**Dzero Forward Proton Detector Safety Review Document**

Mario Vaz, Andrew Brandt, Pierrick Hanlet for the FPD Group

2 April, 2002

# 1 -- Introduction

This document presents the safety conditions for the DZERO, or **D0**,
Forward Proton Detector -- **FPD**. The FPD consists of 18 Roman Pots
installed at Tevatron sections C48 and C49 as shown in Figure 1. Here
D~1~ and D~2~ are single Roman Pots installed in the **Dipole Castles**.
A~1~, A~2~, P~1~ and P~2~ are castles with four Roman Pots each, called
**Quadrupole Castles**. In the Quadrupole castles, the four Roman Pots
are U (up -- above the beam), D (down -- below the beam), I (in -- inner
radius of the accelerator), and O (out -- outer radius of the
accelerator ring). Both Dipole Roman Pots are I.

![](media/image1.wmf){width="5.445833333333334in"
height="3.307638888888889in"}

Figure 1 -- The D0 Forward Proton Detector locations

For the Engineering Run the **FPD Control Room** was located in the D0
Tape Room near the D0 Control Room in D0 Assembly Building floor 1. The
Tape Room, or **Small Control Room** **-- SCR**, is used again during
the Commissioning phase of Run II (the early stages of Run II before the
FPD is fully integrated into the D0 DAQ).

Each Roman Pot has a particle position detector with 112 scintillating
fibers used for tracking and 1 trigger scintillator. Each of the
tracking fibers is connected to 1 channel of a Hamamatsu H6556 16-Anode
Multi Anode Photo Multiplier Tube, or **MAPMT** via a clear fiber. 7
MAPMTs are used to read out each detector. The trigger scintillator is
connected via a light guide to Phillips XP2282B fast Photo Multiplier
Tube, or **PMT**; these PMTs were used for Level 0 Trigger during Run I.

The PMT signal exits the detector chassis through an isolated BNC
connector, in order to reduce noise from ground loops that may be picked
up at the detector chassis. From there the signals are sent through high
quality coaxial cables, LMR400, to the Luminosity System **TDC** and
**Vertex** boards -- **FPDLM** -- located in the Movable Counting House,
or **MCH**, rack MCH115. The Vertex board generates and sends Level 1
trigger signals to the FPD Trigger Manager -- **TM** (located in
MCH120), which in turn generates and sends triggers to the D0 Level 1
Trigger Framework - **L1**.

MAPMT signals are amplified locally by Amplifier Shaper boards --
**A/S**, previously used in the FADC system during Run I, and sent
through flat ribbon 16-channel coaxial cables to a Transition Patch
Panel, or **TPP**. The TPP terminates the signal onto a special flexible
circuit adapter to the Analog Front End boards -- **AFE** - located in
Rack **PW08** of D0 Detector Platform. The AFE sends the digitized
signals to a Sequencer board, or **SEQ**. From there, data is sent to
Level 3 -- **L3** -- of the D0 Data Acquisition System via a VME Readout
Buffer board -- **VRB** -- located at MCH213. The AFE also sends
discriminated signals to the Digital Front End boards -- **DFE**,
located in D0 Platform Rack PW02. The DFEs determine valid tracks from
diffractive and elastic events to generate Triggers. These signals are
sent to FPD TM, which generates L1 triggers using the tracks and signals
from the FPD LM and D0 LM. The FPD TM then sends triggers to the D0
Level 1 Trigger Framework -- **L1**. For monitoring purposes, the DFEs
also send data to a VRB in MCH322. A block diagram of the readout chain
is shown in Figure 2.

![](media/image2.png){width="6.5in" height="2.8541666666666665in"}Figure
2 -- Block Diagram of final configuration of FPD Readout and Trigger
Chains

![](media/image3.png){width="5.5in" height="2.421527777777778in"}In
Figure 2, the MAPMT, PMT, and VETO boxes indicate the detectors we have
installed; the A/S box are recycled Amplifier/Shaper electronics from
Run I; the TPP box are the Transition Patch Panels developed by the FPD
group; the LM box is the D0 Luminosity Monitor; and the remaining boxes
are standard Run II Readout and Trigger electronics.

