If you do not plan to receive any kind of payment in Russia (such as the reimbursement of travel expenses from the conference grants) you may apply for a tourist visa.
Citizens of Israel may enter Russia (and receive reimbursement) without visa.
After arrival to Russia: If you plan to stay in Russia for at most 7 business days then you are not required to register with local authorities. For instance, if you arrive to Russia on June 1 and leave on June 10 then you can stay without registration. If your stay includes more than 7 business days please contact the organizers regarding registration upon your arrival.