High Specific Impulse Operation Research Articles

Magnetic field optimization of hall thruster with large height-radius ratio for high specific impulse operation

Hall thrusters with large height-radius ratio not only have incalculable application values in reducing the volume and weight of thrusters, but also have the potential advantages of higher discharge performance and longer service life. However, the lower propellant density in the main ionization zone and the higher electron temperature in the channel aggravate the loss of propellant and current under high voltage, and significantly reduce the discharge efficiency under high specific impulse mode. To improve the discharge performance of Hall thrusters with large height-radius ratio under high voltage, an optimization scheme of internally loaded magnetic field was proposed in this work. The simulation results show that under the internally loaded magnetic field, both the ionization zone and the acceleration zone move toward the inside of the channel. Although the ion loss on the walls increases, the higher propellant density at the channel upstream greatly promotes the increase of ionization rate and significantly improves the propellant utilization efficiency. The second zone crossed by magnetic field lines in the channel can be established by the internally loaded magnetic field, which enhances the magnetic field intensity on the inner and outer walls, and reduces the electron temperature near the channel outlet significantly. So that the axial conduction of electrons is effectively restrained and the current utilization efficiency is greatly improved. With the introduction of internally loaded magnetic field, the total efficiency of HEP-1350PM can be increased by 7.2% at 400 V. Moreover, the performance optimization effect brought by the internally loaded magnetic field will be gradually amplified with the increase of discharge voltage, which makes the Hall thruster with large height-radius ratio expected to achieve high-efficiency discharge under higher specific impulse.

Study on the influence of magnetic field on the performance of a 5 kW hall thruster

Hall thruster is a kind of plasma optics device, which is used mainly in space propulsion. To study the influence of magnetic field on the performance of a 5 kW hall thruster, a two-dimensional PIC-MCC model was built. The Bohm diffusion was modeled by using a Brownian motion instead of the Bohm collision method and the near-wall conduction was modeled by a secondary electron emission model. When the mass flow rate is 5 mg/s, the thruster performance like thrust, efficiency and discharge current was simulated under a discharge voltage from 300 to 1,000 voltage. At first, the performance under constant magnetic field was simulated. The results showed that the magnetic field could not restrain the electrons as the discharge voltage increased. Later, the performance under varied magnetic field was simulated. The results showed that increasing the magnetic field strength with the increasing discharge voltage could restrain the electrons more efficiently, which proved that increasing the magnetic field strength is necessary for high specific impulse operation of hall thruster. At last, the performance measurement experiment of the thruster was carried out, and the experimental results verified the accuracy of the simulation results.

Low power arcjet thruster using LaB6 hollow cathode

A 100-W class low power arcjet thruster using a hollow cathode was proposed, with the goal of reducing cathode erosion. The hollow cathode's emitter was lanthanum hexaboride expecting its excellent thermionic emission performance. The experiment used argon as a propellant and compared two different emitter lengths. The estimated emitter temperature was almost the same regardless of the emitter length, however, due to of the efficient heat exchange with the longer arc plasma region, the longer emitter provided better performance with higher discharge voltage. Additionally, the hollow cathode was compared to the conventional rod cathode, and the hollow cathode was found to have some advantages. The specific impulse of the hollow cathodes was higher than that of the rod cathode at low flow rate. The results showed that the hollow cathode is best for high specific power and high specific impulse operation. The unstable transition between low- and high-voltage modes has been observed in the rod cathode, but not in the hollow cathode configurations. Helium was put to the test as a propellant and compared to argon for simulate the future use of hydrogen as a propellant. The thrust efficiency was lower due to the high discharge voltage and significant heat loss, but the specific impulse was higher as expected. No severe recession or erosion of the emitter was observed after the test campaign, but some surface color change was seen which may affect in the long-term operation.

Assessment of the T5 and T6 Hollow Cathodes as Reaction Control Thrusters

Hollow cathodes have been proposed as reaction control thrusters for all-electric and small spacecraft. This paper makes an assessment of modified T5 and T6 hollow cathodes for use as millinewton range thrusters. The influence of terminal parameters such as discharge current, mass flow rate, and cathode/anode geometry on thrust production is discussed. The data indicate that the T5 cathode may be able to develop specific impulses in the range of 150–250 s with argon at reasonable thrust efficiencies of up to 14%. As such, hollow-cathode thrusters may meet some limited applications. However, it is unlikely that this type of thruster could be improved significantly or could compete with similar thrusters in the same operating range. High specific impulse operation is also shown to develop large discharge voltage fluctuations, which may significantly limit the lifetime of such a device.

Particle Simulation of High Specific Impulse Operation of Low-Erosion Magnetic Layer Type Hall Thrusters

Particle Simulation of High Specific Impulse Operation of Low-Erosion Magnetic Layer Type Hall Thrusters

High-Specific Impulse Hall Thrusters, Part 1: Influence of Current Density and Magnetic Field

A laboratory-model Hall thruster with a magnetic circuit designed for high-specific impulse (2000‐3000 s) was evaluated to determine how current density and magnetic field affect thruster operation. Results have shown for the first time that a minimum current density and optimum magnetic field shape exist at which efficiency will monotonically increase with specific impulse. At the nominal mass flow rate of 10 mg/s and between discharge voltages of 300 and 1000 V, total specific impulse and total efficiency ranged from 1600 to 3400 s and 51 to 61%, respectively. Comparison with a similar thruster showed how efficiency can be optimized for specific impulse by varying the shape of the magnetic field. Plume divergence decreased from a maximum of 48 deg at 400 V to a minimum of 35 deg at 1000 V, but increased between 300 and 400 V as the likely result of a large increase in discharge current oscillations. The breathing-mode frequency continuously increased with voltage, from 14.5 kHz at 300 V to 22 kHz at 1000 V, in contrast to other Hall thrusters where a sharp decrease of the breathing-mode frequency was found to coincide with increasing electron current and decreasing efficiency. These findings suggest that efficient, high-specific impulse operation was enabled through the regulation of the electron current with the applied magnetic field.