AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Caltech nano-Scanning Electrical Mobility Spectrometer (nSEMS): Design, Modeling, and Characterization for Size Distribution Measurements in the Low Nanometer Regime
STAVROS AMANATIDIS, Weimeng Kong, Huajun Mai, Yuanlong Huang, Richard Flagan, The CLOUD Collaboration, California Institute of Technology
Abstract Number: 549 Working Group: Instrumentation and Methods
Abstract We present the design, modeling and experimental characterization of the Caltech nano-Scanning Electrical Mobility Spectrometer (nSEMS), a recently developed instrument designed to probe particle formation and growth at the “CLOUD” experiment at CERN, Switzerland.
The nSEMS consists of a charge conditioner, a novel differential mobility analyzer, and a two-stage Condensation Particle Counter (CPC). The mobility analyzer was designed and optimized for size classification in the 1.5 – 25 nm range with minimal diffusional losses through 3D finite element modeling of the flows, electric field, and particle trajectories. The classifier operates on a dual high-voltage supply with fast polarity-switching capability to minimize sensitivity to variations in the chemical nature of the ions used to charge the aerosol.
The nSEMS employs a new soft x-ray charge-conditioner that was designed to optimize both particle charging and transmission efficiency in the low nanometer regime. The CLOUD experiment, for which this instrument was designed, probes neutral nucleation by removing all ions from the chamber, and nucleation of clusters on ions produced by galactic cosmic rays, or by a pion beam to probe particle formation under upper-tropospheric conditions. With the soft x-ray source turned on, the nSEMS can, therefore, probe neutral-cluster nucleation; with it turned off, it can measure particles formed by ion-induced nucleation. Particles transmitted through the charge-conditioner and mobility analyzer are measured using a two-stage CPC. The particles are first activated in a fast-mixing diethylene glycol stage that was developed at Caltech; the second, booster and detection stage, is a TSI Model 3760A, butanol CPC.
We will describe the design of the various components of the instrument, and the experimental characterization of the individual components, charge conditioner, mobility classifier, and two-stage CPC, present the transfer function of the integrated instrument, and examine its measurements of transient nucleation and growth events in the CLOUD chamber.