thomas hermanns

Longitudinal Beam Diagnosticswith the LBS Line

17. November 2009

Linac4 Beam Coordination Committee Meeting

Thomas Hermanns

Thomas Hermanns 17. November 2009 2

Geographical Overview

LT.BHZ20

LTB.BHZ40

Transfer Line

Linac4 and

Dump Line

LBE Line LBS Line

LBE LineLBS Line

(1) (2)

(3)Slit (1)

Spectrometer Magnet (2)

SEM Grid (3)

Beam Dump


Introduction

LBS line: Diagnostics line close to PS Booster injection point

Measurement of the Linac4 beam energy and energy spread Correlation between beam energy and vertical beam position induced by

spectrometer magnet

Subject of this presentation

(1) Proposal for a spectrometer line for Linac4 operation

(2) Physical performance of the proposed line

(3) List of requirements and functional specifications for LBS line upgrade


Energy Distribution(behind slit)

<E>159.204

MeV

dE 160.6 keV

Ekin (min.) 158.9 MeV

Ekin (max.) 159.5 MeV


Experimental Principle

Experimental quantity: Fitted vertical spatial particle distribution on SEM grid Maximum Value Mean beam energy (from calibration function) Beam Size Energy/Momentum spread

Install SEM grid at position where beta-function has a local minimumReduce vertical emittance by vertical slitAnalyze particles by strong magnet with large bending angle (high dispersion)

Local dispersion function from simulations


Simulation Tools

Definition of line layout with envelope code (Trace 3-D) Position of slit, spectrometer magnet, and SEM grid Parameters of spectrometer magnet

Proposal for a LBS line layout

Implementation of the LBS line layout in particle tracking code (Path) Single particle tracking through line Create output particle distribution at SEM grid position to analyze Simulation of measurements errors

Data evaluation with analysis package (ROOT)

Physical performance and functional specifications


Proposed Optical Parameters

Slit Position: 4089mm behind LTB.BHZ40 Aperture: 148mm (horizontal) 1mm (vertical) Length: 200mm (absorption length of H--ions at 160 MeV in carbon: 85mm)

Spectrometer Magnet Position: 6286mm behind slit exit Radius: 1500mm (B=1.27T) Bending Angle: 54° Edge angles: 10°

SEM grid Position: 4139mm from mid-point of magnet Wire clearance: 0.75mm (energy resolution 57 keV)

About 20% of all incident particle arrive at SEM grid (I 13mA)


Simulation Results

Correlation factor: -99.7%

Determination of maximum value (Wire-)binned projection on spatial axis to fit 2nd order polynomial

Current per wire: few µA to several 10 µA Lower limit 5.5 nA time-differentiated readout seems possible at MHz-rate

Correlation for Nominal Energy “SEM Grid Simulation” and Data Fit

dE/dy 82 keV/mmdE per wire 13-14 keV


Results for Mean Energy

Shift manually energy within 1MeV

Linear Correlation between fitted position and central energy value

Energy shifts determine vertical length of SEM grid


Results for Energy Spread(reference value 160.6 keV)

Validity of approximation Ratio of total beam size to beam size for virtual beam with dp/p=0: 11.918

=0.0842 Perturbation less than 1%

Reconstructed Energy Spread

Reconstructed

157.9 keV

Deviation -1.7%


Uncertainties

Alignment errors Slit, magnet and SEM grid displaced by 1mm

Manufacturing errors Magnet edge angles: 0.5° Vertical slit aperture: 5% (equivalent to 50µm)

Spectrometer B-field: 0.1%

Variation of vertical slit width

Variation of slit length

Variation of input parameters at LTB.BHZ40


Mean Energy(reference value 159.204 MeV)

Maximum position shifted by ... ... error on fit parameter ... systematic error due to deviations from nominal line design

Intrinsic Error: Energy spread on one wire due to finite vertical slit width

Mean Position

Nominal Fit-0.2938 0.1020

mm

Sys. Error 3.4976 mm

Total Error Mean Energy (with dE/dy 82 keV/mm)

Absolute8.4 keV (fit) 286.5 keV (sys.) 13-14 keV

(intrinsic)

Relative 1.8 10-3


Beam Size and Vertical Dispersion (reference value 158.2 keV)

Beam Size Statistical error of beam size measurement Systematic error due to deviation from nominal line design

Vertical Dispersion Value Systematic error due to deviation from nominal line design

Total Error Dispersion

Absolute 0.6 keV (sys.)

