Development of the BCM system and readout for ATLAS

At a Glance

Metadata	Details
Publication Date	2024-02-05
Authors	Ignacio Asensi Tortajada, Adrien Baptiste, B. Hiti, H. Kagan, H. Frais-Kölbl
Institutions	Fachhochschule Wiener Neustadt, University of Manchester
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for High-Luminosity LHC Beam Monitoring (ATLAS BCM’)

Executive Summary

This documentation analyzes the development of the Beam Conditions Monitoring prime (BCM’) system for the ATLAS High-Luminosity LHC (HL-LHC) upgrade, focusing on the critical role of Chemical Vapor Deposition (CVD) diamond sensors.

Application Focus: The BCM’ system is designed to monitor background activity, measure luminosity, and trigger beam aborts to safeguard the ATLAS Inner Tracker (ITk) in the extreme radiation environment of the HL-LHC.
Material Selection: The system relies exclusively on high-purity Polycrystalline CVD (pCVD) diamond sensors due to their inherent radiation hardness and fast response characteristics.
High Performance Achieved: Preliminary tests demonstrated an analog signal-to-noise ratio (SNR) of 25 at ±1000 V and a detection efficiency exceeding 99% for multi-Minimum Ionizing Particles (MIPs).
Radiation Tolerance: The associated front-end electronics (Calypso FE ASIC) are engineered to endure a Total Ionizing Dose (TID) up to 3 MGy, matching the stringent HL-LHC requirements.
Custom Sensor Geometry: The system utilizes segmented planar pCVD detectors of varying sizes (10x10 mm² for luminosity, 5x5 mm² for abort) all fabricated at a precise 500 µm thickness.
Advanced Readout: The system successfully integrates the diamond sensors with the radiation-hard Calypso FE ASIC and the FPGA-based ATLAS FELIX readout chain, demonstrating accurate Time-over-Threshold (ToT) and Time-of-Arrival (ToA) measurements.

Technical Specifications

The following table summarizes the critical performance and material parameters extracted from the BCM’ development paper.

Parameter	Value	Unit	Context
Sensor Material	pCVD Diamond	N/A	Beam Conditions Monitoring (BCM’)
Sensor Thickness	500	µm	Uniform thickness for all planar detectors
Luminosity Sensor Area	10 x 10	mm²	Planar pCVD diamond
Abort Sensor Area	5 x 5	mm²	Planar pCVD diamond
Operating Voltage (Test)	±1000	V	Voltage used to achieve SNR of 25
Analog Signal-to-Noise Ratio (SNR)	25	N/A	Measured at ±1000 V bias
Multi-MIP Detection Efficiency	> 99	%	Measured at the 5σ threshold
Total Ionizing Dose (TID) Tolerance	Up to 3	MGy	Suitability of the Calypso FE ASIC environment
FE ASIC Rise Time	1	ns	Calypso FE ASIC specification
FE ASIC Jitter	200	ps	Calypso FE ASIC specification
Readout Sampling Rate	1.28	Gbps	Optical transceiver data rate
Readout Clock Frequency	40	MHz	Reference clock for ToA measurement

Key Methodologies

The BCM’ system development involved stringent material selection, custom fabrication, and integration with radiation-hard electronics and high-speed readout systems.

Material Selection and Fabrication: High-purity Polycrystalline CVD (pCVD) diamond was selected for its radiation hardness. Sensors were fabricated to specific planar dimensions (10x10 mm² and 5x5 mm²) with a precise 500 µm thickness.
Front-End Integration: Diamond sensors were coupled with the Calypso_D Front-End (FE) ASIC, a radiation-hard chip manufactured using TSMC 65 nm process technology, designed to handle doses up to 3 MGy.
Signal Processing: The Calypso FE processes sensor signals, providing two output channels (luminosity and abort) with gain and Constant Fraction Discriminator (CFD) settings, achieving a 1 ns rise time.
Beam Testing: The integrated modules were tested at the H6 SPS beam line at CERN using a 120 GeV pion beam. A MALTA planes-based telescope provided high-resolution tracking (4.1 µm spatial, 2.1 ns timing) for reference.
Readout Chain Implementation: Signals were transmitted semi-digitally via LAPA drivers over 5 m of Twinax cable, converted to optical signals (1.28 Gbps) by Opto Boards, and fed into the ATLAS FELIX readout system.
Data Extraction and Tagging: The FELIX firmware calculates Time-over-Threshold (ToT) and Time-of-Arrival (ToA) data relative to a 40 MHz clock, enabling proper Bunch Crossing ID (BCID) and Level 1 Accept (L1A) tagging.

