Beam Energy Measurements with Elastic Scattering

• At Jefferson Lab an electron beam is used to probe the At Jefferson Lab an electron beam is used to probe the nucleus. In these experiments it is essential to know the nucleus. In these experiments it is essential to know the precise energy of the beam.precise energy of the beam.

• To measure the energy, Jefferson Lab uses a device To measure the energy, Jefferson Lab uses a device that measures the angles of an elastic collision. that measures the angles of an elastic collision.

By: Idaykis Rodriguez

Florida International University, Miami, Fl 33199

Mentor: Douglas W. Higinbotham

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Scattered proton

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• The target in the device is a polymer film rich in The target in the device is a polymer film rich in hydrogen, ie. rich in protons. The film is made of hydrogen, ie. rich in protons. The film is made of polypropylene (Cpolypropylene (C33HH66) material which runs constantly ) material which runs constantly

on the rollers controlled by a motor. This is done to on the rollers controlled by a motor. This is done to prevent the electron beam from melting the target. prevent the electron beam from melting the target.

• As the electron beam travels through the target, it As the electron beam travels through the target, it looses some energy that turns into heat. The energy looses some energy that turns into heat. The energy loss correction can be calculated using the Bethe-Bloch loss correction can be calculated using the Bethe-Bloch equation.equation.

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eP DEVICEeP DEVICEeP DEVICEeP DEVICEINTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTION

• The eP device measures a fixed proton angle at 60The eP device measures a fixed proton angle at 6000 and and simultaneously measures the electron from the elastic collision.simultaneously measures the electron from the elastic collision.

• Detectors within the eP device include scintillators, Cherenkov Detectors within the eP device include scintillators, Cherenkov detectors, and silicon strips detectors.detectors, and silicon strips detectors.

• In order to have the eP device operational again, many updates and In order to have the eP device operational again, many updates and mechanical parts need to be replaced. mechanical parts need to be replaced.

• Updates to the system’s data analysis program needed to be made. Updates to the system’s data analysis program needed to be made. With the help of CODA experts, we were able to identify glitches and With the help of CODA experts, we were able to identify glitches and bugs that needed repair. bugs that needed repair.

• Bearings for the rollers of the target film were replaced. We Bearings for the rollers of the target film were replaced. We determined that the ceramic ball on steel races bearing does not determined that the ceramic ball on steel races bearing does not perform well under a vacuum environment. We found a ceramic ball perform well under a vacuum environment. We found a ceramic ball on ceramic races bearing which perform very well in vacuum.on ceramic races bearing which perform very well in vacuum.

This is the eP device along the beamline. These are the Cherenkov light detectors and close to the octagon, are the scintillators and photomultiplier tubes which detect charged particles.

TARGETSTARGETSTARGETSTARGETS

ACKNOWLEDGEMENTSACKNOWLEDGEMENTSACKNOWLEDGEMENTSACKNOWLEDGEMENTSSpecial thanks are given to:Special thanks are given to:

• Douglas W. HiginbothamDouglas W. Higinbotham

• Jan TylerJan Tyler

• Ed FoltsEd Folts

• Marcy Stutzman Marcy Stutzman

• David MeekinsDavid Meekins

• Alexandre CamsonneAlexandre Camsonne

• Robert MichaelsRobert Michaels

• Pierre BertinPierre Bertin

• Phil Atterly Phil Atterly

• Lisa Surles-LawLisa Surles-Law

• David Abbott (both)David Abbott (both)

..

These are samples of a full ceramic bearing.

12 GeV UPGRADE12 GeV UPGRADE12 GeV UPGRADE12 GeV UPGRADE

The figure on the left shows the energy acceptance of eP device for the current location of the The figure on the left shows the energy acceptance of eP device for the current location of the silicon strips. The silicon strips. The greengreen and and orangeorange indicate silicon strips proposed to move to an angle of 5 indicate silicon strips proposed to move to an angle of 500 for the new 11GeV for the new 11GeV desired energydesired energy in the in the redred and the other silicon strip to move to an angle of and the other silicon strip to move to an angle of 49.249.200 for detecting protons, which refers to the figure on the right. for detecting protons, which refers to the figure on the right.

The desired energies for the 12 GeV upgrade are 2.2, 4.4, 6.6, The desired energies for the 12 GeV upgrade are 2.2, 4.4, 6.6, 8.8, and 11 GeV. We propose to move four silicon strips to 8.8, and 11 GeV. We propose to move four silicon strips to new locations to detect the whole range of desired energies.new locations to detect the whole range of desired energies.

Inside the octagon piece are the silicon strips at their specific angles and the entire device is symmetric about the beamline.

Target Material

Density (g/cm3)

Thickness (cm)

Ratio of H nucleons

Thermal Conductivity (Wm-1K-1) @300K

Energy loss dE (MeV)

Polypropylene (C3H6) 1 0.95 0.003 2:1 0.20 8.8E-3

Water (H2O) 2 1.00 0.5 2:1 0.60 1.49 Kapton Polyimide (C22H10N2O5)

3 1.42 0.0025 ~1:4 0.12 9.6E-3

CVD Diamond foil 4 3.52 0.015 0 3320 1.41 C3H6 and Carbon Nanotube Mixture 10% wt 5

~1.00 ~0.005 ~2:1 6600 9.3E-3

11 C C33HH66 is the current target in eP, chosen for its high hydrogen ratio but it quickly melts in the is the current target in eP, chosen for its high hydrogen ratio but it quickly melts in the

beam due to its low thermal conductivity.beam due to its low thermal conductivity.

22 H H22O is a flowing target with a large energy loss (creates heat) due to its thickness.O is a flowing target with a large energy loss (creates heat) due to its thickness.

33 Kapton was considered because of its high melting point but, its hydrogen ratio is very poor. Kapton was considered because of its high melting point but, its hydrogen ratio is very poor.

44 CVD Diamond foil was considered as a backing material to the current polymer for it’s high CVD Diamond foil was considered as a backing material to the current polymer for it’s high thermal conductivity, but it could be too thick for the eP device.thermal conductivity, but it could be too thick for the eP device.

55 Carbon Nanotubes alone have the best thermal conductivity. A composite mixture with 90% Carbon Nanotubes alone have the best thermal conductivity. A composite mixture with 90% polypropylene and 10% carbon nanotubes could be an ideal target. polypropylene and 10% carbon nanotubes could be an ideal target.

• The energy of the beam is then calculated using the The energy of the beam is then calculated using the following equation:following equation:

Acceptance of eP at proposed thetaP = 49.20

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