CCDTL 7th technical meeting for production of 7 CCDTL modules for Linac4 (ISTC contract #3888 and #3889), 6-11 November 2011 at BINP

Participants:

BINP Novosibirsk: A. Tribendis (ISTC Projects 3888/89 manager, deputy RF group leader BINP), E. Kenzhebulatov (RF scientist), N. Matyash (senior support engineer), V. Stepanov (technician), Ya. Kryuchkov (design group leader), Yu Biryuchevsky (design engineer)

VNIITF Snezhinsk: M. Naumenko (ISTC Projects 3888/89 sub-manager, design group leader VNIITF), P. Taushkanov (senior technologist), D. Vavasov (design engineer), Yu. Kretinin (technologist)

ISTC Moscow: Yu Malahkhov (principal senior project manager), A. Ryakhovsky (procurement manager)

CERN Geneva: Frank Gerigk (ISTC Projects 3888/89 coordinator at CERN, RF scientist), Jean-Michel Giguet (senior RF technician), J.H. Hansen (vacuum engineer), E. Page (vacuum engineer), B. Riffaud (mechanical designer), M. Vretenar (Linac4 project leader, senior RF scientist)

Contents

1. Supporting documents in EDMS
2. Work plan
3. Technical summary
3.1 Construction status and planning
3.2 Vacuum tests on module 2
3.3 Mechanical observations on modules 1,2,3
3.4 Helicoflex surfaces
3.5 RF measurements on module 2,3
3.6 Support structure
3.7 Installation of RF springs on fixed tuners
3.8 ISTC contract status
4. Action list

1. Supporting documents in EDMS

• support drawings, version November 2011
• RF measurements on module 2 and 3
• Visit report for EN-MME, B. Riffaud
• Visit report of vacuum group, J. Hansen, E. Page

2. Work plan

3. Technical summary

3.1 Construction status and planning

module	tanks	location	RF measurements	drift tubes	comments
1	machined, one half cell has a void on the stem joint and needs to be Cu plated	at BINP	done	done	the 2 pumping ports have been repaired (see Fig. 1) and the concerned half-cells have been Cu plated, to be sure that the 2nd Cu plating is good (see Fig. 2) the half-cells will be baked at BINP
2	ready	BINP	done	done	vacuum leak tests on the stem joints still pending
3	ready	BINP	done	done	will be vacuum leak tested at BINP (Jan 2012) and mounted on support in March 2012
4	ready	VNIITF	pending	pre-machined
5	ready until 15.12.11	VNIITF	pending	pre-machined
6	ready in February 12	VNIITF	pending	pre-machined
7	ready in April/May 12	VNIITF	pending	pre-machined	worst case date

• According to the schedule made at the last meeting (March 2011) the last module should have been machined by VNIITF by the end of February 2012. It is now estimated that the last module will be ready by April/May 2012, which was accepted by CERN.
• The tools for making grooves in the vicinity of all Helicoflex joint areas have been ordered via ISTC. Once they are available at BINP, the grooves will be added to all joint areas.
• Modules 4-7 will be ready for shipment to CERN approximately 2.5 months after delivery to BINP.
• Most likely the modules will be shipped to CERN in 2 batches, e.g. modules 2,3 + 1,4,5,6,7, or 2,3,4 + 1,5,6,7
• A water pressure test (16 bar) was made on a faulty drift tube using the stiffeners. The test was successful. Figure 3 shows the inserted stiffener and Fig. 4 the set-up.

Figure 1: Repaired pumping port on module 1 large picture

Figure 2: Cu plating on repaired half-cells of module 1 large picture

Figure 3: Stiffener inserted into drift tube Cu water channel large picture

Figure 4: Water connections to apply 16 bar water pressure to the drift tube cooling channels large picture

3.2 Vacuum tests on module 2

A detailed report is given in EDMS 1171700

3.3 Mechanical observations on module 1,2,3

• The orientation of the pumping port grids on the 2 half-cavities of module 1 has been corrected and the 2 half-cavities have been re-copper plated. If there is no degradation of the plating during a baking at BINP, the 2 half-cavities are accepted by CERN.
• The half-cavity of module 1, which has the void in the stem joint area (see Fig. 4) was inspected and it was decided to make a vacuum test with a Helicoflex joint. If the half-cavity is leak tight it will be sent back to VNIITF for copper plating.
• The alignment of drift tubes was demonstrated, see Fig. 6 and 7. The actual alignment was done by bending the drift tube stem into its position.
• On module 2 cavity 6, the Cu around the nose area showed some dark patches, which result from a repair of Cu plating in that area. (Fig. 8)
• The Electron Beam Welding of stem and drift tube was considered excellent (Fig. 9)
• It was observed that the O-rings, which were used for transport from VNIITF to CERN were greased. Traces of this grease were identified in the spectrometer test and it was agreed that for future transports no grease will be used.

