Low-Energy Ion Composition Analyzer (LICA)

The LICA experiment was designed to measure 0.5--5 MeV/nucleon solar and magnetospheric ions (He through Ni) arriving from the zenith in twelve energy bands. The mass of an ion was determined with simultaneous measurements of its time-of-flight (TOF) across a path length of approximately 50 cm and its residual kinetic energy in one of four 4 x 9 cm silicon solid state detectors. Ions passing through the 0.75 micrometer nickel entrance foils emitted secondary electrons which a chevron microchannel plate assembly amplified to form a signal to begin timing. A double entrance foil prevented single pinholes from allowing sunlight to enter the telescope and provided immunity to solar and geocoronal ultraviolet. Another foil and microchannel plate assembly in front of the solid state detectors gave the signal to stop timing. Wedge-and-strip anodes on the front sides of the timing anodes determined where the ion passed through the foils and, therefore, its flight path length. The velocity determined from the path length, the TOF, and the residual energy measured by the solid state detectors were combined to yield the mass of the ion with a resolution of about 1%, adequate to provide complete isotope separation. Corrections for the energy loss in the entrance foils gave the ion's incident energy. The geometric factor of the sensor was 0.8 sq cm sr and the field of view was 17 x 21 degrees. On-board processing determined whether ions triggering LICA were protons, He nuclei, or more massive ions. Protons were counted in a rate and not further analyzed. Heavier nuclei were treated as low (He) or high (more massive than He) priority for transmission to the ground. The instrument data processing unit ensured that a sample of both priority events was telemetered, but that low priority events did not crowd out the rarer heavy species. Processed flux rates vs. energy of H, He, O, Si group, and Fe groups were picked out every 15 s for transmission. Appropriate magnetic field models enabled specification of the atomic charge state by means of rigidity cut-off calculations. In addition, the proton cut-off vs. energy during an orbit helped charge identification of the other species. On-board calibrations of the sensor were done by command about once per week. Data was stored in on-board memory of 26.5 MB, which was then dumped twice daily over ground stations. The instrument functioned normally as of 15 July 1996; the next update will be only when any significant status change occured.

LICA实验旨在测量0.5至5 MeV/nucleon的太阳和磁层离子（氦至镍），这些离子以顶点方向到达，并被划分为十二个能带。通过在约50厘米的路径长度上同时测量离子的飞行时间（TOF）及其在四个4 x 9厘米硅固态探测器中测得的剩余动能，来确定离子的质量。离子穿过0.75微米的镍入口箔时，会发射次级电子，这些电子通过V形微通道板阵列放大，形成信号以启动计时。双重入口箔防止单孔允许阳光进入望远镜，并提供了对太阳和地球冕紫外线的免疫。在固态探测器前方的另一箔和微通道板阵列提供了停止计时的信号。位于计时电极前侧的楔形和条形阳极确定了离子穿过箔的位置，从而确定了其飞行路径长度。由路径长度、TOF和固态探测器测量的剩余能量确定的速率，结合了离子质量，其分辨率约为1%，足以提供完整的同位素分离。对入口箔中能量损失的校正给出了离子的入射能量。传感器的几何因子为0.8平方厘米·球面度，视场为17 x 21度。机载处理确定了触发LICA的离子是质子、氦核还是更重的离子。质子以速率计数，未进行进一步分析。较重的核被处理为低（氦）或高（比氦更重）优先级，以传输到地面。仪器数据处理单元确保了两种优先事件的样本被遥测，但低优先级事件不会挤占更稀有的重物种。每15秒选择处理后的H、He、O、Si组以及Fe组的通量速率与能量数据进行传输。适当的磁场模型通过刚度截止计算允许通过刚度截止计算指定原子的电荷状态。此外，在轨道期间的质子截止与能量的关系有助于其他物种的电荷识别。传感器在机载的校准大约每周通过命令进行一次。数据存储在26.5 MB的机载内存中，然后每天两次通过地面站进行下传。该仪器自1996年7月15日起正常运行；下一次更新仅当发生任何重大状态变化时才会进行。