arXiv subjects

Xi Yang

Publications and source records attributed to Xi Yang.

252 records · Page 14Linked to original sources

arXiv2005

Temperature Dependence of Piezoelectric and Electrostrictive Properties in a PBN:65 Morphotropic Phase Boundary Thin Film

We used an optical reflection method to measure the temperature-dependence of the piezoelectricity, electrostriction and time constant of a morphotropic phase boundary (MPB) thin film. We obtained the piezoelectric constant and the electrostrictive constant as a function of temperature by curve fitting the experimental data. We also obtained the time constant as a function of temperature and applied voltage. An abnormal behavior of the strain that was larger at 275 K than at 285 K was observed. This observation was also consistent with the minimal hysteresis behavior of the time constant at 275 K. We provided a possible explanation for this observation.

cond-mat.mtrl-sci↗

arXiv2005

Booster 6-GeV Study

Since a wider aperture has been obtained along the Booster beam line, this opens the opportunity for Booster running a higher intensity beam than ever before. Sooner or later, the available RF accelerating voltage will become a new limit for the beam intensity. Either by increasing the RFSUM or by reducing the accelerating rate can achieve the similar goal. The motivation for the 6-GeV study is to gain the relative accelerating voltage via a slower acceleration.

physics.acc-ph↗

arXiv2005

Reshape of the Bunch-by-bunch BPM Signal to a Turn-by-turn Matrix during the Fast RF Frequency-sweeping Time in Booster

The bunch-by-bunch BPM signal array has to be reshaped into a turn-by-turn (TBT) matrix in order to make the TBT beam position information of a single bunch available for further data analysis, such as via the Fourier transform to obtain the synchrotron tune and betatron tune, etc. Since the RF frequency sweeps more than 10 MHz in the first 8 ms of a Booster cycle, the revolution time decreases more than 20%. The number of data points for each Booster turn (BT) should be varied in the same pace with the revolution time since the sampling rate of a digital oscilloscope is usually fixed. And this can be done by pre-determining the relationship between the RF frequency and the time in a cycle via the curve fit.

physics.acc-ph↗

arXiv2005

Improvement in RF Curves for Booster Running at High Intensities

A feed-forward ramp can be implemented in Booster to compensate the beam energy loss at different beam intensities for the purpose of minimizing the radial error signal. This can be done only when we have a good understanding about the dependence between the beam energy loss per turn and the beam intensity experimentally. Besides, based upon this understanding we can predict the required accelerating voltage at the transition crossing for different beam intensities, which can be extremely helpful for Booster running at higher beam intensities than ever before.

physics.acc-ph↗

arXiv2005

Booster High-level RF Frequency Tracking Improvement Via Bias-Curve Optimization

It is important to improve the frequency tracking between the RF drive and the cavity field for the purpose of reducing longitudinal phase oscillations and increasing the effective accelerating voltage. And this is especially beneficial for Booster running at higher intensity with smaller beam emittance. Optimizing the bias supply current curve for the ferrite tuners can reduce the phase error between the RF drive and the cavity field, and also improve the HLRF-to-LLRF frequency tracking efficiency.

physics.acc-ph↗

arXiv2005

Numerical Reconstruction of the Linac Beam De-bunching in the DC-operated Booster

It is difficult for us to measure the Booster ring impedance up to the GHz range due to the instrumentation limit. Since the de-bunching process in the Linac to Booster transfer is determined by the complex impedance of the Booster ring, one can obtain an impedance model, which has the best match to the machine impedance, just by searching the optimal fit between the simulated and measured turn-by-turn resistive wall signal (RWS).

physics.acc-ph↗

arXiv2005

Analytical Solution for BPM Reading the Multi-bunch Average in Booster

The BPM system in Booster only can provide the beam position from the average of about 15 bunches due to the electronic limitation. Numerically calculating the difference made by this average can nearly give all the information, which is needed for extrapolating the BPM data. It is still useful to derive the analytical expression for the BPM reading, which can be helpful in getting the insight for the BPM system optimization.

physics.acc-ph↗

arXiv2005

Beam-Based Determination of the Offset of Booster gamma-T Quads

Twelve pulsed gamma-T quads have been installed in the Booster to provide fast transition crossing. The less time the beam stays in the non-adiabatic period near transition, the less the longitudinal emittance grows. From the past experience, the gamma-T quads are not well aligned relative to the usual closed orbit. Quad steering can cause beam loss and a dispersion wave after transition. To make the gamma-T quads routinely operational, procedures for finding the center of the beam relative to the quads and centering the beam through all of them are very important. A program, which uses the difference in the closed orbits when gamma-T quads are on and off and calculates the offsets of the beam relative to gamma-T quads, has been developed and tested. A radial orbit offset (ROF) of about 3 mm has been experimentally determined to be nearly the optimal radial position for centering the beam through all the gamma-T quads, thereby eliminating the immediate need for repositioning the quads.

physics.acc-ph↗

arXiv2005

Pulsed Laser Deposition of a PBN:65 Morphotropic Phase Boundary Thin Film with Large Electrostriction

We deposited epitaxial thin films of Morphotropic Phase Boundary (MPB) Pb0.65Ba0.35Nb2O6 (PBN:65) on MgO substrates using pulsed laser deposition. Afterwards, a novel transmission optical experiment was developed to measure the electric field-induced bending angle of the thin film sample using a divergent incident light. From which the electric field-induced strain was obtained, and it was used to calculate the electrostrictive constant of the PBN thin film. The result is 0.000875 um2/V2, and it is consistent with what we measured in the reflection experiment.

