Development of Three-dimensional
Spiral Injection Scheme by Using
Electron Beam

Report of Qualifying
Research in High Energy Accelerator Science
Rehman Muhammad Abdul
ID#20151253
School of High Energy Accelerator Science
Department of Accelerator Science
SOKENDAI(The Graduate University for Advanced Studies)

Abstract
The muon's anomalous magnetic moment (g – 2)μ is one of the most importantmeasurement in elementary particle physics. In order to resolve the current discrepancy
between the measurement and the standard model prediction, the J-PARC new muon g −2/EDM (E34) experiment is proposed. The key idea to measure (g – 2)μ is to store
polarized muon beam in a magnetic field and measure the evolution of spin precession
vector. In E34 a very low emittance ultra-cold muon beam of 300 MeV/c from muon
accelerator will be stored in a 3-T MRI-type solenoidal magnet within a 0.66-m diameter
orbit. A newly developed spiral injection scheme will overcome all technical challenges
with small storage orbit. A demonstration experiment to prove the feasibility of this newly
proposed scheme is inevitable. Therefore, a scale down Spiral Injection Test Experiment(SITE) by the use of electron beam is under development at KEK Tsukuba campus. The
first stage goal of SITE is to detect a DC electron beam spiral track in the storage chamber
as fluorescent light from N2 gas excitation along the electron beam path. The second stage
goal is to store the pulsed electron beam for the order of milliseconds.
In the first stage of SITE, DC 80 keV electron beam line of length 2 m has been
designed and developed. The electron beam in straight beam line was successfullycommissioned and confirmed at several locations by using fluorescent screen (FS)monitors. For further investigation of the straight beam line, a simulation was done in
CST-PS. Meanwhile, a solenoidal type storage magnet was manufactured to store electron
beam into 24 cm diameter orbit. Simulation of the storage magnet and particle tracking
studies has been carried out in CST-PS. Injection of the electron beam in the storage
chamber has been performed with several different experimental settings and optimal
condition for injection of the electron beam has been determined from this systematicii

study. Many other efforts also have been made for the successful injection of the electron
beam from the straight beam line into the storage magnet. Finally, the electron beam was
successfully injected from straight beam line to the storage magnet and confirmed byusing FS monitors. Electron beam of 80 keV in the storage magnet was observed in a
non-interceptive way, as fluorescent light due to excitation of nitrogen gas along beam
track using a CCD-camera. However, we found one major issue. Due to the radial fieldof the storage magnet beam was vertically defocused and only two turns were clearlyobserved. Twiss parameters at the injection point will be controlled in order to solve
vertical defocusing of the beam.
For the first stage of SITE experimental setup has been built successfully and goal toobserve electron beam as fluorescent light in the storage magnet is achieved. It is figuredout that what is needed to be done in order to achieve the second stage goal.
For the second stage of SITE, an electric chopper system has been designed, simulated
and fabricated to produce a pulsed electron beam of a pulse length 50 ns. This report will
describe the achievements of the first stage of SITE and the progress towards the second
stage.

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Table of Contents
Abstract ....................................................................................................................... ii
List of Figures ............................................................................................................ vi
List of Tables ............................................................................................................. xii
Acknowledgments .................................................................................................... xiv
1. Introduction ............................................................................................................ 1
2. Three-Dimensional Spiral Injection Scheme........................................................ 4
2.1 The Basic Concept of Muon Injection Scheme .............................................. 4
2.2 Spiral Injection Test Experiment (SITE) by Using Electron Beam ............. 7
2.3 Experimental Setup of SITE............................................................................ 7
2.3.1 Electron Gun ............................................................................................ 10
2.3.1.1 Thermionic Emission ...........................................................................112.3.1.2 Simulation of Electron Gun ................................................................ 122.3.1.3 Twiss Parameters ................................................................................ 15
2.3.2 Magnetic Lens .......................................................................................... 17
2.3.3 Main Dipole Magnet ................................................................................ 19
2.3.4 Differential Vacuum System ................................................................... 23
2.3.5 Particle Tracking of Straight Beam Line in CST-PS ............................ 24
2.3.6 Storage Magnet ........................................................................................ 28
2.3.6.1 Field Measurement ............................................................................. 29
2.3.6.2 Particle Tracking in Storage Magnet .................................................. 30

2.4 Second Stage Upgrade of Straight Beam Line ............................................. 31
2.5 Electric Chopper System................................................................................ 32
2.5.1 Electrical Design ...................................................................................... 34
2.5.2 Mechanical Design ................................................................................... 36
2.5.3 CST Simulation ........................................................................................ 37
2.5.4 Experimental Setup ................................................................................. 39
3. Beam Commissioning and Results ...................................................................... 41
3.1 Beam Commissioning and Monitors in Straight Beam Line ...................... 41
3.2 Issues during the Beam Commissioning ....................................................... 46
3.2.1 Beam Hit at the Injection Pipe ............................................................... 46
3.2.2 Field Leakage from the Storage Magnet ............................................... 49
3.2.3 Alignment Stage for the Storage Magnet .............................................. 50
3.2.4 Polarity of the Storage Magnet Auxiliary Coil ..................................... 51
3.3 Beam Monitors in the Storage Magnet ......................................................... 52
3.3.1 Interceptive Monitor in the Storage Magnet.......................................... 52
3.3.2 Non-interceptive Monitor in the Storage Magnet................................. 54
3.3.2.1 Working Principle ............................................................................... 54
3.3.2.2 Setup ................................................................................................... 55
3.4 Experimental Results of the Non-interceptive Monitor .............................. 55
3.4.1 Electron Beam Injection at Lower Injection Angle .............................. 56
3.4.1 Electron Beam Injection at Higher Injection Angle: ............................ 58
3.4.1 Electron Beam Injection at (43.5o < injection angle < 44o) .................. 60
3.5 Defocusing of the Electron Beam in the Storage Magnet ........................... 62ii

3.6 Solution for Defocusing of the Electron Beam ............................................. 63
3.7 Future Plans .................................................................................................... 66
3.7.1 Reflection from Chamber Walls ............................................................. 66
3.7.2 Magnetic Kicker ...................................................................................... 66
3.7.3 Beam Monitors: ....................................................................................... 67
4. Summary and Conclusions .................................................................................. 68
References: ................................................................................................................ 71
Appendix A ................................................................................................................ 73

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v

List of Figures
Figure 2.1: The Basic concept of three-dimensional spiral injection scheme [6] ............ 5
Figure 2.2: Radial field of solenoidal type magnet will deflect vertical momentum ofmuon beam to the horizontal [6]. ..................................................................................... 6
Figure 2.3: Schematic diagram of test experiment. .......................................................... 9
Figure 2.4: Photo of test experiment setup at the KEK-LINAC building. ....................... 9
Figure 2.5: Layout of electron gun H.V power supply [9]. .............................................11
Figure 2.6: LaB6 cathode used in electron of test experiment [9]. ..................................11
Figure 2.7: Model of electron gun in CST...................................................................... 13
Figure 2.8: (a) Potential contours on the electrodes of electron gun. (b) Electric field
pattern and strength among electrodes of electron gun. ................................................. 14
Figure 2.9: Beam trajectories from electron gun at -80 kV cathode potential, 2 kV apertureelectrode and cathode temperature of 1250 K. ............................................................... 14
Figure 2.10: Beam current as a function of cathode temperature. .................................. 15
Figure 2.11: x-phase space of particle distribution at the 50 mm away from cathode. .. 16
Figure 2.12: x-y cross section of beam in post anode region (50 mm away from cathodesurface). .......................................................................................................................... 16
Figure 2.13: y-phase space of particle distribution at the 50 mm away from cathode. .. 16
Figure 2.14: Magnetic lens model with its dimensions. ................................................. 17
Figure 2.15: (a) Absolute value of magnetic lens. (b) Radial component of magnetic field.
........................................................................................................................................ 18

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Figure 2.16: Transverse beam size (+x direction) as it is evolving in beam direction.
Different colors curves show focusing strength of magnetic lens at different magnetic lenscurrent. ............................................................................................................................ 19
Figure 2.17: (a) Design of bending magnet and it dimensions. (b) CST-EM results ofmagnetic field pattern and strength. ............................................................................... 20
Figure 2.18: Transverse magnetic field profile along z-axis. Blue curve is measured values
and red curve is CST simulation results. ........................................................................ 21
Figure 2.19: Transverse magnetic field map on Z (mm) and Y (mm) plane. ................. 21
Figure 2.20: B0 of dipole magnet as a function of current. ............................................ 22
Figure 2.21: Collimator and dipole magnet. ................................................................... 23
Figure 2.22: Schematic of beam line components in straight section. ........................... 25
Figure 2.23: Tracking of beam through straight beam line component. ........................ 25
Figure 2.24: Beam phase space at the exit of electron gun ............................................ 26
Figure 2.25: Beam phase space at the collimator ........................................................... 26
Figure 2.26: Beam phase space after collimator. ............................................................ 27
Figure 2.27: Schematic view of storage magnet with reference trajectory and monitors.
........................................................................................................................................ 28
Figure 2.28: Storage Magnet and vacuum chamber. ...................................................... 28
Figure 2.29: Left. Measurement of BZ component as a function of vertical position. Colordata correspond to different auxiliary coil current Grey data represent OPERA results.
Right: BX component as a function of vertical position. ................................................ 29
Figure 2.30: Single particle tracking in storage magnet field. Red circle is showing thestarting point of tracking calculation. ............................................................................. 30
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Figure 2.31: Left: Single particle tracking in the x-z plane of the storage magnet, which
encompass ~24 cm diameter orbit. Right: Single particle tracking in x-y plane of thestorage magnet. ............................................................................................................... 31
Figure 2.32: Schematic layout of chopper system. ......................................................... 33
Figure 2.33: Left: Effect of length of chopper’s electrode plates on required deflecting
voltages. Right: Effect of electrodes length on electric field. ........................................ 34
Figure 2.34: Left: Capacitance of chopper plates as a function of chopper electrode length.
Right: Charging time of chopper electrodes as function of electrode’s length. ............. 34
Figure 2.35: (a) Electrical design of chopper system. (b) Ideal beam pulse generated byelectric chopper system. ................................................................................................. 35
Figure 2.36: Mechanical structure and dimension of chopper system. .......................... 36
Figure 2.37: Left: H.V electrode and its support. Right: Chopper’s electrodes in vacuum
chamber .......................................................................................................................... 37
Figure 2.38: Left: Potential contours on the electrodes. Right: Electric field pattern ofelectrodes in vacuum chamber of chopper system. ........................................................ 38
Figure 2.39: Electric field profile in (x-z)-plane. ........................................................... 38
Figure 2.40: Electrical component setup for chopper system (DC power supply, pulse
generator, function generator) ........................................................................................ 40
Figure 2.41: Output from PVX 4140 Pulse generator on Tektronix 5054 Oscilloscope.40
Figure 3.1: (a) Schematic of the first FS monitor (top view). (b) Mirror and FS used infirst monitor. ................................................................................................................... 42
Figure 3.2: Top view of straight beam line and first FS monitor. ................................... 42
Figure 3.3: Beam profile from first FS monitor. ............................................................ 43
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Figure 3.4: Beam diagnostic at injection region. ............................................................ 43
Figure 3.5: (a) Schematic of interceptive FS monitor used in straight beam line (b) andon the injection pipe. ...................................................................................................... 44
Figure 3.6: (a) Beam spot on fluorescence plate in straight section of beam line. Original
black and white image was converted to false color for better visibility. (b) Intensity ofbeam as a pixel values on x and y axis. .......................................................................... 44
Figure 3.7: (a) Beam spot on fluorescence plate after bending magnet. Original black andwhite image was converted to false color for better visibility. (b) Intensity of beam as a
pixel values on x and y axis. ........................................................................................... 44
Figure 3.8: Beam trajectory in injection region while Storage chamber was filled with N2gas. .................................................................................................................................. 46
Figure 3.9: Old and new injection pipe for the injection of electron beam in storage
magnet. ........................................................................................................................... 47
Figure 3.10: Beam hit at the injection pipe. Red circle is showing the hit point withtemperature 43.3oC. ........................................................................................................ 48
Figure 3.11: New injection beam pipe. ........................................................................... 48
Figure 3.12: Field distribution around the storage magnet. ............................................ 49
Figure 3.13: Second dipole magnet to compensate field leakage from storage magnet..50
Figure 3.14: Additional bending magnet on the injection pipe of storage chamber. ...... 50
Figure 3.15: Alignment stage for the storage magnet. .................................................... 50
Figure 3.16: Axial field profile of (By) of storage magnet. Red is showing the field profile
with wrong polarity and blue is correspond to correct polarity of auxiliary coil. .......... 51ix

