 350 A 353-2749 6000 DCMAG No No AMBW 12 units @ 30 A, Iinj > 40 A 41-318 810 No No AMBX 10-15 units @ 300 A 345-2686 6000 DCMAG No No AMBXW 6 units @ 30 A 43-335, 650-650 830 No No AMBWMD Lack of measurements 428-428 595 No No AMBXWS Lack of measurements 722-722, 754-754 810 No No AMBXWT 50 units @ 20 A 555-555, 512-512 650 RESMAG No No AMCBCH/V 100 units @ 5 A 0.1-30 100 Some do Yes Some operate w ith low current, some change sign of dI/dt BMCBH/V 100 units @ 5 A 0.1-30 55 Some do Yes Some operate w ith low current, some change sign of dI/dt BMCBWH/V 3-5 units @ 30 A 0.1-40 600 Some do Assume yes Some operate w ith very low current BMCBXH/V 400 units @ 5 A 2-228 550 Yes, squeeze some Sign of dI/dt changes frequently during squeeze BMCBYH/V 100 units @ 5 A 2-20 88 Yes, squeeze some Sign of dI/dt changes frequently during squeeze BMCD 100 units @ 20 A 0-120 550 Yes Yes Crosses 0-current, sign of dI/dt changes BMCO 500 units @ 50 A 2-40 100 No Yes Operate w ith low current BMCOSX 600 units @ 10 A 100 Unused in 2010 BMCOX 500 units @ 10 A 100 Unused in 2010 BMCS 150 units @ 20 A 40-150, 20-250 550 Yes (MB b3 decay) Yes Crosses 0-current, sign of dI/dt changes CMCSSX ~0 100 Unused in 2010 AMCSX 200 units @ 20 A 0-40 A 100 Unused in 2010 BMCTX Lack of cold measurements 100 Unused in 2010 BMO 100 units @ 20 A 0-101 550 No No AMQ 4 units @ 760 A 686-5334, 717-5577 12000 RESMAG,DCMAG No No AMQM/C/L DCMAG 20 units @ 300 A 160-2300 5390 PEN,RESMAG,DCMAG Yes Yes Sign of dI/dt changes during squeeze DMQS 200 units @ 5 A 0-60 550 Yes, squeeze Yes Sign of dI/dt changes frequently during squeeze BMQSX 100 units @ 20 A 0-30 550 No Yes Ramps at end of squeeze BMQT 200 units @ 5 A 5-60, 0-2, 2-20 550 Yes, squeeze Yes Sign of dI/dt changes during squeeze, some w ith low current BMQTLH 100 units @ 10 A 15-150 550 No No AMQTLI 100 units @ 10 A 0.5-220 550 Yes, squeeze some Some change sign of dI/dt during squeeze BMQWA 100 units @ 40 A 35-300 810 RESMAG No No AMQWB 500 units @ 40 A 2-220 600 RESMAG No Yes AMQXA 30 units @ 430 A 408-3195, 453-3550 7400 DCMAG Yes some About 1/2 of the magnets ramp dow n during the squeeze DMQXB 55 units @ 670 A 700-5490, 780-6080 12000 DCMAG Yes some Many ramp dow n during the squeeze DMQY Yes, ???? 160-1300 3610 PEN,RESMAG,DCMAG Yes, squeeze some Many ramp dow n during the squeeze DMS 450 units @ 10 A 10-80, 5-45 550 No Yes BMSS 450 units @ 10 A 0.5-10 550 No Yes B

6

Cat A – no operational issues

o Magnets which operate in a current range with little hysteresis

o and .. or …

o Magnets which only ramp-up with beam present, well-defined pre-cycle and relevant hysteresis components are included in the FiDeL model

o Most main magnets belong to this category

Il buono (the good)

7

Cat B – minor operational issues

o Magnets which operate in a current range with hysteresis and relevant hysteresis components are NOT included in the FiDeL model

o … but it is assumed that they do not cause operational problems

o We pretend they behave linearly in the low-current region

o Most corrector magnets belong to this category…

o The neglect of hysteresis in orbit, tune and coupling correctors is compensated by real-time measurements and adjustments

o Correctors without well-defined operational cycles are probably impossible to model wrt hysteresis

o Nevertheless, we believe there are corrector magnets which have known cycles and where model could be improved if justified by operation: MCD, MCO, MQTLI, MSS ?Il buono? (the good?)

8

Cat C – assumed operational issue

il brutto (the bad)

o Magnets which operate in a current range with hysteresis and relevant hysteresis components are NOT included in the FiDeL model

o … and it is assumed that they do cause operational problems

o We have so far only put the corrector MCS into this category

o The current crosses 0 during LHC ramp-up so there will be an error in TF of several %

9

Cat D – known operational issue

il cattivo (the ugly)

o Magnets which change ramp direction during operation (dI/dt) and which include a FiDeL DCMAG component

o This happens to the final focus and insertion quads during the squeeze: MQXA, MQXB, MQM/C/L, MQY

o This causes the TF to jump, if we literally follow the FiDeL model

o LSA adds smoothing in order to keep power supplies happy

o They require continuous I function with well-defined constraints on dI/dt, d2I/dt2

o But … trims of these magnets become unpredictable as it may cause the DCMAG component to change sign, so it gives an upper limit on the smallest possible trim

10http://www.youtube.com/watch?v=1hYV-JSjpyU

The question is, to branch or not to branch?

Ignorance (pretend it does not happen)

Or … Complexitywhen trimming

A persistent answer is needed for 2011 runKeep in mind the effect will ~ disappear with 7 TeV

11

MQXA1.L2 (1.9K)

In following slides, red numbers give DCMAG

in units of GEOmetric component. This is ½ width of hysteresis

0.7

12

RQ10.L1B2 (MQML @ 1.9K)

1.9 1.9

1.6

13

RQ10.L2B2 (MQML @ 1.9K)

1.8

1.7

14

RQ10.L4B2 (MQML @ 1.9K)

1.8

15

RQ4.L1B2 (MQY @ 4.5K)

0.0

0.0

16

RQ4.L2B1 (MQY @ 4.5K)

0.0

0.2

~ worst case DCMAG amplitude for MQY

17

RQ7.L4B2 (MQM @ 1.9K)

1.8

18

RQ7.L8B2 (MQM @ 1.9K)

2.3

2.6

19

RQ7.R2B1 (MQM @ 1.9K)

2.6

2.7

2.5

2.82.7

2.8

20

RQ8.R2B1 (MQML @ 1.9K)

2.7

3.1

4.2

~ worst case DCMAG amplitude for MQM

21

RQ9.L5B2 (MQMC @ 1.9K)

2.1

2.2

2.1

22

23

RQ10.R5B2 (MQML @ 1.9K)

1.8 1.8

ΔI DCMAG = 2 * 1.8 / 10000 * 2334 A = 0.84 A

The trim discrepancy of 5 A seems not justified!