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Progress on Design and R&D of ITER Diagnostic-Radial X-ray Camera

L. Hu1, K. Chen1, Y. Chen1, H. Cao1, S. Li1, H. Yu1, J. Zhan1, J.Shen1, S. Qin1, X. Sheng1, J. Zhao1, L. Niu1, C. Feng1, J. Ge1, S. Zhang1, B. Zhang1

1Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China

E-mail contact of main author: lqhu@ipp.ac.cn, kychen@ipp.ac.cn

Abstract. Great progress has been made to the design of ITER Radial X-ray Camera (RXC). The structure

design is optimized and installation process is studied considering the simplification and easiness of

maintenance. Remote handling skills and tools are designed for the system maintenance after being activated.

For detector cooling against high environment temperature which can be up to 240℃, a dedicated gas cooling

system using heat exchanger is designed. The structure analysis indicates that the maximum stress on main

components is still less than allowable stress. Through putting B4C material in the front part of DSM and around

detectors for neutron shielding, the detectors are expected to survive the whole D-D phase. As for electronics,

preliminary design of highly integrated pre-amplifier and program controllable mid-amplifier has been

completed, both with bandwidth greater than 100 kHz to meet time resolution requirement of 20 kHz. To protect

the electronics from intensive neutron and gamma irradiation, shielding cabinet capable of attenuating neutron

flux down to 0.0001 and gamma dose 0.01 is designed. Based on EAST tokamak and technical experience from

diagnostics development acquired on it, many R&D has been done to support the design. The tests of

pre-amplifier and mid-amplifier indicated the electronics had no functional problem when debugging together

and generally passed preliminary Electro Magnetic Compatibility (EMC) test and nuclear test. The

highly-integrated compact pre-amplifier has been used in EAST and proved useful. To test the feasibility of

dedicated gas cooling system for detectors, a cooling test platform was built and preliminary cooling test has

been done, indicating that during 250℃ baking the detector temperature is promising to be cooled down to the

detector temperature limit of 75℃. To increase signal to noise ratio, large area detector with dark current less

than 2nA has been manufactured and worked steadily in EAST experiments.

1. Introduction

ITER Radial X-ray Camera (RXC) is designed to measure the poloidal profile of the plasma x-ray emission with high spatial and temporal resolution. The primary diagnostic role of the RXC is to measure low (m,n) MHD modes, sawteeth and disruption precursors; ELMs indicator. RXC also provides supplementary measurements of plasma position, radiative power, runaway electrons, impurity content, etc [1, 2]. An overall view of RXC is shown in Fig.1.

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FIG.1. Overall view of RXC

RXC, Glow Discharge Cleaning (GDC) and Hard X-ray Monitor (HXM) share middle module of EQ12 port plug [3]. RXC consists of two subsystems, i.e. in-port and ex-port cameras which view the outer and core region respectively through vertical slots in the diagnostics shield module of an equatorial port plug, both have secondary vacuum housing with beryllium window assemblies. Fig.2 shows Layout of internal camera and external camera.

FIG.2. Layout of internal camera and external camera

In the following sections, design progress, R&D and tests will be presented.

2. Design of camera

Internal camera is designed to install on DSM through pushing the camera into DSM from back, fix it on DSM side wall and connect with closure plate through welding, while external camera is supported on closure plate and connected to closure plate through vacuum extension, Be window assembly, chain clamp and double bellow. For detector cooling against high environment temperature which can be up to 240℃ [4], a multi-hole gas heat exchanger is tightly attached to detector for dedicated cooling. To guarantee machining precision and assemble precision, the internal camera slits are welded with bottom plate firstly and then machined together. The machining of external camera slit and light path block follow the

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same procedure. To mitigate nuclear radiation leakage into Interspace, a concrete shielding shell enclosing

the external camera is designed. Through putting B4C material in front part of DSM and around detectors, the detectors are expected to survive the whole D-D phase without detector replacement.

The structure analysis results shown in Fig.3 and Fig.4 indicated that in the worst case, the maximum stress in main components was still less than allowable stress, although there are some weak point exceeding the limit which can be easily improved through optimizing the design. This means that the camera could be stable and reliable.

