COOLED CHARGED PARTICLE SYSTEMS AND METHODS
Cooled charged particle sources and methods are disclosed. In some embodiments, a charged particle source is thermally coupled to a solid cryogen, such as solid nitrogen. The thermal coupling can be design to provide good thermal conductivity to maintain the charged particle source at a desirably low temperature.
1 . A system, comprising:
a charged particle source;
a dewar;
a cryogen comprising a solid, the cryogen being housed in the dewar; and
a thermal conductor that thermally connects the charged particle source and the dewar so that, during use of the charged particle source when the cryogen is in the dewar, the charged particle source can be maintained at a temperature of 80K or less.
2 . The system of claim 1 , wherein the thermal conductor thermally connects the charged particle source and the dewar so that, a period of time between when the cryogen in a liquid state is added to the dewar and when the charged particle source reaches a temperature of 80K or less is three hours or less.
3 . The system of claim 1 , wherein the dewar comprises sensors configured to determine a temperature of the cryogen.
4 . The system of claim 1 , wherein the charged particle source is a gas field ion source.
5 . The system of claim 1 , wherein the system is a gas field ion microscope.
6 . The system of claim 1 , wherein the cryogen comprises a solid.
7 . The system of claim 1 , further comprising means for enhancing thermal contact between the cryogen and the dewar.
8 . The system of claim 1 , wherein the dewar comprises walls with inwardly extending fins that contact the cryogen.
9 . The system of claim 1 , wherein the thermal conductor is configured to allow the charged particle source to be tilted.
10 . The system of claim 1 , wherein the thermal conductor vibrationally isolates the charged particle source from the dewar.
11 . The system of claim 1 , wherein the dewar comprises sensors configured to determine a cryogen parameter, and the system further comprises a feedback system configured to adjust an amount of cryogen in the dewar based on the determined cryogen parameter.
12 . The system of claim 1 , wherein the dewar comprises at least one heater configured to heat the dewar.
13 . The system of one claim 12 , wherein the dewar comprises an outer thermal jacket configured to thermally isolate the cryogen from an environment exterior to the dewar, and the at least one heater is configured to heat an interior of the outer thermal jacket.
14 . The system of one of the claims 13 , further comprising a pump configured to pump gas from an interior of the outer thermal jacket.
15 . The system of claim 14 , wherein, after turning off the pump, a pressure in the outer thermal jacket does not change by more than 10% for a least one day.
16 . The system of claim 15 , wherein the pump is also configured to pump a volume adjacent the charged particle source.
17 . A method, comprising:
measuring a temperature of a region of a dewar near a bottom of the dewar;
determining whether the temperature of the region of the dewar near the bottom of the dewar is at or above a target temperature;
adding a liquid cryogen to the dewar if the temperature of the region of the dewar near the bottom of the dewar is at or above the target temperature; and
after adding the liquid cryogen to the dewar, reducing a gas pressure in the dewar to solidify the cryogen.
18 . The method of claim 17 , further comprising, if the temperature of the region of the dewar near the bottom of the dewar is below the target temperature, heating the dewar.
19 . The method of claim 18 , wherein heating the dewar changes a state of solid cryogen in the dewar to a liquid or a gas.
20 . The method of claim 17 , further comprising determining whether the temperature of the region of the dewar near the bottom of the dewar is at or above the target temperature, and adding a liquid cryogen to the dewar if the temperature of the region of the dewar near the bottom of the dewar is at or above the target temperature.
21 . The method of claim 17 , further comprising, if the temperature of the region of the dewar near the bottom of the dewar is above the target temperature, waiting a period of time, and, after waiting the period of time, measuring a first temperature of the region of the dewar near the bottom of the dewar.
22 . The method of claim 21 , further comprising determining whether the temperature of the region of the dewar near the bottom of the dewar is at or above a target temperature, and adding a liquid cryogen to the dewar if the temperature of the region of the dewar near the bottom of the dewar is at or above the target temperature.