Method of operating a discharge lamp system and a discharge lamp system using a combination radial and longitudinal acoustic mode to reduce vertical segregation

1. A method of operating a discharge lamp system in which vertical segregation of vapor phase species is reduced, the method comprising the steps of providing a lamp, and modulating lamp power with an arc-straightening frequency and with a frequency that excites a combination radial plus longitudinal acoustic mode of the lamp, wherein each time period of the arc-straightening frequency is 2 to 16 times longer than a subsequent modulation at the combination radial plus longitudinal mode of the lamp.

2. The method of claim 1 , wherein the arc-straightening frequency is provided in spaced apart time periods and the excitation of the combination radial plus longitudinal acoustic mode occurs between the arc-straightening frequency time periods.

3. The method of claim 1 , wherein the excitation of the combination radial plus longitudinal acoustic mode is provided at the same time as the arc-straightening frequency.

4. The method of claim 1 , wherein the combination radial plus longitudinal mode is a combination of a first radial mode and an nth longitudinal mode.

5. The method of claim 4 , wherein “n” is one of 2, 4, and 6.

6. The method of claim 1 , wherein the combination radial plus longitudinal mode is excited with a single power frequency.

7. The method of claim 1 , wherein the combination radial plus longitudinal mode is excited with a swept power frequency range.

8. The method of claim 7 , wherein the swept power frequency range includes a combination of a first radial mode and an nth longitudinal mode and is within a power frequency band about 1 kHz wide.

9. The method of claim 8 , wherein the power frequency band is within the range of one of 179-182 kHz and 188-190 kHz.

10. The method of claim 1 , wherein the arc-straightening frequency is in a power frequency band about 15 kHz wide that includes a frequency that excites a second azimuthal mode of the lamp.

11. The method of claim 10 , wherein the power frequency band is within a range of 130-150 kHz.

12. A discharge lamp system with reduced vertical segregation of vapor phase species, comprising a lamp, a first generator that modulates lamp power with an arc-straightening frequency and a second generator that modulates lamp power at a combination radial plus longitudinal acoustic mode of the lamp, said first generator provides a range of frequencies that includes a second azimuthal mode of the lamp.

13. The lamp system of claim 12 , further comprising a circuit with a first multiplier providing a signal from said first generator, a second multiplier providing a signal from said second generator, an adder for combining the signals from said first and second multipliers, and a controller for providing a non-zero multiple to only one of said first and second multipliers at a time.

14. The lamp system of claim 13 , wherein said controller provides the non-zero multiple to said first generator during separate arc-straightening frequency periods that are 2 to 16 times longer than interleaved time periods when said second multiplier receives the non-zero multiple during modulation at the combination radial plus longitudinal mode of the lamp.

15. The lamp system of claim 12 , wherein said second generator provides a signal that modulates lamp power at a combination of a first radial mode and an nth longitudinal mode.

16. The lamp system of claim 15 , wherein “n” is one of 2, 4, and 6.

17. The lamp system of claim 12 , wherein said second generator outputs a single frequency.

18. The lamp system of claim 12 , wherein said second generator outputs a swept frequency range.

19. The lamp system of claim 18 , wherein the swept frequency range excites a combination of a first radial mode and an nth longitudinal mode.