1. Yoshinori Sato (IPNS/KEK) for J-PARC Hadron Group
Residual Gas Ionization Profile Monitors in J-PARC Hadron Experimental Facility
Yoshinori Sato (IPNS/KEK)
for J-PARC Hadron Group

2. J-PARC Hadron Experimental Facility
Pacific Ocean
RCS
3GeV MR
30GeV
Liniac
400 MeV
MLF
ν to SK
～500m
Hadron Experimental Facility
This is an overview of J-PARC accelerators and experimental facilities. Hadron Experimental Facility is located here. Proton beams are accelerated up to 30 GeV in Min Ring, and extracted to Hadron Hall with the slow-extraction method. Accelerator operating cycle is 5.2 second, and spill length during extraction is 2 second in average.
Hadron Hall
photo by Google
30 GeV proton beam from Main Ring (MR) with the slow-extraction method
Currently available beam power: 53 kW (6.0x1013 protons / shot)
Operating cycle: 5.2 s
Spill length: 2.0 s

3. Primary and secondary beam lines in HEF
Primary line-B
(now under construction)
Hadron
Hall
T1 target
(50%)
K1.8
K1.8BR
Main Ring (MR)
Beam Switching Yard (SY) KL
Primary line-A
Primary line-A
Beam dump
(100%)
This is a schematic drawing of primary and secondary beam lines in HEF. We have the primary line-A in the beam switching yard tunnel. Currently we can accept 53 kW beam power, which corresponds to 30GeV-5.8x10^13 protons per shot. In the hadron hall, there is a production target, T1, which can accept up to 50% beam. We have three secondary beam lines, named K1.8BR, K1.8, and KL for particle and nuclear physics experiments.
Primary line-B and line-C are now under construction. Primary line-B will provide 30GeV proton beams of 24 W, which can directly be used for Hadron physics experiments.
Primary line-C will provide 8GeV bunched proton beam for the my-e conversion experiment named COMET.
South Experimental Hall
for COMET exp.
Primary line-C
(under construction)
Primary line-A (in operation)
Beam power: 53 kW (30 GeV-1.7 mA, 5.8x1013 p/shot)
Secondary beam lines: K1.8BR, K1.8, KL for Particle and Nuclear Physics　experiments
Primary line-B (under construction)
Beam power: 24 W (30 GeV-0.8 nA, 2.6x1010 p/shot)
Direct use of 30 GeV proton beam for hadron physics experiments
Primary line-C (under construction)
Beam power: 3.2 kW (8 GeV-0.4 mA, 1.3x1013 p/shot)
Bunched slow extraction of 8 GeV proton beam for the COMET experiment (Phase I)

4. Beam diagnostic devices on the primary beam lines
Vacuum window
Al 100 mm
T1 target
Beam dump
Vacuum pressure
< 10-5 Pa
Vacuum pressure
> 0.1 Pa
Beam Switching Yard (SY)
Extraction point
HD-hall
Beam Loss Monitor (24)
Optical Transition Radiation (3)
Residual Gas Ionization Profile Monitor (13)
Target Monitor (1)
Scintillation Intensity Monitor (1)
This show locations of beam diagnostic devices on the primary beam line. We have 24 BLM, 3 optical transition radiation profile monitor in the upstream section. There is a vacuum window of Al 100 um to separate vacuum pressure of the MR accelerator and our primary beam line. The vacuum pressure of our primary beam line is order of 0.1 Pa. In the primary line-A, we have 13 residual gas ionization profile monitors. 10 rgipms are installed in SY, 3 are in HD-hall.
Around the production target T1, radiation level is extremely high.

