We explore the use of gas-filled plasma-discharge capillaries for laser wakefield acceleration (LWFA) by employing a hybrid system that integrates an external high-voltage source to driven an electrical discharge, generate plasma within the capillary channel before to the main laser pulse. The process enhances plasma formation, boosts operational efficiency, and maintains laser intensity over multiple Rayleigh lengths, enabling high-energy electron acceleration. The electrical discharge creates a stable, uniform plasma environment, improving beam charge, energy stability, and reducing energy spread. This uniform plasma ensures better laser coupling and mitigates instabilities, leading to improved beam quality. This method supports efficient acceleration and the production of very-high-energy electron (VHEE) pencil beams (250 MeV) in a compact, cost-effective system designed for radiobiological studies at the future I-LUCE (INFN-Laser indUCEd Radiation Production) facility at the Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali del Sud (INFN-LNS) in Catania, Italy. The system aims to generate high-energy electron beams tailored for VHEE and FLASH radiotherapy (FLASH-RT) applications. In this paper, we present simulations of capillaries performed using COMSOL Multiphysics software, where plasma density is obtained as a function of the applied voltage. We analyze plasma behavior under varying voltage and compare the results with experimental data, demonstrating the model's accuracy in predicting plasma characteristics and its potential to optimize discharge conditions.

Plasma spectroscopy is a versatile tool for diagnosing key properties of plasmas, including those generated by discharges. It provides critical parameters-such as electron density and temperature-needed to optimize plasma sources for laser wakefield acceleration (LWFA). Stable, uniform plasma channels are essential to sustain GV/m wakefield and generate high-quality electron beams for advanced applications like radiation therapy (RT). Accurate spectral measurements require reliable wavelength calibration, as optical components can drift with environmental changes. In this study, atomic emission (AE) lamps-specifically mercury (Hg) and neon-argon (Ne-Ar) were utilized as reference light sources for wavelength calibration of a spectrometer system coupled to an intensified charge-coupled device (ICCD) camera. The known emission lines from these lamps ensured high-precision calibration across the relevant spectral range, facilitating accurate extraction of plasma parameters. This precise calibration enabled the determination of electron density and temperature through spectroscopic diagnostics, which are critical for understanding plasma behaviour. These measurements contribute to the development of gas-filled capillary discharge systems for LWFA and support the experimental objectives of the I-LUCE facility, dedicated to exploring laser-plasma interactions and advancing very high-energy electron beam (VHEE) applications. Monte Carlo (MC) simulations were conducted to assess the dose distribution of VHEE beams for RT applications.