Magnet

This page discusses the previous and current magnet designs for the eRHIC detector. The magnet designs have varied, and our most current design is one that evolves as experiment goals and implementation are better realized. Previous designs (up to 2012) are summarized in the 2012 Magnet Design Report. Also, there is a tutorial on how to create a model in COBHAM's OPERA-3d and how an analysis of the model is performed here.

Current Magnet Design

Bifurcated EncLosed LinEar solenoid: BELLE

Our most current working design is the 2.477 m long Bifurcated EncLosed LinEar solenoid (BELLE). This design was preceded by the Multiple Ring Solenoid version B1 (MRS-B1). A poster which describes the comparison between the BELLE and the MRS-B1 in detail may be seen here. The magnet modeling and some of the particle trajectory simulations are completed in COBHAM's OPERA-3d software suite.

BELLE Conductor Specifications
	Length [mm]	Inner Radius [mm]	Outer Radius [mm]	Current Density [A/mm2]
Inner Solenoid	1200.0	1220.0	1320.0	25.0
Outer Solenoid (each side)	638.5	1200.0	1340.0	33.0
Sample Magnetic Field Values
(x,y,z) [mm]	Bmodulus [T]		Bradial [T]
(0, 0, 0)	2.9		0.0
(0, 0, ±1300)	2.0		0.0

The BELLE is designed to be enclosed by iron yokes. The varying radii of the inner and outer solenoids are designed to limit the current density required to have a uniform field modulus at a certain radial position. This field uniformity may be seen as a function of the z-axis, which is parallel to the beam line. The design was optimized to have this uniformity by adjusting the ratios between the length and between the radii of the two solenoids. Once the proper ratios were established, the current densities were varied to shift the radial position of the field uniformity. This ability to shift the radial uniformity presents itself as a powerful tool for tuning the magnet to incorporate and optimize the efficacy of particle detection technologies such as TPC’s.

Magnetic Field Profile

BELLE Magnetic Field Profile
	Bmodulus [T] vs. z-axis [mm] at r= 0mm
	Bmodulus [T] vs. z-axis [mm] at r= 550mm
	Bmodulus [T] vs. z-axis [mm] at r= 1100mm
	Bradial [T] vs. z-axis [mm] at r= 550mm

OPERA Particle Trajectories

OPERA-3d allows for some very basic particle trajectory simulations. These simulations have been organized and plotted with mapper3.py (see OPERA Files). These plots allow for more careful consideration of a design's ability to provide useful physics. More complete and thorough particle trajectory simulations are done using the EICROOT simulation suite. All designs created are compared with a simple solenoid (SS). The SS is 2400 mm long, with an inner radius of 1000 mm and B_modulus(0, 0, 0) = 3.0 T. The simulated particle energies and initial angles are given on the plots.

BELLE and SS Particle Trajectory Comparison
BELLE vs. SS for electrons at 500MeV fired at 2° in the x-axis
BELLE vs. SS for electrons at 500MeV fired at 10° in the x-axis
BELLE vs. SS for electrons at 5GeV fired at 2° in the x-axis
BELLE vs. SS for electrons at 5GeV fired at 10° in the x-axis

As may be noted form above, the BELLE is able to deflect particle's from their trajectories more than the simple solenoid model. These differences in deflection do occur within the confines of the actual conductor, but are only of order ~5 mm with beam energies ~300MeV. The ability to resolve these kinds of differences is a key factor in whether or not the BELLE is truly an effective replacement for a simple solenoid.

OPERA Tutorial

A tutorial on creating a model and performing some studies on it using COBHAM's OPERA-3d Modeler and Post-Processor can be found here.