HLRF Technical System Weekly Meeting

Thursday 30 Nov 2006, 03:00 → 05:00 US/Pacific

SLAC: SCS 115, 3-5PM PDT (High Level RF TS Review)

1. Review status of major HLRF subsystem, components in Baseline Conceptual Design. 2. Review progress of RDR Cost Modeling and Estimates, resource assignments, standard methodologies. 3. Review R&D progress for Alternate Conceptual Designs.

1 Agenda & Working Decisions

Speaker: Raymond Larsen (SLAC)

document HLRF_Draft_Wrkg_Descr_112906_Rev5_rsl.doc HLRF_Draft_Wrkg_Descr_112906_Rev5_rsl.pdf

Slides HLRF_Agenda_Nov_30_2006.pdf HLRF_Agenda_Nov_30_2006.ppt

Minutes of November 30 2006 Attendees: KEK: S. Fukuda, M. Akemoto, T. Shidara FNAL: C. Jensen, J. Reid, O. Nezhevenko, B. Chase SLAC: C. Nantista, M. Neubauer, C. Corvin, R. Larsen (Chair and Scribe) The agenda and supporting documents are posted to the meeting website at: http://ilcagenda.cern.ch/conferenceDisplay.py?confId=1004 1. HLRF Working Decisions and Description The updated document is attached in the minutes. Its purpose is to define technical and cost boundaries for HLRF. We reviewed all the changes since last issue six months ago; these are mostly minor clarifications, or notes that some points of discussion are still in progress. 2. Heat Loads Table The meeting reviewed the latest Heat Loads update by Emil Heudem. Chris Jensen noted an error and subsequently sent the following Email to Emil: On the most recent heat table (Nov 27) there is a 0.5 kW load for LCW listed under "Switching Power Supply 4 kV, 50 kW". This load is supposed to be under "Modulator". So, under "Switching Power Supply 4 kV, 50 kW" please increase the power to dirty water from 4.0 to 4.5 kW to keep the total average heat load at 7.5 kW and under "Modulator" add the 0.5 kW to LCW heat load and reduce the heat load to dirty water from 4.5 kW to 4.0 kW to keep the total to 7.5 kW. I believe this was a simple data entry problem. Emil responded that he would modify the table accordingly. 3. Klystron Water A number of people questioned using "dirty" (non-LCW) water for the klystrons to save money, as shown in the table, noting that the manufacturers called for low conductivity or distilled water. Subsequently three notes were sent out related to this topic, as follows: From Shigeki Fukuda on 12/4: I checked the water specification of Toshiba MBK which was discussed at last HLRF. Their specification was similar as the other klystron vendors and required to use the de-ionized pure water. Though they didn't specified the pH-value, they prefer around pH=8 to prevent the welding and brazing part of the klystron from electrolytic corrosion. From Mike Neubauer on 12/4: I have a response from CPI as well that is a little more detailed in how they specify water requirements. The concern for CPI is also galvanic corrosion, so they specify their collector cooling water like this: * 1. The resistivity of the water shall be maintained at a level of 100 kOhm-cm or higher at 30*C. * 2. Dissolved oxygen should not exceed 0.5 parts per million. * 3. The pH factor shall be within the range of 6 to 8. * 4. The particulate-matter size shall not be greater than 50 microns (325 mesh). Here is what I propose: since this is a large cost driver, we decide what water PH and resistivity we can live with cost effectively, and then require the tube manufacturers to design a collector water cooling jacket that works with that water. (It is common for tap water to be about 15-kOhm-cm, and ultra-pure deionized water can be 18.31 MOhm-cm, so a 100 kOhm-cm system may be something we can guarantee? I have yet so see a specification for the water we are proposing... did I miss it?) We can also fund studies that address the long-term reliability of such a system, and assist in the design of such a system, so the significant cost savings are realized. From Ralph Pasquinelli on 12/4: From extensive experience here at Fermilab, I suggest you DO NOT skimp on the water systems in an attempt to save money. Everyone thinks water is low tech and straight forward. Water system failures at Fermilab have caused us significant down time, destruction, and big bucks to fix. From acid producing bacteria, to pipes clogged by "dirty" industrial water, oxygen rich LCW that precipitates copper oxide clogging gunk, to hoses hoses hoses.... Most of the heat must be taken out of the tunnels via water, so it is a vital system and should be made as robust as possible. This is an area