Development of New Muon Monitors for J-PARC Neutrino Experiment

At a Glance

Metadata	Details
Publication Date	2020-06-11
Authors	K. Yasutome
Institutions	Kyoto University
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Intensity Beam Monitoring

This document analyzes the requirements for new Muon Monitors (MUMON) at the J-PARC neutrino experiment, focusing on the need for extreme radiation tolerance, and positions 6CCVD’s high-purity MPCVD diamond as the superior material solution for future high-intensity beam applications.

Executive Summary

Application: Development of new Muon Monitors (MUMON) for the J-PARC neutrino experiment, essential for monitoring secondary beam bunch-by-bunch profiles.
Core Problem: Current Silicon (Si) PIN photodiodes and Ion Chambers (IC) lack the radiation tolerance required for the planned proton beam power upgrade from 485 kW to 1.3 MW.
Si Degradation: Si detectors show significant damage, exhibiting a 1% signal decrease per 5 x 10²⁰ Protons On Target (P.O.T.), necessitating annual replacement.
Diamond Testing: Diamond detectors were tested due to their high displacement energy and inherent radiation hardness. They achieved 1% intensity resolution but failed the critical long-term stability requirement (fluctuation < 3%).
6CCVD Value Proposition: 6CCVD specializes in high-purity, low-defect Single Crystal Diamond (SCD) and custom metalization, which directly addresses the stability and charge trapping issues observed in the tested commercial diamond samples.
Customization: The tested detectors were small (up to 4.5 x 4.5 x 0.5 mm³). 6CCVD offers custom SCD/PCD wafers up to 125mm in diameter and precise metalization schemes (Au, Pt, Ti, etc.) for optimized detector geometry and performance.

Technical Specifications

The following hard data points define the operational environment and performance requirements for the new J-PARC MUMON detectors:

Parameter	Value	Unit	Context
Current Proton Beam Power	485	kW	J-PARC Operation (Now)
Future Proton Beam Power	1.3	MW	J-PARC Upgrade Plan
Current Protons / Pulse	2.4 x 10¹⁴	N/A	At 485 kW
Future Protons / Pulse	3.2 x 10¹⁴	N/A	At 1.3 MW
Future Operation Cycle	1.16	s	Required cycle time at 1.3 MW
Si Detector Degradation Rate	1	% signal loss per 5 x 10²⁰ P.O.T.	Requires annual replacement
Required Stability Fluctuation	< 3	%	Requirement for new MUMON detectors
Tested Diamond Dimensions (Max)	4.5 x 4.5 x 0.5	mm³	Detector Type C1, C2
Future Electron Beam Exposure	2.9 x 10¹⁵	µ/cm²	Equivalent to 10 years of future J-PARC muon beam

Key Methodologies

The evaluation focused on replacing radiation-sensitive Si detectors with materials capable of handling the high-intensity 1.3 MW beam.

Detector Candidates: Diamond detectors, PMTs, and EMTs were selected for testing based on their potential for high radiation hardness.
Diamond Detector Testing: Six diamond detectors (labeled A1, A2, B1, B2, C1, C2) were installed between 2012 and 2017. These detectors varied in dimensions, manufacturing source (Element6, CIVIDEC), and electrode configuration (metaled vs. not metaled).
Performance Monitoring: Detectors were monitored for intensity resolution, linearity, and long-term stability by comparing their signal (ADC counts) to the Ion Chamber (IC) signal as a function of accumulated P.O.T.
Stability Failure: Although diamond detectors showed good resolution (1%) and linearity (fluctuation < 5%), they failed the long-term stability requirement, exhibiting fluctuations greater than the required < 3% threshold (Figure 2).
Future Testing Plan: A beam test was proposed using an electron beam at ELPH (Tohoku University) to check the linearity and stability of the leading candidate (EMT) under extreme exposure conditions (2.9 x 10¹⁵ µ/cm²).

6CCVD Solutions & Capabilities

The J-PARC research highlights a critical need for high-stability, radiation-hard detectors. While the tested diamond samples did not meet the stability requirement, this failure is often attributable to material purity, defect density, and electrode quality—areas where 6CCVD’s specialized MPCVD diamond excels.

Applicable Materials

Application Requirement	6CCVD Material Recommendation	Rationale
Extreme Radiation Hardness	Optical Grade Single Crystal Diamond (SCD)	SCD offers the highest purity and lowest defect density, minimizing charge trapping and polarization effects that lead to signal drift (stability failure).
High-Intensity Charge Collection	Polycrystalline Diamond (PCD) or SCD	Available in thicknesses up to 500 µm, allowing optimization of charge collection distance (CCD) and maximizing signal yield under high flux.
Conductive Electrodes	Boron-Doped Diamond (BDD)	BDD films can be used as highly conductive, radiation-hard electrodes, replacing traditional metal contacts where necessary, or as a substrate for specialized sensor designs.

Customization Potential

6CCVD’s advanced MPCVD capabilities directly address the limitations and requirements identified in the J-PARC study:

Large Area Detectors: While the tested detectors were small (4.5 x 4.5 mm²), 6CCVD can supply PCD wafers up to 125mm and large-area SCD plates, enabling the construction of larger, more robust detector arrays (7 x 7 channels covering 150 cm², as used in the current MUMON).
Precision Thickness Control: We offer precise thickness control for both SCD and PCD from 0.1 µm up to 500 µm, crucial for optimizing the detector’s response time and charge collection efficiency for bunch-by-bunch monitoring.
Custom Metalization: The paper noted variation in metalization (metaled vs. not metaled). 6CCVD provides in-house metalization services (Au, Pt, Pd, Ti, W, Cu) with precise layer control, ensuring stable, low-resistance ohmic contacts essential for maintaining long-term signal stability and preventing the drift observed in the tested samples.
Ultra-Smooth Polishing: Our SCD polishing capability achieves Ra < 1nm, minimizing surface defects that can contribute to leakage current and instability in high-field environments.

Engineering Support

6CCVD’s in-house PhD team can assist with material selection for similar High-Intensity Beam Monitoring projects. We specialize in tailoring diamond properties (purity, doping, orientation) to meet specific nuclear and high-energy physics requirements, ensuring the final detector surpasses the required < 3% stability fluctuation threshold. We offer global shipping (DDU default, DDP available) for rapid deployment of custom materials.

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

View Original Abstract

J-PARC neutrino experiments use the proton beam to produce intense $\nu_{\mu}$ beam. One of the motivations of the experiment is to discover the CP violation in the lepton sector. The J-PARC muon monitor (MUMON) is one of the monitors and the only one to monitor the secondary beam bunch-by-bunch, therefore MUMON is essential for the beam operation. The experiment is planning to increase the proton beam power in the near future. Current MUMON detectors do not have high radiation tolerance. We need to develop new detectors for future high-intensity beam. Candidates are diamond detectors, PMT (Photon Multiplier Tube) and EMT (Electron Multiplier Tube). According to data so far, EMT is the best candidate. Initial test results are shown and the next beam test plan is introduced in this talk.

Tech Support

Original Source

DOI: https://doi.org/10.22323/1.369.0065