CLIC meeting minutes - 30 April 2004

Maxim presented the results for the 360m circumference DR with 76 wigglers of 2m each in the two straight sections. The wiggler period has been reduced from 20 (very conservative approach) to 10cm. This significantly improves the emittances, for example with 3x10⁹ particles and 1.1% coupling: γεx = 500nm, γεy = 5.5nm, γmc²σ_sσ_ΔE/E = 4710eVm. With smaller coupling, also the vertical design emittance can be reached, at the expense of slightly higher longitudinal ε. So for the first time, the nominal parameters have been reached!
The equilibrium emittances are reached after 10ms, allowing for a repetition frequency of 900Hz with 9 trains.
The present alignment tolerances are very tight due to the strong sextupoles, and Maxim is working on a modified optics.

copy of Maxim's transparencies (pdf format)

Potential of Non-Standard Emittance Damping Schemes for Linear Colliders

Abstract:
The potential of various non-standard schemes for producing low-emittance electron/positron beams in a linear collider was estimated and their projected performance compared with that achieved by the present design of the CLIC damping ring. The options considered include the use of rf-wigglers and the integration of radiation damping into the linac.

Frank showed studies for rf wigglers/undulators and s.c. wigglers in the linac he had presented at the ATF colloboration meeting and APAC.
High field and short wiggler period is desirable to obtain small emittances, but conventional magnets have smaller fields for smaller periods. If an rf wiggler is used, one can get very short periods of 1/2 the rf wavelength (for a counter-propagting wave). A prototype rf wiggler was first built and operated by Shintake in 1982/83.
Due to rf power limitations (~200MW required), such a device might have to be operated as an rf undulator. Replacing the wigglers in last year's DR design, one gets results comparable to the conventional case (20cm period).
The second approach is damping with s.c. wigglers in the linac, with the advantages of negligible IBS and no quantum excitation contribution from the arcs, at the expense of additional linac length and rf power. An example for a linac wiggler of 2x2.6km total length shows that the small design emittances can be obtained.

Another possibility was proposed to combine a conventional DR with relaxed parameters with additional s.c. linac wigglers of much shorter length.

Agenda:	The Equilibrium Emittances of the CLIC Damping Ring with Short Period Wigglers, Potential of Non-Standard Emittance Damping Schemes for Linear Colliders
Speakers:	Maxim Korostelev, Frank Zimmermann