CCDTL 2nd technical meeting for production of 7 CCDTL modules for Linac4 (#3888, #3889), October 26 - 28, 2009

Participants:

BINP, Novosibirsk: A. Tribendis, Y. Kryuchkov
VNIITF, Snezhinsk: M. Naumenko, D. Vavasov
CERN: M.Vretenar, F.Gerigk, P.Bourquin, E. Page, S. Sgobba, C. Saint-Jal, M. Savino, G. DeMichele, G. Favre, J. Stovall, A. Lombardi, Y. Cuvet,

list of talks:

Indico meeting 71563

supporting EDMS documents for this meeting

• geometry of alignment "bridge"
• position of wave-guide ports on the CCDTL modules
• calculations to determine coupling cell frequency
• coupling cell dimensions used for machining
• inter-tank layout and elements

Technical summary (F. Gerigk)

1. Construction Issues
2. Water Cooling
3. Support And Alignment
4. Dimensions Of Coupling Cell
5. Vacuum
6. Material Order
7. Qualification Of Welds And Welders
8. Copper Plating
9. Ownership of Tooling
10. Action List

1. Construction Issues

Drift tube mock-up

• The necessary material has been sent to BINP. It was received with a 10 days delay caused by customs officials because the SERTO fittings were not explicitly mentioned in the shipping papers. This means for all future shipments we must make sure that all items are listed, included their material composition and weight.
• The construction of the mock-up is foreseen to start next week.
• 3 Helicoflex joints for the stem/tank connection have been given to A. Tribendis during this meeting.
• A test volume has been found at BINP, which can be used for vacuum tests.
• Two different drift tube construction techniques will be used: i) brazing of the stem/drift tube connection, ii) e-beam welding of this connection.
• Vacuum tests are foreseen for January. A visit by a CERN team at BINP is planned for this occasion.

RF port

We will try to design the height of the RF port for the CCDTL such, that the height of the ports on the connecting wave-guide piece have the same dimensions for at least the complete CCDTL section. It seems likely that the same height as for the PIMS can be chosen. CERN will provide the necessary drawings.

Exchange of drawings

For the exchange of construction drawings we continue to use the step format. In case of difficulties, VNIITF offered to export CATIA files direclty from Solid Works.

2. Water Cooling

Serto fittings

SERTO fittings are not available in Russia. After a discussion with Y. Malakhov it was decided that a list of the needed fittings should be provided to the ISTC and ISTC will then procure the fittings (e.g. at CERN). Alternatively the CERN financial contribution to the project could be lowered and the in-kind contribution could be increased, but this probably means more paper work. They can be delivered with the 2nd shipment.

Simulation work

The cooling simulations, which are needed to decide how many circuits can be connected in series need to be concluded (see last meeting).

Radiation resistant hoses

The hoses proposed by CERN are not available in Russia. BINP/VNIITF will define the amount of hoses needed. Apparently it is not 100% clear from the contract if the hoses have to be procured by BINP/VNIITF or by CERN. This needs clarification. If these hoses need to be bought by BINP/VNIITF a similar arrangement as for the SERTO fittings (see above) could be found.

Other issues

• It was agreed that external "fixed" connections of water channels can be made out of copper. Like all other outside connections, these connections will be dismountable.
• Channels will only be connected in series if this set-up is suitable for 10% duty cycle operation. CERN can then put more connection in series for Linac4 operation if necessary.

3. Support And Alignment

Support frame

• In the last meeting it was agreed that BINP/VNIITF are developing the design of the support using the CERN requirements (inter-tank tables for quads/ diagnostics, longer frames to cover inter-module area), and that they also provide construction drawings in English.
• It became clear that CERN will have to work on the design of the support to be certain that all integration requirements are met.
• CERN will soon provide the weight (of all elements other than cavities) and additional length, which is needed for the inter-module region. BINP/VNIITF will make a concept for the support, which is accompanied by technical specifications for the interface between cavities and support (alternatively the specs could also be included in the 3D step files).
• CERN will take this concept (3D step file) and the specifications and adapt it to the specific needs of the Linac4 environment and western production technologies. CERN will then derive construction drawings and launch the construction of the supports.
• Foresee final discussion on concept at next meeting at CERN.

Alignment

Two alternative solution were discussed: option A and B (after the actual meeting). Option B is the now the reference solution. Description of both options follows below:

• For both solutions it was established that the tilt of the structure is not important for RF or beam dynamics, but that it is needed for metrology to be able to determine the exact position of each half tank.

