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TY - CONF AU - Barnard, A.H. AU - Broodryk, J.I. AU - Conradie, J.L. AU - De Villiers, J.G. AU - Mira, J. AU - Nemulodi, F. AU - Thomae, R.W. ED - Conradie, Lowry ED - De Villiers, John Garrett ED - Schaa, Volker RW TI - Vertical Focussing with a Field Gradient Spiral Inflector J2 - Proc. of Cyclotrons2019, Cape Town, South Africa, 23-27 September 2019 CY - Cape Town, South Africa T2 - International Conference on Cyclotrons and their Applications T3 - 22 LA - english AB - Traditional spiral inflectors suffer from vertical defocussing, leading to beam loss. In this study the electrode shape of an inflector is modified to intentionally produce transverse electric field gradients, which have a significant influence on the optics. This is done by placing the traditionally parallel electrodes at an angle relative to each other in the transverse plane, creating a quadrupole field on the central path. Varying the electrode angle along the path length creates an alternating-gradient effect. The electrode entrance and exit faces are also shaped to create quadrupoles inside the fringe field. By numerical optimisation a design with good vertical focussing is obtained. Experiments show a roughly 100% increase in transmission in cases where the buncher is turned off. However, high losses at extraction are observed with the buncher turned on, due to RF-phase spread introduced by longitudinal defocussing in the inflector. This results in an improvement of only 20% during normal cyclotron operation, and shows that an inflector should ideally focus vertically and longitudinally at the same time. Ongoing work to achieve such combined focussing is described. PB - JACoW Publishing CP - Geneva, Switzerland SP - 58 EP - 61 KW - cyclotron KW - experiment KW - quadrupole KW - emittance KW - optics DA - 2020/06 PY - 2020 SN - 978-3-95450-205-9 DO - doi:10.18429/JACoW-Cyclotrons2019-MOP016 UR - http://jacow.org/cyclotrons2019/papers/mop016.pdf ER -