Antiproton Production Targets

Keith Gollwitzer

Antiproton Source Department

Accelerator Division

Fermilab

16 June 2008

Disclaimer

• I am not well versed in targets

• The Antiproton Target Station Group of the Mechanical Support Department of the Accelerator Division have been working for years on the improvements of the target, lens, collimator and pulsed magnet

• I can put you in contact with the engineers involved with the target station

Style A Target

Target stack consists of target disks (nickel alloy) and copper heat sinks

Air is directed through the center of cylinder from the top and then through the copper baffle sections

Beam goes through a chord of the target disk

Target stack is rotated ~17o after each proton pulse

Entire target stack is moved vertically to fresh target material

Style has been in use for several years

Style A Target

This target stack was installed Dec 27 and removed May 22

Precision beam control needed to not target copper

Heat sink and target material separation can be seen; lose cooling effectiveness

Believed missing material caused by oxidation which leads to weakened material that is then subject to beam

Nominal spot size ~200μm; smaller beam size causes “sputtering” which can coat the lens with unwanted heat sources

Style B Target

No stacking of disks; target cylinder means nearly twice as much target material

Center of target cylinder still has air flow with heat sink

Heat sink consisted of deformed copper balls brazed together and to inner copper tube.

Beryllium cover to remove chance for oxidation as well as keeping sputtered material contained.

Operational Plan• Run normal beam until see degradation• Run ~1 week with no beam sweeping• Run a few days with reduced spot size (with

beam sweeping)– Check visually for any problems

• Ran 1 week and saw change in air flow– Compromised heat exchanger

• Ran additional 10 days before degradation• Ran two days with no beam sweeping• Saw opportunity to do last step; ran less than

one day with smaller spot size

Operational Plan• Run normal beam until see degradation• Run ~1 week with no beam sweeping• Run a few days with reduced spot size (with

beam sweeping)– Check visually for any problems

• Ran 3 days and saw change in air flow– Compromised heat exchanger

• Ran additional 2 weeks before degradation• Ran two days with no beam sweeping• Saw opportunity to do last step; ran less than

one day with smaller spot size– Rotation problem

Style B Target

Ran 17 days of normal beam conditions.

After 3 days heat exchanger disappeared

Can see heat band on beryllium cover

Probably developed crack after losing cooling

Note that we ran without moving target stack for >2X longer than Style A Target.

Also note discoloration at top probably due to excessive heat

Style B Target

Ran less than a day with smaller spot size and beam sweeping

Lack of target cooling and targeting near bottom of disk caused the beryllium cover to move and interfere with rotation

Can see shift in cover pieces

Can see where targeted for two days without sweeping

Can see evidence for sputtering at last position

Don’t know if large cover separation was before/after rotation problems

Status and Plans• Believe failure of heat exchanger led to further

problems• Believe better performance with Style B Target

has been achieved

• Have all material and parts for Style A Target; will assemble

• Have all material for Style B Target; design more robust heat exchanger followed by assembly of complete target

• Will complete both in next few months; current Style A target should last 4-5 months