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Diagnostics with force probes in plumes of electric propulsion systems for spacecraft (thrusters) are presented. This contribution focuses on showing example measurements with force probes for the most common gridless ion thruster types. The gridless thrusters are investigated at typical operation modes with a force probe at fixed or variable positions in the plume. The probe measures the force on a tiny plate that is attached to a sensitive cantilever in the plume. The elastic deflection of the cantilever is measured interferometrically and translated into a proportional force. Several variants of the instrument have been developed. A HEMP thruster is investigated with a variant of the force probe that simultaneously measures two components of the force vector. With this vectorial probe, it is possible to determine the force vector acting on the probe target while moving the probe through the thruster plume. A Hall thruster is investigated with a simplified variant of the probe, which measures the force along one axis and is equipped with an additional shutter in front of the target. This allows monitoring over long periods of operation. Finally, a force probe is used as an indirect thrust balance for a FEEP thruster. In this case, the force probe can collect the entire plume. [ABSTRACT FROM AUTHOR]

The plasma diagnostics presented in this article target the plasma surrounding a spacecraft that is created by the electric thruster and its surface modifying effects. The diagnostic package includes a retarding potential analyzer, a plane Langmuir probe, and an erosion sensor. The paper describes the instrument as well as suitable test environments for mimicking the effects expected in space and shows test results. The system is to fly for the first time on the Heinrich Hertz satellite, which is scheduled to be launched in 2023. The spacecraft will be equipped with a pair of Highly Efficient Multistage Plasma Thrusters (HEMPT) and a pair of Hall thrusters for redundancy. [ABSTRACT FROM AUTHOR]

A novel probe for the measurement of forces exerted by a beam of ions and neutral atoms on a small target is described. The force probe is intended for various applications: First, diagnostics of thruster plumes of electric spacecraft propulsion engines, in particular the determination of the spatial distribution of the momentum in an exhaust beam, and second, the study of sputtering of solid targets by means of the related momentum transfer. The instrument makes use of a sensitive cantilever whose elastic deflection is measured interferometrically along two axes and enables that way a simultaneous measurement of two independent components of the force vector. The present contribution focuses on setup and calibration of the probe. Example measurements with obliquely irradiating ion beams are performed. [ABSTRACT FROM AUTHOR]

Forces on a small plane measurement target caused by sputtered atomic particles originated at plane sputter targets by a beam of argon particles are investigated. The rotatable sputter targets are centrally mounted in front of the ion source and allow a variation of the angle of incidence. The measurement surface of the force probe is arranged laterally beside the sputter target; it collects the particles released perpendicularly to the beam direction. Sputter targets of silver, copper, aluminum, titanium, and carbon are studied. The measurements are compared with a model that traces the trajectories of the argon ions and the sputtered target atoms between the ion source, the sputter target, and the force probe. The sputtering is calculated with the popular SRIM code based on binary collision cascades. The measured forces are found to be in general greater than the simulated forces. The dependence on the angle of incidence is similar in case of the elements heavier than the ions. In case of the lighter elements, only the simulation exhibits a pronounced maximum at angles between 65° and 70°. Graphical abstract: [ABSTRACT FROM AUTHOR]

During the last few years, deep brain stimulation (DBS) of the subthalamic nucleus (STN) has emerged as a promising therapy, alleviating major motor symptoms of Parkinson’s disease (PD). However, in times of growing budgetary limitations, medical decisions are no longer merely based on clinical efficacy, but also on cost-effectiveness. Here we assess treatment costs (i. e. costs for conservative pharmacological treatment and all in-patient admissions) of 46 PD patients for one year before and two years after STN-DBS. The present data show that total treatment costs were increased by 32 % for the first year and decreased by 54 % for the second year of STN-DBS in comparison with preoperative values while the Unified Parkinon’s Disease Rating Scale (UPDRS III) was significantly improved. The increase for the first year after surgery was mainly due to the implantation of the STN electrodes and the stimulation device. Taken together, STNDBS pays off from the second year of stimulation while motor symptoms are significantly improved. The present study provides first data of an important number of patients on clinical effectiveness and expenses in relation to STNDBS. [ABSTRACT FROM AUTHOR]

