Norbert Koch

High Power HEMP-Thruster Module, Status and Results of a DLR and ESA Development Program

Within a development project, the German Space Agency DLR has supported the investigation of scaling the HEMP thruster technology from nominal 50 mN, 1.5 kW to higher thrust and power levels of 250 mN and 7.5 kW, respectively. As a result, first demonstration models of cylindrical and coaxial HEMP 30250 thrusters have been built. For the cylindrical design, two demonstration models - HEMP 30250cyl DM1 and DM2 - have been built and tested at the Thales facility in Ulm. Due to its magnetic confinement, the DM1 thruster could be operated up to high power and anode voltage levels. The highest anode power operation point was about 18 kW at 1.8 kV anode voltage providing a thrust of 371 mN. The first results of a second DM2 thruster are reported in this paper. It achieved at 110 sccm Xe flow and 680 V anode voltage and 10 kW anode power a thrust of 332 mN at much improved specific impulse of 3,154 s at a total efficiency of 51.5 %. The goals of the development program are building and comparing three approaches for a high power HEMP thruster module at 7.5 kW nominal anode power: - A) Cylindrical HEMP 30250 - B) Coaxial HEMP 30250 - C) Cluster of 4 small HEMP 3050 thrusters. The thruster module is intended to provide both, high specific impulse operation of 3000 s at 250 mN thrust and high thrust operation of 375 mN at a specific impulse of 2000 s. I) Introduction

Development of electron guns for excimer light sources in the vacuum UV

Two types of electron guns for ultraviolet (UV) and vacuum UV light sources are presented. The first type is a very compact electron gun which produces a highly collimated beam with a beam diameter of about 0.6 mm. This gun is designed for operation in continuous and pulsed modes with beam currents from 2 /spl mu/A to 20 mA. The second electron gun is a high current gun with rectangular beam profile. The transverse dimensions of the beam are 0.6 by 40 mm. The maximum peak current in pulsed mode produced by the gun is on the order of 5 A. A ceramic membrane (300 nm thick) separates the vacuum part of the gun from the cell which contains a target gas. The membrane is attached to the gun with a new brazing technique. This technique produces complete vacuum-tight sealing and allows operation of the gun without any external pumping. The other advantage of the technique is inertness of the brazing material in respect to aggressive gases and short wavelength radiation. Permeability measurements of argon, neon and helium through the membrane were performed at different temperatures and electron beam currents.

First Test Results of the 1 to 15 kW Coaxial HEMP 30250 Thruster

We present a new type of HEMP (High Efficiency Multi Stage Plasma) thruster with a coaxial discharge channel. While maintaining the extreme throttle ability of the cylindrical HEMP thruster concept, the extension towards a coaxial geometry will allow for scaling up to high power and thrust levels as required for orbit raising and station keeping of medium to large geostationary satellites. The first version of a laboratory model named HEMP30250 shall provide a nominal thrust and specific impulse of 250mN and 3000s at an anode efficiency of 55%, respectively. Based on the experience made with our cylindrical HEMP3050 type thrusters models, we expect a wide operational range in applicable discharge voltages from 200 to 2000 V and xenon propellant mass flows from 1 to 15 mg/s, resulting in anode power levels from below 1 up to 15 kW and thrust values of up to 500 mN with only small variations in thrusters efficiency. This is mainly due to the effective plasma confinement provided by the HEMP thruster specific magnetic field topology, where by means of a system of periodically arranged permanent magnets a high density discharge is maintained along the median of the coaxial discharge channel keeping the plasma off the channel walls. As a consequence, thermal losses typically amount only 10% of the electrical input power and are mainly dissipated at the anode rather than at the discharge channel which in addition is kept free from erosion. At this conference we will review the concept of a coaxial HEMP thruster and show design aspects of our HEMP30250 laboratory model DM1. First operational characteristics will be presented and an outlook to future works will be given.

The highly efficient multistage plasma (HEMP) thruster, a new electric propulsion concept derived from tube technology

In this paper, a new Thales Electron Devices GmbH (TEDG) patented thruster concept is presented, which was successfully investigated. The results showed, that the concept advances the electric propulsion (EP) capabilities by relying on plasma confinement with the means of PPM structures used in TWTs to focus electron beams through delay lines and multistage depressed collectors (MDC). The performance improvements obtained recently are summarised. The total efficiency shown is the product of electrical and the ionisation efficiency. The ionisation efficiency approaches values close to 1 for higher Xe flows. For DM6 MS1 version, this is the case at Xe flows above 10 sccm, resulting at 14 sccm in a total efficiency of about 50%.

A New Diagnostic Chamber For Fast Thruster Development

To support the further development of the cylindrical and coaxial HEMP thruster family, Thales assembles a new vacuum test chamber equipped with diagnostic tools to completely characterise the ion beam of a thruster. The measurement of the global parameters thrust, power to thrust ratio and specific impulse is performed by means of high resolution mechanical thrust balance, power and flow metering, respectively. The full information on the angular distribution, velocity distribution and charge state of the ions is obtained by means of an energy selective mass spectrometer mounted on the chamber wall. The polar beam angle variation is obtained by rotation of the thruster exit centre around a vertical axis. The new diagnostic chamber allows to identify the effects of modified permanent magnetic circuits or channel geometries within fast iteration cycles. The chamber volume of 2.4 m diameter x 4.0 m length and an effective Xenon pumping speed up to 100.000 l/s, mainly by means of cryo pumps, guarantees minimal impacts of the test environment on the thruster performance. A special geometrical arrangement of the chamber wall shields minimises the deposition of sputtered chamber wall material on the thruster channel ceramics and thus eases the free space life prediction of a thruster. This paper gives an overview of the current status of the facility and the planned activities.