GridLeak Simulations

Nikolai Smirnov & Alexei Lebedev:

Data for STAR TPC supersector.   05.05.2005  07.11.2005
Jon Wirth, who build all sectors provide these data.

Gated Grid Wires: 0.075mm Be Cu, Au plated, spacing 1mm
Outer Sector 689 wires, Inner Sector 681 wires. Total 1370 wires per sector

Cathode Grid Wires: 0.075mm Be Cu, Au plated, spacing 1mm
Outer Sector 689 wires, Inner Sector 681 wires. Total 1370 wires per sector

Anode Grid Wires:0.020mm W, Au plated, spacing 4mm
Outer Sector 170 wires, Inner Sector 168 wires. Total 338 wires per sector
Last Anode Wires: 0.125mm Be Cu, Au plated
Outer Sector 2 wires, Inner Sector 2 wires. Total 4 wires per sector

We are most interested in the gap between Inner and Outer sector, where ion leak is important for space charge. On fig. 1 wires set is shown. The distance between inner and outer gating grid is 16.00 mm. When Grid Gate is closed, the border wires in Inner and Outer sectors have -40V, each next wire have -190V and after this pattern preserved in whole sector - see fig. 2. When gating grid is open, each wire in gating grid have the same potential -115V. Above grid plane we have a drift volume with E~134V/cm to move electrons from tracks to sectors and repulse ions to central membrane. Cathode plane has zero voltage, while anode wires for outer sector holds +1390V and for inner sector +1170V.

Fig. 1. Wire structure between Inner and Outer sector.

Fig.2 Voltages applied to Gating Grid with grid closed.

Another configurations of voltages on gating grid wires are presented on fig.3. All these voltages are possible by changing wire connections in gating grid driver. Garfield simulations should be performed for all to find a minimum ion leak.

Fig.3 Different voltages on closed gating grid (top: inverted, bottom: mixed).

This is a key for Nikolai's files: there are 4 sets of files in each set there is simulation for Gating Grid voltages on last wires. Additionally he artificially put a ground shield on the level of cathode plane and simulated collection for last-thick anode wire and also ground shield and last thin anode wire.

Setups:	Standard	Inverted	Mixed	Ground Strip	Ground Strip and Wire
Equipotentials	PS	PS	PS	PS	PS
Electron paths	PS	PS	PS	PS	PS
Ion paths (inner sector)	PS	PS	PS	PS	PS
Ion paths (outer sector)	PS	PS	PS	PS	PS