report on investigation of possible magnet related issues in the tevatron

Feb 20th 2003 Pierre Bauer 1 - Tevatron RunII Meeting

REPORT ON INVESTIGATION OF POSSIBLE MAGNET RELATED

ISSUES IN THE TEVATRON

G. Annala, P. Bauer, R. Cargagno, J. DiMarco, N. Gelfand, H. Glass, R. Hanft, D. Harding, R. Kephart, M. Lamm, A. Makulski, M. Martens, T. Peterson, P. Schlabach, D. Still, C. Sylvester, M. Tartaglia, J. Tompkins, G. Velev, M. Xiao

Also many thanks to L. Bottura (CERN), H.D. Brueck and B. Holzer (DESY), G.L. Sabbi (LBNL), A. Tollestrup and V. Shiltsev for their ideas, opinions, suggestions and help!


1) Tevatron Dipole Magnets – an Overview

2) Measurement of Dynamic Effects in Tevatron Dipoles

3) Discussion of Possible Magnet Issues in the Tevatron

INTRODUCTIOND. Finley et al. 1987


I TEVATRON DIPOLE MAGNETS

1) Dipole Models

2) Production Magnetic Measurement Data

3) Field Profiles


THE TEVATRON DIPOLE MODELS - BODY

Bore field at injection (T) 0.66

Bore field at collision (T) 4.3

Magnetic length (m) 6.116

Averagex) b2* in body (x 10-4B0) 14.4xx)

Sigmax) b2* distr.in body (x 10-

4B0)3.1

Pole angle var.for 1 in b2* () 0.15

Azim.coil position var.for 1 (m)

100

Saturation effect (% of b2* inj.) +1.9

Stray-field (mT) ?* magnetic multipoles quoted at 1 inch (=2/3 of bore radius)

x) Data are from production measurements (more details later).

xx)Tevatron dipoles have strongly differing b2 in body and ends, that, on average compensate when integrated over the magnet length!


THE TEVATRON DIPOLE MODELS - END

* magnetic multipoles quoted at 1 inch (=2/3 of bore radius)

Length of end (arbitrary) (cm) 50

Type of end: compact

Length of non-yoked end-section (cm)

~12

Average dipole field end/body ratio 0.86

Length (arbitrary) (cm) 50

Averagex) b2* in end (units of 10-

4B0)-115

Sigmax) b2* in end (units of 10-4B0) ?

x) Data derived from production measurements (more details later).


FIELD PROFILE IN END

-1000

-800

-600

-400

-200

0

2.6 2.65 2.7 2.75 2.8 2.85 2.9 2.95 3 3.05 3.1 3.15 3.2

Axial distance from center (m)

Sextu

po

le a

nd

Dec

ap

ole

(u

nit

s o

f 10-4

0.6

6T

)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Main

Fie

ld, n

orm

ali

zed

to

cro

ss-s

ecti

on

fie

ld

yoke

coil

end

sextupole

decapole

dipole

Results of the calculations presented here are not for the “average” end.


MAGNETIC MEASUREMENT ARCHIVE DATA*


J. Tompkins / R. Hanft


THE TEVATRON DIPOLE NORMAL MULTIPOLES*


Calculated from “Up-down-average” of archived production magnetic measurements for approx. all magnets installed.


Down-stream position Up-stream position Body position

~1.9 m ~2.3 m ~1.9 m

14.4 u

-6.9 u-6.8 u

6.1 m

b2

z

~1.9 m ~2.3 m ~1.9 m

14.4 u

-6.9 u-6.8 u

6.1 m

b2

z

enddenddenduendubodybody

enddenddenddn


enduenduendun


bodybodybodyn

totn

BLBLBL

BLb

BLBLBL

BLb

BLBLBL

BLbb

,0,0,0

,0

,0,0,0

,0

,0,0,0

,0


THE TEVATRON DIPOLE SKEW MULTIPOLES*



Calculated from “Up-down-average” of archived production magnetic measurements for approx. all magnets installed.