Figure 3 \-- Block diagram for present readout and triggering with
stand-alone DAQ

Until the standard D0 Run II Readout and Trigger electronics is
available, and we are prepared to use them, we are using a stand-alone
Trigger and DAQ as shown in Figure 3. Here, jumper cables for one
spectrometer of tracking detectors run from the D0 detector platform
rack PW08 to the SCR. We also have jumper cables of LMR400 and LMR200
for the PMT signals for all PU, PD, AU, AD, and D trigger PMTs which run
from the collision hall to the SCR.

For calibration and monitoring purposes a Light Mixing Box, or **LMB**,
sends light through optical fibers to the photo cathodes of each channel
of each MAPMT and PMT.

# 

# 2 -- Roman Pot Control and Monitoring

Each **FPD Roman Pot** is moved by a NEMA 23 **stepping motor**. The
**step motor driver** is an industrial \"dumb\" driver PDS 15-2,
controlled by a custom-made **Index Interface Board - IIB**. The IIB
exchanges digital signals with a **1553 Rack Monitor Module - RM**.
Roman pot position is also measured by a Linear Variable Displacement
Transducer - **LVDT** with a **signal conditioner** connected to the
1553 Interface RM. All this equipment is located near the Roman Pots.

A **Rack** **Monitor Interface -- RMI,** connected to a 1553 Rack
Monitor, is installed in each of the five FPD Control, or **CTL**,
Electronics racks. An A/S Rack and a CTL Rack are located near each of
the A~1~, A~2~, P~1~, P~2~, and between D~1~ and D~2~ Castles, as shown
in Figure 4. Any smoke created inside one of the enclosed racks will
reach the smoke detector located at the top of each rack. The smoke
sensor activates the RMI directly disabling the control power boxes, or
**CPB**s, in the CTL and A/S racks connected to Tevatron electric power
outlets -- one for the step motor drivers and the second for the low
voltage power supplies for the A/S electronics. The CPBs can also be
turned off by software. The driver CPBs may also be disabled by the
control switches that are located in the control room. There is also an
Emergency switch located in the control room that overrides the software
and forces the IIBs to remove the pots to their home positions.

The block diagram in Figure 4 shows the physical location of the
electronics with respect to the castles. The A/S and CTL boxes represent
19" relay racks and the RP boxes represent the Roman Pot Castles.

![](media/image4.wmf)

Figure 4 - FPD Racks position floor plan.

![](media/image5.png){width="7.5in" height="3.1145833333333335in"}The
reason for the separation of A/S electronics and CTL electronics into
separate racks is because we need to isolate the Tevatron electrical
ground from the D0 detector platform ground due to noise considerations.
This is accomplished by requiring that the A/S electronics, which send
signals to the D0 detector platform, have their AC current supplied by
an Elgar line conditioner or Sola. Both the Elgar and Solas have been
modified with satiable inductors to ground on the ground lines. This is
shown for the quadrupole detectors in Figure 5.

Figure 5 -- Final configuration of relay racks for A and P quadrupole
detectors

Only one pair of A/S and CTL racks is required for the dipole detectors.
In all cases, the A/S racks are raised off of the ground and rest on top
of G10 pads for isolation. The two Solas are located in the Dipole and
the P2 A/S racks, and the Elgar line conditioner is installed in the A2
A/S rack. Until the multiplexors are installed, the Multiplexor unit in
Figure 5 will be a second RM. Note that there will also be a **Control
Unit** that will contain the logic and control over the voltage required
for the motor driver operation.

A blowup of the present connections in the CTL rack is shown in Figure
6. The view is from the back of the rack. On the front side of the IIBs,
the CN4 and CN5 connectors read from the limit switches and encoders,
and write to the motor drivers, respectively. "Uncontrolled" AC powers
all the RMs, RMIs, and Line Conditioners; the IIBs are powered from the
internal power supply of one of the RMs. The AC for the Drivers is
controlled via the RMI and a CPB, as described earlier. Figure 6 shows
the present configuration and will be modified with the addition of the
Multiplexor units and Control Units during the May/June 2002 shutdown.

As of the writing of this document, we now have five months of
experience with the present tunnel configuration of the A/S racks. We
are satisfied with their operation and see no need to change anything in
the A/S racks.

![](media/image6.png){width="4.496527777777778in"
height="4.718055555555556in"}

Figure 6 -- Present Layout of CTL racks

Figure 7 shows the block diagram for the FPD electronic modules and
cabling for Run II, and is a reference for the discussions in the
following sections. A more detailed schematic for electric power is in
**Appendix VIII**.

