Beam Profile Monitors

Product Features

Monitors beams up to 2.75” (6.98cm) in diameter
Handles a beam power density of 140W/mm² or more
Custom mounting flanges and housings available

NEC beam profile monitors (BPM) provide a continuous scope display of the shape and position of the beam cross section in both X and Y coordinates. They can monitor positive or negative beams of electrons, ions and energetic neutral particles.

The unique design of NEC’s beam profile monitors has made them among the most popular and reliable beam diagnostic instruments available, with over 2,000 BPMs provided for customers worldwide. The NEC beam profile monitor reliably gives accurate information concerning the beam cross-section for ion beams with currents as low as 1 nA for most models. Our low current model can monitor currents in the fA range.

Application

The NEC beam profile monitor system is ideally suited for applications that require instantaneous scope display of beam cross-sectional shape and position without significantly interrupting beam transmissions. Particle beams of electrons, ions or energetic neutrals can all be monitored.

Beam Profile Monitor Design

The unique patented design of the NEC beam profile monitor relies on the collection of secondary electrons from a grounded scanning wire. This arrangement eliminates contact noise at the rotating scanning wire. Here’s how it works:

A helical wire sweeps across the beam twice during each revolution to provide a Y profile and X profile in each successive half revolution.
A cylindrical collector around the grounded wire collects beam-induced secondary electrons from the wire to provide a signal proportional to the intercepted beam intensity at every instant.
This signal is then sent to the NEC controller and an oscilloscope for direct viewing of the beam profile.

NEC Beam Profile Monitors: 8 vs. 9 Series

The 8-series has proven to be efficient and reliable over the past several decades. The next generation 9-series model offers even more precise control and responsiveness.

Enhancements incorporated into the BPM 9-series include:

• Servo controlled motor

Using a servo controlled motor instead of the 8 series AC motor, the 9 series provides precise control of the wire and speed. This is advantageous for high power beams by maintaining safe speeds as the wire passes through the beam path when starting and stopping to prevent damage to the wire.
The rotational speed of the wire is no longer coupled to the AC line frequency when using the servo controlled motor. This allows the rotational speed to maintain consistency across all units.
The servo controlled motor provides controlled stop (parking) on power loss, which protects the wire from the beam.
The motor operates at a reduced noise level compared to the AC motor.

• Improved magnetic coupling

Increased torque capability allows more responsive changes in speed and direction as needed.
The improved magnetic coupling provides more reliable startup after long periods of dormancy.

How do you know which one is right for you?

There are several variables that determine the best BPM for your application and NEC will help you elect the most favorable BPM for your needs. In general, the BPM 8 series works best when controlling the BPM locally or via a 24 V control signal with your own control system. The BPM 9 series works best when controlling the BPM remotely via CAMAC or ACT.

Learn more about BPM controllers, here.

Within each series, NEC offers four standard models of BPMs, with various versions and options for each model. Below are brief descriptions of each model

Model BPM80/BPM90	The Original Beam Profile Monitor – and Most Popular Model Monitors beams up to 1.0″ (2.54 cm) diameter Maximum beam power density of 140 W/mm² (1 kW for 3 mm dia. beam) Typically provided in an NEC supplied housing
Model BPM83/BPM93	For Large Diameter Ion Beams Monitors beams up to 2.75″ (6.98 cm) diameter Maximum beam power density of at least 150 W/mm² Typically provided in an NEC supplied housing
Model BPM81/BPM91	For Existing Housings Monitors beams up to 1.0″ (2.5 cm) diameter Maximum beam power density of 140 W/mm² Designed for insertion into a customer supplied housing
Model BPM82/BPM92	For Existing Housings & Larger Diameter Beams Monitors beams up to 2.0″ (5 cm) diameter Maximum beam power density of 140 W/mm² Designed for insertion into a customer supplied housing

The standard beam profile monitor system will routinely monitor positive or negative beams with current densities to 10 nA/cm². NEC has recently developed a low current beam profile monitor with a minimum detectable beam current in the FemptoAmp range. Please contact NEC for further information.

Required Beam Profile Monitor Accessories

For a complete beam profile monitor system, the BPM must be connected to an NEC controller and a display oscilloscope.

BPM Controllers:

NEC offers single-unit and multi-unit beam profile monitor controllers. There are also options within the multi-unit controllers for local or computer control.

Display Oscilloscope:

The digital display oscilloscope to be used with the BPM must have the following specifications:

Time base: 5 ms/div.
Band Pass: 10 kHz
Vertical sensitivity: 50 mV to 5 V/div.

An analog oscilloscope can be used if it has simultaneous Z axis intensification and remote
trigger. Upon request, NEC can recommend and/or supply an oscilloscope that meets the above requirements.