R. Iwai (ETHZ) on behalf of muCool collaboration
muCool: Towards a high-brightness ultra-cold positive muon beam line at PSI
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019
Muon beams at PSI
p+
• High power proton beam colliding graphite target
protons
π+μ+
surface muons from pions stopped on the target surface
x
π+/-
μ+/-
cloud muonspion decay-in-flight
• Surface μ+ at 4.1 MeV most widely used (Δx ~cm)
�2
1.4 MW cyclotron Production target
• Standard beam cooling techniques not applicable due to limited τμ (2.2 μs)muCool scheme
Large room for improvement in phase space quality
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019 3
muCool project
0 mm
10 mm
20 mm
30 mm
• Reduce energy (4.1 MeV → <1 eV) and beam size (10 mm → <1mm)
• Cryogenic He gas stopping target with complex fields
• Device to compress the phase space of a standard muon beam by 10 orders of magnitude
• Efficiency ~10-3
• Conserve initial polarisation
3
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019
Motivation
4
• Muon g-2/EDM
Particle physics
Test anti-matter gravity
• High quality Mu beam from SFHe
1S-2S spectroscopy μ+
e-
Solid state physics (μSR)
• Study thin materials, small samples
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019
Q
�5
Working principle (old)Working Principle
4
D. Taqqu, PRL97, 194801 (2006)
IN
OUT
Transverse compression
Longitudinal compression
Y. Bao et al., PRL 112, 224801 (2014)He gas
Muon Cooling: Longitudinal Compression
Yu Bao,1 Aldo Antognini,2,* Wilhelm Bertl,1 Malte Hildebrandt,1 Kim Siang Khaw,2 Klaus Kirch,1,2 Angela Papa,1
Claude Petitjean,1 Florian M. Piegsa,2 Stefan Ritt,1 Kamil Sedlak,1 Alexey Stoykov,1 and David Taqqu21Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
2Institute for Particle Physics, ETH Zurich, 8093 Zurich, Switzerland(Received 11 February 2014; published 4 June 2014)
A 10 MeV=c positive muon beam was stopped in helium gas of a few mbar in a magnetic field of 5 T.The muon “swarm” has been efficiently compressed from a length of 16 cm down to a few mm along themagnetic field axis (longitudinal compression) using electrostatic fields. The simulation reproduces the lowenergy interactions of slow muons in helium gas. Phase space compression occurs on the order ofmicroseconds, compatible with the muon lifetime of 2 μs. This paves the way for the preparation of a high-quality low-energy muon beam, with an increase in phase space density relative to a standard surface muonbeam of 107. The achievable phase space compression by using only the longitudinal stage presented hereis of the order of 104.
DOI: 10.1103/PhysRevLett.112.224801 PACS numbers: 29.27.-a, 14.60.Ef, 29.38.Db, 82.20.Tr
Standard muon (μþ) beams have a relatively high energyand poor phase space quality. A new scheme has beenproposed making use of stopped μþ in a He gas target [1].Through the stopping process high intrinsic phase spacecompression is achieved. The remaining challenge is toextract the muons fast enough into vacuum. This is done bycompressing the stopped muon swarm with electric fieldsand guiding it into a small extraction hole. In this Letter wereport the successful demonstration of muon swarm com-pression along the magnetic field lines.Related schemes have been used in the field of rare
isotope investigations [2,3]. High energy ion beams arestopped in He gas and compressed. Typical manipulationand extraction times are 5–200 ms. For muons, much fastertechniques are vital.The new concept for fast compression is based on a
position-dependent muon drift velocity ~vD in gas. In a longHe gas target placed in a longitudinal high magnetic field,the stopping muons are first transversely, then longitudi-nally compressed and finally extracted through a 1 mm2
