Download GPI-2016-065 Report hands-on training at GANIL

Report on the first hands-on training at GANIL
“ Iron production with the oven method ”
Date: 15-17 November 2016
Participants: D. Cortazar (UCLM), M. Gigliore (LPSC), P. Hajdu (ATOMKI), H. Koïvisto (JYFL), R. Lang (GSI),
V. Toivanen (GANIL  CERN).
Organizing staff: C. Barué, F. Lemagnen, and V. Métayer.
Introduction:
The hands-on training has been carried out following the schedule in appendix. In addition, a
short daily debriefing took place in view of the fruitful discussions.
The presentation “Introduction to the hands-on training at GANIL” is available on the
ENSAR2/MIDAS website:
https://webapps.jyu.fi/wiki/display/ensar2/Training+workshop+on+iron+beam+production+
with+ECR4+Ion+source+using+oven+technique
General feedback on the hands-on training:
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Everybody expressed the desire to do the same training (oven method) in the other
laboratories of the MIDAS collaboration using this technique (GSI, JYFL, ATOMKI).
The participants expressed the desire to extend this exchange of ideas and knowledge.
The 3 days period and the beginning on Tuesday morning seem to be preferred.
The number of 5 participants maximum is appropriate for hands-on training.
Technical feedback on the hands-on training:
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The assembling of the GANIL LCO HT oven during the hands-on has shown an electrical
contact problem at the bayonet-system location (see slide 19 of the presentation). The oven
head casing has been disconnected and reshaped by force to solve the problem.
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The electrical contact could be improved by clamping the center wire in place with a small
(Torx) screw. The screw is inserted in a threaded hole on the side of the center block of the
oven where the wire is inserted. The screw is accessed through a hole on the side of the oven
outer cover. The idea is illustrated in the figure below.
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The bayonet connection could be replaced by 3 stainless steel screws on the stainless
pushing rod if the depth of the rod is large enough to be threaded (as down with the CERN
oven). The principle is shown below:
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The GANIL LCO HT Oven has been successfully mounted and heated up to 1500°C in the test
vacuum vessel. The intense color observed on the lateral part of the oven indicates that the
thermal shielding of the oven could be improved. The GSI oven is using multiple turns of a Ta
foil, as well as the JYFL and CERN ovens, and the oven lateral side is almost black.
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The deformation of the heating filament observed with the GANIL LCO Oven, has been also
observed with the GSI high temperature oven (1 mm diameter filament / 50 A). This
problem has completely disappeared by changing the axial magnetic field polarity. This could
simplify and reduce the cost of the oven by using a simple alumina tube instead of a
corrugated alumina (see presentation slide 19).
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Due to the opening part of the oven facing the plasma, the temperature at this position is
much lower (radiation loss α T4). This lower temperature has been increased by ~ 400°C with
the standard GSI oven simply by using 8 turns of a very thin corrugated Ta foil located at the
front end in the oven as a well as by using of an alumina end plug located inside the
container. The resulting metal vapor condensation is then reduced and a typical value of 30%
loss is measured with the GSI oven for Ni and Fe.
With the GANIL LCO HT Oven (used during the hands-on training), with the end plug located
at the front end of the oven, and without extra radiation shield, about 80% of the metal
vapor is lost on the plug (For iron production).
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The use of a tantalum tube, having a much better thermal conductivity than alumina, placed
inside the oven could help to increase the front-end temperature of the oven?
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The use of a corrugated alumina having more threaded turns at the front-end could also
improve the profile temperature.
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The idea of adding a separate secondary filament circuit with a few loops at the tip of the
oven for added localized heating and heat tuning flexibility was also mentioned and
discussed briefly.
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This metal condensation has been also observed at ATOMKI using Pantechnik oven for
calcium production. The metal condensation observed outside the container but inside the
oven maybe explained when the front end of the oven is completely blocked by condensed
metal. The visual aspect of the heating filament looks strange (check composition). If the
observed condensation is calcium, it should become white by leaving the oven at the air
(color of calcium oxide).
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For lower charge state optimization of the ion source (requested by ATOMKI), GSI and GANIL
have outlined the problem to do it with ECR4 and Caprice. It is very difficult to get high
intensity at low charge state because the radial magnetic confinement cannot be changed. At
GANIL, the 48Ca10+ intensity is always higher than 48Ca7+ for example.
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The problem of calcium over evaporation has been overcame at GSI by placing some Ta wires
inside the container and in front of the calcium load, as well as by using a negatively biased
electrode (~-1 kV) in the extraction area just in front the grounded electrode. The biased
electrode prevents secondary electrons to be accelerated into the plasma.
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A beam intensity of ~5 µA has been produced on Wednesday after about 2 hours. The
intensity has been increased to 10 µA on Thursday (the ion source is off during night). The
production tests will continue after the hands-on training until the end of the load. Then a
technical report will be written and sent to the participants.
Technical feedback on the GANIL Ta hot screen:
Taking the opportunity of the expertise of GSI with the hot screen technique used for calcium
recycling, the GANIL hot screen (unsuccessfully tested until now) has been visually inspected:
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The GANIL Tantalum hot screen shows a cold point at the injection side. The end cup tube of
the hot screen should not be in contact with the cold plasma chamber. If there is a small
space between this end cup tube and the tail of the plasma chamber, it should not make any
problem for the coaxial RF transmission into the plasma.
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The depth of the lateral Ta cylinder is 0.3 mm at GANIL, while it is 0.1 mm at GSI.
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The end cup at the extraction side has a diameter hole just a bit bigger than the plasma
electrode one.
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The RF power required to make an efficient recycling of calcium with Caprice ion source (GSI)
is around 600 W.
Presentation of the ENSAR2/MIDAS website:
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In the “database on beams”, a tabular appears after clicking the desire element. This one
contains one line only for each laboratory, showing the best intensity obtained for a given
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charge state, whatever the method used. The details (source, method, etc…) are given by
clicking the link attached to laboratories.
Each laboratory must keep in mind that all information contained in the website can be
accessed by anyone.
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Appendix
Schedule proposed before the hands-on training
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