Search Results (8 total)

Studies of the longitudinal beam dynamics in the small isochronous ring (SIR) at Michigan State University revealed a fast, space-charge driven instability that did not fit the model of the negative mass instability. The observed beam behavior can be explained by the transverse horizontal component of the coherent space-charge force and its effect on the longitudinal motion. This force effectively modifies the slip factor, shifting the isochronous point and enhancing the negative mass instability. This paper presents results of numerical and experimental studies of the longitudinal beam dynamics in SIR and proposes a simple analytical model explaining these results.

Three 6-cell 805 MHz superconducting cavity prototypes for acceleration in the velocity range of about 0.4 to 0.53 times the speed of light have been fabricated and tested. The quality factors (Q₀) were between 7×10⁹ and 1.4×10¹⁰ at the design field (accelerating gradient of 8–10  MV/m). The maximum gradients reached were between 11 and 16  MV/m; in each case, the Q₀ values were ≥3×10⁹ at the maximum gradient. The design, fabrication, surface preparation, and rf testing of the 6-cell cavities are reported in this paper.

A novel approach for modeling high-current, charged particle beams in a three-dimensional manner is introduced. While the integration of beam motion equations is done as in completely 3D particle-in-cell codes, the space charge forces are found by an approximately self-consistent inclusion of the transverse and longitudinal fields. The algorithm is dramatically faster than fully 3D algorithms with computational times comparable to 2D field solvers. In addition, a sparser spatial grid and fewer required macroparticles provide significantly reduced memory demands. The proposed sub-3D technique has been verified with good agreement with other independent algorithms.

We have measured inelastic electron-deuteron, electron-proton, and electron-aluminum cross sections at 10° in the kinematic region between elastic deuteron scattering and the second resonance region at six beam energies between 9.8 and 21 GeV. The elastic electron-neutron cross section was extracted from the quasielastic data at Q²=2.5,4.0,6.0,8.0, and 10.0 (GeV/c)². The ratio of elastic cross sections σ_n / σ_p falls with increasing Q² above 6 (GeV/c)². The inelastic data are compatible either with y scaling (scattering from a single nucleon) or with ξ scaling (scattering from quarks).

The elastic electron-neutron cross section has been measured at four-momentum transfers squared (Q²) of 2.5, 4.0, 6.0, 8.0, and 10.0 (GeV/c)² with use of a deuterium target and detection of the scattered electrons at 10°. The ratio of neutron to proton elastic cross sections decreases with Q². At high Q² this trend is inconsistent with the dipole law, form-factor scaling, and many vector dominance models, although it is consistent with some parton models.

Magnetic electron scattering cross sections for ²⁵Mg and ⁹³Nb have been measured by means of 180° elastic electron scattering at momentum transfers from 0.8 to 2.2 fm^-1. The M1, M3, and M5 form factors extracted from the data for ²⁵Mg agree with shell model and Nilsson model calculations over most of the momentum transfer range. The M3 form factor is strongly suppressed with respect to the M1 and the M5. The measured relatively small quenching of the M1, M3, M5, M7, and M9 form factors of ⁹³Nb are in good agreement with a shell model calculation of Gloeckner, and show that the magnetic effects in ⁹³Nb are predominantly due to the single 1g_{9 / 2} proton.

NUCLEAR REACTIONS ²⁵Mg(e,e), ⁹³Nb(e,e), E=80-215 MeV, θ=180°, measured σ(E,180°); deduced magnetic moment from factors.

Transverse (E6) and longitudinal (C6) cross sections for the excitation of the J^π=6⁺, E_x=5.125 MeV state in ⁵⁸Ni were measured by means of inelastic electron scattering. The deduced isoscalar component of the particle-hole wave function is found to be two orders of magnitude greater in amplitude than the isovector. This implies that the particle-hole isospin is relatively pure τ=0 and is not significantly mixed with τ=1.

The transverse electromagnetic form factors squared of the ¹²C 2⁺ levels at 4.439 MeV (T=0) and at 16.107 MeV (T=1) have been measured by means of 180° electron scattering over a momentum-transfer range from q=0.51 to 2.05 fm^-1. Evidence is presented for appreciable contributions of nuclear convection currents to the transverse 4.439-MeV form factor at low q, and spin magnetization contributions to the transverse 16.107-MeV form factor at higher q.