5. Residual Gas Ionization Profile Monitors in HEF
Working in relatively high vacuum pressure: > 0.1 Pa
Signal yield: [nC] / (1 [Pa] * 1E+12 [protons/shot])
Direct measurement of ionization electrons with charge integration
Omit amplification device such as MCP →　Low cost, good S/N ratio
Use of magnetic field applied parallel to the electric field (10 V/cm)
Reduce diffusion effect of electrons drifting in >0.1 Pa vacuum pressure
Field strength: 200 to 400 gauss at center
Sr-ferrite permanent magnet to reduce cost
Free from maintenance
Working under extremely high radiation environment
1 m upstream of T1 target (gold target, 50 % loss)
Estimated dose rate: ~2 MGy / year (30GeV-1014 protons/sec, 2500 hour beam operation)
Shot by shot monitoring of beam profiles
Issue alarm signal to stop accelerator
Avoid damage to the production target (T1)
3 types of RGIPM installed in SY and Hadron Hall
Type-100: Non-invasive region f100、　Magnet gap 200、　B=400 gauss　(10 in SY, 1 in HD-hall)
Readout: 32 ch or 64 ch
Signal pad pitch: 1 mm, 2 mm, 3 mm
Type-300: Non-invasive region f300、　Magnet gap 400、　B=200 gauss (3 in SY)
Signal pad pitch: 6 mm
Type-400: Non-invasive region f400、 No permanent magnet (positive ion collection) (2 in HD-hall)
Signal pad pitch: 10 mm
For large beam size at entrance of the beam dump
Our residual gas ionization profile monitors in HED have these characteristics. The monitors are working in relatively high vacuum pressure, more than 0.1 Pa. Signal yield is order of 1 nC, so we can directly measure ionization electrons without MPC or amplification devices

6. Experimental Setup in EP2-C Beam Line at KEK 12GeV-PS (2005)
Side view
Front view
Read-out electrodes (6mm, 32ch)
Install in EP2-C line
RGIPM
This is an previous R&D work when the KEK 12GeV-PS were operated. We have tested a prototype RGIPM with magnetic coils and installed to the primary beam line. There is a reference SPIC (segmented ionization chamber) near the test RGIPM.
SPIC
Beam

7. Beam Profile Measured with RGIPM (2005)
s=1.1cm
This is a typical result of profile measurement with the test RGIPM for 2.1x10^12 proton beam under 1.0E-2 torr (1.41 Pa). Beam profiles measured with RGIPM and reference monitor well agreed.
Good agreement with reference SPIC
Collected charge： 1.6 nC / spill
Expected charge： 2 nC / spill

8. Magnetic Field Dependence
Saturate over 300 Gauss
This is a data of profile widths changing applied magnetic field strength. As the field strength was increased, the profile width shrink to the desirable profile width by magnetic confinement of electrons over 300 gauss.

9. Remanence loss of permanent magnet materials by radiation exposure (2005-2006)
110 MGy (1010 rad)
KENS　500MeV-p
Indirect exposure
CYRIC　70MeV-p
Direct exposure
An issue on using permanent magnet is remanence loss of permanent magnet materials by radiation exposure. We had studied it using indirect exposure by KEK neutron source with 500 MeV-proton and direct exposure of 70 MeV proton beams at Cyclotron facility at Tohoku university. At KENS, we had tested remanence loss up to 10^14 h/cm2 integrated fluence. It is well known that Nd-Fe-B is weak against radiation exposure.
At CYRIC, we had tested up to 10^17 hadron fluence, corresponding to 110 M Gy. Although Nd-Fe-B and Sm-Co materials showed a significant remanence loss , Sr-ferrite showed no significant remanence loss up to 110M Gy.
Sr-ferrite is desirable material for RGIPM.

10. Schematic view of RGIPM (Type-100)
Cross-sectional view
Permanent magnet
（Sr-ferrite, t25）
Pole pieces
（Fe, t5）
High-voltage electrode
(-100V)
150
Field shaping
electrodes
280
200
Vacuum chamber
Non-invasive region
F100
B = 400 gauss
200
Flux-returning yoke
（Fe, t10）
Readout electrode
280

11. Schematic view of RGIPM (Type-100)
900
280
Side view
Beam
200
Vertical monitor
Horizontal monitor
Permanent magnet
（Sr-ferrite, t25）
Vacuum / signal ports
field clump

12. Photos of internal electrode (Type-100)
Internal electrodes in vacuum chamber
Gold-plated readout electrode (32 ch signal pads, 2mm-pitch)
100 80
G10 board
(ceramic board also available)
Ni wire with ceramic felt
Ceramic insulator
Inorganic resistors (10MΩ)

13. Photos of permanent magnet (RGIPM Type-100)
Vacuum chamber
(SUS304)
After assembly of permanent magnet
Vertical
Horizontal
Permanent magnet
(Sr-ferrite)

