Automated Collimation Operation - Cern

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Nov 15, 2013 (3 years and 9 months ago)

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Automated Collimation
Operation

LHC
-
MAC 2007 06 15

M.Jonker


On behalf of the collimation project

(as the controls coordinator)

Collimation Controls


Collimation Controls Steering team (Cocost)


Stefano Redaelli

(high level control applications)


Maciej Sobczak

(css, middle level)


Roberto Losito

(low level control)


Alessandro Masi

(low level control)


Ralph Assmann

(project leader)


Michel Jonker

(controls coordinator)


Invited


Philippe Gayet

(plc’s)


Rudiger Schmidt

(machine protection)


Bernd Dehning

(beam loss monitors)


Outline


94 (up to 160 in final upgrade) collimators, to protect
against machine damage and magnet quenches.


The collimation process is a multi
-
staged process
that require precise (0.1

beam
)

setting of the jaws with
respect to the beam envelope.

Goal for positioning accuracy is

20

m (0.1

beam

at 7
TeV).


Actual beam envelope (position and size) may
change (from fill to fill ?, by how much?)

Collimation Optimisation


Adapt to changing beam parameters to guarantee
machine protection and to keep good cleaning
efficiency



There are 376 degrees of freedom (4 motors per
collimator) (188 if not considering the angle of the
jaws)



30 seconds per degree of freedom (a very efficient
operator) still requires about 3 hours.




We need automated tools and procedures

Side view at one end

Motor

Mot
or

Temperature sensors

Gap opening (LVDT)

Gap position (LVDT)

Resolver

Resolver

Reference

Reference

Microphone

Vacuum tank

+ switches for IN, OUT, ANTI
-
COLLISION

CFC

CFC

Sliding table

Movement
for spare
surface
mechanis
m


(1 motor,

2 switches,

1 LVDT)

Setup Procedures


Beam probing


Determine beam positions and size at every collimator by touching the beam.


Required for initial setup of a machine optics (injection and top energies ), or
after substantial changes in beam parameters.


Setup at with a low intensity beam 5 nominal LHC bunches (equivalent to the
Tevatron Beam in stored energy).

Extrapolation from 5 to 3000 bunches…(bunch train effects?)


Fast beam based setup


Position collimators based on loss patterns, not on measured beam positions
and sizes


Further systematic optimisation with nominal intensity beam


Response matrix corrections


Correct collimator positions guided by loss patterns.

Response matrix corrections


Fine tune and optimise the cleaning efficiency (at
injection or top energy).


Collimator response matrices to translate a given beam
loss pattern into an adjustment of multiple collimator
positions:




P
C

= M
blc


BL



Theoretical matrices have been calculated based on
Fluka and Struct programs.


Ambitious procedure, commissioning of this process will
require many machine studies.


Not for the beginning


Not discussed here

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BLM loss pattern

Collimator Settings

Beam Probing

Beam Loss Monitor

Beam Loss Monitor

Establishes the beam positions, angle and size by probing the actual beam.

A traditional method:


Starts with producing a well
-
defined cut
-
off in the beam distribution.


Each collimator jaw is moved until the beam edge is touched. This step defines an
absolute reference position for each jaw.
(and angle if two motors are moved independently)

Note: Best done from the last element in the cleaning insertion to the first


Collimators may stay in place


Machine is better protected against quenches

Disadvantages:


Only possible with low intensity beam (i.e. 5 bunches).


Slow if done manually (
188 positions

)


Delicate (e.g. moving a collimator too far changes the cut
-
off in the beam distribution).

Beam probing was tested in the collimation MD at the SPS in 2006 with the
collimation control system.


The jaws were driven in by the control application either manually or in
repetitive steps.


The control application simultaneously displays jaw position and Beam
Loss Data

Beam Probing in SPS MD

In the MD, to speed up we used successively smaller steps, and while doing so we
scraped the beam away bit by bit.

by Chiara Bracca

Fast beam based setup

Beam Loss Monitor

Beam Loss Monitor


Complements the traditional set
-
up method.


Adjust positions to reproduce known beam loss pattern.


Based on experience of other accelerators:

Collimation efficiency is more closely related to beam loss patterns than to absolute
collimator positions, which are sensitive to orbit deviations, beta beat, etc.


Move jaws in hierarchical order into the beam halo up to the point where a specified beam
loss level is recorded in the adjacent beam loss monitors.


Fast if implemented as an automated procedure:


Start at a fixed offset relative to a previously known position (only have to
move short distances, no need to be retracted.


Two beam can be tuned in parallel in the two cleaning insertions IR3 and IR7

Fast beam based setup

Procedure in practice:


The collimators are set at 1.5 σ retracted with respect to the last
optimised value.


