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The present paper investigates the characteristics of the supersonic turbulent flow in a wavy channel by direct numerical simulations. The Mach number, based on the bulk velocity and sound speed at the wall, is 1.5 and the Reynolds number, based on the bulk velocity, the channel half‐width and the kinetic viscosity at the wall is 3 460. The wave amplitude to wavelength ratio is 0.05. To validate the numerical algorithms, a weak compressible flow at Mam = 0.33 is also simulated and the results agree well with available experimental measurements and results of DNS. The statistic quantities and flow structures for the supersonic flow are compared with those for the low Mach number case. It is found that, the statistic quantities profile for supersonic flow differs substantially from profile for the incompressible case as the appearance of the shock waves and their interaction with the turbulent flow field.

Beam‐gas collision created experimental background, i.e., singles, has affected heavy ion and polarized proton operations in Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The gas molecules in interaction region are mainly caused by the electron induced gas desorption, and the electrons are produced from the beam induced electron multipacting, or called electron cloud. The background has a dependence on the usual electron cloud related parameters, such as the bunch intensity, bunch spacing, and the solenoid field. With the RHIC upgrade plan, the experimental background may become a luminosity limiting factor. Mitigations are discussed.

During Run‐8, the Relativistic Heavy Ion Collider (RHIC) provided collisions of spin‐polarized proton beams at two interaction regions. Physics data were taken with vertical orientation of the beam polarization, which in the “Yellow” RHIC ring was significantly lower than in previous years. We present recent developments and improvements as well as the luminosity and polarization performance achieved during Run‐8, and we discuss possible causes of the not as high as previously achieved polarization performance of the “Yellow” ring.

Electron cloud and ion desorption are currently intensity limit of several hadron machines in operation, and possibly of concern for several accelerators in construction and planning. In this summary, the background, the progress, and the working session discussion of this aspect are reported.

The RHIC warm section electron cloud is distinguished from normal short bunch electron cloud, observed in many machines, by the much longer bunch spacing and non‐uniform distribution in the ring. It is suspected that the beam halo scraping produced positive ions may help secondary electrons to stay longer. Local desorption leading to more residual gas being ionized by the beam may be important too. Anti‐grazing ridges are designed to counteract these mechanisms. This article reviews the RHIC warm section electron cloud, the beam scraping effect, and the test of anti‐grazing ridges.

A proposed new heavy ion preinjector for RHIC is described. The progress made at BNL on the development of an Electron Beam Ion Source (EBIS) has increased our confidence that one can build a preinjector meeting RHIC requirements using an EBIS producing intermediate charge state heavy ions. A new RFQ and Linac will be required to accelerate beams from this source to an energy sufficient for injection into the AGS Booster. These are both straightforward devices, very similar to ones already in operation at other laboratories. Injection into the Booster will occur at the same location as the existing heavy ion injection from the Tandem Van de Graaff.

The technique of laser-generated and laser-detected Lamb waves is a powerful tool for characterizing elastic property of plates. However, the transient waveforms depend strongly on the longitudinal acoustic wavelength L and the plate thickness H. For a thick plate (bulk material), L/H≪1, a typical waveform consists of arrivals of longitudinal, shear, and surface wave pulses, if a detecting position is localized at the same side as the exciting laser beam. For a very thin plate L/H≫1, the transient waveform is characterized by the lowest Lamb wave modes, i.e., the first arrival of the spike signal from the lowest symmetric mode, and higher frequencies and the later lower frequency signal of the lowest antisymmetric mode. However, for thicker plates (H∼2.0 mm), the transient waveforms excited by a laser pulse are much more complicated, because of contributions of the higher-order Lamb wave modes, due to lower cut-off frequency. Thus, it is necessary to clarify theoretically dynamic response of the thicker c...

The frequency bandwidth of photothermal technique for thermal conductivity depth profiling has been studied, which is based on an iterative numerical algorithm for inverse calculation of inhomogeneous thermal conductivity depth profiles of solid samples. This inversion algorithm should require a sufficient frequency bandwidth since the numerical experiments have demonstrated that systematic errors will occur in the inversion from insufficient data. According to the thermal wave propagation property, at low frequency range, the thermal wave can penetrate into deep region of the sample, but it will depress spatial resolution because of its long thermal wavelength. Nevertheless, lack of low frequency the detected information will cause the derivation of the depth profiling in the deep part. On the other hand, with high frequency, the thermal wave only can penetrate into shallow regions near the surface of the sample, although the spatial resolution will be intensified because of its short thermal wavelength....

The impedance and beam instability issues of the SNS storage ring is reviewed, and the effort toward solutions at the BNL is reported. Some unsettled issues will be raised, indicating the direction of planned works.

The impedance working group was charged to reply to the following 8 questions relevant to the design of high-intensity proton machines such as the SNS or the FNAL driver. These questions were first discussed one by one in the whole group, then each ne of them assigned to one member to summarize. On the lst morning these contributions were publicly read, re-discussed and re-written where required—hence they are not the opinion of a particular person, but rather the averaged opinion of all members of the working group. (AIP)

In this article the fundamentals of spectrum analysis in beam diagnostics is discussed, where several representative particle motions in a circular accelerator are considered. The general properties of the Fourier transform are introduced first, then the coasting and the bunched beam motions in longitudinal and transverse planes are presented for single particle, multiple particle, and Schottky noise cases, respectively. To demonstrate the properties of the beam motion spectrum, time domain function are generated, and then the associated spectra are calculated and plotted.

For beam control during acceleration, it is conventional to derive the frequency from an external reference, be it a field marker or an external oscillator. In addition, phase and radius feedback loops are also provided to ensure the phase stability, radial position and emittance integrity of the beam. The open and closed loop behaviors of both feedback controls and their responses under the possible frequency, phase and radius errors are derived from fundamental principles and equations. The stability of the loops is investigated under a wide range of variations of the gain and time delays. Actual system performance of the AGS Booster is analyzed and compared with commissioning experiences. Such analysis is useful for setting design criteria and tolerances for new proton synchrotrons.