Speaker
Description
We developed the GEM-based Time Projection Chamber, HypTPC, for the hadron experiment at J-PARC. The HypTPC has a unique design that allows for the installation of the experimental target inside the field volume, thereby achieving large acceptance. Consequently, we need to inject the beam into the TPC active area, and the HypTPC should have a high rate capability.
To achieve this, we adopted a triple GEM configuration with thicknesses of 100 μm, 50 μm, and 50 μm, along with a gating grid wire system. The first experiment with the HypTPC, the JPARC E42 experiment to search for the H-dibaryon, was successfully completed in 2021. In this experiment, we injected a beam with a rate of about 10⁶ Hz into the HypTPC, and no GEMs failed during the experimental period. However, we also found that the 10⁶ Hz beam intensity is close to the operational limit for the current HypTPC. To improve the rate capability, we have begun developing a new type of GEM, the Glass GEM.
In the current HypTPC, the GEMs use Polyimide and Liquid Crystal Polymer as the insulating material, which is widely used for TPC detectors. Recently, the Glass GEM has been developed for neutron imaging [1]. The Glass GEM offers several advantages over the conventional GEM for the following reasons. The flatness is better because glass is stiffer compared to conventional one. A flat GEM can create a uniform electric field, leading to a uniform gain. Glass does not contain organic material, so the probability of shorting the electrodes due to sparks is lower compared to the conventional GEM, which is an organic material.
However, producing thin Glass GEMs is challenging because glass is fragile, and the thickness was previously limited to about 500 μm. Here, a multilayer configuration with thin GEMs is essential for rate capability to avoid ion backflow. We have developed a 100 μm thick GEM in collaboration with NSC company, which has specialized techniques for chemical etching.Recently, we succeeded in measuring the signal with triple 100 μm Glass GEMs. In this workshop, we will present an overview of the HypTPC and the current status of the thin Glass GEM development to achieve high rate capability.