Jongsub Lee

Mode transition for power dissipation induced by driving frequency in capacitively coupled plasma

We measured electrical characteristics of capacitively coupled plasma at low pressure (2.67 Pa) with different driving frequencies. From these measurements, we observed a significant change in discharge power characteristics during the frequency increase. While increasing the frequency, a square dependence of power characteristics (P∼I2) changes to a linear dependence (P∼I). This observed result reflects that a power dissipation mode transition from an ion-dominated dissipation mode to an electron-dominated dissipation mode takes place during the driving frequency increase. Both the results calculated from a simple sheath model and a particle-in-cell simulation are in a good agreement with the experimental data.

Effect of the annular region on the performance of a cylindrical Hall plasma thruster

Performance characteristics of a cylindrical Hall thruster depending on the depth of the annular region (La) in front of the anode were investigated. The effect of the annular region was examined by operating thrusters corresponding to four different values of La (0, 4, 6, and 10 mm) and a fixed length of the cylindrical region (25 mm). Various measurements such as electron and ion currents, thrust, anode efficiency, current and propellant utilizations, and ion energy distribution functions were performed. Such measurements lead to an interpretation that (1) a considerable potential difference may exist between the anode and the ionization region, which is presumably located near the end of the annular region where magnetic field lines converge; (2) this potential difference increases with respect to increasing La; and (3) the presence of the annular region near the anode reduces the specific impulse and anode efficiency for the examined thrusters.

Performance characteristics according to the channel length and magnetic fields of cylindrical Hall thrusters

Performance characteristics of low power cylindrical Hall thrusters are investigated in terms of the length of the discharge channel. Thrust, efficiency, discharge current, and propellant utilization are evaluated for different channel lengths of 19, 22, and 25 mm. It is found that the propellant utilization and ion energy distribution function are strongly associated with the channel length. Increase of thrust and efficiency are also found with increasing channel lengths. These characteristics of the thruster are interpreted with possible generation of multi-charged ions due to increased residing time within the extended space inside the channel.

Radial scale effect on the performance of low-power cylindrical Hall plasma thrusters

Investigation of the radial scale effect on low-power cylindrical Hall thrusters has been undertaken by comparing the thrusters with three different channel diameters of 28, 40, and 50 mm. The investigation found that both the anode efficiency and the thrust of the larger thruster are higher as the anode power is raised. On the other hand, higher current and propellant utilizations are achieved for the smaller thruster, which is due to higher neutral density and better electron confinement. The large plume angle of the small cylindrical Hall thruster causes thrust loss, resulting in the reduction of anode efficiency.

Development of the Head Unit of a 300 W Cylindrical Hall Thruster for Small Satellites

The thruster head unit of a 300 W cylindrical Hall thruster was developed for the propulsion system of small satellites. The magnetic topology in the thruster channel is a key parameter to achieve high performances. Two types of magnetic circuit structures were designed and manufactured to compare the thrust levels and efficiencies. Also the endurance test was conducted to measure the stable operation duration of the thruster head and to find degree of erosion after extended operation.

Development of Xenon feed system for a 300 W Hall-effect Thruster

A Xenon feed system has been dev eloped for a 300 W Hall-effect thruster intended for orbit maintenance of small satellite. The system can store about 2 kg of xenon gas at 150 bar and is capable of controlling the mass flow rate of the gas at 0.5 SCCM resolution. The performance of t he system is verified with a laboratory experiment. It is confirmed that the operation of the feed system is successfu l at a pressure level of 1.0×10 -6 torr in the vacuum chamber.

Development of Hall-effect Thruster for Orbit Correction and Transfer of Small Satellites

A small Hall-effect thruster with a thrust range near 10 mN and a specific impulse of about 1500 s has been designed to control or maintain the orbits of small satellites. The thruster system consists of a hall-effect thruster head, a power processing unit and a Xenon (Xe) gas feed system. The total mass, the consumed electric power and the efficiency of the thruster are approximately 10 kg, 300W and 30%, respectively. Analyses results that support the selection of the thruster for small satellites are provided along with a brief description of the thruster system.

Comparison Study of the Low Power Hall Thrusters Performance

A low power Hall thruster is under development for orbit maintenance of a small Earth observing satellite. Both cylindrical and annular type thrusters were manufactured and tested to characterize the performance of cylindrical Hall thrusters. Results were described through comparative analyses. Cylindrical thrusters were manufactured in two different channel diameter dimensions, 28 mm and 50 mm. Thrust, ion velocity and ion current were measured in various operating conditions. The results show that cylindrical thrusters are more efficient in mass utilization and voltage utilization, but less efficient in current utilization than annular one.

Development of Xenon Feed System for a Hall-Effect Thruster to Space-propulsion Applications

A Xenon Feed System (XFS) has been developed for hall-effect thruster to small satellite space-propulsion system applications. The XFS delivers low pressure gas to the Anode and Cathode of thruster head unit from a xenon storage tank. Accurate throttling of the propellant mass flow rate is independently required for each channel of the thruster head unit. The mass flow rate to each channel is controlled using the accumulator tank pressure regulation through a micron orifice and isolation valve. This paper discusses the Xenon Feed System design including the component selections, performance estimation and functional test.

Power dissipation mode transition induced by a driving frequency increase in capacitively coupled plasma

Summary form only given, as follows. Electrical characteristics of capacitively coupled plasma at low Pressure (20 mTorr) are measured with different driving frequency. From these measurements, we found a significant change of the power characteristics during frequency increase, which is square dependence of power characteristics changes to a linear dependence. The observed result reveals a power dissipation mode transition induced by driving frequency modulation. Both calculated result from a simple sheath model and PIC have a good agreement with the experimental data.