Emittance Of Injected Beam Research Articles

Beam-loss driven injection optimization for HIAF-BRing in the presence of space charge

BRing is the booster ring of the HIAF project in which the beam intensity is designed up to 1.0 × 1011 ppp (238U34+). In order to reach the required intensities, an efficient injection scheme is crucial and the beam loss during injection must not exceed the limits defined by machine protection and dynamic vacuum requirements. An injection scheme called two-plane painting multiturn injection is consequently proposed, which exploits both the horizontal and vertical acceptance of the BRing by a tilted electrostatic septum. The influence of the space charge on the injection process is important for the two-plane multiturn injection scheme which should provide the required intensity with a minimal beam loss. The impact of the space charge on the efficiency of the injection process is investigated using a modified ORBIT code. In order to achieve lower beam loss, the particle swarm algorithm is proposed for a detailed injection optimization with space charge effect. Detailed studies on the two-plane painting multiturn injection scheme and the dependence on the lattice tune, the injected beam current, and the injected beam emittance are also presented. The results provide an important guideline for the design optimization of the injection system for the HIAF-BRing.

A transverse emittance and acceptance measurement system in a low-energy beam transport line

A transverse beam emittance and acceptance measurement system has been developed to visualize the relationship between the injected beam emittance and the acceptance of a cyclotron. The system is composed of a steering magnet, two pairs of slits to limit the horizontal and vertical phase-space, a beam intensity detector just behind the slits for the emittance measurement, and a beam intensity detector in the cyclotron for the acceptance measurement. The emittance is obtained by scanning the slits and measuring the beam intensity distribution. The acceptance is obtained by measuring the distribution of relative beam transmission by injecting small emittance beams at various positions in a transverse phase-space using the slits. In the acceptance measurement, the beam from an ion source is deflected to the defined region by the slits using the steering magnet so that measurable acceptance area covers a region outside the injection beam emittance. Measurement tests were carried out under the condition of accelerating a beam of (16)O(6+) from 50.2 keV to 160 MeV. The emittance of the injected beam and the acceptance for accelerating and transporting the beam to the entrance of the extraction deflector were successfully measured. The relationship between the emittance and acceptance is visualized by displaying the results in the same phase-plane.

Time structure of an accelerated beam using a radio-frequency quadrupole linac with direct plasma injection scheme

In direct plasma injection scheme, the relation between the ion current from a laser ion source and the accelerated beam current by a radio-frequency quadrupole (RFQ) linac was studied by a series of the following analyses. First, ion current at beam extraction was calculated from measured plasma parameters using a scaling law. Second, the beam emittance at the entrance of acceleration electrode region was evaluated by the simulation of the ion extraction out of the ion source plasma using the result of the first calculation. Last, the accelerated beam current could be reproduced by the simulation of beam acceleration using the results of the second. The second calculation revealed the time variation in the injected beam parameter to the RFQ linac. Then it was proved that the time structure of the accelerated beam was different from that of the injection beam because the degree of the matching between the injected beam emittance and the RFQ acceptance varied with time.

Acceleration of high current heavy ions using a variable energy radio-frequency quadrupole linac and measurement of the input beam emittance

A high current ion beam injection system and a variable energy radio-frequency quadrupole (RFQ) accelerator with an external LC resonance circuit are tested. A four-rod RFQ electrode of 2.3 m length is newly designed to obtain a milliampere class MeV ion beam. To increase accelerated beam current, injected beam emittance into the RFQ is measured and compared with the designed RFQ acceptance. Injected beam emittance tends to increase with the beam current increase. The beam acceleration tests are carried out with a cw rf power supply of 100 kW (10–30 MHz, continuously variable). Results show that the time-averaged beam currents of N+ and Ar2+ are 1.1 mA (0.4 MeV) and 1.03 mA (1.0 MeV), respectively, and that the peak current of these beams is about 5 mA. As representative ion species for fabricating semiconductor devices, P+ and P2+ are accelerated, and the time-averaged beam current of 0.48 mA (0.56 MeV) and 0.28 mA (0.81 MeV) are obtained, respectively. This high current MeV ion implanter has great potential for application to high-dose implantation and high throughput production of semiconductor devices and material surface modifications.