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Minutes of the CLIC Meeting - 14 January 2005


Agenda:
Beam Emittances and Damping Time Measurements at ATF Damping Ring
Coherent Synchrotron Radiation and Touschek Scattering in the CLIC Damping Ring
Speakers:
M.Korostelev,  F.Zimmermann


Abstract

Beam Emittances and Damping Time Measurements at ATF Damping Ring  / Maxim Korostelev


Beam emittances and damping times measurement at ATF with four wigglers operation was done in December 2004. In single bunch mode the transverse equilibrium beam size and beam length were measured by SR interferometer. Then  measurements of beta and dispersion functions were carried out at the location of the SR monitor. In that way the beam emittances were calculated. The damping time was measured by the streak camera.

Coherent Synchrotron Radiation and Touschek Scattering in the CLIC Damping Ring / Frank Zimmermann

The unprecedentedly high charge density and short bunch length in the CLIC damping ring could aggravate the effects of coherent synchrotron radiation and Touschek scattering. The Touschek lifetime can now be computed by a MADX development version for the exact ring optics, using a formalism due to Piwinski. A novel programme by K. Yokoya and T. Agoh at KEK allows – for the first time – simulations of the microwave instability caused by coherent synchrotron radiation in a lepton storage ring. Both effects are found to be surprisingly benign for the CLIC parameters and the present CLIC damping-ring lattice.


Maxim described the ATF damping ring and presented emittance and damping time measurements.
Dispersion measurements were performed by changing the RF frequency. The vertical dispersion was corrected from ~10 to 5mm using SAD calculations. Beta functions were measured by gradient strength changes. The damping times were measured by a streak camera. The results with wiggler magnet operating were: τx=7ms, τy=22ms, τz=7ms; without wiggler the values were:  τy=27ms, τz=11.4ms,. These values were compared to MAD calculations. While the emittance and the damping time for the vertical plane agrees well between model and measurement, the MAD predictions for the horizontal emittance and horizontal and longitudinal damping times are a factor 2 higher than the measurements.
Maxim also showed his damping ring design for the ILC where he could obtain a factor 2 smaller horizontal emittance compared to previous designs.
It was mentioned that ATF is usually run without the wigglers and the reason for this was not obvious to us.
copy of his transparencies (pdf format)

After recapitulating the Touschek effect, Frank presented recent results about Touschek scattering in the CLIC DR. The effect had been implemented in MAD-X and simulations show that the Touschek lifetime in the CLIC DR has a comfortably high value of 4.2 hours, even higher than in ILC.
Also for coherent synchrotron radiation (CSR), a new tracking code including CSR has been developed, taking into account the shielding effect by vacuum chamber geometry. It differs substantially from the free space solution and for small wave numbers, the CSR impedence is strongly suppressed. For the CLIC DR with 2cm vacuum chamber radius, the tool predicts a bunch lengthening by only 5% and no momentum spread increase, for 4mm the bunch length would grow by ~20%. So the CSR effect for the present CLIC DR parameters is surprisingly benign.
copy of his transparencies (pdf format)

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Frank Tecker  - Last updated  14-01-2005