Investigation of high current electron beam dynamics in linear induction accelerator for creation of a high-power THz radiation source

The work addresses the use of electron beam produced by the linear induction accelerator to generate terahertz radiation pulses of 100 MW power level based on a free electron laser scheme. The beam parameters required for efficient generation are given. The features of transverse beam dynamics when transporting the beam through the linac are investigated. Emphasis is put on the electron injector which geometry and operation parameters mainly determine the beam characteristics at the linac exit. Most of the possible factors contributing to the beam emittance gain in the accelerator are considered. The obtained analytical estimates are compared to the numerical simulation results. The experimental results on compressing and transporting the beam having the electron energy of 5 MeV and the current of 1 kA in the transport system of free electron laser are presented.

Influence of the initial winding displacement on the indicators of the electromechanical induction accelerator of cylindrical configuration

Purpose. The purpose of the article is to determine the influence of the initial displacement of the windings on the indicators of an electromechanical induction accelerator of a cylindrical configuration with pulsed excitation from a capacitive energy storage and with short-term excitation from an alternating voltage source. Methodology. To take into account the interrelated electrical, magnetic, mechanical and thermal processes, as well as a number of nonlinear dependencies, we use the lumped parameters of the windings, and the solutions of the equations describing these processes are presented in a recurrent form. The mathematical model of the accelerator takes into account the variable magnetic coupling between the windings during the excitation of the inductor winding. When calculating the parameters and characteristics of the accelerator, a cyclic algorithm is used. Results. At a frequency of an alternating voltage source of 50 Hz, the current amplitude in the armature winding is less than in the inductor winding. With an increase in the source frequency to 250 Hz, the phase shift between the winding currents decreases. The current in the inductor winding decreases, and in the armature winding it increases. The accelerating components of the force increase, and the braking ones decrease. With an increase in the source frequency to 500 Hz, the current density in the armature winding exceeds that in the inductor winding. In this case, the phase shift between the windings is further reduced. Originality. When a cylindrical accelerator is excited, the largest amplitude of the current density in the inductor winding occurs at the maximum initial displacement of the windings, but the amplitude of the current density in the armature winding is the smallest. The largest value of the current density in the armature winding occurs in the absence of an initial displacement. When excited from a capacitive energy storage, the electrodynamic force between the windings has an initial accelerating and subsequent braking components. As a result, the speed of the armature initially increases to a maximum value, but decreases towards the end of the electromagnetic process. When a cylindrical accelerator is excited from an alternating voltage source, a phase shift occurs between the currents in the windings, which leads to the appearance of alternating accelerating and decelerating components of electrodynamic forces. The accelerating components of the force prevail over the braking components, which ensures the movement of the armature. Practical value. At a frequency of an alternating voltage source of 50 Hz, the highest speed at the output of the accelerator vzf=0.5 m/s is realized at an initial displacement of the windings z0=6.2 mm, at a frequency of 250 Hz, the highest speed vzf=2.4 m/s is realized at z0=3.1 mm, and at a frequency of 500 Hz the highest speed vzf=2.29 m/s is realized at z0=2.3 mm.

Megavolt bremsstrahlung measurements from linear induction accelerators demonstrate possible use as a FLASH radiotherapy source to reduce acute toxicity

Recent studies indicate better efficacy and healthy tissue sparing with high dose-rate FLASH radiotherapy (FLASH-RT) cancer treatment. This technique delivers a prompt high radiation dose rather than fractional doses over time. While some suggest thresholds of > 40 Gy s−1 with a maximal effect at > 100 Gy s−1, accumulated evidence shows that instantaneous dose-rate and irradiation time are critical. Mechanisms are still debated, but toxicity is minimized while inducing apoptosis in malignant tissue. Delivery technologies to date show that a capability gap exists with clinic scale, broad area, deep penetrating, high dose rate systems. Based on these trends, if FLASH-RT is adopted, it may become a dominant approach except in the least technologically advanced countries. The linear induction accelerator (LIA) developed for high instantaneous and high average dose-rate, species independent charged particle acceleration, has yet to be considered for this application. We review the status of LIA technology, explore the physics of bremsstrahlung-converter-target interactions and our work on stabilizing the electron beam. While the gradient of the LIA is low, we present our preliminary work to improve the gradient by an order of magnitude, presenting a point design for a multibeam FLASH-RT system using a single accelerator for application to conformal FLASH-RT.

Megavolt Bremsstrahlung Measurements from Linear Induction Accelerators Demonstrate Possible Use as a FLASH Radiotherapy Source to Reduce Acute Toxicity

Recent studies indicate better efficacy and healthy tissue sparing with high dose-rate FLASH radiotherapy (FLASH-RT) cancer treatment. This technique delivers a prompt high radiation dose rather than fractional doses over a longer period of time. The threshold is >40 Gy-s-1 with a maximal effect at >100 Gy-s-1 that must be maintained in the treatment volume. Mechanisms are still widely debated, but toxicity is minimized while inducing apoptosis in malignant tissue. Delivery technologies to date show that a capability gap exists with clinic scale, broad area, deep penetrating, high dose rate capability. Based on present trends, if FLASH-RT is adopted, it may become a dominant approach except in the least technologically advanced countries. The linear induction accelerator (LIA) developed for high current, high repetition rate, species independent charged particle acceleration, has yet to be considered for this application. We briefly review the status of LIA technology, explore the physics of bremsstrahlung-converter-target interactions and our work on stabilizing the electron beam. While the gradient of the LIA is low, we present our preliminary work to improve the gradient by an order of magnitude, presenting a point design for a multibeam FLASH-RT system using a single accelerator for application to conformal FLASH-RT.