FIG.3. Structure analysis of internal camera under load combination of dead weight, heat, VDE,

seismic and vacuum vessel ingress of coolant

FIG.4. Structure analysis of external camera under load combination of dead weight, VDE, seismic

and vacuum vessel ingress of coolant

Considering the future maintenance may be done in nuclear environment which strictly

restrict the access of workers, remote handling procedure and tools are designed and/or

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selected. The basic assumption is that the internal camera will be installed and maintained as a whole, which also applies for external camera. The basic procedure to remove internal camera as shown in Fig.5 is: disconnection of connectors, weldings, pipes, etc. outside closure plate transport the whole port plug and DSM with internal camera inside into hot cell extraction of middle DSM from port plug unbolting of anchoring point of internal camera from DSM extraction of internal camera cleaning or replacement of the whole camera. The installation follows the reverse procedure. The basic procedure to remove external camera as shown in Fig.6 is: removal of shielding block disconnection of connectors, weldings, pipes, etc. disconnection of external camera from closure plate transport of the whole external camera and shielding block into hot cell cleaning or replacement of the whole camera. The installation of external camera follows reverse procedure. The only difference is that the installation needs to be adjusted for alignment. Note the external camera and shielding block should be removed first to allow for space for the removal of internal camera and installed lastly in assembly situation. During the installation and removal of internal camera and external camera, several tools have been identified, i.e. standard tools (bolt runner, crane, manipulator) and special tools (external camera storage, shielding storage, lip cutting/welding tools, lifting devices).

FIG.5. Internal camera maintenance procedure

FIG.6. External camera maintenance procedure

To improve RXC signal to noise ratio, the detector active area is doubled. To meet

measurement requirement in Annex B [5], i.e. localization of MHD modes to a/10 and vertical spatial resolution of 40mm for edge region (r/a>0.85), 64 channels are allocated to central region and another 64 channels to edge region. This chord arrangement is shown in Fig.7 (a). This change will not affect the diagnostic measurement requirements agreed in the Annex B. The edge region (r/a from 0.85 to 1) in the low-field-side is covered by ~15 effective chords

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(observing upper plasma; overlapping has been considered). Similar coverage is observed for the chords looking at the lower plasma. This edge region expands on the vertical magnetic axis to a 600 mm chord. The vertical resolution is then evaluated to ~40mm (600mm/15=40mm) which is the Annex B requirement. It can be noted that, in fact, there will be about 35 chords covering the edge region when counting the upper and lower views. This redundancy of coverage will help to improve the analysis of the plasma soft x-ray emission. Simulation results as shown in Fig.7 (b) and (c) indicate that features of sawteeth and ELMs can be grabbed with the diagnostic. In order to measure detector background noise and heat drift, one single detector is put behind each detector chip. Two marginal channels on adjacent chips which view nearly the same plasma area as that of adjacent detector array made the camera allow for the poloidal position error.

FIG.7. Chord arrangement and simulation results. (a) Chord arrangement; (b)soft x-ray flux contour

with sawtooth; (c) soft x-ray flux contour with ELM.

As for electronics, preliminary design of highly integrated pre-amplifier and program

controllable mid-amplifier has been completed to process 140 channel of signals, both with bandwidth greater than 100 kHz to meet time resolution requirement of 20 kHz. The number of channels to be processed is 140. The pre-amplifier is designed based on highly-integrated PXI plug-in containing 24 channels each with gain ~ 1.0×106 V/A. A customized standard 6U and 8-socket chassis is used for preamplifier housing and EMC compliance. To change the gain and drive long distance (~50m) signal transmission, mid-amplifier is designed based on 3U standard PXI plug-in each with 16 channels. The gain is program controllable by PLC from slow controller. Since there are strong EM and nuclear radiation in port cell and some of the electronics components are susceptible to these external radiation, multi-layer (20cm Iron, 20cm boron-contained polyethene and 4cm lead) shielding cabinet is designed to protect the pre-amplifier and mid-amplifier. The simulation results indicate that the neutron attenuation factor is ~0.0001 and gamma ~0.01, which will make the internal neutron flux less than 100n/cm^2/s and total integrated dose less than 10Gy as required by ITER electronics policy.

I&C design has also been done following the PCDH [6], diagnostic I&C requirements and ITER hardware and software specification. The I&C function includes: Measurement of Soft X-Ray flux (128 channel of linear array signal+ 12 channel of single detector signal); Calibration for DAQ card, amplifier and detector; Gain control of mid-amplifier; Gas cooling system control and monitoring (valve, pump, temperature sensor, pressure sensor and flow sensor); Provide equipment health monitoring; Provide standard CODAC distributed control

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system functions, i.e. Control, monitoring, alarming, data archiving, HMI, etc.; Sequence RXC plant-system operating states (PSOS) to match ITER Common Operating States (COS). I&C functional analysis, architecture design, fast controller design, slow controller design, definition of signals and variables, identification of boundaries and interfaces, cubicle configuration design, software design and state machine design have been completed.

