A Beam Condition Monitor Investigation for CMS

1. 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

2. Beam accidents scenarios 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.

3. 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.

4. 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.

5. Machine Protection Secondary collimator Primary collimator Triplet Absorber Absorber Critical apertures in units of beam size  14 10 7-8  6 I.R. 5 I.R. 6 I.R. 7 • 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.

6. Beam Interlock Loops optical fiber at 10 MHz Injection BEAM I Injection from SPS BEAM II from SPS Machine Group’s Interlock System • 16 Beam Interlock Controllers • 2 fast links • if one loop open  Beam Dump BIC BIC BIC BIC BEAM DUMP CONTROLLERS Pt.5 BIC BIC CMS Pt.4 Pt.6 RF Beam Dump BIC BIC Betatron Pt.3 Momentum Pt.7 cleaning cleaning BIC BIC • 2808 bunches on beam separated 25 ns • Kicker magnets rise time = 3 μs • Gap in beam of 3 μs ALICE LHC-B Pt.8 Pt.2 ATLAS BIC BIC BEAM 1 Pt.1 clockwise BIC BIC BEAM 2 counter- clockwise BIC BIC BPC BPC BPC

7. QPS Vacuum A N D Warm Magnets Experiments Beam Dump BLM Access RF Injection Beam Permit loop . Interlock System Inputs Output Beam Permit Collimators O R Powering Interlock

8. DCS • Monitoring and control of the detector • DSS • Safeguard of experimental equipment • BCM • Input into DSS. • Protect subdetectors from adverse beam conditions BCM sensors

9. Beam Conditions Monitor 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 ~4.3 cm ~2 m I.P. 5 Decision box Digital signal to interlock Digital signals from sensor readout Digital signal to DSS DSS abort signal BCM sensors DSS backend Analog signals from sensor readout

10. 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.

11. 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

12. 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.

13. A pattern of bits, with a clock signal and a command line, is sent by a data generator to the chip 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 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 Sensors PLD/FPGA Response to be treated in the Decision Box Output data can be handled by an FPGA or a Programmable Logic Device

14. Signal to Beam Interlock Signal to Beam Interlock Signal to Beam Interlock Signal to Beam Interlock Decision Box Decision Box Decision Box Decision Box 1 1 1 1 Strategy for readout The readout from the sensors is compared with 2 threshold levels.   Low threshold High threshold I.P. 5 0 0

15. Test Beam Plans Date: During the 8th- 20th Oct LHC irradiation period Place: T7 irradiation facility in the CERN East hall Beam: 24 GeV protons in fast extraction spill from the CERN PS Each spill ~ 3.6 x 1011 protons Beam 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

16. 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