According to a first aspect of the present invention there is provided a vessel for an EUV radiation source, the vessel comprising a guide portion for directing fuel debris from a plasma formation region of the EUV radiation source towards a fuel debris removal device, a wall comprising an opening, wherein at least a part of the guide portion is arranged in the opening of the wall so that a gap is defined between the guide portion and the wall and a gas supply system configured to supply a gas into the gap to control a transfer of heat between the guide portion and the wall. By configuring the gas supply system to supply the gas into the gap, cooling or heating of the guide portion may be controlled and/or improved. For example, it may be desirable to cool the guide portion, when EUV radiation is produced by the EUV radiation source. The gas may be supplied into the gap to allow for cooling of the guide portion, e.g. to below a melting temperature of a fuel that may be used in the EUV radiation source. In use, fuel debris may be deposited on the guide portion. By cooling the guide portion to a temperature below the melting temperature of the fuel, dripping, bubbling and/or spitting of liquid fuel debris may be prevented or reduced. This may result in a decrease of the contamination of one or more components of the EUV radiation source. Additionally or alternatively, when EUV radiation is produced by the EUV radiation source, a temperature of the guide portion may increase to about 300℃ or larger. This may cause damage and/or corrosion of the guide portion. For example, the guide portion may comprise a metal material or metal alloy material, such as stainless steel. Some metal alloy materials, such as stainless steel, may start to corrode and/or become damaged at a temperature of about 400℃ or above. By configuring the gas supply system to supply the gas into the gap. cooling of the guide portion may be controlled and/or improved, e.g. when EUV radiation is produced by the EUV radiation source. This may lead to a reduction in corrosion and/or damage of the guide portion and/or an increase in the lifetime of the guide portion. It may be desirable to heat the guide portion, e.g. when no EUV radiation is produced by the EUV radiation source, e.g. to remove fuel debris from the guide portion. The vessel may be or comprise a vacuum vessel, pressure vessel, vacuum chamber or pressure chamber or the like. The vessel may be configured to enclose a vacuum or low pressure environment of the EUV radiation source. The term "low pressure environment" may be considered as an environment comprising a gas at a pressure below atmospheric pressure, e.g. at a pressure between about 100 Pa and 200 Pa. The gas supply system may be operable between a first configuration and a second configuration. In the first configuration, the gas supply system may be configured to supply the gas into the gap, e.g. to increase a transfer of heat between the guide portion and the wall. In the second configuration, the gas supply system may be configured to supply no gas into the gap, e.g. to decrease a transfer of heat between the guide portion and the wall. For example, in the second configuration, the gas supply system may be configured to terminate or slop a supply of gas into the gap. By operating the gas supply system between the first configuration and the second configuration a transfer of heal between the guide portion and the wall may be controlled. This may allow for cooling or heating of the guide portion to be controlled and/or improved. The gas supply system may be configured to operate in the first configuration, e.g. when EUV radiation is produced by the EUV radiation source. The gas supply system may be configured to operate in the second configuration, e.g. when no EUV radiation is produced by the radiation source. The EUV radiation source may comprise an on state, in which EUV radiation is produced. The EUV radiation source may comprise an off sta
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