Superconducting RF control issues at CESR

Abstract

RF controls of the superconducting cavities have to deal with an extremely heavy beam loading in CESR. A feature of the CESR RF system operation is that superconducting cavities are under-coupled at high beam currents. This means that the RF system operates very close to Robinson stability limit. Analysis of the steadystate stability of the CESR RF system and the results of measurements with beam are presented. Two more SRF cavities will be installed in CESR for short bunch operation. This will tighten tolerances to RF signal regulation errors. New control electronics is under development to meet the challenge.

Superconducting RF system upgrade for short bunch operation of CESR

“…Then for V 0 = 1.67 MV, I 0 = 100 mA, and Q l = 1×10 6 one can calculate δV/V 0 = 1.5×10 -3 and δψ = 0.0044° for beam current of 360 mA. This modulation is much smaller than typically observed in CESR and will not cause any degradation of the RF system performance [5].…”

“…Even one transmitter is more than adequate to supply necessary power. On the other hand, such a low power demand at very high voltage will present a problem for RF regulation loops [5]. To ease this problem we propose to operate two out of six cavities in active mode and the other four in passive mode.…”

Microphonics detuning in the 500 MHz superconducting CESR cavities

“…This is especially true for high-Q superconducting cavities. Though this noise was an issue when the very first s.c. cavity has been installed in CESR [3], it was drastically reduced later and is not considered a limiting factor in the present configuration of the CESR RF system with external cavity quality factors of approximately ¢ £ ¤ § ¦ . However, as CESR is being modified for operating at lower energies, there will be changes in the RF system parameters and configuration [4].…”

Using passive cavities for bunch shortening in CESR

“…Requirements to the CESR-c RF system were analyzed elsewhere [2,4]. Table 2 compares RF parameters for different number of active and passive cavities and different cavity coupling at 1.88 GeV.…”

“…For CESR-c this means operating at high values of Q ext , which will significantly increase the beam loading parameter Y. In the past CESR typically operated with Y ≈ 9, which is considered heavy beam loading [4]. Using two passive cavities will alleviate the beam loading problem as well as significantly reduce power consumption (third and forth sets of parameters in Table 2).…”