Relative 0.4 10-2

Total Error Beam Size

Absolute2.7 keV (stat.) 0.9 keV

(sys.)

Relative 1.8 10-2


Error on Energy Spread(reference value 158.2 keV)

Total error on energy spread Error on beam size and dispersion Intrinsic Error: Energy spread on one wire due to finite vertical slit width

Total Error Energy Spread

Absolute2.9 keV (Beam Size) 0.6 keV (Dispersion)

13-14 keV (intrinsic)

Relative 8.3 10-2 - 8.9 10-2

Example for Gaussian distributions with energy width 14 keV and energy difference 57 keV


Perturbation Coefficient (reference value 0.0842)

Systematic error due to deviation from optimal design

Perturbation still remains below 1% if error is included

Difference between energy spread neglecting and respecting well below other sources of errors

dE ( = 0) − dE ( << 1) = 0.5 keV

Total Error Perturbation Coefficient

Absolute 0.0064 (sys.)

Relative 7.6 10-2


Additional Studies I

Variation of slit length (select more dense material than carbon) Perturbation coefficient increases by 0.5% if slit length is reduced to 20

mm Transmitted current through slit increases by 6%

No significant influence on line design

Variation of vertical slit aperture Change vertical aperture by factor k=0.5 and k=2 Perturbation coefficient and intrinsic resolution scales with 1/k

Transmitted current scales with k

Lower aperture Reduction of perturbation and better resolution, but production more

challenging (accuracy and potentially cooling)

Larger aperture Beam size must potentially be corrected for contribution from beta-function

to obtain true energy spread (result becomes more dependent on simulation code)


Additional Studies II

Variation of beam input parameters Input beam at LTB.BHZ40 approximated by Gaussian distributions Vertical Twiss-parameters and vertical emittance separately set to half and

twice of their nominal values

Values of perturbation coefficient coincide to each other Slit acts as a kind of “equalizer” Contribution to total beam size due to evolution of beta-function remains less

than 1%

Transmitted current varies by a factor of up to 2 Effect on design of beam dump behind SEM grid Could be compensated by variable slit aperture


LBS Line with Quadrupoles(based on an initiative by C. Carli)

Build LBS line with a pair of quadrupole magnets instead of slit to create local minimum of beta-function

Avoid construction of a slit, which gets activated Full beam dump required at the end of line

Specifications for spectrometer magnet and SEM grid similar

Energy spread sampled per wire 50 keV (compared to 13-14 keV) Intrinsic error at the order of required resolution Further systematic error study missing

Total beam size contains a 10% contribution due to evolution of beta-function (compared to 1 %)

Technical advantages, but reduced physical performance First steps towards an alternative scenario available


Summary(reference values E=159.204 MeV and dE=160.6 keV)

Mean Energy Measurement

Absolute Error 286.9 - 287.0 keV

Relative Error 1.8 10-3

Energy Spread Measurement

Offset -2.7 keV (-1.7 %)

Absolute Error 13.3 - 14.3 keV

Relative Error 8.3 10-2 - 8.9 10-2


LBS Line --- List of Wishes

LTB.BHZ40 (keep present deflection angle) Increase current to 111 A for LBS line and 179 A for LBE line (Imax = 210 A) In principle power supply can provide 250 A Water-cooled magnet, needs to check if flow sufficiently high for higher

current

Slit (reference point of alignment at exit of slit) Vertical aperture 1mm (precision of a few 10 µm tolerable) Sufficiently long to absorb incident particles (simulations between 20 and 200

mm done) If cooling necessary check in experimental area if enough space is available

Spectrometer magnet (not yet designed) Bending angle: 54° Radius: 1500 mm (B=1.27 T) Edge angles: 10° Beam size at entrance: 5.1 mm 2.0 mm (horizontal vertical) dB/B dEkin/p 210-4

Power supply (and cooling infrastructure?) NMR probe for B-field measurement


LBS Line --- List of Wishes II

SEM grid Extension 1: 5 mm to sample the entire distribution at nominal energy Extension 2: 17 mm to allow for energy shifts by 1 MeV Wire spacing: 0.75 mm Time-resolved readout with about 1MHz to measure resolve longitudinal

energy painting Check option of to steer beam to high-resolution centre in case of energy

shifts (avoid high costs for large grid with small clearance)

