Nobuyoshi Kitamura

Nobuyoshi Kitamura

IceCube Project

University of Wisconsin-Madison

222 West Washington Avenue,

Madison, WI 53703

(608) 262-2482

http://icecube.wisc.edu

Supplementary Information for the IceCube High Voltage Toroidal Transformer Specification

IceCube is a neutrino observatory under construction in Antarctica. The toroidal transformer is a piece part, requiring an extremely high reliability, used in each one of over 5000 detector modules to be permanently installed in deep ice (1400 – 2400 m).

The function of the toroidal transformer is to ac-couple the high speed transient signals from the anode high potential of the photomultiplier tube to the analog frontend of the digitizer circuitry.

Key points in the specification are:

1. High voltage isolation up to 5kVDC (min).

This is to be achieved by the custom high voltage cable medium; the slotted carrier board geometry; parts cleanliness; and, corona prevention precaution at solder joints. All solder joints are to be retouched after initial soldering to create a smooth dome-shape with no asperities. Binding posts, in-board pins, etc., must be clipped as short as possible (2mm max height above carrier board).

1. Frequency response (8kHz to 100MHz)

The high frequency response is achieved primarily by capacitive coupling between the wire pair. The custom two-conductor construction assures tight coupling between the pair throughout the winding.

The low frequency response relies on magnetic coupling. The design maximizes the number of windings within the footprint constraints. The minimum OD and maximum ID are specified to assure tight winding around the core.

1. Mechanical requirements

The part is intended to be a drop-in replacement of an existing design.

Current Implementation (August 2005)

The current implementation consists of a bifilar winding of silicone-insulated wires. The slots on the board are to provided for high-voltage isolation. All the solder joints have been re-touched after waving to form a smooth dome (after IPC-A-610C, Jan 2000, Section 6.8.4 ).

/ Figure 1

New Design Implementation

Laboratory sample photos are shown below.

Figure 2 / Figure 3

The pins in Figure 3 are Vector Electronics & Technology K24A/M inboard pins. The carrier board shown (demonstration only) has been laser-cut from a 1/16"-thick Delrin sheet.

Laboratory Data

The following are scope shots of the response of the sample shown in Figure 1. All measurements have been done with a 100 Ohm source and load.

Low Frequency Response (room temperature)

Figure 4 Room temperature response. Trace “4” is a single sweep trace; Trace “D” is an average over many such traces. Horizontal: 10 usec per division. The decay constant is approximately 97 usec.

Low Frequency Response (-45 deg C)

Figure 5 Wide pulse response at -45 deg C. The decay constant is approximately 27 usec.

The marked increase in droop (smaller time constant) is attributable to the decrease with temperature of the permeability of the toroidal core.

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