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