Work supported by U.S. Dept of Energy

#gravesvb@ornl.gov

Systems Testing of a Free Hg Jet System for Use in a High-Power Target Experiment*

V. Graves#, ORNL, Oak Ridge, TN 37831, U.S.A.
H. Kirk, H. Park, T. Tsang, BNL, Upton, NY 11973, U.S.A.
A. Fabich, I. Efthymiopolous, CERN, Geneva, Switzerland
P. Titus, MIT, Cambridge, MA 02139, U.S.A.
A. Carroll, P. Spampinato, ORNL, Oak Ridge, TN 37831, U.S.A.
K. McDonald, Princeton University, Princeton, NJ 08544, U.S.A.

Abstract

 The design and operational testing of a mercury jet delivery system is presented. The equipment is part of the Mercury Intense Target (MERIT) Experiment, which is a proof-of-principle experiment to be conducted at CERN in the summer of 2007 to determine the feasibility of using an unconstrained jet of mercury as a target in a Neutrino Factory or Muon Collider. The Hg system is capable of producing a 1 cm diameter, 20 m/s jet of Hg inside a high-field solenoid magnet. A high-speed optical diagnostic system allows observation of the interaction of the jet with a 24 GeV proton beam. Performance of the Hg system will be presented, along with results of integrated systems testing without a beam.

INTRODUCTION
 The Mercury Intense Target (MERIT) Experiment is a proof-of-principle experiment to investigate the interaction of a proton beam with an unconstrained jet of liquid Hg within a high-strength magnetic field [1]. MERIT is scheduled to be conducted at CERN during the summer of 2007; the experiment has been approved at CERN with the designation of nTOF11. MERIT follows earlier efforts which observed how a Hg jet is constrained by a magnetic field [2] and dispersed by a proton beam in a zero-field condition [3]. It is envisioned that the MERIT experiment will prove that this type of high-power target concept can be used for a Neutrino Factory or Muon Collider. Design requirements for this experiment were that the Hg jet should have a velocity of 20 m/s and a diameter of 1 cm; the maximum magnetic field strength should be 15 T. It is expected that approximately 100 proton pulses will be conducted during the duration of the experiment. Beam momentum shall be either 14 GeV/c or 24 GeV/c, with up to 30x1012 protons per pulse, and the total number of protons on target shall be limited to 3x1015.

EQUIPMENT DESCRIPTION
 Figure 1 shows a cross-section view of the experimental equipment. The Hg system provides double containment of the hazardous liquid metal, and the Hg system can be inserted or removed from the solenoid bore without disassembly of either system.

Figure 1. MERIT experiment equipment cross section.

 In Figure 1, the proton beam is shown as a horizontal line; direction of the beam and the Hg jet is from right-to-left. The magnetic axis is positioned at a slight angle (66 mrad) to the beam, with the tilt provided by a common baseplate supporting all the equipment. Four viewports shown within the solenoid bore represent viewing locations for observation of the Hg jet within its primary containment. Numbered 1-4 from right to left, viewport #2 is positioned at the center of the high field within the solenoid and is the location where the center of the proton beam interacts with the center of the Hg jet. Descriptions of the major experiment components are given below; additional information can be found in [4].

Solenoid
 Shown in Figure 2, the MERIT magnet is a DC-pulsed solenoid capable of producing a 15 T field at 7200A; with a maximum operating voltage of 700 V, its peak power is 5.5 MW. Its fabrication consists of three nested copper coils with a warm bore length of 1 m and diameter of 15 cm. It is a normally-conducting solenoid with an operating temperature of 77 K provided by liquid N2 (LN2) cooling. Mechanical design was provided by the Plasma Science and Fusion Center at MIT [5].

 To minimize the activation of LN2 during the experiment, prior to each beam pulse the solenoid is flushed of LN2 with 5-bar N2 gas. The magnet incorporates a field ramp-up of 9 s and is capable of sustaining its peak field for a duration of approximately 1 s. During this time the electrical energy input raises the magnet's temperature by approximately 30 K. The time required to cool the magnet down to operating temperature after each pulse is approximately 30 minutes.

Figure 2. 15 T solenoid.

Hg System
 The Hg delivery system is a hydraulically-actuated syringe pump that produces the desired unconstrained liquid metal target jet. Due to discharge pressure and fluid heating concerns, as well as the intermittent nature of the experiment, a syringe pump was chosen over a centrifugal pump. The pump is shown in Figure 3 and consists of three hydraulic cylinders – a centered 25 cm diameter Hg cylinder actuated by a pair of side-mounted 15 cm diameter drive cylinders through a mechanical tie beam. The syringe can provide a maximum steady-state jet duration of 12 s. The Hg flow rate during a 20 m