Dr Suzie Sheehy

Abstract:

In this paper we present a quantitative measurement of the change in frequency (tune) with intensity of four transverse resonances in a high intensity Gaussian beam. Due to the non-linear space charge forces present in high intensity beams, particle motion cannot be analytically described. Instead we use the Simulator of Particle Orbit Dynamics (S-POD) and the Intense Beam Experiment (IBEX), two linear Paul traps, to experimentally replicate the system. In high intensity beams a coherent resonant response to both space charge and external field driven perturbations is possible, these coherent resonances are excited at a tune that differs by a factor $C_{m}$ from that of the incoherent resonance. By increasing the number of ions stored in the linear Paul trap and studying the location of four different resonances we extract provisional values describing the change in tune of the resonance with intensity. These values are then compared to the $C_{m}$ factors for coherent resonances. We find that the $C_{m}$ factors do not accurately predict the location of resonances in high intensity Gaussian beams. Further insight into the experiment is gained through simulation using Warp, a particle-in-cell code.

Abstract:

The annual global incidence of cancer is projected to rise in 2035 to 25 million cases (13 million deaths), with 70% occurring in low- and middle-income countries (LMICs), where there is a severe shortfall in the availability of radiotherapy [1] – an essential component of overall curative and palliative cancer care. A 2015 report by the Global Task Force on Radiotherapy for Cancer Control estimated that by 2035 at least 5000 additional megavolt treatment machines would be needed to meet LMIC demands, together with about 30 000 radiation oncologists, 22 000 medical physicists and 80 000 radiation therapy technologists [2]. Among the main reasons for the shortfall identified in the workshop and thoroughly discussed in the Clinical Oncology special issue on radiotherapy in LMICs [3] are: (i) the initial cost of linear accelerators, (ii) the cost of service on the machines and (iii) a shortage of trained personnel needed to deliver safe, effective and high-quality treatment. A number of authors who contributed to the Clinical Oncology special issue are participating in the CERN, International Cancer Expert Corps (ICEC), Science and Technology Facilities Council (STFC) collaborative effort described in this editorial (Aggarwal, Coleman, Court, Grover, Palta, Van Dyk and Zubizarreta).