## 1 Introduction  
The FLASH effect, first observed in 1969 and demonstrated further over the following decade [1, 2, 3, 4], was rediscovered in 2014 [5]. It has since been heavily investigated due to its potential for tissue sparing, while maintaining effective tumour control [6, 7, 8, 9, 10]. Using ultra-high dose rates (UHDRs), many teams have managed to reproduce the FLASH effect with protons, electrons, and X-rays [11; 12; 13; 14]. As early as 2000, the use of very-high-energy electrons (VHEEs, electrons above 50 MeV) was suggested as a potential solution to treating deep-seated tumours [15]. More recent work has investigated this property, as well as delivering the FLASH effect, as VHEE linacs, while not designed for the purpose of radiotherapy, are generally operated with parameters that place their output firmly within the UHDR regime [16; 17; 18; 19; 20]. Currently, there are only a few facilities available to users globally. Facilities that have been made available to external research groups include the CERN Linear Electron Accelerator for Research (CLEAR) at CERN, Switzerland [21], the Accelerator Research Experiment at SINBAD (ARES) at DESY Hamburg, Germany [22], the Sources for Plasma Accelerators and Radiation Compton with Lasers and Beams (SPARC) at INFN-LNF Italy [23], the Next Linear Collider Test Accelerator (NLCTA) at SLAC in the United States [24], and, most recently, the Pulsed Energetic Electrons for Research (PEER) facility at the ANSTO Australian Synchrotron [25]. These facilities feature state-of-the-art VHEE accelerators, and have facilitated significant advances towards dosimetry capable of characterising an UHDR electron beam, as well as diagnostic tools such as current transformers [26], parameter optimisation [27], and Faraday cups [28]. However, accurate dosimetry featuring real-time measurements suitable for on-patient quality assurance is currently lacking. There has been a consensus on the importance of reporting the temporal structure of a beam to advance understanding of the FLASH effect [29]. Most VHEE accelerators provide beams consisting of an underlying bunch structure, where bunches of charged particles delivered sequentially are referred to as a pulse, or a bunch-train [30; 31], though some facilities accelerate single bunches with varied bunch repetition frequency [22]. Pulses can be delivered in either a single pulse mode, or with a pulse repetition. To realize an in vivo FLASH effect, studies have shown that two of the most important parameters are the pulse dose rate (also referred to as instantaneous dose rate, though we believe this term should be reserved for the bunch dose rate) and the average dose rate, which is related to the total time of irradiation [12; 29; 32; 33]. While this is important for positive biological outcomes, delivering radiation at the frontiers of what is possible places strenuous demands on dosimetry and the diagnostics required for eventual, successful clinical implementation of FLASH radiotherapy. Many studies have shown that dose per pulse (DPP), rather than dose rate, may be the limiting factor for existing detectors [34; 35; 36; 37]. As pulsed electrons consist of a bunched sub-structure on timescales orders of magnitude smaller than the pulse, the dose rate within the bunch is greater than that of the pulse. These parameters may affect not only the biological response to UHDR irradiations but also the response of detectors exposed to these extreme environments. While the radio-biological community is yet to agree on the exact parameters to induce the FLASH effect, detectors are being tested at ultra-high DPP. If a detector produces valid results within both clinical and ultra-high DPP environments, it is reasonable to expect that its performance will be equivalent within an intermediate regime if required.