Down-stream position Up-stream position Body position

~1.9 m ~2.3 m ~1.9 m

14.4 u

-6.9 u-6.8 u

6.1 m

b2

z

~1.9 m ~2.3 m ~1.9 m

14.4 u

-6.9 u-6.8 u

6.1 m

b2

z


enddenddenddn


enduenduendun


bodybodybodyn

totn

BLBLBL

BLb

BLBLBL

BLb

BLBLBL

BLbb

,0,0,0

,0

,0,0,0

,0

,0,0,0

,0


AVERAGE FIELD

PROFILES IN DIPOLE

CALCUL-ATED FROM

TABUL-ATED

(Geometric) MULTI-POLES

J. Tompkins 2002

nanbinanbR

RBiBB nnnn

n

n refrefxy cossinsincos


II DYNAMIC EFFECTS

IN TEVATRON DIPOLES

1) Introduction to Dynamic Effects

2) Historical Review of Tevatron Magnet Measurements

3) Some Recent Results


DYNAMIC EFFECTS -BASICS

P. Schlabach

5

7

9

11

13

15

17

19

21

23

25

0 500 1000 1500 2000 2500 3000 3500 4000 4500

current (A)

b2

(un

its)

no injection porch

with injection porchTC0504

MP drift at constant coil current & SB to the hysteresis loop at the ramp- start.

Drift & SB in all ”hysteretic” multipoles -powering history dependent.

1-2u

~15 A / 15 mT/ 7 GeV

back porch

time

currentinjection porch

flat top

reset

pre-cycle:


DYNAMIC EFFECTS IN TEVATRON DIPOLES – QUALITATIVE MODEL

Current distribution is not uniform in the cables and changes as a function of time, generating a time-variable,

-B +B

alternating field along the Strands.

L. Bottura/CERN 2002


DYNAMIC EFFECTS IN TEVATRON DIPOLES – PREVIOUS STUDIES

YR MAGNET COMMENT87 AA1001 (1m) discovery of drift

88/89 RL1001 (1m) discovery of snapback

88/89 TB447, TB223, TB271, TC1194, TB338, TC537, TC1200

remnant field in full length dipoles, drift found also in other mps

92 TB353, TB1220, TB1207, TB492, TB862

first full length magnet measurements

96 TC1052, TB504 back-porch, flattop energy

02/03 TC1220, TB834, TB438, TC269

tune and coupling drift, b2 compensation


MAGNETIC MEASUREMENTS AT MTF

MTF today has 7 test-stands to perform magnetic measurement of Fermilab magnets, superconducting IR quads for LHC, high field (Nb3Sn) magnets.


87 - DISCOVERY

D. Finley et al. 1987


88 - MEASUREMENTS

Magnet Meas. – RL 1001

R. Hanft et al. 1988


92-MEASUREMENTS

D. Herrup et al. 1992


96-MEASUREMENTS

J. Annala et al. 1996

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3 4 5 6 7 8 9

time (sec)

sn

ap

ba

ck

(u

nit

s)

TC1052 - 4.5 K, 2 precycles to 4 kA 10 min FT, 1 min BP, 15 min injTC1052 - 3.5 K, 1 precycle to 4440 A 10 min FT, 10 min BP, 15 min injTC1052 - 4.5 K, 1 precycle to 4000 A 10 min FT, 10 min BP, 15 min injTC0504 - 4.5 K, 1 pre-cycle to 4000A 10 min FT, 1 min BP, 15 min injTC1052 - 4.5 K, 1 pre-cycle to 4000A 10 min FT, 1 min BP, 15 min injTC1052 - 4.5 K, 2 precycles to 4 kA 10 min FT, 10 min BP, 15 min injcomputed snap-back from arbitrarily chosen b2 drift amplitude (units)computed snap-back from arbitrarily chosen b2 drift amplitude (units)

no correction for "loop" included!

