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Electrophoretic and diffusional movements of concanavalin A (Con A) receptors and acetylcholine (ACh) receptors in the plane of the plasma membrane of mononucleate, spherical Xenopus myoblasts were studied by microfluorimetry and iontophoresis. We found that (a) a uniform electric field of 10 V/cm applied along the cell surface produces a partial accumulation of both types of receptors toward the cathodal pole of the cell within 30 min: (b) post-field relaxation of the culture results in the complete recovery of the uniform distribution of the Con A receptors within 10 min; and (c) in contrast to the Con A receptor in general, accumulation of ACh receptors by the electric field results in the formation of stable, localized receptor aggregates. Theoretical analyses were carried out for the distribution of charged membrane receptors at equilibrium between electrophoresis and diffusion, and for the rate of back diffusion after the removal of the field. These analyses indicated that, at 22 degrees C, the average electrophoretic mobility of the electrophoretically mobile population of the Con A receptors is about 1.9 X 10(-3) micron/s per V/cm, while their average diffusion coefficient is 5.1 X 10(-9) cm2/s.

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We report the results of observations of a new regime of ion instabilities at the Advanced Light Source (ALS). With artificially increased pressure and gaps in the bunch train large enough to avoid multiturn ion trapping, we observed a factor of 2 -3 increase in the vertical beam size along with coherent beam oscillations which increased along the bunch train. The observations are qualitatively consistent with the "fast beam-ion instability" [T. O. Raubenheimer and F. Zimmermann, Phys. Rev. E 52, 5487 (1995) Ion trapping has long been recognized as a potential limitation in electron storage rings. The ions, generated by beam-gas collisions, become trapped in the negative potential of the beam and accumulate over multiple beam passages. The trapped ions are then observed to cause a number of deleterious effects such as an increasing beam phase space, a broadening and shifting of the beam transverse oscillation frequencies (tunes), collective beam instabilities, and beam lifetime reductions [1][2][3]. All of these effects are of concern for the next generation of accelerators, such as the B factories or damping rings for future linear colliders, which will store high beam currents with closely spaced bunches and ultralow beam emittances.One of the standard solutions used to prevent ion trapping is to include a gap in the bunch train which is long compared to the bunch spacing. In this case, the ions are first strongly focused by the passing electron bunches and then over focused in the gap. With a sufficiently large gap, the ions can be driven to large amplitudes, where they form a diffuse halo and do not affect the beam.In this paper, we describe experiments studying a new regime of transient ion instabilities that was predicted to arise in future electron storage rings [4,5] and linacs with bunch trains. These future rings and linacs, which will be operated with higher beam currents, small transverse beam emittances, and long bunch trains, will use ion clearing gaps to prevent conventional ion trapping. But, while the ion clearing gap may suppress the conventional ion instabilities, it will not suppress a transient beamion instability, where ions generated and trapped during the passage of a single train lead to a fast instability. While both conventional and transient ion instabilities have the same origin, namely, ions produced by the beam, they have different manifestations and, more importantly, the new transient instability can arise even after the conventional ion instability is cured.In many future rings, this transient instability is predicted to have very fast growth rates, much faster than the damping rates of existing and proposed transverse feedback systems, and thus is a potential limitation. To study this instability at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory, we intentionally added helium gas to the storage-ring vacuum system until the residual gas pressure was increased from the nominal value of 0.25 nTorr by about 2 orders of magnitude. This brought the predicted...

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A highly accurate self-consistent particle code to simulate the beam-beam collision in e 1 e 2 storage rings has been developed. It adopts a method of solving the Poisson equation with an open boundary. The method consists of two steps: assigning the potential on a finite boundary using Green's function and then solving the potential inside the boundary with a fast Poisson solver. Since the solution of Poisson's equation is unique, our solution is exactly the same as the one obtained by simply using Green's function. The method allows us to select a much smaller region of mesh and therefore increase the resolution of the solver. The better resolution makes more accurate the calculation of the dynamics in the core of the beams. The luminosity simulated with this method agrees quantitatively with the measurement for the PEP-II B Factory ring in the linear and nonlinear beam current regimes, demonstrating its predictive capability in detail.