![](media/image7.wmf)

Figure 7 -- Block Diagram for the FPD electronic components and cables.

# 3 -- Roman Pots and High Voltage Power Supplies -- HVPS

Bias for the MAPMTs and PMTs come from D0 High Voltage -- **HV** --
Power Supply Motherboards with HV Pods connected to a HV FANOUT unit,
located in the MCH222. There are 23 pods in 3 motherboards. Four
8-channel Reynold cables bring power to another HV FANOUT unit located
at the bottom of the PW08 rack on the D0 detector platform. From there,
red RG58/U HV cables bring the HV supply to the Roman Pots.

The MAPMT HV cables from the PW08 HV FANOUT connect directly to isolated
SHV BNC connectors on each detector chassis. Inside each chassis, the HV
is fanned out to the 7 MAPMTs, and the ground is connected to the
chassis via a 440Ω resistor. Though the D0 HV Power Supply has a maximum
of 3mA at 3kV, the voltage trip limit for the MAPMTs is set at --1kV;
the current trip limit is set to 2.3mA. The distribution of HV inside
the chassis is shown in **Appendix I**.

The PMT HV cables from the PW08 HV FANOUT connect to an **HV 1:4
Splitter Box** near each castle. A Splitter Box has an LC circuit to
filter noise potentially picked up on the RG58/U HV cable from the D0
collision hall. A drawing of the **HV Splitter** is shown in **Appendix
II**. The voltage trip limit for the PMTs is set to --2kV and the
current trip limit to 1.2mA for 2 PMTs and 2.4mA for 4 PMTs.

The lengths of the RG58/U HV cables needed for the HV supply are \~50m
longer than the distances from the Roman Pots to the D0 Interaction
Point shown in Figure 1. A dipole cable has a length of \~100m, and thus
a total capacitance of 10nF. The HV cables are grounded at both sides;
at the Power Supply side they are grounded through a small series
resistor to reduce noise. At 2 kV a 200Ω human body resistance will
result in a factor of:

> I^2^ \* t = 0.5 \* C \* V^2^ / R = 0.5 \* 10^-8^ \* 2000^2^ / 200 =
> 10^-4^ A^2^s.

According with M. Johnson document on Safety Analysis of the D0 High
Voltage System, June 1991 (**Appendix III**), this corresponds to less
than 5% of the maximum I^2^ \* t a person can safely receive. Although
the added capacitance of the HV Filter increases the I^2^ \* t to 15% of
the maximum, this is still well within a safe range. Even with this
large safety margin, a special procedure is provided to handle these
cables. To remove a cable from its HV connector its power supply need to
be turned off by an operator in the control room. It is mandatory to
contact this operator to confirm that the high voltage is off. The cable
is then disconnected and immediately connected to GROUND HV coaxial
connector in the HV 1:4 Splitter box, to discharge from it any residual
charge. Figure 8 shows the cabling block diagram and describes the
connections of FPD high voltage system.

Additionally, documentation regarding HV safety procedures is in place
at each castle location in the Tevatron tunnel.

![](media/image8.wmf)

Figure 8 - PMT and MAPMT high voltage power connections

PMT - Single anode photo multiplier tube for trigger scintillators

MAPMT - 16-anode photo multiplier tube for scintillating fiber position
detector

# 4 - Trigger and Data Acquisition

FPD scintillator PMT signals go through LMR400 coaxial cables to NIM
electronics in the SCR. The MAPMT signals go through flat coaxial 16
channel cables to CAMAC FERA ADC modules during the Commissioning phase.
Later, the PMT cables will terminate at the TDCs of the same type used
for the Luminosity Monitor, and the MAPMT cables will terminate at TPPs
and on to AFE boards via Flexible Printed Circuit Adapter that couples
via a TPP with the AFE Cin::Apse connectors. The TPPs serve to make the
transition to the Cin::Apse connectors, isolate detector ground from
platform ground, shape the signals to mimic VLPC signals, and discard
excess charge so that the MAPMT signals are within the dynamic range of
the SIFT chips on the AFE MCM modules. A block diagram for the FPD
trigger and data acquisition modules and cables is shown in Figure 9.