1 min BP "group"

10 min BP "group"


MAGNETIC MEASUREMENTS – 02/03

J. Tompkins / G. Velev / R. Hanft


III Discussion of Possible Magnet

Issues in the Tevatron

1) Temperature Variations

2) Tune and Coupling Drift

3) Main Field Drift

4) Analysis of the b2-Compensation in the Tevatron


QUANTITATIVE ESTIMATE OF DRIFTING SKEW AND NORMAL QUADS

b1 drift needed in dipole to explain tune drift:

L4

11x Kx

mLK

x

x 1103.3

4 31

mm

TLKBLG 65.11 units

B

Grb 102104

0

01

a1 drift needed in dipole to explain coupling drift:

m

LKLK sqyxsq1

0022.057

02.02

2

111min

units

Tm

mTmm

BL

rBLKa

dip

sq6810

66.02.6

0254.05001

0022.010 44

0

011

b1/ a1 = ~0.1 u in dipole to explain tune/coupling drift


DRIFTING a1 AND b1 IN DIPOLES?possible sources of 1u of a1 (up-down asym) & b1(left-right asym):

However, all the above explains GEOMETRIC a1/b1! The only mechanism that we found to explain HYSTERETIC a1 is: up-down difference in superconductor properties (e.g. Jc)! b1 drift maybe main field decay in quads?

0.2mm0.1mm 0.05mm

0.03°0.015°0.012°0.006°

0.1mm 0.2mm

coil roll (“cryostat- instability”) – has been addressed!

“smart-bolting” should have taken care of most of these!


DRIFTING a1 AND b1 IN DIPOLES?Feed-down from b2 due to misalignment of dips & T:SD is most likely cause (see M. Martens talk) of most of the tune and coupling drifts; Is there drifting

Production goal: zero geometric a1 and b1.

TC0269 clearly shows a hysteretic and a drifting skew quadrupole:

a1, b1 in the magnets?

1.3

1.35

1.4

1.45

1.5

1.55

1.6

1.65

1.7

1600 2000 2400 2800 3200

time (sec)

a1

(u

nit

s)

a1 (units) TC0269

R. Hanft / G. Velev

This, however, does not exclude hysteretic b2:


DRIFTING MAIN FIELD?~0.5 units of main field drift in quads could explain Tev tune drift. Measuring main field decay with rotating coils is difficult, NMR is preferred technology. HERA and LHC observe dipole field drift at const excitation (note: issues related to longitudinal field variations);

also: low-beta quad effects were checked (running tune drift experiments with low-beta off) – see M. Martens et al.

L. Bottura et al / CERN


b2 DRIFT & SB FIT USED IN TEVATRON

current b2 drift&SB correction was derived from magnetic measurement campaign of 96:

tttmttbtttb ftextftextini

ftext ln,,,, 22

ftextextftext

ini tt

CBt

Attb ln60

ln60

ln,2

ftextftext ttEDttm lnln2,

22

22 1,,,,,,

sbinjftextsbinjftext

snap

t

ttttbtttttb

snapback:

drift:

J. Annala


b2 DRIFT & SB FIT: CURRENT VS 96

There were, however, small modifications made to improve machine performance:

-2.5

-2

-1.5

-1

-0.5

0

0.1 1 10 100

time at backporch (min)

inte

rcep

t (u

nit

s)

0

0.1

0.2

0.3

0.4

0.5

0.6

slo

pe

Fit 2002 TC1052 Fit 96 - PB

Fit 2002 TC1052 Fit 96 - PB

60 min FT

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.1 1 10 100

time at flat-top (min)

inte

rcep

t (u

nit

s)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

slo

pe

Fit 2002TC1052 Fit 96 - PBFit 2002TC1052 Fit 96 - PB

1 min BP

Parameter A B C D E As used today 0.04 0.161 0.0277 0.342 0.0208 Fit to TC1052 data 0.206 0.172 0.0539 0.456 0.019


COMPARISON b2 FIT VS MAGNET MEASUREMENTThe (relative) agreement with magnet TC 1052 is very good at t>1 min, especially for flat-top times>10 min (standard flat-top in Tev pre-cycle is 20 min).

