Director's Corner

6 October 2005

The main goal of the GDE this fall is to determine a baseline configuration for the ILC. This baseline will serve as the basis for the reference design process that we will carry out next year. I plan to describe our process and outline some of the key issues that we must decide in this weekly column during the coming months, while we are defining our baseline configuration.

Rolf Heuer

In general, the design of a large complex project should ‘flow down’ from a set of performance and technical requirements. Fortunately, we have such a set of parameters for the ILC that are contained in a report dated September 30, 2003 and entitled, ‘Parameters for the Linear Collider.’ This document is the report of a subcommittee appointed by the International Linear Collider Steering Committee (ILCSC), which also serves as the parent body for the GDE. The parameter group who created this report consisted of Sachio Komamiya and Dongchul Son from Asia, Rolf Heuer (chair) and Francois Richard from Europe, and Paul Grannis and Mark Oreglia from North America.

This concise and well written document nicely lays out a set of basic parameters with values for the ILC. Although this study should probably be updated at some point, the published set of parameters is based on a broad review of the anticipated physics program for the linear collider, and the basic science goals have not changed.

Some of the key parameters that define the baseline include the energy range (200 – 500 GeV); the luminosity and reliability enabling the collection of approximately 500 fb^-1 of science data in the first four years of running after commissioning; energy scans at all centre-of-mass energy values between 200 GeV and 500 GeV with less than 10% loss in data taking; beam energy stability and precision below 0.1 %, in the continuum as well as during energy scans; the capability to produce electron beams with polarization of at least 80%; and the upgradeability to 1 TeV.

In designing the ILC, we are not taking these parameters as strict requirements, but rather as design goals. As we develop our design we will need to make sure that the requirements don't drive the costs or the risks beyond an affordable and robust design. Therefore, we will be doing many studies where we vary these parameters in optimizing the machine. In some cases, we will actually be assessing some of the design decisions that are inherent in the documents, in order to make sure they are sound and affordable.

Just to give concrete examples, the parameters document asserts that “two interaction regions should be planned, with space and infrastructure provided for two experiments,” and also that “one interaction region should allow a crossing angle compatible with a ãã interaction region.” Of course, both these options are highly desirable and we hope we can arrive at a design that will enable them to be included, but it is our responsibility to make certain that whatever options we include in the final design have been fully justified, in terms of the benefits, as well as the cost and other impacts on the machine. Let me emphasize that the fact that we will scrutinize all such options for the machine will finally put us in the best possible position to make the strongest case for our design, as well as be able to defend what we finally propose for the project.

In future columns, I intend to continue with discussions of how these top-level parameters discussed today translate into technical design parameters and then into the actual baseline configuration decisions.