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