where money well spent will become evident by reliable operation. I believe the ILC should hire a water expert from the Navy! Chair's Comment: We all need to understand the technical risks as well as the cost impacts. Ralph's caution should be heeded. Meanwhile, we are de facto assuming that dirty water is OK for this largest of the loads. This may be a hasty judgment. There is also a cost to be borne up front if it is possible, as Mike suggests, to design to specifications of the water that is proposed to be used; but what are the risks? Perhaps a Navy expert can tell us. We certainly need more discussions with manufacturers before adopting this as a solution. 4. Waveguide Cooling Oleg is exercised that we assume cooling channels on the long runs of waveguide as it is a small load (~4 kW) and (he states) the cooling channels are expensive. Everyone seems to agree that circulators and loads need water cooling. Chair's Comment: Since we have been haggling over the last few KW in the service tunnel we suppose that all heat that can be, should be captured in water rather than dumping into air and then re-capturing with an air-to-water conditioning system. Oleg wants cost comparisons of the latter which we did not have. Assuming there are water channels is a conservative cost approach that can always be abandoned if it seems like overkill. There are many such issues at this early stage of design and we do not have time to debate every one. In the interests of stabilizing the baseline I believe we should leave this one as is -- water channels on the WG. 5. Klystron Power Output Specification/ Overhead/ End of Life considerations The discussion continues of whether we have a set of self-consistent numbers for klystron maximum power, average operating power, power losses for waveguide and couplers, and overhead for LLRF control. It's still not clear that we do. Adolphsen put out a set of numbers based on the present BCD which states the tube puts out 10MW maximum and operates at an average of 9MW. Chase countered with numbers of his own which brought in the concept of an "End-of-Life" derating which in fact would require us to specify a higher power rating for the klystron. Neubauer gave a detailed discussion (attached) of the failure mechanism of linear tubes to show that it is not a slow degradation of output, but a rapid wear-out of the cathode after 90% of lifetime is expended. At that point the heater can often be adjusted to milk out the last 10% from the klystron, AT OR NEAR the full power performance. Therefore, he concludes, we do not need a de-rating for EOL; we simply have to recognize that at the onset of EOL we need to be prepared to exchange the tube as it signals that it is within 10% of EOL. Chair's comment: This discussion has obvious cost implications, which can be interpreted in a number of ways. Again I propose we stick with the baseline power assumptions of 10KW max, 9 KW operating, and figure from there how many RF units we need to make 250 on 250 GeV, maximum. The cost people can argue whether to leave out the overhead units that were planned for high availability at the maximum energy. In practice there may be many reasons to hold the line on costs, but we should understand exactly what compromises are being made operationally, such as reduced energy capability whenever a single station is offline. 6. Power Reduction Strategy w/ no beam Last time Chris A. noted three strategies: Lower modulator voltage, shorten modulator pulse, lower PRF to 3 Hz. For the first of these, Jensen/Chase noted that lowering the modulator voltage with the ACD Charger scheme proposed by Cassel would limit voltage drop to 80% of nominal operating since we only have the 20% supply to work with. Chair's Comment: In Neubauer's talk he stated that the power out is proportional to V**(7/2), because efficiency is also nonlinear) so a voltage drop from 120 to 96 kV can reduce the power to 46% of maximum. Since the beam nominally aborbs about 40% of the power isn't this enough? In any case, the ACD is not adopted at this point so it has no relevance to the present cost model. Next Meeting: Thursday December 7th 3PM PST. Ray Larsen

2 Heat Loads Update

Speaker: Emil Heudem (FNAL)

Slides Pushback_ML_989_Criteria_NOV_27_2006.pdf

3 Klystron End-of-Life

Speaker: Mike Neubauer (SLAC)

Slides Linear_Beam_Tube_End-of-Life_Characteristics-mn061130.pdf Linear_Beam_Tube_End-of-Life_Characteristics-mn061130.ppt