Main Drift Chamber Yuanbo Chen Ihep

Motivation (MDC IV) The BGO crystal used in L3 will be used for BES III ’ s Calorimeter. The space for MDC IV will be limited. In MDC IV design, some items have to be considered in the limited space: Cell structure should be small; The height of the cell should be as small as possible, and reduce the space between layers for setting more layers; Since the momentum resolution is dominantly limited by the multiple scattering, a low- Z working gas and low-Z field wires are needed; The inner part of the end-plates of the MDC IV will be designed as a multi-step to allow micro-β components at both ends, and have maximum polar angle coverage.

BES III (MDC location)

The position of micro-β in IR

Baseline design of the drift chamber Expected performance R&D program Time schedule MDC IV

Baseline design  General description  The mechanical design  Drift cell configuration and layer organization  Working gas selection  Low Z-field wire selection  Electronics readout

General description (1)  Length: 1,856 mm  Outer cylinder  Thickness: 5 mm  Material: Al  Inner cylinder  Thickness: 1 mm  Material: carbon fiber  : 0.45%  Endplate  Thickness: 25 mm  Material: Al  Inner section: stepped  Outer section: flat

General description (2)  Layer 8(first-step)+4*2(four steps)+20(outer) = 36 layers  Sense wire 30μm, tungsten gold-plated  Field wire 110μm, aluminum gold-plated  Cell  Small cell configuration  Total number: 5,322  Height: 12 mm (first step) 14 mm (others)  Width: mm

Mechanical design  Multi-step endplate design ( refer to CLEOIII )  Cosθ=0.93 (L 18)  Cosθ=0.83 (L 36)  The inner diameter: 80 mm  The outer diameter: 1,320 mm  The length : 1,906 mm (end-plates are included)  Stepped endplates: 5 steps are interconnected with nonmagnetic steel bands via radial screw.

The structure of MDC IV

Layer organization (1) Small cell configuration with super-layer arrangement is chosen for MDC IV  36 sense wire layers 8 sense wire layers: first stepped section, each layer has different number of cells. 8 sense wire layers: from second step to fifth step,every two layers have the same number of cells..

Layer organization (2) 20 sense wire layers: in the plane section, every four layers have the same number of cells All cells will be symmetrical at 90°  Wire configuration of MDC IV (table.)  The z-direction resolution: σ z < 3 mm

Layer organization (3)

The Cell configuration of MDC IV

Drift cell configuration Cell design of the inner layers of MDC IV

Working gas selection (1)  Important factors to be considered X0 (radiation length) Vd (drift velocity) Electric stability Availability cost  Helium is the only low-z gas condidate Radiation length: 50times longer (≈5300m) than Argon (≈110m)

Working gas selection (2) The properties of various He based gas mixture Gas mixture RatioRadiation length (m) Primary (i.p./cm) Total (i.p./cm) Comment He/C 2 H 6 50/ BELLE He/iC 4 H 10 90/ KLOE He/iC 4 H 10 80/ (20.6)(45.4)BABAR He/CO 2 /iC 4 H 10 83/10/ BABAR He/CH 4 90/103087(7.0)(12.5)KLOE He/CH 4 80/202178(9.1)(17.0)BTCF He/C 3 H 8 60/ CLEOIII

Working gas selection (3)  60% He-40% propane gas mixture as MDC IV working gas will be chosen (refer to CLEO III) Long radiation length (550m) A drift velocity that saturates about 4 cm/μs for a relatively low electric field.

Working gas selection (4)

Working gas selection (5)  The drift velocity were measured using specially constructed test chamber.(K.K.Gan,…,1996)

Working gas selection (6) A Small prototype for Tau-Charm feasibility study ( R&D program ) Field wires: Al Working gas: He/CH 4 (80/20) Cell size: 2×2cm 2 Wire length: 1m  The average spatial resolution of 155μm was obtained. The average time resolution

Low z-field wire (1) Several kinds of light material wires have been proposed and tested.Aluminum wire has a relatively long radiation length and is a good field wire candidate. results of the long term creeping test by BTCF (tension lost <10%) The observation result for long time creeping of 0.1mm Al wires

Low z-field wire (2)

 Our choices: (refer to CLEOIII) Sense wire: 30μm gold-plated tungsten, to maximize the drift electric field. Field wire: 110μm aluminum, to reduce the material of the chamber.  A candidate aluminum wire with little creep has been tested.  With the proposed diameter wires, the electric field strength at the surface of the aluminum field wires is always less than 20kv/cm, a necessary condition for avoiding radiation damage.

