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Beam Tomography for non-destructive Projected Emittance Measurements
The Maximum Entropy Tomography (MENT) program has been developed by Gerald Minerbo at the Los Alamos
Scientific Laboratory in New Mexico (USA) [1] and some time later successfully applied to
Beam Tomography by scientists at the same laboratory [2]. This Beam Tomography Program is coded in FORTRAN-77
with the exception of the Xlib-interface for the graphics, which is done in C by Urs Rohrer. Versions for Windows NT4/2K/XP,
x86-Linux and Mac OS X - X11 are available. MENT offers a very useful
method to do a projected emittance computation on a charged particle beam transport line.
Usually one can only get a few (between 3 and 6) different views (profiles), which is by far not sufficient for
conventional beam tomography programs to reconstruct the originating source. With MENT the lack of data is
compensated by selecting from the infinite amount of possible solutions the one with the
lowest information content consistent with the available data (maximum entropy beam tomography). At PSI
the maximum entropy method used in this beam tomography code has been applied successfully at several proton beam lines
(780 keV DC beam line, 72 MeV injection beam lines 1 and 2, 590 MeV beam lines near the Splitter, between Target M
and E and at the peeled off beam to the Pirex target).
For some more details about the application of Beam Tomography with Maximum Entropy see also reference [3].
A disturbing problem for the beam tomography at the PSI proton beam lines is
often the excessive, uncorrelated noise added to the measured profiles. This noise
is mostly due to intensity fluctuations and position jitter of the proton beam
(f = 50 Hz). By using an automatic Fast Fourier Transform (FFT) filter applied
to the measured beam profiles, the quality of the reconstruction with beam tomography may be substantially
improved. Fig. 1 (20 kB) shows such a noisy
beam profile and the cleaning effect by applying the FFT filter with a cut-off
frequency of about 16 Hz. A short résumé
about the usefulness of Beam Tomography with the MENT-code (together with Transport and Turtle) has been published in the
PSI Scientific and Technical Report 2000 Volume VI (Large Research Facilities) on
pages 24 & 25.
It should be mentioned here that the application of the beam tomography code MENT is not restricted to a proton
beam. For example this Beam Tomography code may also be applied to a alpha particle beam for testing large aperture
multipole magnets or to a pulsed electron beam from a linac (eg. SLS). The way this beam tomography code is adjusted
today, the only restriction is the span of the measured beam profile data to not be less
than about one mm. The beam profiles may be measured with different devices such as wire scanners,
harps, strip detectors or photographic (CCD) cameras. Instead of gathering profile information at
different locations along the beam line it may
also be preferable to measure only at one location and getting the multitude of information for doing beam tomography
through the variation of the optics (by controlled modification of the settings of some
quadrupoles) between the source and the location of the beam profile observation device.
Only non-dispersive beams are treated correctly by this version of beam tomography code (2 x 2 transfer matrices from
source to the observation device[s] ).
The code is also capable of reconstructing 2D-x/y-sources from different angle projections at one location (at least 3)
if the rotation matrices {Rij} for each projection are properly given in the input (see reference [4]
equation 3 and the APPENDIX). The quality of such a source reconstruction with 3 views of a (hollow) cylinder may be seen by
running the Test_numbers 1 and 3.
References:
[1] Gerald Minerbo, MENT: A Maximum Entropy Algorithm for Reconstructing a Source from
Projection Data, Computer Graphics and Image Processing 10 (1979) p. 48 - 68
[2] O.R. Sander, G. N. Minerbo, R.A. Jameson and D.D. Chamberlin, Beam Tomography in two
and four dimensions, 1979 Linear Accelerator Conference, Montauk, NY, Sept. 9-14, 1979
Los Alamos Scientific Laboratory internal report LA-UR-79-2540
[3] Urs Rohrer and Werner Joho, Introduction of 2-Dimensional Beam Tomography for Monitoring
Transverse Beam Emittances at SIN. Annual Report 1982, NL 5-6
(30 kB).
[4] C.T. Mottershead (LANL, AT-6) Maximum Entropy Beam Diagnostic Tomography.
IEEE Transactions on Nuclear Science, Vol. NS-32, No. 5, October 1985
This version of MENT maintained by Urs Rohrer at PSI is freely available and
distributable with one restriction:
If you use it for some work whose results are made public in a report or a journal publication,
then in a gentlemen's agreement you have to reference it properly.
Notice:
PSI and the author of this program do not
guarantee the accuracy and/or usefulness
of the results achieved with this program.
The output of it is strongly dependent on
the given input and therefore the confirmation
of the correctness of all the results is the
responsibility of the user.
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Get Maximum Entropy Tomography source code (MENT-srce) for x86-LINUX (tested with most modern x86-Linux versions
running with kernels 2.4.x or 2.6.x) (before downloading, please read 00-index.txt and 1-readme.txt).
Be aware that this source code is mostly legacy Fortran code ported over several platforms, OSes and compilers for the last 25 years. Currently
it compiles with compat-g77/gcc-3.4.6 (Fortran-77/C/C++).
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A bootable live CD has been created which contains among many other preinstalled programs
'MENT for Cygwin'. (Cygwin is a UNIX/Linux-like OS
running on top of Windows.) It may be downloaded as iso-file (
U_R_live_CD.iso, 655 MB,
instructions at
1-readme.txt). With low-speed internet connections you may download the
split images.
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Last updated by
Urs Rohrer on 11-July-2007
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APPENDIX: Description of Beam Tomography MENT-Input/Output parameters