Transverse Optics Measurement at MEBT-3 · • Each magnet package includes x and y steering...

Transverse Optics Measurement at MEBT-3

Arun SainiPIP-II Technical MeetingDate: 3rd April 2018

A Review of previous measurements (1) • Summary of presentation delivered on 8th August 2017 in this

meeting.– Objective was to prepare an optics model that could predict

beam trajectory and beam sizes. – A Java program was developed to perform the differential

trajectory measurements –

– Measurements were performed at MEBT-2

4/12/2018Presenter | Presentation Title2

axis‐lineNominal trajectory

Differential TrajectoryTrajectory after kick

A Review of previous measurements (2)• An optics model based on OPTIM

was developed.– Quad strengths were reduced by

~5% from magnetic measurements.– Corrector hysteresis effect was not

accounted. • Beam sizes measured only at few

location, agreed with simulation– Initial beam Twiss functions were

evaluated. – Quad corrections were applied.– Errors bars correspond to +/-5%

• Does the Model stand for a longer beamline ? – MEBT-3 provides a longer beam

line. 4/12/2018Presenter | Presentation Title3

Measurement: 5th July 2017.

M10CXI = 0.55A;

M10CYI = 0.41A;

Y‐trajectoryx‐trajectory

Outline

• Differential Beam trajectory measurements– Preparation– Analysis: Method– 1mA v/s 5mA data– Reproducibility of data

• Beam Sizes• Summary


MEBT-3-1 Layout


• MEBT-3 is full version of PIP2IT MEBT.• It consists of two quadrupole doublets and seven triplets. • Two type of quadrupoles i.e. F-type and D-type (100 and 50 mm effective

length respectively).• There are 3 bunching cavities.

• Each magnet package includes x and y steering correctors and a BPM.• Design specification of BPM resolution is 30 m.

• Diagnostic includes: Allision Scanner, five sets of beam scraping system, two toroids, Ring pickups, fast Farady cup etc.

Bunching Cavity Bunching Cavity

scrapers scrapersscraper

Beam Dump

Toroid

Allision Scanner

Differential Pumping Insertscraper

RESULTS

• Differential Trajectory Analysis:– 5mA bunch current– 1mA bunch current

• Beam Sizes


All data were taken on 18 Jan.2018 afternoon shift.

Differential Trajectory Measurement : Preparation

• A complete cycle of correctors current was carried out before starting differential measurements.


• Range of corrector current variation (I) is chosen so that dump current remain constant.

• Current in a given corrector is changed only in one direction.• Stay one side of hysteresis.

• Beam pulse length was10s and repetition rate was 20 Hz.

• RFQ was operating at 60kV and Buncherswere set to 60,50, 50kV.

• MEBT quadrupole settings were set to as in File # 1535.

Differential Trajectory: Measurement

• Model trajectories were fittedwith measured trajectories byadjusting individualquadrupole and correctorstrength.– Initial quadrupole strengths

used in the model weretaken from magneticmeasurements of individualquadrupoles at 10A.

– Bunching cavities phaseswere varied


M00CXI = 0.4A

• A set of differentialtrajectories were obtainedalong MEBT-3 beam line.– 12 differential trajectories

from M00 to M50 correctorswere measured.

Diff. Trajectory refnew xxx 222refnewdif RMS Error bars:

• BPMs readings were average over 50 pulses.

Differential Trajectory: Analysis • Fitting of model trajectory with measurement is an iterative process. I

started fitting with trajectory that has lower no. of measured points (M50trajectories in this case).– It provides an idea about initial values of subsequent quads (M60

and following quads in this case).


M50CXI = 0.4A

• The fitting is carried out byadjusting downstream quads andcorrector that excites the trajectory.

• Later, I will fit differentialtrajectories excited using upstreamcorrectors (M40,M30..M00).

Model Limitation: Several free parametersand lower constraints may result in severalcombination of fitting. (e.g. for M00Ctrajectories, 16 free parameters and 16constraints. No dispersion trajectory in linac

Differential Trajectory Analysis: 5mA Beam Trajectories


M00CXI = 0.4A; M00CYI =0.4A M10CXI = 0.4A; M10CYI =0.4A

Y‐trajectory

• Model trajectories were fitted to all 12 measured trajectories by adjustingquadrupole and corrector strength.

• A set of scaling factor of quadrupole strength were obtained by fitting of 12trajectories.