side hole in the transverse direction (see Fig. 1). Theoperation takes place in 8 μs [1].This tertiary beam line is an add on to a secondary
surface muon beam line, reducing the phase space of theinput beam by 1010 with 10−3 efficiency.By using, e.g., the PSI μE4 surface beam with
4 × 108 μþ=s, an eV-energy beam can be obtained with1 mm2 transverse area and intensity of 5 × 105 μþ=s, 2orders of magnitude larger than presently achieved [4]. Thisdevelopment is also highly attractive in view of the HiMBproject [5] aiming at a surface muon beam of ∼1010 μþ=s.Space charge effects will limit the output intensity of thecompressed beam to about 1 × 107 μþ=s.It is important to note that depolarization during muon
swarm compression is only a few percent because of the
strong longitudinal magnetic field [6]. Thus, starting fromhighly polarized muons, such a beam can be used for nextgeneration μSR applications, muonium (Mu) spectroscopy,a muon g-2 experiment, searches for a muon electric dipolemoment, and Mu-Mu conversion. Because of space chargeeffects and muon losses it is not suited for muon colliderprojects.The drift velocity of charged particles in gas in the
presence of electric ~E and magnetic ~B fields is [7]
~vD ¼ μE1þ ω2τ2c
½Eþ ωτcE × Bþ ω2τ2cðE · BÞB&; (1)
where E and B are the unit vectors along ~E and ~B, ω ¼eB=m the cyclotron frequency withm the muon mass, μ themuon mobility in the gas, and τc the mean time between
µ+ Tertiary beamE < eVD < 1 mmTagged beam
D=10 mmContinuos beam
E=4 MeV
T = 290 K
compression
compression
T = 4 K
Transverse
Longitudinal
E
E
y
xz
µ+
B−field
Secondary beam
T = 12 K
FIG. 1 (color online). Schematic of the beam line proposed in[1]. μþ traveling in the −z direction are stopped in 5 mbar He gasat cryogenic temperatures. First, transverse (y direction) com-pression occurs within a density gradient in He gas (blue region).Then at room temperature the longitudinal (z direction) com-pression takes place (red region). In the yellow region a mixedtransverse-longitudinal compression precedes before extractioninto vacuum.
PRL 112, 224801 (2014) P HY S I CA L R EV I EW LE T T ER Sweek ending6 JUNE 2014
0031-9007=14=112(22)=224801(5) 224801-1 © 2014 American Physical Society
!⌧c
µ : muon mobility: cyclotron frequency: mean time between collisions
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019
Transverse compression‣ 5 mbar He gas
�6
‣ Temperature gradient at cryogenic temperature
‣ Crossed E- and B-field
Muon Cooling: Longitudinal Compression
Yu Bao,1 Aldo Antognini,2,* Wilhelm Bertl,1 Malte Hildebrandt,1 Kim Siang Khaw,2 Klaus Kirch,1,2 Angela Papa,1
Claude Petitjean,1 Florian M. Piegsa,2 Stefan Ritt,1 Kamil Sedlak,1 Alexey Stoykov,1 and David Taqqu21Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
2Institute for Particle Physics, ETH Zurich, 8093 Zurich, Switzerland(Received 11 February 2014; published 4 June 2014)
A 10 MeV=c positive muon beam was stopped in helium gas of a few mbar in a magnetic field of 5 T.The muon “swarm” has been efficiently compressed from a length of 16 cm down to a few mm along themagnetic field axis (longitudinal compression) using electrostatic fields. The simulation reproduces the lowenergy interactions of slow muons in helium gas. Phase space compression occurs on the order ofmicroseconds, compatible with the muon lifetime of 2 μs. This paves the way for the preparation of a high-quality low-energy muon beam, with an increase in phase space density relative to a standard surface muonbeam of 107. The achievable phase space compression by using only the longitudinal stage presented hereis of the order of 104.