3. R&D and tests

In addition to the design, many R&D has been done to support the design. The pre-amplifier prototype and mid-amplifier have been manufactured and the output noise is ~10mV and 50-100mV respectively. The design of the later will be improved to reduce the noise in the future. These two set of amplifiers has be debugged together and no functional problem was found. Prototypes of pre-amplifier and mid-amplifier and the testing equipment are shown in Fig.8. Preliminary tests of Radiated Electromagnetic Fields (E-Field) Immunity, Electric Fast Transient (EFT) Immunity and Electrostatic Discharge (ESD) Immunity have been done following standards introduced in Electrical Design Handbook (EDH) [7]. The test results indicated that all the components functions pass the tests except for some minor deviation of 1-2 components like the communication errors of chassis controller’s USB devices which will not be used in ITER. Preamplifier was tested with Cf-252 source at neutron flux of ~2.23×103n/cm2/s and neutron fluence greater than 1010n/cm2. No change was found in signals of detector and pre-amplifier. In the Co-60 test with gamma dose rate of 0.5 Gy/min and integrated dose of 200 Gy, the pre-amplifier and mid-amplifier worked well during the gamma irradiation, while the power module in the board had some radiation damages. This implies the necessity to increase radiation resistance of the power supply chip.

FIG.8. prototypes of pre-amplifier and mid-amplifier and the test equipment

To test the feasibility of dedicated gas cooling system for detectors, a cooling test

platform was built as shown in Fig.9, containing simplified internal camera, baking box, detector heat exchanger and supporting equipment and components like heating controller, vacuum pump, air compressor, data acquisition system, etc. In the cooling test, the surface of detector box and cooling pipes were wrapped with several layer of heat insulation. The test results indicate that during 250 baking with compressed air of pressure 0.5 MPa and flow ℃

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rate 50L/min, the detector temperature can be cooled down to 85-95 which is very close to ℃

the detector store temperature limit of 75 . It is promising that this requirement can be met ℃

in the future through optimizing design of insulation, heat exchanger and cooling loop layout.

FIG.9. prototypes of pre-amplifier and mid-amplifier and the test equipment

To increase signal to noise ratio, detector active area is enlarged to 24mm2 (~6 times as

large as Centronic LD35-5T) and the customized detectors with 35 channels were manufactured and tested. It is found that the dark current is less than 2nA and worked steadily in EAST experiments. An even larger detector containing 16 channels is envisaged and to be customized in the future.

There are also some I&C tests that has been done on EAST. To test the data acquisition system and the response time from data receiving to calculated data uploading, a set of simplified I&C system including cubicle, DAQ card (PXIe-6368), programmable amplifier, Industrial Personnel Computer and CODAC Core System 4.3 has been built. It is found that the response time is estimated to be 1.4 ms when collecting and processing 200 channel of signals. This response time is sufficient for real time data display.

4. Summary

In summary, preliminary design of RXC has been completed and produced useful results. In the next step, the RXC design will be furthered towards final design review (FDR). It is believed that the FDR meeting can be held on time and fruitful results will be presented.

Acknowledgement

ITER is a Nuclear Facility INB-174. The views and opinions expressed herein do not

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necessarily reflect those of the ITER Organization. Thanks to people in ITER Organization and other organizations or institutes supporting RXC design. Special thanks to Robin Barnsley, Antoine Sirinelli, Barry Alper, Martin O’Mullane and Michael Walsh.

References

[1] COSTLEY, A. E., et al., “Measurement Requirements and the Diagnostic System on ITER: Modifications Following the Design Review,” 22nd IAEA Fusion Energy Conference, Geneva (2008).

[2] WANG, S., et al., “Electromagnetic behavior on ITER radial soft x-ray camera,” 2013 IEEE 25th Symposium on Fusion Engineering (SOFE), San Francisco (2013).

[3] VAYAKIS, G., et al., “Current status of ITER diagnostics development,” 26th ITPA Spring Meeting, Pohang (2014)

[4] HU, L., et al., “Outline Design of ITER Radial X-Ray Camera Diagnostic”, Fusion Science and Technology, 70 (2016) 112

[5] BARNSLEY, R., “Annex B_55 E7_Radial X Ray Camera”, private communication, 2013. [6] JOURNEAUX, J., “Plant Control Design Handbook”, private communication, 2013. [7] BELTRAN, D., “EDH Part 4: Electromagnetic Compatibility (EMC)”, private

communication, 2012.