The particle trajectories run in the vacuum from the target region to the extension box which is attached to the exit of the D magnet to minimize the multiple scattering effect and/or unnecessary activation of materials. Figure 25 shows the vacuum chamber of the HKS. The vacuum chambers in Q1 and Q2 are shaped to fit the pole faces in order to maximize the solid angle of the spectrometer. The vacuum chamber in the D magnet consists of side walls, and the upper and lower pole faces. They are hermetically sealed with O-rings, and thus there exists a flexibility to adjust the relative position to the Q1, Q2 vacuum chambers. The vacuum extension box is attached to the exit of the D magnet. A Mylar window reinforced by a Kevlar mesh (or thin metal foil), which is placed just in front of the first drift chamber, separates the vacuum system and air. Between the splitter and the Q1 vacuum chamber, a removable sieve slit made of tungsten alloy (2'' thick HEAVIMET) is placed for the calibration of the HKS spectrometer optics. The splitter vacuum chamber is also connected to the vacuum chamber of the Enge spectrometer. The photon beam line goes through the Q1 and D magnets to the Hall-C beam dump. The electron beam deflected by the splitter magnet is guided also through Q1 and D magnets' cuts and is finally bent back to the beam dump by a set of steering (BZ) magnets. The HKS vacuum chamber is evacuated from bottom of the extension box with a Turbo Molecular Pump to be provided by Jlab.
The HKS vacuum chamber was already completed in Japan and all vacuum components were separately tested. After the HKS magnets' field mapping, all components will be assembled to be leak-tested before shipping to Jlab. The design of the sieve slit box and target chamber is in progress by the Jlab engineering group (figure 26).