The position detector MAPMT signals go to A/S boards housed in special
VME crates located near their respective Roman Pots. Seven A/S boards
receive 224 signals from the 14 MAPMTs located at D1 and D2, amplify,
shape and send them through 14 flat coaxial 16 channels cables to one D0
8-MCM AFE located in PW08. Each quadrupole has 28 MAPMT and use 14 A/S
boards and 28 flat cables.

Power is enabled by a Power Box (shown in **Appendix IV)** controlled by
an RMI which is connected to the smoke detector. In this way shutdown
can be done automatically by the smoke detector or by software.

The A/S boards have low voltage power supplies of ±15V at 5A, ±12V at
30A, +5V at 12A. Each board is fuse protected, as shown in the schematic
in **Appendix V**. The VME backplane for the A/S boards was reviewed by
Haldeman and Vissar in 1990, and shown in **Appendix VI**. The design
for low voltage power supplies for the A/S crates installed in the
Tevatron tunnel has already been reviewed and approved in December 2001
and is given in **Appendix VII**. These power supplies also power the
PIN/Diodes for the LMB monitoring, and have their voltages monitored via
the RMs.

![](media/image9.png){width="6.197916666666667in" height="7.65625in"}

Figure 9: Final Configuration for FPD Readout and Trigger

# 5 - Roman Pots Movement Control

Each step motor is connected to the driver by a 3m long braided shield 3
AWG #16 wire cable. A ferrite absorber at the driver cable end is used
to help keep noise at low level. A slow blow AG3 fuse protects each
driver. The driver and filter are installed in a closed convection
ventilated 19\" aluminum crate with fuse accessible at the crate back.
Driver power cable from the filter is a custom made braided shield 3
16AWG wire cable and has a ferrite absorber at the driver end. A braided
shield control cable (TTL level), 3m length, connects the driver to the
Index Interface and has a ferrite absorber at the driver end. All cables
braids are connected to the crate back plane ground to keep noise at low
level.

The driver crate is connected to a special Tevatron Mains through a
modified Power Box (Driver Box) to automatically cut off the power in
case of fire detected by a Photoelectric type Smoke Detector connected
to an RMI. Like the standard power box, the Driver Box can be software
controlled by the RM, but also can be manually operated from the Control
Room.

The Index Interface is a double face TTL logic (HCT family) board with a
maximum consumption of 30mA with all LED turned on. It\'s powered by the
RM and fused by an on board 3AG 250mA quick blow fuse. The board accepts
TTL signals from the RM, the step motor encoder, limit switches, and the
driver and sends TTL signals to the RM. Power and signals from the rack
monitor come on a 0.5m standard flat cable with 37 28AWG wires. The
board fits in a 19\" crate and it shares the crate space with the LVDT
signal conditioners. An Emergency line, manually operated from the
Control Room, can make the IIB move all Roman Pots completely out in
case of problems with the beam or Roman Pots movement control.

LVDTs monitor the Roman Pot positions. Signal conditioners, commercial
units that consume 25 mA from a Power Box via three wires 28AWG, send
their signals to 1553 RM Analog inputs. There is a maximum of four LVDTs
per crate, all protected by a single 1A quick blow fuse, installed at
the back of the crate. Signal conditioners are inside the closed and
convection ventilated part of the 19\" crate that holds the IIBs.

A Python program is used in conjunction with the RM and IIB to move the
pots. The program allows for one or more pots to be moved simultaneously
and gives information on the location both from the step motor/encoders
and from the LVDTs. Alarms indicate the consistency of these positions
and stop the pot motion if they are not consistent. An alarm signals if
communication with the RM is lost for some reason. We are also adding
alarms based on the halo rates in the trigger scintillator that will be
tuned based on experience with beam.

The whole electronics chain was operated successfully during the
Engineering Run (Sep-Nov 2000). A problem, which resulted in the failure
of the RM due to current spikes when the castle limit switches were
operated, was fixed by adding resistors to the switches. In addition,
since we have the longest run of 1553 cables, we replaced the original
1553 cables in the tunnel with ones with less attenuation. Another
problem that happened was the loss of information on the pot positions
when the Power Box disconnected the power for IIB. So for Run II, the
IIBs will be kept on at all times, but the drivers will be turned off
once the pots are in place using the Driver Box.

Both the new Multiplexor and Control Circuits will be installed in the
spring of 2002. The Control Circuit is shown in **Appendix IX**.