DOI: 10.1103/PhysRevLett.112.224801 PACS numbers: 29.27.-a, 14.60.Ef, 29.38.Db, 82.20.Tr
Standard muon (μþ) beams have a relatively high energyand poor phase space quality. A new scheme has beenproposed making use of stopped μþ in a He gas target [1].Through the stopping process high intrinsic phase spacecompression is achieved. The remaining challenge is toextract the muons fast enough into vacuum. This is done bycompressing the stopped muon swarm with electric fieldsand guiding it into a small extraction hole. In this Letter wereport the successful demonstration of muon swarm com-pression along the magnetic field lines.Related schemes have been used in the field of rare
isotope investigations [2,3]. High energy ion beams arestopped in He gas and compressed. Typical manipulationand extraction times are 5–200 ms. For muons, much fastertechniques are vital.The new concept for fast compression is based on a
position-dependent muon drift velocity ~vD in gas. In a longHe gas target placed in a longitudinal high magnetic field,the stopping muons are first transversely, then longitudi-nally compressed and finally extracted through a 1 mm2
side hole in the transverse direction (see Fig. 1). Theoperation takes place in 8 μs [1].This tertiary beam line is an add on to a secondary
surface muon beam line, reducing the phase space of theinput beam by 1010 with 10−3 efficiency.By using, e.g., the PSI μE4 surface beam with
4 × 108 μþ=s, an eV-energy beam can be obtained with1 mm2 transverse area and intensity of 5 × 105 μþ=s, 2orders of magnitude larger than presently achieved [4]. Thisdevelopment is also highly attractive in view of the HiMBproject [5] aiming at a surface muon beam of ∼1010 μþ=s.Space charge effects will limit the output intensity of thecompressed beam to about 1 × 107 μþ=s.It is important to note that depolarization during muon
swarm compression is only a few percent because of the
strong longitudinal magnetic field [6]. Thus, starting fromhighly polarized muons, such a beam can be used for nextgeneration μSR applications, muonium (Mu) spectroscopy,a muon g-2 experiment, searches for a muon electric dipolemoment, and Mu-Mu conversion. Because of space chargeeffects and muon losses it is not suited for muon colliderprojects.The drift velocity of charged particles in gas in the
presence of electric ~E and magnetic ~B fields is [7]
~vD ¼ μE1þ ω2τ2c
½Eþ ωτcE × Bþ ω2τ2cðE · BÞB&; (1)
where E and B are the unit vectors along ~E and ~B, ω ¼eB=m the cyclotron frequency withm the muon mass, μ themuon mobility in the gas, and τc the mean time between
µ+ Tertiary beamE < eVD < 1 mmTagged beam
D=10 mmContinuos beam
E=4 MeV
T = 290 K
compression
compression
T = 4 K
Transverse
Longitudinal
E
E
y
xz
µ+
B−field
Secondary beam
T = 12 K
FIG. 1 (color online). Schematic of the beam line proposed in[1]. μþ traveling in the −z direction are stopped in 5 mbar He gasat cryogenic temperatures. First, transverse (y direction) com-pression occurs within a density gradient in He gas (blue region).Then at room temperature the longitudinal (z direction) com-pression takes place (red region). In the yellow region a mixedtransverse-longitudinal compression precedes before extractioninto vacuum.
PRL 112, 224801 (2014) P HY S I CA L R EV I EW LE T T ER Sweek ending6 JUNE 2014
0031-9007=14=112(22)=224801(5) 224801-1 © 2014 American Physical Society
x
y
z
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019�711
Detector 1
Detector 2
Detector 1
Detector 2
• Demonstrated in 2015
I. Belosevic, Joint annual meeting of
Swiss and Austrian Physical Societies 2017
+ + data
— — simulation
μ+
Demonstration of transverse comp.‣ Demonstrated in 2015‣ Excellent agreement between measurement and simulation
