AVS 70 Session VT-ThP: Vacuum Technology Poster Session

presented.

The ITER Diagnostic Residual Gas Analyzer (DRGA) performs fusion neutral gas analyses. The ROI comprises low-amu species (1 thru 6), and includes the isotopic profiles of hydrogen and helium [1]. There are challenges in obtaining accurate measurements. First, the method sensitivity must suffice to resolve trace amounts accurately (≤1%). Second, the gas signal must be free of bias caused by the latent presence of these gases to acquire accurate measurements. For the lightest gases, backstreaming a fraction of the pumped gas load can be a source of such latency effects. This phenomena is attributed to modest inertia due to their lowest weight and smallest size. As a result, collisional effects create a reverse flow into the analysis region, which can contaminate the real-time measurement. To fully eliminate this adverse effect, a conductance-limiting device – or orifice – has been installed in the high-vacuum pumping system of the present DRGA prototype. It is intended to eliminate backstreaming by increasing the back pressure within the inter-pump volume (IPV).

An added benefit of the orifice-restricted pumping concept is that the upstream pressure increase is beneficial to the DRGA plasma cell used optical gas analysis. These sensors are attached to the IPV in the present DRGA design. The glow discharges will typically have a brighter light emission with increasing plasma cell pressure. For the DRGA, one of the glow discharge sources being evaluated for this system is a prototype made by Gencoa Limited (UK), which has been designed to exhibit satisfactory immunity to fringing fields, simulated for the tokamak environment. Also, the unique circuitry control for the input power control of the cell, when coupled with the specialized magnetic confinement of the plasma, have optimized the profile shapes of line emissions of interest for these isotopes, of which some emission lines are difficult to deconvolute.

Described herein are two ITER-DRGA related concepts: Vacuum system testing to validate elimination of light gas backstreaming and test results from using the prototype light source and a modified, Penning cathode.

This work was supported by the U.S. D.O.E. contract DE-AC05-00OR22725.

[1] C.C. Klepper et al., 2022 IEEE-TPS 50 (12) 4970

Collision studies involving the open shell nitric oxide (NO) molecule have been central in many detailed investigations of molecular reaction dynamics as a prototype system for probing inelastic collisions. These processes have proven a powerful means of investigating molecular interactions, and much current effort is focused on the cold and ultracold regime where quantum phenomena are clearly manifested. Here I present our recent work on state-to-state spin-orbit changing collisions of highly vibrationally excited NO molecules prepared in single rotational and parity levels at v=10 using stimulated emission pumping (SEP). This state preparation is employed in a near-copropagating beam geometry that permits very wide tuning of the collision energy, from far above room temperature down to 2 K where we test the theoretical treatment of the attractive part of the potential and the difference potential for the first time. We have obtained differential cross sections for state-to-state collisions of NO(v=10) with Ar/Ne in spin-orbit excited manifold using velocity map imaging. Overall good agreement of the experimental results was seen with quantum mechanical close-coupling calculations done on coupled-cluster potential energy surfaces. Probing cold collisions of NO carrying ~2 eV of vibrational excitation allows us to test state-of-the-art theory in this extreme nonequilibrium regime. The current experimental setup is now modified to permit a near-counterpropagating geometry for the molecular beams which allows us to look into really high collision energies to study chemistry in high temperature hypersonic flows. This takes us to a new direction where vibrationally inelastic processes may appear and the latest results along these experiments will also be presented.