LOW INTENSITY BEAM CURRENT MEASUREMENT OF THE
ASSOCIATED PROTON BEAM LINE AT CSNS*
R. Y. Qiu, W. L. Huang†, F. Li, L. Zeng, Muhammad Abdul Rehman, M. Y. Liu, Q. R. Liu, R. J. Yang, T. Yang, Z. H. Xu, Z. X. Tan
Institute of High Energy Physics ,China Spallation Neutron Source, Dongguan, China

TU3C05

IV. Calibration

I. Introduction
The Associated Proton beam Experiment Platform (APEP) beamline is the first proton
irradiation facility to use naturally-stripped protons which come from H- beams interacting with theresidual gas in the linac beampipe at CSNS. The stripped beam current, which is in the order of 0.1%of the original H- beam and approximately 10 mi-croamperes, should be measured precisely toprovide the proton number for irradiation experiments.

◆ Precise DC/AC current source: KEITHLEY 6221

25Hz pulsed square wave
Pulse Width: 500 μs
Current Range: 2~10 μA◆ Current goes through the calibration coil of the APEP-CT sensor.

Linearity of the current measurement:error ≤ 1% FS

Parameters of the Associated Proton Beam

APEP beamline

Parameter

ValueProton Beam Energy

80 MeV

Repetition Frequency

25 Hz

Number of Particles~5.0*1010 ppp@100kW

Macro Bunch Length

100 μs ~ 500 μs

Proton Beam Intensity

20 μA@400 μs,100 kW

II. Design

The blue signal is the electronics output
with 1 uA calibrated input current.

CT Electronics Calibration Data

Ⅴ. Interference Investigation

When the accelerator is running, it is found that the measurement system outputs alarge interference signal.
A thorough examination of the CT interference sources.
◆ Along the APEP beamline◆ RCS, especially the injection section(BH&BV Magnet)
Orange is BV
painting curveOrange is BH
painting curve

Sense:◆ Soft magnetic core:
Fe-based nanocrystalline alloy (μr≈100000@10 Hz)
ffill: filling factor of core (tape thickness: 20μm)◆ Calculation of the equivalent inductance:
Do=160mm; Di=130mm; h=25mm
Secondary coil: 50 turns for the signal
Additional coil: 1 turn for the online calibration.
◆ a double-layered DT4 magnetic shield to reduce
environmental stray magnetic field impact.
Calculation of Different Magnetic Shields
LayerbMaterial mm
DT4162.0
DT4158.0
Permalloy 162.0apmm
160.0 1.0252
156.0 1.0258
158.0 1.0513

μr

S

6000
6000
106

37.8
38.7
1220

with the BH & BV
magnet enabled.

only with the BH
magnet enabled.

with only the BV
magnet enabled.

without BH and BV
magnets operation.

Output of APEP-CT electronics under different accelera-tor operation conditions.
The main contribution of interference is from BH, followed by BV, which has a highsimilarity to the current curve of the power supply during the beam injection in the phasespace painting mode.
magnetic shield

Sense

Electronic:◆ A trans-impedance circuit to get a smaller load impedance.
◆ A low-noise operational amplifier with a low input bias current Ib.
◆ A technique of baseline dynamic feedback for the baseline drifting.
◆ Effective low-pass filtering will improve the signal-to-noise ratio.

Diagram of CT electronics

III. Shielding and Grounding

ⅤI. Troubleshooting◆ Bypass capacitor installed◆ Interference signal subtracted in DAQ system
 DAQ is triggered by the Timing system Collect the Interference signal once without a beam andsave it as the background interference signal.
 Subsequently, for each subsequent signal collection witha beam, the interference signal is subtracted in order torestore the beam signal.
Without Bypass Capacitor

With Bypass Capacitor

A comparative experiment was made among the noise measurements of four-core cables (twocore twisted pair with braided outer shield) and triaxial cables under different ground-ing methods
with the same sensor and electronics.
A bypass capacitor over the ceramic gap was built in the APEP-CT sensor.

ⅤII. CONCLUSIONS
60m tri-coaxial cable(single-end grounded)

60m tri-coaxial cable(double-end grounded)

60m four core cable(double-end grounded)

Diagram of the Grounding and cable selection experiments

Improved by the above methods, we successfully measured the associated pro-ton
beam in low intensity. the amplitude of the pulsed associated proton beam intensity isclearly measured as 16.8 μA. The APEP-CT system achieves a signal-to-noise ratio
improvement and meets the design specification for microampere-level current intensity
measurement.

After the multi-point grounding test, it was found that outermost layer of triaxial cable wasgrounded to the vacuum pipeline at the sensor end, and the electronic end was grounded to cabinet
ground to achieve the best effect.
The blue waveform is thesignal from the APEP-CT.
The red waveform is thesignal from the Faraday Cup.

Diagram of the triax cable grounding to minimize noises.
†huangwei@ihep.ac.cn qiury@ihep.ac.cn★ National Mega-Science ProjectOutput of the electronics of the APEP-CT and Faraday cup

China Spallation Neutron Source (CSNS), No. 1, Zhongziyuan Road, Dalang Town,Dongguan City, Guangdong Province, P.R. China