status report of the non—destructive emittance instrument
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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
2
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
3
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
4
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 !)
5
Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008
Entrance Distribution and Beam Envelope
6
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
7
Christoph Gabor, ASTeCHIPPI Annual Meeting, CERN, 30.September 2008
Comparison of rms--EmittancesImplemented Method: yy' in combination with movable angle
detector
8
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
9
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
10
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
11
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
12
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