Electronics readout  The MDC IV has a total of 5,322 sense wires. Both the time (T) and charge (Q) information for each wire will be read out.  Since the single wire spatial resolution is designed to be σχ ≤130μm, the time measurement error from electronics readout ≤ 0.5 ns (20μm) is desirable,assuming a drift velocity of = 4 cm / μs.  The charge deposition could be measured by integrating the signal current from sense wires with an accuracy better than the intrinsic chamber resolution of about 7%. Therefore a charge measurement with a precision of 2 % is sufficient to match the chamber resolution.

Expected performance  Solid angle coverage  Single wire spatial resolution  Momentum resolution  resolution

Solid angle coverage As show in Fig. 2, the solid angle coverage in the Layer 18 (sense wire) is cos  =0.93 and in the last layer is cos  =0.83

Single wire spatial resolution  Single wire spatial resolution consists of following terms: where, : is the contribution from the diffusion, about 60μm in our case, : is the contribution from time measurement error of readout electronics, assumed to be 20μm here, : is the contribution from the statistic distribution of primary ionization electron to the  From the experience of similar chambers, a single wire spatial resolution ≤130μm can be achieved.

Momentum resolution (1) Where, L (lever arm) =56 cm, B ( magnetic field ) = 1.0 Tesla, (spatial resolution)=0.013 cm, N (number sampling) = 30 and ~1. Taking the radiation length of gas mixture,, as 550m, and assuming the wire material uniform distributed in the chamber volume, the total is =163 m. The momentum resolution from both contributions can be written as: So the momentum resolution can be achieved.

Momentum resolution (2) The result from simulation

dE/dx resolution  The dE/dx resolution of CLEO III (experimental results ) is 5% (electrons),  The dE/dx resolution of the MDC IV will be about 7%.

dE/dx resolution ( Simulation results )

The main performances of MDC IV are: single wire position resolution ≤ 130 µ m momentum resolution: efficient tracking down below 100 Mev/c dE/dX resolution around 7% the solid angle coverage is cos  =0.93 The z-direction resolution: σ z < 3 mm

R&D program  Geometry of the MDC IV chamber  Cell and layer organization  Track reconstruction and full simulation  Cooperation with CLEO III and other experiments  Prototype making and testing

R&D program (continue) In process : Feedthrough: Designing, making capability investigation, Structure: Designing & Simulation with ANYSYS, Cell : Designing & Garfield Simulation, Wire: Creeping test,Crimping tool investigation, Prototype : Designing & preparation.

Time schedule itemsTime(year) R&D and chamber design1.5 Machining1.5 Assembly and wiring1 testing0.5 total4.5

The end Thanks a lot !

Referents From Tue Sep 25 09:56: Date: Mon, 24 Sep :35: (EDT) From: To: Re: layer spacings The only place that I have heard about gas cooling was in the BESS-III April description. I recommended that you do not cool the gas. Instabilities in the cooling system could lead to rapid temperature changes of the wires which could lead to broken wires. CLEO does not cool the gas. The CLEO gas system recirculates the gas. In the process of recirculation we remove oxygen and restore the helium to propane ratio to the specified level. The system was built by a SLAC group, lead by Martin Perl,which is a part of CLEO. The total cost was $250,000. I do not have a reference.

R&D:900k Endplates:5,500k Inner cylinder:30k Outer cylinder:200k Feedthrough:1,600k Wires:400k Assembly:500k Wiring:1,800k(clean room,wiring machine,manpower) High voltage boards and cables:700k Gas system:1,000k Cosmic ray test:200k Scientific exchanging and others:300k No predict:800k Total:13,930 K Cost estimate (in RMB)