How to close the current tab of the browser in protractor with out closing the complete browser

You can try the following:

Switch to the new opened tab. Close the current windows (in this case, the new tab). Switch back to the first window.

browser.getAllWindowHandles().then((handles) => {
    browser.driver.switchTo().window(handles[1]);
    browser.driver.close();
    browser.driver.switchTo().window(handles[0]);
});