Figure 3.17: Radial field profile. Red correspond to wrong polarity and blue is withcorrect polarity of auxiliary coil. .................................................................................... 52
Figure 3.18: Schematic view of fluorescent screen monitor to detect vertical position ofbeam in storage magnet. ................................................................................................. 53
Figure 3.19: Left: Upper Iron yoke view of storage magnet which consist of CCD-camera,
linear feedthrough and valve for N2 gas. Right: Inside view of storage magnet from B/W
CCD camera. .................................................................................................................. 53
Figure 3.20: (a) Image of fluorescent screen in mirror viewed by CCD-camera withoutbeam. (b) Beam spot at fluorescent plate in the absence of magnetic flied of storage
magnet. (c) Beam spot in the presence of magnetic field of storage magnet. ................ 54
Figure 3.21: Single particle tracking in CST-PS at the different lower injection angle, (a b) are correspond to the injection angle of 42o, 42.5o, 43o, 43.5o respectively. As injection
angle increased beam hit advanced on the vacuum chamber of the storage magnet. ..... 57
Figure 3.22: Gas monitor results from the storage magnet. The electron beam was injected
into the storage magnet at 42o. Small variations in the range of 0.5o were introduced by
the help of the second dipole magnet. (a - d) are correspond to the cases when the injection
angles were increased up to 43.5o. .................................................................................. 58
Figure 3.23: Single particle tracking in CST-PS at the different high injection angle, (a f) are correspond to the injection angle of 44o, 44.5o, 45o, 46o, 46.5o, 47o, respectively.
Only two turns are visible at those higher injection angles. As injection angle increase
distance between these two turns also increase. ............................................................. 59
Figure 3.24: Beam injection into the storage magnet at the higher injection angles.
Injection angle was 44o from the main dipole magnet and small variations in the injectionxangles were introduced by using the second dipole magnet. (a -f) are the case when theinjection angles were increased in the steps of 0.5o up to 47o. (False colors are to theoriginal B/W pictures for the better visibility) ............................................................... 60
Figure 3.25: Single particle tracking in the storage magnet at the angle 43.5o. ............. 61
Figure 3.26: The electron beam injection into the storage magnet at the angle greater than
43.5o and less than 44o (43.5o < injection angle < 44o). ................................................. 61
Figure 3.27: (a) At the injection angle greater than 43.5 and less 44o (43.5o < injection
angle < 44o) multi turns appears. (b) Multi particle tracking in the storage magnet shows
defocusing of electron beam the storage magnet. .......................................................... 62
Figure 3.28: Left: Radial field profile of the storage magnet. Right: is the derivative ofradial filed profile with respect to the solenoidal axis of the storage magnet. ............... 63
Figure 3.29: Assumed particle distribution at the radius 120 mm in the storage magnet.
........................................................................................................................................ 63
Figure 3.30: Multi-Particle tracking in the storage magnet. ........................................... 64
Figure 3.31: Left: Multi-Particle tracking in the x-y plane of the storage magnet. Blackcircle represent the required beam shape at the injection point. Right: Particle tracking
plot in the x-z plane. ....................................................................................................... 64
Figure 3.32: Phase space plots of the required beam at the injection point. .................. 65xi

List of Tables
Table 2.1: Comparison of parameters between J-PARC g - 2/EDM experiment and test
experiment. ....................................................................................................................... 8
Table 2.2: Parameters of electron gun. ........................................................................... 10
Table 2.3: Twiss parameters at the exit of anode. ........................................................... 17
Table 2.4: Geometrical parameter of electric chopper. ................................................... 33
Table 2.5: Electrical parameters for chopper system. ..................................................... 35
Table 3.1: Twiss parameters at the injection point of the storage magnet………………65

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Acknowledgments
There are so many people I wish to thank who have in one way or another made thisreport possible. I would like to express my sincere gratitude to my supervisor Prof.
Kazuro Furukawa for his constant support, guidance and motivation academically andotherwise. The door to Prof. Kazuro Furukawa office was always open whenever I ran
into a trouble spot.
I wish to give special thanks to my Co-supervisor Tsutomu Mibe for his incredible
support and encouragement. I am much obliged to him for providing me an opportunity
to participate in Muonium Production Experiment at J-PARC, which greatly benefit me
for enhancing my experimental expertise. I would like to express my deepest gratitude toProf. Hiromi Iinuma for her continuous support and providing me an opportunity to study
in SOKENDAI. I have been extremely lucky to have her one of my supervisor who caredso much about my work, and who responded to my questions and queries so promptly.
I am much obliged to Prof. Satoshi Ohsawa for his support academically and in mydaily life. His teaching and support was indispensable for the completion of this report. I
would like to thank Prof. Hisayoshi Nakayama. He has been supportive since the days I
began my work at the experiment. I am indebted to Prof. Hiromi Hisamatsu for his kind
help during the experiment and for providing us many crucial vacuum component.
I am grateful to Prof. Nahito Saito for giving me many constructive comments andsuggestion during weekly meetings. I would also like to thank all saito’s lab member: Ryo
Kitamura, Masashi Otani, Sirui Li, Yutaro Sato, Hiromasa Yasuda, Shoichiro Nishimura.
Finally, I must express my gratitude to my mother and siblings for their prayers andcountless love for me.

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Chapter 1
Introduction
Ever since the discovery of muon, physicists are trying to decipher the properties ofmuons. A precise measurement of muon anomalous magnetic moment property can give
hint for new physics beyond the standard model.
The BNL [1] experiment measured the muon's anomalous magnetic moment (g – 2)μ to
an accuracy of 0.54 ppm, and there is ~3 σ discrepancy between the experimental value
and the Standard Model prediction. More precise measurement of the muon (g – 2)μ andits electric dipole moment (EDM) is in preparation at the J-PARC in order to searchphysics beyond the standard model. The J-PARC new muon g − 2/EDM (E34) experiment
aims to measure (g – 2)μ to the precision of 0.1 ppm and EDM down to the sensitivity of
10-21 e.cm [2].
The E34 experiment will employ a completely different and innovative experimental
approach as compared to the previous measurements at CERN and BNL [1, 3] to realize
this experiment. The key idea to measure (g – 2)μ is to store polarized muon beam in themagnetic field and measure the evolution of spin precession vector with respect to time.
An ultra-cold muon beam [4, 5] of 300 MeV/c from muon LINAC with very small
emittance (1.5π mm mrad) will be injected into the 3-T MRI type superconducting magnet
to store muon beam in 0.66 m diameter orbit [6]. A novel three-dimensional spiralinjection scheme has been proposed to inject ultra-cold muon beam into such compact
storage ring. This newly proposed spiral injection scheme has no real precedent, therefore,
it is necessary to prove the feasibility of this injection scheme. This new injection scheme
will be establish with an electron beam. Spiral Injection Test Experiment (SITE) is a scale1

down demonstration for the establishment of newly proposed injection scheme and underdevelopment at KEK LINAC’s klystron gallery Tsukuba campus. SITE will provide thefreedom to perform the experiment without stringent time constraint of muon beam
availability at J-PARC. It is also easier to handle electron beam parameters such as beamenergy and current which will provide freedom to choose them according to experimentneeds.
SITE is divided into two stages:
1) In the first stage of SITE DC electron gun (80 keV), straight beam line to transport
electron beam and normal conducting storage magnet have been prepared and assembled
together. Storage magnet for SITE contains all important features as in the original
storage magnet. In the first stage, it is decided to observe electron beam as fluorescentlight due to introduced nitrogen gas excitation along the beam track. The final goal of thefirst stage is to observe 80 keV electron beam trajectories of 24 cm diameter as afluorescence light in the storage magnet 83 gauss field.
2) In the second stage of SITE electric chopper system to produced pulsed electron
beam is developed. A magnetic kicker to guide electron beam to the very center of storage
region and beam monitors to determine the efficiency of this scheme are also planned todevelop in the second stage. The second stage goal is to store the pulsed electron beam
for the order of few milliseconds.
Many challenges have to face during the commissioning of the first stage. This reportwill describe the progress and results from the first stage of SITE. Electric chopper system
to produce pulsed beam also has been developed for the second stage and will be
described in details.

2The organization of this report is as follow. Chapter 2, introduce the need and basic
concept of spiral injection scheme briefly. Experimental setup and detail of eachcomponent and simulation are also given in Chapter 2. Results from the first stage of
SITE, problems and challenges faced during beam commissioning are discussed inchapter 3. Summary and conclusion are given in chapter 4.

3Chapter 2
Three-Dimensional Spiral Injection Scheme
One of the key challenge in new g - 2/EDM experiment at J-PARC (E34) is to injectultra-cold muon beam into a compact and highly uniform magnetic field storage ring. A
3 T MRI-type solenoidal magnet will be used to store muon beam into a diameter of 66
cm orbit. Mid-plane of the solenoidal magnet is defined as the storage region for muon
beam with field uniformity of < 1 ppm variation [6]. In this chapter, the necessity for the
spiral injection and basic concepts of muon 3-D spiral injection scheme will be describedbriefly. Spiral Injection Test Experiment (SITE) setup and detail of each component arealso given in this chapter.

