er at
CERN will require over ten thousand photomultiplier tubes. These
photomultiplier tubes will be subjected to rigorous testing in order to ensure
that they fulfill their operational requirements before installation in the
detector. Testing such a large volume of photo-multiplier tubes on schedule
has necessitated the construction of a number of test benches. These tests are
performed by comparing the performance of photomultiplier tubes to that of a
large-area photodiode. Intercalibration of these test benches is required to
ensure that the test results are consistent at all test sites. This will be
accomplished through precise testing of the photodiodes used in each of the
test benches. This necessitated the design and construction of a unit capable
of performing the precision testing of these large-area photodiodes.


2
TABLE OF CONTENTS

Chapter 1. Introduction............................................................................................. 4
Chapter 2. Prototype Design Objectives .................................................................. 4
2.1. Main Chassis ............................................................................................... 5
2.2. Central Shaft................................................................................................ 5
2.3. Source Cap .................................................................................................. 5
2.3.1. Filter Holder ....................................................................................... 6
2.4. LAP Cap...................................................................................................... 7
2.5. Power Supply and Power Circuitry ............................................................. 7
2.6. Connections, Controls, and Displays .......................................................... 7
Chapter 3. Prototype Electrical Systems.................................................................... 9
3.1. Power System Design.................................................................................. 10
3.1.1. Power System Connections, Switches, and Controls......................... 11
3.1.2. Internal Power Supply........................................................................ 11
3.1.3. Voltage Regulators ............................................................................. 11
3.2. Input Circuit Design .................................................................................... 11
3.2.1. Light Emitting Diode (LED) .............................................................. 11
3.2.2. LED Intensity Control and LAP Size Selection Control.................... 13
3.3. Output Circuit Design ................................................................................. 13
3.3.1. Large Area Photodiodes (LAPs) ........................................................ 13
3.3.2. Amplifier Circuit ................................................................................ 14
3.3.3. Voltmeter/Display .............................................................................. 15
3.4. Circuit Analysis........................................................................................... 15
3.4.1. Analysis of Output Circuit ................................................................. 17
3.4.2. Analysis of LED/LAP Interaction ...................................................... 18
3.4.3. Analysis of Input Circuit .................................................................... 19
3.4.4. Conclusions Based on Numerical Analysis........................................ 19
Chapter 4. Viability Testing ..................................................................................... 19
4.1. Experimental Set Up ................................................................................... 19
4.2. Data from Viability Tests ............................................................................ 20
4.3. Conclusions from Viability Tests................................................................ 20
Chapter 5. Prototype Construction ........................................................................... 22
5.1. Design of Mechanical Components ............................................................ 22
5.1.1. LAP Cap............................................................................................. 22
5.1.2. LED Cap............................................................................................. 24
5.1.3. Central Shaft....................................................................................... 25
5.1.4. Main Chassis ...................................................................................... 28
5.2. Construction of Mechanical Components ................................................... 28
5.3. Selection and Purchase of Electrical Components ...................................... 28
5.4. Assembly of the Prototype .......................................................................... 28
5.5. Troubleshooting .......................................................................................... 29

5.5.1. Readout Fluctuation ........................................................................... 29


3

5.5.2. Low Output ........................................................................................ 29

5.5.3. Internal Capacitance ........................................................................... 29

5.5.4. LAP Connection................................................................................. 30

5.5.5. Temperature Gauge ............................................................................ 30
Chapter 6. Testing the Prototype.............................................................................. 31
6.1. Testing the Light Tight Chamber ................................................................ 31
6.2. Temperature Testing.................................................................................... 31
6.3. Repetition of Photodiode Installation.......................................................... 31
6.3.1. Data from Repetition Tests ................................................................ 31
6.3.2. Data Analysis ..................................................................................... 35
6.4. Testing Operation with 220VAC Input Power............................................ 43
Chapter 7. Conclusions ............................................................................................ 43
Appendix A. Parts List ............................................................................................. 48
Appendix B. Specifications for Electronic Components ......................................... 49
Appendix C. Dimensional Outlines for Mechanical Components........................... 55
Bibliography.............................................................................................................. 98


4
1. Introduction

The ATLAS detector calorimeters will use over ten thousand photomultiplier tubes
(PMTs). Due to the large number of PMTs, these will be tested at a number of locations
using identical test benches, constructed for this purpose. It is important that the results
from different PMT testing stations be comparable at the same level. To this end, a
method of intercalibrating the test stands has been developed. The various test benches
assess the quality of PMTs by comparing their response when stimulated by an
assortment of light emissions to the response of a central photodiode. Consequently, we
can intercalibrate the different test stands by testing their internal LAPs. Though no
specific requirements on the accuracy of this intercalibration were specified in the
technical design report of the ATLAS tile calorimeter, it offers a general statement that
the calibration of PMTs during operation should be ~1%. Thus, our goal will be to
achieve similar accuracy.

There are two possible ways of achieving our goal. Either we bring the LAPs to one place
for testing, or we ship the test equipment to each different location. Having the versatility
to operate in either of these ways is preferable and easily obtainable. This requires that
our unit must be compact enough to be easily shipped. Our prototype will operate solely
in DC mode in which the LAP is excited by a continuous, steady level of light. This will
be the most simple to construct, allowing testing to commence as soon as possible. Our
basic design will allow for increased capabilities to be added to future versions. One
improvement is the inclusion of a pulse mode, where the LAP is excited by a short burst
of light. Another possibility is the addition of an intermittent mode, where the photodiode
is excited by the emissions of a radioactive source. The emissions of a radioactive source
are more consistent that other sources, and this could lead to more accurate
measurements. We could also include a control port, which will allow an outside
computer to control all of these modes.

In this thesis, we will discuss the design and construction of a unit to test LAPs in DC
mode. We will present how this design achieves our goals. We will then present the
results of extensive studies of the performance of the test unit.

2. Prototype Design Objectives

The highest priority is reproducibility. We must be able to create the exact test conditions
every time we perform a test on a LAP. This includes ensuring the p