VME Crates

VME crate on Gammasphere and a closeup of what the front of a crate can look like.

VME (Versa Module Extension) crates house the digitizers, triggers, and IOC modules for Gammasphere's DAQ system. The crate has specific connectors that plug into a standard backplane for power and communication. VME backplanes are mounted into mechanical assemblies referred to as “crates” or “subracks” that in turn mechanically mount into larger mechanical objects called “racks” or “relay racks”. The crates are underneath the power supply and collector box, and host extremely important signal processing hardware. The image to the right shows the VME crate on one side of Gammasphere, with a closeup of what the crate may look like from the front. The VME crate is the largest box on the rack, and although the sketch of Gammasphere does not show modules inside the crate, the closeup shows what a crate looks like with some modules inserted.

Each VME crate contains 3 individual VME backplanes, and each of them act as an individual VME system. Each of these VME systems has four digitizers, for a total of up to 12 digitizers per crate. One of the 12 VME systems is reserved for housing the System Trigger and the associated electronics, meaning each of the four racks has one Router Trigger. The System Trigger is then connected to all routers in the system. However, whereas the original setup used short copper cables to make these connections, the new distributed system uses optical connections between the System Trigger and the Routers. This required the designing of a VME Fiber Expander to provide a fully optical interface to the System Trigger. Furthermore, each VME backplane has one VME input output controller (IOC).

Prior to upgrades, Gammasphere used crates called "VXI crates", which had a similar function to VMEs. A larger number of crates were needed within the VXI system, making it necessary to place them in an electronic "shack" room. During the upgrade to digital Gammasphere, one of the goals was to divide the system into 4 separate crates and mount them directly onto Gammasphere's frame in the hopes of making all of Gammasphere a "movable detector". As of 2023, the upgraded system has been implemented, and the VXI system dismantled. Figure 1 on the DAQ system page shows what the system now looks like (albeit without the cabling and wires).