Beam-induced Signals Research Articles

基于束流位置探测器的束团长度测量

This paper summarizes the results of the study of a bunch length monitor based on the button BPM (Beam Position Monitor). The monitor consists of a BPM installed on the beam pipe and a spectrum analyzer. We use the button-BPM's button pickups as the electrodes to pick up the signal. The bunch length can be derived from the spectrum of the beam-induced signal got by the spectrum analyzer. We show the theoretical results and the simulations performed by CST

Determination of field amplitude and synchronous phase using the beam-induced signal in an unpowered superconducting cavity

At the Spallation Neutron Source superconducting linear accelerator, RF fields excited by a pulsed, high-intensity drifting beam in an unpowered superconducting cavity are measured with the cavity control circuit, in order to determine the synchronous phase and to calibrate the pickup probe of the cavity. Measurement errors arising from noise and from the excitation of other pass-band modes in the cavity are analyzed. The phase change due to beam acceleration as well as due to cavity detuning is computed with a model which is described in this paper. Simulation results show excellent agreement with measurements performed in drifting beam experiments. The measured cavity synchronous phase and accelerating gradient determined from the drifting beam measurements are in good agreement with those obtained from a time-of-flight based technique.

Superconducting resonator used as a beam phase detector

Beam-bunch arrival time has been measured for the first time by operating superconducting cavities, normally part of the linac accelerator array, in a bunch-detecting mode. The very high $Q$ of the superconducting cavities provides high sensitivity and allows for phase-detecting low-current beams. In detecting mode, the resonator is operated at a very low field level comparable to the field induced by the bunched beam. Because of this, the rf field in the cavity is a superposition of a ``pure'' (or reference) rf and the beam-induced signal. A new method of circular phase rotation (CPR), allowing extraction of the beam phase information from the composite rf field was developed. Arrival time phase determination with CPR is better than 1\ifmmode^\circ\else\textdegree\fi{} (at 48 MHz) for a beam current of 100 nA. The electronics design is described and experimental data are presented.

Comparison of calculated, measured, and beam sampled impedances of a higher-order-mode-damped rf cavity

Accelerating structures with damped higher-order modes (HOMs) have been the focus of many studies over the past decade. This report compares the results of numerical simulations of damping of HOMs using a new calculation technique applied to the case of the PEP-II rf cavity. We compare these results using this technique, which was not yet developed at the time of the original design, with bench and beam-based measurements of the HOM damping. These results show agreement with bench measurements of the shunt impedances of the strongest HOMs as well as measurements of the beam-induced signals on cavities installed in PEP-II.

Spatially resolved detection of phase locking in Josephson junction arrays

Abstract Two-dimensional arrays of shunted Nb/AlOx/Nb Josephson junctions have been investigated. Shapiro steps in the current–voltage ( I – V ) curve of an on-chip detector junction can be used to sense mutual phase locking of the array junctions. By scanning the array with a low-power electron beam, the phase locked junctions remain locked, whereas the unlocked junctions generate a beam-induced additional voltage drop along the array. In regions of the array’s bias current where pronounced Shapiro steps occur in the detector’s I – V curve, practically no array junction generates a beam-induced voltage signal, thus indicating complete mutual locking. For other bias currents of the array with less than maximum detected power, some of the junctions generate beam-induced signals, and can be identified as being non-locked. Our investigations allow a detailed and spatially resolved analysis of mutual phase locking in arrays of Josephson junctions. Moreover, the results obtained with autonomous arrays are compared to experiments performed with injection locked arrays.

Nonintrusive position measurement of magnetically scanned ion beams

In ion implantation systems using a hybrid magnetic-mechanical scanning, the scan along the implant disc radius is realized by magnetic scanning of an ion beam at an average frequency of 0.1 Hz. To achieve a uniform implant, a relationship has to be known between the scanning magnetic field and the resulting ion beam position. A measuring system has been developed to estimate the lateral position of an ion beam without interfering physically with the beam. The beam position is inferred from two random signals induced by the beam on two sensing electrodes, obtained by splitting a bias ring of the implanter's Faraday system. The beam-induced signals are processed digitally and the position estimate, represented by a 9-bit number, is updated at 1.5 ms (or 12 ms) intervals. Preliminary tests have demonstrated that the technique presented can be exploited for adaptive shaping of a current waveform driving the scan magnet.

Phase measurement and control of pulsed charged beams

A method and system is described that measures and controls the arrival phase of a pulsed ion beam. The repetitive beam pulse passes through and resonantly excites a high- Q structure, tuned to the beam repetition frequency or to a higher harmonic thereof. A reference signal of the same frequency is phase-flipped from −90° to +90° t a high audio rate and also coupled to the resonator. The low-level output signal, comprised of the vector sum of the beam-induced signal and the phase-flipped reference, is amplified and processed to obtain phase information. The system is usable for beams with average currents as low as a few picoamperes and can be used in the measurement and control of pulsed beam experiments involving timing, the control of beam phase for rf particle accelerators and the nondestructive measurement of beam energy.

On scanning electron microscope conduction-mode signals in bulk semiconductor devices: annular geometry

Beam-induced signals in the scanning electron microscope provide a means of studying the bulk of semiconductors. This paper develops a two-dimensional theory to predict the spatial distribution of the signal in annular devices and it is shown that geometry and field-dependent contrast can occur. These signals provide a means of studying crystal defects and resistivity variations. Experiments on planar geometry GaAs transferred electron devices support the theoretical predictions.