UMAN, Manchester
CERN, Geneva
EPFL, Lausanne
The largest contribution to the LHC transverse resistive wall impedance is given by the graphite collimators. Such a contribution is predicted by analytical calculations. A series of laboratory measurements were performed to experimentally validate the analytical results in the case of small gaps and in a low frequency regime where the skin depth becomes comparable to the collimator thickness. The measurement method consists in determining the dependence of a probe coil input impedance on the surrounding materials and was applied to sample graphite plates, stand alone LHC collimator jaws and a full collimator assembly. After reviewing the measurement procedures, problematics and stages, the results are compared to analytical predictions and numerical simulations.
BNL, Upton, Long Island, New York
A strong interest in running RHIC at low energies in a range of 2.5-25 GeV/nucleon total energy of a single beam has emerged recently. Providing collisions in this energy range, which in RHIC case is termed “low-energy” operation, will help to answer one of the key questions in the field of QCD about existence and location of critical point on the QCD phase diagram. To evaluate the challenges of RHIC operation at such low energies there have been several short test runs during RHIC operations in 2006, 2007 and 2008. The beam lifetime observed during the test runs was clearly limited by machine nonlinearities. This performance can be improved provided sufficient time is given for machine development at these low energies. After the lifetime caused by nonlinearities is improved the strongest limitation comes from transverse and longitudinal Intra-beam Scattering (IBS), and ultimately by the space-charge limit. A significant luminosity improvement can be provided with electron cooling applied directly in RHIC at low energies. This report summarizes various beam dynamics limiting effects and possible improvement with electron cooling.
BNL, Upton, Long Island, New York
MIT, Middleton, Massachusetts
The design status of the high luminosity electron-ion collider, eRHIC, is presented. The goal of eRHIC will be to provide collisions of electrons and possibly positrons) on ions and protons in the center-of-mass energy range from 25 to 140 GeV, at luminosities exceeding 1033 cm-2s-1. A considerable part of the physics program calls for a high polarization level of electrons, protons and He3 ions. The electron beam is accelerated in a recirculating energy recovery linac. Major R&D items for the electron beam include the development of a high intensity polarized source, studies of various aspects of energy recovery technology for high power beams and the development of compact magnets for recirculating passes. In a linac-ring scheme the beam-beam interaction has several very specific features which have to be thoroughly studied. In order to maximize the collider luminosity, several upgrades of the existing RHIC accelerator are required. Those upgrades may include the increase of total beam intensity as well as transverse and longitudinal cooling of ions and protons.
Jefferson Lab, Newport News, Virginia
TRIUMF, Vancouver
A conceptual design of a ring-ring electron-ion collider based on CEBAF with a center-of-mass energy up to 90 GeV at luminosity up to 1035 cm-2s-1 has been proposed at JLab to fulfil science requirements. Four interaction points on two crossing straight sections of Figure-8 shape rings are planed for collisions of both highly polarized electron and light ion beams. The Green field design of the ion complex including electron cooling and new way of organizing interacting regions are directly aimed at full exploitation of science program. Here, we summarize design progress including collider ring and interaction region optics with chromatic aberration compensation. Stacking of ion beams in an accumulator-cooler ring, beam-beam simulations and a faster kicker for the circulator electron cooler ring are also discussed.