Store current workspace path in variable for a later stage

I am using the declarative syntax for my pipeline, and would like to store the path to the workspace being used on one of my stages, so that same path can be used in a later stage.

I have seen I can call pwd() to get the current directory, but how do I assign to a variable to be used between stages?

EDIT

I have tried to do this by defining by own custom variable and using like so with the ws directive:

pipeline {
  agent { label 'master' }
  stages {
    stage('Build') {
      steps {
        script {
          def workspace = pwd()
        }
        sh '''
          npm install
          bower install
          gulp set-staging-node-env
          gulp prepare-staging-files
          gulp webpack
        '''
        stash includes: 'dist/**/*', name: 'builtSources'
        stash includes: 'config/**/*', name: 'appConfig'
        node('Protractor') {
          dir('/opt/foo/deploy/') {
            unstash 'builtSources'
            unstash 'appConfig'
          }
        }        
      }
    }
    stage('Unit Tests') {
      steps {
        parallel (
          "Jasmine": {
            node('master') {
              ws("${workspace}"){
                sh 'gulp karma-tests-ci'
              }
            }
          },
          "Mocha": {
            node('master') {
              ws("${workspace}"){
                sh 'gulp mocha-tests'
              }
            }
          }
        )
      }
      post {
        success {
          sh 'gulp combine-coverage-reports'
          sh 'gulp clean-lcov'
          publishHTML(target: [
            allowMissing: false,
            alwaysLinkToLastBuild: false,
            keepAll: false,
            reportDir: 'test/coverage',
            reportFiles: 'index.html',
            reportName: 'Test Coverage Report'
          ])
        }
      }
    }
    }
}

In the Jenkins build console, I see this happens:

[Jasmine] Running on master in /var/lib/jenkins/workspace/_Pipelines_IACT-Jenkinsfile-UL3RGRZZQD3LOPY2FUEKN5XCY4ZZ6AGJVM24PLTO3OPL54KTJCEQ@2
[Pipeline] [Jasmine] {
[Pipeline] [Jasmine] ws
[Jasmine] Running in /var/lib/jenkins/workspace/_Pipelines_IACT-Jenkinsfile-UL3RGRZZQD3LOPY2FUEKN5XCY4ZZ6AGJVM24PLTO3OPL54KTJCEQ@2@2

The original workspace allocated from the first stage is actually _Pipelines_IACT-Jenkinsfile-UL3RGRZZQD3LOPY2FUEKN5XCY4ZZ6AGJVM24PLTO3OPL54KTJCEQ

So it doesnt look like it working, what am I doing wrong here?

Thanks