KEK, Ibaraki
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
This talk will review the impedance and beam instabilities study for the J-PARC RCS and MR rings. RCS is possibly the first synchrotron employing a massive amount of ceramic chambers to reduce the eddy current effects on the chambers. The resulting RF shields on the chambers to reduce the beam impedance required new considerations on impedance calculation procedure. MR, on the other hand, uses conventional stain-less steel chambers due to its relatively small rep rate (0.3Hz), but then induces huge resistive-wall impedance. The recent study of resistive-wall impedance shows that the actual impedance will be even larger than the calculated one using the conventional formula, when the typical skin depth becomes comparable to the thickness of the chamber. In my talk, I will also touch on the issues of kicker impedances and their possible cures.
Fermilab, Batavia, Illinois
If large enough the beam space charge strongly affects the beam stability in a circular accelerator. It results in a separation of coherent and incoherent tunes and, consequently, instability. Effects of space charge on the beam stability are considered in application to Fermilab Booster, Main injector and Recycler.
ORNL, Oak Ridge, Tennessee
Beam phase synchronous oscillations and the damping curves of the SNS linac are investigated with linac models and measured with all the linac beam phase monitors. It provides a useful beam diagnostic solution to detect RF cavity phase and/or field amplitude errors in the linac with many independently phased cavities. And the phase damping curves predicted in the longitudinal model could also be utilized to analyze the longitudinal lattice of the superconducting linac, in which each cavity gradient varies widely from the nominal design and smooth the beam longitudinal focusing is very important to preserve beam emittance.
ORNL, Oak Ridge, Tennessee
UW-Madison, Madison, Wisconsin
An analog wideband feedback system for damping e-p instabilities has been demonstrated at the PSR at Lansce. A mixed signal system is being developed and deployed at SNS. The status and expected performance of the of the system is discussed.