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Status Report of the Non—Destructive Emittance Instrument

Status Report of the Non—Destructive Emittance Instrument. Photo 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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Status Report of the Non—Destructive Emittance Instrument

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  1. Status Report of the Non—Destructive Emittance Instrument Photo 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

  2. Overview • Introduction • Photo detachment, slit—point transformation, • movable detector • Maximum Entropy as a Method for Emittance • Reconstruction • Experimental Results, measured at the Ion Source • Development Rig (ISDR) • Summary • Outlook, further development

  3. Photo—Detachment Principle Implemented Method: yy' in combination with movable angle detector Slit—Point Transformation • Displacement & Spread of • neutralized particles •  Angle profile I(y') • 2D Beam distributions • along the neutrals drift + Non—destructive + Preferable for high power + On line measurements

  4. Problem of Data Reconstruction Very often incomplete and/ or noisy data where MaxEnt has its strength Object of Study Measuring Instrument Data { fi }i =1,…, Nobject {dk}k=1,…, Ndata e.g. Telescope, spectrometer, emittance scanner, ..... e.g. Line-integral Fourier transform Blurred image Beam profiles e.g. Density of electrons Spectral intensity An image: 2D, 3D T . {fi} = {dk + hk} Traditional solution: {fi} = T-1 . {dk + hk} 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 !)

  5. Entrance Distribution and Beam Envelope

  6. Variable Number of Profiles using MaxEnt A 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

  7. Comparison of rms--Emittances Implemented Method: yy' in combination with movable angle detector

  8. Ion Source Development Rig (ISDR) Pepperpot emittances + Beam profiles at various z—positions Slit slit emittances Seperate, movable slit in combination with scintillator Slit height: 0.3mm Slit length: 110mm Drift in between: 107mm Beam parameters: H- @ 50mA 17 keV extraction voltage 35 keV total beam energy field gradient n=1.4 (w)

  9. Collimated Ion Beam (Pseudo Coloured) 1.) Beam distribution at 260mm 2.) Collimated beam parts after a separation drift of 107mm

  10. Pepperpot measurement "simulation" At -30mm and =26mm original collimated beamlets For 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

  11. 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 generalprinciples 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

  12. 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—68O.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—6C.T.Mottershead (LANL, AT-6) "Maximum entropy beam diagnostic tomography", IEEE Trans. on Nucl. Sc., Vol. NS—32, No.5, 1985D.S.Siva, "Data Analysis A Bayesian Tutorial", Oxford Science Publications (Clarendon Press Oxford), 1996, 2006http://pc532.psi.chWeb page of Uli Rohrer, partly Co—author of MENTXhttp:www.maxent.co.uk

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