HQ - ramp rate effects

D.Tsirigkas, E. Todesco

Acknowledgements: B. Auchmann, L.Fiscarelli

02/08/2012 1

Context

02/08/2012 2

• HQ is very dependent on ramp rate (nominal = 13 A/s)

• Goal: investigate ramp rate effect

• Measurements @CERN, SM18, 28/3 – 4/4

• T = 1.9 K

Available measurements

02/08/2012 3

0 5000 10000 150000

5000

10000

15000

t(s)

I(A)

0 1000 2000 3000 4000 50000

2000

4000

6000

8000

10000

t(s)

I(A)

05000

10000

15000

20000

25000

0

5000

10000

15000

t(s)

I(A)

Variable minimum current

02/08/2012 4

0 2000 4000 6000 8000 10000 12000 140000

2000

4000

6000

8000

10000

12000

14000

16000

t(s)

I(A)

02/08/2012 5

0 2 4 6 8 10 12 14 1610.6

10.8

11

11.2

11.4

11.6

11.8

12

12.2

12.4

0kA0.1kA0.7kA1.3kA1.9kA

I(kA)

TF(T/m/A)

Variable minimum current

If dI/dt is the same, TF is the same (I>5kA)

Variable ramp rate

02/08/2012 6

0 500 1000 1500 2000 2500 3000 3500 4000 45000

1000

2000

3000

4000

5000

6000

7000

8000

9000

t(s)

I(A)

±20A/s±40A/s±60A/s±90A/s

Variable ramp rate (ramp up)

02/08/2012 7

0 1 2 3 4 5 6 7 8 911

11.2

11.4

11.6

11.8

12

12.2

12.4

90 A/s60 A/s40 A/s20 A/s

I(kA)

TF(T/m/kA)

Ramp rate has an effect that persists at high currents

15 20 25 30 35 40 45 50 55 60 6511.5

11.55

11.6

11.65

11.7

11.75

f(x) = 0.00354973574369 x + 11.5223226278655

dI/dt

TF(T/m/kA)

Extrapolation to dI/dt=0

02/08/2012 8

• For a specific current- Plot TF vs dI/dt- Extrapolate to

dI/dt = 0

• Repeat for different I’s

Variable plateau

02/08/2012 9

05000

10000

15000

20000

25000

02000400060008000

10000120001400016000

t(s)

I(A)

10350 10850 11350 11850 1235010

10.5

11

11.5

12

12.5

t(s)

TF(T/m/kA)

10350 10850 11350 11850 123500

2

4

6

8

10

12

14

16

t(s)

I(kA)

Extrapolation to dI/dt=0

02/08/2012 10

0 1 2 3 4 5 6 7 811.211.311.411.511.611.711.811.9

1212.1

13 A/s20 A/s40 A/s60 A/sextr. 0 A/sPlateau

I(kA)

TF(T/m/kA)

0 1 2 3 4 5 6 7 89.5

10

10.5

11

11.5

12

-60 A/s-40 A/s-20 A/s-13 A/sextr. 0 A/s

I(kA)

TF(T/m/kA)

Multipole analysis

02/08/2012 11

• Dependence on the ramp rate suggests an Eddy current effect.

• Where does it come from? n

fn R

RI

dtdIb

,

RR

nbRR

b fn

nf

n lnln

• Plot the difference |Δbn| vs n

0 2 4 6 8 10 12 14 16

-2

-1

0

1

2

3

4

5

6

• Solving for R ≈ 0.06 m

n

|Δb n|

sA

dtdI

sA

dtdIkAI 60,20,1.1

21

Repeat for different currents

02/08/2012 12

• The data suggests that the effect comes from the coil – not the collar

0 2 4 6 8 10 12 14 16 18-9

-7

-5

-3

-1

1

3

5

7

I=1kAI=3kAI=5kAI=7kACoil inner RCollar position

n

|Δbn|

Conclusions

02/08/2012 13

• HQ has been tested at 1.9 T to investigate ramp rate effects

• Strong dependence on the ramp rate that persists at high currents

• The TF at dI/dt=0 has been approximated by extrapolation and by measurements at current plateaux

• Analysis of the multipoles suggests that the ramp rate effect originates from the coil