[en] A novel tuner has been developed by the Omega-P company to achieve fast control of the accelerator RF cavity frequency. The tuner is based on the ferroelectric property which has a variable dielectric constant as function of applied voltage. Tests using a Brookhaven National Laboratory (BNL) 1.3 GHz electron gun cavity have been carried out for a proof-of-principle experiment of the ferroelectric tuner. Two different methods were used to determine the frequency change achieved with the ferroelectric tuner (FT). The first method is based on a S11 measurement at the tuner port to find the reactive impedance change when the voltage is applied. The reactive impedance change then is used to estimate the cavity frequency shift. The second method is a direct S21 measurement of the frequency shift in the cavity with the tuner connected. The estimated frequency change from the reactive impedance measurement due to 5 kV is in the range between 3.2 kHz and 14 kHz, while 9 kHz is the result from the direct measurement. The two methods are in reasonable agreement. The detail description of the experiment and the analysis are discussed in the paper

[en] The aim of the paper is to describe the status and prospects of magnicons - devices with electron beam modulation by circular scanning. The parameters of developed magnicons are not worse than parameters of the best modern devices (gyro-klystrons). The magnicon ability to operate with varying loads without circulator using ensures effective application of magnicons in large accelerating complexes

[en] We report on the progress made during the initial stage of our research to study charging rate and charge distribution in a thin walled dielectric wakefield accelerator (DWA) from a passing charge bunch and the physics of conductivity and discharge phenomena in dielectric materials useful in accelerator applications. The issue is the role played by the beam halo and intense wakefields in charging the dielectric, possibly leading to undesired deflection of charge bunches and degradation of the dielectric material: the effects that may grow over many pulses, albeit perhaps differently at different repetition rates. During the initial stage of development, a microwave apparatus was built and signal processing was developed to observe time-dependent charging of dielectric surfaces and/or plasmas located on or near the inner surface of a thin-wall hollow dielectric tube. Three frequencies were employed to improve the data handling rate and the signal-to-noise. The test and performance results for a plasma test case are presented; in particular, the performance of the test unit shows capability to detect small changes ~0.1% of a dielectric constant, which would correspond to the scraping-off of only 0.3 nC to the walls of the dielectric liner inside the cavity from the passing charge bunch.

[en] We report progress in the development of a nondestructive technique to measure bunch rms-length in the psec range and below, and eventually in the fsec range, by measuring the high-frequency spectrum of wake field radiation which is caused by the passage of a relativistic electron bunch through a channel surrounded by a dielectric. We demonstrate both experimentally and numerically that the generated spectrum is determined by the bunch rms-length, while the choice of the axial and longitudinal charge distribution is not important. Measurement of the millimeter-wave spectrum will determine the bunch rms-length in the psec range. This has been done using a series of calibrated mesh filters and the charge bunches produced by the 50MeV rf linac system at ATF, Brookhaven. We have developed the analysis of the factors crucial for achieving good accuracy in this measurement, and find the experimental data are fully understood by the theory. We point out that this technique also may be used for measuring fsec bunch lengths, using a prepared planar wake field microstructure

[en] The intrapulse phase instability of the 34 GHz magnicon that will be used as a high-power RF source for the Yale project 'Weakly interacting sub-eV particle searches' was measured using a heterodyne technique. The measured intrapulse RMS phase deviation averaged over a series of runs is approximately 22.1±6.8 degrees. This is shown to be due mainly to magnicon modulator ripples. The ripples cause variable beam loading of the magnicon cavities resulting in frequency modulation of the magnicon output signal. Simulation of the beam dynamics (considering variations of the modulator voltage and the magnicon gun current) demonstrates a good agreement with the measured RMS value of the phase deviation for the magnicon steady-state regime. Measured RMS values of the phase deviations for similar parameter sets demonstrate good repeatability from one run to another one.