Measurement of Electron Cloud Density Using Microwaves February 28, 2014 John Sikora, Stefano De Santis and Kiran Sonnad

Microwave Measurements Microwave Measurement and Simulation Resonant Beam-pipe Vorpal Simulation Effect Due to Reflections Periodic EC Density Produces Phase Modulation Standing Wave Resonant Frequency Shift Cyclotron Resonance February 28, 2014

Resonant Microwaves The Present Understanding of Hardware and Analysis The original microwave transmission technique is actually difficult to perform in practice because of reflections and resonances of microwaves in the beam-pipe. Analysis that is based on the resonant microwave response of the beam-pipe has shown good agreement with the overall shape of the measured spectra produced by a periodic EC density. Bead-pull measurements on beam-pipe have been very useful in understanding the distribution of the resonant fields. These measurements have been essential in showing the mitigating effect of titanium nitride on EC density using the microwave technique. Measurements using phase detection (observing the phase shift on an oscilloscope) have been made. Deconvolution techniques can be used to extract the changing EC density from the resonant response. REU students have made significant contributions -- Benjamin Carlson (REU 2009) Fourier analysis, frequency shifts due to a plasma, evanescent resonances; Kenneth Hammond (REU 2010) waveguide resonances and simulations; Danielle Duggins (REU 2012) bead pull measurements and waveguide simulations; Alister Tencate (REU 2013) multiple sideband analysis with convolution. February 28, 2014

Microwave Simulations The Present Understanding of Microwave Simulations Significant contribution from undergrad students (2 REU and one Cornell student). Worked in collaboration with Seth Veitzer, using Vorpal/VSim simulation program. Simulated traveling wave propagation, and contamination of measurement due to reflection (Ken Hammond), Standing waves with partial reflection and shift in resonant frequency due to clouds, evenascent waves (Robert Schwartz) Progress has been made in analytic derivation of wave dispersion relationship. Several results of effect from external fields, (dipole and wiggler). Studied wave propagation through grooved chambers at L3, to complement bead pull measurements. (Danielle Duggins) Submitted paper to NIM. Referees have suggested minor changes. February 28, 2014

Resonant Microwaves Topics for Future Development and Measurements Further development of the analysis and confirming this with special measurements, especially the effects of AM and FM and how they contribute to the spectrum. Understand asymmetric sidebands. Continuing the incorporation of EC simulation results in data analysis and the comparison of microwave measurements with other techniques. Use bead-pull and other techniques to measure the microwave distributions. “Create” resonances through chamber design or the insertion of masks (gaskets?) Hardware development of the phase detection for improved signal to noise. Improve the accuracy of Q measurements – automate. Measurements and analysis that includes magnetic fields: Dipole fields, including cyclotron resonance (are we actually increasing the EC density?) Quadrupole fields, including further attempts to measure trapped cloud (using phase detection). February 28, 2014

Microwave Simulations Topics for Future Simulation Work Continue with analytic derivation of dispersion relationships : propagation in the presence of external magnetic fields. Continue with simulation of wave propagation in presence of external magnetic fields. See if time resolved measurements can be made by sending pulsed signals. February 28, 2014

Microwave Measurements Plans for Specific Measurements Distinguish PM and FM contributions through spectral envelope. (FM goes as 1/m2) Cyclotron resonance: Two hardware setups on one (Chicane) chamber – one to excite the cyclotron resonance the other to measure EC density (at a different frequency). Phase detector in quadrupole with higher signal, dump beam and look for trapped cloud. Resonance measurement in a dipole magnet (14E?) versus beam current February 28, 2014