Researchers have envisioned an electron-ion collider with ion species up to heavy ions, high polarization of electrons and light ions, and a well-matched center-of-mass energy range as an ideal gluon microscope to explore new frontiers of nuclear science. In its most recent Long Range Plan, the Nuclear Science Advisory Committee (NSAC) of the US Department of Energy and the National Science Foundation endorsed such a collider in the form of a 'half-recommendation.' As a response to this science need, Jefferson Lab and its user community have been engaged in feasibility studies of a medium energy polarized electron-ion collider (MEIC), cost-effectively utilizing Jefferson Lab's already existing Continuous Electron Beam Accelerator Facility (CEBAF). In close collaboration, this community of nuclear physicists and accelerator scientists has rigorously explored the science case and design concept for this envisioned grand instrument of science. An electron-ion collider embodies the vision of reaching the next frontier in Quantum Chromodynamics - understanding the behavior of hadrons as complex bound states of quarks and gluons. Whereas the 12 GeV Upgrade of CEBAF will map the valence-quark components of the nucleon and nuclear wave functions in detail, an electron-ion collider will determine the largely unknown role sea quarks play andmore » for the first time study the glue that binds all atomic nuclei. The MEIC will allow nuclear scientists to map the spin and spatial structure of quarks and gluons in nucleons, to discover the collective effects of gluons in nuclei, and to understand the emergence of hadrons from quarks and gluons. The proposed electron-ion collider at Jefferson Lab will collide a highly polarized electron beam originating from the CEBAF recirculating superconducting radiofrequency (SRF) linear accelerator (linac) with highly polarized light-ion beams or unpolarized light- to heavy-ion beams from a new ion accelerator and storage complex. Since the very beginning, the design studies at Jefferson Lab have focused on achieving high collider performance, particularly ultrahigh luminosities up to 10{sup 34} cm{sup -2}s{sup -1} per detector with large acceptance, while maintaining high polarization for both the electron and light-ion beams. These are the two key performance requirements of a future electron-ion collider facility as articulated by the NSAC Long Range Plan. In MEIC, a new ion complex is designed specifically to deliver ion beams that match the high bunch repetition and highly polarized electron beam from CEBAF. During the last two years, both development of the science case and optimization of the machine design point toward a medium-energy electron-ion collider as the topmost goal for Jefferson Lab. The MEIC, with relatively compact collider rings, can deliver a luminosity above 10{sup 34} cm{sup -2}s{sup -1} at a center-of-mass energy up to 65 GeV. It offers an electron energy up to 11 GeV, a proton energy up to 100 GeV, and corresponding energies per nucleon for heavy ions with the same magnetic rigidity. This design choice balances the scope of the science program, collider capabilities, accelerator technology innovation, and total project cost. An energy upgrade could be implemented in the future by adding two large collider rings housed in another large tunnel to push the center-of-mass energy up to or exceeding 140 GeV. After careful consideration of an alternative electron energy recovery linac on ion storage ring approach, a ring-ring collider scenario at high bunch repetition frequency was found to offer fully competitive performance while eliminating the uncertainties of challenging RD the third is for low energy ion beams stored in a dedicated low-energy compact storage ring, as a possible follow-on project.« less

Science Requirements and Conceptual Design for a Polarized Medium Energy Electron-Ion Collider at Jefferson Lab

Although a rectangular waveguide coupler has the conceptual advantages of simplicity and capability of withstanding higher power, builders of modern superconducting accelerators are routinely choosing instead a coaxial coupler for its proven performance. Multipacting induced discharge has been found to be an operating mechanism that prevents a rectangular waveguide coupler from reaching its full potential. Earlier calculations predicted the existence of two-sided multipacting in a rectangular waveguide geometry. In the present study, special waveguide sections of CESR type were built and tested. Multipacting characteristics of the waveguide were identified. Two multipacting suppression methods, the slotted waveguide method and the DC magnetic bias method, were experimentally evaluated. The multipacting current is suppressed by a factor of more than 2 by opening a slot on the broad wall. Complete multipacting suppression can be realized by using the DC magnetic bias method.

Suppression of multipacting in rectangular coupler waveguides.

