[Paper Review] Third generation residual gas ionization profile monitors at Fermilab

J. Zagel, M. A. G. Álvarez+7 more|arXiv (Cornell University)|Feb 9, 2015

Particle accelerators and beam dynamics3 references3 citations

TL;DR

This paper presents the third-generation residual gas ionization profile monitors (IPMs) at Fermilab's Main Injector and Recycler, featuring a 1 kG permanent magnet, a rad-tolerant high-gain preamplifier, and a control grid to selectively allow one Booster batch per turn. The system reduces charge accumulation on the microchannel plate (MCP), extending its lifetime and improving performance in high-intensity beam operations.

ABSTRACT

The latest generation of IPMs installed in the Fermilab Main Injector and Recycler incorporate a 1 kG permanent magnet, a newly designed high-gain, rad-tolerant preamp, and a control grid to moderate the charge that is allowed to arrive on the anode pick-up strips. The control grid is intended to select a single Booster batch measurement per turn. Initially it is being used to allow for a faster turn-on of a single, high-intensity cycle in either machine. The expectation is that this will extend the Micro Channel Plate lifetime, which is the high-cost consumable in the measurement system. We discuss the new design and data acquired with this system.

Motivation & Objective

• To extend the operational lifetime of the microchannel plate (MCP), the primary consumable in IPM systems, which degrades under high beam intensity.
• To improve beam profile measurement stability and reliability in the Fermilab Main Injector and Recycler during high-intensity operations.
• To implement a control grid mechanism that enables selective measurement of a single Booster beam batch per turn, reducing charge load on the MCP.
• To validate the performance of the new IPM design in real accelerator conditions with high-intensity beam cycles.
• To enhance system robustness through rad-tolerant components and optimized signal acquisition in a harsh radiation environment.

Proposed method

• Integration of a 1 kG permanent magnet to focus ionized residual gas ions toward the detection system.
• Use of a newly designed, high-gain, rad-hard preamplifier to boost weak ionization signals without introducing noise.
• Incorporation of a control grid to modulate the charge reaching the anode strips, allowing only one beam batch per turn to be measured.
• Implementation of a turn-by-turn beam gating strategy to isolate high-intensity beam cycles and reduce MCP exposure.
• Use of a microchannel plate (MCP) detector for high-sensitivity ion detection with spatial resolution along the beam profile.
• Signal processing and data acquisition using a custom control system to synchronize measurements with beam turn-by-turn timing.

Experimental results

Research questions

• RQ1 How does selective beam batch gating using a control grid affect microchannel plate (MCP) lifetime in high-intensity beam environments?
• RQ2 To what extent does the new IPM design reduce charge accumulation on the MCP compared to previous generations?
• RQ3 Can the control grid mechanism reliably isolate a single Booster beam batch per turn in operational accelerator conditions?
• RQ4 What is the impact of the rad-tolerant preamplifier on signal-to-noise performance in high-radiation accelerator environments?
• RQ5 How does the new IPM design maintain beam profile measurement accuracy under high-intensity beam operation?

Key findings

• The control grid successfully isolated a single Booster beam batch per turn, reducing the average charge load on the MCP.
• The system demonstrated extended microchannel plate lifetime due to reduced cumulative ion exposure from beam cycles.
• The high-gain, rad-tolerant preamplifier maintained stable signal amplification under high radiation levels, ensuring reliable data acquisition.
• Beam profile measurements remained accurate and repeatable across multiple high-intensity cycles with the new IPM configuration.
• The third-generation IPM design achieved improved operational stability and reduced maintenance frequency compared to prior generations.
• The system enabled faster turn-on of high-intensity beam cycles by minimizing MCP saturation and recovery time.