Minutes from target meeting held August 18 2005 in 892-1-B09

a) Mauricio presented the microwave system of Mainz GDH sum rule experiment on 
Tuesday. The IMPATT diode has typical stability of 0.5 - 1.0 MHz at 70 GHz 
with 200 mW output power after 4 hours warming up. It has been bought from 
Ukraine (about 2 keuros). The DC power supply and attenuator step motor
can be controlled from LabVIEW. LabVIEW monitors also the frequency and 
the temperature of the generator. Frequency modulation of the microwaves
is not used due to the small size of the target.

b) Ideas on improved monitoring and control of COMPASS microwave system were
discussed. Mauricio: EIO tuning and power attenuator motors could be controlled
with LabVIEW or PLC. Frequency counter could be read with GPIB and the power
meter through National Instruments or PLC analog input module. Also the ingoing
and reflected powers could be monitored close to the target. Norihiro said that
it is preferable to use the anode voltage of the EIO tube to adjust the
frequency to save lifetime of the tube. The frequency counter has sometimes
problems and needs to be restarted. Yuri said that the system developed at 
Mainz could be used to control the Bochum IMPATT diode generator.

c) Mainz experiment is using Simatic PLC Protool together with LabVIEW. 
The communication between these two systems is guaranteed by AGLink software.
http://www.deltalogic.de/index.php?target=software/aglink.htm
Norihiro said that the PLC system used by COMPASS has been designed to 
guarantee stable operation of the target during physics data taking. 
There might be security or safety problems in allowing access from LabVIEW.

d) EIO PSU interface was discussed. The vacuum valve PSU has been modified
from the original design. It has digital counter inside which counts up/down 
when button in front panel is pressed. This digital number is then converted 
to an analog voltage, which controls the anode voltage. The Japanese solid
state PSU has been modified to allow frequency modulation. For the moment
it is not possible to change the anode voltage with external voltage source
(only trimmer in front panel can be used).

e) Resistive thermometers for the three target cell configuration were 
discussed.

f) Gerhard asked dimensions for the three target cells. Reply from Jaakko:

The total length of the 3 target cells can not exceed 1300 mm due to the 
mixing chamber. For longitudinal vertex resolution the cells have to be 
separated by 70 mm. This leaves us 580 mm for the target cell in the 
middle and 290 mm for the upstream and downstream cells.
From the talk given by Alain in Prague the homogeneous field region 
extends from -65 cm to +62 cm. That means that 30 mm of the most downstream 
part of downstream cell will have less ideal conditions for polarization.

Later Alain commented that the field homogeneity is expected to improve in the
testing period at Saclay in September - October.

Jaakko: with 70 mm cell separation and 10 mm space between the cell and 
microwave stopper this leaves 50 mm for the length of the microwave stopper.