Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
LBNL, Berkeley, California, USA
ISU, Pocatello, Idaho, USA
A change in electron cloud (EC) density will change the resonant frequency of a section of beam-pipe. With a fixed drive frequency, the resulting dynamic phase shift across the resonant section will include the convolution of the frequency shift with the impulse response of the resonance. The effect of the convolution on the calculated modulation sidebands is in agreement with measured data, including the absolute value of the EC density obtained from ECLOUD simulations. These measurements were made at the Cornell Electron Storage Ring (CESR) which has been reconfigured as a test accelerator (CesrTA) with positron or electron beam energies ranging from 2 GeV to 5 GeV.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
LBNL, Berkeley, California, USA
The resonant TE wave technique can use modulation sidebands for the calculation of electron cloud (EC) density. An alternative is to mix the drive and received signals to form a phase detector. Using this technique, the phase shift across the resonant section of beam-pipe can be observed directly on an oscilloscope. The growth and decay of the EC density has a time constant of roughly 100 ns, while the measured phase shift will include a convolution of the EC density with the impulse response of the resonant beam-pipe - typically about 500 ns. So any estimate of the growth/decay of the cloud requires deconvolution of the measured signal with the response time of the resonance. We have also used this technique to look for evidence of EC density with a lifetime that is long compare to the revolution period of the stored beam. These measurements were made at the Cornell Electron Storage Ring (CESR) which has been reconfigured as a test accelerator (CesrTA) with positron or electron beam energies ranging from 2 GeV to 5 GeV.
LBNL, Berkeley, California, USA
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
The evaluation of the electron cloud density in storage rings by measuring its effects on the transmission of electromagnetic signals across portions of the beampipe is a widely used technique and the most suited for measurements over extended regions. Recent results show that in a majority of cases the RF signal transmission takes place by coupling to standing waves excited in the vacuum chamber. In such a case the effect of a varying cloud density is a simultaneous amplitude, phase and frequency modulation of a fixed frequency drive signal. The characteristics of the modulation depend not only on the cloud density values and spatial distribution, but also on its temporal evolution and on the damping time of the standing waves. In this paper we evaluate the relationship between measured modulation sidebands amplitude and the electron cloud density when cloud and electromagnetic resonance rise and fall times are of the same order of magnitude, as it is the case in the accelerators where we have conducted our experiments.