Director's Corner

20 July 2005
Almost a year ago, the International Technology Recommendation Panel (ITRP) recommended that the linear collider be based on superconducting RF technology. The panel report added some important comments regarding this technology:

"The superconducting technology has features, some of which follow from the low RF frequency, that the Panel considered attractive and that will facilitate the future design:

Barry Barish
  • The large cavity aperture and long bunch interval simplify operations, reduce the sensitivity to ground motion, permit inter-bunch feedback, and may enable increased beam current.
  • The main linac and RF systems, the single largest technical cost elements, are of comparatively lower risk.
  • The construction of the superconducting XFEL free electron laser will provide prototypes and test many aspects of the linac.
  • The industrialization of most major components of the linac is underway.
  • The use of superconducting cavities significantly reduces power consumption."
A central theme of the present work toward the ILC by the GDE and the ILC community is focused on making choices among various options for the other components of the machine (the source, damping rings, beam delivery system, detectors, etc.). In fact, the primary goal for the rest of this calendar year will be to determine a baseline configuration that defines all the subsystems in enough detail to be used as the basis for the reference design effort next year.

But, this raises the question of what we should do about the design of the main linac itself. We all know of the decision to base the main linac on superconducting RF technology; and we have a very good starting point, the impressive design and development of cavities, couplers, etc. in the TESLA proposal. So should we just go ahead and adopt the TESLA cavity and coupler designs and call it a day? After all, these same cavities will be used for the XFEL at DESY. Staying with or very near that design would allow us to use the XFEL experience to help with industrializing and testing. Overall, it would serve as a significant systems test. Nevertheless, even if we do decide to take that route, we still must ask what gradient to pick as the baseline for the ILC. For example, 30 MV/m might seem relatively safe, but that would require us to design a very long linac. So, maybe we should push to 35 MV/m or even higher-but in that case what are the risks?

Whatever we choose, the question remains how to develop reliable fabrication and processing techniques to manufacture structures that will consistently give the required performance. And, what should we do to develop the various options that promise higher gradient, or that could save power or reduce costs? Grappling with such difficult issues will be one of the focuses of our work at Snowmass, especially for Working Group #5 (Accelerating Cavities).

Superconducting RF has emerged over the past several decades as a key technology for particle accelerators. Last week, many of the leaders of that field participated in the "12th International Workshop on RF Superconductivity," held at Cornell University from July 10-15.

This year's workshop was very capably organized by Hasan Padamsee (chair of the organizing committee) and his colleagues. The meeting covered many of the latest advances in the science, technology and applications of RF superconductivity to particle accelerators. It included reviews of the status of a large range of applications currently underway, as well as many ideas and proposals for applications. Not surprisingly, at this year's meeting, there was much emphasis on the linear collider. There were talks on new developments of various types that could improve the performance of ILC cavities, there was a special session with industry, and the final "ILC fest" featured talks by Maury Tigner, Gerry Dugan and me.

Much work remains to be done in order to develop the best solution for the design of the RF superconducting main linac for the ILC. One of our biggest and most important challenges will be to craft a program that will begin with a realistic baseline for the cavities, couplers, etc. that can be used for our reference design next year. At the same time, we want to continue a program aimed at developing improvements in fabrication, processing, and even in cavity design. Our objective, of course, is to be in a position to build the best possible linac we are capable of technically and cost-wise, at whatever time the construction of the ILC gets underway.