[en] Beam stability issues of the VLHC rings in Phase 1 and Phase 2 are reviewed. For accelerator rings of circumference 232 km and beam pipe radius of the order of 1 cm, the impedance of the vacuum chamber is dominated by the resistive wall. The most dangerous instabilities are the single-bunch transverse mode coupling instability and the transverse coupled bunch instability driven by the resistive wall at sub-revolution frequency. Scaling is studied concerning the thresholds of these instabilities and the dominance of the resistive wall impedance as the size of the accelerator increases

[en] During polarized beam experiments, the 50 GeV proton synchrotron, proposed by the Institute of Nuclear Study of Japan, requires zero-dispersion straight sections. This will be implemented by turning on a special excitation of the quadrupoles resulting in a dispersion wave through the arcs of the machine. Aside from the inconvenience of the power supply, this special excitation also brings about unwanted high betatron functions and high dispersion functions, which will eventually limit the performance of the accelerator at high intensities. In this paper, dispersion suppressors are introduced. A new preliminary lattice that contains two straight sections with nonzero dispersion and two straight sections with zero dispersion is presented. The whole ring remains having a reasonable imaginary γ_t. The horizontal and vertical betatron functions have been kept to below 32.4 m and dispersion function between -0.52 and 1.86 m. The number of 6.2 m dipoles is reduced from 96 to 92, and the dipole field at 50 GeV will become slightly above 18 T. Some analysis of the new lattice is discussed. 10 refs., 9 figs., 1 tab

[en] Some issues are presented on the rf system in the future Fermilab prebooster, which accelerates 4 bunches each containing 0.25 x 10₁₄ protons from 1 to 3 GeV kinetic energy. The problem of beam loading is discussed. The proposal of having a non-tunable fixed-frequency rf system is investigated. Robinson's criteria for phase stability are checked and possible Robinson instability growth is computed

No abstract available

[en] Space-charge effects on beam stabilities are studied for the proposed two-ring high-intensity Fermilab booster destined for the muon collider. This includes microwave instabilities and rf potential-well distortions. For the first ring, ferrite insertion is suggested to cancel the space-charge distortion of the rf wave form. To control the inductance of the ferrite during ramping and to minimize resistive loss, perpendicular biasing to saturation is proposed

[en] The lattice design of the 50-50 Gev muon collider is presented. Due to the short lifetime of the 50 GeV muons, the ring needs to be as small as possible. The 4 cm low betas in both planes lead to high betatron functions at the focusing quadrupoles and hence large chromaticities, which must be corrected locally. In order to maintain a low rf voltage of around 10 MV, the momentum-compaction factor must be kept to less than 10^-2 , and therefore the flexible momentum-compaction modules are used in the arcs. The dynamical aperture is larger than 6 to 7 rms beam size for ±5 rms momentum offset. Comments are given and modifications are suggested

[en] The miscellaneous components of an accelerator may contribute a substantial or even dominant part of the interaction between beam and surroundings. We have estimated the beam impedances of a few of these components. When needed, we have added our own conceptions to the descriptions available at the Workshop on the RHIC Performance in order to make definite the calculations of impedance. These assumed parameters, while not unique, hopefully illustrate feasible and typical designs. 8 refs., 4 figs., 2 tabs

[en] Ag/BSCCO and Fe/Ag/BSCCO planar tunnel junctions were constructed in order to study experimentally the effect of an exchange potential on the spin polarized current transported through Andreev bound states appearing at the interface with a superconductor with broken time reversal pairing symmetry. The zero bias conductance peak (ZBCP) resulting from the Andreev bound states (ABS) is split into two symmetric peaks shifted at finite energies when the counterelectrode is normal. Four asymmetric peaks are observed when the ferromagnetic spin polarized charge reservoir is added, due to the combined effect of a spin filtering exchange energy in the barrier, which is a spin dependent phenomenon, and the spin independent effect of a broken time reversal symmetry (BTRS). The polarization in the iron layer leads to asymmetry. Due to the shift of ABS peaks to finite energies, the conductance at zero energy behaves as predicted by recent theoretical developments for pure d-wave junctions without Andreev reflections

[en] The collisionless cold dark matter (CCDM) model predicts overly dense cores in dark matter halos and overly abundant subhalos. We show that the idea that CDM are decaying superheavy particles which produce ultra-high energy cosmic rays with energies beyond the Greisen-Zatsepin-Kuzmin cutoff may simultaneously solve the problem of subgalactic structure formation in CCDM model. In particular, the Kuzmin-Rubakov's decaying superheavy CDM model may give an explanation to the smallness of the cosmological constant and a new thought to the CDM experimental search

[en] We have synthesized MgB₂/Pb planar junctions to study the temperature and field dependence of the superconducting energy gap of MgB₂. The major peak occurs at Δ of about 2 meV, and this corresponds to a 2Δ/k_BT_cvalue of 1.18. While this is significantly smaller than the BCS weak coupling value, there are features in the tunneling spectra indicating the possibility of another larger gap. By fitting the dI/dV curves with a simple model, the larger gap is estimated to be about 4.5 times the smaller gap. The temperature dependence of both gaps is BCS-like, and start to open up at temperatures just below T_c (39.5 K). This confirms that these gaps are indeed bulk properties of MgB₂. The junction is stable only up to a field of 3.2 T then 'collapsed' into Josephson tunneling for higher fields