BEAM CONTROL AND MONITORS FOR THE SPIRAL INJECTION TESTEXPERIMENT∗M. A. Rehman† , SOKENDAI (The Graduate University for Advanced Studies),Kanagawa 240-0193, Japan
H. Iinuma, Ibaraki University, Mito, Ibaraki, Japan
S. Ohsawa, H. Nakayama, K. Furukawa, T. Mibe, H. Hisamatsu, High Energy Accelerator Research
Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
Abstract
A new experiment at J-PARC (E34) is under construction
to measure the muon's g – 2 to unprecedented precision of0.1 ppm and electric dipole moment up to the sensitivityof 10−21 e.cm in order to explore new physics beyond thestandard model. A novel three-dimensional spiral injection
scheme has been devised to inject and store the beam intoa small diameter MRI-type storage magnet for E34. The
new injection scheme features smooth injection with highstorage efficiency for the compact magnet. However, spiralinjection scheme is an unproven idea, therefore, a Spiral Injection Test Experiment (SITE) at KEK Tsukuba Campus isunderway to establish this injection scheme. SITE consistsof a 80 keV thermionic electron gun, two-meter-long beamline, and a solenoid storage magnet. The DC electron beamspiral track has been confirmed by the de-excitation of thenitrogen gas in the vacuum chamber of the storage magnet.
A new wire scanner system has been developed to extract
the beam current, profile and geometrical information of
three-dimensional trajectory.

INTRODUCTION
The most recent measurement of muon g – 2 atBNL(E821) conclude a 3 σ [1] discrepancy with the equally
precise standard model prediction. The new J-PARC muong – 2/EDM (E34) is under preparation to resolve this tantalizing discrepancy. The E34 experiment will employ acompletely new approach in order to measure the muon’s g –2. The final goal of E34 is to measure the muon’s g – 2 witha precision of 0.1 ppm and EDM down to the value of 10−21e.cm [2].
In order to measure the muon g – 2 a low emittance polarized muon beam will be stored in a precise magnetic field
to measure the evolution of the spin precession vector withrespect to time. In E34 a low emittance muon beam of momentum 300 MeV/c will be injected into a 3-T MagneticResonance Imaging (MRI) type solenoid magnet in order tostore the muon beam on a 0.66 m diameter orbit. The MRItype storage magnet will provide an unprecedented local
field uniformity of 0.2 ppm. A new three-dimensional spiralinjection scheme has been invented in order to inject thebeam into the MRI-type magnet. This new injection scheme∗ Work supported by “Grant in Aid” for Scientific Research, JSPS (KAK-ENHI#26287055, KAKENHI#19H00673)† rehman@post.kek.jp

will enhance injection efficiency and overcome technicalchallenges related to the small storage orbit diameters. In
the spiral injection scheme, the beam will be injected at thevertical angle into the storage magnet. The radial field of thesolenoid will decrease the vertical angle of the beam as it
approaches the mid plane of the magnet. Finally, a magnetic
kicker will guide the beam to the storage volume where thebeam will be stored under a weak focusing field [3–6].
The three-dimensional spiral injection scheme is an unprecedented injection idea, therefore, a demonstration experiment to establish the feasibility of this new injection scheme
is necessary. A scale down Spiral Injection Test Experiment(SITE) with an electron beam is under development at KEK
Tsukuba campus. This paper will describe the developmentof the wire scanner type monitors for the Spiral Injection
Test Experiment.

SPIRAL INJECTION TEST EXPERIMENT(SITE)The SITE setup is consists of a 2 m long straight beamline,
a solenoid storage magnet to store the electron beam and aforty degree bend section to guide the electron beam towards
the storage magnet. A triode type thermionic electron gun
with LaB6 cathode is used to generate the DC electron beamof 80 keV with the beam current in the range of a few µA.
After the electron gun, a magnetic lens focuses the beam. A
pair of steering coils also have been installed to control thetransverse position of the beam. An electric chopper systemafter the electron gun produces a pulsed beam. Details of theelectric chopper can be found in [7]. A collimator of diameter 3 mm and depth 5 mm is placed after the electric chopper.
The collimator serves as the beam dump for the chopper

Figure 1: The side view of the 3D model of Spiral Injection
test Experiment.

