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Experiment Safety Assessment Document (ESAD)
CLAS12 Silicon Vertex Tracker
June 16, 2016
1
Introduction
This ESAD document describes identified hazards of the CLAS12 Silicon
Vertex Tracker system and the measures taken to eliminate, control, or
mitigate them. This document is part of the CEBAF experiment review
process as defined in Chapter 3120 of the Jefferson Lab EHS&Q
manual, and addresses the hazards associated with the specific
equipment and their mitigation. Responsible personnel is also noted. This
document does not attempt to describe the function or operation of the
detector. Such information can be found in the TDR or SVT
Commissioning document.
2
2.1
CLAS12 Silicon Vertex Tracker
Overview
In this document the hazards, mitigations, and responsible personnel
are noted.
The material in this chapter is a subset of the material in the full
CLAS12 Silicon Vertex Tracker commissioning document and is only
intended to familiarize people with the hazards and responsible personnel
for these systems. It in no way should be taken as sufficient information
to use or operate this equipment.
2.2
Silicon Vertex Tracker
The Silicon Vertex Tracker consists of 66 double-sided microstrip
modules connected by 15-20 feet electrical cables to VXS readout
boards (VSCM), MPOD power supply crates and the patch panel. The
VXS and MPOD crates are enclosed in the electronics racks. The
system is located in the EEL124 clean room. The modules are arranged
into 4 cylindrical coaxial regions. In order to operate the SVT, high
voltage and low voltage are supplied to each module. All power supplies
are rated as class 1. The high voltage for the module is 85 V (10 A).
The required low voltage is 3.5 V (2 A) for the readout electronics. High
voltage PS (3 kV, 4 mA) is used for the PMT trigger planes. Constant
temperature inside the SVT is kept by running a coolant through the
copper pipes that are integrated into cold plate using a laboratory chiller.
Cooling system should provide temperature stability at the level of 1 C.
To avoid moisture build-up in the calorimeter enclosure a steady flow of
nitrogen gas is maintained and
the temperature and humidity in the SVT enclosure are monitored with
sensors interfaced to the SVT slow control system.
Long term stability test stand is installed in EEL124. Several SVT
modules are mounted inside the carrier boxes and placed on a
workbench. They are connected to the standard SVT power supplies and
readout electronics.
2.2.1
Hazards
Hazards to personnel are associated with this device are high
voltage, which is supplied to the silicon sensors and low voltage, which
powers the front-end electronics and slow controls. Hazards are electric
shock if the SVT enclosure is opened without switching off the HV and
LV. Low level hazard for personnel due to voltage/current range.
Hazards to the detector include mechanical damage, cooling fluid
leaks or condensation in the sensors and hybrid region, over-voltage to
the sensors, front-end or slow control monitoring system that could
damage the related subsystem, absence of cooling or cooling failure
when voltage is applied to the modules or slow controls, which could lead
to overheat of the electronics.
The SVT sensors can be damaged if they are subjected to overvoltage or over-current and are sensitive to electrostatics.
The SVT sensors and electronics can be damaged if modules are
powered up when temperature is close to the dew point and there is a
possibility for condensation.
2.2.2
Mitigations
All SVT operation and maintenance work is performed by trained
personnel.
Interlock system is installed to ensure safe operation of the SVT. It
includes software and hardware interlock protection on currents, voltages,
temperature, humidity, dew point, coolant flow, chiller operation.
Monitoring of critical system parameters is in service. Proper turn-on/turnoff sequence is established by the slow controls software.
High Voltage: high voltage up to 85 V is supplied to the silicon
microstrip sensors. A very low current limit (4 A) is set (hardware) on
each HV channel. A low hardware current limit (1 A) is set on all LV
channels. All cables and connectors are certified for this rating. All
mechanical structures are properly grounded. HV and LV distribution
boards on the detector cannot be accessed during operation. If high
voltage is applied when the low voltage is turned off, the FSSR2
preamplifiers may be damaged. The HV operation is interlocked to the LV
settings, so that HV cannot be supplied if LV is off. A very low current
limit (0.8 mA) is set on the PMT PS. Voltage limit is set to 2.4 kV.
Over-voltage: applying HV and LV above certain values can damage
the sensors and preamplifiers. Both HV and LV are monitored via the
EPICS slow controls system; reading above predefined limits will
automatically trigger the supplied voltage to be turn off.
Oxygen deficiency hazard for nitrogen purging system was analyzed
and reviewed following the ES&H manual chapter 6540 appendix T1,
signed form attached. Class 0 ODH signs displayed at the entrance of
EEL124 clean room.
Temperature, humidity, and dew point interlocks turn off the modules
or the whole detector if monitoring variable goes outside the predefined
limits.
Over-temperature: absence of cooling or cooling failure when LV is
supplied to the FSSR2 chips may cause over-heating of the front-end
electronics. Cooling status and temperature inside the SVT enclosure are
checked by slow-control and interlocked to the LV operation so that,
when the cooling is not in operation or temperatures exceed predefined
limits, the SVT power is turned off.
Cooling fluid: leaks of the cooling fluid may cause damage to the
electronic components. The design of the cold plate was chosen in order
to minimize risks and the cold plate, after the assembly, was tested at
high pressure to verify the absence of leaks. During operation the
temperature, flow, and pressure of the liquid at the chiller output as well
as the temperatures of the SVT inlet and outlet lines are monitored
continuously via the EPICS slow control system. The chiller operation,
also controlled via EPICS, is interlocked to these parameters so that
variation outside appropriate limits will trigger the chiller and the SVT
being turned off.
Whenever any maintenance work has to be done on the SVT, HV and
LV cables are disconnected from the power source (crates powered off).
Cable junctions for the SVT modules (located at the L1 disconnect
side of the Hybrid Flex Circuit Board (HFCB)) are: HV, LV, Slow Controls,
Data, and Pulser. All of those junctions should be without power when
connecting/disconnecting the cables. ESD protection rules must be
followed. ESD mats and grounded wrist straps are installed in the testing
area.
Faraday Cage should be mounted when sensors are powered to
protect the preamplifiers from saturation from the ambient light.
2.2.3
Responsible personnel
Individuals responsible for the system are:
Name
Dept.
Phone
email
Comments
Y. Gotra
JLAB
x5571
[email protected]
1st contact
JLAB
x6018
[email protected]
2nd contact
JLAB
x7303
[email protected]
3rd contact
B. Eng
L. Elouadrhiri
Table 1: Personnel responsible for the Silicon Vertex Tracker.
References
[1] EPICS Documentation. URL: http://www.epics.org/. See also
http://www.aps.anl.gov/asd/controls/epics/EpicsDocumention
/WWWPages/EpicsDoc.html
[2] JLAB EH&S Manual. URL: http://www.jlab.org/ehs/ehsmanual/.
[3] JLAB/CEBAF Personal Safety System (PSS) Manual. URL:
http://www.jlab.org/accel/ssg/user info.html
[4] Accelerator Operations Directive. URL: http://www.jlab.org/ops
docs/online document les/ACC online les/ accel ops directive.pdf
(URL is available inside JLAB site).
[5] SVT Technical Design Report URL:
https://userweb.jlab.org/~gotra/svt/doc/TDR4.pdf
[6] SVT Commissioning document URL:
https://userweb.jlab.org/~gotra/svt/doc/commissioning_svt_1.2.pdf
[7] SVT Interlock fault charts URL:
https://userweb.jlab.org/~bonneau/SVT%20Slow%20Controls
/Interlock%20Fault%20Charts/