CERN CH-1211 Geneva 23 Switzerland
LHC
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LHC-XRP-EC-0011
Date: 201x-mm-dd
BRIEF DESCRIPTION OF THE PROPOSED CHANGE(S):
The CMS-Totem Precision Proton Spectrometer (CT-PPS) Upgrade Project Proposal [1][2]
foresees the installation of additional horizontal Roman Pots (RPs) between the existing
RP units at 215 and 220 m from IP5. These new RPs, intended to house time-of-flight detectors for elastically or diffractively scattered protons, have been designed in cylindrical geometry minimising the beam impedance and offering enough space for 12 cm long Cerenkov detectors, one of the technologies being explored for the time measurement.
This ECR elaborates on the technical details of the new CT-PPS timing detectors and its associated infrastructure (electronics, cables, etc). The RP elements and their integration
in the LHC has already been approved in a separate ECR [4].
The lifetime of this upgrade project is foreseen to last until LS3.
PREPARED BY: CHECKED BY: APPROVED BY:
DISTRIBUTION LIST: LMC members
Note: When approved, an Engineering Change Request becomes an Engineering Change Order.
This document is uncontrolled when printed. Check the EDMS to verify that this is the correct version before use.

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SUMMARY OF ACTIONS TO BE UNDERTAKEN:
 Install the infrastructure necessary to the CT-PPS timing detector operation
 Install detector packages in the RPs.

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The layout of the LHC cells 6L5 and 6R5 between the quadrupoles Q5 and Q6 after
completion of the already approved consolidation programme [4] is shown in Figure 1 for sector 4-5 and Figure 2 for sector 5-6. Items existing before LS1 are shown in
grey, whereas items relocated within the consolidation and upgrade programme are
shown in yellow. The new collimator TCL-6 [5] is shown in pink. Beam pipe elements
produced for the relocation are indicated in green.
Figure 1: Situation between Q5 and Q6 in sector 4-5 after upgrade [4].
Figure 2: Situation between Q5 and Q6 in sector 5-6 after consolidation [4].
As explained in the CT-PPS Technical Design Report, the exploration of low-crosssection processes implies Roman Pot operation at high luminosities and hence requires the resolution of event pileup and identification of the vertex of the primary

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Page 3 of 9 interaction. This can be accomplished by measuring the time of flight of leading protons with a precision of a few tens of picoseconds to resolve the longitudinal event vertex position and thus to attribute the protons to the correct vertices given by the central CMS detectors. The time-of-flight measurement will be realised by timing detectors to be installed in additional RPs between the existing units of the 220 m RP station. These new RPs have been designed in cylindrical geometry to provide enough space for 12 cm long Cerenkov counters, one of the timing detector technologies presently being explored.
A schematic drawing of the components associated to the timing detector upgrade project is shown in Figure 3. The individual components for one arm are listed below.
Two arms, one on each side of the CMS interaction point IP5, are instrumented.
Figure 3: A schematic drawing of the timing detector CT-PPS project and its associated components. The cyan shaded area (top) includes the components inside of the RP; the light brown (bottom) and the
“reference timing box” below those located in the close proximity of the RP; the pink boxes (labelled
“power supplies”) correspond to components in the nearest tunnel alcove.
The new timing detectors are hosted inside the new cylindrical Roman Pots, RPs (Fig.
4). One RP is located on each side of IP5.

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Be
Figure 4: 3D model of the new cylindrical RP mounted on the vacuum flange. The ferrite ring (brown) is held in place by a spring ring (left); Cut through a 3D model of the new cylindrical RP inserted into the new vacuum chamber (right).
Figure 5 (left) shows the L-shaped quartz bars of one Quartic module. Each module is composed of a 4x5 array of quartz bars. There are two modules in-line inside each RP.
Two assembled modules, including the front-end electronics is shown in Fig. 5 (right).
Figure 5: One Quartic module, with the 4x5 array of L-shaped quartz bars. The beam is entering from the left (left); two assembled Quartic modules, including the front-end electronics (right).
The 20 quartz bars are pushed against 20 silicon photomultipliers (SiPMs) and are held in place on a SiPM support board that provides the electrical connection to the frontend electronics. The SiPM (Hamamatsu, model MPPC S12572-050) is shown in Fig. 6
(left), and the SiPM support board is shown in Fig. 6 (right). The SiPMs are operated at a voltage of approximately 80V.