cond-mat.mtrl-sci↗

arXiv2004

Photon-induced switching and tunneling phenomna in a YBCO thin film junction

In the persistent photoconductivity (PPC) phenomenon, illumination of a YBCO thin film junction with a 1mW He-Ne laser leads to the decrease of the critical critical voltage (similar to the threshold voltage). The decrease of the critical votage was reversed by illumination with incadenscent light. The critical voltage across the junction was experimentally decreased and increased by alternating illumination between He-Ne laser and incandescent light. We also observed visible quenching of the photo-induced state using a 5mW He-Ne laser. Finally, the threshold behavior of the junction was destroyed by illuminating it with incadenscent light.

cond-mat.mtrl-sci↗

arXiv2004

Observations of magnetic field induced contraction of fission yeast cells using optical projection microscopy

The charges in live cells interact with or produce electric fields, which results in enormous dielectric responses, flexoelectricity, and related phenomena. Here we report on a contraction of schizosacchraoymces pombe (fission yeast) cells induced by magnetic fields, as observed using a phase sensitive projection image technique. Unlike electric fields, magnetic fields only act on moving charges. The observed behavior is quite remarkable, and may result from a contractile Lorentz force acting on diamagnetic screening currents. This would indicate extremely high intracellular charge mobilities. Besides, we observed a large electro - optical response from fission yeast cells.

q-bio.SC↗

arXiv2004

Indicators of the Energy Error in the Linac to Booster Transfer

The match between the Linac beam energy and the energy determined by the bending field of the Booster magnets is crucial for rf capture, beam quality, and the transmission efficiency in a Booster cycle. The observation of the injection energy match is important for injection tuning. Several signals, such as phase shift drive (PSD), radial position error (RPOS), synchrotron phase (SPD), and fast phase error (FPERR), provide consistent information on the energy match and can be used for a injection match tuning.

physics.acc-ph↗

arXiv2004

Booster Synchrotron Frequency Below Transition

The dipole mode synchrotron frequency is a basic beam parameter; it and a few similarly basic quantities measured at small time intervals serve to characterize the longitudinal beam dynamics throughout the acceleration cycle. The effective accelerating voltage, in conjunction with the amount of rf voltage required for the acceleration, is important for the estimate of the beam energy loss per turn. The dipole mode frequency can be used to obtain the effective accelerating rf voltage, providing that it can be measured precisely. The synchrotron frequency measured from the synchrotron phase detector signal (SPD) generally agrees well with calculation, and it can be applied for such purposes as inferring the effective rf voltage.

physics.acc-ph↗

arXiv2004

Implications of beam phase and RFSUM measured near transition

Understanding the transition-crossing process is crucial for improving Booster performance at high intensity. The synchronous phase appears to drop toward 90 degrees right after transition regardless of beam intensity, more so at higher beam intensity. The implication is that the effective rf voltage (RFSUM) will run into a limit right after transition when the synchronous phase reaches 90 degrees for high intensity beam. A reduction in RFSUM is also observed at the same time. Solutions, such as raising the rf voltage during the transition period or controlling the RFSUM reduction by increasing longitudinal emittance before transition, are potentially important for high intensity operation.

physics.acc-ph↗

arXiv2004

RF Bucket Reduction as an Experimental Tool for Beam Diagnostics and Manipulation

A technique using RF bucket reduction for acquiring information about the particle distribution in longitudinal phase space has been applied in the Fermilab Booster. Data sets were obtained at six important time intervals of a Booster cycle for three different beam intensities. Controlled RF bucket reduction also provides other opportunities for beam manipulation.

physics.acc-ph↗

arXiv2004

Applying Synchrotron Phase Measurement to the Estimation of Maximum Beam Intensity in the Fermilab Booster

It is important to have experimental methods to estimate the maximum beam intensity for the Fermilab Booster as objective input into long term program commitments. An important existing limit is set by the available rf power. This limit is difficult to set a priori because the real longitudinal impedance is not well known. The synchrotron phase at transition crossing was measured using both the mountain range plot and the direct phase measurement of the RF accelerating voltage relative to the beam, and results were consistent. They were applied to predict 6E12 maximum Booster beam intensity with present running conditions.

physics.acc-ph↗

arXiv2004

Stability Analysis of the Laser System for the TTF Photoinjector at Fermilab

A solid-state laser system that produces a 1MHz pulse train of 800 pulses with 18 mJ per pulse at the wavelength of 263.5 nm has been developed to meet the requirements of the TESLA Test Facility (TTF) at Fermilab and in operation since 1998.[1,2] Besides the production of high charges, high brightness electron beams, the need for high bunch charge stability requires that each laser pulse in the pulse train must have the same energy, and the energy per laser pulse should not vary significantly from shot to shot. This motivates the stability analysis of the laser system for the TTF photoinjector.

physics.acc-ph↗

arXiv2004

Experimental Estimate of Beam Loading and Minimum rf Voltage for Acceleration of High Intensity Beam in the Fermilab Booster

The difference between the rf voltage seen by the beam and the accelerating voltage required to match the rate of change of the Booster magnetic field is used to estimate the energy loss per beam turn. Because the rf voltage (RFSUM) and the synchronous phase can be experimentally measured, they can be used to calculate the effective accelerating voltage. Also an RFSUM reduction technique has been applied to measure experimentally the RFSUM limit at which the beam loss starts. With information on beam energy loss, the running conditions, especially for the high intensity beam, can be optimized in order to achieve a higher intensity beam from the Fermilab Booster.

physics.acc-ph↗