14. Photos of RGIPM Type-100 and Type-300
Before installation
RGIPM-300
Before installation
900
1140

15. Photos of installed RGIPMs in SY
900
1140
First installation: 2007
First beam extraction: Jan. 28th, 2009

16. Readout electronics and Data acquisition
32 ch charge integrator board on VME(GNV-370)
Input: -1nC, -4nC, -40nC, -400nC
Output: 5V
64 ch scanning A/D board on VME
Advanet ADVME-2607
EPICS-IOC on VME CPU board
VMIVME-7807 (GE)
Generate waveform record
On-line Gaussian fitting
DAQ
EPICS Channel Archiver
GUI
WxPython + EpicsCA
J-PARC Accelerator cycle: 5.2 s
Beam extraction
2.0 s
Charge
integration
A/D conversion
A/D conversion
Off-beam
Measurement
(pedestal)
On-beam
measurement
Background subtraction is important.
Multi-scan measurements in the on-beam measurement

17. Typical RGIPM profile distributions with 30 GeV-51 kW beam (June, 2018)
After background subtraction
Vacuum pressure: Pa
Red: Horizontal profile
Blue: Vertical profile
MR-MWPM
Upstream
T1 target
Beam dump

18. Evaluation of beam emittance of 30Gev-51kW beam by fitting (June, 2018)
Beam optics calculated by TRANSPORT
[kW]
[yymmdd]
εH(2σ)
εV(2σ)
T1 σ [H mm x V mm]
51.0
180629
0.79
1.18
2.69 x 0.95

19. Multi-scan measurement at T1 target
Profile distributions at T1 target during extraction
Measurement by 8 scan x 200 msec at T1 target
Beam center (Mean), width (Sigma), and area (SigmaX*sigmaY) are monitored.
Keep beam size (1mmH x 2.5 mmV) to avoid damage on the T1 target
No radiation damage or remanence loss on the RGIPM is observed so far.
Maximum
SUM
Mean
Sigma

20. Vertical profile measurement at SM1 by moving wire scatterer (2012)
To design the shape of Lambertson Magnet at SM1 for the new primary beam line (line-B), the vertical profile distribution at the separating point had been studied in detail by moving wire scatterer.
RGIPM-Y distribution at SM agreed well with the result of the scanning method.
RGIPM at SM
Near
scintillating
counter
Far
scintillating
counter
Moving wire scatterer
Run45-10 kW beam
◆ Near scintillating counter
■ Far scintillating counter
▲ Vertical profile by RGIPM-SM
vertical wire position [mm]

21. Alarm system with RGIPM
Graphical trend display by PyQt
Accelerator stop signals (MPS) are issued from VME modules (TTL).
Set threshold to position and width of horizontal and vertical profile distributions
EPICS alarm handler tells operators by beeping.
EPICS
Alarm handler

22. Summary
All the RGIPMs in HEF are stably working with 30GeV-51kW proton beam.
No difficulty is found with 8 GeV bunched beams for COMET
No maintenance and replacement due to damage since the first beam in February, 2009.
Successfully working under extremely severe radiation environment near the production target
No remanence loss is observed on Sr-ferrite permanent magnet.

23. supplements

24. Residual Gas Ionization Profile Monitor (RGIPM) in Low Pressure
Working Principle
300G
10cm
HV: 50V
Pressure: 1Pa
GND
Apply uniform electric and magnetic fields between electrodes in the beam pipe.
N2+ e-
Primary proton beams ionizes residual gas (1Pa) and electron-ion pairs are produced.
Beam
Electrons confined in Larmor-radius drift toward the read-out electrodes.
Beam profiles are measured as a charge distribution on the read-out electrodes.
Complete non-destructive monitor

25. Confinement of Knock-on Electrons with Magnetic Field
VG=50V
Knock-on electrons (typical energy: ~50eV) are emitted perpendicular to protons. e-
B~300G p
G=10cm
The resolution of RGIPM is determined by diffusion of electrons crossing over the magnetic flux.
Magnetic field strength (G)
Profile width in Gaussian sigma (cm)
Saturate over 300 Gauss
Monte-Carlo simulation
Shrinkage of profile widths should be observed.

26. Proof-of-Principle Prototype of RGIPM
Maximum Field ~ 500 Gauss
Field uniformity ~10%