Option A

• Onto each half tank 2 cylinders will be welded, which have sockets for laser tracker target holders. These sockets are holes with a depth of 11-12 mm and a diameter of 10 mm. The holes are in a plane of either 50 x 50 mm square or 50 mm diameter round. Specifications on tolerances, surface roughness, will be given to BINP/VNIITF (example drawing).
• These cylinders can have an angle of 60 degrees between them (see Figure 1) and will be located on the left side of the structures (looking downstream). The cylinders must not be obstructed by the support structure, when looking horizontally from the left side. None of the cylinders should be located at exactly 90 degrees from the top on the left side. CERN will confirm the suitability of the proposed positions (see Figure 1).

Figure 1: Alignment solution A.

Option B

• In a second meeting a preferable solution was discussed were a tilt surface is used to measure the tilt of the cavity. The tilt surface is combined with 2 laser tracker target holder sockets and is welded onto the lifting cylinders on the top of the cavity. This "bridge" is used on both sides of each cavity (see Figure 2).
• a step file and a pdf are stored in EDMS:1045859

4. Dimensions Of Coupling Cell

• CERN has re-calculated the coupling cell frequencies with HFSS. (slides.
• Since the calculation show no big difference to the results of BINP, there remains an uncertainty with the prediction of the coupling cell frequency.
• CERN will re-measure the frequency spectrum of the prototypes and calculate the single-cell frequencies assuming equal volumes of the accelerating cells. We will then try to include the effects of the changing volumes...
• For the 1st module VNIITF will leave excess length on the two coupling cell cylinders (~0.5 mm). The final length can then be machined (on the flanges) after measuring the frequencies at BINP. These dimensions should then be valid for all further coupling cells assuming the same coupling slot shape.
• In order to be able to use a larger coupling slot for the last 3-4 modules, BINP will do the necessary RF simulations. When the 1st module is tested we will take a decision whether to change the slot shape or whether to remain with one shape for all structures.

5. Vacuum

• The results of the recent pumping test on the ISTC prototype were presented and it was decided to use a DN 150 CF flange (on the pump side) for the pumping ports and to use it with a 100 mm port (the original size of the port on the cavity side, as on the prototype).
• The port will be machined out of bulk steel and will have a conical shape that opens the diameter from 100 mm to 150 mm to the flange were the pump is connected. It was decided to foresee 80 mm long pieces of bulk material (diameter 165 mm) for each port.
• We use 300 l/s pumps instead of the planned 150 l/s pumps, price difference: 5500 Eur/4250 Eur,
• The port geometry will be slightly optimised (4 bars instead of 5, maybe slightly thinner, ideally with rounded edges).
• When the vacuum test of the 1st module is done at BINP, CERN should send 2 pumps for a real test. To be confirmed after a discussion with BINP vacuum team.

6. Material Order

• Nuts and bolts for final assembly at CERN still need to be quantified (BINP) and purchased (CERN),
• A first set of SERTO fitting will be sent as soon as possible (~70, value ~1120 CHF) to enable the construction of the 1st module. Presently CERN is out of stock, but a delivery is expected within 2 weeks.
• Material for the fixed tuners needs to be specified and sent with the 2nd shipping.
• A complete list of materials has to be given to ISTC (including number, dimensions, weight, and material composition of all pieces).

7. Qualification Of Welds And Welders

It was agreed that for each welder (VNIITF) who will work on the CCDTL, 2 welding samples will be provided:

• welding of a port (tube to a flange)
• covering of a water channel with a thin plate, including 2 welded pipes to the water channel (welded to the cover), and a crossing of the welds,

The material will be provided by CERN, and CERN will then test the welding samples.

8. Copper Plating

During the inspection of the ISTC prototype (and later of the CERN prototype), corrosion was found spreading from trapped volumes. It is assumed that chemicals were trapped in these volumes, which were used to remove the protective paint on the outside of the cavities. This paint is used to prevent the outside of the cavities from copper plating. Examples in Figures 3,4,5. In case of the water connections this problem can be eliminated by welding the fittings from the outside instead of from the inside. For the port weldings, however, and the volume between accelerating cell and coupling cell there is no such obvious solution.

One can either:

• protect these volumes from the chemicals by using paint, filler material ...
• avoid the use of chemicals on the outside of the cavity (leave the protective paint, copper plate the outside, mechanically remove the paint on the outside)

In order to understand the parameter space we will collect all relevant information:

• chemicals used for the copper plating procedure of the ISTC prototype and the procedure which is foreseen for the series production,
• the same for the CERN prototype,
• get the advice from the CERN experts,
• get the material composition of the Russian steel used for the prototype,

Figure 3

Figure 4

Figure 5

9. Ownership of Tooling

It was agreed that:

• the tooling used at BINP will be available for CERN, it can be shipped together with the last modules,
• VNIITF will make photos of the various tools being used during construction. The photos will then be sent to CERN and CERN can then decide which tools it wants to own.

10. Action list:

-- FrankGerigk - 03-Nov-2009