Advanced beam manipulations and diagnostics in the injectors of proton and ion linear accelerators

Abstract

Accelerators are important and valuable tools for basic scientific research and have numerous applica- tion fields. For instance, accelerators are employed as neutron sources, in microscopy, particle colliders, and more. The diverse range of application fields necessitates that accelerators can produce beams with varying energy, shape, and parameters. Consequently, numerous beam manipulation techniques have been developed and adapted for use in accelerators. Furthermore, as beam manipulation techniques have evolved, so too have beam diagnostic techniques, which are essential for assessing the beam pa- rameters resulting from these new manipulation methods. In this thesis, we will discuss several beam manipulation techniques and beam diagnostic methods. The space charge compensation technique is a well-known and important method in high-intensity particle accelerators for effectively mitigating space charge effects. Typically, this technique is employed in low-energy beam lines and it is well-known that a magnetic field, such as a solenoid field, enhances its effectiveness. However, there is limited research on magnetic quadrupole and electrostatic quadrupole lattices. Therefore, we will investigate space charge compensation in a solenoid field as reference data and also explore space charge compensation in magnetic quadrupole and electrostatic quadrupole beam- lines. The next beam manipulation technique involves spinning beams, often referred to as angular mo- mentum dominated beams. Research on spinning beams has expanded with research on flat beams, which can be generated using skew quadrupoles and spinning beam techniques. However, recent dis- coveries have revealed additional benefits of spinning beams, such as mitigating emittance growth and halo formation by suppressing fourth order resonance in linear accelerators. This discovery motivates us to investigate the potential of spinning beams in mitigating emittance growth caused by machine im- perfection errors, which are inevitable in accelerators. The third beam manipulation technique is focused on single bunch selection. In accelerator-based neutron sources, neutrons are generated through the collision of accelerated beams with target materials. Consequently, the rate of neutron production is contingent on the time structure of the beam. When a continuous wave (CW) accelerator is employed, the beam’s repetition time typically spans from a few to tens of nanoseconds, corresponding to the frequency of the accelerating cavity. This repetition time is insufficient for conducting high-resolution neutron time of flight (TOF) experiments. To overcome this limitation and enable neutron TOF experiments at the RAON heavy ion accelerator facility, we propose a method for selecting a single bunch by integrating a fast chopper and a double gap buncher at the low energy beam transport (LEBT) section. The fast chopper is capable of rapid switching with timescales in the order of tens of nanoseconds, thereby transforming a continuous wave (CW) beam into a pulsed beam. Subsequently, the double gap buncher is employed to bunch the particles, reducing the pulse length to less than one cycle of the radio frequency quadrupole (RFQ). The ultimate goal is to achieve a single isolated bunch of particles after passing through the RFQ. The final topic is a beam diagnostic method, specifically for beam emittance measurement. Emit- tance is a fundamental parameter in accelerators and one of the most critical ones. Consequently, several emittance measurement methods have been developed, such as the quad scan, the three-grid method, the Allison scanner, phase space tomography, etc. We will investigate the advantages and disadvantages of these methods and their real-world applications in accelerators.