the implementation of hysteresis in the fidel model and implications for the lhc operation
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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!
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