Figure 5: void on Helicoflex joint area on half cavity in module 1 large picture

Figure 6: Alignment check of drift tube large picture

Figure 7: Alignment check of drift tube large picture

Figure 8: Dark patches around nose of module2 cavity 6 large picture

Figure 9: EBW of stem and drift tube large picture

3.4 Helicoflex surfaces

• Before the visit all surfaces have been polished with scotch brite to a mirror-like state.
• Since some the joints were leaking, these surfaces have then been roughened with sanding paper in a circular sense and any radial marks have been removed. This seemed to be the best approach to get the joints leak tight.
• On the half-cavity joints it was found that the joints leave 2 circular imprints (see Fig. 10 and 11), which probably means that the joint has 2 small contact areas instead of one broader area in the centre. Garlock was contacted by J. Hansen to ask for clarification.
• It was observed that the drawings do not indicate a flatness tolerance for the area of the large half-cavity joints. Measurements indicated, however, that the surface flatness is within 20 um.

Figure 10: double surface imprints left by Helicoflex joint on half cavity large picture

Figure 11: double imprints on the corresponding Helicoflex joint large picture

3.5 RF measurements on module 2,3

• The RF measurements (field flatness, tuning, preparation for cutting of fixed tuners, coupling to waveguide) were discussed and the results were given to CERN: EDMS 1170960.
• For test purposes shims with different thickness have been placed between the coupling iris on the cavity side and the waveguide coupler to study the influence on the coupling factor.
• The latest drawings of the Linac4 adjustable RF coupler were given to BINP: SPLACDTW0017 Version AB.

Tuning principle

• tuning of single cell frequencies, while the connected half cell cavities are detuned,
• after connection of all cells, the frequency of the pi-mode is found to be very close (10s of kHz) to its design value,
• then used Helicoflex joints are inserted, drift tubes are re-aligned, and the frequencies are re-measured,
• finally the fixed tuners are cut to their final length.
• a test measurement will be done to verify the influence of RF contacts on the fixed tuners.
• the penetration of the fixed tuners is around 20 mm.

Coupling cell deformation

• It was noted that there is a large (~0.5 MHz) difference in the coupling cell frequency when using Helicoflex joints and when using simple RF joints (Cu tube). It was decided to do further tests.
• It was also noted the CC frequency changes much more (~300 kHz) than the accelerating cell frequencies, when going from air to vacuum. Also here further tests will be done.

3.6 Support structure

• BINP will test mount all modules on their actual supports.
• For the first module to be mounted (module 2), CERN will come with experts from survey and the mechanical design office (March 2012). During this visit the assembly procedure on the modules should be finalized and an alignment check should be made to see if the concept reaches the required alignment precision.
• The drawings of all supports have been given to CERN EDMS 1170940.
• It was confirmed by CERN that the geometry of the support parts which receive the jacks is correct.
• CERN will provide a short assembly table when the structures are assembled at CERN.
• A transport test should be done at CERN with a fully assembled module. A bead-pull measurement before and after the transport can indicate if the position of the drift tubes has moved. An external measurement of the cavity alignment can be done with a laser tracker.
• The eccentric cams for transverse cavity alignment were presented by BINP and discussed. The principle was appreciated by CERN, and final drawings will be given to CERN as soon as they are available.
• The transfer of drawings to CERN was discussed.
• It was pointed out by CERN that the tolerances for the back support pins is very demanding (-+ 0.01 mm). So far the BINP workshop has accepted these values.
• The tolerance values of the support plain bearing housing holes were, which are used by BINP so far (OD 47 M6 (-0.02/-0.04) have been confirmed. They can be used with the following commercial products:
  • SCHAFFLER GROUP: Bearing GE25-SX (ELGES) ID 47 (0/-0.14)
  • SKF : Bearing GAC25F ID 47 (0/-0.12)
  • FLURO GELENKLAGER GmbH : Bearing GE25-SX ID 47 (0/-0.14)
  • LDK BEARINGS : Bearing GX35T ID 47 (0/-0.14)

3.7 Installation of RF springs on fixed tuners

It was decided that the fixed tuners can remain in the cavities once their are cut to final length and installed with the RF contacts.

Installation procedure

• cleaning in alcohol or in an ultrasonic bath
• tear the spring slightly, to have roughly the distance of one coil between coils,
• connect the ends of the spring so that there is an overlap of 2 coils at the connection,
• install the coils around the tuners
• put the tuner into the port and turn slightly to bend the coils, otherwise the coil is too thick to be pushed inside together with the tuner,
• push the tuner straight in, and turn slightly in the opposite direction once the tuner is in its final position,
• to remove a fixed tuner, it must first be slightly turned and then taken out of the tuner port.

3.8 ISTC contract situation

All ISTC projects have to be terminated until the end of September 2014.

Projects #3888 and #3889

• Due to a slight delay in the construction at VNIITF and the fact that all modules will be test mounted on their support (constructed under a separate contract at BINP), both projects need to be extended.
• #3888 should be extended by 3 months from February 2012 to May 2012.
• #3889 should be extended by 9 months from May 2012 to February 2013.
• These dates should give enough time to finalize the assembly of the modules at CERN.

Transfer of funds from #2888 and #2889

• Project #2889 was terminated on October 14th, and #2888 was terminated on November 14th.
• By January 2012 it should be clear if and how much money can be transferred to projects #3888 and #3889

4. Action list

-- FrankGerigk - 14-Nov-2011