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Figure 6: One SiPM (Hamamatsu, model MPPC S12572-050) (left); SiPM support board (right).
The Quartic modules, the SiPM support board, and the front-end electronics are held in place by a mechanical structure shown in Fig. 7.
Figure 7: Schematic drawing of the support for the two Quartic modules.
The NINO board (Fig. 8) is located inside the RP and it is directly connected to the
SiPM support board from which it receives the signals. Each board hosts 1 NINO ASIC that amplifies and discriminates the input signals; each ASIC has 32 channels. There are two NINO boards inside each RP, one for each Quartic module. The power dissipated by the two NINO boards inside the RPs is 2 W.

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Figure 8: Picture of the front and back of the NINO board.
The feed-through board closes the RP and it secures the secondary vacuum to be kept. It hosts the electrical connections between the components inside and those outside the RP. There is one feed-through board for each RP.
This board has yet to be produced.
The RP readout box is located in the close proximity of the RPs and it contains the control and digitization boards. The RP readout box hosts the components that connect the control and data transfer to the CMS Underground Service Cavern (USC).
Figure 9 shows a schematic drawing (and dimensions) and the location foreseen for the installation in the LHC tunnel.
Figure 9: Schematic drawing of the RP readout box (left); Picture of the location (inside the blue rectangle) foreseen for the installation of the RP readout box (right). (FIGURES TO BE REDONE). ADD
PICTURES (WITH DIMENSIONS) OF LOCATION FOR INSTALLATION.

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The motherboard (Fig.11, left) and the mezzanine board (Fig.11, right) are used together to digitize the input discriminated signals out of the NINO board and provide a time-to-digital conversion of those signals. One mezzanine board hosts 4 HPTDC
ASICs (each has 8 channels) that are controlled by one FPGA on the motherboard.
An alternative SAMPIC mezzanine board (to be used in place of the HPTDC mezzanine board described above) may be used instead.
The mezzanine board is mounted on the motherboard, and they are located inside the
RP readout box. One pair (one motherboard and one mezzanine board) is used to read-out one Quartic module. There are two pairs in the RP readout box.
The digitizer motherboard also provides LV power and control (I2C) to the NINO boards.
The boards are currently in production.
Figure 11: Pictures of the motherboard (left) and mezzanine board (right). FIGURES TO BE REDONE.
The SiPM control board (Fig. 12) is located in the close proximity of the RP, and more precisely inside the RP readout box. The SiPM control board provides the bias voltages to the individual SiPMs (through an on-board 8V-to-100V converter), allows the monitoring of temperature, humidity, and SiPM leakage currents. It is controlled by the Digitizer board (see Section 3.7).

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Figure 12: Picture of the SiPM control board.
The low voltage (LV) power is supplied by a Marathon power supply located in the
Alcove closest to the RP position. Four separate LV power supply channels are needed.
The digitizer board requires 3 separate LV power supplies: 2 Volts, 5 Volts (for the analog part), 5 Volts (for the digital part). The SiPM control board requires 8 Volts.
The number of LV power supplies needed is listed in Table 1.
Power cables from the Marathon to the RP position are already in place (installed previously by TOTEM). The cables have the reference xxxx (to be confirmed).
Table 1: Summary of LV power supplies needed.
The digitizer board allows the data transfer and control between the CMS Trigger/DAQ system located in the CMS Underground Service Cavern (USC), level S2, and the RP.
Optical links are used for this purpose. The fibers are bundled in groups of twelve. A total of three fiber bundles are used for each arm. One bundle is used for sending/receiving the controls; two bundles are used for sending the data, one from the HPTDC and the other from the SAMPIC mezzanine boards, respectively.
The needed single mode fiber bundles are already in place (installed previously by
TOTEM). The fiber bundles have the reference xxxx.

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Table 2: Summary of the optical links needed.
Additionally to the slow control provided by the Digitizer Board and its interface to central CMS, the timing RP is equipped with pressure, temperature, and radiation monitoring sensors readout via the TOTEM DCS system already in place.
All electrical components are to be grounded to… (WHAT IS THE STANDARD? SHOULD
ALL BE GROUNDED TO THE SAME GROUNDING AS CMS? OR WILL ALL BE GROUNDED
TO THE RP CHASSIS AND LHC TUNNEL?). THIS NEEDS TO BE CHECKED/DETERMINED.
[1] CMS-TOTEM Precision Proton Spectrometer Upgrade Proposal, CERN-LHCC-2014-021
[2] Scope and implementation plan of the CT-PPS baseline program, CERN-LHCC-2014-
026
[3] TOTEM Upgrade Proposal, CERN-LHCC-2013-009; LHCC-P-007.
[4] TOTEM Consolidation Project, LHC-XRP-EC-0010, EDMS 1314925.
[5] S. Redaelli et al., Infrastructure Installation for Physics Debris Absorbers (TCL) on both sides of IP1 and IP5 in front of Q6 Quadrupole, LHC-LJ-EC-0033, EDMS 1283867.