Diamond Radiator Thinning and Mounting for GlueX R.T. Jones GlueX collaboration meeting, Regina,...

R.T. Jones, GlueX Collaboration Meeting, Regina, Sept. 9-11, 2010 1

Diamond Radiator Thinning and Mounting for GlueX

R.T. Jones

GlueX collaboration meeting, Regina, Sept. 9-11, 2010


Outline• Diamond ablationDiamond ablation

laser lifetime issue – resolved facility construction continues

• Diamond mountingDiamond mounting tests with carbon wires measurements with glue droplets

• Diamond assessmentDiamond assessment plans for a run this Fall at CHESS outlook for the next 12 months


Diamond ablation facility Where we were at the May meeting:

– first light pulses expected in ~1 week – then what?– UConn engineer/tech Brendan Pratt designed the optics setup (see below)– ……then on June 1, then on June 1, first light pulses seenfirst light pulses seen, low power at first, but increasing …, low power at first, but increasing …– however the lifetime remained less than however the lifetime remained less than 5 minutes per gas fill5 minutes per gas fill


Diamond ablation facilityCould the gas recirculating volume be somehow contaminated?

Lasing happens in hereLasing happens in herealong the line of sight.along the line of sight.

Gas gets recirculated throughGas gets recirculated throughhere to remove heat andhere to remove heat andfilter out dust produced byfilter out dust produced byreactions with the walls.reactions with the walls.

Decision:Decision: undertake a major disassembly to remove any debris that could contaminate the fluorine gas.


Diamond ablation facility

The inside was caked withresidue from years of operationwith a chlorine – xenon mixture.



before

after


Diamond ablation facility After reassembly, lasing lasts 30 minutes30 minutes with a single gas fill ! Passivation process: lifetime gets longer with each fresh fill

There are two ways to refresh the gas:1. top-up – takes 20 seconds2. flush and refill – takes 5 minutes

We are now at the point where laser lifetime will not limit anything that we want to do.

Power per pulse starts out at 150 mJ, threshold is 35 mJ. Major remaining limitation is pulse rate: 2 Hz without cooling

laser lifetime is now 8 hours for one fill



20% spot-RMS displacements between adjacent spots to get good uniformity

complete coverage with less than 10,000 spots

conservative estimate 1 m in depth per pulse

net result: required to thin a 300 mm diamond to 30 mm

2 Hz is not good enough2 Hz is not good enough4 mm

laser focal spot 300 x 200 laser focal spot 300 x 200 mm

200,000 pulses



• Work now underway– Chilled water recirculator has been ordered

– Precision stages for raster are on the bench– Labview software for raster control is in

development– Ablation vacuum chamber is in final design,

fabrication will take place in physics machine shop• First ablation tests anticipated Dec. 2010

increases maximum pulse rate to 50 Hz50 Hz


• Advantage of wires: minimize material in the tails of the electron beam, allow for full 90° rotation.

• Advantage of carbon wires over tungsten:– factor 5 times stronger per area– factor 60 longer radiation length– possibility to sinter carbon to the diamond

• Disadvantages of carbon wires– more brittle, can break when flexed– cannot solder to the mounting frame

• Samples and expert help obtained from Fermilab accelerator physicist with experience using carbon wires as targets.

Diamond mounting: carbon wires

studied by studentsin summer 2010


Diamond mounting: carbon wires


The Principles Behind Our Experiment: Ensuring Radiator Stability

• Vibrating Wire– Crystal radiator must be stable – Must be finely tunable to create Coherent Bremsstrahlung

• Resonance-

a system’s tendency to vibrate with a larger amplitude at certain frequencies

• Constructive intereference

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UConn Mentor Connection 2010 Chelsea Sidrane


Weighting the Wire

14

M

Tension (T)Tension (T)

Length (L)

L/2L/2

drop of glue

Wires assumed massless

AngularFrequency

Making Measurements-resonance frequency of carbon fibers-increased mass lowers resonant frequencies



•Theoretical Data estimated to find resonant curve

15

Weighting the Wire:Theory V. Data

Peak of Resonance Curve is maximum resonant frequency

*Enlarged view*



Diamond mounting: carbon wires Conclusions from resonance study

1.1. Carbon wires are robustCarbon wires are robust enough to hold a mass similar to a 20 micron 4x4 mm2 diamond.

2.2. Simple holding techniqueSimple holding technique suggested by Fermilab colleagues is reliable, even with 30 m wires.

3.3. Handling carbon wires is manageableHandling carbon wires is manageable, even for inexperienced students.

If multiple strands are wound together, we can achieve a fundamental frequency > 10,000 kHz which is far out on the tail of the ground motion spectrum – more than factor of 100 in amplitude.


New run planned for November, 2010

1. Element Six 10 micron diamond (1)

2. Element Six 500 micron type IIa crystals (2)

Ideas for mounting technique– slotted pin– stretched mylar

Diamond assessment at CHESS


Future Outlook Diamond thinning

– assessment of first 10 m diamond – 11/2011

– first ablated diamond at UConn – 12/2010

– first thinned diamond by SINMAT – 3/2011

Diamond mounting– proof of concept with 30 m carbon wires – 7/2010– search underway for larger carbon ``thread’’, with

fall-back solution to bundle them out of 30 m strands


Material is ablated (vaporized) from the diamond surface by a focused beam from a pulsed UV laser.

Each pulse creates a pit ~100 m diameter.

Rastering the beam over the surface of the diamond creates a smooth surface (sub-micron roughness).

Residual amorphous carbon on the surface is removed by chemical reaction (e.g. ozone, RIE process).

BNL diamond ablation facility


152 µm 207 µm

Results presented by J. Smedley et.al.,BNL Instrumentation Group, Feb. 2009.

Deep ablation of polycrystaline sample:

BNL diamond ablation facility


laser beam fromexcimer (not shown)

laser pulsepower monitor

focusing lens (fused silica)

ablation plumeat an angle so the plumedoes not deposit on theablation chamber window

Optics setup, with vacuum chamberand CaF2 entrance window removed

UConn diamond ablation facility


Small Business Innovation Research (SBIR) grant proposal submitted to DOE in November, 2009.

Phase I – one year, feasibility studies, $100K total with $30K for UConn to carry out assessment with X-rays at CHESS

Notice of grant awarded: April 2010 !

Company: Sinmat Inc2153 SE Hawthorne Road, Suite 124 (Box 2)Gainesville Fl 32641-7553Phone / Fax : 352-334-7270

Principal Investigator: Arul ArjunanProject Title: Defect Free, Ultra-Rapid Thinning/Polishing

(20μm) of Diamond Crystal RadiatorTopic Number: 46 - Nuclear Physics Instrumentation,

Detection Systems and TechniquesSub-topic: e - Specialized Targets for Nuclear Physics Research

SINMAT diamond RCMP facility


Element Six marketing: available for online orders

HPHT single-crystal plates:

HPHT synthetics

purity class: type Ib

500 microns x 4.5 mm x 4.5 mm

CVD single crystals:

CVD monocrystals

purity class: unstated

300 microns x 4.5 mm x 4.5 mm or 1.2 mm x 8 mm x 8 mm

167 £150 £ or 1800 £

Element Six monocrystal inventory

Diamond Radiator Thinning and Mounting for GlueX R.T. Jones GlueX collaboration meeting, Regina,...

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