ILC Global Design Effort

Accelerator WG3b - Damping Rings
Summaries, Question Responses and Supporting Documents

Updated 22 September 2005

WG3b workspace from Snowmass


We briefly report the conclusions of the WG3b working group summary presented on August 19th [1].

The working group, about 30 active participants, has been organized in task forces dedicated to specific items. The goals of the task forces are to produce information that can be used to inform the configuration selection. The task forces (and co-coordinators) are:

1.        Acceptance (Y. Cai, Y. Ohnishi)

2.        Emittance (J. Jones, K. Kubo)

3.        Classical Instabilities (A. Wolski)

4.        Space-Charge (K. Oide, M. Venturini)

5.        Kickers and Instrumentation (T. Naito, M. Ross)\

6.        Electron Cloud (K. Ohmi, M. Pivi, F. Zimmermann)

7.        Ion Effects (E.-S. Kim, D. Schulte, F. Zimmermann)

8.        Cost Estimates (S. Guiducci, J. Urakawa, A. Wolski)

9.        Polarization (D. Barber)

Various configuration options of the Damping Rings are being studied, using seven “reference” lattices as a basis, and applying a consistent set of analysis techniques and tools. The seven lattices cover a range of configuration parameters, including different layouts, circumferences, energies and cell structures. The parameters of the seven lattices are reported in “Parameters MegaTable” [2] and the references are at [3].

The Task Forces will complete their studies by mid November 2005. The results of the studies will be documented in a “Configuration Recommendation” report that will describe the seven “reference” lattices, the analysis tools and methods, present the analysis results and provide an “executive summary”. The executive summary will contain the configuration recommendations and the list of remaining R&D that is required.

We shall hold a mini-workshop to reach consensus on the configuration recommendations, and prepare the executive summary. This workshop will be held at CERN on 9-11 November 2005.

The large amount of work presented and discussed at Snowmass can be seen from the presentations of each task force [4÷11]. Each task force has also presented the plans for the completion of the work, which are reported in the slides [12÷20]. The program of the session is at [21]. The content of the presentations is not summarized here, it will be reported in the  “Configuration Recommendation” document that we are preparing.

The final discussion has been focused on the choice of size and layout, which is the key issue for the Baseline Configuration recommendation (number 7 in the Question list [22]). Different layout and circumference configurations have been proposed:

1.  A 17 Km “dogbone” shape ring, installed in the linac tunnel, as in the TESLA TDR

2.  A nearly circular (or racetrack) ring in an independent tunnel with a circumference in the 3-6 Km range.

The length of the TESLA DR and the idea of the dogbone shape (to save tunnel length) were originated by the unavailability of ultra fast kickers. 17 Km were needed to accommodate ~3000 bunches with 20 ns bunch distance, which, for the TESLA TDR, was considered a feasible value for the rise/fall time of the kickers. At present three different types of fast pulsers have been tested on a strip line kicker at ATF (KEK). All of them have very short rise/fall time (~3ns) and fulfill nearly all of the requirements for the damping ring injection/extraction. R&D programs are in progress in various laboratories (see presentations [7]) both on the pulser and on the electromagnetic design of the electrode and the task force 5 participants are confident that:

-         The kickers for a 6 Km (i.e. 6 ns bunch spacing) are a “low risk” issue

-         The kickers for the 3 Km ring are considered at present a “high risk”.

With a 6 Km ring in an independent tunnel the efficiency of commissioning and operation would be improved and the effects of the stray fields in the linac tunnel, which could prevent the achievement of the ultra low vertical emittance [4], would be eliminated. Another advantage of the 6 Km ring with respect to dogbone is that space charge effects are reduced [6].

The work to compare the different configurations is still in progress. Some of the participants have expressed the statement that the 6 Km ring can fulfil the requirements of their specific task (for example task1 - Acceptance [11]).

On the other hand there are some tasks (in particular e-cloud [8], Ion Effects [9] and Classical Instabilities [5]) that have a crucial dependence on bunch distance and current. The results of these task forces will be crucial for the choice of the ring length. A longer ring, with larger bunch distance and lower current, would be more relaxed for e-cloud and other instabilities.

It has also been proposed to build two 6 Km rings in the same tunnel (stacked vertically as, for example, at PEPII) to provide adequate bunch spacing.

Further studies are needed to make a firm decision on the circumference.  


1)   Summary of first week – 8/19/05

2)   Parameters Megatable

3)   Lattices

4)   Acceptance

5)   Emittance

6)   Classical Instabilities

7)   Space charge

8)   Kickers & Instrumentation

9)   e-cloud

10) Ion Effects

11) Cost Estimates

12) TF1 Plans - Acceptance issues

13) TF2 Plans – Low Emittance Tuning

14) TF3 Plans – Classical Collective Effects

15) TF4 Plans – Space Charge

16) TF5 Plans – Kickers

17) TF6 Plans – Electron Cloud

18) TF7 Plans – Ion Effects

19) TF8 Plans – Cost Estimates

20) TF9 Plans – Ploarization Preservation

21) WG3b Parallel Session Schedule

22) Question Responses