• Mean quad strength for F-type and D-type quads are 146.01+/-2.66 and 85.3+/-0.3 T/kA respectively.

• Quad strength obtained after differential trajectory analysis are: 139.8 +/‐ 4.19 and 80.7+/-2.4 T/kA for F-type and D –type quads.

Note: First doublet and last quad triplet have same calibration as magnetic measurement for MEBT 3-1 case.

Comparison of Quads Strength: Magnetic Measurements v/s Beam Based Measurement


134

136

138

140

142

144

146

148

150

0 2 4 6 8 10 12

Calib

ratio

n Co

efficient (T

/kA)

F type Quads #Magnetic Measurement Optics Model: MEBT 3‐1 Optics Model : MEBT 2

77

78

79

80

81

82

83

84

85

86

87

0 5 10 15

Calib

ratio

n Co

efficient (T

/kA)

D Quads # Magnetic Measurement Optics Model: MEBT 3‐1 Optics Model: MEBT 2

• Statistical errors in x and y measurements of all BPMs are: 94 and 200 um respectively.

Fitting Error v/s Statistical Measurement error


√ /

• Minimum error in y plane is : 90 um while in x is 0.7mm.• Total error (xy) in analysis is governed by x-trajectory fitting.

. . /

+…)

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.84 0.86 0.88 0.9 0.92 0.94 0.96 0.98 1 1.02

Erro

r Mag

nitu

de (

cm)

Quad Scaling Factor

Xerror Yerror XYerror Xymin-XYmea XYmin+XYmea=0.023

• All quads were adjusted with same scaling factor.• Error with respect to measurement is estimated.

Optics Model and measurement limitation• Optical model used individual quad

magnetic measurement data: Quadstrength measured in triplet assemblydiffers from individual quad strengthmeasurement.– Difference is highlighted especially at

low current. • Quad hysteresis was not accounted :

Magnetic measurement confirm 7mTfield in D-type Quad i.e. 0.8% at 10Afield.

4/12/2018Arun Saini | Optics Measurement at MEBT 1.113

Magnetic Measurement: Triplet assembly (S. Stoyan)

• Magnetic center changes by 1mm when all quads in triplet assembly were powered.

• Large RMS error bars: Consequently, relatively less fitting constraint on model based trajectory.– BPM and Beam noises

Differential Trajectory Measurements at 1mA

• In order to understand if there is unreported effect that scales with beam current, differential trajectory measurements were performed at 1mA.

• 1mA beam is formed by intercepting 4mA beam current at the first scraper. (1mA at each paddle).


• 1mA beam trajectory fits reasonably with model prediction that was made using quad strength obtained through fitting of 5mA beam data.

• A set of differential trajectory data were taken on two different days for same MEBT quad settings (file#1535).

• Above plots show difference in M00C trajectories (left) and, trajectory difference in number of RMS error at each BPM .• Maximum difference is ~150 um and errors are distributed within 1RMS.

Reproducibility of Measurements


‐1

‐0.8

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

0 2 4 6 8 10

Diff/ (sum)

BPMs #

Scattering in RMS number

YerrorXerror

‐0.015

‐0.01

‐0.005

0

0.005

0.01

0.015

0 2 4 6 8 10Diff (cm)

BPMs #

Difference of Trajectories

YdiffXdiff

RESULTS

• Differential Trajectory Analysis:– 5mA bunch current– 1mA bunch current

• Beam RMS Sizes


Beam RMS Size Measurements in MEBT-3:


• Beam scrapers are utilized to measure beam RMS sizes. – Each scraper consists of 4 paddle.

• Intercepted beam current is measured atpaddle and at the dump.

• This data allows to determine beam RMSsize in respective plane.

Java Program: Bill Marsh

A Typical scan fitting

Simulation Set-Up: Beam RMS Size prediction


• Allison scanner provides verticalemittance. Same emittance isused for horizontal plane in thesimulation.– In this study y= x =0.2 mm mrad

• Initial transverse Twissparameters were obtained byfitting RMS beam sizes at thefirst two scrapers.– Tracewin code is used for this

purpose.– Space charge forces were

included.Vertical Phase Space from Allison Scanner

Alpha X BetaXmm/mrad

Alpha Y Beta Ymm/mrad

Alpha z Beta Z

TRACEWIN 1.34 0.33 -0.176 0.133 -0.059 1.473

• Quadrupole settings correspond to File# 1535. • Quadrupole correction factors obtained from differential trajectories were

applied. • An arbitrary 10% error bars were applied on measured sizes.

