Installation and Removal of the SiO₂ Tray

PLEASE NOTE: The SiO₂ aerogel panels are extremely fragile and sensitive to water and chemical vapour. Do not handle with bare hands, use clean cotton, or other fabric type, gloves instead. Surgical gloves often are contaminated with lubricants and are not suitable for this purpose.

The tray is secured to the main section by hex bolts. Removal of the bolts results in the straightforward removal of the tray. There is minimum clearance between the tray walls and the main section; as a result, the tray has to be removed and installed in a uniform translation with respect to the main body. The frame supporting the fish net (or tennis racket) can be removed from the tray proper by removal of the two small screws in the middle of the tray walls and a tool (hook) is provided for this operation. The SiO₂ aerogel panels can now be removed or replaced. Reverse the procedure for installation. The securing bolts do not need to be tightened very much and, although spacers are inserted between the rubber strips to prevent damage, care and common sense should be exercised. Light and gas sealing is provided by the rubber strips NOT by brute force.

WARNING: After each removal of any components of the counter, check for light leaks before turning the HV on at operating values. Even a small light leak can destroy the PMTs if they are at -2,950 V! Check for light leaks with lights out, using a small portable light, and reduced voltage around -2,000 V.

   

1B 4.0 1T 0.2

2B 0.8 2T 0.3

3B 0.6 3T 0.1

6.0 7.5

   

5B 0.5

6B 1.0 6T 0.1

7B 3.5 7T 0.2

8B 1.0 8T 0.1

9B 0.5

  

Figure: Schematic diagram of the aerogel Cerenkov counter as viewed by the incoming particles. The numbers indicate the sections, 1 to 13, in the counter. Each section is viewed by two PMTs, one on the top (T) and one in the bottom (B). The labeling carries no significance other than identifying the PMTs during the testing phase, as described in the text.

  

Figure: Cross sectional drawing of the counter, along the particle direction, showing the planar parabolic nature of the mirrors and the geometry of the PMTs, as well as the final dimensions. The joint of the two mirror surfaces in the middle of the counter defines the mirror ``ridge''.

  

Figure: Photograph showing the final arrangement of the double sidewall structure, and the close spacing of the housings for the PMTs. The bottom section of the counter, with the tray and the aluminized mylar reflector lining, is also shown. In this picture, the particles would be incident from the bottom toward the top of the counter. The upper (mirror) section has been removed for clarity.

  

Figure: Photograph showing the middle (PMT) section with the double sidewall structures and the housings for the PMTs, with the top (mirror) section attached. The tray has been removed, and the white tabs on the mirrors are pieces of tape holding a temporary protective film in place to prevent damage to the mirror surfaces during transportation. In this figure, the particles would be incident from the top toward the bottom of the picture.

  

Figure: Typical reflectivity curve of a mirror as a function of the wavelength, , of the incident light.

  

Figure: A photograph showing the upper (mirror) section with the planar parabolic mirrors. The mirror surface is protected by a vinyl film in this picture. The mirror ``ridge'' separating the counter into two halves is clearly seen. This section fits over the open top of the counter in Fig.

  

Figure: Schematic diagram of the electronic amplification chain. The total resistance of 600 between the cathode and the first dynode is shown as three 200 resistors for sake of clarity. In the actual PC boards, the arrangement is of six resistors of 100 each, in order to keep the voltage across each resistor low and avoid surface discharge between the closely packed resistors.