LSTs in the IFR gaps Workshop on IFR replacement SLAC November 14, 2002 L. Piemontese INFN Ferrara

Outlook The iron: dimensions, available space To install: LSTs, gas, HV, readout Minimizing dead space Electronics and cabling Installation

The Iron  The gaps : nominally 35mm, guaranteed 22mm (29mm for last 85mm). They have been checked by sliding a 22mm thick Al slab, 1.22 m* 0.51m. They are 3.75m long, widths varying from 2 to 3m.  Once the gaps are visible: It would be very fast to check their height again with other slabs (26mm, or other values), to see if more space is actually available.  Cable conduits: There are 8 conduits for the IFR, for each sextant, symmetrically Front/Back and Left/Right. 4 conduits are for signals, 12.5*5cm**2 next to filler plates, and 4 are HV and gas, 3*3, behind corner blocks.

The Iron

To be installed LST chambers; Gas lines; HV cables; signal cables; FE electronics. Guidelines for installation: minimize dead spaces and allow easy access to electronics. Gas lines: all LSTs in a layer in series: only one line feeding a whole layer (à la SLD), and small connecting blocks between adjacent tubes. HV cables: each LST has its own line. Install unipolar cables, diameter 1mm, from distribution boxes on the outside. The total cross section, for 12 layers in a sextant, each with one layer of standard LSTs, is 8cm**2. As an option, we may consider putting HV distribution boards at the ends of gaps with brass absorbers.

The CHAMBERS Whichever the geometry of the LSTs, there will be (most likely) z-strips and Ф-strips. (OPTION: read wires instead of Ф-strips; would cost as dead-space for HV capacitors at the ends of the wires). Ф-strips arrive nicely at the gaps ends. 2 ways to carry there the signals from the z-strips: a) printed circuits or b) cables (à la SLD). We are working on a solution based on printed circuits, with the aim to have a chamber with flat surfaces, with as few cables glued on as possible.

Proposal for the LST-based BaBar IFR upgrade: electronics related issues. 1.a Detector layout: segmentation of a detector layer Z strip readout Layer of LST Ф strip readout Z strip signal collection PCB Ф strip signal collection PCB (a similar one in the opposite corner) The detector could be assembled in two longitudinal halves at the cost of doubling the number of signal cables for the Z view PCB for cable connectors Servizio Elettronica INFN Ferrara

How many chambers per layer? One chamber per layer is awkwardly big to deal with, to transport, to install. Three chambers per layer may make it easier to replace faulty chambers. That also means: 3 cables to carry the signals of the z-strips, three times more signals to deal with at the gaps’ ends. Unless (OPTION to be verified) we can install separately a wide sheet of z-strips and then, over it, the three chambers. Main reason for such choice: the request to have the layers in three separate chambers, so one can be “easily” replaced if necessary without having to take out the corner blocks. Alternative: 2 chambers: easy (easier!) to handle; can be replaced by taking out only one corner block.

Chambers:dead spaces Those dead spaces are in practice less large, since tracks are not precisely perpendicular to the tubes; we address this problem with the option: large cell/double layer. There are 2 other dead spaces: The 8-cell modularity and the connections at the ends of the LSTs (both inside and outside the tubes). Dead spaces : separation between adjacent LSTs accounts for 4mm (5%); sides of profiles (7 * 8 mm) account for ~9% (for worst case, ie 90º tracks only).

Dead regions The 8-cell modularity: the space covered by the detector is a multiple of 8cm. Therefore, in the worst gaps we may lose up to 7cm (over at least 2m), i.e. 3.5%. We can order some 7cm tubes, and also put brass in the most difficult gaps. Dead spaces at the ends of the LSTs, both inside and outside the tubes, used for gas and HV connections.

Dead regions The ends of the LSTs, with HV and gas connectors, wire supports etc, both inside and outside the tubes. Inside the tubes, we lose 4.5cm at the HV connector side, 3cm the opposite side. If we read the wires, we lose an additional ~5cm at the HV side, (capacitors). Plus, ~2cm for gas connections between LSTs, but ~5cm for the side with the HV connectors. We plan to put HV connectors in the Backward side.

Proposal for the LST-based BaBar IFR upgrade: electronics related issues. 2.a Front end module design : block diagram of the NEW 96 channel (1 view of 1 layer) FEC 96x Amplifier-Discriminator 11us Digital OneShot Shift/Load Ck_Chain Data Out SHIFT REGISTER 96 x Threshold 12us Digital OneShot 11us Digital OneShot 12us Digital OneShot Shift/Load To the Active Patch Panel ahead of the FIFO Board 6 x Implemented in a single high performance FPGA (Field Programmable Gate Array) Cost per channel inclusive of: -components -PCB -crate&power supply 10 € / channel

Proposal for the LST-based BaBar IFR upgrade: electronics related issues. 2.c Front end module design : analog simulations - effect of strip capacitance and impedance Simulation of the amplifier/discriminator output from a 4pC input signal (0.1mA * 40ns) Comparator threshold = 50mV dielectric thickness 0.75mm a) dielectric FOAM (ε r =1) b) dielectric PTE (ε r =3.3) c) dielectric FR4 (ε r =4.8) a) b) c)

Front End Electronics We want something that has the same readout as the FECs (talks to the FIFO board), but with a settable threshold. WHERE can we put it? Four options: –Everything OUTSIDE. –Amplifiers in the gaps, first few (~10) cm. –Amplifiers and discriminators in the gaps, ~10cm. –Everything in the gaps, ~15cm dead space. CHOICE still to be made. In the “everything outside” solution, we need ~10’ access to replace a module (~1 day of beam lost if we have to open endcaps). There is enough space for the cables. The decision will be made based on cable availability and cost, and noise considerations. If the electronics has to be in the iron, we prefer it to be in the Backward side, in the first ~15 cm of the gaps.

How many channels? (ie, strip pitch?) The issue of strip pitch has to be decided primarily by physics studies (MonteCarlo works in progress). NOW (I mean, with the present RPCs), we have 19 layers, each with 96 z-strips (3.85cm) and 96 Φ-strips (pitch varying according to layer, 1.97  3.28cm) New setup: we assume we will have 12 layers of LSTs. We much prefer having a fixed strip pitch, owing to the fixed cell size (4 cm would be fine). The less channels, the better (cables, cost,…).

Installation Not worked out in detail yet. Preliminary plan is to have LSTs made and tested in Italy and shipped to US (Princeton, Ohio?), where they will be tested again and chambers will be fabricated. Chambers will be shipped to SLAC and stored (test needed again?). The IR2 crew will be involved with installation and its tooling. We need flat tables - to be aligned with the gaps – on which the chambers will be located, ready to slide into the gaps. Installation will be from the Forward side, which will have its corner blocks removed. In fact, the corner blocks in the Backward will stay in place. The space available for installation is 15cm short on the bottom sextant. Whole layer chambers may be difficult to handle and insert. Split chambers too.

Conclusions We have a large detector, with many channels, to put in a very limited space. Considerations of maintainability and efficiency are of paramount importance. Solutions and options have been identified for the construction of the LST chambers and the location of all the elements in the iron. A possible Front End electronics readout has been designed and is being evaluated. The mechanics of the iron has already been inserted in CAD software for design work. Mechanical and electronics design are being continued.