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

Executive Summary

The J-PARC neutrino experiment requires a critical upgrade of its Muon Monitor (MUMON) system to accommodate a planned increase in proton beam power from 485 kW to 1.3 MW.

Problem Statement: Current Silicon PIN photodiodes (Si) and Ion Chambers (IC) lack the necessary radiation tolerance for future high-intensity operation. Si detectors show a 1% signal decrease per 5 x 10²⁰ Protons On Target (P.O.T.).
Candidates Evaluated: Diamond detectors, Photon Multiplier Tubes (PMTs), and Electron Multiplier Tubes (EMTs) were tested for high radiation hardness.
Candidate Failure: Diamond detectors, while having good resolution (1%), failed stability requirements (fluctuation greater than 3%). Standard PMTs (Hamamatsu R9880) were unstable and non-linear at high beam intensity.
Proposed Solution: Electron Multiplier Tubes (EMTs) are selected as the best candidate due to their inherent radiation tolerance, achieved by replacing the sensitive photocathode with an aluminum foil structure.
Performance Metrics: EMTs demonstrated stability fluctuations of less than 1% after an initial 3% drift period, showing comparable or better performance than existing detectors.
Verification Plan: A dedicated electron beam test is proposed to verify EMT linearity and stability under future J-PARC conditions, simulating 10 years of exposure (2.9 x 10¹⁵ µ/cm²).

Technical Specifications

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 power
Future Protons / Pulse	3.2 x 10¹⁴	N/A	At 1.3 MW power
Current Operation Cycle	2.48	s	At 485 kW power
Future Operation Cycle	1.16	s	At 1.3 MW power
Si Detector Degradation Rate	1	%	Signal decrease per 5 x 10²⁰ P.O.T.
Diamond Detector Stability	less than 3	%	Fluctuation observed (Failure criterion)
EMT Stability Fluctuation	less than 1	%	After initial 3% drift period
EMT Test Linearity Range (Current)	1.7 x 10⁷	µ/cm²/3µs	Electron beam intensity for testing
EMT Test Linearity Range (Future)	3.9 x 10⁷	µ/cm²/3µs	Electron beam intensity for testing
EMT Test Exposure Target	2.9 x 10¹⁵	µ/cm²	Equivalent to 10 years of future J-PARC exposure
Diamond Detector Dimensions (C1, C2)	4.5 x 4.5 x 0.5	mm³	Newest type (CIVIDEC electrode)

Key Methodologies

The development and testing process focused on evaluating radiation tolerance and stability under high-intensity beam conditions:

Baseline Performance Assessment: Current Silicon PIN photodiodes (Si) and Ion Chambers (IC) were monitored to quantify signal degradation and yield worsening under existing J-PARC beam operation (485 kW).
Diamond Detector Evaluation: Six diamond detectors (manufactured by Element6 and CIVIDEC) were installed in the J-PARC muon pit between 2012 and 2017. Their intensity resolution (1%) and long-term stability were checked against the requirement of less than 3% fluctuation.
PMT Testing: Two standard PMTs (Hamamatsu R9880) were installed and tested for linearity and stability, confirming their failure at high-intensity beam due to instability.
EMT Customization and Testing: Custom Electron Multiplier Tubes (EMTs) were developed, including modifications to capacitance and the application of Sb doping to the dynodes to recover gain loss associated with the aluminum foil structure.
EMT Performance Check: EMTs were evaluated for time response, intensity resolution, and linearity, confirming performance comparable to or better than current detectors, and stability fluctuations of less than 1% after initial usage.
Future Beam Test Proposal (ELPH): A detailed beam test was proposed at the Research Center for Electron Photon Science (ELPH) using an electron beam to:
- Check linearity across the current and future J-PARC intensity range.
- Verify long-term stability by exposing the EMTs to a fluence equivalent to 10 years of future muon beam exposure.

Commercial Applications

The development of radiation-hardened, high-stability Electron Multiplier Tubes (EMTs) is critical for instrumentation in high-radiation environments.

High-Energy Physics (HEP) Facilities: Essential for beam monitoring, profile measurement, and intensity calibration in high-power accelerator complexes (e.g., J-PARC, future neutrino facilities, high-luminosity colliders).
Radiation-Hardened Sensor Technology: Provides a robust alternative to traditional PMTs and Si detectors in environments where high displacement damage energy is expected.
Nuclear and Fusion Research: Monitoring high-flux particle beams and plasma diagnostics where sensors must withstand intense neutron and gamma radiation fields.
Industrial Beam Processing: Used in industrial accelerators for sterilization or material modification, requiring reliable, real-time monitoring of beam intensity and stability.
Space Instrumentation: Applicable for particle detection and radiation monitoring in space environments where components must survive long-term exposure to cosmic rays and trapped radiation.

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