BNL, Upton, Long Island, New York, USA
Cornell University, Ithaca, New York, USA
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
JLab, Newport News, Virginia, USA
An option as an injector into the polarized-electron storage ring of eRHIC EIC is a rapid-cycling synchrotron (RCS). Cornell's 10 GeV RCS injector to CESR presents a good opportunity for dedicated polarized bunch rapid-acceleration experiments, it can also serve as a test bed for source and polarimetry developments in the frame of the EIC R&D, as polarized bunch experiments require disposing of a polarized electron source, and of dedicated polarimetry in the linac region and in the RCS proper. This is as well an opportunity for a pluri-disciplinary collaboration between Laboratories. This paper is an introduction to the topic, and to on-going activities towards that EIC R&D project.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
BNL, Upton, Long Island, New York, USA
JLab, Newport News, Virginia, USA
Cockcroft Institute, Warrington, Cheshire, United Kingdom
Cornell University, Ithaca, New York, USA
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
HZB, Berlin, Germany
A collaboration between Cornell University and Brookhaven National Laboratory has designed and is constructing CBETA, the Cornell-BNL ERL Test Accelerator on the Cornell campus. The ERL technology that has been prototyped at Cornell for many years is being used for this new accelerator, including a DC electron source and an SRF injector Linac with world-record current and normalized brightness in a bunch train, a high-current linac cryomodule optimized for ERLs, a high-power beam stop, and several diagnostics tools for high-current and high-brightness beams. BNL has designed multi-turn ERLs for several purpose, dominantly for the electron beam of eRHIC, its Electron Ion Collider (EIC) project and for the associated fast electron cooling system. Also in JLEIC, the EIC designed at JLAB, an ERL is envisioned to be used for electron cooling. The number of transport lines in an ERL is minimized by using return arcs that are comprised of a Fixed Field Alternating-gradient (FFA) design. This technique will be tested in CBETA, which has a single return for the 4-beam energies with strongly-focusing permanent magnets of Halbach type. The high-brightness beam with 150~MeV and up to 40~mA will have applications beyond accelerator research, in industry, in nuclear physics, and in X-ray science. Low current electron beam has already been sent through the most relevant parts of CBETA, from the DC gun through both cryomodules, through one of the 8 similar separator lines, and through one of the 27 similar FFA structures. Further construction is envisioned to lead to a commissioning start for the full system early in 2019.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
High intensity and highly spin-polarized electron source is of great interest to the next generation Electron Ion Colliders. GaAs prepared by the standard activation method, which is the most widely used spin-polarized photocathode, is notorious for its vacuum sensitivity and short operational lifetime. To improve the lifetime of GaAs photocathodes, we activated GaAs by Cs2Te, a material well known for its robustness. We confirmed the Cs2Te layer forms negative electron affinity on GaAs with a factor of 5 improvement in lifetime. Furthermore, the new activation method had no adverse effect on spin-polarization. Considering Cs2Te forms much thicker activation layer (~ 2 nm) compared to the standard activation layer (~ monolayer), our results trigger a paradigm shift on new activation methods with other robust materials that were avoided for their thickness.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
LBNL, Berkeley, California, USA
UCLA, Los Angeles, California, USA
Operating photocathodes near the photoemission threshold holds the promise of yielding small intrinsic emittance, at the cost of significantly reduced quantum efficiency. In modern femtosecond photoemission electron sources, this requires a very high intensity (10s of GW/cm2) to extract a useful quantity of electrons. At this intensity, the electron occupation function is far from equilibrium and evolves rapidly on sub-ps timescales. Thus, ultrafast laser heating and multiphoton photoemission effects may play a significant role in emission, thereby increasing the minimum achievable emittance. In this work, we use a Boltzmann equation approach to calculate the non-equilibrium occupation function evolution in time for a copper photocathode, yielding a prediction of quantum efficiency and mean transverse energy as a function of input intensity.
Cornell University, Ithaca, New York, USA
UIC, Chicago, Illinois, USA
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Single crystalline photocathodes with small electron effective mass are supposed to enable ultra-low emittance beams, by taking advantage of the conservation of transverse (crystal) momentum. We present a preliminary study on photoemission from epitaxial films of La-doped BaSnO3 with (100) orientation. We demonstrate here the possibility of generating and characterizing electron beams by exciting photoelectrons solely from the conduction band. We report quantum efficiency and mean transverse energy meaurements as a function of photon energy from the bare and Cs-activated La-doped BaSnO3 surface.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA