a beam condition monitor investigation for cms
DESCRIPTION
A Beam Condition Monitor Investigation for CMS. Beam accidents scenarios. The machine Interlock System. The DCS and the DSS. The BCM. System possibilities. Proposed prototypes Test beam at T7 Conclusions and Outlook. Luis Fern ández Hernando, UNIL- EST/LEA-CMS; 2003. - PowerPoint PPT PresentationTRANSCRIPT
A Beam Condition Monitor Investigation for CMS
• Beam accidents scenarios.• The machine Interlock System.• The DCS and the DSS.• The BCM.• System possibilities. • Proposed prototypes• Test beam at T7• Conclusions and Outlook.
Luis Fernández Hernando, UNIL- EST/LEA-CMS; 2003
Beam accidentsscenarios
The dose rate during normal operation is ~16 mGy/s
Unsynchronized beam abort: dose rate is ~38 kGy/s
ie ~106 orders of magnitude increase
Our Question:
Can we implement a monitoring system to provide protection for our detectors?
Worst Case Scenario: Unsynchronized beam abort. Occurs over ~300 ns.
Deterioration of beam conditions due to equipment failure will look similar to the above, but will develop over the sec, msec timescale.
Failures that lead to beam loss where the BCM should act in time to prevent major damage
• The BLM has one turn resolution.
• A D1 failure is the most critical. Dipole magnet failures cause orbit distortions.
Name Operation Mode
Loss Location ΔT
D1 warm Collision Triplet/collimator 5 turns
Damper Injection Arc/triplet 6 turns
Warm quadrupoles Any Collimator 18 turns
Warm orbit corrector Collision Triplet/collimator 55 turns
RF Any Arc/triplet/septum 55 turns
D1 warm Injection Arc/triplet/collimator
120 turns
D1 Failure
A power converter failure for the D1 magnets in IP5 leads to a particle impact at the primary horizontal collimator in IR7. It takes 12 turns until the displacement of a fraction of 10-5 of the initial number of particles has exceeded 6 sigma in that place.
Machine Protection
• The machine protection already ensures the integrity of CMS in case of unsynchronized beam abort.
• The BCM will be an auxiliary (and monitoring) system for protecting the experiment.
• In case that the beam arrives to the collimators with a deviation of 2-3 it could scrap the triplets in I.R. 5.
I.R. 5 I.R. 6 I.R. 7
14 107-8 6
TripletPrimary collimator
Secondary collimatorAbsorber Absorber
Critical apertures in units of beam size
Machine Group’s Interlock System
• 16 Beam Interlock Controllers
• 2 fast links• if one loop open
Beam Dump
Pt.1
Pt.2
Pt.3
Pt.4
Pt.5
Pt.6
Pt.7
Pt.8ATLAS
CMS
LHC-BALICE
Momentumcleaning
RFBeam Dump
Betatroncleaning
BEAM 1clockwise
BEAM 2counter-clockwise
BEAM II Injection
from SPS
InjectionBEAM I from SPS
BEAM DUMPCONTROLLERS
Beam Interlock Loopsoptical fiber at 10 MHz
BIC
BPCBPCBPC
BIC
BIC
BIC
BIC BIC
BIC
BIC
BIC
BIC
BIC
BICBIC
BIC
BIC BIC
• 2808 bunches on beam separated 25 ns
• Kicker magnets rise time = 3 μs
• Gap in beam of 3 μs
Collimators
Vacuum
Warm Magnets
Experiments
Beam Dump
BLM
Access
RF
Injection
Powering Interlock
Inputs
Beam Permit loop .
OutputBeam Permit
AND
OR
Interlock System
QPS
DCS
Monitoring and control of the detector
DSS
Safeguard of experimental equipment
BCM
• Input into DSS.
• Protect subdetectors from adverse beam conditions
BCM sensors
Beam ConditionsMonitor
Protection against fast beam losses
Independent action from the DSS
2 “collars” of sensors around the beam pipe near the pixel region and more sensors located near the TAS
BCM geometry must allow for the detection of showers within the experiment that result from beam deterioration Analog signals from
sensor readout
Digital signals from sensor readout
Digital signal to interlock
Digital signal to DSS
BCM sensors
Decision box
DSS backend
DSS abort signal
I.P. 5~2 m
~4.3 cm
System Possibilities
The sensors that can be used are:
• CVD diamonds: good radiation hardness.
