Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0
d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - W E P 0 3 0

FIRST RESULTS FOR A 50 MeV BEAM INDUNCED FLUORESCENCEMONITOR FOR BEAM PROFILE MEASUREMENTS
G. Rosenthal, J.I. Anderson, A. Cao, E. Cramer, T. Gordon, K. Kuhn, O. Vazquez, J. Lopez
S. Lynam, J. Ringuette, L. Szeto, J. Zhou, Nusano, Salt Lake City, UT, USA
E. Dorman, R. Emery, B. Smith, University of Washington Medical Center, Seattle, WA, USA
Abstract
4++

Nusano is developing a 50 MeV alpha ( He ) particle
accelerator (The Nusano accelerator can also accelerate
2 + 3
H , He++, 6Li3+, 7Li3+, and a few other heavier ions), primarily to produce medical radionuclides. The accelerator
produces an average current of 3 mAe with 20 mAe average
macro pulse current. This results in an average beam powerof 75 kW, and an average beam power within the macro
pulse of 500 kW. The beam profile at the exit of the DTL
is approximately Gaussian with a radius (FWHM) of about
3 mm. Designing diagnostics for this beam is challenging,as diagnostics that intercept beam will receive a very highheat load. A BIFM (Beam Induced Fluorescence Monitor)
is being developed to measure beam profiles. Nitrogen gas
is leaked into the beamline. Excitation of the nitrogen bybeam particles is captured using an image intensifier. The
signal generated is directly proportional to the beam current. A prototype system has been constructed and tested
on a lower intensity alpha beam. First results indicate wecan measure beam profile to a 100 µm accuracy. Production system is currently being designed.

EXPERIMENTAL SYSTEM
The 50 MeV alpha particle accelerator Nusano is developing will be commissioned in 2025. The 47.3 MeV at theUniversity of Washington Medical Cyclotron Facility wasused as a test facility to evaluate the BIFM (Beam InducedFluorescence Monitor) intended to be installed on thebeamline. The cyclotron provides 20-40 µAe alpha beam,
which is a good model for the Nusano beam.
The experimental apparatus is shown in Figure 1, consists of a vacuum chamber that the beam passes through. In
the chamber the beam particles interact with nitrogen
leaked into the chamber and photons are generated by decay in excited nitrogen. The light exits the chamber
through a window and is directed by lenses and mirrors
into an image intensified camera (Photonis iNocturn HIQE Blue). Since the light emitted is directly proportional
to the density of nitrogen and the beam current, by analyzing the images generated the beam distribution can bemeasured. A calibrated PMT is also provided to measurelight intensity received by the camera.
Control of the nitrogen pressure is critical to correct operation of the BIFM. The experimental system allowed forboth pulse and CW nitrogen flow, but the data presented
here is entirely based on CW flow. One of the key goals of
the project was to determine the ideal nitrogen pressure forthe system. The system also includes vacuum chokes thatallow the pressure in the measurement chamber to be about

an order of magnitude higher than the pressure in the surrounding vacuum system.

Figure 1: CAD drawing of experimental system.

RESULTSA basic raw data image is show in Figure 2. The beam is
the horizontal strip shown in the blue outline. The crescentshape, and the three dots (red outline), are compound reflections of light generated by ionization of backgroundgas in the cold cathode pressure gauge.
In order to understand the resolution of the BIFM a picture was taken with a test pattern located at the beam position. Combining this with the data averaged across thebeam part of the image indicates a spatial resolution on theorder of 100 µm (see Figure 3).

Figure 2: Basic image show the beam induced fluorescence(show in the blue box). The crescent shape, and the threedots (red box), are a compound reflection from the cold
cathode pressure gauge.

WEP030418

03 Transverse Profile and Emittance Monitors

IBIC2023, Saskatoon, CanadaJACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - W E P 0 3 0

Figure 3: Spatial resolution of the BIFM. The upper left
shows a beam induced image. The upper right is the calibration image. Note the blue and red boxes represent
matching areas. The lower image indicates the averaged
data from pixels in the beam box.

