Experimental benchmark of the NINJA code for application to the Linac4 H − ion source plasma

AIP Conference Proceedings

Bertolo

Fantz

et al. 2018

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.

Section: Introductionmentioning

confidence: 91%

Linac4 H− source R&D: Cusp free ICP and magnetron discharge

AIP Conference Proceedings

Bertolo

Fantz

et al. 2018

“…A magnetic cusp-field created by permanent magnets in a Halbach-configuration confines the plasma [17]. Viewing ports are available for studying the plasma parameters using optical emission spectroscopy [18][19][20]. A dipole filter field created by permanent magnets prevents fast electrons from reaching the extraction zone [9].…”

Section: Simulation Toolsmentioning

confidence: 99%

H− extraction systems for CERN’s Linac4 H− ion source

Fink

Kalvas

Nuclear Instruments and Methods in Physics Research Section A:

et al. 2018

A B S T R A C T Linac4 is a 160 MeV linear H− accelerator at CERN. It is an essential part of the beam luminosity upgrade of the Large Hadron Collider (LHC) and will be the primary injector into the chain of circular accelerators. It aims at increasing the beam brightness by a factor of 2, when compared to the currently used 50 MeV linear proton accelerator, Linac2.Linac4's ion source is a cesiated RF-plasma H − ion source. Several beam extraction systems were designed for H − beams of 45 keV energy, 50 mA intensity and an electron to H − ratio smaller than 5. The goal was to extract a beam with an rms-emittance of 0.25 mm mrad.One of the main challenges in designing an H − extraction system is dumping of the co-extracted electrons. Separating the electrons from the negative ions as early as possible reduces space-charge induced emittancegrowth. However, a strong magnetic field close to the extraction might cause unnecessary strong deflection in a region of low beam energy. For this purpose a novel magnetic configuration was designed using a magnetic shield between the magnetic fields of the source and the electron dump, which conserves the filter field strength to keep the electron to H − ratio low and effectively dumps the co-extracted electrons. Magnetic configuration and beam trajectories were calculated using the TOSCA Opera 3D code and IBSimu, respectively. Three extraction systems will be discussed in terms of electron dumping efficiency, emittance and transport through the extraction system and LEBT to the RFQ and compared to the simulations.An improved emittance conservation through the extraction system and LEBT is predicted and further design improvements are proposed. Measurements show that the novel electron dump successfully traps the co-extracted electrons.

“…The combination of physics modelling and simulation with experimental methods is the key to improved understanding of NBI's hydrogen and deuterium plasma; Hatayama presents a thorough review of the low temperature plasma modelling [21] and Tsumori presents the most sophisticated measurement techniques to investigate plasma population's properties including those specific to large sources for fusion reactors' NBI heating [22]. As an example, Briefi applied a collisional radiative modelling to analyse high-density low temperature hydrogen plasma; he presents the simulation of inductively coupled plasma (ICP) heating of CERN's Linac4 ion source and its experimental validation via state-of-the-art optical emission spectroscopy measurements of the Balmer lines and Fulcher band [23]. Mochalskyy developed the Orsay Negative Ion eXtraction code [24] which simulates the beam formation across the plasma meniscus taking into account the complex 3D geometry of the fields [25].…”

Section: Negative Ion Source Beam Intensities Across 20 Orders Of Magmentioning

confidence: 99%

Focus on sources of negatively charged ions

Fantz

2018

New J. Phys.

This focus issue presents theoretical investigations, modelling and technical achievements across the large variety of sources of negatively charged ions (NCI). The twenty contributions cover a fraction of the very broad range of applications requiring very different time structure, intensities and beam energies. The world's largest NCI source area is 1×2 m 2 and shall provide 1280 beamlets of ∼30 mA intensity each, while the smallest unit of our selection is only a few mm 2 and requires the highest ionization efficiencies to deliver negative radioisotope-ions far from stability produced via nuclear reactions at rates down to or below few atoms per seconds.