We proposed and examined experimentally that the charge of the 100 MeV-class electron bunches from laser wakefield accelerators (LWFAs) can be improved to ∼400 pC with the aid of a structured nozzle system. A 43 TW laser pulse driver with 30 fs duration is incident on a density structured gas target, which is created by a 4 mm long gas jet and a moveable slender needle nozzle with 0.8 mm diameter. The charge of produced beam increases compared with that from merely a gas jet (∼100 pC) and reaches its maximum (∼400 pC) at an optimal relative position. Particle-in-cell simulations show that the self-focused spot size and intensity of the laser pulse can be tuned continuously and reveal how the detailed dynamics of the laser pulse evolution, the electron injection, and acceleration in this structured gas target affects the beam charge. This work demonstrates the feasibility of adjusting the laser pulse distribution through its evolution in a plasma to significantly improve the injected charge in LWFAs, which is beneficial for many applications.

Ultrahigh dose rate radiotherapy (FLASH-RT) is under intensive investigation for its biological benefits. The mechanisms underlying its ability to spare normal tissues while suppress tumor growth still remain controversial. Here we reveal that compared to the low dose rate electron irradiation (0.36 Gy/s), FLASH electron irradiation at 61 or 610 Gy/s enhances the cytochrome c leakage from mitochondria in human breast cells MCF-10A, which elicits substantial caspase activation, suppresses both the cytosolic mitochondrial DNA (mtDNA) accumulation and IFN-β secretion. Besides, the deletion of mtDNA severely decreases the radiation-induced cGAS-STING activation. Conversely, the cytochrome c leakage in carcinoma cells MDA-MB-231 post electron irradiation is limited, especially for the case of FLASH irradiation, resulting in less cytosolic cytochrome c but stronger cGAS-STING activation than those in MCF-10A cells. The enhanced difference of cytochrome c leakage between cancer cells and normal cells post FLASH irradiation indicates a potential mechanism of FLASH effect by regulating the apoptotic and inflammatory pathway.

Laser plasma accelerators (LPA) can produce very high-energy electrons (VHEE) with ultra-short bunch duration, which may facilitate the application of ultra-high dose rate radiotherapy (FLASH-RT) to treat deep-seated tumors. The study aims to evaluate the dose rate delivery by spot-scanning VHEE beams produced by LPA and to discuss the feasibility and beam specifications for FLASH-RT implementation. Various dose rate metrics, including averaged dose rate (ADR), dose-averaged dose rate (DADR), and dose-threshold dose rate (DTDR), are examined in the context of spot-scanning. Theoretical analysis and Monte Carlo simulations are employed to quantify the dose rate distribution for a water phantom and explore the impact of beam parameters. All the beam parameters are based on experimental results. With a lower pulse repetition rate of 5 Hz, ADR can only reach a dose rate in the order of 10−1Gy/s, while attaining the FLASH-RT dose rate of 40Gy/s necessitates the utilization of high-power lasers with a kilohertz working repetition rate. In contrast to ADR, DADR and DTDR remain independent of the scanning path and can reach the ultra-high dose rate surpassing 1014Gy/s at the phantom surface. Meanwhile, the ultrashort electron bunch can be stretched during scattering within the water, resulting in a dependence of DADR and DTDR on the penetration depth. Both the charge per shot and angular spread are important parameters in dose rate calculations. This investigation offers insights into practical beam parameters for preclinical applications and supplies guidance for designing the LPAs suitable for future spot-scanning VHEE FLASH-RT.

We report on 6Li neutron capture therapy (LiNCT) in anticipation of using carbon nanoparticles to deliver targeted, high linear energy transfer radiation to non-resectable tumors. Our investigations show that, compared with existing 10B neutron capture therapy (BNCT), 6Li offers similar dose potential for equal mass density (DLi∼DB when mLi=mB), for capture products that span 7 times more range and approximately three cell lengths. Consequently, 6Li-filled nanoparticles dispersed more than half-a-cell-length apart, better convey high doses and ultra-high dose-rates, as LiNCT generates substantially less γ-rays and becomes more targeted than BNCT. To this end, we propose a neutron production scheme involving laser-plasma driven protons incident on various 7Li targets, capable of producing >109 n/sr/pulse. For high repetition frequency, efficient neutron moderation, and ideal 6Li concentration, the modality offers greater precision than existing neutron capture therapy.

The interaction between an ultrastrong laser and a cone-like target is an efficient approach to generate high-power radiations such as attosecond pulses and terahertz waves. The objective is to study the $\gamma$-ray generation under this configuration with the help of 2D particle-in-cell simulations. It is deciphered that electrons experience three stages, including injection, acceleration and scattering, to emit high-energy photons via nonlinear Compton scattering (NCS). These spatial-separated attosecond $\gamma$-ray pulses own high peak brilliance (>10²² photons/(s·mm²·mrad²·0.1%BW)) and high energy (6 MeV) under the case of normalized laser intensity $a_0=30(\mathrm{I}=2\times {10}^{21} \mathrm{W}/{\mathrm{cm}}^2)$. In addition, the cone target turns out to be an order of magnitude more efficient in energy transfer compared to a planar one.

DC-SRF-II gun, a high-brightness continuous-wave photocathode gun, has greater potential in electron beam irradiation applications. This paper presents the in-vacuum and in-air irradiation dosimetry study of the high repetition rate electron beam from the DC-SRF-II gun with both Monte Carlo simulations and experiments. Especially, high-dose uniform irradiations with flexible and accurate tuning of dose rate across orders of magnitude are demonstrated. Good stability and repeatability of the doses are also shown. The ultra-wide tuning range and precise control of irradiation time and dose rate are expected to pave the way for innovative applications across a wide range of fields.