Humidity

["Alexander Vasilyev" <vassilie@mail.pnpi.spb.ru>]

Dear Peter,
Sorry for the previous letter. After some investigation I understand now that the humidity question is much more difficult. 

Chilled mirror is very good method. But I am not sure that existing commercial devices are suitable for our cases. The reasons are very simple. All these devices use the periodical changing of the mirror temperature. Hydrogen has extremely big thermal conductivity. In this case the real temperature of the mirror surface can be another then measured. Even small mistake in the temperature gives a big difference. I did not find (I used commercial database) any specific  hydrogen investigation. Another problem is not clear dependence between dew point for hydrogen at 10 bar and real molar concentration of the water. 10 bar hydrogen is not ideal gas and to use linear dependence is not true. This question we have to investigate too. 
	I agree with you that we have to use absolute method of chilled mirror to finalize the results. But my opinion, it is not enough. With the commercial device we have to carry out some tests for 10 bar hydrogen. I propose to make cryo device which I proposed for our humidity sensor calibration and in pair with chilled mirror device carry out tests. The main idea of the tests is to create the necessary humidity with the cryo method at one pressure and the same gas send into the chilled mirror device at another pressure. It gives us necessary metrology for the 10 bar hydrogen.
	In principle chilled mirror method is rather simple. Now I am investigating possibilities to produce this device myself. It is very interesting for us because we are working with ultra pure gases. But exist the question shell we make better and cheaper then commercial device? In any case I will try to make some experiments in this direction in December.
	Practical steps. I propose you to discuss with Alexey Vorobyev these questions. In any case humidity is one of the most problematic things in our experiment. For the deuterium measurements we have more or less all components and clear tasks. This is only the job. With the humidity we have to define the strategy.
-	buy or produce (we have enough time for the attempts) chilled mirror device.
-	make cryo device for the fixed humidity production.
-	carry out tests in Gatchina with chilled mirror device.
- make the final measurements in PSI.

If we will concentrate CRDF money on these task it will be very good.

These is only preliminary statements "to start the discussion".

With best regards   Sasha.



-- 
Vasilyev Alexander

Petersburg Nuclear Physics Institute,
Laboratory of Cryogenic and Superconductive Technique.