CBP-910, LBNL- CLNS-12_2084 CLNS-12-2084 The CESR Test Accelerator Electron Cloud Research Program Phase I Report Editors: M. A. Palmer, M. G. Billing, G. F. Dugan, M. A. Furman and D. L. Rubin January 11, 2013

The CESR Test Accelerator Electron Cloud Research Program Phase I Report

A number of high power fundamental input couplers for superconducting cavities operating in CW mode have been developed in recent years around the world. Some couplers have already been in service for many years delivering hundreds of kilowatts of RF power to beams. In this paper we will summarize experience accumulated in different laboratories and review design options and technical issues associated with R&D, testing and operation of the CW high power couplers. Several future projects will be discussed to highlight new requirements and design challenges.

/pdf/review-of-high-power-cw-couplers-for-superconducting-ygotey3ckr.pdf

Review of high power cw couplers for superconducting cavities

Details of design and fabrication of a beamline RF load suited to accommodate SRF cavities are presented Bonding an RF absorber to a heat sink is the key aspect of the load Production loads have been effectively tested to 108 kW and operated in situ up to 3 kW

/pdf/beamline-rf-load-development-at-cornell-2kb0ci2bbb.pdf

Beamline RF load development at Cornell

The new superconducting RF system consisting of four single-cell cavity modules is an important part of the CESR Luminosity Upgrade. We describe the commissioning of the first three accelerating modules. This includes in situ testing and conditioning, pulsed power and beam processing of RF windows, commissioning of various cryogenic feedback loops, measuring cavity spacing and phasing with beam, and high-current operation.

/pdf/commissioning-of-the-superconducting-rf-cavities-for-the-2dvy7v657f.pdf

Commissioning of the superconducting RF cavities for the CESR Luminosity Upgrade

The prototype superconducting cavity system for CESR-Phase III was tested in CESR in August 1994. The performance of the system was very gratifying. The cavity operated gradients of 4.5-6 MV/m and accelerated beam currents up to 220 mA. This current is a factor of 3 above the world record 67 mA for SRF[1]. The high circulating beam current did not increase the heat load or present any danger to the cavity. No instability attributable to the SRF cavity was encountered. A maximum of 155 kW of rf power was transferred to a 120 mA beam. The window was subjected to 125 kW reflected power and processed easily. In the travelling wave mode, vacuum bursts and are trips prevented us from going above 165 kW. The maximum HOM power extracted was 2 kW. Beam stability studies were conducted for a variety of bunch configurations. In other tests a 120 mA beam was bumped horizontally and vertically by /spl plusmn/10 mm. While supporting a 100 mA beam, the cavity was axially deformed with the tuner by 0.4 mm to sweep the HOM frequencies across dangerous revolution harmonics. In all such tests, no resonant excitation of HOMs or beam instabilities were observed, which confirms that the potentially dangerous modes were damped strongly enough to be rendered harmless.

Beam test of a superconducting cavity for the CESR luminosity upgrade

As part of the "CESR-c" upgrade project, a full-scale prototype superferric wiggler module has been installed into the Cornell Electron Storage Ring (CESR) and successfully operated since October 2002. At least eleven more wigglers are to be installed to enable full operation of the CESR-c. The wiggler magnets are chosen to achieve the necessary damping for optimum operation of CESR-c at a beam energy of 1.88 GeV. The wiggler cryostat units are designed to be modular, of fixed length flange-to-flange, so that they can be easily installed and exchanged. The cryostat incorporates several novel features including a suspension system with very low heat leak that prevents any significant motion during cool down, a custom triple cryogenic feedthrough, and a helium vessel made in two halves, each enclosing a half-magnet. This article presents the design, fabrication, and operation of the CESR-c wiggler cryostat.

/pdf/design-and-operation-of-the-cryostat-for-the-cesr-c-1rvzzvl2bx.pdf

Design and operation of the cryostat for the CESR-c superconducting wiggler magnets

The authors describe the cryostat development for the superconducting CESR-B cavity beam test. They describe external beamline components, the tuner, instumentation and control. >

https://epaper.kek.jp/p93/pdf/pac1993_0995.pdf

Cryostat for a beam test with the CESR-B cavity

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Commissioning of the superconducting RF cavities for the CESR Luminosity Upgrade

Beam test of a superconducting cavity for the CESR luminosity upgrade

Design and operation of the cryostat for the CESR-c superconducting wiggler magnets

Cryostat for a beam test with the CESR-B cavity