Abstract:
A method and an apparatus for cooling an arc lamp have been disclosed. In one embodiment, the arc lamp assembly includes an arc lamp, a first heat sink coupled to an anode of the arc lamp, and a thermally conductive ring surrounding a first part of the outer surface of a reflector body of the arc lamp to thermally couple the reflector body to the first heat sink. Other embodiments have been described and claimed.

Description:
FIELD OF INVENTION 
     The present invention relates to arc lamps, and more particularly, to cooling an arc lamp. 
     BACKGROUND 
     In optical systems involving the generation and controlled radiation of long or continuous pulses of light, such as spectroscopy, or solar simulation, where high intensity, color correct illumination of sensitive working areas is required, such as in fiber optics illumination devices, it is advantageous to have a light source capable of producing the highest possible light flux density. Products utilized in such applications include short arc inert gas lamps, which may also be referred to as arc lamps. At least one short arc lamp includes a sealed chamber containing a gas pressurized to several atmospheres, and an opposed anode and cathode defining an arc gap. A window provides for the transmission of the generated light, and a reflector body may be positioned surrounding the arc gap. 
     During operation of an arc lamp, the anode and the cathode generate a significant amount of heat. The anode and the cathode are inside the sealed chamber of the arc lamp. As a result, the reflector body is also subjected to high heat during operation of the arc lamp. The operating power of the arc lamp may be limited by the reflector body temperatures. A lower temperature reflector body allows for a higher operating lamp power. Furthermore, the reflector body may crack, and the lamp will fail, when operated at high temperatures over a long period of time. 
     One existing technique to aid cooling of the reflector body is to directly couple a heat sink to the underside of the reflector body. However, the above technique is unsatisfactory because of the lack of adequate surface area in contact with the heat sink to dissipate heat from the reflector body to the heat sink. 
     Another existing technique is to add a copper band along the underside of the cathode heat sink to help cool off the reflector body. Alternatively, a thermal heat transfer pad is coupled to one end of the reflector body that is near the anode to facilitate heat dissipation from the reflector body. However, these techniques also suffer from the problem of inadequate surface area in contact with the heat sink to dissipate heat from the reflector body to the heat sink. 
     SUMMARY 
     A method and an apparatus for cooling an arc lamp are described. In one embodiment, the arc lamp assembly includes an arc lamp, a first heat sink coupled to an anode of the arc lamp, and a thermally conductive ring surrounding a first part of the outer surface of a reflector body of the arc lamp to thermally couple the reflector body to the first heat sink. 
     Other features of the present invention will be apparent from the accompanying drawings and from the detailed description that follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood more fully from the detailed description that follows and from the accompanying drawings, which however, should not be taken to limit the appended claims to the specific embodiments shown, but are for explanation and understanding only. 
         FIG. 1  shows one embodiment of an arc lamp assembly. 
         FIG. 2  shows a cross-section view of an embodiment of an arc lamp assembly. 
         FIG. 3  shows an alternate embodiment of an arc lamp assembly. 
         FIG. 4  shows a cross-section view of one embodiment of an arc lamp assembly. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known components, structures, and techniques have not been shown in detail in order not to obscure the understanding of this description. 
       FIG. 1  illustrates one embodiment of an arc lamp assembly  100  with various components separated from each other for the purpose of illustration. An assembled view  199  of the various components is shown in the bottom right corner of  FIG. 1 . The arc lamp assembly  100  includes a cathode heat sink  110 , an arc lamp  120 , an electrical insulator ring  130 , a wave washer spring  140 , a retainer ring  150 , a thermally conductive ring  160 , and an anode heat sink  170 . In addition to the above components, the arc lamp assembly  100  includes a cathode and an anode (not shown) mounted inside the arc lamp  120 . The cathode is mounted near the end of the arc lamp  120  closer to the cathode heat sink  110  while the anode is mounted near the opposite end of the arc lamp  120 . 
     The thermally conductive ring  160  may be pre-loaded to the arc lamp  120  using the wave washer spring  140 . To hold the thermally conductive ring  160  in place to assure good contact between the thermally conductive ring  160  and the arc lamp  120 , a retainer ring  150  may be coupled to the outer surface of thermally conductive ring  160 . In one embodiment, the thermally conductive ring  160  is made of copper. Detail of the way heat is dissipated from the arc lamp  120  is discussed below with reference to  FIG. 2 . 
     To prevent arcing from the thermally conductive ring  160  to the cathode heat sink  110  of the arc lamp, the electrical insulator ring  130  is coupled to the reflector body  120  to surround the outer surface of the arc lamp  120  and in between the cathode heat sink  110  and the wave washer spring  140 . In one embodiment, the electrical insulator ring  130  is made of glass silicon. Alternatively, the electrical insulator ring  130  is made of Teflon or an equivalent material that is electrically non-conductive and has a high thermal conductivity (e.g., up to 1800° C.) that is capable of sustaining operating temperature of the arc lamp. 
       FIG. 2  shows a cross-sectional view of one embodiment of an arc lamp assembly  200 . For the purpose of illustration, only the right half of the cross-section is shown, which provides sufficient details to one of ordinary skill in the art to practice the embodiment of the present invention. The arc lamp assembly  200  includes a cathode heat sink  210 , a cathode  215 , an anode heat sink  270 , an anode  275 , a reflector body  220 , an electrically insulator ring  230 , a spring  240 , a thermally conductive ring  260 , and a retainer ring  250 . 
