# Design and Operation of a Windowless Gas Target Internal to a Solenoidal Magnet for Use with a Megawatt Electron Beam

## TL;DR

This paper presents the design, simulation, and testing of a windowless hydrogen gas target for high-power electron beam experiments, demonstrating its feasibility within an ERL environment.

## Contribution

It introduces a novel windowless gas target design for megawatt electron beams, including experimental assembly, calibration, and COMSOL simulations for optimal operation.

## Key findings

- Feasibility of a high-density windowless hydrogen target in an ERL environment
- Successful assembly and calibration at Jefferson Lab and MIT Bates
- Simulation results support operational stability and design choices

## Abstract

A windowless hydrogen gas target of nominal thickness $10^{19}$ cm$^{-2}$ is an essential component of the DarkLight experiment, which is designed to utilize the megawatt electron beam at an Energy Recovery Linac (ERL). The design of such a target is challenging because the pressure drops by many orders of magnitude between the central, high-density section of the target and the surrounding beamline, resulting in laminar, transitional, and finally molecular flow regimes. The target system was assembled and operated at Jefferson Lab's Low Energy Recirculator Facility (LERF) in 2016, and subsequently underwent several revisions and calibration tests at MIT Bates in 2017. The system at dynamic equilibrium was simulated in COMSOL to provide a better understanding of its optimal operation at other working points. We have determined that a windowless gas target with sufficiently high density for DarkLight's experimental needs is feasible in an ERL environment.