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Subject: RE: ILC BDS mtg.@SLAC, November 29, 1:30pm PST

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Andrei and BD group:

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Unfortunately, I will not be able to attend your meeting today. Here some comments on the requirement and use of additional high power dumps. As one might expect, the comments deal mostly with systems upstream of the dump.

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1) The most important purpose for additional high power dumps results from the desire to keep upstream systems in equilibrium during short interruptions. Other functions include the desire to have beam instrumentation and related feedback / stabilization systems in operation during the interruptions (these are soft requirements in comparison). The critical parameters are the degree to which the upstream machine configuration (includes field strength, phase, alignment etc) depend on the average beam power in those locations. If it is guaranteed that there is no difference between full power operation and very low power operation, then additional high power dumps are not needed at all.
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2) There are 3 primary subsystems whose configuration depends on average beam power: 1) damping ring alignment, 2) positron capture system phases, 3) collimation. In each of these cases, beam heating is a significant part of the total heat flow and will necessarily have some impact. At SLC, the beam power on target was ~30KW, about 20% of this was absorbed in the positron capture RF section. Much can be done to reduce these effects using more careful initial engineering, but since the beam power is much more than 30KW, I think we should consider the impact of residual temperature changes carefully and assume they will be a problem. Based on measurements at TTF, we should determine what it takes to make sure that the SCRF linac does not have residual thermal effects associated with the beam rate. This is very important.
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3) There are two basic kinds of interruptions, 1) short (MPS or beam tuning) driven where it would be useful if the system recovered more or less instantly and 2)longer interruptions involving access etc where upstream thermal time scales are unimportant. High power beam auxiliary beam dumps are only needed for the first of these. Not the second. 
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4) Given the dumps under consideration, we must note that all of the systems listed in 2) are upstream of the linac (except the BDS collimators themselves). The most logical place to dump the full rep rate/n_bunch beam is before the entrance to the linac, not after it. I therefore recommend removing the baseline requirement for full power dumps at the entrance to the beam delivery. These dumps are important but need not take full power, only the full bunch train. A much lower power, lower cost dump could be implemented, for example one capable of 0.1Hz full train operation. Access to the BDS would be possible with beam in the linac. I expect that 0.5MW dumps will be much cheaper and easier to deal with than full power beam dumps. A full power dump will cost ~ 50M$. Lower power dumps may cost 1/10 of this, based on the SLC design.
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5) Full power dumps are needed in the damping ring (complex) and at the entrance to the linac. These will be used to keep the DRs as warm as possible. The undulator positron system should also remain operating at full power. This requires a full power charged beam dump at that location. In principle, if there were a problem on the positron side, the electron beam could be transported to the main BDS dumps.
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6) During access to the BDS area, where the interruption is long compared to these thermal time scales, the power in the entire machine, except the stored beam in the DR, should be scaled back to reasonable levels.

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7) This is the 'minimum dump' configuration. There are 6 1/2 MW class dumps, one 15 MW (at the e+ source) and 2 nominal full power 20MW dumps. Not including dumps needed in the injector, undamped, system.


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-----Original Message-----
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From: Seryi, Andrei 
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Sent: Tuesday, November 29, 2005 12:43 AM

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Subject: ILC BDS mtg.@SLAC, November 29, 1:30pm PST


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We will on Tuesday, November 29, at 1:30pm PST, in Fuji. 

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Tentative Agenda

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It is suggested to discuss pro/cons of
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a) separate full power tune-up beam dumps, as in baseline (six full power beam dumps in total);
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b) eliminating the tune-up beam dump, and using main dumps for tune-up mode as well. 

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Please bring any relevant materials or thoughts, to answer questions such as for example:

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  What is the amount of cost reduction? 

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  What is impact on ILC availability due to elimination of "tune-up" mode (cannot simultaneously access detector and tune the linac?) ? 

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  What is technical feasibility of beam dump design, with windows on both sides? 

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  What is feasibility from optics point of view? 

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  What are conventional facility implications, e.g. do we need to widen the tunnel? 

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  Would it improve the ILC availability if the tune-up dump would be kept but with reduced power rating, e.g. 
to "keep-alive" intensity?

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  Would it be possible to dump "keep-alive" beam intensity to the main dump in tune-up mode and have people accessing detector? 


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Connection info:
Call: 510-665-5437
Meeting ID: 0144

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Files will be placed here:
http://www-project.slac.stanford.edu/ilc/acceldev/beamdelivery/new/
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This agenda, as well as notes from the earlier meetings are posted here:
http://www-project.slac.stanford.edu/ilc/acceldev/beamdelivery/

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Andrei