Uniaxial Strain Tuning of Superconductivity in 2$H$-NbSe$_{2}$.

We explore the effect of lattice anisotropy on the charge-ordered superconductor 2H-NbSe$_{2}$. Using a novel strain apparatus, we measure the superconducting transition temperature $T_{sc}$ as a function of uniaxial strain. It is found that $T_{sc}$ is independent of tensile(compressive) strain below a threshold of 0.2% (0.1%), but decreases strongly with larger strains with an average rate of $1.3,$K/% ($2.5,$K/%). Transport signatures of charge order are largely unaffected as a function of strain. Theoretical considerations show that the change in the behavior of $T_{sc}$ with strain coincides with a phase transition from 3Q to 1Q charge order in the material. The spectral weight on one of the Fermi surface bands is found to change strongly as a consequence of this phase transition, providing a pathway to tune superconducting order.