The influence of the brainstem motor system on cerebral motor areas may play an important role in motor control in health and disease. A new approach to investigate this interaction in man is combining acoustic stimulation activating the startle system with transcranial magnetic stimulation (TMS) over the motor cortex. However, it is unclear whether the inhibition of TMS responses following acoustic stimulation occurs at the level of the motor cortex through reticulo-cortical projections or subcortically, perhaps through reticulo-spinal projections. We compared the influence of acoustic stimulation on motor effects elicited by TMS over motor cortical areas to those evoked with subcortical electrical stimulation (SES) through depth electrodes in five patients treated with deep brain stimulation for Parkinson’s disease. SES bypasses the motor cortex, demonstrating any interaction with acoustic stimuli at the subcortical level. EMG was recorded from the contralateral biceps brachii muscle. Acoustic stimulation was delivered binaurally through headphones and used as a conditioning stimulus at an interstimulus interval of 50 ms. When TMS was used as the test stimulus, the area and amplitude of the conditioned motor response was significantly inhibited (area: 57.5±12.9%, amplitude: 47.9±7.4%, as percentage of unconditioned response) whereas facilitation occurred with SES (area: 110.1±4.3%, amplitude: 116.9±6.9%). We conclude that a startle-evoked activation of reticulo-cortical projections transiently inhibits the motor cortex. [ABSTRACT FROM AUTHOR]

Current concepts of transcranial magnetic stimulation (TMS) over the primary motor cortex are still under debate as to whether inhibitory motor effects are exclusively of cortical origin. To further elucidate a potential subcortical influence on motor effects, we combined TMS and unilateral subcortical electrical stimulation (SES) of the corticospinal tract. SES was performed through implanted depth electrodes in eight patients treated with deep brain stimulation (DBS) for severe dystonia. Chronaxie, conduction velocity (CV) of the stimulated fibres and poststimulus time histograms of single motor unit recordings were calculated to provide evidence of an activation of large diameter myelinated fibres by SES. Excitatory and inhibitory motor effects recorded bilaterally from the first dorsal interosseus muscle were measured after SES and focal TMS of the motor cortex. This allowed us to compare motor effects of subcortical (direct) and cortical (mainly indirect) activation of corticospinal neurons. SES activated a fast conducting monosynaptic pathway to the alpha motoneuron. Motor responses elicited by SES had significantly shorter onset latency and shorter duration of the contralateral silent period compared to TMS induced motor effects. Spinal excitability as assessed by H-reflex was significantly reduced during the silent period after SES. No ipsilateral motor effects could be elicited by SES while TMS was followed by an ipsilateral inhibition. The results suggest that SES activated the corticospinal neurons at the level of the internal capsule. Comparison of SES and TMS induced motor effects reveals that the first part of the TMS induced contralateral silent period should be of spinal origin while its later part is due to cortical inhibitory mechanisms. Furthermore, the present results suggest that the ipsilateral inhibition is predominantly mediated via transcallosal pathways. [ABSTRACT FROM AUTHOR]

Renewed interest in stereotaxy for dystonia followed the introduction of deep brain stimulation (DBS) in Parkinson's disease and essential tremor in the 1990s. DBS evolved from ablative surgery, which was applied with varying results in the 1950s in patients with movement disorders such as Parkinson's disease, essential tremor and dystonia. The present review summarizes the current knowledge on clinical aspects of DBS in dystonia (Dec. 2002). Excellent results have been achieved in dystonic patients carrying a mutation in the DYT1 gene with improvements up to 90 %. Similar results may also be obtained in patients with idiopathic generalized dystonia, myoclonus-dystonia syndrome, and tardive dystonia. Substantial improvement has been observed in patients with focal dystonia (for instance cervical dystonia). Patients with secondary dystonia often display a lesser and more variable degree of improvement. Long-term studies are warranted to assess both motor and neuropsychological sequelae of DBS in dystonia. Furthermore, the optimal target for different dystonic disorders remains to be determined, although the globus pallidus internus has currently emerged as the most promising target for dystonia. [ABSTRACT FROM AUTHOR]