Binyamin Rubin

Total and Differential Sputter Yields of Boron Nitride Measured by Quartz Crystal Microbalance

We present differential sputter yield measurements of boron nitride due to bombardment by xenon ions. A four-grid ion optics system is used to achieve a collimated ion beam at low energy (<100 eV). A quartz crystal microbalance (QCM) is used to measure differential sputter yield profiles of condensable components from which total sputter yields can also be determined. We report total and differential sputter yields of three grades of boron nitride due to bombardment by xenon ions for ion energies in the range of 60-500 eV and ion incidence angles of 0°, 15°, 30°, and 45° from normal. We also present preliminary results of the temperature dependence of the sputter yield. Comparisons with published values are made where possible.

Differential Sputter Yields of Boron Nitride, Quartz, and Kapton Due to Low Energy Xe+ Bombardment (Preprint)

Abstract : In this contribution we present results of differential sputter yield measurements of boron nitride, quartz, and kapton due to bombardment by xenon ions. The measurements are made using a sputtering diagnostic based on a quartz crystal microbalance (QCM). The QCM measurement allows full angular resolution, i.e. differential sputtering yield measurements are measured as a function of both polar angle and azimuthal angle. Measured profiles are presented for 100, 250, 350 and 500 eV Xe+ bombardment at 0?, 15?, 30? and 45? angles of incidence. We fit the measured profiles with Modified Zhang expressions using two free parameters: the total sputter yield, Y, and characteristic energy E*. Total yields are calculated from the differential profiles and are compared with published values and weight loss values where possible.

Magnetic filter type plasma source for ground-based simulation of low earth orbit environment

Simulation of the low Earth orbit (LEO) plasma environment in ground-based vacuum facilities is important for studies of spacecraft interaction with ionospheric plasmas. In this paper we describe the design and performance of a magnetic filter-equipped plasma source. Experimental data collected in the expanding plasma downstream of the source suggest it is a good candidate for use as a LEO plasma simulator in that the expanding plasma has a very low electron temperature and contains streaming ions—the plasma environment encountered by satellites in LEO. Adjustable plasma source operating conditions of flow rate, discharge current and discharge voltage enable production of plasma electron temperatures over the range from 0.17 to 0.35 eV and streaming ion energies over the range from 1 to 4 eV.

Space Demonstration of Bare Electrodynamic Tape-Tether Technology on the Sounding Rocket S520-25

A spaceflight validation of bare electro dynamic tape tether technology was conducted. A S520-25 sounding rocket was launched successfully at 05:00am on 31 August 2010 and successfully deployed 132.6m of tape tether over 120 seconds in a ballistic flight. The electrodynamic performance of the bare tape tether employed as an atmospheric probe was measured. Flight results are introduced through the present progressive report of the demonstration and the results of flight experiment are examined as the premier report of the international cooperation between Japan, Europe, USA and Australia. Future plans for maturing space tether technology, which will play an important role for future space activities, are also discussed.

Sputter erosion sensor for anode layer-type Hall thrusters using cavity ring-down spectroscopy

We report the development of a sputter erosion monitoring system to study Hall thruster lifetime and contamination. The laser-based sensor uses the continuous-wave cavity ring-down spectroscopy technique and allows for in situ measurements in near-real time. The continuous-wave cavity ring-down spectroscopy technique diagnostic allows direct probing of sputter products in their ground state, thereby providing a reliable quantitative measure of their overall number density. Combining the number density of sputtered particles with their velocity allows determination of the flux of sputtered particles and erosion rate. We perform proof of principle experiments, in which sputtered manganese atoms from the acceleration channel of an anode layer-type Hall thruster are measured. The measurement strategy is to detect the manganese atoms via an absorption line from the ground state at a wavelength of 403.076 nm (air). The measured path-integrated number density of sputtered manganese atoms is 1.7 ± 0.3 × 10 13 m -2 for an argon anode mass flow rate of 2.08 mg/s and a discharge voltage of 250 V. A finite element sputter model is used to compare the cavity ring-down spectroscopy results against validating mass loss measurements and shows good agreement.

Hollow cathode conditioning and discharge initiation

In the framework of developing a fast-starting hollow cathode, one must understand how a cathode is conditioned for operation. The desorption of known contaminates as a function of heater power was measured to quantify cathode conditioning characteristics. In addition to conditioning, a study of hollow cathode emission characteristics under vacuum conditions was performed. Results of these two studies are described herein along with measurements of the temperature of the cathode as a function of time and heater power. The data are used to validate a transient surface diffusion model that describes the migration and surface coverage fraction of low-work-function material from the interior of the hollow cathode to the orifice barrel and to the exterior surface of the orifice plate of the cathode. A sufficiency condition is presented for our cathode geometry of vacuum emission current level and the ability to start a hollow cathode discharge once gas flow is initiated.

Quartz crystal microbalance-based system for high-sensitivity differential sputter yield measurements

We present a quartz crystal microbalance-based system for high sensitivity differential sputter yield measurements of different target materials due to ion bombardment. The differential sputter yields can be integrated to find total yields. Possible ion beam conditions include ion energies in the range of 30-350 eV and incidence angles of 0 degrees-70 degrees from normal. A four-grid ion optics system is used to achieve a collimated ion beam at low energy (<100 eV) and a two-grid ion optics is used for higher energies (up to 750 eV). A complementary weight loss approach is also used to measure total sputter yields. Validation experiments are presented that confirm high sensitivity and accuracy of sputter yield measurements.

Preliminary Results of Low Energy Sputter Yields of Boron Nitride due to Xenon Ion Bombardment (Preprint)

Abstract : We describe the development of an experimental apparatus geared towards measurement of boron nitride sputtering by low energy ions. A four-grid system is used to achieve a collimated beam at low energy (<100 eV). A weight loss approach is used to measure total sputter yields and a quartz crystal microbalance (QCM) is used to measure differential sputter yield profiles of condensable components. Integration of the QCM profiles also gives total sputter yields of condensable components. We report initial results of total and differential sputter yield measurements of three grades of boron nitride due to bombardment by xenon ions with ion energies in the range of 60-250 eV and at ion incidence angles of 0, 15, and 45 degrees from normal. Comparison with past measurement results are made where possible.

Magnetic Sensing of Azimuthal Current in Hall Thrusters: In-Flight Diagnostic Potential

In this paper, the method of Hall current spatial structure estimation based on the measurements of steady-state magnetic fields induced by this current outside the acceleration channel is proposed. The approach to Hall current structure determination is based on the inverse magnetostatic problem solution using two-dimensional constrained regularization. The optimal number and positions of magnetic sensors are determined, and the solutions using simulated measurements with and without simulated noise are obtained.