2.1 The Basic Concept of Muon Injection Scheme
In the previous BNL muon g − 2 experiment muon beam of 3.09 GeV/c was injected
into a 1.45 T storage ring of radius 7.11 m. A device called an inflector [7] was used tocancel fringe field of storage magnet to prevent deflection of the beam due to a fringe
field. To avoid beam hit at the wall of inflector after one turn beam kicked horizontallyby the kicker to move the central orbit.
This type of scheme is applicable if the radius of the storage ring is sufficiently large
as compared to the thickness of inflector wall. In BNL case radius of the storage ring was
711 cm and the thickness of the inflector wall was 1 cm, hence kick angle of 1.5 mrad
was required within 149.2 ns (cyclotron period).
E34 storage magnet strength is 3 T which is too high field to cancel by any device. In
E34, the radius of the central beam orbit is only 33 cm using BNL type kicker will needa horizontal kick angle of 30 mrad within 7.4 ns (cyclotron period). 30 mrad kick angle
4within 7.4 ns is not possible by using any existent technology. Hence, BNL injection
scheme is not applicable in the case of E34.
To overcome these difficulties three-dimensional spiral injection scheme has beendeveloped to inject muon beam into the storage magnet. The basic concept of threedimensional spiral injection is depicted in Fig. 2.1. Muon beam will be injected at avertical angle into a 3-T MRI type solenoidal magnet. A carefully designed radial fringe
field will convert the vertical component of momentum into horizontal as its approach tothe storage region. When muon beam will reach to the storage region a double antiHelmholtz type kicker will completely remove the vertical component and muons will be
stored in mid plane as shown in Fig. 2.2. A weak focusing will be applied to a muon beamin the storage region in order to reduce the requirement of the muon beam “coldness” [6].
Detailed study of this new injection scheme is published in [6].

Figure 2.1: The Basic concept of three-dimensional spiral injection scheme [6].

5Figure 2.2: Radial field of solenoidal type magnet will deflect vertical momentum of muon beam tothe horizontal [6].

It is the first instance to employ the idea of 3-D spiral injection scheme. Therefore, atest experiment to establish the feasibility of this new injection scheme is indispensable.
In the next section, detailed experimental setup for the establishment of this new scheme
is described in detail.

62.2 Spiral Injection Test Experiment (SITE) by Using Electron
Beam
Spiral Injection Test Experiment (SITE) by the use of electron beam is underdevelopment for the establishment of spiral injection scheme. As described earlier SITE
is divided in to two stages. In the first stage of SITE experimental setup has been prepared,
namely electron beam line and storage magnet. In the second stage of SITE, electricchopper system to produced pulsed electron beam has been developed. In this section,
experimental setup of SITE has been described in detail.

2.3 Experimental Setup of SITE
A comparison of SITE with E34 is given in Table 2.1. Test experiment is consist of
straight beam line and storage magnet, a schematic diagram of the experiment is shownin Fig. 2.3. The straight beam line is 2 m long. At the beginning of straight beam line a
DC thermionic electron gun of 80 keV is used to produce an electron beam. A magnetic
lens at the distance of 70 mm away from the electron gun serves as a focusing element
for the electron beam in the straight section. A collimator of 3 mm diameter and length of
5 mm is placed at 700 mm away from electron gun to control the beam halo in a drift
section of straight beam line and also used to maintain the differential vacuum for storage
magnet. A dipole magnet on the straight beam line is used to bend electron beam into thestorage magnet. To control the transverse position (x - y) of electron beam, five pairs ofsteering coils have been installed on the straight beam line. Two of them are placed justafter magnetic lens. A pair of x–steering coil and y–steering coil are placed before
collimator to control the beam transverse position at the collimator. The fifth x-steering
coil is placed on the injection pipe after main dipole magnet to control the horizontal
7

positon of the electron beam. Three fluorescent screen (FS) monitors have been placed todetect transverse profile of the electron beam along beam line. First FS monitor is placedon the collimator and beam profile from this FS monitor has been captured by the use of
mirror and digital camera 1. Second FS monitor is placed at the end of beam line andbeam profile is captured by CCD-camera 2. Third FS monitor is placed at the injection
pipe and seen by CCD-camera 3. The detail setup of FS monitors will be described inchapter 3. The photo of actual experimental setup is shown in Fig. 2.4. The detail of eachcomponent is presented in the subsequent sections.

Table 2.1: Comparison of parameters between J-PARC g - 2/EDM experiment and test experiment.

Parameters

E34

Test experiment

Storage magnetic field

3-T

0.0083 Tμ+Particle speciee-300[MeV/c]

0.296 [MeV/c]

Cyclotron period

7.4 nsec

5.0 nsec

Storage orbit diameter

0.66 m0.24 mMomentum8

Figure 2.3: Schematic diagram of test experiment.

Figure 2.4: Photo of test experiment setup at the KEK-LINAC building.

92.3.1 Electron Gun
A thermionic electron gun with LaB6 cathode of 2 mm diameter is in use to produce
the electron beam. This electron gun was previously used for the production highbrightness X-ray experiment [9]. The electron gun is operating at 80 keV and maximum
achievable beam current is <100 mA. From radiation and thermal safety point of view,electron gun is in operation at 74 μA. An isolation transformer of 200 kV is used totransfer electrical power from AC source to high voltage power supply of electron gun.
Specifications of electron gun are given in Table 2.2. Experimental layout of electron gun
H.V power supply is shown in Fig. 2.5.

Table 2.2: Parameters of electron gun.

Parameters

Value

Extraction Voltage

80 keV

Maximum current<100 mA

Grid Type

Aperture

Cathode emission

ThermionicCathode material

LaB6

Cathode Diameter

2.0 mmCathode Grid Voltage

2 keV
a few mm mrad

Emittance

10

Figure 2.5: Layout of electron gun H.V power supply [9].

Cathode: The low work function (2.70 eV) and high electron yield make LaB6 one ofbest candidate material for cathode of electron gun. LaB6 require modest vacuum and 50
times the service life of tungsten cathode. LaB6 cathode of diameter 2 mm is used in theelectron gun of SITE as shown in Fig. 2.6.

Figure 2.6: LaB6 cathode used in electron of test experiment [9].

2.3.1.1 Thermionic Emission
When a piece of a metal is heated to very high temperatures, electrons achieve enoughenergy to overcome the potential barrier and flee away from the metal. The electron
11

emission subject to thermal excitation is called “thermionic emission”. For the electrons
to be free from the metal, need energy at least equal to “potential barrier φ” or “workfunction” of that particular metal. In other words the energy of an electron after escaping
from the metal would be
E ≥ Ef +φIn thermionic emission model, the maximum amount of emitted particles is strongly
dependent on the temperature of the surface. The thermionic emission model isprincipally based on the space-charge limited model in combination with a maximal
extractable current. In temperature limited case Richardson's law gives the current density
Jx [A/m2] of emitted electrons
𝐽(𝑥) = 𝐴𝑅 𝑇 2 exp (

−𝑊
)
𝑘𝑇

(2.1)

Where AR is Richardson's constant with a value AR = 1.2x106 A/m2K2. W is work
function the metal. T is applied temperature; k is Boltzmann constant [10 - 11].
In space charge limited case Childs-Langmuir Law gives the current density Jx [A/m2]
of emitted electrons
3/2

4𝜖0 2𝑒 𝑉𝐴
𝐽(𝑥) = [√ ]9 𝑚 𝑏2(2.2)

Where JA is current density, VA applied voltage, 𝜖0 is permittivity of free space, b isthe distance from emitting surface, m and e are mass and charge of electron [12].

2.3.1.2 Simulation of Electron Gun
CST PARTICLE STUDIO is an expert tool for the fast and precise study of charged
particle dynamics in 3D electric and magnetic fields [13]. Simulation of electron gun has
been carried out in CST-PS to study beam dynamics at the exit of electron gun.

12

Figure 2.7: Model of electron gun in CST

Figure 2.7 is the 3D model of the electron gun in CST. Figure 2.8 (a) shows potential
contours on the electrodes and (b) depicts electric field pattern and strength on gun’s
electrodes. For a low current application, electron gun has to be operated in temperature
limited regime in which cathode temperature (heater current) decide beam current.
Thermionic emission model (Richardson's law) has been selected for the particle emission
from cathode surface. Maxwell-Boltzmann distribution is chosen for particles (8036) at
the surface of the cathode. Beam trajectories at -80 kV cathode potential, aperture voltage
2 kV and temperature of 1250 K are shown in Fig. 2.9. Figure 2.10 is CST-PS simulation
result of beam current as a function of cathode temperature. At 900 K, beam current is
2.3 × 10−9 𝐴 which increases up to 52 × 10−3 𝐴 at after 1700 K temperature limited
regime reach and cathode temperature has no effect on beam current. In order to increase
beam current after this temperature-limited regime we have to increase aperture electrodepotential.
13

Figure 2.8: (a) Potential contours on the electrodes of electron gun. (b) Electric field pattern andstrength among electrodes of electron gun.

In Fig. 2.9 beam waist is visible after aperture electrode this waist also cause beam haloin post anode region. To avoid beam halo a collimator has been used which will be
discussed in later section.

Figure 2.9: Beam trajectories from electron gun at -80 kV cathode potential, 2 kV aperture electrode andcathode temperature of 1250 K.

14

10 2

10 2

Beam Current A

1700K, 0.052A

10 3

10 3

10 4

10 4

10 5

10 5

10 6

10 6

10 7

10 7

10 8

10 8

10 9
1000

1500

10 9
2500

2000
Temp K

Figure 2.10: Beam current as a function of cathode temperature.

2.3.1.3 Twiss Parameters
To calculate Twiss parameters in post anode region, distribution of 8038 particles from
CST-PS have been taken. Figure 2.11 is a transverse (x-y) cross section of a beam at 50mm away from the cathode. Figure 2.12 and 2.13 are x-phase space distribution and yphase space distribution respectively.

εrms 

x  x  x  x   x  x x  x 
2

2



2
xrms

2

(2.3)
(2.4)

 rms

( xx) rms

(2.5)

2
xrms

(2.6)

   2  1

(2.7)





 rms

 rms

15

Equation 2.3 is the statistical definition of emittance. Equation 2.4 to 2.6 are definitionof Twiss parameters, those are used to calculate Twiss parameters at the exit of anodefrom CST-PS output. Table 2.3 shows the results of these calculations.
0.03
1.0

0.02

0.0

Vz

0.01
Vx

Y mm

0.5

0.00
0.01

0.5

0.02
1.0

0.03
1.0
1.0

0.5

0.0
X mm

0.5

0.5

1.0

0.0
X mm

0.5

1.0

Figure 2.12: x-y cross section of beam in post

Figure 2.11: x-phase space of particle

anode region (50 mm away from cathode surface).

distribution at the 50 mm away from cathode.

