Report on investigation of possible magnet related issues in the tevatron
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Report on investigation of possible magnet related issues in the tevatron

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!

Pierre Bauer


Introduction

INTRODUCTION

D. Finley et al. 1987

  • Tevatron Dipole Magnets – an Overview

  • Measurement of Dynamic Effects in Tevatron Dipoles

  • Discussion of Possible Magnet Issues in the Tevatron

Pierre Bauer


I tevatron dipole magnets

I TEVATRON DIPOLE MAGNETS

  • Dipole Models

  • Production Magnetic Measurement Data

  • Field Profiles

Pierre Bauer


The tevatron dipole models body

THE TEVATRON DIPOLE MODELS - BODY

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!

Pierre Bauer

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


The tevatron dipole models end

THE TEVATRON DIPOLE MODELS - END

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

Pierre Bauer

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


Field profile in end

FIELD PROFILE IN END

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

Pierre Bauer


Magnetic measurement archive data

MAGNETIC MEASUREMENT ARCHIVE DATA*

J. Tompkins / R. Hanft

Pierre Bauer

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


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

J. Tompkins / R. Hanft

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

THE TEVATRON DIPOLE NORMAL MULTIPOLES*

Pierre Bauer


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

J. Tompkins / R. Hanft

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

THE TEVATRON DIPOLE SKEW MULTIPOLES*

Pierre Bauer


Average field profiles in dipole calcul ated from tabul ated geometric multi poles

helix

AVERAGE FIELD PROFILES IN DIPOLECALCUL-ATED FROM TABUL-ATED (Geometric) MULTI-POLES

Pierre Bauer

J. Tompkins 2002


Ii dynamic effects in tevatron dipoles

II DYNAMIC EFFECTS IN TEVATRON DIPOLES

  • Introduction to Dynamic Effects

  • Historical Review of Tevatron Magnet Measurements

  • Some Recent Results

Pierre Bauer


Dynamic effects basics

current

flat top

injection porch

pre-cycle:

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

reset

time

1-2u

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

~15 A / 15 mT/ 7 GeV

DYNAMIC EFFECTS -BASICS

back porch

Pierre Bauer

P. Schlabach


Dynamic effects in tevatron dipoles qualitative model

+DB

-DB

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,

alternating field along the Strands.

Pierre Bauer

L. Bottura/CERN 2002


Dynamic effects in tevatron dipoles previous studies

DYNAMIC EFFECTS IN TEVATRON DIPOLES – PREVIOUS STUDIES

Pierre Bauer


Magnetic measurements at mtf

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.

Pierre Bauer


87 discovery

87 - DISCOVERY

Pierre Bauer

D. Finley et al. 1987


88 measurements

Magnet Meas. – RL 1001

88 - MEASUREMENTS

Pierre Bauer

R. Hanft et al. 1988


92 measurements

92-MEASUREMENTS

Pierre Bauer

D. Herrup et al. 1992


96 measurements

96-MEASUREMENTS

Pierre Bauer

J. Annala et al. 1996


Magnetic measurements 02 03

MAGNETIC MEASUREMENTS – 02/03

J. Tompkins / G. Velev / R. Hanft

Pierre Bauer


Iii discussion of possible magnet issues in the tevatron

III Discussion of Possible Magnet Issues in the Tevatron

  • Temperature Variations

  • Tune and Coupling Drift

  • Main Field Drift

  • Analysis of the b2-Compensation in the Tevatron

Pierre Bauer


Quantitative estimate of drifting skew and normal quads

QUANTITATIVE ESTIMATE OF DRIFTING SKEW AND NORMAL QUADS

b1 drift needed in dipole to explain tune drift:

a1 drift needed in dipole to explain coupling drift:

Db1/ Da1 = ~0.1 u in dipoleto explain tune/coupling drift

Pierre Bauer


Drifting a1 and b1 in dipoles

0.2mm

0.1mm

0.1mm

0.05mm

0.2mm

0.015°

0.03°

0.012°

0.006°

possible sources of 1u of a1 (up-down asym) & b1(left-right asym):

DRIFTING a1 AND b1 IN DIPOLES?

