29/04/03 f. caspers (cern):chopper development evolution iphi-spl meeting april 2003 1 brief...

29/04/03

F. Caspers (CERN):Chopper development evolution

IPHI-SPL meeting April 2003

1

Brief review of present status Why to consider an alternative printing

technology for the metallic meander on alumina Discussion of first results and difficulties

experienced with moly-mangan structures An experimental approach to define the cross-

over frequency S-parameters of our standing wave/ traveling wave approach

Conclusion and outlook

Chopper Development EvolutionF. Caspers [CERN-AB-RF-FB]

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2

Present status

Below our “standard” meander structure is shown again (as a reminder; length depicted here =200mm, width of the meander =42 mm); in reality the length will be 400 mm [blue=alumina, red =metal]

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3

Why to think about an alternative printing technology (1)

So far we used silk screen thick film printing on alumina:

How does it work: The alumina substrate is coated with a 20 micron thick layer of an emulsion containing silver and glass particles. After drying this layer at 150 C the photo-etching process is applied (removing all the undesired coating from the surface) and the remaining structure is fired in air (oxygen from air required during the firing process)@ 900 C

Afterwards increase of silver-layer thickness by chem. electro-deposition

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Normally the structures produced by thick-film technology on alumina are extremely solid.

However in our case we have to add some more silver by chemical methods (electrolytic bath) since after firing the silver traces are just 10 micron thick and have a much lower bulk conductivity (presence of glass as binder) than normal massive silver.

We have noticed that the chemical bath can weaken the normally very good bond between the fired silver layer and the alumina surface.

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5


Thus the question: What is the best known ceramic (alumina) – metal

bond Answer:

Moly-mangan ( = molybdenum - mangan) How does it work

A paint made from fine molybdenum and mangan particles in an organic suspension is brought onto the ceramic surface, dried and fired at 1400 C under hydrogen atmosphere

Chemical etching is done afterwards

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6

Results and difficulties seen with Moly-mangan (1)

The meander structure produced with MM (moly-mangan) technology also needs an additional silver layer of about 30 micron, to be deposited in a chemical bath.

Otherwise we would get intolerable conductor losses, since the MM layer is just 10 micron and its conductivity 10 times below copper.

However, silver cannot be deposited directly onto MM by chemical methods. One uses normally an intermediate nickel layer of a few micron.

But for the SPL chopper we are allergic to nickel, since the structure is in a magnet (quad)

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Thus we have deposited as intermediate layer silver (few micron) by evaporation after the structure has been etched and subsequently went into the chemical bath for increase of the layer thickness by another 30 micron

It worked well with nice results DC resistance over 40 cm slightly above1 Ohm Minor degradations (resistive loss) in RF parameters RF match not yet perfect (45 Ohm instead of 50

Ohm) as in previous thick-film versions DC current test done with 10 Ampere (100 Watt

loss!); result ok, but this again showed the need for water-cooling

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In a subsequent test with slightly modified width of the meander line (0.35 mm instead of 0.45mm in order to get closer to 50 Ohm) we have added the silver layer by evaporation before the etching process of the MM and then did the addition of silver in the chemical bath.

poor result; very bad adhesion between silver and MM

According to the experts the MM surface was perhaps not properly cleaned when doing the silver evaporation. But this process should work, if done properly. Thus after several discussions it was decided to deposit the silver by sputtering and doing an in situ gas discharge cleaning if the MM surface beforehand.

We should know more in a few weeks from now…

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9

How to measure on the bench the cross-ver frequency (1)

Global view of the chopper structure with surrounding tank and quadrupole;

Note the triaxial feed-throughs upstream and down stream of each deflecting plateThe N-connector is

the inner part of the triax system

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How to measure on the bench the cross-over frequency (2)[detailed view]

Collimators 13.5 mm high

Aluminum support, 10mm thick, electrically floating wrt the vacuum tank2nd triax conductor

Meander structure on alumina (3 mm high)

Coaxial feed, center conductor,1st triax conductor

beam

Wall of vacuum tank

(3rd triaxial conductor)

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How to measure on the bench the cross-over frequency (3)[measurement concept]

The concept is to carry out a transmission measurement between both meander structures, using one meander structure in the traveling wave mode as a beam simulator

The other electrode is operated either also in traveling wave mode (forward coupler, properly terminated, inner coax system of the triaxial structure) or in standing wave mode (like a capacitive PU (outer coax system of the triax structure)

Results:Are shown this afternoon in the lab….

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12

Conclusion

We have found very solid and promising technology for printing a meander structure on alumina

High DC current load tolerated Very solid metal-ceramic contact (heat transfer) Good RF properties Excellent radiation hardness

A simple in situ measurement technique is a good candidate for experimental determination of the RF transmission properties of the frequency diplexer formed by the meander in triax operation(floating ground plane)

29/04/03 f. caspers (cern):chopper development evolution iphi-spl meeting april 2003 1 brief...

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