Power Supplies and Electronics Procedures

The power supplies and readout electronics associated with the HRS VDCs are all commercially designed. The reader is directed towards the manuals made available by the manufacturer for the detailed information not provided here.

Figure 5.4: VDC overview.

A Bertan 377N HV power supply provides -4.00 kV nominal to each of three HV planes in a given VDC detector package via a 10 M$\Omega$ Hammond splitter box (see Figure 5.4). The power supply is located in the detector hut in a NIM bin on the upper level of the space frame. This unit may be controlled either manually or remotely via the EPICS control software, and also provides a monitor of the current drawn (nominally 70 nA) by the VDCs to which it is attached. Connections from the power supply to the Hammond splitter box, as well as from the Hammond splitter box to the VDCs are made using standard SHV connectors mounted on red RG-59/U HV cable good to 5 kV.

A Kepco ATE 15-3m discriminator power supply provides +3.0 V (92 cards draw $\leq$ 2 A) and the Kepco ATE 6-100m pre-amp power supply provides $\pm$5 V nominal to the LeCroy 2735DC pre-amp/discriminator cards used to instrument the chambers via a heavy-duty fuse panel. The precise voltages provided are +5.0 V (92 cards draw 22 A) and -5.2 V (92 cards draw 58 A). These LV supplies are located in the detector hut on the main level of the space frame for the HRS$_{\rm e}$ and on the upper level of the space frame for the HRS$_{\rm h}$. Complete connection schematics and instructions for making or breaking the connections are located on the aluminum Faraday cage protective plates covering the respective interface nodes between the power supplies and the VDCs.

Each VDC wire plane consists of 400 20 $\mu$m $\phi$, Au-plated tungsten wires. The first 16 wires on each end of the wire plane are connected to ground for field-shaping purposes. There are 368 wires per wire plane which act as signal wires. Thus, each spectrometer is instrumented with 1472 channels of LeCroy 1877 multihit Fastbus TDCs. These TDCs are located in a Kinetic Systems F050 Fastbus crate with a BiRa FB8189-4 power supply located on the main level of the spectrometer space frame in the detector hut. The connections between the pre-amp/discriminator cards mounted on the VDCs and the TDCs are made with 16-conductor twisted-pair cables. Clip-on ferrites are used to filter noise. A connection schematic is posted on the side of the rack holding the Fastbus crate on the space frame in the detector hut.

Power-up Procedure

1. ensure gas flow has been established in the chambers as previously outlined. If it has not, STOP RIGHT HERE! Gas flow must be well-established and steady-state BEFORE the HV may be enabled.
2. Ensure that all power supplies as well as the Fastbus crate are off and then connect the LV, HV, and TDC cables.
3. enable the LV. Set points are clearly labeled on the face of the power supplies. Note that they have overcurrent setpoints, and some fine adjustments over the first 30 minutes after a cold start power-up may be required. Appropriate LEDs should all be active on both the power supplies and the pre-amp/discriminator cards.
4. slowly (steps of no more than -300 V) ramp the HV to its nominal set point of -4.00 kV using either the manual or the remote controls. While the trip current is set to 10 $\mu$A, do not allow the chambers to draw more than 1 $\mu$A during the ramping procedure or serious damage may result. If the power supply trips during the ramping procedure, you are moving too fast. Rezero things and begin the procedure again. NEVER USE THE AUTO-RESET FUNCTION. If the power supply trips again, STOP IMMEDIATELY AND INVESTIGATE.
5. enable the Fastbus crate. Appropriate LEDs should all be active.
6. check for poor signal connections evidenced by hot wires (wires counting extremely fast) or dead wires (wires with no counts) using the histograming software and cosmic rays. Remake any connections as necessary by first powering down the Fastbus crate.

If at all possible, the HV and LV power supplies should be left on continuously if and only if gas is available to the chamber. This avoids time loss to reconditioning and maintains the desirable steady-state operating condition.