CERN's 160 MeV H(-) linear accelerator (Linac4) is a key constituent of the injector chain upgrade of the Large Hadron Collider that is being installed and commissioned. A cesiated surface ion source prototype is being tested and has delivered a beam intensity of 45 mA within an emittance of 0.3 π ⋅ mm ⋅ mrad. The optimum ratio of the co-extracted electron- to ion-current is below 1 and the best production efficiency, defined as the ratio of the beam current to the 2 MHz RF-power transmitted to the plasma, reached 1.1 mA/kW. The H(-) source prototype and the first tests of the new ion source optics, electron-dump, and front end developed to minimize the beam emittance are presented. A temperature regulated magnetron H(-) source developed by the Brookhaven National Laboratory was built at CERN. The first tests of the magnetron operated at 0.8 Hz repetition rate are described.
CERN's Linac4 45 kV H-ion sources prototypes are installed at a dedicated ion source test stand and in the Linac4 tunnel. The operation of the pulsed hydrogen injection, RF sustained plasma and pulsed high voltages are described. The first experimental results of two prototypes relying on 2MHz RF-plasma heating are presented. The plasma is ignited via capacitive coupling, and sustained by inductive coupling. The light emitted from the plasma is collected by viewports pointing to the plasma chamber wall in the middle of the RF solenoid and to the plasma chamber axis. Preliminary measurements of optical emission spectroscopy and photometry of the plasma have been performed. The design of a cesiated ion source is presented. The volume source has produced a 45 keV H-beam of 16-22 mA which has successfully been used for the commissioning of the Low Energy Beam Transport (LEBT), Radio Frequency Quadrupole (RFQ) accelerator and chopper of Linac4.
The 2MHz radio-frequency inductively coupled plasma heating (ICP RF) of Linac4's IS03 Hsource is more efficient without its octupole cusp in offset hallbach configuration. This was shown by Particle in cell Monte-Carlo (PIC-MC) simulation using the NINJA software [1] and confirmed by plasma characterization via optical emission spectroscopy [2,3], an easier plasma ignition is also anticipated. In this paper, we present preliminary results of an Alumina plasma chamber IS03 Hsource [4] operated without magnetic cusp. Operation under monthly cesiation induces a slow evolution of the molybdenum cesiated surface correlated with an increase of the co-extracted electron yield. An improved stability of the extracted Hbeam is achieved by compensating the Cs-losses. The high intensity option for Linac4 features an adaptation of BNL's Magnetron. Simulation of this complex H2-Cs arc discharge plasma, where electrons are emitted from a cesiated molybdenum cathode, requires characterization of the plasma impedance and knowledge of hydrogen and cesium densities. We present a measurement of plasma impedance over the range of discharge current, hydrogen and cesium-densities.
Abstract.Linac4 cesiated surface H -sources are routinely operated for the commissioning of the CERN's Linac4 and on an ion source test stand. Stable current of 40-50 mA are achieved but the transmission through the LEBT of 80% was below expectations and triggered additional beam simulation and characterization. The H -beam profile is not Gaussian and emittance measurements are larger than simulation. The status of ongoing development work is described; 36 mA H -and 20 mA D -beams were produced with a 5.5 mm aperture cesiated surface ion source. The emittances measured at the test stand are presented. During a preliminary test, the Linac4 proton source delivered a total beam intensity of 70 mA (p, H2 + , H3 + ).
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