CCDTL: results of extension of #2875, new ISTC project on CCDTL series production, March 08 at CERN

list of talks:

supporting documents for this meeting (final versions will be different):

Technical summary (F. Gerigk)

of the meeting on the CCDTL at CERN, 10-14 March 08


BINP, Novosibirsk: A. Tribendis, Y. Kryuchkov
VNIITF, Snezhinsk: V. Simonenko, M. Naumenko, D. Batin
CERN: M.Vretenar, M.Pasini, F.Gerigk, R.Wegner, Y.Cuvet, P.Bourquin, S.Ramberger, R. Garoby, T. Kurtyka, G. Vandoni, E. Page, T. Tardy, I. Sexton, M. Malabaila, M. Thiebert, G. Arnau Izquierdo, C. Saint-Jal, M. Jones, M. Savino

Main results:

1. Water cooling system
CERN insisted to review the water connections on the outside of the tanks to be sure that they are not damaged during handling operations. An exchangable design is proposed and CERN will prepare a sketch with a proposal.

The temperature measurements, which were taken on the VNIITF/BINP prototype during high-power tests at CERN were compared with calculated values (see presentation. For most values a good agreement was found. The calculated deformation of the tank body due to the heating was 0.1 mm at maximum. It was agreed to eliminate cooling channel no. 2 on the coupling cells, since its effect on the temperature is negligible. It was also agreed to eliminate the cooling channel around the drift tube, which is mounted on the tank body.

2. Tuners
It was agreed that CERN will procure the movable tuners and that VNIITF/BINP will produce fixed tuners without cooling channels. When the change is made from Linac4 to SPL operation, the average temperature of the cavity will change and a re-positioning of the fixed tuners will become necessary. At that time new tuners with cooling channels will be produced.

3. Proposal for a new stem/drift tube design

  • A new design was proposed that moves the e-beam welding point from the original position (slightly inside of the drift tube) to the nose tip of the drift tube. A deep welding with subsequent maching was proposed. CERN has worries about the fact that machining is applied over a welded surface and that this might lead to vacuum or water leakage (a problem observed at SNS). From the welding point of view it was remarked that the presented weld with a width and depth of 3 mm should yield an very good compactedness in the weld area: little porosity and and no material defects along the weld. BINP proposed a deeper weld, which ideally should not be too wide. For a wider weld (6 mm) one has to be careful with the state of the copper after the welding, because a slow welding speed with a large width will yield a degradation of the material properties.

  • For the 2nd weld (W2) it was remarked that a welding penetration of 3mm is needed for mechanical stability. Subsequent machining must be avoided, so a good surface quality of the weld is essential. A polishing of the weld should be possible.

  • The 3d weld (W3) fixes the drift tube to the stem. The presented solution seems interesting but needs to be validated by tests. In this solution the alignment is given by a plane that is parallel to weld, meaning that its positioning will not be affected by the weld. The 2 surfaces that are to be welded have a small distance, which will then be connected by the welding process. Concerns were voiced about the danger of trapping air inside of the welded volume, which could then "explode" when closing the welding circuit, but this can be avoided by having a 2nd "escape" for the air.

  • A solution for a dismountable drift tube was presented, which is inspired by the CERN DTL design. The design was encouraged by CERN. However, it would be preferrable to find a solution where only copper surfaces are exposed to the RF.

  • The mechanical resonances of the tuner/drift tube system were found at 26, 27 and 73 Hz.

  • In a subsequent discussion the possibility of brazing the drift tubes was discussed. This seems a promising approach, but also here one should try to find a solution, where any machining over brazed surfaces can be avoided. Further R&D on this subject is planned at BINP and will be discussed in the next meeting.

  • The mechanism to fix the drift tubes in position, which is also responsible for putting pressure onto the Helicoflex gaskets around the drift tubes, will be exchanged to a spring-loaded version as it is used for the CERN DTL.

4. Helicoflex gaskets

Aluminum gaskets will be used for all flanges and inter tank connections. For the VNIITF/BINP prototype it was found that the groove for the gasket connecting the half tanks with the tanks was much larger than the gasket. The sizes need verification.

5. Analysis of the rectangular vacuum flanges production technology (surface preparation)

Test with various surface conditions of the flanges were made in Snezhinsk (see presentation). The flange surfaces were rectified and achieved a roughness of 0.28 < Ra < 0.32, which is finer than specified for the use with Helicoflex gaskets. Tests with HN and HNV type gaskets showed no vacuum leaks. After copper plating the surface, there was no leak with an HNV gasket, but a subsequent test with a HN gasket produced a leak. Looking at the gasket it seems that a small surface area was ripped from the aluminum gasket. It was not clear if this leak was a consequence of the previous test with the sharp edged HNV gasket. After a 2nd copper plating the flange was leak tight with an HN gasket. It was concluded that copper plating should be avoided and that the flange surfaces must be rectified.

6. Analysis and improvement of copper plating technology

The copper plating process and VNIITF was reviewed (see presentation. It was found that the colouring of the copper was caused by the paint, that was used to protect the inner tank surface during the chemical removal of the copper on the outside of the tank. As a consequence it was decided either i) to remove the copper on the outside of the tanks mechanically, probably by sandblasting, or ii) to paint the outside of the tanks. The 2nd method was preferred because there is no risk of particles falling into the cavity after the removal of the paint.

7. Transport

Originally it was foreseen to disassemble the modules for transport but this means that two sets of Helicoflex gaskets (~50 k$ each) have to be bought. The possibility to transport complete modules will be studies, which would also save considerable work for the assembly at CERN. After a discussion with the CERN alignment experts, a method was identified to measure the position of the drift inside of the closed cavities using a mole that holds a target. This principle seems feasible but needs to be developed at CERN in case the transport of full modules seems reasonable. The transport could be tested with the first module and then a decision can be taken for the remaining modules.

