Thailand to Participate in the Development of the PandaX III Field Cage P. Chaiyabin1, J. Lomon1, Prayoon Songsiriritthigul1*, P. Poolcharnansin2, N. Pasaja2, S. Rujirawat1, C. Kobdaj1, Y. Yupeng1, X. Chen3, K.L. Giboni3, J. Liu3 and X. Ji3 1Suranaree University of Technology, Thailand 2Mahasarakham University, Thailand 3Shanghai Jiao Tong University, China XeSat2017, Khon Kaen 4/5/2017

Outline Background – PandaX, DLC Experiments & Preliminary Results Challenges

1. Background - The PandaX III Field Cage PandaX III is a large gaseous xenon TPC filled with 200 kg of 90 % enriched Xe isotope 136 The cathode is in the center plane of the cylindrical detector, and two Micro Mega planes form the read out anodes at the two ends. Naturally there has to be a field cage to shape a homogeneous electric field in two separate drift regions. The conditions the electric field shaping are not at all similar to the more common liquid xenon detectors for Dark Matter Search. Gaseous Xenon has a much lower dielectric strength than liquid. The xenon outside the field cage does not contribute to self shielding The enriched Xe is much more expensive. Using the gaseous xenon outside the field cage to stand-off the HV would be very, very expensive. (Design of PandaX III by Shaobo WANG XeSAT2017 on April 4th, 2017)

No more SMD resistors, no soldering, no connections between panels 1. Background - Alternative Field Shaping Field shaping panels can be coated with resistive layers. No more SMD resistors, no soldering, no connections between panels Large resistive layers can be screen printed, e.g. MMs for ATLAS However, our resistive values are too high. The resistivity cannot be precisely controlled because the layers must be too thin. Ochi et al.: Sputtering of Diamond Like Carbon (DLC). See Proc. of MPGD2015 With DLC very thin layers can be reliably reproduced (down to 10 nm). Resistivities up to 2 GW/” can be realized reliably.

1. Background - HV Stand - Off Cu clad HV Panels Earlier tests showed that 20 mm of acrylic are sufficient to stand off 100 kV. However, we have gaps where panels meet. Therefore, 50 mm. The plan is to stand-off the HV in acrylic panels, i.e. the outside of the HV panels is coated with a conductive surface on ground potential.

1. Background - Schematic of PandaX III

Field shaping panels on the inside Field Shaping Panels : SUT 1. Background - Panels to Stand-Off HV HV panel thickness 50 mm. Inner Vessel Diameter 1.6 m Clearance to walls about 2 mm Number of HV Panels 24 Width of HV panels 20 cm Length of Panels 2 m Total Weight 550 kg Panel Cross Section Field shaping panels on the inside of HV panels Material: Acrylic,Nylon, or Delrin. Thickness of panels 5 mm Length of panels 1 m Width 10 cm Number of Panels 2 x 48 Cathode Ring Field Shaping Panels : SUT HV Panels : SJTU

Required layer might be too thin. 1. Background - Favored Geometry Required resistivity: about 1 GW / Required layer might be too thin. Then use pattern.

Used to coat the large mirrors of the The NARIT Sputter Station Designed & built at SUT and SLRI Used to coat the large mirrors of the 2.4 m telescope

1. Background - Resistivity of DLC DLC is semiconductor and its properties are determined by the relative ratio of the two hybridizations (sp2 and sp3) and impurities (H, N, B, etc.).

1. Background - Surface resistivity vs DLC thickness @ ATLAS The blue line shows the resistivity of pure carbon sputtering, and the red line shows that of Nitrogen doped foils. The orange band represents the required resistivity for the ATLAS MicroMEGAS. [Ochi et. al., Proc. of MPGD2015]

2. Experiment & Results DLC film deposition techniques RF Magnetron Sputtering @ SLRI High Power Impulse Magnetron Sputtering (HIPIMS) @ MSU

Substrate Holder Glass & Acrylic Square width x length: 2 x 2, 1 x 1 [c m 2 ] Glass & Acrylic Pattern width x length: 2.5 x 5 [c m 2 ]

2. Experiment & Results Characterization Techniques Resistivity measurements Raman spectroscopy Scanning electron microscopy (SEM) X-ray photoelectron spectroscopy (XPS) X-ray absorption spectroscopy (XAS)

Sheet Resistivity @ RT DLC10 DLC20 DLC30 [Ochi et. al., Proc. of MPGD2015] DLC10 DLC20 DLC30

XPS spectra sp3 : sp2 ratio 1 : 2.7 for DLC10 1 : 3.3 for DLC20

XANES spectra of C K-edge C-H sp2

Resistance vs Temperature

3. Challenges Homogeneous film & Reproducibility Scale up Resistivity/Composition Thickness Uniformity Scale up Formal support from the Thai Government through a networking organizations (SUT, MSU, KKU, NECTEC, SLRI & NARIT)