Drift distance survey in direct plasma injection scheme for high current beam production.
In a laser ion source, plasma drift distance is one of the most important design parameters. Ion current density and beam pulse width are defined by plasma drift distance between a laser target and beam extraction position. In direct plasma injection scheme, which uses a laser ion source and a radio frequency quadrupole linac, we can apply relatively higher electric field at beam extraction due to the unique shape of a positively biased electrode. However, when we aim at very high current acceleration such as several tens of milliamperes, we observed mismatched beam extraction conditions. We tested three different ion current at ion extraction region by changing plasma drift distance to study better extraction condition. In this experiment, C(6+) beam was accelerated. We confirmed that matching condition can be improved by controlling plasma drift distance.
BNL-96669-2012-CP RFQ LINAC commissioning and carbon 4 + acceleration for Ag + 15 acceleration via direct plasma injection scheme
Various species of high intensity highly charged state heavy ion beams with small emittance are required in many fields including particle physics, medical uses, inertial fusion, and simulator of space radiations. Direct Plasma Injection Scheme (DPIS), we have developed for several years, is a unique scheme to provide heavy ion beams to meet the above requirements. A high-density plasma created by a laser ablation with an initial drift velocity flies to entrance of a Radio Frequency Quadrupole (RFQ) LINAC; ions will be separated from plasma via high voltage at the inside of the RFQ LINAC. Then ions are captured by the RF buckets and are accelerated remaining high current over 10mA. In the past, we had accelerated carbon4+, carbon5+, and carbon6+ using a RFQ with partially modulated vanes. Due to the un-modulated section of the electrodes, accelerated beams were not bunched. In 2011, we replaced the vanes with a newly designed one. The designed charge to mass ratio (q/A) is 1/6 and the output energy is 270 keV/u. The beam commissioning with carbon 4+ was successfully carried out. In the next step we'll try to accelerate carbon 2+ (q/A=1/6), which is to demonstrate the feasibility of the Ag+15 ion acceleration. INTRODUCTION We are studying high current highly charged beam acceleration using direct plasma injection scheme (DPIS) which has been developed for several years [1]. We established how to capture and accelerate intense carbon beams with carbon beam. Using a table top small NdYAG laser system, carbon can be easily ionized up to fully stripped condition and the vanes in the RFQ was designed to accelerate more than 4/12 of charge to mass ration. We had tested carbon 4+, 5+ and 6+ acceleration. In the next step, we plan to accelerate heavier species like silver, bismuth or uranium, newly designed vanes were demanded. Currently we are testing laser irradiation conditions. In parallel, we modified the RFQ to accelerate lower charge to mass ratio particles. In this paper we describe the beam-commissioning test with a new set of vanes. LASER ION SOURCE High power laser irradiation on the solid target makes laser ablation plasma. A laser power density of more than 10^10[W/cm^2] is required to induce high charge state ions, therefore laser light is needed to be focused by an optical lens. The plasma contains a stream of high brightness highly charged ion flux. By extracting ions from the plasma, intense ion beams can be easily provided. Since the ablated plasma is emitted from a target material, the plasma moves away from the target. Simultaneously, the plasma expands three dimensionally. So the plasma plume volume expands longitudinally and transversely in a free space. The longer length of the plasma in the space gives a longer ion beam pulse width and thinner ion current density. These relations are shown in equations (1) and (2). The is a pulse length, and the is a current density of generated ion beam. The L is a plasma drift distance, the length from target to the ion extraction position. In a conventional laser ion source, however, once high intensity ion beam is extracted, the beam quality is suffered by its own repulsion forces called space charge effect. Due to severe non-linear force of the space charge, the emittance of the extracted beam grows immediately. This is a common issue of a Low Energy Beam Transport (LEBT) line with high current beams. DIRECT PLASMA INJECTION SCHEME The DPIS was developed to mitigate the problem of the strong space charge effect. The ablation plasma is created in a high voltage region and is transferred to an RFQ with its initial expanding velocity. At the entrance of the RFQ, the contained ions by the plasma are extracted from a nozzle which is connected to the plasma expansion high voltage region. Then the beam is captured by the RFQ electric field, and is accelerated efficiently. The ion beam Figure 1: Laser Ion Soource. is not exposed by the strong space charge effect in the transport line. RFQ LINAC Radiofrequency Quadrupole Linear Accelerator (RFQ LINAC, Figure 3) is accelerator for low energy ion beam. The quadrupole electric field excited by the modulated quadrupole electrode can accelerate ions on longitudinal axis with focusing on transverse axis (Figure4). On the longitudinal axis, ions follow a synchrotron oscillation, and on the transverse axis, ions follow a strong focusing. The RFQ parameters we used in this experiment are shown in Table1.The output energy and Beta is calculated from the input energy by the PteqHI, and the Q value is measured using a network analyzer. INJECTION STRUCTURE ALIGNMENT Since the extracted ion beam starts from the nozzle at the entrance point of the RFQ, the alignment of the nozzle and vanes are important. We measured 3D coordinates of the beginning section of the RFQ vanes by a FARO gage.
On the ontology of particle mass and energy in special relativity
Einstein claimed that the fundamental dynamical insight of special relativity was the equivalence of mass and energy. I disagree. Not only are mass and energy not equivalent (whatever exactly that means) but talk of such equivalence obscures the real dynamical insight of special relativity, which concerns the nature of 4-forces and interactions more generally. In this paper I present and defend a new ontology of special relativistic particle dynamics that makes this insight perspicuous and I explain how alleged cases of mass–energy conversion can be accommodated within that ontology.