Contents lists available at ScienceDirect Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem Dose-current discharge correlation analysis in a Mather type Plasma Focus device for medical applications M. Sumini a,d, ⁎ , D. Mostacci a , A. Tartari d , A. Mazza a , G. Cucchi a , L. Isolan a , F. Buontempo c , I. Zironi b,d , G. Castellani b,d a Industrial Engineering Department, University of Bologna, Via dei Colli 16, Bologna 40136, Italy b Physics and Astronomy Department, University of Bologna, Via B. Pichat 6/2, Bologna 40126, Italy c Biomedical Sciences Department, University of Bologna, Via Irnerio 48, Bologna 40126, Italy d INFN, Italy ARTICLE INFO MSC: 00–01 99-00 Keywords: Plasma focus Signal analysis Wigner-Ville transform Dose rate Medical applications ABSTRACT In a Plasma Focus device the plasma collapses into the pinch where it reaches thermonuclear conditions for a few tens of nanoseconds, becoming a multi-radiation source. The nature of the radiation generated depends on the gas filling the chamber and the device working parameters. The self-collimated electron beam generated in the backward direction with respect to the plasma motion is one of the main radiation sources of interest also for medical applications. The electron beam may be guided against a high Z material target to produce an X-ray beam. This technique offers an ultra-high dose rate source of X-rays, able to deliver during the pinch a massive dose (up to 1 Gy per discharge for the PFMA-3 test device), as measured with EBT3 GafchromicⒸfilm tissue equivalent dosimeters. Given the stochastic behavior of the discharge process, a reliable on-line estimate of the dose-delivered is a very challenging task, in some way preventing a systematic application as a potentially interesting therapy device. This work presents an approach to linking the dose registered by the EBT3 GafchromicⒸfilms with the information contained in the signal recorded during the current discharge process. Processing the signal with the Wigner-Ville distribution, a spectrogram was obtained, displaying the information on intensity at various frequency scales, identifying the band of frequencies representative of the pinch events and define some patterns correlated with the dose. 1. Introduction As is well known, a Plasma Focus (PF) is a pulsed power device able to confine the plasma produced in a discharge phenomenon in a small region, in the so called ‘pinch’ event, through electromagnetic accel- eration of a current sheet (Sumini, 2006). When the plasma is in the pinch status, it can reach thermonuclear pressures and energy den- sities; in such conditions it acts as emitter of several kinds of radiation like thermal bremsstrahlung X-rays, ion and electron beams and of any kind of products allowed by the nuclear reactions that could possibly take place in that environment (Lee and Saw, 2011). The underlying physics of this peculiar class of devices is still debated and it is safe to say that it is not yet well understood. The pinch phenomenon is extremely fast (a few tens of nanoseconds) and it is believed to be highly non linear with respect to the control parameters and chaotic. These combined characteristics make the study of the whole phenom- enon quite difficult. In the past, some efforts have been put in finding a way to predict the neutron yield from D-D or D-T fusion reactions coming from a PF pinch by considering its constructional and opera- tional parameters, like the capacitor's bank energy, the chamber pressure and the operating voltage (Patran, 2005). Recently, the PF technology has been proposed as a viable fast X-ray source: the electron beam emitted from inside the pinch can be used to produce X-rays via the interaction with a suitable target (Tartari (2004), Ceccolini (2012); Sumini (2015)). The main unsolved issue with this technology is that, under very similar operating conditions, the radiation yield and spectrum can vary at every discharge: this is particularly true for the spectrum of the electrons emitted from the pinch. The scope of this work is to study the characteristics of the current signal registered from the PF circuit of an experimental Mather type device actually operated in our laboratory, the PFMA-3 (Plasma Focus for Medical Applications #3) and to extrapolate some features that can be correlated with the dose delivered to a stack of GafchromicⒸfilms to be considered as tissue equivalent (Ceccolini (2012a), Ceccolini (2012b)). Starting from a quite high number of recorded shots, the current signals have been processed using high- http://dx.doi.org/10.1016/j.radphyschem.2017.03.022 Received 29 September 2016; Received in revised form 8 March 2017; Accepted 11 March 2017 ⁎ Corresponding author. E-mail address: marco.sumini@unibo.it (M. Sumini). Radiation Physics and Chemistry xxx (xxxx) xxx–xxx 0969-806X/ © 2017 Elsevier Ltd. All rights reserved. Please cite this article as: Sumini, M., Radiation Physics and Chemistry (2017), http://dx.doi.org/10.1016/j.radphyschem.2017.03.022