Controversial issues

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This page is dedicated to new, recent or tentative ideas in the field of ion surface interactions (or others), which may be controversial and be used as an open forum.
 Readers may send me contradictory claims:
jpbriand920@aol.com

which I would be pleased to post in this page


Issue 1:
 
The beams of the ECR sources

or
the complain of the users


The only goal of most builders of ECR sources, challenging each others, is to get as much as possible ions of the highest possible charge state. They usually set,  just at the exit of the magnet selecting the charge state, a Faraday cup  as large as possible, and try to get the maximum currents by tuning parameters of the sources.

 The users take the ions on the focal point of the magnet and try to direct the beam on their targets to get a beam spot as well characterized as possible.

This is the time at which troubles come. As everybody knows that the ions are extracted from a plasma of large size, in which the ions may not be uniformly prepared, the users are not  expecting to get a good emittance and accept to spent quite a long time to get an approximate beam spot by tuning lenses, steerers and so on in an erratic way until they get an acceptable spot.

Our experiments

 In our lab we have been carried out experiments in various places through the worldand with various ECR sources and found that each time we try  to direct the beam directly from the focal point of the selectring magnet the beam was about 2 cm lower than expected. Finding the same trouble with fully different sources build with different people made us puzzled.
We then build a special mechanical design allowing to move a large fluorescent target  in any direction from the focal point of the magnet and found that actually there were three different beams coming from this point in three different direction approximately at 120 d. We  always found that there was always one of these  beams pointing to the ground in the right mechanical axis of the magnet and  two other beams pointing, approximately, to the top on the right and left direction.These finding obviously led us to think about the well know three branches star imaging the octupolar character of the confined plasma.  We succeded in usung  the first of these beams by directlng the pipes of the beam line to the ground but it was much more difficult to use the two others.

 We presented these results in a meeting of the European network on the Multicharged beam we organized in Versailles few years ago. There was a lot of dicussions, some colleagues agreeing and claiming that they actually already observed more than one beam while others who never got any experimental evidence for an effect disagreeing.  We realized that those who never observed this three  beams  used actually a solenoid just before the binding magnet while all the others directly sent the extracted beam from the plasma to the magnet . It may then be possible that the solenoid in a quite complex way may reconcentrate the
extracted beams .

Comments  welcome