I. Belosevic et al., Hyperfine Interact (2019) 240: 41.
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019
Longitudinal compression‣ 5 mbar He gas
�8
‣ Room temperature
‣ Parallel E- and B-field
Muon Cooling: Longitudinal Compression
Yu Bao,1 Aldo Antognini,2,* Wilhelm Bertl,1 Malte Hildebrandt,1 Kim Siang Khaw,2 Klaus Kirch,1,2 Angela Papa,1
Claude Petitjean,1 Florian M. Piegsa,2 Stefan Ritt,1 Kamil Sedlak,1 Alexey Stoykov,1 and David Taqqu21Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
2Institute for Particle Physics, ETH Zurich, 8093 Zurich, Switzerland(Received 11 February 2014; published 4 June 2014)
A 10 MeV=c positive muon beam was stopped in helium gas of a few mbar in a magnetic field of 5 T.The muon “swarm” has been efficiently compressed from a length of 16 cm down to a few mm along themagnetic field axis (longitudinal compression) using electrostatic fields. The simulation reproduces the lowenergy interactions of slow muons in helium gas. Phase space compression occurs on the order ofmicroseconds, compatible with the muon lifetime of 2 μs. This paves the way for the preparation of a high-quality low-energy muon beam, with an increase in phase space density relative to a standard surface muonbeam of 107. The achievable phase space compression by using only the longitudinal stage presented hereis of the order of 104.
DOI: 10.1103/PhysRevLett.112.224801 PACS numbers: 29.27.-a, 14.60.Ef, 29.38.Db, 82.20.Tr
Standard muon (μþ) beams have a relatively high energyand poor phase space quality. A new scheme has beenproposed making use of stopped μþ in a He gas target [1].Through the stopping process high intrinsic phase spacecompression is achieved. The remaining challenge is toextract the muons fast enough into vacuum. This is done bycompressing the stopped muon swarm with electric fieldsand guiding it into a small extraction hole. In this Letter wereport the successful demonstration of muon swarm com-pression along the magnetic field lines.Related schemes have been used in the field of rare
isotope investigations [2,3]. High energy ion beams arestopped in He gas and compressed. Typical manipulationand extraction times are 5–200 ms. For muons, much fastertechniques are vital.The new concept for fast compression is based on a
position-dependent muon drift velocity ~vD in gas. In a longHe gas target placed in a longitudinal high magnetic field,the stopping muons are first transversely, then longitudi-nally compressed and finally extracted through a 1 mm2
side hole in the transverse direction (see Fig. 1). Theoperation takes place in 8 μs [1].This tertiary beam line is an add on to a secondary
surface muon beam line, reducing the phase space of theinput beam by 1010 with 10−3 efficiency.By using, e.g., the PSI μE4 surface beam with
4 × 108 μþ=s, an eV-energy beam can be obtained with1 mm2 transverse area and intensity of 5 × 105 μþ=s, 2orders of magnitude larger than presently achieved [4]. Thisdevelopment is also highly attractive in view of the HiMBproject [5] aiming at a surface muon beam of ∼1010 μþ=s.Space charge effects will limit the output intensity of thecompressed beam to about 1 × 107 μþ=s.It is important to note that depolarization during muon
swarm compression is only a few percent because of the
strong longitudinal magnetic field [6]. Thus, starting fromhighly polarized muons, such a beam can be used for nextgeneration μSR applications, muonium (Mu) spectroscopy,a muon g-2 experiment, searches for a muon electric dipolemoment, and Mu-Mu conversion. Because of space chargeeffects and muon losses it is not suited for muon colliderprojects.The drift velocity of charged particles in gas in the
presence of electric ~E and magnetic ~B fields is [7]
~vD ¼ μE1þ ω2τ2c
½Eþ ωτcE × Bþ ω2τ2cðE · BÞB&; (1)
where E and B are the unit vectors along ~E and ~B, ω ¼eB=m the cyclotron frequency withm the muon mass, μ themuon mobility in the gas, and τc the mean time between
µ+ Tertiary beamE < eVD < 1 mmTagged beam
D=10 mmContinuos beam
E=4 MeV
T = 290 K
compression
compression
T = 4 K
Transverse
Longitudinal
E
E
y
xz
µ+
B−field
Secondary beam
T = 12 K
FIG. 1 (color online). Schematic of the beam line proposed in[1]. μþ traveling in the −z direction are stopped in 5 mbar He gasat cryogenic temperatures. First, transverse (y direction) com-pression occurs within a density gradient in He gas (blue region).Then at room temperature the longitudinal (z direction) com-pression takes place (red region). In the yellow region a mixedtransverse-longitudinal compression precedes before extractioninto vacuum.