-1

-0.5

0

0.5

1

1.5

2

0.01 0.1 1 10 100

Minutes at 150 GeV

b2

dec

ay (

un

its)

computed b2 decay (units)

b2 measured in TC1052 (units)

computed snap-back (units)

1 min back porch 10 min flat-topb2@150GeV: -4.4 units

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10 12 14 16 18

Current (A)

b2

snap

-bac

k (u

nit

s)

measured snapbackcomputed snap-back (units)


b2 DRIFT&SB in RECENT MEASUREMENTS

MAGNET Drift after 30 min (units)

SB time (sec)

TC1220 0.99 6.6

TC0834 0.88 9.8

TB0483 1.56 10.4

TC0269 1.58 8.6

TEV-fit 1.25 6

Drift amplitude at injection (after a 30 min injection porch) and SB time after a standard pre-cycle (20 min flat-top, 1 min back-porch) as recently measured in different magnets and as calculated with Tevatron b2 compensation fit.

G. Velev

tSB

TC0269


DRIFT STARTING VALUE VARIATION

ftextextftext

ini tt

CBt

Attb ln60

ln60

ln,2

b2 at start of drift is ~-1 unit to allow matching of fit with data at times t>1min + additional history dependent contribution of ~0.1-0.2 u). Hysteretic loop is believed to be invariable, that is un-affected by powering history and (within the range of interest) more or less independent of ramp-rate.

G. Velev

Artifact of longitudinal field variations?


EXPLORING DIFFERENT SB FITSExploring different fit algorithms for snap back: Exponential vs. polynomial fit of snap-back. Advantages of the exponential fit:

1) Less sensitive to variations in snap-back time

2) More in tune with physics (see 2 strand models)

3) Better fit?G. Velev

22

22 1,,,,,,

sbinjftextsbinjftext

snap

t

ttttbtttttb

sbt

t

injftextsbinjftextsnap etttbtttttb

,,,,,, 22


EFFECT OF DRIFT DURATION

G. Velev

Physics argument: the further the drift the longer the snapback time. Beam and magnet measurements show a ~constant snapback time independent of the porch duration parabolic ramp!!

Varying the injection porch time between 30 and 120 min

TC0269

Drift compensation algorithm was formulated on the basis of 15 min measurements.


BEAM & MAGNET b2 STUDIES COMBINED

There, the reconstructed b2 loop is compared to recent beam-based b2 measurements and recent magnet measurements. The magnet

measurements are clearly “off” the average. This, however, is consistent with the production variations of the “width” of the loop (see error bars). Issue: single magnet vs. average of all magnets!

M. Martens / M. Xiao

-5

-4

-3

-2

-1

0

1

2

0 10 20 30 40 50 60 70 80 90 100

time up the ramp (sec)

b2

(un

its)

TC 1220 (02 meas, 30 m IP, 20 m FT, 1 m BP, 02ramp, 980 GeV FT, 4K, upramp from 0)TC 0483 (02 meas, 30 m IP, 20 m FT, 1 m BP, 02ramp, 980 GeV FT, 4K)TB 0834 (02 meas, 30 m IP, 20 m FT, 1 m BP, 02ramp, 980 GeV FT, 4K)b2 derived from beam (study Dec 4th)b2 derived from beam (study Sept. 18th?)b2 - Meiqin's point at FTaverage Tevatron magnet hysteresis (corr. To 4 K, "out-liers" removed)


CONCLUSIONS AND OUTLOOK

• Increase measurement sample - more drifts and snapbacks

• More data on possible a1, b1 drifts in Tev dipoles• Collaboration with Cern – improvement of

understanding of dynamic effects in magnets• Test a quadrupole for main field drift• Elimination of pre-cycle?• Continue to support Tevatron operation

Expect further report from G. Velev on magnetic measurements soon..

