Apex Target  

Marco Oriunno, April 23, 2014

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Design and fabrication by:

Marco Oriunno, Dieter Walz, Jim McDonald, Clive

Field, Douglas Higginbotham, and many others…

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Beam parameters assumed40 µA

Vertical width 400 µm

Horizontal width 400 µm

Vertical dither 5 mm

Horizontal dither 1.5 mm

.Requirements

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Beam direction

General Layout

1. First Row (from the top) Carbon foils 100um, calibration of the spectrometer with wide angle pion. The first foil is probably BeO.

2. Second Row: Wires H/V for low current beam position and angle scanner.3. Third Row: Tungsten Foil 15um (more stable that Tantalum). More foils

downstream increase the Rate.

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10 layers of 15 µm thick tungsten ribbons (4.3% rad length)2.5 mm wide in X

Separated by 5.5 cm along beam

- Tracks from A´ decays produced in a ribbon, and going into the spectrometers, will not be intercepted by the next ribbon

Production target:

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beam

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At 40 µA, the target will become hot!The tungsten will expand- The frames that hold the tungsten have enough spring to maintain the ribbons under tension, even when hot.The hot tungsten may be much weaker than at room temperature- The temperature range and tension are selected to stay away from breaking point.- 250 g tension (Verify the tension is still 250 g)

Cooling in the beam region is mostly by black-body radiation. Conduction becomes more important at lower temperatures closer to the supports.

Numerous calculations of thermal effects and a simulation allowing for temperature dependence of thermal properties:--

Target issues:

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Tungsten foil, 15 microns thick ± 4 cm tall.Beam 40 A, dither ± 2.5 mm high, beam sigma 0.4 mm,beam just fills 2.5 mm wide ribbon

distance from beam center (cm)

-4 -2 0 2 4

Tem

p. (

K)

400

600

800

1000

1200

1400

0.1 sec0.5 sec1 sec2 sec5 sec10 sec20 sec Peak temp

1300 K

Steady State after 20 sec.

Temperature Transient (black body radiation only)

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Temp difference(K) between inner 0.25 mm strip and outer 0.25 mm of 2.5 mm wide ribbon, vs. distance up from beam center, after various beam times.15 m tungsten; 40 A beam, 5 mm vertical dither, 1.5 mm horiz dither, 0.4 mm RMS spot size

vertical distance from beam center (cm)

0 1 2 3 4

tem

p di

ffere

nce

(K)

0

2

4

6

8

10

12

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0.1 sec1 sec5 sec10 sec

Across the beam width

Temperature Distribution

Temp. fairly uniform horizontally across ribbon

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Thermal expansion after beam turn onof 80 mm long tungsten ribbon, 15 m thick.Beam 40 A, 5 mm vertical dither, sigma 400 m.

time from beam-on (sec)

0 5 10 15 20

expa

nsio

n (m

m)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14Elongation130 µm

Thermal Expansion

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Beam at < 5 µA for alignment work

A set of tungsten wires spaced along the length of the target4 horizontal wires in 5 mm vertical steps, at -25, -10, 10, 25 cm along the beam3 vertical wires in 0.25 mm horiz steps, at -20, 0, 20 cm along the beam

100 µm diameter tungstenStill gets hot! But not as bad as the production target ribbons.- Still, use similar tensioning technique as for the ribbons- 150 g tension

Alignment relative to target

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Tungsten wire 100 m diam, ± 4 cm tall.Beam 5 A, dither 2 mm X & Y:beam sigma 0.4 mm. Various times after beam on.

distance from beam center (cm)

-4 -2 0 2 4

Tem

p. (

K)

300

400

500

600

700

800

900

1 sec2 sec5 sec10 sec20 sec30 sec

Peak temp 900 K

Tungsten wire Calibration Target - Heating

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Produce copious pion signal8 foils spaced along the length of the target

(-30, -22.5, -15, -7.5, 7.5, 15, 22.5, 30 cm)

• Target frames are mounted on an aluminum plate• Plate is cooled by N2 flow through heat sinks on reverse side• Optical targets for use during installation are inserted in the

back of the plate, (ruby balls)• The wire positions have been surveyed relative to the optical

alignment targets.

BeO scintillator for beam diagnostics

Calibration Target - carbon foils

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Work that should be done on the target

-Visually inspect it

-Check that the target ribbons and wires are under adequate tension

-Check that the structure is clean enough for vacuum

-I believe that one or two of the target ribbons were made oftantalum, the intention being to hedge our bets and see if either metal survived better during special test runs (not carried out).The tantalum was found to be mechanically liable tocrack during flexing.

->Decide whether to replace the tantalum with tungsten.

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