BaBar Prototype II Drift Chamber

Hardware Setup and Upgrade Instructions

Last modified: Jignesh Parikh 15 Mar 2002

The Prototype II drift chamber (Proto II) is a full-scale mockup of the BaBar Drift Chamber, covering a narrow angular region (1/8, 45°) of the first four superlayers. It is installed at SLAC in Central Lab Annex B273.

This document describes how the detector hardware is installed, and how to update the data-acquisition firmware as needed. A more detailed description of the hardware is included in Lisa Manning's project report.

Starting Prototype II

  1. Check water level in the Chiller. Maintain water level in the chiller such that thermometer is dipping in the water. Start the chiller when this is done.
  2. Put the power on for Low Voltage.
  3. Put the power on for High Voltage.
  4. Check the Proto II chiller status.Green light indicates water is flowing. Red light indicates water is not flowing.

Cosmic Ray Trigger

The Prototype II trigger consists of a three-fold coincidence of scintillator paddles, one above the chamber, one immediately below, and one below a 62 cm steel range stack.

Diagram of trigger layout (16K PostScript)

Plateau and relative efficiency curves were taken for all three scintillators (see links below) to determine the PMT voltage and discriminator settings.
Voltage Threshold
(mV)		 Width
(ns)
T1 1900 40 24
T2 2000 40 52
T3 2050 40 72

High Voltage

Proto II's high voltage supply is interlocked with the gas system so the chamber can be only operated while the proper gas mixture is flowing.

Low Voltage

Proto II's low voltage supply is interlocked with the water chiller.

Gas Mixing

A helium-isobutane gas mixture is contiously pumped through the chamber. As energetic particles traverse the chamber, they ionize gas molecules. The liberated electrons drift towards positive sense wires and the ions drift towards field wires. Each electron showers in the very strong electric field near the sense wire, and this shower generates a negative pulse on the sense wire, which is shipped to electronics on the front-end of the chamber. By analyzing the timing and magnitude of this pulse, physicists can reconstruct where the particle was in the chamber and (sometimes) what type of particle it was.

Environmental Monitors

Operating conditions of proto II in the gas chamber are monitored using the following sensors:

temp_front_gas :
For measuring the temperature of gas at the forward end of the gas chamber
temp_rear_gas :
For measuring the temperature of gas at the rear end of the gas chamber
temp_front_cover :
For measuring the temperature inside the cover at the forward end of the gas chamber
temp_rear_cover :
For measuring the temperature inside the cover at the rear end of the gas chamber
rh_front_cover :
For measuring the relative humidity in the front cover of the gas chamber
rh_rear_cover :
For measuring the relative humidity in the rear cover of the gas chamber
press_chamber(P2) :
For measuring the absolute pressure of the gas chamber in millibar
press_atmosphere(P1) :
For measuring the atmospheric pressure in millibar
flow_helium :
For measuring helium flow in standard litres per minute
flow_C4H10 :
For measuring isobutane flow in standard litres per minute
flow_nitrogen :
For measuring nitrogen flow in standard litres per minute
volts_anode :
For measuring the 1930V
volts_cathode1 :
For measuring the 335V
volts_cathode2 :
For measuring the 870V
current_anode :
For measuring the current for 1930V
current_cathode1 :
For measuring the current for 335V
current_cathode2 :
For measuring the current for 870V
The table below gives all the information about these sensors:

Number Sensors Location on detector Input Range Supply (V DC) Output (V DC) Connector Type Company Model
1 press_atmosphere (P1) 0-30Psi 5 0.5-4.5 3-pin lemo Kavlico corp P350-30A-D1A
2 press_chamber (P2) 0-30Psi 5 0.5-4.5 3-pin lemo
3 temp_front_gas Front End 0-100C 2 0.135-0.67 3-pin lemo Omega OL 710
4 temp_rear_gas Rear End 0-100C 2 0.135-0.67 3-pin lemo
5 temp_front_cover Front End 0-100C 24 1-5 1-pin lemo Omega HX 13V
6 temp_rear_cover Rear End 0-100C 24 1-5 1-pin lemo
7 rh_front_cover Front End 5-95% 24 1-5 1-pin lemo Omega Omega
8 rh_rear_cover Rear End 5-95% 24 1-5 1-pin lemo
9 volts_anode Voltage(1930V) 0-5KV 10V=10KV 0-5 1-pin lemo Bertan Associates, inc. 1755P
10 volts_cathode1 Voltage(335V) 0-5KV 10V=10KV 0-5 1-pin lemo
11 volts_cathode2 Voltage(870V) 0-5KV 10V=10KV 0-5 1-pin lemo
12 current_anode Current(1930V) few nA 10V=1mA 0-5 1-pin lemo
13 current_cathode1 Current(335V) few nA 10V=1mA 0-5 1-pin lemo
14 current_cathode2 Current(870V) few nA 10V=1mA 0-5 1-pin lemo
15 flow_helium He Flow 0-1 SLPM N/A 0-5 3-pin lemo Sierra instruments, inc. 840-L-1-V1-S1
16 flow_c4h10 C4H10 Flow 0-1 SLPM N/A 0-5 3-pin lemo
17 flow_nitrogen N2 Flow 0-250 SCCM N/A 0-5 3-pin lemo Sierra instruments 840-L-2-0V1-SK1-E-V1-S1

In March 2002, all these sensors were verified experimentally and a new box was designed.

Front-end Electronics

Front-end electronics are water-cooled. Front-end and read-out electronics consist of two Front-end Assemblies (FEAs), a data I/O Module (DIOM), a triggered Read-Out Module (ROM), a Fast Control Distribution Master (FCDM), and a Fast Control Partition Master (FCPM). Input triggers are processed by the FCPM and FCDM, then distributed to the ROM. The ROM collects data from the drift chamber front-end electronics and ships it to data acquisition system.

On the real chamber, there are four DIOMs, each reading out one quadrant's worth of data. Each DIOM is configured for its quadrant via a jumper attached to its J12 connector. For Prototype II, we have prepared four jumpers, so that the hardware and software can emulate any part of the real detector. The quadrant selected must be matched to the ROM's identification number.

The two front-end elements have separate cables connecting them to the DIOM. The four DIOM connectors labelled J10, J8, J7, and J5, correspond to the four wedges in each quadrant of the real BaBar drift chamber. Any two of the connectors can be used, so that the readout system can emulate any portion of the real chamber.

Data Acquisition

The data acquisition system consists of a BaBar TPC Readout Module (ROM) and a Fast Control Partition Master in a 9U VME Crate. The ROM is connected to the front-end DIOM with a dual fiber-optic cable. The ROM is based on a Motorola 68040 CPU, and runs the VxWorks operating system, with the standard BaBar Online Data Flow (ODF) core and DCH-specific applications.

The ROM has an eight-bit identification number which is set via DIP switches on the back of the module. For the drift chamber software to function correctly, the ROM ID must match the quadrant jumper selected for the Data I/O module.

Note: The installed version of the core DataFlow software does not permit an isolated ROM (as we use on Proto II) to be configured with ROM ID 0. We can only set up Proto II as quadrants 1, 2, or 3.

Periodically, the core ODF group will release an update to the core software, which should be installed in the Proto II ROM flash memory. The installation process is straightforward, but must be followed carefully to avoid leaving the ROM in a unusable and inaccessible state.