Laser ablation of silicon under an external applied magnetic field with different orientations was investigated in respect to the scanning direction and polarisation of the laser beam, by observation of the ablation patterns and debris deposition. Ultra-short ∼230 fs laser pulses of 1030 nm wavelengths were used in the single and multi-pulse irradiation modes. Ablation with an externally applied magnetic B-field (B ≈ 0.1 T) is shown to strongly affect debris formation. The mechanism of surface plasmon polariton (SPP) wave can explain the ablated periodic patterns observed with alignment along the magnetic field lines.