CPBP0 pages

CHARGED PARTICLE BEAM IMAGING SYSTEM
B. Laprade, W. Netolicky, V. Grib, PHOTONIS USA, Sturbridge, MA 01566, and
E. Schyns, Ph.D., PHOTONIS France SAS, Brive Cedex, France 19106
Abstract
The high energy physics community has long sought a
capability to determine location and focus of charged
particle beams racing through accelerator tubes. Imaging
a charged particle beam traveling at nearly the speed of
light without changing the velocity or focus has proved to
be a challenging task.

emission array can be constructed from mosaic panels
which are 80 X100 mm (each), typically 240 X 100 mm
in the final configuration, Figure 1.

One approach is used by astronomers to determine the
location of black holes by observing the gravitational
effects on nearby stars. A similar approach for imaging
high velocity charged particle beams has proven
successful.
The PHOTONIS electron beam imager consists of a large
electron generator array, a matching microchannel plate
assembly and a readout. Voltage is applied to the EGA to
create a high density shower of relatively low energy
electrons. These electrons are accelerated to the matching
MCP assembly and readout.
As the charged particle beam travels through the “cold”
electron shower, it will cast an electron shadow on the
MCP. The width of the shadow and the timing
information at arrival and departure provide critical
information about the positioning and speed of the beam.
These devices are UHV compatible and can be custom
designed for each beam line.

INTRODUCTION
The precise determination of transverse beam profiles in
accelerator and collider systems is critical to proper
operation. One approach, known as an Ionization Profile
Monitor (IPM), uses free electrons and ions produced as
the bunches collide with light element residual gas
molecules. The resultant ions and electrons can be
laterally swept away and the resultant signals used to
determine the beam profile [1].

Figure 1. 100mm x1000mm EGA array

Electron Generator Arrays
• An Electron Generator Array is a specially processed
microchannel structure which emits an Electron Beam
from each channel when a voltage is applied across the
array.
The emission current can be modulated by
simply changing the voltage across the array,
Figure 2.
Unlike filament-based devices, the EGA
produces no heat.
Electron Generator Arrays can be fabricated in
various sizes and shapes with seamless active
dimensions ranging from 3 to 150 mms.
Very large arrays can be fabricated by tiling
large rectangular arrays together.
Emission Current (A) vs Applied Voltage (KV)

Whenever scientists have had difficulty measuring small
or fast events, they often find the answers lie in observing
the things around the event of interest which can be
observed. This approach is used by astrophysists to
determine the location of black holes by observing the
gravitational effects on nearby stars. A similar approach
for imaging high velocity charged particle beams may
also prove useful.

APPROACH
The PHOTONIS charged particle beam imager is a twopart system: The first part consists of a large area
Electrogen™ Electron Generator Array (EGA). The

Figure 2. The EGA emission current can be modulated
by adjusting the array voltage. Data shown is for a 50
mm x 8 mm array.