0.03
0.02

Vz

Vy

0.01
0.00
0.01
0.02
0.03
1.0

0.5

0.0
Y mm

0.5

1.0

Figure 2.13: y-phase space of particle distribution at the 50 mm away from
cathode.

16

Only simulation study has been carried out for the electron gun, results are notconfirmed experimentally yet because our first target was to inject electron beam into thestorage magnet. In near future I will confirm these results experimentally.
Table 2.3: Twiss parameters at the exit of anode.

Parameters

Value
3.12×10-7

ε rms(m rad)



0.098



3.37



126.4
1

   2

2.3.2 Magnetic Lens
A magnetic lens is used to focus the electron beam after the anode of the electron gun.
Magnetic lens is consists of a coil of copper wires inside the iron pole pieces. A current
through the coils produces a magnetic field in the bore of the pole pieces. The rotationallysymmetric magnetic field is inhomogeneous in such a way that it is weak in the center ofthe gap and becomes stronger close to the bore. Electrons close to the center are lessstrongly deflected than those passing the lens far from the axis. The overall effect is thata beam of parallel electrons is focused into a spot.

Figure 2.14: Magnetic lens model with its dimensions.

17

The magnetic lens in test experiment is consists of a single coil with 560 windings and 5mm thick iron shielding. The magnetic lens length is about 30 mm. Magnetic lens is aircooled. The magnetic iron cover of solenoid provides a return path for magnetic field
screening effectively the field in the outer space and concentrating it inside solenoid gapof 5 mm. Focusing power (reciprocal of focal length) of a magnetic lens is given by thefollowing formula [14]1e2
 2 2 2 2  ( Bz )2 dz
f sol 4  m c(2.8)

Figure 2.14 is showing the schematic of magnetic lens. Figure 2.15 (a) and (b) arerepresenting absolute value of magnetic absolute and radial component respectively.

Figure 2.15: (a) Absolute value of magnetic lens. (b) Radial component of magnetic field.

18

Magnetic Lens Effect on Beam focusing
1.2

X(cm)

1
0.8

1.4 A

0.6

1.3 A

0.4

1.2 A
1.1 A

0.2

1.0 A

0
0

10

20

30

40

50

60

Z(cm)
Figure 2.16: Transverse beam size (+x direction) as it is evolving in beam direction. Different colors
curves show focusing strength of magnetic lens at different magnetic lens current.

To find the optimal condition for the focusing of the electron beam by the use of themagnetic lens, tracking simulation in CST-PS has been carried out. Figure 2.16 present
magnetic lens effect on focusing of the electron beam. Magnetic lens center position is 11
cm in Fig. 2.16. Different colors correspond to different values of magnetic lens current.
Collimator position is assumed at 50 cm away from the electron gun. As we change thecurrent of magnetic lens, the focal length of beam change. At current 1 A, beam almost
focus at collimator, which means most of the beam will pass through collimator without
much dissipation. I performed this simulation study but so far didn’t have chance to checkthese values experimentally due to other more important ongoing studies in theexperiment.

2.3.3 Main Dipole Magnet
As a part of SITE, a dipole magnet was designed, fabricated, and tested. The magnet
design and geometry are resulted on Ø 46 mm circular poles with a gap of 18 mm andyoke size of 103 mm × 140 mm. In the simulation, linear material with permeability of19

5000 was used, which is close to actual material used in magnet fabrication. The magnet
consists of two coils with 32 windings each.
Bending radius  of a particle moving in a magnetic field applied to transverse direction
can be calculated by magnetic rigidity

10 p(GeV )c
B  (T  m)
2.9979(2.9)

Taking radius of curvature ρ = 100 mm, for 80 keV electron beam, magnetic fieldrequired to bend the beam is 125 gauss. To find out number of Ampere-turns
NI 

Bg

(2.10)

0

For a pole gap of g = 18 mm, number of ampere-turns required are NI = 180. Figure
2.17 (a) present design of dipole magnet and its dimensions (b) is showing CST-EM
results of 3D field distribution. Transverse magnetic field profile along z-axis are shown

Figure 2.17: (a) Design of bending magnet and it dimensions. (b) CST-EM results of magnetic field
pattern and strength.

in Fig. 2.18. Blue curve in Fig. 2.18 are measured values and red curve is showing the
CST simulation results.

20

Figure 2.18: Transverse magnetic field profile along z-axis. Blue curve is measured values and red
curve is CST simulation results.

Figure 2.19 is the transverse field map on y-z plane. Figure 2.20 present measured B0of dipole magnet as a function of current.

Figure 2.19: Transverse magnetic field map on Z (mm) and Y (mm) plane.

21

B0 Gauss

130
120
110
100
90
2.0

2.2

2.4
2.6
Current A

2.8

3.0

Figure 2.20: B0 of dipole magnet as a function of current.

Magnetic field of the dipole magnet was measured by “Alpha lab Gauss meter”,(Resolution 0.01 Gauss, Max. 800G) [15]. Successful injection of the electron beam
highly depends upon the injection angle, which is determined by the dipole magnet
strength and effective length. The effective length of dipole magnet at the current 2.79 Afrom measured magnetic field values is 59.4 mm and deflection angle is 43o.



B0 leff

𝑙𝑒𝑓𝑓 =

 43o(2.11)∫ 𝐵𝑑𝑙= 59.4𝑚𝑚
𝐵0(2.12)B

The deflection angle and effective length from CST simulation are 61.4 mm and 44.4o
respectively. The difference between measured values of the magnetic field and CST
simulation arises due to imperfect coils shape of dipole magnet and parallax error insetting position of hall probe. Moreover, center of the dipole magnet was not determined
precisely.

22

2.3.4 Differential Vacuum System
Differential pumping is a technique in which large pressure difference is maintained
between different regions of a single vacuum system. The pressure difference ismaintained by a small aperture between the two parts and extra pumping on the highvacuum region part.
In the straight section of beam line, a high vacuum is require to protect electron gun
and transfer electron beam without any disturbance but in the storage chamber, a medium
vacuum is needed to fill it with N2 gas to observe fluorescence light due to ionization of
nitrogen gas along a beam path. Differential vacuum pumping has been employed tomaintain the high vacuum ( 1.5 × 10−6 𝑚𝑏𝑎𝑟) in straight beam line and medium
vacuum (1.5 × 10−3 𝑚𝑏𝑎𝑟) in the storage magnet. A collimator of 3 mm diameter and 5mm depth is used to separate two vacuum regions. Figure 2.21 is showing the collimatorand dipole magnet. The collimator is also reducing a beam halo and related backgrounds.

Figure 2.21: Collimator and dipole magnet.

23

2.3.5 Particle Tracking of Straight Beam Line in CST-PS
In order to check beam dynamics in straight beam line particle tracking in CST-PS has
been carried out. For the simulation of straight beam line three components wereconsidered namely
Electron gun

Magnetic lens

Dipole magnet

There are five weak steering coils along straight beam line are present to overcome
misalignment of the beam line. For CST-PS simulation, steering coils, have been ignored
due to simplicity. Figure 2.22 is the representation of straight beam line, which starts fromthe electron gun and follows magnetic lens, collimator and bending magnet.
Figure 2.23 shows the tracking of electron beam through beam line elements. Figure2.24-26 are transverse cross section (x-y) and phase space (x-x'), (y-y'), (x'-y') at the exitof the electron gun, collimator and after collimator respectively. It is clear in Fig. 2.25 aselectron beam reach to the collimator beam size and halo grows. The collimator removes
beam halo as it is mentioned in Fig. 2.26 but it also reduced beam intensity. From electron
gun, beam current was 74 μA and it reduced to 11.2 μA after the collimator. This study is
not verified experimentally yet, because our major goal was to inject electron beam into
the storage magnet. In near future this study will be verified experimentally.

24

Figure 2.22: Schematic of beam line components in straight section.

Figure 2.23: Tracking of beam through straight beam line component.

25

Figure 2.24: Beam phase space at the exit of electron gun

Figure 2.25: Beam phase space at the collimator

26

Figure 2.26: Beam phase space after collimator.

27

2.3.6 Storage Magnet
Storage magnet is a solenoidal electromagnet placed inside a cylindrical iron yoke ofheight 800 mm and diameter of 600 mm, the thickness of iron yoke is 5 mm. Top andbottom sides of the iron yoke are closed by 20 mm thick iron plate to avoid field leakage
from the storage magnet. The iron poles of 120 mm height and thickness 20 mm areplaced at the center of the top and bottom iron plates. Both upper and lower iron plates
have four viewing windows. Upper windows are used to install CCD camera, vacuum
valve and feed through for fluorescent plate. Lower windows will serve to inject electron
beam and some diagnostic components.

Figure 2.28: Storage magnet and vacuum

Figure 2.27: Schematic view of storage

chamber.

magnet with reference trajectory andmonitors.

28

The main solenoidal coil is 540 mm in height and its inner diameter is 440 mm. The
auxiliary coil of 80 mm height is mounted at the center plane of the main coil to provide
weak focusing.
n

Ro B yBoy x

Focusing condition is 0 < n < 1. Figure 2.27 is the schematic of storage magnet andalso describes the beam monitoring inside storage magnet. Inside storage magnet, avacuum chamber of height 680 mm and diameter of 400 mm is installed, that is shown in
Fig. 2.28.

2.3.6.1 Field Measurement
The magnetic field is measured using a Gauss meter (Lakeshore model 460) with athree-axis hall probe. The hall probe was movable vertically and radially. Figures 2.29
show results of field measurements as a function of vertical position (z). The main drive
current was fixed at 8 A. Colored data correspond to different drive currents (0 ∼ 10A)

Figure 2.29: Left. Measurement of BZ component as a function of vertical position. Color data correspondto different auxiliary coil current Grey data represent OPERA results. Right: BX component as a functionof vertical position.

29

of the auxiliary coil. The uncertainty of these measurements is estimated to be smaller
than 1 gauss. Gray solid lines show OPERA [16] calculations for comparison.
There is discrepancy between radial component in measured values and OPERA
simulation as shown in Fig. 2.29 right. During field measurement, some flanges wereopen but this effect is not included in OPERA model.

2.3.6.2 Particle Tracking in Storage Magnet
Particle tracking is one of key calculation to determine particles motion inside storage
magnet. Tracking calculations has been carried out in CST-PS studio. The magnetic fieldof storage magnet is calculated at main coil current 8 A and auxiliary coil current 4 A
which is correspond to central field strength B0 = 83 gauss and field index value n=0 at
median plane of storage magnet.

Figure 2.30: Single particle tracking in storage magnet field. Red circle is showing the starting pointof tracking calculation.

Figure 2.30 is showing the single particle tracking in the storage magnet field, red circle
30

is the entering point of particle. Beam encompass diameter of ~24 cm in the median planeof the storage magnet.