Beam Dump Installation at ceiling height of experimental area Beam size at SEM Grid: 3.0 mm 2.0 mm (horizontal vertical) Beam angle at SEM Grid: 0.6 mrad 0.7 mrad (horizontal vertical) Current to be absorbed (up to 20 mA) Pulse length 100 µs

Transformer (presently three are installed) Keep/upgrade at least one behind slit and one behind spectrometer

magnet


LBS Line --- List of Wishes II

Interlocks Temperature sensors (LTB.BHZ40, slit, spectrometer magnet, beam dump) Power supply sensors (B-field controlling) for LTB.BHZ40 and spectrometer

magnet Transformer signals ...

Software Data display Data fit and beam size simulations Calculation of mean energy and energy spread


Merci vielmals!

Thanks a lot for

patient explanations, valuable assistance, and intense discussions to

Giulia Bellodi, Christian Carli, Mohammad Eshraqi,Klaus Hanke, Alessandra Lombardi, Bettina Mikulec, Uli Raich

Backup Slides


Initial Bias of the Measurement

Measurement is unbiased Correlation factor: 0.4%

Selecting a beam slice by slit does not favour a certain energy interval

Correlation for Nominal Energy at the Entrance of the Slit


Acceptance-Rejection-Method

Beam size from fit function to SEM grid signal by statistical approachAcceptance-rejection method

Generate pairs of random numbers and decide to accept/reject with fitted curve

Projection of accepted numbers to vertical position axis

RMS of distribution = Beam Size

Series of ten repetitions with 107 random numbers

Statistical error O(10-4)acceptance

region


Error on SEM Grid Resolution (reference value 57 keV)

Error sources Systematic error due to deviation from nominal line design Manufacturing error on wire distance

Total error dominated by error on wire distance Length L between spectrometer magnet and SEM grid is much larger than

wire distance s s/L=O(10-4), but error differ only by one order of magnitude

Error SEM Grid Resolution

ds = 0.1 mm

7.6 keV

ds = 0.02 mm

1.5 keV

ds = 0.01 mm

0.8 keV


Results Additional Studies I

Beam Size dE/dydE per wire

I behind Slit

Slith Width

0.5 mm

1.9672 mm 0.0452 81.8 keV/mm 7-8 keV 6.1 mA

1.0 mm

1.9593 mm 0.0842 81.9 keV/mm 13-14 keV 13.2 mA

2.0 mm

1.9828 mm 0.1629 78.5 keV/mm 26-27 keV 25.6 mA

Slit Length

200 mm

1.9593 mm 0.0842 81.9 keV/mm 13-14 keV 13.0 mA

150 mm

1.9587 mm 0.0854 81.9 keV/mm 13-14 keV 13.2 mA

100 mm

1.9579 mm 0.0867 81.9 keV/mm 13-14 keV 13.4 mA

50 mm 1.9586 mm 0.0883 81.8 keV/mm 13-14 keV 13.6 mA

20 mm 1.9601 mm 0.0891 81.8 keV/mm 13-14 keV 13.8 mA


Results Additional Studies II

For modification of input ellipses beam in Gaussian approximation

Beam Size dE/dydE per wire

I behind Slit

Modified Input Parameters

Nominal

1.9593 mm 0.0842 81.9 keV/mm 13-14 keV 13.0 mA

Nominal

(Gauß)1.8664 mm 0.0843 81.9 keV/mm 13-13 keV 10.9 mA

0.5 0 1.8816 mm 0.0859 81.8 keV/mm 13-14 keV 7.3 mA

2.0 0 1.8708 mm 0.0785 82.0 keV/mm 12-13 keV 21.3 mA

0.5 0 1.8527 mm 0.0820 81.9 keV/mm 12-13 keV 16.6 mA

2.0 0 1.8713 mm 0.0869 82.2 keV/mm 13-14 keV 5.4 mA

0.5 0 1.8627 mm 0.0850 82.0 keV/mm 13-13 keV 15.6 mA

2.0 0 1.8788 mm 0.0821 82.1 keV/mm 12-13 keV 7.5 mA

thomas hermanns

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