• No show-stopper found!• Not conclusive regarding main field and a1/b1 drifts• b2 compensation OK except for minor details


MISCELLANEOUS SLIDES

n

refnnnrefxy R

iyxiabByxiByxB

0

410,,


TEV DIPOLE – TEMPERATURE PROFILE

22 g/sec

Linear heat load: ~10 W/dipole ~25 mK / longitudinal

magnet T

Issues:

1) stratification of two-phase

2) poor heat exchange betw. in/out single-phase flow

~ 100 mK T across coil bottom/top

T. Peterson et al. 1997


THE TEVATRON DIPOLE – CRYO-SYSTEM

J. Theilacker/A. Klebaner

Heat load: 10 W/dipole 250 mK T along magnet string), “day-to-day” temperature variations less than 50 mK. Average temperature ~ 3.9 K


b6, b8 & b10 PROFILES IN END*


-200

-150

-100

-50

0

50

100

2.6 2.65 2.7 2.75 2.8 2.85 2.9 2.95 3 3.05 3.1 3.15 3.2

Axial distance from center (m)

HO

Mu

ltip

ole

s (u

nit

s o

f 10

-4 0

.66T

)

yoke

coil

end

14-pole

18-pole

22-pole

Note: The end multipole distribution presented here is not that of the average Tevatron dipole as defined from the production magnetic measurements. It is, however, within ~1 of the average, and therefore a realistic end.


AVERAGE FIELD

PROFILES IN DIPOLE

BODYCALCUL-

ATED FROM

TABUL-ATED

MULTI-POLES

J. Tompkins 2002

nanbinanbR

RBiBB nnnn

n



AVERAGE FIELD

PROFILES IN DIPOLE

ENDCALCUL-

ATED FROM

TABUL-ATED

MULTI-POLES

J. Tompkins 2002

nanbinanbR

RBiBB nnnn

n



TEV b2 ANALYSIS SUMMARY

We can use our knowledge of the magnet properties to reconstruct approximately the “average” hysteresis loop. The loop shown here was reconstructed from the archive data and recent magnet measurements.

Besides some minor issues regarding the details of the b2 compensation we found no “smoking gun”.

-6

-4

-2

0

2

4

6

8

10

12

0 1000 2000 3000 4000

current (A)

b2

(un

its)

"average" hysteresis looparchive datageometric


MAGNETIC FIELDS - NOMENCLATURE

The following conventions are used here for the multipole expansion of the magnetic field: Complex formulation of cross-sectional fields By+iBx is analytical outside conductor expansion in a Taylor series multipole coefficients

n

refnnnref

n

refnnn

n

n

nxy

R

iyxiabB

R

iyxiAB

n

zByxiByxBzB

0

4

0

0

10

??????????!

~0~~

,,~~

22

402

22

24

0

210,10),(

refx

refy R

xybByxB

R

yxbByxB

e.g. – if only b20, that is a pure sextupole field:


TEVATRON STRING

Dipoles Quads Spools

Number 772+2 90+90 88+88

F D

Tevatron Dipole

F Tevatron Quadrupole

Tevatron Quad corrector

Tevatron Sextupole corrector

Tevatron Beam Position Monitor

T:QF

T:SF

HorzBPM

T:QD

T:SD

VertBPM

(There are 772 Tevatron dipoles)

Courtesy - M. Martens


MAGNETIC MEASUREMENTS - 2

report on investigation of possible magnet related issues in the tevatron

Documents

bore field

tevatron dipole models

magnetic multipoles

tevatron dipolesintroduction

magnet length

average end

tc1200remnant field

length dipoles