The jaws are optimised one by one in a precise order.


Optimization by moving in steps of 0.05 σ until the associated set of
Beam Loss Monitors (BLM) detects a predefined value of beam loss.

The BLM reference levels are found empirically and may be updated from
fill to fill.


Timing implications:


Starting position

1.5 σ, step size of 0.05 σ (

50 μm @ 450 GeV)




30 steps/motor


9600 steps in total
(only position, no angles, final upgrade)
.


Available time 5 min. two rings in parallel


60 ms per step (16 Hz)


@ 2mm/s 50 μm


25 ms per step needed for motor movement


=> 35 ms for driving, data collection, reading BLM, deciding

LHC tunnel

Underground, low radiation area


Surface support building

Control room

Controls Architecture

Collimator Supervisory System


(one or two per LHC point)

BLM system


Beam
Permit

Central Collimation

Application

Ethernet

Controls Network

Data Base

Actual Machine Parameters

Data Base

Critical

Settings


. . .

Machine Timing

Machine Timing Distribution

Synchronisation

Fan out


Control room software:


Management of (critical) settings (LSA)


Preparation for ramp


Assistance in collimator tuning

Post Mortem data collection and Analysis


Based on standard LSA components


Dedicated graphical interface for collimator control
and tuning


Collimator Supervisor System
(CSS):


Support building, VME / FESA


Fesa Gateway to Control Room Software


Synchronization of movements


Beam Based Alignment primitives


Takes action on position errors (FB)


Receives timing, send sync signals over fiber to low
level (Ramp & Beam Based Alignment)


Synchronization and communication with BLM


Low level control systems


3 distinct systems


Motor drive
(PXI)


Position readout and survey
(PXI)


Environment Survey
(PLC)

Local Ethernet Segment

Motor Drive Control

PXI

Position Readout and
Survey


PXI

Environment Survey


PLC

Fast Optimisation Primitives

Collimator Supervisory System

(CSS)


Send a trigger to adjacent BLM system
on every motor movement


BLM system sends a short “transient”
data to the CSS


Optimization primitive command
(on CSS)


Move until BLM
-
level

Parameters


Motors and step size


BLM signals and limits


Repetition frequency


Maximum steps


Example:

Move Jaw
-
left in steps of 10 um every 30 ms
until BL signal reaches 10
3


This optimization primitive can be used by
a central application for


Beam Probing


Fast beam based optimization

Collimator Supervisory System


(one or two per LHC point)

BLM system


Synchronisation

Fan out

Local Ethernet Segment

Motor Drive Control

PXI

Position Readout and
Survey


PXI

Beam Loss Monitor

Fast Optimisation Primitives

During optimization, positions are
continuously measured,

If the position gets out of tolerance, the
procedure will be interrupted.

Collimator Supervisory System


(one or two per LHC point)

BLM system


Synchronisation

Fan out

Local Ethernet Segment

Motor Drive Control

PXI

Position Readout and
Survey

PXI

LVDT Calibration Repeatability test (TT40)
36 repetitions
0.95
0.955
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0.965
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0.975
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1
1.005
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distance [mm]
Normalized position [mm]
15 µm

~ 25 µm mechanical play

R. Losito et al

BLM Transient in SPS MD

Adjacent BLM triggered
by collimator movements.

Collected data:


Transient Data Buffer (2.5 ms
sampling 80 ms for BLM based
FB).


Post mortem data (40 us
sampling over 1.7 seconds)


(For analysis)


Data needs carefull
interpretation.


LHC acquisition chain
tested, including link with
collimators (trigger and
data transmission).



Plots from Daniel Kramer

Motor
movement

10ms (20

m)

Motor movement

10 ms (20

m)

Conclusion


Fast collimator optimisation is technically possible.


The controls architecture contains the necessary elements to
deal with these requirement (synchronisation lines, BLM data
acquisition and connection)


The principles have been tested during an SPS MD in 2006


Fully automated steering application and procedures to be
developed and tested (2008)


However, the real challenge…


beam dynamics…


SPS md: BLM responds to collimator movement over time scales of
100th of ms

Conclusion

Motor movement

10ms (20

m)

50, 150, 300, 450 &

600 Hz noise

Loss tails with echo

12 sec

Long tails after collimator movement,

Large noise components

SPS MD in 2007 to investigate the origins of these problems

If these effect are also present in the LHC, optimisation will me more challenging.

During the SPS MD, not able to make
clean cut in the beam distribution

Re
-
populatution of tails over 100
th

of
ms.

Motor movement

50ms (25

m)

(70 Hz)