8. Alignment

CERN will provide details on the needed alignment pads on the half tanks. There will 2 alignment arms mounted on the support girders. Only the middle tank will be fixed in position horizontally, the other 2 tanks can then move on the support if the structure is heating up. The construction should be made such that the flexibility of the cavities is used for movement and not the flexibility of the Helicoflex gaskets. The support will be rigid, while the structure is allowed to move slightly.

9. Support

It was decided that quadrupoles and diagnostics between the cavities will have a separate table, which is adjustable and which is mounted on the CCDTL support girders. One support leg is up-stream and two legs are down-stream as indicated in SPLACDTL0058.

10. Discussion of the new ISTC contract

A. Tribendis gave a presentation on the contents of the new ISTC contract for the production of the CCDTL. With this basis the following points were agreed:

The work will be organised within 2 ISTC projects:

  • a regular project (funded by the ISTC, value: ~1.35 M$ (ISTC) + OFHC copper for drift tubes (CERN)), which includes: i) construction of frames, ii) construction of drift tubes, iii) assembly of CCDTL modules and acceptance tests at CERN,
  • a partner project (funded by CERN, value: ~1.35 M$ + 304L steel for the tanks), which includes: i) construction of CCDTL tanks and coupling cells

BINP will be the leading institute in both projects. The funding is distributed as outlined in

The acceptance tests include only one high-power test on the first module. The acceptance of the remaining modules will be done after the results of tests on vacuum, water pressure, metrology, and low-level RF at CERN.

CERN reserves the right to visit VNIITF during the production of the 1st module and a visit will be planned before the copper plating. Further visits at VNIITF are only foreseen in case of production delays or manufacturing problems. In that case CERN will notify VNIITF ~1 month in advance. It is not necessary for CERN to see the workshops but an inspection of the manufactured pieces and a discussion with the involved technicians and engineers will be necessary. Visits at BINP can be organised at any time during the production and testing of the modules.

The starting date of the contract should be October, 1st 2008

obligations by VNIITF/BINP:

  • production, assembly and test of 7 CCDTL modules, each consisting of 3 accelerating cavities (with 3 accelerating gaps) and 2 coupling cavities,
  • all 2D execution drawings will be given to CERN in English,
  • frames for the modules are included, but not the alignment feet,
  • water manifolds,
  • fixed tuners without cooling,
  • tests for the positition of the short circuit, the results will be transmitted to CERN for production of the short circuits,
  • a summary of dimensional checks,
  • results from vacuum tests and water pressure tests of the cooling circuits (VNIITF),
  • RF tuning (frequency, tuner positions, RF characteristics) by BINP,
  • water pressure tests and vacuum tests with all metal seals (BINP),
  • alignment of drift tubes and precision machining to achieve minimum tuner penetration (BINP),
  • VNIITF will produce the frames, cavities, coupling cavities, cavity ports, and do the copper plating,
  • BINP will produce the copper drift tubes, water manifolds, fixed tuners, alignment mechanisms for drift tubes, external water circuits and connections,
  • shipment of the modules to CERN in batches of 1,2,2,2,
  • BINP will provide manpower to assemble the modules at CERN (if shipped in parts), which includes: i) assembly external water circuits, ii) assistance in vacuum tests and probably water pressure tests, iii) low-level RF measurements, v) mounting and adjustment of tuners and RF coupler, v) assistance for high-power tests,

obligations by CERN:

  • material for tanks & drift tubes, nuts & bolts that avoid the problem of "cold welding",
  • all Helicoflex gaskets,
  • alignment feet for the frames,
  • movable tuners,
  • waveguide T section and movable short circuit,
  • Conflat flanges made of 316 LN steel (price for 304 flanges will be deducted from the "partner project"),

The draft planning is as follows (more details in


11. Action list:

action institute/person target date
send sketch on exchangable cooling water connection (tank/tubes) to A. Tribendis CERN, Y. Cuvet sketch
specify location and requirements for the alignment pads on the half tanks to A. Tribendis CERN, M. Jones soon
drawings for the latest layout specifications (e.g. drift tube girder, support girders...) to CERN BINP, A. Tribendis as soon as available
specify a list of people that may want to visit Snezhinsk and send it to Snezhinsk CERN, F. Gerigk soon
clarify: i) the equipment ownership after the end of the ISTC contract, ii) if the ISTC contract currency has to be $, iii) "warranty issues" CERN, T. Kurtyka soon
complete specifications for all external interfaces (e.g. number and size of ports for vacuum) CERN, F. Gerigk, G. Vandoni end of June
a draft version of the ISTC contract, containing the complete text, will be sent to CERN (numbers and specification can still be changed later) BINP, A. Tribendis end of March
proof reading of ISTC contract CERN, S. Ramberger, F. Gerigk, R. Garoby, M. Vretenar one week after reception
send design specs of RF coupler ports to partner CERN/BINP soon
specify the shapes and dimensions of steel pieces, if half tanks are constructed out of 2 or 3 pieces BINP/VNIITF, M. Naumenko, A. Tribendis very soon
ask for preliminary price estimate and delivery times from steel suppliers for 3 scenarios: construction of half tanks out of i) one bulk piece, ii) 2 pieces, iii) 3 pieces CERN, C. Saint-Jal after reception of the dimensions of the pieces
access to EDH materials catalogue and EDMS drawings to M. Naumenko CERN, F. Gerigk done
description of welding of 304L tubes and 316 LN conflat flanges CERN, G. Favre done: either direct welding of the materials without fillers or with a filler like this one

12. Next meeting

A design review meeting will be planned for the beginning of September.

-- FrankGerigk - 13 Mar 2008

Topic attachments
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