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

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

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?

Pierre Bauer


Drifting a1 and b1 in dipoles1

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

a1, b1 in the magnets?

Production goal: zero geometric a1 and b1.

This, however, does not exclude hysteretic b2:

TC0269 clearly shows a hysteretic and a drifting skew quadrupole:

Pierre Bauer

R. Hanft / G. Velev


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);

DRIFTING MAIN FIELD?

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

Pierre Bauer

L. Bottura et al / CERN


B2 drift sb fit used in tevatron

b2 DRIFT & SB FIT USED IN TEVATRON

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

drift:

snapback:

Pierre Bauer

J. Annala


B2 drift sb fit current vs 96

b2 DRIFT & SB FIT: CURRENT VS 96

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

Pierre Bauer


Comparison b2 fit vs magnet measurement

The (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).

COMPARISON b2 FIT VS MAGNET MEASUREMENT

Pierre Bauer


B2 drift sb in recent measurements

TC0269

D

tSB

b2 DRIFT&SB in RECENT MEASUREMENTS

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.

Pierre Bauer

G. Velev


Drift starting value variation

DRIFT STARTING VALUE VARIATION

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.

Artifact of longitudinal field variations?

Pierre Bauer

G. Velev


Exploring different sb fits

  • Exploring different fit algorithms for snap back: Exponential vs. polynomial fit of snap-back. Advantages of the exponential fit:

  • Less sensitive to variations in snap-back time

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

  • Better fit?

EXPLORING DIFFERENT SB FITS

Pierre Bauer

G. Velev


Effect of drift duration

EFFECT OF DRIFT DURATION

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.

Pierre Bauer

G. Velev


Beam magnet b2 studies combined

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

BEAM & MAGNET b2 STUDIES COMBINED

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!

Pierre Bauer

M. Martens / M. Xiao


Conclusions and outlook

CONCLUSIONS AND OUTLOOK

  • No show-stopper found!

  • Not conclusive regarding main field and a1/b1 drifts

  • b2 compensation OK except for minor details

  • 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..

Pierre Bauer


Miscellaneous slides

MISCELLANEOUS SLIDES

Pierre Bauer


Tev dipole temperature profile

TEV DIPOLE – TEMPERATURE PROFILE

  • Issues:

  • stratification of two-phase

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

  • ~ 100 mKDT across coil bottom/top

22 g/sec

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

Pierre Bauer

T. Peterson et al. 1997


The tevatron dipole cryo system

THE TEVATRON DIPOLE – CRYO-SYSTEM

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

J. Theilacker/A. Klebaner

Pierre Bauer


B6 b8 b10 profiles in end

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 ~1s of the average, and therefore a realistic end.

b6, b8 & b10 PROFILES IN END*

Pierre Bauer

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


Average field profiles in dipole body calcul ated from tabul ated multi poles

helix

AVERAGE FIELD PROFILES IN DIPOLE BODYCALCUL-ATED FROM TABUL-ATED MULTI-POLES

Pierre Bauer

J. Tompkins 2002


Average field profiles in dipole end calcul ated from tabul ated multi poles

helix

AVERAGE FIELD PROFILES IN DIPOLE ENDCALCUL-ATED FROM TABUL-ATED MULTI-POLES

Pierre Bauer

J. Tompkins 2002


Tev b2 analysis summary

TEV b2 ANALYSIS SUMMARY

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

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.

Pierre Bauer


Report on investigation of possible magnet related issues in the tevatron

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

e.g. – if only b20, that is a pure sextupole field:

Pierre Bauer


Tevatron string

F

D

T:QF

Horz

BPM

T:QD

Vert

BPM

T:SF

T:SD

Tevatron Dipole

Tevatron Quad corrector

(There are 772 Tevatron dipoles)

Tevatron Sextupole corrector

Tevatron Quadrupole

Tevatron Beam Position Monitor

F

TEVATRON STRING

Pierre Bauer

Courtesy - M. Martens


Magnetic measurements 2

MAGNETIC MEASUREMENTS - 2

Pierre Bauer


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