Figure 2.31: Left: Single particle tracking in the x-z plane of the storage magnet, which encompass~24 cm diameter orbit. Right: Single particle tracking in x-y plane of the storage magnet.

Figure 2.31 left is the representation of single particle trajectory in the x-z plane whichshows the diameter of tracking ~24 cm. Figure 2.31 right is showing the x-y plane oftrajectory as it moves in the upward direction vertically.

2.4 Second Stage Upgrade of Straight Beam LineThe second stage of SITE aims to upgrade following three items
 DC beam to pulse beam
 Magnetic Kicker to guide electron pulses to very center of storage chamber
 Beam monitors to measure storage time of electron beam and kicker efficiency
Development of electric chopper system for the generation of pulse beam has been
completed and will be described in the next section in detail. Magnetic kicker and beam31

monitors are still under plan stage.

2.5 Electric Chopper System
To produce pulse beam for the SITE, the original plan was to use RF cavity but due tohigh cost of RF source, it was decided to utilize some cheap and efficient option. Fast
response, simple structure and low cost make electric chopper system best choice for thegeneration of pulse beam.
For the electric chopper system structure designing process following aspects were A maximum effective field in the same deflecting voltage condition
 A minimum loaded capacitance of electrodes to achieve the fast rise/ fall time
The chopper voltage depends on the electron beam energy, the distance, and length ofthe plates and on the beam stop location. The required deflection voltage can be calculatedby the following equation
𝜃(𝛾𝑚𝑐2)𝛽2𝑉𝑑 =𝑑𝑙(2.13)

Where Vd is the deflecting voltage, l is the length of plate, 𝜃 is required deflection
angle, d is the gap length. 𝛾 𝑎𝑛𝑑 𝛽 are relativistic factor of beam.
𝑦=

𝑉𝑑 𝑙
(𝐷` )
2𝑑𝑉𝑎𝑐𝑐(2.14)

Equation 2.14 present the dependence of y on different parameters. Where y is distanceon which beam deflect, Vacc is the accelerating voltages of beam, l is the length of plate;
Vd is the deflecting voltage, d is the gap length. D` is the distance from the middle ofplates to dump location.

32

In our case, the electrode length was chosen 35 mm and mutual separation between
electrodes plates are 10 mm. The collimator to control beam halo and for differential
vacuum system will serve as a beam dumper for chopper system. The electron beam of
80 keV will be deflected on the collimator at a distance of 20 mm, which corresponds tothe deflection angle of 0.04 rad, which require deviating voltage of 1.6 kV. Schematiclayout of chopper system is given in Fig. 2.32. Table 2.4 presents geometrical parameterof chopper system.

Figure 2.32: Schematic layout of chopper system.
Table 2.4: Geometrical parameter of electric chopper.

Parameters

ValuesInjected beam energy

80 keV

Chopper Deflecting voltages

1.6 kVElectrode length

35mm

Aperture (width

20mm×10mm

height)Deflection angle

0.04radFigure 2.33 is showing the effect of electrode length on required deflecting voltages
and electric field to deflect electron beam on collimator. As mentioned in the equation
2.13 the required deflecting voltages to deflect the beam of constant energy and angle
reduce as we increase the length of chopper electrodes.
33

Figure 2.33: Left: Effect of length of chopper’s electrode plates on required deflecting voltages. Right:
Effect of electrodes length on electric field.

Figure 2.34: Left: Capacitance of chopper plates as a function of chopper electrode length. Right:
Charging time of chopper electrodes as function of electrode’s length.

Capacitance and full charging time of chopper plates also depend upon length ofchopper’s electrodes. Figure 2.34 present the effect of electrodes length on capacitanceand charging time.

2.5.1 Electrical Design
The schematic of electrical design of the chopper system is presented in Fig. 2.35. The
high voltage power supply is connected to pulse generator, which acts like a switch. Pulse
generator alternatively connects the electrode to ground and to the positive and negative
high voltage power supply following the timing signal repetition rate and pulse widthfrom a function generator (trigger).

34

The key component of chopper system is PVX 4140 pulse generator. Agilent 81101A
function generator is used to feed timing signal for pulse generator. Parameters forchopper’s power supply system are given in Table 2.5.

Figure 2.35: (a) Electrical design of chopper system. (b) Ideal beam pulse generated by electricchopper system.

Table 2.5: Electrical parameters for chopper system.

Parameters

ValuesMax Voltage
PVX 4140±3.5 kV

Pulse rise/ fall time

≤25 ns 3500V (load)

Loaded capacitance

50 pF

Pulse width

50 ns to DC
Controlled by input gate Agilent
81101A

Pulse Recurrence Frequency

Controlled by input gate
50Hz, Agilent 81101A

35

2.5.2 Mechanical Design
The mechanical assembly of chopper system is shown in Fig. 2.36. A cross beam pipeof asymmetric diameter is used to host the electrodes. Bigger diameter pipe is used to
produce easy support structure for the insertion of electrodes. Each electrode is consist ofa plate of 3 mm thick stainless steel sheet supported by two a ceramic column. They are
inserted from opposite sides and their vacuum flange supports each one. The groundelectrode is directly connected to the flange while the polarized plate is welded to the
Miniature High Voltage (MHV) feed-through connector. Figure 2.37 (Left) present the
support structure and feed through connection to the H.V plate, Right is showing the crosssection of electrodes assembly in the vacuum chamber. The ceramic feed through is astandard 5 kV single ended coaxial MHV connector.

Figure 2.36: Mechanical structure and dimension of chopper system.

36

Figure 2.37: Left: H.V electrode and its support. Right: Chopper’s electrodes in vacuum chamber

2.5.3 CST Simulation
To check electric field profile and examined the effect of maximum electric field on
vacuum chamber walls, simulation of chopper system is carried out in CST-EM studio.
1.6 kV were applied to the lower electrode plate while upper plate and vacuum chamber
were at ground potential. Figure 2.38 left shows the potential contours over cross sectionof chopper system and right present the electric field profile over cross section of beam
pipe. The equipotential lines near high voltage electrode are dense which indicates a large
electric field in the z direction. Maximum field calculated from analytical formula andfrom simulation are in agreement with each other. Figure 2.39 present the uniform regionof electric field in the x-z plane of chopper’s plates.

37

Figure 2.38: Left: Potential contours on the electrodes. Right: Electric field pattern of electrodes invacuum chamber of chopper system.

Figure 2.39: Electric field profile in (x-z)-plane.

382.5.4 Experimental Setup
All electrical components used in chopper system are commercially available devices.
The electrical components used are as follow
1) Pulse generator: DXI PVX 4140
2) Function generator: Agilent 81101A
3) Matsuda H.V power supply
4) Oscilloscope: Tektronix
The PVX-4140 pulsar is used to generate pulse voltage for chopper system. The PVX4140 features single-ended output pulses from ground to +3500V or from ground to 3500V, and can also generate pulses originating from a voltage offset from ground. Riseand fall times is 25 ns and minimum pulse width is 50 ns with maximum frequency of 30
kHz. H.V power supply from MATSUDA Precision [17] is used to provide H.V to thepulse generator. Agilent 81101A function generator [18] is used to trigger the PVX-4140
pulse generator [19]. It offer maximum frequency 50 Hz and an individually adjustablepulsed width and pulse delay. 5 V output from function generator is used to trigger pulse
generator. Detail setup and equipment are depicted in Fig. 2.40. Figure 2.41 shows theoutput of 100 V from pulse generator.

39

Figure 2.40: Electrical component setup for chopper system (DC power supply, pulse generator,
function generator)

Figure 2.41: Output from PVX 4140 Pulse generator on Tektronix 5054 Oscilloscope

40

Chapter 3
Beam Commissioning and Results
Conventional fluorescent screen monitors were used to detect electron beam transverse
profile during the commissioning and operation of SITE in the straight beam line. In orderto monitor the electron beam in a non-interceptive way, storage magnet was filled withnitrogen gas and fluorescent light due to the excitation of nitrogen gas was observed using
a Charge Coupled Device (CCD)-camera. In this chapter setup of beam monitors instraight beam line and storage magnet and their results will be described in detail. Several
challenges had to overcome during the beam commissioning from the straight beam line
to the storage magnet. Those problems will also be discussed in this chapter.

3.1 Beam Commissioning and Monitors in Straight Beam Line
Fluorescent screen (FS) monitors is a simple interceptive beam diagnostics device tomeasure the transverse beam profile. When a charged particle collides with a material its
energy loss can be converted to fluorescence light. The released light output from FS isin the optical wavelength range (450 nm <λ< 700 nm). A CCD-camera can be used tocapture light from FS. High dynamic range, no absorption of emitted light, radiation
hardness, fast decay time and good mechanical properties makes FS one of best choicefor intercepting beam diagnostic [21-22].
The FS material is made of Al2O3 and doped with Cr activator. Black and White (B/W)
Hamamatsu Chilled CCD camera (model C5985) and digital camera were used to capture
fluorescence light. FS monitors were installed at the three different locations on thestraight beam line to investigate beam profile at those locations. First diagnostic FS isplaced on the collimator perpendicular to the beam direction and the light extraction
41

mirror was placed at 45o with respect to the FS. Mirror guide fluorescent light to thedigital camera. Figure 3.1(a) is the schematic of first FS monitor and (b) is showing themirror and FS monitor used in experimental setup.

Figure 3.1: (a) Schematic of the first FS monitor (top view). (b) Mirror and FS used in first monitor.

Figure 3.2: Top view of straight beam line and first FS monitor.

42

Figure 3.3: Beam profile from first FS monitor.

Beam profile from the first FS monitor is shown in Figure 3.3. Second diagnostic FS
monitor is placed at the end of straight beam line at 45o with respect to the beam direction
and CCD camera-1 is adjusted below the screen to capture fluorescent light. The detailsetup is depicted in Fig. 3.4. Figure 3.5 (a) shows the schematic of second FS monitors.

Figure 3.4: Beam diagnostic at injection region.

43

Figure 3.5: (a) Schematic of interceptive FS monitor used in straight beam line (b) and on theinjection pipe.

Figure 3.6: (a) Beam spot on FS monitor in straight section of beam line. Original black and white
image was converted to false color for better visibility. (b) Intensity of beam as a pixel values on x andy axis.

Figure 3.7: (a) Beam spot on FS monitor after dipole magnet. Original black and white image wasconverted to false color for better visibility. (b) Intensity of beam as a pixel values on x and y axis.