     The anode  275  is mounted at one end of the reflector body  220  and the cathode  215  is mounted by a strut  217  near the opposite end of the reflector body  220 . The outer surface of the reflector body  220  is surrounded by the thermally conductive ring  260 . In one embodiment, the thermally conductive ring  260  is pre-loaded by the spring  240 . Furthermore, to ensure good contact between the thermally conductive ring  260  and the outer surface of the reflector body  220 , the retainer ring  250  is coupled to the outer surface of the thermally conductive ring  260  to provide radial compression onto the thermally conductive ring  260 . In one embodiment, the thermally conductive ring  260  is made of metallic material, such as copper. Alternatively, the thermally conductive ring  260  may be made of non-metallic material, such as aluminum nitride. 
     During operation of the arc lamp assembly  200 , the reflector body  220  is subjected to high heat generated by the anode  275  and the cathode  215 . To cool off the reflector body  220 , the thermally conductive ring  260  allows a heat flow  201  to travel from the reflector body  220  to the anode heat sink  270 , which dissipates the heat. Since the thermally conductive ring  260  provides a large surface area in contact with the reflector body  220 , the rate of heat flow through the thermally conductive ring  260  may be increased. 
     To further facilitate the heat flow  201 , one or more heat transfer pads or compounds  252  may be added at the locations between the thermally conductive ring  260  and the reflector body  220  or between the thermally conductive ring  260  and the anode heat sink  270 . 
     To prevent arcing from the thermally conductive ring  260  to the metal ring of the arc lamp, the electrical insulator ring  230  may be coupled between the spring  240  and the cathode heat sink  210 . In one embodiment, the electrical insulator ring  230  is bonded to the outer surface  237  of the reflector body  220 . 
       FIG. 3  illustrates an alternate embodiment of an arc lamp. Various components of the arc lamp assembly  300  in  FIG. 3  are separated from each other for the purpose of illustration. The arc lamp assembly  300  includes a cathode heat sink  310 , an arc lamp  320 , a retainer ring  350 , a thermally conductive and electrically insulative ring  360 , and an anode heat sink  370 . The arc lamp assembly  300  further includes an anode and a cathode (not shown) mounted inside the arc lamp  320 . When assembled, the thermally conductive and electrically insulative ring  360  is coupled to the outer surface of the arc lamp  320 , surrounding the arc lamp  320 . To improve contact between the arc lamp  320  and the thermally conductive and electrically insulative ring  360 , the retainer ring  350  may be coupled to the outer surface of the thermally conductive and electrically insulative ring  360  to provide radial compression onto the thermally conductive and electrically insulative ring  360 . In one embodiment, the thermally conductive and electrically insulative ring  360  is made of aluminum nitride. More detail on the operation of the arc lamp assembly  300  is discussed below. 
       FIG. 4  shows a cross-sectional view of one embodiment of an arc lamp assembly. For the purpose of illustration, only the right half of the cross-section is shown, which provides sufficient details to one of ordinary skill in the art to practice the embodiment of the present invention. The arc lamp assembly  400  includes a cathode heat sink  410 , a cathode  415 , an anode heat sink  470 , an anode  475 , a reflector body  420 , a thermally conductive and electrically insulative ring  460 , and a retainer ring  450 . The thermally conductive and electrically insulative ring  460  may be made of aluminum nitride. 
     The inner surface of the thermally conductive and electrically insulative ring  460  is coupled to the outer surface of the reflector body  420  to surround the reflector body  420 . A first end of the thermally conductive and electrically insulative ring  460  is coupled to the cathode heat sink  410  and the second end of the thermally conductive and electrically insulative ring  460  is coupled to the anode heat sink  470 . By surrounding the outer surface of the reflector body  420 , the ring  460  provides more surface area for heat transfer to improve cooling of the reflector body  420 . Heat may flow from the reflector body  420  through the ring  460  to either the cathode heat sink  410  and/or the anode heat sink  470  as indicated by the arrows  403  and  401 , respectively. 
     In one embodiment, the retainer ring  450  is coupled to the outer surface of the thermally conductive and electrically insulative ring  460  to provide radial compression onto the thermally conductive and electrically insulative ring  460  in order to hold the thermally conductive and electrically insulative ring  460  in position and to improve the contact between the thermally conductive and electrically insulative ring  460  and the reflector body  420 . Furthermore, one or more heat transfer pads or compounds may be coupled to the surfaces of the thermally conductive and electrically insulative ring  460  that are adjacent to the reflector body  420  or one of the heat sinks  410  and  470 . Some exemplary positions at which the heat transfer pads or compounds may be coupled to are indicated by the reference numerals  452  and  454  in  FIG. 4 . 
     By increasing the surface area of the thermally conductive and electrically insulative ring  460 , via which the reflector body  420  may dissipate heat to the heat sinks  410  and/or  470 , the reflector body  420  may be cooled faster. With a faster cooling rate, the reflector body  420  may operate at higher temperatures, and hence, the power of the arc lamp  400  may be increased without risking increasing the likelihood of cracking the reflector body  420 . In an exemplary embodiment, the power of the arc lamp assembly  400  may be increased by approximately 30%, such as, for example, from approximately 300 watts to about 400 watts. 
     The foregoing discussion merely describes some exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, the accompanying drawings and the claims that various modifications can be made without departing from the spirit and scope of the invention.