Will get samples for next test beam experiment.
• Silicon: widely used in other applications.
May be suitable for more accessible locations.
• CdTe: Being considered.
• Quartz: No need of biasing the sensor and fast signal.
Yet to be investigated.
System readout for the diamond/silicon/CdTe approach:
• Current amplifier: simplest solution. Analog reading.
• APVB: binary response chip. More complicated. Signal already treated.
Readout chain available and preliminary test setup built.
• CARIOCA: Fast amplifier, and comparator. Test boards available next week.
• APV25: Investigating possibility of running in conjunction with APVB.
CVD Diamond Sensors
Material with outstanding radiation hardness
Ionization chamber. The energy necessary for creation of an electron-hole pair in diamond is 13 eV (in Silicon is 3.6 eV)
A mip traversing 100 μm of material produces 3600 eh-pairs (in Silicon 8900)
The bias is of the order of 1 V/μm
Fast charge collection
Silicon shows better resolution than diamond for tracking of particle hits but for the BCM spatial resolution is not as important as radiation hardness
CVD Diamond Sensors
For a 1 cm2 sensor area, with collection distance of 150 μm, located at a radial distance of 4.3 cm from the beam we have that:
• During normal operating conditions, dose rate of 1.66E-2 Gy/s, per 100 ns time bin the MIP equivalent fluence passing through the sensor is on average 5.9 MIPs. Expected signal of 51 nA.
• In the case of D1 failure at the same level as an unsynchronized beam abort the flux per 100 ns is 2.2E9 MIPs. This implies a current of ~20 A !!!!.
•These two extremes imply a large range of signal
•Not possible to deal with the full range !
•Will focus on the need for a readout chain that is sensitive to the development of adverse beam conditions.
System Readout
The readout chip that has been tested for the preliminary investigation is the APVB
This chip has an internal frequency clock that can be adjusted for seeing the beam crosses
It reads the current signal from the sensors and compares it with the set threshold, giving a binary response
This digital response is afterwards treated in the decision box
A pattern of bits, with a clock signal and a command line, is sent by a data generator to the chip
PLD/FPGA
Sensors
The APVB sends a string of 0’s and 1’s that has to be decoded
This response is given after 7 μs processing delay, limiting the readout frequency to 0.14 MHz
Response to be treated in the Decision Box
Output data can be handled by an FPGA or a Programmable Logic Device
1Decision Box
Signal to Beam
Interlock
1Decision Box
Signal to Beam
Interlock
1Decision Box
Signal to Beam
Interlock
Strategy for readout The readout from the sensors is compared with 2 threshold levels.
1Decision Box
Signal to Beam
Interlock
00
Low threshold
High threshold
I.P. 5
Date: During the 8th- 20th Oct LHC irradiation periodPlace: T7 irradiation facility in the CERN East hallBeam: 24 GeV protons in fast extraction spill from the CERN PS
Each spill ~ 3.6 x 1011 protonsBeam Time: one 8-hour machine operator’s shift
2-stage programme is proposed
Stage 1: Repeat of the 1-shot testbeam: • 2 spills separated by 256ns • Target flux ~109 protons/cm2 at centre of beam spot• Approximates to unsychronized beam abort scenario
Stage 2: Single spill running• Lower intensity beam spot•‘‘Controlled‘‘ beam loss on the T7 beamline to be attempted• Programme to be set out once sensors are up and running
Test beam to be done in close cooperation with the PS machine operators
Test Beam Plans
Conclusions
• Have identified beam loss scenarios that could be problematic to CMS sub-systems.
• The “ worst case” unsynchronised beam abort is used to define the fluence, and this sets the sensor constraints and overall system design.
• A BCM development is in terms of beam loss scenarios that we can detect and react to.
• CVD diamond sensors now metalised and arriving in June. CVD diamond is our primary sensor candidate for the upcoming Test Beam.
• An APVB setup has been built and tested.
• The Carioca chip will be tested this month
•A test beam programme is in preparation (October 2003).
•Present efforts done on a restricted equipment budget (+ help from friends)
… and still considering different BCM design options