research activities in 2007 - CSEM

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Space Hydrogen Active Maser S. Zivanov, C. Weber One of the two frequency standards that will be part of the Atomic Clock Ensemble in Space (ACES) payload to be flown on the International Space Station (ISS) is an active Space Hydrogen Maser (SHM) mandatory for its ultimate frequency stability performance in the mid-term range (3 s ≤ τ ≤ 3000 s). The Engineering Model developed in CSEM reaches the weight of the 35 kg SHM, the lightest ever built active maser. The SHM instrument is divided into two principal functional packages, the Physics Package (Figure 1), that provides the actual atomic oscillator, and the Electronics Package (Figure 2), that provides the atomic signal processing circuits, parameter control functions, telemetry and telecommand. The Physics Package is made of the microwave cavity and magnetic shield assembly, the electronics unit and several integrated peripherals like the hydrogen distribution assembly and the ion pumps. Figure 1: The photo of the Engineering Model and cross-section schematics view of SHM instrument: 1: Microwave cavity and shields assembly; 2: Hydrogen-vacuum assembly; 3: Ions pumps; 4: Low noise RF amplifier 5: External fixation structure; 6: Hydrogen distribution assembly. In order to fulfill miniaturization, the sapphire resonator acts as a "dielectric load" reducing the size of the microwave cavity and serving at the same time as the storage container for the atomic hydrogen. The microwave cavity is made of titanium and tuned mechanically, thermally and electrically at the hydrogen hyperfine frequency. The atomic storage bulb is a sapphire cylinder of 1.7 liters bonded to the titanium cavity covers and Teflon coated. This volume, comparable to a full size maser design, and the Teflon coating technology developed at CSEM reach a high atomic signal and operating quality factor. The hydrogen atomic beam and storage bulb are maintained under high vacuum with an ensemble of getters and ion pumps. The getter ensemble allows a vacuum autonomy of 10 days without electrical power and an instrument life time of more than 5 years. The thermal regulation is based on three pairs of concentric heaters regulating the microwave cavity temperature with a stability of 1 mK. The heat is evacuated by conductance through the mechanical structure only. An Automatic Cavity System (ACT), based on a sampled interrogation scheme, prevents SHM drifts due to the cavity pulling. The magnetic shielding is enhanced with an active compensation control loop. A step further in the direction of the size reduction is the removal of the external vacuum enclosure which provides the so called “thermal vacuum”. This vacuum will be provided instead and directly by the “space vacuum”, given that the SHM is operating in the space environment. The Electronics Package is composed of an RF unit in charge of frequency locking the local quartz oscillator on the hydrogen clock transition frequency as well as frequency locking the microwave cavity using the ACT, of providing the proper microwave frequency to the hydrogen dissociation power amplifier, and finally of delivering a stable 100 MHz signal to the ACES payload. The Control Unit and the Power Supply Unit provide and/or control the necessary powers for an optimal operation of SHM. Finally, the Control Unit interfaces to the ACES payload in terms of telecommands and telemetries. Figure 2: The functional block diagram of the SHM Electronics Package The main objective of the current development is to perform an end-to-end performance demonstration, to be used as a stepping stone for pursuing the development of the SHM and aiming at the delivery of the SHM Proto Flight Model (PFM). 105
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centre suisse d’électronique et
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CONTENTS PREFACE 5 RESEARCH ACTIVIT
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PREFACE Dear Reader, In this report
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spectrometer applications so CSEM h
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As a first step, CSEM is building s
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Efficient Screening and Formulation
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Sol-Gel based Nanoporous Layers as
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