IceCube PMT HV
Base Development Status
Nobuyoshi Kitamura – UW-Madison / SSEC
August 12, 2003
0. Introduction
This report summarizes the most up-to-date comparison among the three distinct PMT HV Base prototype designs mainly in performance aspects. Other known characteristics associated with the designs, such as the cost factor, are also outlined here.
The three designs are referred to as:
*Iseg Spezialelektronik, GmbH, Rossendorf, Germany (www.iseg-hv.com)
**EMCO High Voltage Corp., Sutter Creek, CA, USA (emcohighvoltage.com)
1. The Designs
A. The “Old Iseg Base” integrates a Cockroft-Walton generator, output stablizer (regulator), and digital interface (DAC, ADC) on a single PCB, and is to be directly mounted on the PMT. (See diagram from Iseg). In this design, the first dynode voltage is fixed to an optimum value (600V) regardless of the cathode-to-anode voltage.
A similar design with an analog control interface (i.e., without DAC and ADC) has been used in AMANDA String 18.
B. The “New Iseg Base” employs essentially the same HV circuitry as the Old Iseg Base, however, it is distinct from the old version in that it implements a split-ground configuration using an isolation amplifier, whereby two DC-isolated grounds are created: the “noisy section” consisting of the digital interface and the oscillator for HV generation and the “analog” section consisting of the cathode and the dynode chain circuitry.
The requirement for the isolated grounds was described to NK by Jerry Przybylski (JP) during the In-Ice Devices Workshop at UW-Madison in August, 2002. See the sketch created by NK from that conversation.
The split-ground design is intended to allow experimentation with various grounding configrations in the integrated DOM. The two grounds, for instance, may be jumpered with a wire so that the both grounds share the same DC ground. Alternatively, the analog ground may be connected to the ground at the analog front-end of the DOM Main Board, whereas the digital ground is referenced to the DOM Main Board through the ribbon cable.
As in the Old Iseg Base design, the first dynode voltage in the New Iseg Base is fixed, regardless of the cathode-to-anode voltage.
C. The “EMCO Base” is a design approach consisting of three component groups: the passive resistor chain PCB mounted on the PMT; the modular HV generator; and the digital interface controlling the HV generator. The HV generator, Model 9730, an EMCO product customized from Model CA20P, is a regulated HV supply with analog program input and monitor output. The passive resistor chain is a custom product from EMCO. The digital interface is of NK’s design. The HV generator is mounted on the digital interface board, which, in turn, is mounted on the flasher board.
The total resistance of the passive bleeder chain is approximately 150MW, which leads to a considerably low bleeder current that is uniquely permissible for IceCube where the PMT is operated in the photon-counting mode. The low bleeder current also leads to a smaller output current requirement for the HV generator and low power consumption.
The first dynode voltage in the EMCO Base design is proportional to the cathode-to-anode voltage, and therefore, the peak-to-valley ratio, the collection efficiency and the PMT gain are not independently adjustable.
2. Key Design
Considerations
The components / assembly and/or vendor selection have been subject to the following considerations.
o
Low noise
*The New Iseg Base interface was taken as the baseline and the interface for the Old Iseg Base and the EMCO base were created to match the baseline.
3.
The Prototype Performance Evaluation Results
A. Oscilloscope
Measurements
The Method
The PMT HV Base was digitally controlled by a DOM Main Board and the analog output was observed with an oscilloscope (50W input). The analog output cable (RG180—100W) was replaced by an RG58 (50W) cable and a 50W resistor was inserted between the analog output (transformer secondary) and the RG58 cable to realize a 100W load. The measurements were done at room temperature.
The Results
These results have been reported at Instrumentation Workshop, LBNL, July 23-24, 2003.
Summary
B. DOMMB ATWD
Measurements
The Method
The measurements were done with the integrated DOMs at room temperature. The data were taken from ATWD#0 with CPU trigger. The analog MUX value was set to 2 (chan 3 for LED current).
Each curve presented here is after the subtraction of the baseline obtained by averaging 100 scans captured while the analog front-end was shunted with a 100W load and the HV base ribbon cable disconnected.
The data were captured using a Phython script written by Kael Hanson. Additional Tkinter script by NK allowed continuous data capture and display on the screen. The data presented here were the screen shots taken at random intervals.
The Results
PMTBaseComparisonWithATWD1.pdf
pp 5-9: DOMMB with no HV base cables attached.
pp 10-14: EMCO Base with DAC=0
pp 15-19: EMCO Base with DAC=2000 (1000V)
pp 20-24: Old Iseg Base with DAC=0
pp 25-29: New Iseg Base with DAC=0
Summary
C. Performance Evaluation
Summary
4. Overall Comparison of the Prototypes
|
|
EMCO |
Old Iseg |
New Iseg |
|
Noise levels |
~5 counts p-p in high-gain channel |
problematic |
|
|
1st Dynode Voltage |
Scales with output |
Fixed (desirable) |
|
|
Power dissipation at max output (mW) |
250 |
130 |
280 |
|
Cost (US$) |
~600 |
~150 |
~260 |
The EMCO Base performs comparably as the Old Iseg Base in terms of noise. The EMCO Base, however, does not have the performance advantage of the fixed first dynode voltage. It is also that the high power consumption and component cost of the EMCO Base translate into an overall cost that is significantly higher than that of the Old Iseg Base. With the exception of the fixed first dynode voltage, the New Iseg Base does not exhibit any desirable characteristics comparable to the others.
5. Conclusion
The above comparative studies show that the Old Iseg Base is the most desirable in overall characteristics.
/nk