Beam Sizes at MEBT -3


Measurement: 18th January 2018.

• Beam sizes were measured lately (in MEBT 3-2 configuration) after a downtime period of 12 weeks.• RFQ and all bunchers are operating in CW mode now.

• Initial beam conditions were changed.

Recent Beam Size Measurements at MEBT 3-2


Alpha X BetaXmm/mrad

Alpha Y Beta Ymm/mrad

Alpha z Beta Zmm/mrad

Obtained from measurement 0.72 0.21 -0.116 0.107 -0.059 1.473

CDR Optics 0.175 0.23 -0.095 0.117 -0.059 1.473

Summary • Differential trajectory measurements were performed at MEBT 3-1.• Quadrupoles and steering correctors strength in optics model were varied

to obtain a good fit with measurement data.

• Optics model suggested 5% average reduction in quad strength. However, individual quads strength correction varies from -2% to -9%– Different from what predicted at MEBT 2.0.

• Trajectory measurements at beam current of 5mA and 1mA agrees reasonably

• Measurement reproducibility of the measurement is good. Maximum difference between is ~150 um and errors are distributed within 1RMS.

• Beam RMS sizes were also measured. Understanding of initial beam condition and optics prediction reasonably agrees within 10%.


unit Magnetic Measurement (Mean +/- RMS)

After Fitting(Mean +/- RMS)

F-Type Quads T/kA 146.01+/-2.66 139.8 +/‐ 4.19

D-Type Quads T/kA 85.3+/-0.3 80.7+/-2.4

• Back-ups


• Difference in quad current settings w.r.t case 1 is shown in table.• Quad changes are limited due to aperture limitation imposed by

kicker masks and differential pumping insert.

Beam Size measurements: CASE 2


M0D M0F M10D M10F M20D M20F M30D M30F M40D M40FDiff. (A)

0.15 0 0.34 0.13 0.05 0.24 0.55 0.26 0.61 0.45

M50D M50F M60D M60F M70D M70F M80D M80F0.54 0.57 0.04 0.27 0.80 0.50 1.09 1.26

Conclusion• Fitting of measured data with optics model suggests that quad

strengths are largely deviated from individual quadrupole magnetic measurement.

• Working to acquire a clear understanding of this deviation. Potential sources are:– Quad hysteresis : Magnetic measurement confirm 7mT field in D-

type Quad i.e. 0.8% at 10A field.– Quad magnetic measurements in triplet assembly differ from

individual quad measurement : more than 1% at low current. – BPMs resolution and Beam Noise: Large RMS errors and

therefore, relatively relax fitting constraint on trajectory. – Method limitation: Several free parameters and lower constraints

may result in several combination of fitting.• No dispersion trajectory in linac.


• Initial Quadrupole calibration coefficients were taken from magnetic measurements.• These measurements were performed for individual quadrupoles at 10A.

Differential Trajectory: Model Limitation


138

140

142

144

146

148

150

1 2 3 4 5 6 7 8 9 10 11

Cal

ibra

tion

Coe

ffici

ent (

T/kA

)

Quads #

F‐Type Quadrupole Calibration Coefficients

84.4

84.6

84.8

85

85.2

85.4

85.6

85.8

86

86.2

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Cal

ibra

tion

Coe

ffici

ent (

T/kA

)

Quads #

D‐Type Quadrupole Calibration Coefficients

Mean 85.314RMS 0.303

Mean: 146.011 T/kARMS : 2.66

Individual Magnet v/s Triplet Configuration Measurement


• Transfer function obtained through magnetic measurement in triplet assembly differs from individual quadrupole measurement especially at low current.

Calibration Coefficient of the Steering Correctors

• Beam centroid shift at following BPM isgiven as:

– where L is length from corrector tomeasured device, is change inintegral field of corrector and c isvelocity of light.

– , where C is calibrationcoefficient.

• Calibration Coefficient of corrector isthen expressed as:

– is slope estimated frommeasurement.