44Third FS monitor is placed after bending magnet and attached to pneumatic feedthrough. Pneumatic feed through inserts the FS into the injection pipe and vice versa. The
emitted fluorescent light from the FS was guided through a mirrors and glass viewport to
the CCD camera 2. This setup is elaborated in Fig. 3.4 and 3.5 (b), CCD-camera-2 wasused to capture fluorescent light from third FS.
In order to make pictures more visible image processing of black and white CCD
camera figures had been done in MATHEMATICA [23] and “imagej” [24] software. False
colors have been added to the original B/W photos for better visibility.
Figure. 3.6 (a) is the beam profile from second FS monitor and captured by CCDcamera 1, (b) represent the x-y projection of beam in terms of image pixel. Figure 3.7 (a)is the beam profile from the third FS monitor, which is placed after the bending magnet
and image was captured by CCD-camera 2. Figure 3.7 (b) represent the x-y projection ofbeam in terms of the image pixels. Beam profile after dipole magnet is twisted vertically
due to focusing effect of bending magnet. When we filled storage magnet with N2 gas it
also results in increased pressure in injection region. Due to the excitation of nitrogen gas
in the injection region path of the electron trajectory become visible. Detail of thisphenomena will be described in section later section. Figure 3.8 is depicting the electron
beam path when it enters into the storage magnet. Red dotted line is the encasing of beam
trajectory which presented as Region of Interest (ROI).

45

Figure 3.8: Beam trajectory in injection region while Storage chamber was filled with N2 gas.

3.2 Issues during the Beam Commissioning
Many issues have to overcome during the beam commissioning from the straight beamline to the storage magnet. Some modifications in the original plan were made in order toovercome these problems. Before discussing the detail of results from the storage magnet,
challenges faced during the beam commissioning into the storage magnet will be
described briefly. Following are some selective issues, those will be described briefly
 Beam hit at injection pipe Field leakage from injection hole
 Alignment stage for storage magnet
 Wrong polarity of auxiliary coil of storage magnet

3.2.1 Beam Hit at the Injection Pipe
In trial operation of beam commissioning in the storage magnet we did not succeed in
injecting beam into the storage magnet due to the particular shape of the beam pipe. Old
beam had bellows on both sides of pipe which makes it bend in the center region as shown46

in Fig. 3.9. Red circle in Fig. 3.9 is showing the hit point with temperature 43.3oC. Dueto this center bend at injection pipe, beam couldn’t enter into the magnet. Using thermal
camera beam hit at injection pipe has been confirmed as it is shown in Fig. 3.10.
To overcome this problem a new beam pipe was prepared with straight pipe near the
injection and installed on the beam line as shown in Fig. 3.11. After the replacement ofbeam pipe, electron beam successfully injected into the storage magnet and confirmed byusing FS monitors.

Figure 3.9: Old and new injection pipe for the injection of electron beam in storage magnet.

47

Figure 3.10: Beam hit at the injection pipe. Red circle is showing the hit point with temperature
43.3oC.

Figure 3.11: New injection beam pipe.

48

3.2.2 Field Leakage from the Storage Magnet
Successful injection highly depends upon on the incidence angle of the electron beam
into the storage magnet. In trail operation of beam injection, it was found that injection
angle cannot be controlled by only one bending magnet due to the leakage field frominjection hole of storage magnet as depicted in Fig. 3.12. Second dipole magnet was
installed on injection pipe to compensate the effect of the leakage field from the storage
magnet as shown. Figure 3.13 is showing the second dipole magnet. Figure 3.14
represents the second dipole magnet on the injection beam pipe.

Figure 3.12: Field distribution around the storage magnet.

49

Figure 3.14: Second dipole magnet Figure 3.13: Additional bending magnet on the injection
to compensate field leakage frompipe of storage chamber.

storage magnet.

3.2.3 Alignment Stage for the Storage Magnet
In order to align the storage magnet with respect to the straight beam line an alignment
stage has been installed beneath the storage magnet. The alignment stage is able move thestorage magnet 2 mm in left and right and also in up and down stream directions.

Figure 3.15: Alignment stage for the storage magnet.

50

3.2.4 Polarity of the Storage Magnet Auxiliary Coil
Auxiliary coil is mounted on the main coil of storage magnet to provide weak focusing
in the median plane. The polarity of the auxiliary coil should be opposite to the polarityof main coil in order to provide weak focusing in the median plane. For many early trials
of beam injection into the storage magnet the polarity of the auxiliary coil was wrong(polarity of main coil and auxiliary coil was same). The wrong polarity of auxiliary coilchanges the required field profile at the center of the storage magnet. Fortunately, during
the inspection of the storage magnet power supplies, we found the problem of the wrong
polarity and fixed it.

By
Correct Polarity

120

Wrong Polarity

By (Gauss)

100
80
60
40

20
0
-400

-200

0

Y (mm)

200

400

Figure 3.16: Axial field profile of (By) of storage magnet. Orange is showing the field profile withwrong polarity and blue is correspond to correct polarity of auxiliary coil.

Figure 3.16 and 3.17 are axial and radial field profile from CST-EM simulation. Red
curves are correspond to the field profile at the wrong polarity of auxiliary coil while blue
curves represent filed profile at correct polarity.

51

Bx

15

Correct Polarity

Wrong Polarity

Bx(Gauss)

10
5

0
-5
-10
-15
-400

-200

0

Y (mm)

200

400

Figure 3.17: Radial field profile. Orange correspond to wrong polarity and blue is with correct polarity ofauxiliary coil.

3.3 Beam Monitors in the Storage Magnet
In the first stage of the SITE two kinds of beam diagnostic monitors have been used instorage magnet 1) Interceptive fluorescent screen monitor to detect vertical positon ofbeam 2) Non-interceptive beam induced fluorescence monitors to observe beam track in
N2 gas. In this section beam monitoring for the first stage of SITE in the storage magnet
will be discussed in detail.

3.3.1 Interceptive Monitor in the Storage Magnet
To find the vertical positon of beam inside storage magnet FS monitor had been
attached to the vacuum linear feedthrough. Linear feedthrough can move fluorescentscreen position vertically up and down. A mirror was positioned in front of FS to reflect
light from FS to the CCD-camera (Hamamatsu-C5985). Mirror angle was adjustable form
the outside to span complete vertical positon of fluorescent screen. Schematic view ofthis setup is depicted in Fig. 3.18.

52

Figure 3.18: Schematic view of fluorescent screen monitor to detect vertical position of beam instorage magnet.

Figure 3.19: Left: Upper Iron yoke view of storage magnet which consist of CCD-camera, linear
feedthrough and valve for N2 gas. Right: Inside view of storage magnet from B/W CCD camera.

53

Figure 3.20: (a) Image of fluorescent screen in mirror viewed by CCD-camera without beam. (b) Beamspot at fluorescent plate in the absence of magnetic flied of storage magnet. (c) Beam spot in thepresence of magnetic field of storage magnet.

Figure 3.19 is the representation of experimental setup of monitors in storage magnet.
Figure 3.20 (a) is the image of fluorescent plate from CCD-camera without beam. Figure
3.20 (b) and (c) represent beam profile at FS without and with the presence of magnetic
field in the storage magnet respectively. In the presence of the magnetic field beam deflectaround 1 cm on FS radially which is in agreement with CST-PS tracking results.

3.3.2 Non-interceptive Monitor in the Storage Magnet
Conventional intercepting monitors are not applicable to observe the electron beam
track in the storage magnet. Non-interceptive beam monitoring in the storage magnet todetect electron beam track is a challenging task due to the mechanical constraint of thestorage magnet geometry. To detect electron beam track in the storage magnet nondestructively fluorescent light due to the introduced nitrogen gas has been detected byusing a CCD-camera. In this section the working principle of the gas monitor will be
described and after that results of nitrogen gas monitors from the storage magnet will bepresented.

3.3.2.1 Working Principle
When the charge particles collides with the residual gas or specially introduced gas,54the molecules of gas are not only ionized, but also excitation of internal energy levels canoccur. The excitations of gas decay electromagnetically by the emission of fluorescencelight. The excitation of N2 gas results in a transition spectrum in the optical region. The
spectrum is originated by the decay of molecular ions N+2 excited by the collision withthe beam ions in the wavelength range 390 nm <λ< 470 nm.
In high vacuum the most prominent vacuum constituent is nitrogen gas. N2 gas pressure
can be increased by the help of regulated gas valve in case of low signal strength. The
fluorescence light can be monitored by a CCD or CMOS camera [21, 23, 24].

3.3.2.2 Setup
As depicted in Fig. 3.19 (a) non-invasive nitrogen gas monitor setup consist of MKS
N2 regulated valve [25] and Hamamatsu CCD camera model C5985 [26]. All of thesedevices were located outside of the storage magnet. The regulated valve is a general
purpose mass flow controller valve from MKS instrument and used to fill the storage
magnet with N2 gas in controlled manner. By the use of the controlled valve storage
magnet’s vacuum chamber pressure was maintained to 1.5×10-3 mbar.
Hamamatsu 5985 high resolution chilled CCD camera is used to capture fluorescencelight from storage chamber. The B/W Chilled CCD camera features high-sensitivity underfaint light conditions, which are difficult to achieve with conventional B/W CCD cameras.
Exposures time is 1/10,000 sec to 300 sec and spectral response is 400 to 700 nm [26].

3.4 Experimental Results of the Non-interceptive Monitor
The electron beam has been injected into the storage magnet with several different
injection angles and was observed with a non-interceptive gas monitor. In this section,different injection angle studies and electron beam visualization results from the gas

55monitor will be described in detail.

3.4.1 Electron Beam Injection at Lower Injection Angle
In order to find the correct injection angle for the injection of the electron beam into
the storage magnet, injection study has been performed with several different injection
angles. Injection angle of the electron beam was varied with the help of the two dipole
magnets. Particle tracking in CST-PS also has been done in order to understand theexperimental results. Firstly beam injection was performed at the lower angle, which
results in beam hit at the lower plate of the vacuum chamber of storage magnet. Figure
3.21 represents the single particle tracking in CST-PS when the beam was injected into
the storage chamber at the lower angle. In the Fig. 3.21 (a - d) injection angles were varied
from 42.0o, 42.5 o, 43.0 o and 43.5 o respectively. At these angles beam hit at the vacuum
chamber of the storage magnet. When the injection angle was increased in the steps of
0.5o beam hit position advanced on the vacuum chamber base plate. Figure 3.22 (a – d)
are the experimental results from the gas monitor of the storage magnet. False colors areadded to the original Black and White images for better visibility. Figure 3.22 (a - d)represents the case when the electron beam was injected in the storage magnet at the
injection angle about 42.0o by the help of main dipole magnet. Small variation in therange of 0.5o were introduced by the help of the second dipole magnet. It is evident fromthe Fig. 3.22 (a – d) as the injection angle increases beam hit position advanced on thelower plate of the vacuum chamber.
Reflection from the Storage Magnet Vacuum Chamber:
Reflection from the chamber walls and from lower the base plate is the cause of unwanted
light background in Fig. 3.22. In order to observe beam more clearly it is planned toblacken the chamber walls in order to avoid the light reflection. Detail of this plan will56

be described in the next section.

Figure 3.21: Single particle tracking in CST-PS at the different lower injection angle, (a - b) arecorrespond to the injection angle of 42o, 42.5o, 43o, 43.5o respectively. As injection angle increased
beam hit advanced on the vacuum chamber of the storage magnet.