PRL 112, 224801 (2014) P HY S I CA L R EV I EW LE T T ER Sweek ending6 JUNE 2014
0031-9007=14=112(22)=224801(5) 224801-1 © 2014 American Physical Society
x
y
z
‣ Demonstrated in 2011/2014
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019
Mixed transverse & longitudinal compression
‣ New scheme with simpler setupB
ET
EL
y
xz
x [mm]40− 20− 0 20 40
y [m
m]
20−
10−
0
10
20h
Entries 1380652Mean x 3.905Mean y 2.016− RMS x 17.37RMS y 3.291
0
200
400
600
800
1000
1200
1400
hEntries 1380652Mean x 3.905Mean y 2.016− RMS x 17.37RMS y 3.291
step_y:step_x {step_x < 34}
x [mm]20− 0 20 40
z [m
m]
40−
20−
0
20
40h
Entries 1380652
Mean x 3.905
Mean y 0.7988−
RMS x 17.37
RMS y 9.545
0
200
400
600
800
1000
1200
1400
1600
1800
2000
hEntries 1380652
Mean x 3.905
Mean y 0.7988−
RMS x 17.37
RMS y 9.545
step_z:step_x {step_x < 34}
‣ Single stage at cryogenic temperature
�9
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019
Realised target • Kapton foil with equipotential lines
10
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019 11
Beam test setup
11
• First demonstration of mixed compression at the end of 2017
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019
Solenoid
Cryo-cooler
μ+
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019 13
Target installation
13
Heating pad He line
Collimator
Cold-finger
μ+
Detectors
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019 14
Measurement of mixed compressionTransverse direction
x
y
Trans 3Trans 2
Trans 1
Tiles 1, 2, 3
Tiles 4, 5, 6
z
x
Tiles 3, 6
Tiles 2, 5
Tiles 1, 4
Longitudinal direction
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019
Extract muons into vacuum
μ
‣ Through 1×1 mm2 orifice‣ He gas injection and efficient pumping to maintain target pressure
15
muCool: Next steps
He IN
He OUT
μ+
He IN
He OUT
He OUT
μ+
B
E
Increase E-field strength
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019
ConclusionsmuCool project developing a high-brightness ultra-cold positive muon beam
‣ Transverse and longitudinal compressions separately demonstrated. Excellent agreement between data and simulation.
‣ Mixed compression scheme partially demonstrated
‣ Next: Improve mixed compression & develop muon extraction
Supported by SNF grant 200020_172639
16
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019
Back up
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019�18
Demonstration of longitudinal comp.‣ Demonstrated in 2011/2014‣ Excellent agreement between measurement and simulation
-500 V
+500 V 0 V
I. Belosevic et al., Eur. Phys. J. C (2019) 79: 430
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019�19
Target for surface muons‣ ~100 cm long needed
R. Iwai Zurich PhD student seminar - Villigen PSI, - 9, Oct, 2019
Improve maximum E-field
‣ Limited by discharging He gas
‣ Coverlay on electrodes, reducing “hot spot”, materials with lower εr
E-field strength
Kapton
Sapphire
Electrode
He
Pressure (mbar)0 5 10 15 20 25
Volta
ge (V
)
0
1000
2000
3000
4000
5000
Discharged Voltage
Graph
20