system and also creates a differential vacuum system for thegas monitor in the storage magnet. After the collimator, twonormal quadrupole magnets control the beam phase space
for the spiral injection. Due to the radial fringe field of thestorage magnet, an XY-coupled beam at the injection pointis required to avoid beam de-focusing. In order to apply theXY-coupling rotated quadrupole magnets are in preparation.
The first bending magnet 1 is placed on the straight beamline to deflect the beam forty degree towards the storage
magnet. A second bending magnet 2 near the injection point
controls the final injection angle.
The storage magnet consists of a 540 mm long solenoid
coil. The solenoid coil is enclosed in the iron yoke. An
auxiliary coil was placed at the center of the solenoid inorder to produce a weak focusing field at the center of thestorage magnet [8]. The pulsed magnetic kicker also underdevelopment will keep the beam to the center of the storage
magnet [9]. The layout of the SITE experimental setup isshown in Fig. 1. A new wire scanner monitor for the beamprofile measurement was developed for the solenoid storage
magnet. The details will be discussed in the forthcoming
section. A comparison of parameters between E34 and SITE
is given in Table 1.
Table 1: Comparison of Parameters between E34 and SITE.
Parameters
Magnetic field strength
Momentum
Cyclotron Period
Storage orbit diameter

E343T
300 MeV/c
7.4 ns0.66 m

SITE
0.0082 T296 keV/c
5 ns
0.24 mFigure 2: Electron beam track in the vacuum chamber ofthe storage magnet is visible due to the de-excitation of
the nitrogen gas. Three turns can be seen clearly from 1D
histogram of CCD-camera photo.

Wire Scanner
The wire scanner monitor was developed to measure thebeam profile in the storage magnet. In the wire scanner type
monitors, the beam hits the wire and deposits energy into
the wire and charges converted to a corresponding current.
The voltage across a resistor is proportional to instantaneous
current absorbed in the wire. In order to measure the verticalbeam profile inside the storage magnet, horizontal wires
are moved vertically to measure the beam current at eachposition.
The wire scanner is consists of a copper wire of 1 mm diameter and a driving system to scan the copper wire throughthe beam. The driving system is composed of a linear
feedthrough and linear actuator [10]. Two wire scanners

BEAM MONITORS FOR THE SOLENOID
STORAGE MAGNET
Two kinds of monitors have been used to diagnose thebeam inside the storage magnet. First, we used a nondestructive gas monitor to confirm the beam inside the storage magnet. Secondly, new wire scanner type monitors havebeen developed to measure the beam profile.

Gas Monitor
In order to observe the electron beam as fluorescent light,
the vacuum chamber of the storage magnet was filled with
the nitrogen gas. When the electron beam collides with thenitrogen gas, some molecules are ionized and some undergo
the excitation. The de-excitation of nitrogen molecules results in the emission of fluorescent light in the visible wavelength of the range (390 nm < λ < 470 nm). A CCD-camera
is used to observe fluorescence light from the de-excitation.
Figure 2 shows a typical beam injected into the storage magnet. The gas monitor is an efficient way to confirm beam
inside the storage magnet, but it cannot provide the beam
size information. Therefore, the wire scanner beam profile
monitor was developed.

Figure 3: (a) Schematic of two wire scanner setup. (b) Wirescanner system on the top of the storage magnet.
were installed on the storage magnet in order to measure thebeam profile and beam evolution in the storage magnet. The
wire scanner 1 was installed at 2 cm away from the injection
point and wire scanner 2 was placed at 180 degrees awayfrom the wire scanner 1 for the beam profile measurement
at half cyclotron period. Figure 3 (a) shows the 3D modelof the wire scanner set up and (b) is a photo of the wire
scanner set up at the storage magnet. In the wire scanner, thecopper wires were placed horizontally in order to measure
the vertical beam profile. The horizontal wire is divided
into the horizontal direction in order to measure the radialoffset of the beam. A vertical wire on wire scanner 1 wasalso installed to measure the horizontal beam profile. The
horizontal beam profile measurements are still in progress.

line of Fig. 6 decrease down to 14% at 1st turns and 2%
decrease at the 2nd turn. The results from the wire scanner 2
are still in progress. Due to the axial symmetric field of thestorage magnet, an XY-coupled beam is required to reducethe de-focusing of the beam.

Figure 5: Left: CST-PS particle tracking simulation withthe real experimental condition in the storage magnet. Thebottom left plot shows the injected beam profile. Right: The
vertical beam profile at wire scanner 1 and 2 position.

Figure 4: (a) Wire scanner 1 dimensions. The red lines arethe wires. (b) Wire scanner 2 dimensions. Wire scanner 2
was placed 180 degrees away from the wire scanner 1.