LcmcBlx 2

)(

Lcmc

dIdxC

2

*

Horizontal Steering Corrector2 at M30 Monitor

Bl

ICBl

dIdx

X Y(mT-m)/A (mT-m)/A

M00C 0.424 0.446M10C 0.448 0.447M20C 0.395 0.395M30C 0.418 0.403M40C 0.421 0.409M50C 0.392 0.378

Calibration Coefficients

Comparison of F type Quads Strength: Magnetic Measurements v/s Beam Based Measurement


Mean: 146.011 T/kARMS : 2.66

138

140

142

144

146

148

150

1 2 3 4 5 6 7 8 9 10 11

Cal

ibra

tion

Coe

ffici

ent (

T/kA

)

Quads #

F‐Type Quadrupole Calibration Coefficients

125

130

135

140

145

150

1 2 3 4 5 6 7 8 9 10 11

Calibratio

n Co

efficient (T

/kA)

Quads #

F‐Type Quadrupole Calibration Coefficients After Correction

Mean: 139.77 T/kARMS : 4.19

• After Correction Standalone quadrupole Magnetic Measurement @ 10A . Note: First and last quads have same

Calibration as from magnetic measurement

After Correction


Mean 85.314RMS 0.303

84.4

84.6

84.8

85

85.2

85.4

85.6

85.8

86

86.2

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Calibratio

n Co

efficient (T

‐m/kA)

Quads #

D‐Type Quadrupole Calibration Coefficients

72

74

76

78

80

82

84

86

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Calibratio

n Co

efficient (T

/kA)

Quads #

D‐Type Quadrupole Calibration Coefficients After Correction

Mean : 80.77RMS : 2.411

Note: last two quads have samecalibrations as from magnetic measurement

Comparison of D-type Quads Strength: Magnetic Measurements v/s Beam Based Measurement

Standalone quadrupole Magnetic Measurement @ 10A

• Design strength of individual dipole is : 0.62 mT-m/A • When installed with quads assembly, its strength is reduced to : 0.41 mT-

m/A

Steering Corrector Strength


0.37

0.38

0.39

0.4

0.41

0.42

0.43

0.44

0.45

0.46

1 2 3 4 5 6 7 8 9

Cal

ibra

tion

Coe

ffici

ent (

mT-

m)

Correctors

Vertical Correctors Calibration Coefficients After Correction

0.4530.025

MeanRMS

0.4280.016

MeanRMS

M10CX Corrector After Fitting:


• 1mA beam trajectory fits reasonably with model prediction that was made using quad strength obtained through fitting 5mA beam data.

• Two set of data taken on 18 Jan and 23 March were compared.• MEBT Magnet settings correspond to file # 1535 in both case.

• Both set of data agree within RMS error bars.

Measurement Reproducibility:


M00CX M00CY

M10CY : 5mA and 1mA beam current Trajectories


Red: 1mABlack: 5mA

Comparison of 5mA and 1mA Differential Trajectory: M10CX


Green: 1mAMagenta: 5mA

Power Supply Current Calibration:


y = 1.0077x ‐ 0.0682

0

2

4

6

8

10

12

0 2 4 6 8 10 12

Measured I (A)

Set I (A)

M40QDI: Upstream

y = 1.0031x ‐ 0.0479

0

2

4

6

8

10

12

0 2 4 6 8 10 12

Measured I (A)

Set I (A)

M40QFI

Influence of Quadrupole on corrector fields

4/12/2018Arun Saini | Optics Measurement at MEBT 1.136

0102030405060708090

100

-1500 -1000 -500 0 500 1000 1500

B (G

auss

)

Z, mm

With quads Without quads

• Corrector Calibration coefficient that implies integral field per unit corrector current is changed.• Need to determine new calibration coefficient for correctors.

• Simulation suggests thatquadrupole presence will affectstrength of steering correctorand result in:• Shift in center of gravity by 88

mm.• Integral field is reduced to

about 44 %.• Magnetic integral field of corrector

is measured standalone withoutquadrupoles.

Some Thoughts

• Hysteresis in quads.– For D type, at 10A,

remnant field is about 0.8%


Initial Parameters

• Beam pulse length is 10s and repetition rate is 20 Hz.

• RFQ was operating at 60kV and Bunchers were set to 60,50, 50kV respectively.– RF phase of each

buncher was set to -90 degree.

• MEBT quadrupole settings were set to as in File # 1535.


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Transverse Optics Measurement at MEBT-3 · • Each magnet package includes x and y steering...

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