57

Figure 3.22: Gas monitor results from the storage magnet. The electron beam was injected into thestorage magnet at 42o. Small variations in the range of 0.5o were introduced by the help of the second
dipole magnet. (a - d) are correspond to the cases when the injection angles were increased up to 43.5o.
(False colors are to the original B/W pictures for the better visibility)

As the injection angle increased the pitch distance between two turns also increase.

3.4.1 Electron Beam Injection at Higher Injection Angle:
In the next step, the electron beam injection was performed at the higher injection angle
in the storage magnet. Figure 3.23 represents the particle tracking in CST-PS at the higher
injection angle. In Fig. 3.23 (a - f) beam was injected into the storage magnet at 44o, 44.5o,
45o, 45.5o, 46o, 46.5o, 47o respectively. Only two turns appear at those higher angle.
Figure 3.24 is the representation of the experimental situation when the electron beam
was injected into the storage magnet at the injection angle 44o by using the main dipole
magnet and variations in the injection angles were introduced by the help of the second
58dipole magnet. Figure 3.24 (a – f) shows the case when the injection angle was increasedin the steps of 0.5o up to 47o. Figure 3.23 and 3.24 are not perfect one to one
correspondence and view of observing trajectory in both figures is also different.

Figure 3.23: Single particle tracking in CST-PS at the different high injection angle, (a - f) arecorrespond to the injection angle of 44o, 44.5o, 45o, 46o, 46.5o, 47o, respectively. Only two turns arevisible at those higher injection angles. As injection angle increase distance between these two turns
also increase.

59

Figure 3.24: Beam injection into the storage magnet at the higher injection angles. Injection angle was
44o from the main dipole magnet and small variations in the injection angles were introduced by using
the second dipole magnet. (a -f) are the case when the injection angles were increased in the steps of
0.5o up to 47o. (False colors are to the original B/W pictures for the better visibility)

3.4.1 Electron Beam Injection at (43.5o < injection angle < 44o)
After performing the above mentioned injection angle studies, electron beam was
injected into the storage magnet in the angle range of 43.5o < injection angle < 44o.
Particle tracking study in this injection angle range in CST-PS is shown in Fig. 3.25, thisinjection angle is correspond to multi turns injection. Figure 3.26 is the picture from thegas monitor of the storage magnet, when the electron beam was injected into the storage
magnet at the angle greater than 43.5o and less than 44o (43.5o < injection angle < 44o).
In the Fig. 3.26 the first turn of the electron beam appear clearly but after completing firstturn beam start diverging. Although the reference trajectory is present but as a collectively
beam lost its intensity and we cannot observe the beam as fluorescent light from the gas
monitor.
As explained in the section 3.3.1, FS monitor was installed in the storage magnet inorder to detect the vertical position of the electron beam. In the case of injection angle
60

(43.5o < injection angle < 44o), beam hit at the FS monitor at its maximum position was
still observed even we lost beam after the first turn. Beam lost its intensity but sometrajectories goes up to the top of the storage magnet. Therefore, some part of beam hit at
the FS monitor in the case of defocusing too.

Figure 3.25: Single particle tracking in the storage magnet at the angle 43.5o.

Figure 3.26: The electron beam injection into the storage magnet at the angle greater than 43.5o andless than 44o (43.5o < injection angle < 44o).

61

3.5 Defocusing of the Electron Beam in the Storage Magnet
Figure 3.25 is the case of single particle tracking in CST-PS when the electron beam
was injected into the storage magnet at the injection angle greater than 43.5o and less than
44o (43.5o < injection angle < 44o), in this case multi turns appeared in the storage magnet.
But multi turns were not observed in the experiment. Therefore, multi particle tracking
with 500 particles also had been performed to understand the situation and it was foundthat the electron beam start diverging after the first turn in the case of multi particle beam.
Figure 3.27 (b) is the multi particle tracking in the storage magnet, it evident from the Fig.
3.27 (b) that beam start diverging after completing the first turn. Defocusing of the beam
happens due to the particular shape of the radial field profile of the storage magnet. Radial
field of the storage magnet varies very rapidly along the axial position of the storage
magnet, thus electron beam of finite size at different vertical positions experience
different radial field and hence take different path in the storage magnet. Radial field
profile of the storage magnet and its derivative are shown in Fig. 3.28 left and right.

Figure 3.27: (a) At the injection angle greater than 43.5 and less 44o (43.5o < injection angle < 44o)multi turns appears. (b) Multi particle tracking in the storage magnet shows defocusing of electron
beam the storage magnet.

62

Figure 3.28: Left: Radial field profile of the storage magnet. Right: is the derivative of radial filed
profile with respect to the solenoidal axis of the storage magnet.

3.6 Solution for Defocusing of the Electron Beam
In order to solve defocusing of the electron beam in the storage magnet Twiss
parameters at the injection point are needed to be controlled. Reverse tracking with finite
size distribution of the electron beam from the center of the storage magnet has been
performed in CST-PS to estimate the required Twiss parameters at the injection point.
Radial field of the storage magnet varies rapidly axially in the storage magnet but inradial direction it do not change much. Therefore, particle distribution of length 1 mm (11particles) radially with no vertical distribution has been assumed. Figure 3.29 represent
the assumed distribution of particles at the distance of 120 mm radially from the centerof the storage magnets. Particle tracking in 3-D coordinates are shown in Fig. 3.30.

Figure 3.29: Assumed particle distribution at the radius 120 mm in the storage magnet.

63

Figure 3.30: Multi-Particle tracking in the storage magnet.

Figure 3.31 shows the particle tracking in x-y vertical plane and x-z radial plane of thestorage magnet. Black circle in the Fig. 3.31 right shows the required beam at the injection
point of the storage magnet. Figure 3.32 shows the phase space of the required beam at
the injection point. Table 3.1 summarize the required emittance and Twiss parameters of
the beam in both transverse direction (x-z).

Figure 3.31: Left: Multi-Particle tracking in the x-y plane of the storage magnet. Black circle represent
the required beam shape at the injection point. Right: Particle tracking plot in the x-z plane.

64

2.0

0.01

1.5

0.5

X ` rad

Y cm

1.0

0.0

0.00

0.01

0.5
1.0

0.02

1.5
1.5

1.0

0.5

0.0

0.5

1.0

1.5

1.5

1.0

0.5

0.0

0.5

1.0

1.5

X cm

0.04

0.04

0.02

0.02

0.00

0.00

Y ` radY ` rad

X cm

0.02

0.02
0.04

0.04

0.06

0.06
1.5

1.0

0.5

0.0

0.5

1.0

1.5

0.02

2.0

0.01

0.00

0.01

X` cm

Y cm

Figure 3.32: Phase space plots of the required beam at the injection point. Black point represent thereference trajectory.

Small emittance and straight beam is required at the injection point in order to overcome
the defocusing of the beam in the storage magnet. Quadrupole magnets are needed tocreate required beam at the injection point. Simulation in SAD (Strategic Accelerator
Design) will be carried out to estimate the required number of quadrupoles magnets andtheir specifications.
Table 3.1: Twiss parameters at the injection point of the storage magnet.

Twiss Parameters

Values𝜖x4.24 ×10-6 m rad

𝛽x

9.75

𝛼x

11.61

𝜖y

4.01×10-6 m rad

𝛽y

11.95

𝛼y

36.31

65

3.7 Future Plans
In the second stage of SITE, two major development are planned to complete Magnetic kicker system to kick electron pulses to the median plane Beam monitors

3.7.1 Reflection from Chamber Walls
Base plate of storage chamber and walls pose good reflective properties. Reflection offluorescent light from chamber is source of background in the pictures from gas monitors,
it is plan to blacken chamber wall to avoid light reflection.
Two option are under consideration
 Graphite powder solved in Isopropanol (Aerodag g) [29]
 Light Exclusion Sheet Super Black from SHIBUYA OPTICAL CO.,LTD [30]3.7.2 Magnetic Kicker
Kicker coils will be used to kick the electron pulses at appropriate position in storage
magnet and direct it to median plane (storage region). After kick “pitch angle” (vertical
momentum) of electron pulses will become zero and finally electron pulses will be stored
in the storage region. Detail design and simulation study for the fabrication of kicker coilsystem will be done in second stage of SITE. To accumulate electron beam, effectively,a pulsed kicker should fire coincide with electron beam. Careful tuning works of timing
and kick power is required.
Followings are the major tasks associated with kicker system
 Simulation and fabrication of kicker coils.
 Design and fabrication of kicker coil’s pulsed current power supply.
 Trigger control system to fire pulse kicker coincide with electron pulses.
66

 Beam tracking studies in the presence of kicker coils for successful storage ofbeam.
Development and verification of this kicker system with electron beam is directly
related to the success of actual experiment’s kicker system. Understanding the operationof this novel kicker system for test experiment may reduce trial operation cost of J-PARC
muon g - 2/EDM experiment.

3.7.3 Beam Monitors:
Currently we are utilizing fluorescent plate and fluorescence light from N2 gas
excitation to detect electron beam inside storage magnet.
Due to the high voltage of kicker system gas monitor is not applicable after the
installment of the kicker system. N2 gas will also not provide any information about thestored beam. One possible candidate for non-interceptive beam monitor is the installationof two metal plates namely “pick-up plates” at the median plane of the storage magnet.
The measurement of induced electric field of electron pulses on these metal plates canprovide us information about the stored beam too.