RESULTSThe wire scanners were drive by linear actuator with aresolution of 1 mm. The signal from the wires was takenout of the vacuum chamber via vacuum feed-throughs andterminated into the 1 MΩ terminal of an oscilloscope. A C#program was developed to log the data and provide online
plotting during the beam test.
In order to reduce the vertical de-focusing of the beam,
two normal quadrupole magnets were installed on the injection beamline. A CST-PS [11] simulation has been carriedout with the experimental conditions in order to estimate thevertical beam growth in the storage magnet. In the simulation the electron beam of energy 80 keV and current 20 µA
was assumed. In the simulation, the beam emittance was
1 mm−mrad in horizontal and vertical (X-Y) planes and vertical focus beam is preferable for the injection. Figure 5
shows the CST-PS simulation results and left bottom plotshows injected beam dimensions. As the beam moves upward in the magnet the number of counts decrease, but thearea under the curve remains the same.
During the beam tests, the energy of the electron beam
was 80 keV with the beam current of 20 ±1 µA (DC). The
beam emittance is expected to be few mm-mrad but thedetail number is still in study. Figure 6 shows the preliminary
results of the wire scanner 1 and comparison with simulation.
As the beam turns, the area which is indicated in the dashed

Figure 6: Vertical beam profile measurement from wire
scanner 1 as a function of vertical position. The storage
magnet center was defined as a reference point (Z = 0).

SUMMARY
A wire scanner type monitor was designed and constructed for the beam profile measurement in the solenoid
type storage magnet at KEK. A beam test of the wire scannermonitor successfully has been carried out and preliminary
results obtained. The preliminary data from the wire scanneris in good agreement with simulation results.

ACKNOWLEDGMENTS
We thank Prof. Tohru Honda, Prof. Toshiyasu Higo andDr. Izumi Mochizuki for their generous support for thisproject.

REFERENCES[1] G.W. Bennett et al., “Final Report of the muon E821 anomalous magnetic moment measurement at BNL”, Phy. Rev.

D., vol. 73, p. 072003, 2006. doi:10.1103/PhysRevD.73.
072003[2] M. Aoki et al., “Conceptual Design Report for the Measurement of the Muon Anomalous Moment g – 2 and Electric
Dipole moment at J-PARC (2011)”, unpublished.
[3] H. Iinuma et al., “Three-dimensional spiral injection scheme
for the g – 2/EDM experiment at J-PARC”, Nucl. Instr. Meth.,vol. A832, pp. 51-62, 2016. doi:10.1016/j.nima.2016.
05.126[4] H. Iinuma et al., “Three-Dimentional Spiral Beam Injection for a Compact Storage Ring”, in Proc. 9thInt. Particle Accelerator Conf. (IPAC’18), Vancouver,Canada, Apr.-May 2018, pp. 1673–1676. doi:10.18429/
JACoW-IPAC2018-TUPML060[5] H. Iinuma et al., “Development of three-dimensional spiralbeam injection scheme with X–Y coupling beam for MRI
sized compact storage ring”, in Proc. 15th Annual Meetingof Particle Accelerator Society of Japan (PASJ2018) August
7-10, 2018, Nagaoka, Japan, paper WEOM07, pp. 79–83.
[6] M. A. Rehman et al., “Progress of the Novel Threedimensional Spiral Injection Scheme Test Experiment”,

in Proc. 29th Linear Accelerator Conf. (LINAC’18), Beijing, China, Sep. 2018, pp. 717–720. doi:10.18429/
JACoW-LINAC2018-THPO017[7] M. A. Rehman et al. “Development of the three-dimensional
injection spiral injection by using electron beam for muon g –2 experiment”, in Proc. of 14th Annual Meeting of Particle
Accelerator Society of Japan (PSAJ’17), Sapporo, Japan, Aug.
2017, paper WEOM01, pp. 114–117.
[8] M. A. Rehman et al., “Test experiment of 3-D spiral injection
scheme using electron beam for new g – 2/edm experimentat J-PARC”, in Proc. of the 13th Annual Meeting of Particle
Accelerator Society of Japan (PSAJ’16), Chiba, Japan, Aug.
2016, paper TUP056, pp. 1004–1007.
[9] M. A. Rehman et al., “Development of the pulsed magnetic
kicker for the spiral injection test experiment”, Proc. of 15th
Annual Meeting of Particle Accelerator Society of Japan(PASJ2018), Nagaoka, Japan Aug. 2018, paper THP006,pp.768-772.
[10] THK, http://www.thk.com[11] CST, http://www.cst.com