Transformer current spike on flyback converter

[Username1]

I'm designing high voltage output flyback converter using the method in this website
http://www.simonbramble.co.uk/dc_dc_converter_design/flyback_converter/flyback_converter_design.htm
but when I simulated it on LTspice, it shows some unexpected behavior.
High initial current flows on the transformer and when output voltage reaches setpoint, high current spike shows on the primary side of the transformer.
Why this happens and how can I solve them?

[T3sl4co1l]

What transformer are you using?

A real one won't be k=1.

Likewise, you'll probably have to deal with the leakage inductance resonating with the transistor and diode capacitance.  An R+C across one or both addresses this (use R = sqrt(LL / Cc) and C >= 2.5 * Cc, where Cc is Coss or Cjo as the case may be).

The stray capacitance of the secondary may also be significant.

Also, you should probably check the simulations.  That jagged current doesn't make any damn sense, and I suspect it's because of LTSpice's "optimized" solver (which is notorious for sacrificing accuracy to gain that speed).  GEAR 2 is usually best for switching circuits.

Tim