Low-energetic alpha particles will capture electrons quickly, and you get regular helium atoms. Their energy depends on the temperature, but they are not visible in your cloud chamber anyway.
You cannot build a cloud chamber without electrons.
To get thermal, ionized alpha particles, you need a very hot plasma (something like 100 000 Kelvin) - and even there, you need electrons or the plasma will fly apart. An extremely low density in an extremely good vacuum and a very short timescale might work, too. Nothing you can reproduce with your experiments, however.