The OLYMPUS Target System

Brian S. Henderson

for the OLYMPUS Collaboration

Massachusetts Institute of Technology

APS April Meeting 2012

OL MPUS

Introduction

R =�(e+p)�(e�p) � 1 +

4<�

My

1 M2

�

jM1 j2

The OLYMPUS experiment

seeks to definitively measure

the two-photon contribution

to e�p elastic scattering by

measuring the ratio, R, of the

e+ and e� cross sections

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 2 / 15

Image Source: Douglas Hasell

Internal Hydrogen Target

Key Features:

� 2 GeV e+=e� on an internal H2

gas target

� � 1015 atoms�cm�2 thickness

� High H2 purity

� Open-ended, thin-walled

target cell

� Remains in place during DORIS

synchrotron radiation runs

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 3 / 15

Target Chamber and Cell

� Constructed and tested at

MIT Bates (Summer 2011)

� Tapered target chamber

design

� Target was installed in

January 2011

� Tested in the beamline

during February 2011 test

run

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 4 / 15

Target Chamber and Cell

� Cell constructed at INFN,

Ferrara, Italy

� Elliptical tube

� 9 mm � 27 mm cross-section� 60 cm long� 100 �m thick walls

� Gas is internal to the ring; no

windows

� Target cell cooled (<40 K) to

increase density

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 5 / 15

Gas Feed System

� Water-splitting H2 generator supplies gas (99.99998% purity)

� Flow managed by system of solenoid valves and mass flow

controllers (MFCs)

� Reservoir and buffer volumes can be used to drive a smaller

flow rate or calibrate the MFC output

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 6 / 15

Vacuum System

� Large vacuum system maintains the ring pressure

(� 10�9 torr)

� Pumping on the ends of the cell creates the triangular

density

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 7 / 15

Beam Scrapers

� Adjustable copper rods placed around the

ring

� Serve to clean-up beam and block

synchrotron radiation

� Apertures determined empirically

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 8 / 15

Image Source: F. Brinker, 2009

Collimator and Wakefield Suppressors

� Collimator is a cylinder ofsolid tungsten with ellipticalbore

� 15 cm along beamline� 10 cm diameter

� Collimator aperture 2 mm

smaller than cell in each

dimension

� Wakefield suppressors

smooth the transition from

full beam pipe to target to

prevent heating

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 9 / 15

Target Performance

� Initial tests exposed issue with wakefield heating

� Bad electrical contact between suppressor and cell� Heating caused scoring and damage to cell� Issue resolved and new cell installed during Summer 2011

� Thus far, production runs have used a target flow of 0.8 sccm

� System has been tested for a significant range of flows

� No major issues during DORIS synchrotron radiation runs

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 10 / 15

Reconstruction of Target Density

Vertex distributions have been reconstructed from several tests

Test experiment, no B field

Z (mm)-400 -300 -200 -100 0 100 200 300 400

Cou

nts

0

200

400

600

800

1000

Vertex Position of Track Candidate

Preliminary wire chamber tracking, Run 4060

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 11 / 15

Image Source: Jan Bernauer, Axel Schmidt

Beam Lifetime

� Beam lifetime behavior indicates basic functionality of the

target

� Target can be pumped out (“empty”) in about 20 minutes

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 12 / 15

Synchrotron Radiation Runs

Target temperature at 4.5 GeV, 140 mA max current over several

beam fills

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 13 / 15

Image Source: Jan Bernauer

Summary and Outlook

� The OLYMPUS internal hydrogen target has performed well in

the first production runs

� Early issues with cell heating were overcome

� Enhanced tracking will improve resolution on the gas density

measurements

� The target should be in excellent shape for our next run

(October-December 2012)

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 14 / 15

Acknowledgments

The OLYMPUS Collaboration:

� Arizona State University

� DESY

� INFN Bari

� INFN Ferrara

� INFN Rome

� Hampton University

� Massachusetts Institute ofTechnology

� St. Petersburg Nuclear PhysicsInstitute

� University of Bonn

� University of Glasgow

� University of Mainz

� University of New Hampshire

� Yerevan Physics Institute

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 15 / 15

Gas Feed System

Brian S. Henderson (MIT) The OLYMPUS Target System April 3, 2012 16 / 15