Scott Lawrie

First beam measurements on the vessel for extraction and source plasma analyses (VESPA) at the Rutherford Appleton Laboratory (RAL)

In order to facilitate the testing of advanced H− ion sources for the ISIS and Front End Test Stand (FETS) facilities at the Rutherford Appleton Laboratory (RAL), a Vessel for Extraction and Source Plasma Analyses (VESPA) has been constructed. This will perform the first detailed plasma measurements on the ISIS Penning-type H− ion source using emission spectroscopic techniques. In addition, the 30-year-old extraction optics are re-designed from the ground up in order to fully transport the beam. Using multiple beam and plasma diagnostics devices, the ultimate aim is improve H− production efficiency and subsequent transport for either long-term ISIS user operations or high power FETS requirements. The VESPA will also accommodate and test a new scaled-up Penning H− source design. This paper details the VESPA design, construction and commissioning, as well as initial beam and spectroscopy results.

Developing the RAL front end test stand source to deliver a 60 mA, 50 Hz, 2 ms H− beam

All the Front End Test Stand (FETS) beam requirements have been achieved, but not simultaneously [1]. At 50 Hz repetition rates beam current droop becomes unacceptable for pulse lengths longer than 1 ms. This is fundamental limitation of the present source design. Previous researchers [2] have demonstrated that using a physically larger Penning surface plasma source should overcome these limitations. The scaled source development strategy is outlined in this paper. A study of time-varying plasma behavior has been performed using a V-UV spectrometer. Initial experiments to test scaled plasma volumes are outlined. A dedicated plasma and extraction test stand (VESPA-Vessel for Extraction and Source Plasma Analysis) is being developed to allow new source and extraction designs to be appraised. The experimental work is backed up by modeling and simulations. A detailed ANSYS thermal model has been developed. IBSimu is being used to design extraction and beam transport. A novel 3D plasma modeling code using beam...

Design study of a test vessel to investigate the ISIS H− Penning ion source plasma

A vacuum-vessel for extraction and source plasma analyses (VESPA) has been constructed with the aim of understanding the dominant plasma processes of negative hydrogen (H−) ion formation in the ISIS Penning ion source. The VESPA has been designed to be simple and inexpensive, with all features of the ISIS ion source not directly responsible for plasma formation removed such that there is ample space for diagnostics close to the plasma. Diagnostics will include but are not limited to a beam current density monitor, a high resolution visible-light monochromator, a cesium mass deposition monitor, an electrostatic energy analyser, a magnetic mass spectrometer and an emittance scanner. Several existing parts and ancillary equipment are re-used to reduce costs and to speed up installation. The ultimate aim of the VESPA is to perform detailed analyses of the H− production, cesium usage and beam formation such that an upgrade to the ion source is both well informed and possible using this setup. This report detai...

Upgrade of the ITUR extraction system at ESS-Bilbao

The first beam measurements on our modified version of the ISIS Penning source show a beam of relatively low current. As a result of this, the actual extraction system was simulated using IBSimu, and it was found that the configuration is far from the optimal case. We present a simpler post-acceleration extraction system that avoids the use of a long (∼100mm) Cs trap. Due to space and budget constraints, the new extraction is composed of only one electrostatic einzel lens. The same configuration, as the ISIS source, is maintained up to the puller electrode; the changes come afterwards, where two circular electrodes with rectangular apertures make up the einzel lens. This configuration lacks the bending magnet found at ISIS because the permanent magnets used in this version of the source provide the Penning field. This difference results in a low angle beam extraction that is compensated by tilting the source to angles near 15°. In addition to the beam dynamics simulations, the mechanical and electrostatic...