CERN Accelerating science

Thesis
Report number	CERN-THESIS-2024-218
Title	Slow Extraction: Upgrades for Next Ion Medical Machines at FLASH timescales
Author(s)	Taylor, Rebecca (Imperial Coll., London)
Publication	London : Spiral, 2024-11-01 - 214.
Thesis note	PhD : Imperial Coll., London : 2024-03-31
Thesis supervisor(s)	Pasternak, Jaroslaw ; Long, Kenneth ; Benedetto, Elena ; Vretenar, Maurizio
Note	Presented 18 Jul 2024
Subject category	Accelerators and Storage Rings
Study	CERN NIMMS
Abstract	Slow resonant extraction is the control of resonant beams to extract a continuous rate of particles from the accelerator, over seconds. This technique is crucial for hadron therapy synchrotrons, where slowly extracted beams are scanned across tumour volumes. Recent radiobiological research demonstrates that ultra-high dose rates (UHDR) reduce tissue toxicities to healthy tissue, but causes damage to tumour tissue – known as the FLASH effect. This effect, and other open questions in ion radiobiology, motivates the next-generation of ion medical machines with flexible extraction methods. This thesis provides key results in areas of slow extraction, to be applied to the Next Ion Medical Machine Study (NIMMS). It addresses upgrades to existing designs, considering 6× higher emittances and 10× faster timescales. The design for a new Helium Light Ion Compact Synchrotron (HeLICS), is introduced and the extraction is established for two working points. UHDR extraction is performed via quadrupole extraction and radiofrequency knock-out (RF-KO), for 60 s continuous spills, and spills with 10 lots of 3 ms bursts. To study beams under RF-KO conditions, measurements performed at HIT, which displayed unusual tune responses, were reproduced in simulations. These simulations were expanded to single-particle dynamics to show how the tune coherence was a time-oscillating effect. Impacts of higher order magnets were quantified at the CERN Proton Synchrotron (PS) with octupole-island trapping. Measurements with sextupole and octupole scans produced good agreement at 2 GeV and identified an offset at 24 GeV. Finely-tuned octupole strengths increase extracted beam density to reduce losses at the extraction septum by 15% and at the first magnetic septum by 45%, with increased global losses. Measurements demonstrated parabolic relations of octupole strength vs beam loss. Finally, this thesis explored future conceptual methods and simulated the first resonant extraction from scaling fixed field accelerators for LhARA.
Copyright/License	CC-BY-NC-4.0

Email contact: taylor.r@cern.ch