98 research outputs found
Beam Extraction and Transport
This chapter gives an introduction to low-energy beam transport systems, and
discusses the typically used magnetostatic elements (solenoid, dipoles and
quadrupoles) and electrostatic elements (einzel lens, dipoles and quadrupoles).
The ion beam emittance, beam space-charge effects and the physics of ion source
extraction are introduced. Typical computer codes for analysing and designing
ion optical systems are mentioned, and the trajectory tracking method most
often used for extraction simulations is described in more detail.Comment: presented at the CERN Accelerator School CAS 2012: Ion Sources,
Senec, 29 May - 8 June 201
Photoelectron Emission from Metal Surfaces Induced by VUV-emission of Filament Driven Hydrogen Arc Discharge Plasma
Photoelectron emission measurements have been performed using a
filament-driven multi-cusp arc discharge volume production H^- ion source
(LIISA). It has been found that photoelectron currents obtained with Al, Cu,
Mo, Ta and stainless steel (SAE 304) are on the same order of magnitude. The
photoelectron currents depend linearly on the discharge power. It is shown
experimentally that photoelectron emission is significant only in the short
wavelength range of hydrogen spectrum due to the energy dependence of the
quantum efficiency. It is estimated from the measured data that the maximum
photoelectron flux from plasma chamber walls is on the order of 1 A per kW of
discharge power
An Experimental Study of Waveguide Coupled Microwave Heating with Conventional Multicusp Negative Ion Source
Negative ion production with conventional multicusp plasma chambers utilizing
2.45 GHz microwave heating is demonstrated. The experimental results were
obtained with the multicusp plasma chambers and extraction systems of the
RFdriven RADIS ion source and the filament driven arc discharge ion source
LIISA. A waveguide microwave coupling system, which is almost similar to the
one used with the SILHI ion source, was used. The results demonstrate that at
least one third of negative ion beam obtained with inductive RF-coupling
(RADIS) or arc discharge (LIISA) can be achieved with 1 kW of 2.45 GHz
microwave power in CW mode without any modification of the plasma chamber. The
co-extracted electron to H^- ratio and the optimum pressure range were observed
to be similar for both heating methods. The behaviour of the plasma implies
that the energy transfer from the microwaves to the plasma electrons is mainly
an off-resonance process
Empirical study of multidimensional Child-Langmuir law with plasma ion source extraction using round apertures
One dimensional Child-Langmuir (CL) law is commonly used in ion source physics to describe space charge limited ion extraction from the plasma. Recently 2D and 3D CL laws have been derived, but plasma ion extraction does not strictly meet the assumptions in these CL laws. Investigations on the applicability of the CL laws to ion source extraction were conducted using filament-driven ion source, measuring the beam currents as a function of extraction voltage. The experiments are complemented with simulations where IBSimu is used for studying the behaviour of plasma meniscus. Three different voltage regions were identified with low, moderate and high voltage. With moderate voltages the extracted beam current density shows signs of 3D CL law. The results indicate that for the total beam current CL laws are not valid but instead require collimation for the CL effects emerge.peerReviewe
Estimation of Sputtering Damages on a Magnetron H- Ion Source Induced by Cs+ and H+ Ions
An H− ion source is being developed for CERN’s Linac4 accelerator. A beam current requirement of 80 mA and a reliability above 99% during 1 year with 3 month uninterrupted operation periods are mandatory. To design a low-maintenance long life-time source, it is important to investigate and understand the wear mechanisms. A cesiated plasma discharge ion source, such as the BNL magnetron source, is a good candidate for the Linac4 ion source. However, in the magnetron source operated at BNL, the removal of material from the molybdenum cathode and the stainless steel anode cover plate surfaces is visible after extended operation periods. The observed sputtering traces are shown to result from cesium vapors and hydrogen gas ionized in the extraction region and subsequently accelerated by the extraction field. This paper presents a quantitative estimate of the ionization of cesium and hydrogen by the electron and H− beams in the extraction region of BNL’s magnetron ion source. The respective contributions of Cs+ and H+ ions to the sputtering process are estimated
- …