Designing the Next Big Machine

By JoAnne Hewett | February 8, 2007 10:01 pm

The Large Hadron Collider has yet to begin operations and the particle physics community is already looking ahead to the next big machine: the International Linear Collider. The ILC would collide electrons and positrons at energies of 500 GeV. Accelerator projects have a long lead time, and if we want to follow up on the questions that the LHC data will invariably raise, we have to get started now. Broad international support was shown for the ILC in 2003 when a significant fraction of the worldwide particle physics community signed a consensus document, which served as a blueprint for the physics case of the machine. Today in Beijing, the Reference Design Report (10 MB), which is a detailed technical blueprint for the design of the accelerator, was released. It is the first fully integrated design for the ILC and it contains the first full cost estimate.

It’s been a long road to get to this step. The physics case is really rather simple. The discovery of new particles helps us to understand how the universe works. Accomplishing this takes two steps: (i) we have to discover the new particles, and (ii) we have to discover the new theory or symmetry that gives rise to them. The LHC is tailor-made for the former and has an expansive discovery reach for new states. However, the latter requires a more delicate touch — precision measurements of a particle’s properties are needed to learn about the underlying theory. Enter the ILC whose beams are fundamental particles with a known and tunable initial quantum state, enabling ultra-precise measurements. There have been literally thousands of physics studies for the ILC and several large review volumes such as here, here, here, and here (non-technical). I’ve been involved in these studies for ages — I wrote my first ILC paper as a graduate student in 1988 (I was the first to show the reach for new gauge bosons) and either wrote or contributed to the new physics chapters in each of these review volumes. I truly believe we will need high energy electron-positron data to fully understand the physics that awaits us at the TeV scale.

An awe-inspiring physics case isn’t worth much unless it can be matched by the technical feasibility to build the machine. Our hard-working accelerator friends have been studying this mahcine for decades as well. Ideas began to mature in the mid-1980’s when folks understood the basic accelerator concepts for a high energy linear collider and thought one could be realized with a finite amount of research & design. During the next decade, four leading concepts for the accelerating mechanism emerged: (i) TESLA, based on superconducting Radio Frequency accelerating cavities, (ii) NLC/JLC-X based on high frequency (11.4 GHz) room temperature copper cavities, (iii) JLC-C based on lower frequency (5.7 GHz) conventional cavities, and (iv) CLIC based on a two-beam scheme with high gradient room temperature cavities and transfer structures operating at 30 GHz.

Research progressed on these four designs for over a decade and several reviews to evaluate them were undertaken. In 2004, after the physics consensus document was signed, the international community came together and formed a panel to make a recommendation for a RF technology between the superconducting and room temperature cavities. (CLIC was viewed as requiring significantly more R&D to demonstrate feasibility.) The panel chose the cold technology citing, amongst other things, a higher reliability and further progress on industrialization of the components. This choice was promptly accepted by all groups involved and is viewed as a major milestone towards a global realization of the project.

At this point the Global Design Effort (GDE) was formed, headed by Barry Barish of CalTech. About 100 accelerator physicists worldwide participate in the effort. Their first task, known as the baseline configuration, was to choose the parameters for all of the components and subsystems of the 500 GeV machine. Parameters like the accelerating gradient of the cavities (35 MeV/meter peak and 31.5 MeV/meter operating), the length of the accelerator (31 km), the capability to polarize the positron beams (yes), etc. were decided upon. This was completed by the end of 2005, so that the GDE could spend 2006 writing the Reference Design with full costing. I’ll write a step-by-step guide to the accelerator design soon — it’s a story in itself and constitutes a major technological feat. The Reference Design was released today, and now the next task for the GDE is to evolve and improve the design through continuing R&D and value engineering. They hope to make engineering choices for further optimization of the performance relative to cost. This process will take two to three years and will lead to a detailed Engineering Design Report, which can be used for the actual construction of the ILC. The estimated time for construction is seven years, after the project has been formally approved. Here’s a schematic of the GDE timeline:

The big news from today’s document release, the question that has held everyone breathless for years, is the cost. The cost was given in international value units. Each region (Europe, Asia, Americas) has its own peculiar costing scheme, and the trick was to present a cost that can be translated to each of them. So, the cost is….insert drum roll here….

  • $1.9B ILC Value Units for site-related costs, such as tunneling
  • $4.9B ILC Value Units for the value of the high technology and conventional components
  • 13,000 person-years for the required supporting manpower
  • ILC Value Unit? This is new terminology for a currency exchange rate! Their definition is 1 ILC Value Unit = 1 US Dollar in 2007 = 0.83 Euro = 117 Yen.

    It is critical to realize that this costing scheme is most similar to that used in Europe. The $6.7B figure does not include labor or contingency, which we include in the project cost here in the US. There are standard factors that are usually employed to estimate the translation to the American accounting scheme, which invites everyone to do their own calculation. This can lead to rather disparate results. To have a firm, standarized US cost estimate, the Department of Energy and the American Linear Collider Steering Group are performing their own translations of the GDE costing to US accounting procedures. The only thing we know for sure at this point, is that once labor and contingency is included, it will be more than $6.7B. Oh, and don’t forget that we need to include the cost of the detectors too. So, stayed tuned….

    Today’s press release can be found here, as well as articles in the New York Times, and Science, as well as a movie starring my good friend and wine-consuming buddy Phil Burrows being interviewed by the BBC.


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