Host: The Japan Society of Vacuum and Surface Science
Name : Annual Meeting of the Japan Society of Vacuum and Surface Science 2023
Location : [in Japanese]
Date : October 31, 2023 - November 02, 2023
Introduction
An ultra-high vacuum compatible ethanol liquid target is being developed to investigate the reaction products produced by the interaction of a high intensity laser with ethanol. One of the issues to be solved is the need to maintain an ultra-high vacuum in the main chamber for analysis within ~1 m of the liquid target generator, where the reaction chamber containing the generator is planned to be operated about 10 Pa or less. The constraint is to have a straight-through section without obstructions, so that reaction products can fly into the main chamber from the vicinity of the liquid target. In this development, this straight-through section is a cylinder with a diameter of 20 mm, as shown in Fig. 1. We attempted to solve the above problem by installing an in-line liquid nitrogen trap between the reaction chamber and the main chamber and improving the trap.
Trap evaluation experiment
An experimental system was prepared using a thimble-type in-line liquid nitrogen trap. The flanges A and B mating with the liquid target chamber and the main chamber were set to ISO NW25 with a face-to-face distance of 416 mm. The outer diameter and depth of the trap are 140 mm and 90 mm, respectively. A copper plate of 120 mm OD and 5 mm thick was attached to the bottom of the trap. This is for attaching the auxiliary plates and other materials that can be used in the following. Connect C2H5OH vapor introduction system to flange A. Ethanol vapor pressure is monitored by a Pirani vacuum gauge. Then an evaluation system is connected to flange B for flow evaluation and partial pressure measurement. Experiments were conducted at ethanol vapor pressures ranging from 0.01 Pa to 20 Pa.
Examples of the results obtained so far
(1) Trap efficiency with two additional copper plates
When the ethanol vapor was 4.93 Pa, the pressure in the trap was 1.73×10-2 Pa. This indicates that the trap's pumping speed for ethanol vapor is about 2.3 m3/s. Since the area of the cooling surface is ~950 cm2, the ethanol condensation coefficient is evaluated to be ~0.25.
(2) Trap efficiency with the two plates and an additional cooling pipe
When a cooling pipe with an inner diameter of 20 mm and a length of 100 mm was added at flange A to cover the straight pipe section, the pressure in the trap was 8.31 × 10–4 Pa in response to ethanol vapor of 3.97 Pa. From this result, it can be seen that the ethanol vapor conductance between the introduction chamber and the trap was drastically reduced to about 5.5×10−4 m3/s by installing the cooling pipe. Also, if the same cooling pipes are installed not only at the flange A but also at the flange B, and if the main chamber is evacuated with a pump of ~1 m3/s, you can almost certainly keep the main chamber in UHV.
Details will be given at the lecture.
