The Hall thruster generates its thrust by accelerating a plasma jet by the combined operation of perpendicular electric and magnetic fields in a coaxial channel. It can achieve a very high specific impulse, 1000-3000 sec, and thus its use in space missions will lead to large savings in the required propellant mass. The capability of changing their performances by varying parameters such as discharge voltage or mass flow rate makes Hall thrusters ideal for missions where different types of maneuvers require different levels of thrust and specific impulse. This work deals with the performance of low power (200-300W) Hall thrusters. The problem of the degradation of Hall thruster performance, when a given thruster configuration is operated at reduced power levels, is analyzed. Results of experiments performed with a Hall thruster in the 200-600 Watts power range demonstrate this type of degradation. It is explained as being a result of the drop in the efficiency of the ionization process at reduced propellant flow rates. The standard approach to overcome this problem by scaling down the thruster is analyzed and proper scaling rules are outlined. It is demonstrated however that the proper implementation of the required scaling is limited by magnetic material and circuit properties. It is also shown that the main drawback of down sized Hall thrusters in the power range below 300 Watts is the sharp drop in their operating lifetime compared to larger size thrusters. As a consequence, a different approach, to try to improve the propellant utilization by geometric or magnetic modifications but without scaling down the thruster, is preferred for Hall thrusters in the 200-300 Watts power range. The straightforward implementation of this approach, by extending the channel length was investigated experimentally. As part of this investigation, an improved laboratory Hall thruster has been designed and constructed. In order to improve the thrust measurement accuracy and, as well, to reduce uncertainties related to the conditions inside the vacuum chamber during cryopumps and thruster operation, a new calibration system, which allows to calibrate the thrust stand at vacuum conditions and during thruster operation, was designed and built. By using the new calibration system the relative error in the thrust measurement was reduced from 3.1% to ~1.9% (thrust of 12mN). The channel length investigation comprised of an extensive parametric study of thruster performance at five length configurations...(truncated by viXra Admin to < 400 words).