The experience gained in the working of the High Voltage system of the Tile Calorimeter (TileCal) and the new HL-LHC constraints, in particular the increase in radiation, lead to the proposal of moving the embedded regulation system to a Remote system in the electronics room.
The Remote HV system is using the same kind of electronics as the present one, but:
- The individual adjusted voltages are distributed by 100 m long multiconductor cables, with one cable per mini-drawer welcoming 12 channels.
- The in-situ HV distribution is made through passive HV bus cards.
- The regulation loop is revised while now active PMT dividers are used.
The three first challenges were the HV noise studies at the PMT input (Divider output), the impacts of the HV noises on the front end readout noise and the HV regulation stability.
Systematic tests lead to the main conclusion that combining the use of 100 m long HV multiconductor cables and active dividers, we had the obligation to come back to the original HV loop regulation scheme, without additional transistors at the two optocoupler sides.
This design fits all the specifications:
- The HV noise at the divider output is always below 2.5 mV at 700 V, this ratio staying constant in the HV adjustment range of 300 V.
- The regulation stability is always better than 0.090 V, even better than in the present ATLAS setup.
- The HV induced noise on the front end readout is negligible with respect to the intrinsic front end readout noise.
The HV regulation crate offers many advantages.
- It contains the HV regulation cards, the Low and High Voltage power supplies, always accessible in case of problems.
- Using passive individual straps, it is easy to disconnect a channel which could have a short-circuit at the non-accessible detector part (PMT, divider, front end electronics).
The passive HV bus cards offer also new advantages:
- They are all identical.
- Their implementation is easy and quick.
- Once they are implemented, the handling of the drawers is safe.
- Their routing and their connections to the multiconductor cables are simple.
- The HV tracks are protected since they are in the internal layers of the PCB. Made of copper, the external layers act as shielding.
- The long multiconductor cable being connected outside the TileCal modules to the internal cables of the drawers, no space is requested by connectors on the patch panel. Moreover, these HV connections are quick and safe.
The final design should improve the HV card implementation inside the regulation crate, leaving space for the Low and High Voltage power supplies, keeping an easy access to the individual straps and to the main electronic components.
In conclusion, this Remote HV system fulfills all the requested specifications in terms of performances (HV regulation stability and noise) and handling. Moreover, it offers the unique advantage of a permanent access, including an individual channel switching in case of a short-circuit at the front end electronics level.