6CCVD Solutions & Capabilities

6CCVD is an expert supplier of MPCVD diamond materials essential for high-energy physics and radiation detection applications like the ATLAS BCM’. We offer the custom material specifications, dimensions, and processing required to replicate or advance this research.

Applicable Materials

The BCM’ project requires highly uniform, radiation-hard diamond. 6CCVD offers the following materials tailored for this application:

6CCVD Material	Description	Relevance to BCM’ Project
High-Purity Polycrystalline CVD (PCD)	High-quality, detector-grade PCD wafers up to 125mm diameter.	Direct replacement/upgrade for the pCVD material used, offering excellent charge collection distance (CCD) and intrinsic radiation hardness.
Optical Grade Single Crystal Diamond (SCD)	Highest purity, lowest defect density SCD (0.1 µm to 500 µm thickness).	Ideal for next-generation timing detectors requiring sub-nanosecond resolution and superior charge carrier mobility compared to PCD.
Boron-Doped Diamond (BDD)	Conductive diamond films for electrode or sensor applications.	Can be used for creating highly stable, integrated conductive contacts or for specialized electrochemical monitoring within the detector environment.

Customization Potential

The BCM’ project utilized specific, segmented geometries (5x5 mm² and 10x10 mm²) and required reliable electrical contacts. 6CCVD specializes in delivering custom-engineered diamond components.

BCM’ Requirement	6CCVD Customization Service	Specification Match
Custom Dimensions	Precision Laser Cutting and Dicing	Plates/wafers up to 125mm (PCD) or custom-cut segments (e.g., 5x5 mm², 10x10 mm²).
Thickness Control	Precision Growth and Polishing	SCD/PCD thickness controlled from 0.1 µm up to 500 µm, matching the 500 µm requirement exactly.
Electrode Integration	In-House Metalization	Custom deposition of radiation-hard electrode stacks (e.g., Ti/Pt/Au, W, Cu) required for high-voltage operation (±1000 V).
Surface Finish	High-Quality Polishing	Polishing services for PCD achieving surface roughness Ra < 5 nm, ensuring optimal electrode adhesion and minimal surface leakage current.

Engineering Support

6CCVD’s in-house PhD team possesses deep expertise in diamond material science and high-energy physics applications. We can assist researchers and engineers in optimizing material selection for similar Radiation Detection and Beam Monitoring projects.

Material Optimization: Consultation on selecting between PCD (cost-effective, large area) and SCD (highest timing resolution) based on specific HL-LHC performance goals (e.g., maximizing SNR or minimizing jitter).
Processing Guidance: Support for designing optimal electrode geometries and metalization schemes to ensure long-term stability in high-radiation, high-voltage environments.
Global Logistics: We offer reliable global shipping (DDU default, DDP available) to major research facilities worldwide, including CERN and affiliated institutes.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

The High Luminosity upgrade of the Large Hadron Collider will increase the LHC luminosity and with it the density of particles on the detector by an order of magnitude. For protecting the inner silicon detectors of the ATLAS experiment and for monitoring the delivered luminosity, a radiation hard beam monitor has been developed. A set of detectors has been developed based on polycrystalline Chemical Vapor Deposition diamonds and a new dedicated radiation-hard front-end ASIC. To satisfy the requirements imposed by the HL-LHC, our solution is based on segmenting diamond sensors into devices of varying size and reading them out with new multichannel readout ASICs divided into two independent parts, each of them serving one of the tasks of the system. This document describes the system design including detectors, electronics and the ATLAS FPGA FELIX based readout. Additionally, it presents preliminary results of the readout with data from beam tests from 2023 at the SPS beam line at CERN.

Tech Support

Original Source

DOI: https://doi.org/10.22323/1.448.0023