Development of Neutral Mass Spectrometer using Time-of-flight Technique for Space Flight

空间飞行常用的中性质谱仪有四极质谱仪和磁偏转式中性质谱仪。然而，这两种类型在测量空间中的中性质量分布方面都存在基本问题。它们是：1.目标气体与原子氧复合后的效果评价；2.目标气体速度分布函数信息的损失。原子氧是数百公里高度大气层的主要成分，吸收在仪器表面。最近，我们提出了一种利用飞行时间技术的新型中性质谱计，以消除仪器内部复合的影响，实现对目标气体分布函数的测量。在这笔赠款的支持下，我们开发了该探测器的关键部件(脉冲离子源、飞行时间(TOF)加速部件和同时测量飞行时间和二维位置的探测器)，然后将它们集成到火箭飞行系统中。开发人员…更多的被盗用的元素是：1.灯丝电源向灯丝提供低电压的恒定功率，灯丝发射电子束以电离目标中性气体。输出功率由输入控制电压控制。输入和输出之间的泄漏电流被最小化，以便能够正确地测量发射电流。飞行时间加速部分在电离部分和加速部分之间放置一个网格。在电离期使用脉冲电子束将网孔电势设置为OV。这种网格可以有效地抑制由于不存在网格时存在的势梯度而产生的额外光束发散。当电离期结束时，将网格电位改变为-10V，以加速离子正向探测器。网孔电势的高速切换(20nS内0-10V)使电离点不同引起的TOF色散最小。探测器采用Detector3级MCP。在MCP和位置灵敏阳极之间放置网状物。TOF脉冲是由来自该网格的信号测量的。利用这种带有位置灵敏阳极的网格，可以同时测量电离粒子的TOF和位置。进一步改进的是，我们开发的方法存在目标气体分布函数的采样频率的限制。这一局限性来自于同时测量TOF和位置时要求每束脉冲的离子数小于1。为了克服这一限制，我们开始了用CCD摄像机作为位置检测和开关MCP HV进行质量选择的系统的可行性研究。较少

Quadropole type and magnetic deflection type neutral mass spectrometer are commonly used for space flight. However both type have basic problems for measuring neutral mass distribution in space. Those are 1. evaluation of the effect with the recombination of target gas and atomic oxygen, which is major component of the several hundred km height atomosphere and absorb on the surface of the instrument, 2. loss of velocity idstribution function information of target gas. Recently we proposed a new tuype neutral mass spectrometer using time-of-flight technique to eliminate the effect of the recombination inside the instrument and to achieve the measurement of distribution function of target gas. With the support of this grant, we have developed the key components of this detector (pulse ion source, acceleration part for time-of flight (TOF), and detector which measures time-of-flight and 2 dimensional position, simultanously) and then integrate them into a system for rocket flight. The dev … More eloped elements are :1. Filament power supplySupply constant power with low voltage to filament which emits electron beam for ionization of target neutral gas. Output power is controled by the input control voltage. Leak current between input and output is minimized to be able to measure the emission current correctly.2. Acceleration part for time-of-flightA mesh is placed between ionization part and acceleration part. Mesh potential is set to OV during ionization period using pulse electon beam. This mesh is effective to suppress extra beam divergence due to the potential gradient which exists when the mesh is not exist. Mesh potential is changed to -10V when ionization period is finished to accelerates the ion torward detector. High speed switching (0->-10V within 20nS) of the mesh potential enabled to minimize the dispersion of TOF caused by the difference of the ionizing point.3. Detector3 stage MCP is used for detector. A mesh is placed between MCP and position sensitive anode. TOF pulse is measured by the signal from this mesh. Using this mesh with position sensitive anode enables simultanous measurement of TOF and position of the ionized particle.Further improvement :The method which we are developed has a limitation of the sampling frequency of the distribution function of target gas. This limitation comes from the fact that the simultanous measurement of TOF and position detection requires that number of ions per 1 pulse beam should be less than 1.To overcome this limitation, we have starting the feasibility study of the system which uses CCD camera as position detection and switch MCP HV for mass selection. Less