The First 1 ½ Years of TOTEM Roman Pot Operation at the LHCM. Deile, G. Antchev, I. Atanassov, V. Avati, J. Baechler, K. Eggert, J. Kašpar, F. Lucas Rodriguez, J. Morant, H. Niewiadomski, E. Radermacher, F. Ravotti, G. Ruggiero, H. Sabba, W. Snoeys

on behalf of the TOTEM Collaboration;R.B. Appleby, R. Assmann, R. Bruce, M. Dupont, M. Dutour, B. Farnham, X. Pons, S. Ravat, S. Redaelli, M. Sapinski, G. Valentino, D. Wollmann

Roman Pot unit before installation

Forward Physics programme of the TOTEM experiment at the LHC Interaction Point 5:

- Measurement of elastic p-p scattering cross-section d/dt in a wide range of momentum transfer:

first result from 2010 in 0.36 GeV2 < –t < 2.5 GeV2 , ultimate range: 10-3 GeV2 < –t < 10 GeV2

- Diffractive physics: started in 2010

- Total p-p cross section measurement using the Optical Theorem (luminosity independent method)

- Absolute luminosity measurement

This programme requires detection of leading protons with very small scattering angles (a few rad) which will be

accomplished with the Roman Pot system on both sides of the IP.with the Roman Pot system on both sides of the IP.

Stack of 10 Silicon detectors with cooling pipes

inside

Roman Pot insertion with thin window

1 Horizontal Pot 2 Vertical Pots BPM

Roman Pot station (consisting of 2 units) in the LHC

The Long Straight Section on one side of Interaction Point 5 of the LHC: locations of the TOTEM Roman Pot stations. The layout is symmetric with respect to the interaction point.

RP 147 RP 220

220220 mm147147 mm

CMSCMS

The Roman Pot Movement Control System

The RPs are moved from the CCC. The TOTEM DCS (Control Room) can only extract them.

CCC TOTEM Control RoomFESA Server

NI PXI

Motor ControlRoman pots

Position requests + limits

Position requests

Alarms

Alarm

s

single

Ext

ract

ion

emer

gency

ext

ract

ion

CIBU

Beam user interlock control

USER_PERMITINJECTION_PERMIT

FESA ICD

DIM ICD

Interlock logic card

BIC

LHC BeamInterlock controller

RP positions emergency extraction

GMT

General MachineTiming

SMP flags (e.g. beam mode)

Roman Pot Interlock Logic

The Roman Pot Microswitch System

The absolute microswitch positions are calibrated with laser metrologyrelative to the beam-pipe centre during technical stops.

HOME microswitch: used for interlocks

OUT electrical stopper: reference position for movements

Other switches: movement limits

Transmission of interlock signals to the motor control:- if (NOT_BACK_HOME = false): emergency extraction with mechanical springs- other signals: forwarded to DCS (Detector Control System) for information

If (USER_PERMIT1 = false): beam dumped, injection blockedIf (INJECTION_PERMIT = false): injection blocked

Roman Pot Position Measurements

Step Counting by the Step-Motor Encoders: - used for active movement control;- the calibration is relative to

the OUT electrical stopper

OUT Stopper

OUT Switch

max. mech. range

Beam

IN Stopper

IN Switch

mean step size = 4.89 m

LVDT Measurement: - Only used for position interlock;- the calibration is absolute but subject to drifts;

periodical recalibration needed.

Two redundant systems:

Adaptation of the Collimator Control Application in the CCC

RP movement sequence during the interlock tests in 2011.

Beam-Based Roman Pot Alignment(same procedure as for the collimators)

black = motor step counter position, blue = LVDT position, red = outer and inner dump limits, yellow = outer and inner warning limits. At 19:26:40 the inner limits are changed such that the RP position becomes illegal. Consequently the USER_PERMIT is withdrawn and the pot automatically retracted with mechanical springs. The LVDT correctly indicates the new position (~39.7mm). The step counter, however, cannot know the new position because the spring extraction was executed by removing the motor coupling. Hence the step counter reading stays at 37mm. It needs to be reset at the mechanical reference point (OUT Electrical Stopper).

Software Alignment of the Silicon Detectors inside the RPs

A primary collimator cuts a sharp

edge into the beam, symmetrical to

the centre

The top RP approaches

the beam until it

touches the edge

The last 10 m step produces a spike in a Beam Loss Monitor

(BLM) downstream of the RPThe bottom RP approaches

the beam until it

touches the edge

When both top and bottom pots are touching the beam edge:

• they are at the same number of sigmas from the beam centre as the collimator

• the beam centre is exactly in the middle between top and bottom pot

Alignment of the RP windows relative to the beam

Silicon sensor positions (relative to each other and to the beam)

aligned by software methods

Example Sequence:Start with primary collimator at 4.9 beam edge at

Top Pot

Bottom Pot

BLM 1 m downstream

BLM 5 m downstream

4.9

RP approach

BLM response

BLM

Ferrite

Front Window

Beam-facing Window

The top, bottom and horizontal Silicon detector

packages of a RP station. Note the overlap between

horizontal and vertical detectors enabling the relative

alignment.

4 of the 10 planes in a detector package, with

their read-out directions u and v.

Track-Based Alignment

Alignment Exploiting Symmetries of Physics Processes

ANTICOLLISION MICROSWITCH

Residual-based alignment technique

(similar to MILLEPEDE)

Map of all track intercepts in a scoring plane between between the near and far RP unit

Coarse alignment (better than 100 m) to facilitate elastic selection

Map of all track intercepts after elastic selection

Slope mainly caused

by optics (less by detector

rotation!)

Fine horizontal alignment: precision better than 10 m

Fine vertical alignment: about 20 m precision

diffractiveprotons

mainlyelasticprotons

Flip

and shift