Recent negative ion source activity at JYFL

Abstract

A filament-powered multicusp ion source for production of H − has been developed for the Jyväskylä Pelletron accelerator for use in ion beam lithography and particle induced X-ray emission applications. The source can be considered conventional with the exception of the filter field being created with an electric magnet for continuous adjustability. A permanent magnet dipoleantidipole electron dump is integrated in the puller electrode. The source provides 50 µA H − beam at 10 keV energy with 0.019 mm mrad 95 % normalized rms emittance through a 2 mm aperture. Lower emittance is achievable by changing the plasma electrode insert to a smaller aperture one if application requires. A new commercial MCC30/15 cyclotron has been installed at the Jyväskylä accelerator laboratory providing 30 MeV H + and 15 Mev D + for use in nuclear physics experiments and applications. The ion source delivered with the cyclotron is a a filament-powered multicusp source capable of about 130 h continuous operation at 1 mA H − output between filament changes. The ion source is located in the cyclotron vault and therefore a significant waiting time for the vault cooldown is required before filament change is possible. This kind of operation is not acceptable as 350 h and longer experiments are expected. Therefore a project for developing a CW 13.56 MHz RF ion source has been initiated. A planar RF antenna replacing the filament back plate of the existing TRIUMF-type ion source has been used in the first tests with 240 µA of H − and 21 mA of electrons measured at 1.5 kW of RF power. Tests with higher RF power levels were prevented by electron beam induced sparking. A new plasma chamber has been built and a new extraction is being designed for the RF ion source. The extraction code IBSimu has recently gone through a major update on how smooth electrode surfaces are implemented in the Poisson solvers. This has made it possible to implement a fast multigrid solver with low memory consumption. Also a method has been made to import 3D CAD geometries into simulations.

Photoelectron emission from metal surfaces induced by VUV-emission of filament driven hydrogen arc discharge plasma

“…The line-of-sight plasma volume was limited by the 9.5 mm diameter puller electrode aperture and the (6 mm / 8 mm diameter) collimator between the target and the plasma. The target materials used in this study are metals which are typically found in negative hydrogen ion sources as chamber materials (Al, Cu, SS) [8,9,10], filament materials (Ta) [7,11], plasma grid materials (Mo) [12] or so-called collar materials (SS, Mo) [13,14]. The effect of Al, Cu and SS wall materials and Ta covered walls on the volume production of negative hydrogen ions has been studied in [3,15,16].…”

An experimental study of waveguide coupled microwave heating with conventional multicusp negative ion sources

“…The result, namely the 30% performance in comparison to nominal plasma heating method for each chamber, is very promising especially because the systems are far from being optimized for microwaves. Furthermore, a similar test was performed earlier on LIISA with RF-heating and the performance was only 240 µA [14], half of the performance achieved with microwave heating.…”

“…The quartz window is clearly not the optimum technical solution. Alumina (Al 2 O 3 ) and aluminum nitride (AlN) are promising candidates as they are proven to withstand tens of kilowatts of power in pulsed operation [28,29] and several kilowatts in continuous operation [14,27].…”

“…In this study the potential of microwave heating in negative ion production is demonstrated with two different operational CW H − ion sources, RF-driven RADIS ion source [14] and filament driven arc discharge LIISA ion source [15]. The plasma heating methods of the given ion sources were transformed to 2.45 GHz microwave heating by replacing the back plates of the plasma chambers with the back plate of a microwave discharge ion source.…”

Photoelectron emission from metal surfaces induced by radiation emitted by a 14 GHz electron cyclotron resonance ion source

“…The target materials used in this study are metals which are typically found in ion sources as chamber materials (Al, Cu, and stainless steel). [11][12][13] A 1 µm thick mylar film, which is transparent for energies higher than 1 keV, was used to study the X-ray part of the spectrum. A sapphire window, which is transparent in the wavelength range of 150 nm-5 µm, was used to study the VUV-part of the spectrum.…”