Abstract
The High Luminosity LHC project (HL-LHC) foresees the construction and installation of important new equipment to increase the performance of the LHC machine. The Hollow Electron Lens (HEL) is a promising system to control the beam halo. It improves the beam collimation system of the HL-LHC and mitigates possible equipment damage in case of failure scenarios from halo losses. The halo can store up to 30 MJ energy. The specifications for this new device are quite demanding. The source, an electron gun with an annular shaped cathode, must deliver a current up to 5 A. This is five times higher than the current in the existing electron lenses in Fermi and Brookhaven national laboratories. This note describes the programme carried out to design and test high-perveance guns equipped with two types of high-performance scandate cathodes. The size of the final gun for the HL-LHC lenses is now considerably smaller than the one of the first prototype, allowing a reduction of diameter and cost of the superconducting magnet system used to steer the electron beam. The tests carried out at FNAL, BVERI and BJUT demonstrated that the developed cathodes fulfil the specifications and can supply a 5 A fully Space Charge Limited (SCL) current.
Highlights
: The High Luminosity LHC project (HL-LHC) foresees the construction and installation of important new equipment to increase the performance of the LHC machine
The phase 1 electron gun delivered a current of 6.25 A at 10 kV cathode-anode differential voltage
It demonstrated that it is possible to obtain more than 5 A with a 10 kV cathode-anode differential voltage in an electron gun with cathode, anode and other electrodes at the size required for the HL-LHC HEL
Summary
In the HEL an annular thermionic cathode emits the electron beam, which is accelerated and confined, compressed and steered by a magnetic field generated by a set of superconducting solenoids. It was decided to try a further cathode development still ongoing in BJUT (Beijing University of Technology): the design of a high performance scandia doped dispenser cathode able to deliver the nominal current of 5 A, while working at lower temperature than those previously tested. This development is not a must for the HL-LHC lenses, but a lower working temperature is a simplification and a great advantage.
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