Figure 4: Variation of signal with nitrogen pressure. Theupper data is at 2×10-5 torr, middle data is at 5×10-5 torr,
and the lower data is at 7×10-5 torr.

Variation with Nitrogen Pressure

Variation with Beam Position

Varying the nitrogen pressure varies the intensity of received light (Figure 4). The received beam signal is proportional to the nitrogen pressure. The light from the cold
cathode gauge is not because it saturates the detector at thehighest pressures.
Pulsing the nitrogen gas feed, to reduce the load on therest of the vacuum system, was considered but the data
tends to indicate that Nusano can probably operate theBIFMs with a CW nitrogen pressure.

As a test of system performance, the beam was steeredup and down and BIFM was used to track the beam position (Figure 5). The beam centroid moves about 4.5 mm,
which is consistent with the beam optics and limits placedby the collimators.
The beam profile is consistent with a wire scanner diagnostic. Direct comparison is difficult because the wire
scanner is limited to a much smaller beam current than wasused for the BIFM experiments.

UW / Nusano Comparison
The UW experiments were conducted primarily with
22 µAe beam current. Clearly sufficient light was generated for the single layer MCP intensifier to form images(averaging several hundred images was necessary to generate good statistical data). Nusano will operate with
20 mAe beam current, so 1000 times as many photons
would be generated for the same nitrogen pressure. Nusano
will reduce the nitrogen pressure to 5×10-7 torr resulting ina reduction in the number of photons by a factor of 100.
This still results in Nusano generating 10 times the lightseen in these experiments. This low nitrogen pressure
should allow Nusano to operate the BIFMs with a CW gas
flow, simplifying the diagnostics.
We are also evaluating the possibility of operating withthe lower gain camera and using a puffed gas system.

WEP03003 Transverse Profile and Emittance Monitors

419

Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

IBIC2023, Saskatoon, Canada
JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0
d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - W E P 0 3 0

Figure 6: Neutron damage, primarily to the camera system.
The image on the left was taken at the end of the first dayof operation. The image on the right was taken after theneutron treatment beam had been running for an entire day.

NEXT STEPS

Figure 5: Beam steering. The beam centroid was moved up
and down and the position followed on the BIFM. The centroid travel is about 4.5 mm, which is consistent with beamoptics and collimators.

RADIATION DAMGE
The long optical path and shielding are to reduce the radiation dose on sensitive electronic such as the camera. Nusan’s beam line will be exposed to high radiation dose. Up
to 25,000 mrem/hour on the switchyard floor, and morethan order of magnitude higher at beam height. This doseis primarily from neutrons (~90%) and gammas (~10%).
The UW facility also has a high dose of neutrons from theirneutron treatment beam.
Images taken before and after operation of the neutron
beam (Figure 6) clearly show an increase in the number ofdead pixels as well as a reduced sensitivity.
The experimental setup had limited shield due to spaceconstraints on the beamline.

The camera settings were not optimal at the UW experiments. Several pixels were saturated. The gain can beturned down on the camera or we could change the image
size. For example, increasing the image size on the camara
by a factor of two, in both directions, would decrease thebrightness and increase the spatial resolution to 50 µm.
The camera showed some radiation damage so shielding
around the camera will have to be increased. The limited
shielding at UW was mostly a function of space constraints.
We had several problems with small light leaks into thedarkened optics boxes. These will be redesigned to reduce
light leaks and make them easier to work with.
The cold cathode vacuum gauge generated significant
light problems. This will be relocated, and reflective surfaces darkened.

CONCLUSIONS
The first test of the Nusano BIFM was very successful.
All project goals were achieved and then some. An improved version of the system is being designed and constructed. Emphasis is on a system that can be deployed andmaintained along the beamline. Nusano will eventually deploy 35 BIFM systems along the beamline. Some are for
specific diagnostics or tuning applications, but many areexpected to be part of routine operations.

WEP03042003 Transverse Profile and Emittance Monitors