FETS—Meeting 1st August 2007

Status Report of the

Non—Destructive Emittance InstrumentPhoto Detachment Diagnostics for H- High

Current Applications at the Front End Test Stand FETS at 3MeV,Rutherford Appleton Laboratory

C. Gabor, J. Pozimski, A. Letchford, C. Prior

The Front End Test Stand Collaboration

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Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008

Overview

• IntroductionPhoto detachment, slit—point transformation, movable detector

• Maximum Entropy as a Method for Emittance Reconstruction

• Experimental Results, measured at the Ion Source Development Rig (ISDR)

• SummaryOutlook, further development

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Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008

Photo—Detachment Principle

H -beam ,N eutra l a tom s produced in the tra nspo rt section

-

La se r, 1060 n m

H -beam-

N e utra l a to m s p ro d uc ed in th e tra ns po rt se c tio n

M agnet po letips

B X

xz

Region of interactionand separation of thebeam s

sca

n

S cin tilla to rin teraction w ith photons

y

+ Non—destructive+ Preferable for high power + On line measurements

Implemented Method: yy' in combination with movable angle detector

o Displacement & Spread of neutralized particles Angle profile I(y')o 2D Beam distributions along the neutrals drift

Slit—PointTransformation

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Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008

Problem of Data ReconstructionVery often incomplete and/ or noisy data where MaxEnt has its

strengthObject of Study Data

e.g.Density of electrons

Spectral intensityAn image: 2D, 3D

Measuring Instrument

T . {fi} = {dk + k} Traditional solution: {fi} = T-1 . {dk + k}

e.g.Line-integral

Fourier transformBlurred imageBeam profiles

e.g.Telescope,

spectrometer,emittance

scanner, .....

{ fi } i =1,…, Nobject

{dk} k=1,…, Ndata

Maximum Entropy: (MaxEnt) Data like beam profiles linked with a matrix to your test object (constraints) will be fitted with maximum—likelihood Entropy S is "an additional" search direction to fit data (max. this func. S !)

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Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008

Entrance Distribution and Beam Envelope

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Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008

Variable Number of Profiles using MaxEntA small number of profiles is sufficient for reconstruction.

(A) 3 profiles (B) 4 profiles(C) 8 profiles(D)Entrance emittance distribution

Problem:Not the number but the coverage of the phase space is crucial. That can be, e.g., provided by an optical focusing element.

http:// ~www.maxent.co.uk

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Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008

Comparison of rms--EmittancesImplemented Method: yy' in combination with movable angle

detector

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Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008

Ion Source Development Rig (ISDR)

Pepperpot emittances +

Beam profiles at various z—positions

Slit slit emittances

Seperate, movable slit in combination with scintillator

Beam parameters:H- @ 50mA17 keV extraction voltage35 keV total beam energyfield gradient n=1.4 (w)

Slit height: 0.3mmSlit length: 110mmDrift in between: 107mm

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Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008

Collimated Ion Beam (Pseudo Coloured)1.) Beam distribution at 260mm2.) Collimated beam parts after a separation drift of 107mm

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Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008

Pepperpot measurement "simulation"

-70

-50

-30

10

30

50

-70 -50 -30 -10 10 30 50

col imated beam, y=-30 mm colimated + drifted beam

colimated beam, y=+26m m colimated + drifted beam

drift=0.5m

- 6 0 - 4 0 - 2 0 0 2 0 4 0 6 0

0 . 0

0 . 2

0 . 4

0 . 6

0 . 8

1 . 0

1 . 2

P e p p e r p o t , y = + 2 6 m m

S c i n t i l l a t o r p r o f i l e

P e p p e r p o t , y = - 3 0 m m

S c i n t i l l a t o r p r o f i l e

In

te

ns

ity

/a

.u

.

A n g l e / m r a d

At -30mm and =26mm original collimated beamletsFor better separation of both distributions a drift of 0.5m was chosen.

Hardware limited resolution because of "low" number of pinholes which also effects the signal to noise ratio.Further problems with a restricted number of particles ( statistical restrictions), small variations of ion source performance

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Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008

Summary• Photo detachment is the method for non destructive diagnostics • Highly perferable for intense ion beams (no heat loading on mechanical parts ...)• Presented emittance measurement method(s) are general

principles and not restricted to photo neutralization • Additional information about beam distribution are possible: Demonstrated at ISDR using a slit for beam collimation

and a scintillator with spatial resolution for trans. angle

• Outlook: Reconciling with the MEBT developing of diagnostic magnet design ( determinate resolution!)

• Concerning HIPPI: This contribution replaces RALs 3D code contribution (staff problems);

providing a deliverable as status report by end 2008

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Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008

References and Literature

G.N.Minerbo, "MENT: A maximum entropy algorithm for reconstructing a source from projection data", Computer Graphics and Image Processing 10 (1979), p. 48—68

O.R.Sander, G.N.Minerbo, R.A.Jameson, D.D.Chamberlin, "Beam tomography in two and four dimensions", 1979 LINAC--Conference Montauk, N.Y.

U.Rohrer, W.Rohrer, "Introduction of 2—dimensional beam tomography for monitoring transverse beam emittance at SIN", PSI Ann. Rep. 1982, NL 5—6

C.T.Mottershead (LANL, AT-6) "Maximum entropy beam diagnostic tomography", IEEE Trans. on Nucl. Sc., Vol. NS—32, No.5, 1985

D.S.Siva, "Data Analysis A Bayesian Tutorial", Oxford Science Publications (Clarendon Press Oxford), 1996, 2006

http://pc532.psi.chWeb page of Uli Rohrer, partly Co—author of MENTX

http:www.maxent.co.uk