67

Chapter 4
Summary and Conclusions
Three-dimensional spiral injection is one of a key idea for the new J-PARC muon g –2/EDM experiment. For the establishment of this novel scheme, the Spiral Injection Test
Experiment (SITE) by the use of the electron beam is under development at KEK Tsukuba
campus. SITE is divided into two stages. The first stage goal is to detect a DC electron
beam spiral track in the storage magnet as fluorescent light from nitrogen gas excitation
along the electron beam path. The second stage and final goal is to store pulsed electron
beam for the order of milliseconds. In the first stage of SITE, 80-keV thermionic electron
gun has been installed to produce the electron beam. A 2-m long beamline has been
constructed to transport an electron beam from an electron gun to the storage magnet.
Simulation study of straight beam line components has been carried out in CST-PS. At
three different locations on straight beam line fluorescent screen (FS) monitors have beenplaced and beam profiles at those locations were confirmed. Each component of beamline was described in detail.
Beam commissioning from straight beam line to the storage magnet has been done withthe help of five pairs of steering magnets and one main dipole magnet. The main dipole
magnet is one of the most important component in this experiment and used for injectionof the electron beam from the straight beam line into the storage magnet. Field
measurement of the dipole magnet has been done at a typical current value of 2.79 A
which corresponds to the field strength of 125 gauss and the effective length of dipole
magnet is estimated 59.4 mm which deflect electron beam at 43degree.
A solenoidal storage magnet has been designed, simulated and constructed. The storage

68

magnet for SITE represents all important features as in the E34 storage magnet. An
auxiliary coil is mounted on the center of the main solenoidal coil to provide weakfocusing in the storage region. Field measurement of the storage magnet has been
performed at the main coil current 8 A and different auxiliary coil currents (0 A, 2.2 A,
4.3 A, 6.5 A, 8.7 A, 10 A) with the uncertainty of 1 gauss.
Several challenges have to overcome during the beam commissioning into the storage
magnet. Some of them are summarized here.
1) During the electron beam commissioning from straight beam line to the storage
magnet, it was found that due to the particular shape of beam pipe (bellows on both endsof pipes: which makes it bend in the center region) beam hit at injection pipe. Afterconfirming beam hit by the thermal camera, injection pipe has been replaced withappropriate beam pipe (bellows in downstream direction replaced with straight pipe).
After replacing injection pipe electron beam has been confirmed in the storage magnet by
FS monitors.
2) For the alignment of the storage magnet with respect to the straight beam line analignment stage also has been installed.
3) For the initial trials of beam injection into the storage magnet polarity of the auxiliary
coil of the storage magnet was wrong. Due to which, injection was not completely
successful. After the inspection of power supplies for the storage magnet, polarity ofauxiliary has been fixed.
4) Due to the field leakage from the storage magnet injection hole, injected beam
couldn’t enter into the storage magnet at the designed angle. After detecting this problem
additional bending magnet has been installed at the injection pipe to overcome the field
leakage effect.
69

Storage chamber was filled with N2 gas to observe the electron beam in noninterceptive way due to the emission of fluorescent light from the nitrogen gas excitation.
80 keV electron beam in the storage magnet of 83 gauss field with the diameter of 24 cm
has been captured as fluorescent light by using Charge Coupled Device (CCD)-camera.
In order to understand the effect of injection angle on beam trajectory in the storage
magnet, the injection angle of the electron beam was varied and its effect on beam track
were observed.
Furthermore, it was identified that the electron beam vertically defocused due to theradial field of the storage magnet. Due to vertical defocusing of electron beam, only twoturns were observed clearly. In the next step, Twiss parameters at the injection region will
be controlled in order to solve vertical defocusing of the beam in the storage magnet.
In the first stage of SITE, the experimental setup was built successfully and throughmany systematic studies, the optimal conditions for experiment has been determined. The
goal of the first stage to detect electron beam track as a fluorescent light was achieved.
For the second stage of SITE, electric chopper system to produce pulsed beam wasdesigned, simulated and fabricated to produce electron beam of pulse length of 50 ns. The
mechanical design and electrical parameters of electric chopper system were described indetailed. Electric chopper system is almost ready to be installed on the beam line.
In the second stage the magnetic kicker coil system will be installed in order to guideelectron beam pulses to the very center of the storage magnet. Beam monitors also need
to be improved to confirm the storage of the beam. The second stage goal is to store
electron beam pulses for the order of milliseconds to prove the concept of newly
developed spiral injection scheme.

70References:[1] G.W. Bennet et al., “Final Report of the muon E821 anomalous magnetic momentmeasurement at BNL”, Phy. Rev D 73 (2006) 072003[2] H. Ando et al., “Technical Design Report for the Measurement of the Muon
Anomalous and Electric Dipole Moment at J-PARC”, unpublished[3] J. Bailey et al., “Final report on the cern muon storage ring including the anomalous
magnetic moment and the electric dipole moment of the muon, and a direct test of
relativistic time dilation”, Nucl. Phys. B 150 (1979)[4] P. Bakule et al., “Measurement of muonium emission from silica aerogel”, Prog.
Thero. Exp. Phy. (2013) 103C01[5] G.A. Beer et al., “Enhancement of muonium emission rate from silica aerogel with alaser ablated surface”, Prog. Theor. Exp. Phys. 2014 (2014) 091C01,[6] H. Iinuma, H. Nakayama et al., “Three-dimensional spiral injection scheme for the g2/EDM experiment at J-PARC”, Nucl. Instrum. Meth, Vol. A832, pp. 51-62 (2016).
[7] A.Yamamoto et al., “The super conducting inflector for the BNL g - 2 experiment”,
Nucl. Instrum. Methods Phys. Res. Sect. A 491 (2002) 23–40,[8] J. D. Jackson, Classical Electrodynamics, Second Edition (John Wiley & Sons, New
York, 1975).
[9] S. Ohsawa et al., “Performance of an electron gun for a high-brightness X-ray
generator”, J. Synchrotron Rad. (2008). 15, 258–261[10] C. Wall, R. Levine, “Physics laboratory manual”, Prentice-hall, Inc. (1962).
[11] S. Brody, S. Singer, “Experiment on thermionic emission of electrons”, Amer. J.
Phys. 38.

71

[12] H. A. Jones, I. Langmuir, “The characteristics of tungsten filaments as functions oftemperature”, GE Rev., vol. 30, pp. 354-361 (1927).
[13] http://www.cst.com[14] Electron Optics (Second Edition) by P. Grivet, P. W. Hawkes and A. Septier
ISBN: 978-0-08-016226-3[15] https://www.trifield.com/content/vector-magnitude-gaussmeter-model-vgm/[16] http://www.opera.com[17] www.matsusada.com/[18] Agilent 81101A http://www.keysight.com/en/pd-1000001729%3Aepsg%3Apro-pn81101A/pulse-generator-50-mhz?nid=536902328.536881944&cc=US&lc=eng[19] PVX 4140: http://ixyscolorado.com/[21] Lecture Notes on Beam Instrumentation and Diagnostics by Peter Forck GSI Joint
University Accelerator School January – March 2011 p.42
[22] R. Jung, G. Ferioli, S. Hutchins Proc. Diag. Instrum. Part. Acc. Conf. DIPAC 03,
Mainz, p. 28 (2003)[23] http://www.wolfram.com[24] http://https://imagej.nih.gov/ij/[23] P. Forck, Proc. Int. Part. Acc. Conf. IPAC 10, Kyoto, p.1261 (2010)[24] D. P. Sandoval et al., Proc. Beam Instr. Workshop BIW 93, Santa Fe, p. 273 (1993)[25] https://www.mksinst.com/product/Product.aspx?ProductID=1363[26] http://www.spectroscopic.com/Hamamatsu/Hamamatsu_Camera_Catalog.pdf[29] http://www.laddresearch.com/chemicals/aerodag-g[30] http://www.shibuya-opt.co.jp/eng/super_black.html

72Appendix A
Vacuum System of Muonium Production Experiment at
the J-PARC 2016A
Introduction:
Systematic studies has been performed to enhance Muonium yield from different silica
aerogel target at J-PARC from Jan. 14 to 16, 2017. Detail of experiment can be found in [1].
I was responsible for vacuuming of apparatus during my shit duty. In this section I will
describe the procedure of vacuuming during all runs and history of vacuum during all runs.
Figure A.1 is showing the apparatus of Muonium production experiment. Vacuum system isconsist of following components
1) Roughing Pump (Scroll Pump)
2) Turbo Molecular Pump
3) Needle valve (VN) connected to the main chamber to control speed of pumping4) TMP valve (VT)5) Gate valve between TMP and Main chamber
6) Valve for roughing pump VY.
7) Pirani Gauge [Active Pirani Gauge-M (APGM)] for low vacuum 1×10-4 Torr.
8) Cold Cathode Gauge [Active Inverted Magnetron-M (AIMS)] for high vacuum
1×10-8 Torr.
9) Vacuum Monitor and Logger to record vacuum data.
Special caution is required during pumping in the presence of fragile aerogel sample.
Therefore, one has to act on manual carefully in course of exchanging aerogel sample.

73

Figure A.1: Mu Production apparatus with Vacuum components labeled

Target Exchange:
During “silica aerogel target” change, one has to vent chamber first to open it and after
replacement of target vacuum again to maintain required operational vacuum value.
Aerogel targets are very fragile. Mishandling can easily damage targets. Fig. A.2 depicts
the inside view of the chamber with a target.
Aerogel target in its box is covered with papers on both sides, during placement oftarget in the holder try to fit it with paper first and then remove papers from both sides.
Figure A.3 is showing the aerogel target in the holder.

74

Figure A.2: Inside view of Chamber with Aerogel target

Figure A.3: Silica Aerogel target in holder

Vacuuming Procedure:
Vacuum manual is already available on run page website but for the sake of completion,
vacuum procedure is discuss here too.
1.

Close all valves (Gate valve, VN, VY, VT).

2.

Turn ON roughing pump (Scroll pump).

3.

Open VY (attached to roughing pump).
75

4.

Slowly open VN (attached to chamber) in more than 5 minutes. Wait for

1×101 Torr. Be very careful in the presence of target.
5.

When pressure reach to the 1×101 Torr close VY and VN.

6.

Open VT (attached to TMP) completely and wait for 2 minutes.

7.

Open Gate valve completely and wait for 1×10-1 Torr.

8.

Turn ON TMP and AIMS (gauge for high vacuum) within 7 minutes itwill reach to its maximum RPM 33600 and pressure ~ 2×10-5 Torr.
9.

If not check for leak e.g tight bolts.

Procedure of Venting:1.

Close Gate valve completely.

2.

Turn OFF TMP.

3.

Disconnect pipe of chamber from roughing pump.

4.

Slowly open VN in ~10 minutes to reach 7.6×102 Torr (atmosphericpressure). Again, be careful during this step.
5.

Now you are ready to open chamber.

Data logging:
During all runs, vacuum data in form of voltages was saved on midi LOGGER GL820.
After the completion of the experiment, we connected the logger to the PC via LAN andcopied all data. Data was in binary form we converted it into text form using GLconnection software freely available on vendor website [3]. We can also save data in text
form directly on logger but first, we have to choose the extension of file.
We used AIMS (Active Inverted Magnetron-M) for high vacuum monitoring. To
convert voltages into pressure I downloaded the table of conversion from vendor website[2] as shown in Fig. A.4 and write down these values in form of list into the76

MATHEMATICA Then I used “interpolation” command in MATHEMATICA toconstruct new data points within specified data range of this data.
I added timing correspond to each run in excel file then I imported that file into
MATHEMATICA and used its voltage data from CH2 as an input to “Interpolation”
command and drew Log graphs corresponding to each run.

Figure A.4: voltage to pressure conversion Table

Figure A.5: Time vs Vacuum Pressure History during all runs.

77Figure A.5 is representing the vacuum history for all runs. It also gives a rough estimateof run time for each sample. I have drawn vacuum history only for high vacuum gauge.
The cause of noise during preparation could be from activities around high vacuum gauge
during that data taking.
References:[1] T. Mibe, et al.,”Systematic studies on muonium production in vacuum from laserablated silica aerogel (2016A0180)”, MLF proposal.
[2] AIM-S-DN40CF: https://shop.edwardsvacuum.com/products/d14662000/view.aspx[3] http://graphteccorp.com/instruments/gl820/index.html

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